St. Helens

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  • Country
  • Subregion Name
  • Primary Volcano Type
  • Last Known Eruption
  • 46.2°N
  • 122.18°W

  • 2549 m
    8361 ft

  • 321050
  • Latitude
  • Longitude

  • Summit
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9 February-15 February 2011

CVO reported that on 14 February a M 4.3 earthquake near Mount St. Helens, felt widely throughout SW Washington and NW Oregon, was followed over the next few hours by several aftershocks up to M 2.8. The three largest aftershocks were also felt. All of the earthquakes were located about 8 km N of the crater, near the Johnston Ridge Observatory, at depths of about 4-6 km. CVO also noted that a previous earthquake swarm had occurred in the same area on 29 January. The Volcano Alert Level remained at Normal and the Aviation Color Code remained at Green.

Source: US Geological Survey Cascades Volcano Observatory (CVO)



 Available Weekly Reports


2011: February
2008: January | February | July
2007: January | February | March | April | May | June | July | August | September | October | November | December
2006: January | February | March | April | May | June | July | August | September | October | November | December
2005: January | February | March | April | May | June | July | August | September | October | November | December
2004: September | October | November | December
2001: October | November


9 February-15 February 2011

CVO reported that on 14 February a M 4.3 earthquake near Mount St. Helens, felt widely throughout SW Washington and NW Oregon, was followed over the next few hours by several aftershocks up to M 2.8. The three largest aftershocks were also felt. All of the earthquakes were located about 8 km N of the crater, near the Johnston Ridge Observatory, at depths of about 4-6 km. CVO also noted that a previous earthquake swarm had occurred in the same area on 29 January. The Volcano Alert Level remained at Normal and the Aviation Color Code remained at Green.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 July-22 July 2008

On 10 July, CVO lowered the Volcano Alert Level for Mount St. Helens to Normal and the Aviation Color Code to Green, following the cessation of lava-dome growth in late January and about five months with no signs of renewed activity. Earthquakes, volcanic gas emissions, and ground deformation were all at pre-eruptive background levels.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 February-26 February 2008

On 21 February, CVO lowered the Alert Level for Mount St. Helens from Watch to Advisory and the Aviation Color Code from Orange to Yellow. Comparison of photographs taken by remote cameras during late January to mid-February 2008 showed no evidence of extrusion. In addition, very few earthquakes were recorded since late January, gas emissions were barely detectable, and daily ground-tilt events stopped.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 February-19 February 2008

Data from deformation-monitoring instruments indicated that during13-19 February lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds and snow cover frequently inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


6 February-12 February 2008

Data from deformation-monitoring instruments indicated that during 6-12 February lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds and snow cover frequently inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


30 January-5 February 2008

Data from deformation-monitoring instruments indicated that during 30 January-5 February lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


23 January-29 January 2008

Data from deformation-monitoring instruments indicated that during 23-29 January lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. A steam plume that rose from the dome and slightly above the crater rim was visible on 25 January. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 January-22 January 2008

Data from deformation-monitoring instruments indicated that during 16-22 January lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


9 January-15 January 2008

Data from deformation-monitoring instruments indicated that during 9-15 January lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


2 January-8 January 2008

Data from deformation-monitoring instruments indicated that during 2-8 January lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. A new small spine was seen on top of the active lobe during an overflight on 31 December. The spine was hot enough to be snow-free and interpreted as confirmation that the dome continued to grow. Clouds frequently inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


26 December-1 January 2008

Data from deformation-monitoring instruments indicated that during 26 December-1 January lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


19 December-25 December 2007

Data from deformation-monitoring instruments indicated that during 19-25 December lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


12 December-18 December 2007

Data from deformation-monitoring instruments indicated that during 12-18 December lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


5 December-11 December 2007

Data from deformation-monitoring instruments indicated that during 5-11 December lava-dome growth at Mount St. Helens continued. Based on interpretations of flow-monitoring system data, lahars flowed out of the crater on 4 December, after a weather system passed through the region. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


28 November-4 December 2007

Data from deformation-monitoring instruments indicated that during 28 November-4 December lava-dome growth at Mount St. Helens continued. Small inflation-deflation events occurred which were interpreted as dome-growth pulses. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. A GPS receiver on the W part of the active spine showed continued SW advance at a rate of 3-4 mm per day since September 2007. An image from a camera on the NE flank from 28 November showed no notable landscape changes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 November-13 November 2007

Data from deformation-monitoring instruments indicated that during 7-13 November lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


31 October-6 November 2007

Data from deformation-monitoring instruments indicated that during 31 October-6 November lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


24 October-30 October 2007

Data from deformation-monitoring instruments indicated that during 24-30 October lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


17 October-23 October 2007

Data from deformation-monitoring instruments indicated that during 17-23 October lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


10 October-16 October 2007

Data from deformation-monitoring instruments indicated that during 10-16 October lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


3 October-9 October 2007

Data from deformation-monitoring instruments indicated that during 3-9 October lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


26 September-2 October 2007

Data from deformation-monitoring instruments indicated that during 26 September-2 October lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


19 September-25 September 2007

Data from deformation-monitoring instruments indicated that during 19-25 September lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


12 September-18 September 2007

Data from deformation-monitoring instruments indicated that during 12-18 September lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


5 September-11 September 2007

Data from deformation-monitoring instruments indicated that during 5-11 September lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


29 August-4 September 2007

Data from deformation-monitoring instruments indicated that during 29 August-4 September lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 August-28 August 2007

Data from deformation-monitoring instruments indicated that during 22-28 August lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


15 August-21 August 2007

Data from deformation-monitoring instruments indicated that during 15-21 August lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


8 August-14 August 2007

Data from deformation-monitoring instruments indicated that during 8-14 August lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


1 August-7 August 2007

Data from deformation-monitoring instruments indicated that during 1-7 August lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


25 July-31 July 2007

Data from deformation-monitoring instruments indicated that during 25-31 July lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


18 July-24 July 2007

Data from deformation-monitoring instruments indicated that during 18-24 July lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


11 July-17 July 2007

Data from deformation-monitoring instruments and time-lapse cameras on the volcano indicated that lava-dome growth at Mount St. Helens continued during 11-17 July. Based on the time-lapse camera images, the lava dome was displaced southward and westward, at an average rate of 0.5 m per day at particular points. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


4 July-10 July 2007

Data from deformation-monitoring instruments indicated that during 4-10 July lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


27 June-3 July 2007

Data from deformation-monitoring instruments indicated that during 27 June-3 July lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 June-26 June 2007

Data from deformation-monitoring instruments indicated that during 20-26 June lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 June-19 June 2007

Data from deformation-monitoring instruments indicated that during 13-19 June lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


6 June-12 June 2007

Data from deformation-monitoring instruments indicated that during 6-12 June lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. Clouds inhibited visual observations during 6-11 June. A weak gas-and-steam plume was visible rising from the lava dome on 12 June.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


30 May-5 June 2007

Data from deformation-monitoring instruments indicated that during 30 May-5 June lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In general, gas and steam plumes from the active lava dome, as well as dust plumes resulting from rockfalls, occasionally rise above the crater rim; a gas plume may have been visible on 3 June. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


23 May-29 May 2007

Data from deformation-monitoring instruments indicated that during 23-29 May lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 May-22 May 2007

Data from deformation-monitoring instruments indicated that during 16-22 May lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


9 May-15 May 2007

Data from deformation-monitoring instruments indicated that during 9-15 May lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


2 May-8 May 2007

Data from deformation-monitoring instruments indicated that during 2-8 May lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


25 April-1 May 2007

Data from deformation-monitoring instruments and observations from a remote camera showed that during 25 April-1 May lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations. On 27 April, a thermal plume was detected on satellite imagery.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


18 April-24 April 2007

Data from deformation-monitoring instruments and observations from a remote camera showed that during 18-24 April lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5, and occasionally larger, earthquakes. In some instances, clouds inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


11 April-17 April 2007

Data from deformation-monitoring instruments and observations from a remote camera showed that during 11-17 April lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


4 April-10 April 2007

Data from deformation-monitoring instruments and observations from a remote camera showed that during 4-10 April lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. The clear weather allowed for views of the sometimes steaming dome from remote cameras.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


28 March-3 April 2007

Data from deformation-monitoring instruments and observations from a remote camera showed that during 28 March-3 April, lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. On 3 April, a GPS unit on an active spine showed W-ward movement at a rate of about 30 cm/day.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


21 March-27 March 2007

Data from deformation-monitoring instruments and observations from a remote camera showed that during 21-27 March lava-dome growth at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Clouds occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


14 March-20 March 2007

Data from deformation-monitoring instruments showed that during 14-20 March, lava-dome growth and lava-spine extrusion at Mount St. Helens continued. Seismicity persisted at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Inclement weather occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 March-13 March 2007

Data from deformation-monitoring instruments showed that during 7-13 March, the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Inclement weather occasionally inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


28 February-6 March 2007

Data from deformation-monitoring instruments showed that during 28 February-6 March the lava dome at Mount St. Helens continued to grow. Crater views were mostly obscured by clouds.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


21 February-27 February 2007

Data from deformation-monitoring instruments showed that during 21-27 February, the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Inclement weather inhibited visual observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


14 February-20 February 2007

Data from deformation-monitoring instruments showed that during 14-20 February the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Inclement weather inhibited observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 February-13 February 2007

Seismicity from the growing lava dome at Mount St. Helens was low during 7-13 February. Crater views were obscured by clouds.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


31 January-6 February 2007

Data from deformation-monitoring instruments showed that during 31 January-6 February, a spine on the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


24 January-30 January 2007

Data from deformation-monitoring instruments showed that during 24-30 January, a spine on the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


17 January-23 January 2007

Data from deformation-monitoring instruments showed that during 17-23 January, a spine on the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


10 January-16 January 2007

Data from deformation-monitoring instruments showed that during 10-16 January the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


3 January-9 January 2007

Data from deformation-monitoring instruments showed that during 3-9 January the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Inclement weather inhibited observations.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 December-26 December 2006

Data from deformation-monitoring instruments showed that during 20-26 December the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by earthquakes of M 1.5-2.5 and occasionally larger sizes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 December-19 December 2006

Data from deformation-monitoring instruments showed that during 13-19 December the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Observations were hindered due to inclement weather during most of the reporting period, but on 18 December, a steam plume rose several hundred meters above the rim and was visible from the Portland area, about 80 km away.

Sources: US Geological Survey Cascades Volcano Observatory (CVO), Associated Press


6 December-12 December 2006

Data from deformation-monitoring instruments showed that during 6-12 December the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


29 November-5 December 2006

Data from deformation-monitoring instruments showed that during 29 November-5 December the lava dome at Mount St. Helens continued to grow and produce small rockfalls.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 November-28 November 2006

Data from deformation-monitoring instruments showed that during 22-28 November the lava dome at Mount St. Helens continued to grow. Seismicity continued at low levels, punctuated by M 1.5-2.5 and occasionally larger earthquakes. Inclement weather prohibited visual observations during most of the reporting period.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


15 November-21 November 2006

Data from deformation-monitoring instruments showed that during 15-21 November the lava dome at Mount St. Helens continued to grow. Inclement weather prohibited visual observations during most of the reporting period. On 21 November, views from an aircraft and a crater camera showed that an active spine continued to extrude.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


8 November-14 November 2006

Data from deformation-monitoring instruments showed that during 8-14 November the lava dome at Mount St. Helens continued to grow. Inclement weather prohibited visual observations during most of the reporting period.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


1 November-7 November 2006

Data from deformation-monitoring instruments showed that during 1-7 November the lava dome at Mount St. Helens continued to grow. Inclement weather prohibited visual observation during most of the reporting period. On 5 and 6 November, acoustic flow monitors recorded rain-induced debris flows within the crater and in the upper part of the North and South Fork Toutle River valleys.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


25 October-31 October 2006

During 25-31 October, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. On 29 October, a M 3.2 earthquake was accompanied by a rockfall that produced a small plume. The plume filled the crater to just above the rim and quickly dissipated.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


18 October-24 October 2006

Observations and data from deformation-monitoring instruments showed that during 11-17 October the lava dome at Mount St. Helens continued to grow in the S crater and produce small rockfalls. On 22 October, a M 3.5 earthquake triggered the collapse of material from the largest of the lava-dome spines. The resulting ash plume rose to about 3.2 km (10,500 ft) a.s.l. and quickly dissipated to the W.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


11 October-17 October 2006

Data from deformation-monitoring instruments showed that during 11-17 October the lava dome at Mount St. Helens continued to grow and produce small rockfalls.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


4 October-10 October 2006

Lava continued to extrude onto the S crater floor of St. Helens during 4-10 October. Low levels of seismicity and periodic tilt of the crater floor accompanied small rockfalls. A small steam plume was visible on 9 October.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


27 September-3 October 2006

There were minor rockfalls off of the new dome at St. Helens during 27 September-3 October as lava emerged slowly from the vent onto the S crater floor. Seismicity and rates of deformation were low. The new dome is now nearly as high as Shoestring notch on the SE crater wall.

The alert-level system for all volcanoes monitored by the USGS was changed on 1 October from a numerical system to a descriptive system. In the new system, alert-level Normal indicates background conditions and is equivalent to aviation color-code Green. The previous alert levels of Volcanic Unrest (Alert Level 1), Volcano Advisory (Alert Level 2) and Volcano Alert (Alert Level 3) have changed to "Advisory," "Watch," and "Warning," respectively. There is a subtle change to the aviation color-code definitions in that there is no longer an ash-plume threshold given for either Orange or Red. For Mount St. Helens, the current hazard status is "Volcano alert level: Watch; Aviation color code ORANGE." The alert-level "Watch" is used for two different situations: (1) heightened or escalating unrest indicating a higher potential that an eruption is likely, but still not certain; or (2) an eruption that poses only limited hazard. Definition 2 fits the current lava-dome eruption at Mount St. Helens well.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 September-26 September 2006

Lava continued to extrude onto the crater floor during 20-26 September with low seismicity, generating occasional rockfalls as talus sloughed off the flanks of the growing dome.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 September-19 September 2006

Data from deformation-monitoring instruments showed that the lava dome at Mount St. Helens continued to grow during 13-19 September, despite relatively low seismicity levels.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


6 September-12 September 2006

During 6-12 September, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. On 9 and 10 September, five shallow earthquakes greater than M 2 occurred in association with the growing dome.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


30 August-5 September 2006

During 30 August-5 September, the lava dome at Mount St. Helens continued to grow. A moderate sized seismic event and associated rockfall occurred on 3 September. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


23 August-29 August 2006

During 23-29 August, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 August-22 August 2006

During 16-22 August, the lava dome at Mount St. Helens continued to grow. Based on interpretations of seismic data, spine extrusion from the dome continued in conjunction with small earthquakes and rockfalls.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


9 August-15 August 2006

During 9-15 August, the lava dome at Mount St. Helens continued to grow. Earthquakes occurred during the reporting period that occasionally triggered rockfalls. A steam plume was observed rising from the growing lava dome on 13 August. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


2 August-8 August 2006

During 2-8 August, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. On 5 August, two earthquakes (the largest, M 3.6) triggered rockfalls. Resulting dust plumes rose well above the crater rim. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


26 July-1 August 2006

During 26 July-1 August, the lava dome at Mount St. Helens continued to grow. Rockfalls accompanied minor earthquakes ranging from M 3-3.6 on 26, 28, and 31 July. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


19 July-25 July 2006

During 19-25 July, the lava dome at Mount St. Helens continued to grow at a slow and steady rate producing small rockfalls. Wind and rockfalls stirred up ash that occasionally rose above the crater rim or created a haze around the summit. On 25 July, a M 3.1 earthquake generated a rockfall and associated dust/ash cloud that quickly dissipated. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

US Geological Survey Cascades Volcano Observatory

Source: US Geological Survey Cascades Volcano Observatory (CVO)


12 July-18 July 2006

During 12-18 July, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. On 18 July at 0956, a M 3.6 earthquake (one of the largest earthquakes during the ongoing eruption) triggered rockfalls from the spine and crater walls. Dust plumes rose above the crater rim and quickly dissipated. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


5 July-11 July 2006

During 5-11 July, the lava dome at Mount St. Helens continued to grow at a slow and steady rate producing small rockfalls. The hazard status remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


28 June-4 July 2006

During 28 June-4 July, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


21 June-27 June 2006

During 21-27 June, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. A small steam plume from the lava dome and dust from minor rockfalls were visible from the US Forest Service's web camera at the Johnston Ridge Observatory on 25 and 26 June. On 26 June, a pilot reported that dust and ash reached a height of ~2.4 km (8,000 ft) a.s.l. and drifted W. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


14 June-20 June 2006

During 14-19 June, the lava dome at Mount St. Helens continued to grow and produce small rockfalls. According to seismic data, a medium-sized rockfall occurred on 13 June. Incandescence was observed on satellite imagery. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 June-13 June 2006

During 7-13 June, seismic signals indicated that the lava spine continued to grow inside the crater of Mount St. Helens. On 9 June, pilots reported that an ash-and-steam plume, generated after a rockfall following a M 3.2 earthquake, reached an altitude of 4.6 km (15,000 ft) a.s.l. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Sources: US Geological Survey Cascades Volcano Observatory (CVO), Associated Press


31 May-6 June 2006

During 31 May to 6 June, seismic signals indicated the lava spine continued to grow inside the crater of Mount St. Helens and occasionally produced minor rockfalls. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


24 May-30 May 2006

During 24-25 May, seismicity remained at levels typical of the continuing lava-dome extrusion at Mount St. Helens. On 29 May, a M 3.1 earthquake and simultaneous large rockfall occurred. An ash plume was produced at 0810 that reached an altitude of 4.9 km - 6.1 km (16,000-20,000 ft) a.s.l. according to ground observations and pilot reports. An additional pilot report suggested the plume reached an altitude of 7.3 km (24,000 ft) a.s.l. By 1308, ash from the event was no longer visible on satellite imagery. On 30 May, the rockfall was confirmed to predominantly originate from the N side of the growing fin. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Sources: US Geological Survey Cascades Volcano Observatory (CVO), Washington Volcanic Ash Advisory Center (VAAC)


17 May-23 May 2006

During 17-22 May, the lava spine continued to grow inside the crater of Mt. St. Helens producing minor rockfalls and moderately-sized rock avalanches that generated small ash plumes. On 17 May, lava extrusion continued to deform the W part of the lava dome and night-time incandescence from rockfalls was observed.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


10 May-16 May 2006

Analysis of photographs revealed that a slab of rock approximately 50,000 cubic meters in volume was shed from the N margin of the growing spine at Mt. St. Helens sometime during 6-7 May. This activity probably coincided with a large seismic signal recorded on the night of 7 May. Rock-avalanche deposits extended a few hundred meters to the NE. The avalanche was accompanied by an ash cloud. The spine continued to grow during 10-15 May, producing rockfalls that intensified on the evening of 14 May. Incandescence was visible on satellite imagery. The volcano remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


3 May-9 May 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 4-8 May, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. The dome-building eruption that began in October 2004 continued at the same pace as in previous weeks, accompanied by low background levels of seismicity and other eruption indicators. A GPS (Global Positioning System) instrument on the new lava dome W of the vent continued to move W nearly 1 m per day. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


26 April-2 May 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 26 April to 2 May, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismicity continued as very small periodic earthquakes, recurring every few minutes, punctuated by occasional larger earthquakes. The active lava dome continued to build towards the W. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


19 April-25 April 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 20-24 April, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismicity continued as very small periodic earthquakes, recurring every few minutes, punctuated by occasional larger earthquakes. The larger earthquakes were typically less than M 3 and occurred at an average rate of less than one per day. The active lava dome continued to build towards the W. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


12 April-18 April 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 12-17 April, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. The eruption continued unabated as was demonstrated by a steady background of small earthquakes and steady westward movement (~1 m per day) of a GPS (global positioning system) station on the active lava dome. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


5 April-11 April 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 5-10 April, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Small earthquakes occurred once every several minutes, and GPS (global positioning system) data showed that solidified dacite lava continued to extrude slowly. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


29 March-4 April 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 29 March to 3 April, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Although the overall level of seismicity remained low, the eruption of lava into the crater continued as was evidenced by ongoing rockfalls and continuous GPS measurements made on the growing lava lobe. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 March-28 March 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 22-28 March, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Very small periodic earthquakes occurred every few minutes that were punctuated by occasional larger events. The GPS (Global Positioning System) network on the volcano continued to show spine motion on the active lava dome of ~1 m per day. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


15 March-21 March 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 15-21 March, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Monitoring instruments showed no significant change in patterns of earthquake activity or deformation. Very small periodic earthquakes occurred every few minutes that were punctuated by occasional larger (less than M 3) events. The active lava dome continued to build towards the W at about 1 m per day, consistent with the trend established over the previous few weeks. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


8 March-14 March 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 9-12 March, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Small earthquakes occurred every several minutes, punctuated by occasional larger earthquakes. The Global Positioning System (GPS) receiver on the new lava dome showed that new lava emerging from the vent was still plowing WNW at about a meter per day. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


1 March-7 March 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 1-6 March, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Small earthquakes (M 0-1.5) occurred every 2-3 minutes. Lava continued building a dome in the crater and advanced slowly W about 0.9 m per day away from the vent. Small rockfalls produced small ash clouds that rose from the lava dome's NW flank. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 February-28 February 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 22-27 February, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


15 February-21 February 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 16-20 February, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Gas measurements made on 15 February suggested that the volcanic-gas flux remained unchanged from recent measurements. Observations made on 17 February revealed that the northeastern active part of the new lava dome was developing a steeply inclined jagged spine. At its top, temperatures as high as 580 degrees Celsius were measured using a thermal sensor. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


8 February-14 February 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 8-15 February, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Comparison of photos taken between 17 December and 7 February showed that the base of the active lobe of the lava dome enlarged by about 100 meters. A series of photographs taken during the week of 5 February showed that the active part of the new lava dome continued to extrude, with points on the surface of the dome moving a couple of meters per day. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


1 February-7 February 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 1-7 February, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Occasional clear views of the volcano revealed incandescence on the currently growing lava lobe and a few incandescent rockfalls. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


25 January-31 January 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 24-31 January, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. On 24 January a shallow M 2.7 earthquake triggered a rockfall from the new lava dome, generating an ash plume that filled the crater before dissipating and drifting N over the pumice plain. Initial analysis of recent photographs from fixed cameras in the crater showed that the top of the currently active part of the new lava dome was at an elevation of ~2,240 m a.s.l., which is about 90 meters higher than it was in early November 2005. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


18 January-24 January 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 18-24 January 2006, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. The dome-building eruption has proceeded at a slow and steady pace, quietly extruding dacitic lava. Seismometers, GPS receivers, and tiltmeters show patterns basically unchanged since the first of January. With the first clear weather in over a month on 23 January, crews were in the field observing the new dome, repairing instruments, replacing batteries, and exhuming cameras from ice and snow. The new dome is noticeably taller and broader than when last viewed in December. Rockfalls from its summit generated small ash plumes that slowly rose above the crater rim and dissipated as they drifted E.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


11 January-17 January 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 11-16 January, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Small earthquakes continued to be recorded every 2-3 minutes, with slightly larger events occurring intermittently. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


4 January-10 January 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 4-9 January, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Small earthquakes continued to be recorded every 2-3 minutes, with slightly larger events occurring intermittently. Two short lulls in the pattern of earthquake activity occurred after larger than normal earthquakes. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


28 December-3 January 2006

Growth of the new lava dome inside the crater of Mount St. Helens continued during 28 December to 3 January, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Small earthquakes continued to be recorded every 2-3 minutes, with slightly larger events occurring intermittently. Tiltmeters within 500 m of the new lava dome showed small amounts of ground deformation. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


21 December-27 December 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 21-27 December, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Small rockfalls continued from the growing lava dome, with larger ones producing ash plumes that were visible above the crater rim. There were no significant changes in seismicity or deformation during the report period. Seismicity was marked by the repetitive small earthquakes, occurring every 2-3 minutes, that have come to characterize the past 15 months. Tiltmeters within 500 m of the new lava dome showed minute ground deformation; whereas the volcano's flanks were quiet. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


14 December-20 December 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 14-20 December, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Small rockfalls continued from the growing lava dome, with larger ones producing ash plumes that were visible above the crater rim. Repeat images taken on 15 December from fixed cameras within the crater and at the crater rim showed the seventh lava spine to emerge during the current activity. It continued to push upward and southwestward from a source just S of the 1980-1986 dome. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 December-13 December 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 30 November to 12 December, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. The well-established pattern of tiny "drumbeat" earthquakes continued at a rate of one every 1-2 minutes and other monitoring data remained in typical ranges. Despite the continuing procession of earthquakes, the overall seismic energy release was very low compared to that during early phases of the eruption. Small rockfalls continued from the growing lava dome, with larger ones producing ash plumes that were visible above the crater rim. The volume of the lava dome measured on 24 October was 70 million cubic meters-about 90% of the volume of the 1980-to-1986 dome. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


30 November-6 December 2005

Growth of the new lava dome inside the crater of St. Helens continued through 30 November, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


23 November-29 November 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 23-28 November, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 November-22 November 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 16-20 November, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Two notable rockfalls occurred on 22 November at 1200 and shortly after 1500. Both produced dilute ash clouds that rose a few hundred meters above the crater rim. These types of rockfalls are common during lava-dome growth. There were no significant changes in seismicity or deformation during the report period. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


9 November-15 November 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 9-14 November, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


2 November-8 November 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 2-7 November, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


26 October-1 November 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 26-31 October, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Heavy rain at the volcano increased stream flows and triggered a small debris flow on 31 October that did not extend very far down the fan at the crater mouth. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


19 October-25 October 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 19-25 October, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. The results from a gas flight on 18 October revealed low SO2, CO2, and H2S emission rates similar to those measured during the previous flight a few weeks ago. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


12 October-18 October 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 12-18 October, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. During the previous few weeks, a prominent linear feature developed on the disintegrating "whaleback" that grew during the previous spring and summer and was currently located E of the actively growing part of the new lava dome. A digital elevation model of the active lava dome, which was created from aerial photographs taken on 10 August, showed that the volume had grown to 62 million cubic meters. The average rate of growth during late July and early August was about 2 cubic meters per second, a rate that typified most of 2005. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


5 October-11 October 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 6-11 October, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Images taken on 10 October showed that the pattern of dome growth established during the previous few months continued. The actively growing portion of the dome moved northwestward, pushing the W arm of the glacier against the W crater wall, causing the glacier to narrow, thicken, and become increasingly fractured. Rockfalls shed dome debris onto the glacier and onto the N flank of the old lava dome. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


28 September-4 October 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 28 September to 4 October, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period and the level of eruptive activity remained similar to previous weeks. Reanalysis of late September time-series photographs of the active part of the new lava dome indicated that points on the dome moved northwestward and upward at about 5.5 meters per day as extrusion continued. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


21 September-27 September 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 21-26 September, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Time-series images showed that the active northwestern portion of the new lava dome continued to move westward into the W arm of a glacier, spawning rockfalls. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


14 September-20 September 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 14-19 September, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Camera images showed that the northern part of the lava dome continued to move westward. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 September-13 September 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 7-13 September, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. There were no significant changes in seismicity or deformation during the report period. Dry conditions and rockfalls continued to stir ash within the crater, and a persistent gas-and-vapor plume rose from the lava dome. As has happened in the past, large rockfalls from the dome generated conspicuous ash plumes that occasionally rose above the crater rim and drifted downwind. Camera images showed continued slumping of the central part of the dome and westward motion of the presently active area. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


31 August-6 September 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 31 August to 6 September, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Images of the crater showed continued westward motion of the new lava dome. There were no significant changes in seismicity or deformation during the report period. On 6 September, dry conditions and rockfalls from the lava dome generated occasional ash plumes that rose above the volcano and rapidly dissipated. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


24 August-30 August 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 24-29 August accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Growth of the lava dome continued to spawn rockfalls. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


17 August-23 August 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 17-22 August accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Growth of the lava dome continued to spawn rockfalls, which produced ash plumes that occasionally rose above the rim. A large rockfall on 21 August at 2056 generated a bright glow of hot rock and a thick ash plume that temporarily affected radio transmissions from instruments in the crater. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


10 August-16 August 2005

During 10-15 August, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. During the report period, there were no significant changes in seismicity or ground deformation. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


3 August-9 August 2005

Mount St Helen's lava dome growth, low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash continued during 3-9 August. Dry conditions and an E wind combined this week to create a diffuse dust plume that streamed W from the crater rim. Some of the dust came originated with rockfalls from the crater walls and new lava dome, but most of it was probably from wind-eroded ash that had accumulated since the eruption began last October. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


27 July-2 August 2005

Rockfalls and associated minor ash plumes continued to be generated from Mount St Helen's growing lava dome during 27 July to 2 August. Measurements taken on 27 July revealed that emission rates of volcanic gases remained fairly constant, with 60 tons per day of sulfur dioxide and 880 tons per day of carbon dioxide. Analysis of a rock sample collected from the dome on 13 July showed no change in the composition of lava being extruded. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 July-26 July 2005

During 20-26 July, several rockfalls at Mount St. Helens were triggered by earthquakes around M 3. Some of the rockfalls produced ash plumes that rose to low altitudes. Analysis of a digital elevation model created from aerial photographs taken on 15 June showed that the volume of the new lava dome was about 54 million cubic meters, or about 60% of the volume of the lava dome that grew in the crater from 1980 to 1986. The rate of addition of lava to the dome from mid-May to mid-June remained at ~1.5 cubic meters per second. Images of the summit taken around 25 July showed that the lava spine at the N end of the dome continued to extrude at a rate similar to that of the previous few weeks, but the rate of rockfalls was greater and the height of the top of the spine was decreasing. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 July-19 July 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 13-18 July, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. On 16 July at 1308, an M 3.2 earthquake occurred. The earthquake was followed by a rockfall that produced an ash plume that rose above the volcano's crater. Another rockfall at 2110 produced a small ash plume that was visible from the city of Vancouver, Washington ~70 km SW. CVO reported that frequent rockfalls are to be expected due to the steep-sided dome rising hundreds of meters above the crater floor. After the earthquake, seismicity returned to normal levels. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


6 July-12 July 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued during 6-12 July, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. CVO reported on 12 July that rates of seismicity and ground deformation at Mount St. Helens had declined during the previous 2 weeks to some of the lowest levels since the eruption began in September 2004. They reported that a similar lull in activity occurred in December 2004, so it does not mean that the eruption is necessarily ending.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


29 June-5 July 2005

During 29 June to 5 July, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by seismic and deformation data trends similar to those of the previous few weeks. On 2 July at 0630 a rockfall from the growing lava dome removed a large piece of the top of the dome, producing an ash plume that rose above the crater rim and generating a substantial seismic signal. Persistent smaller rockfalls from the growing lava dome built talus aprons on the W and NE flanks of the dome.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 June-28 June 2005

During 22-28 June, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by seismic and deformation data trends similar to those of the past few weeks. The smooth lava spine continued to grow at a rate of about 1.8-3.7 m per day. Rockfalls from the top of the spine keep its height from increasing by that same rate. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


15 June-21 June 2005

During 15-20 June, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Observations made on 15 June revealed that the lava spine continued to grow and that temperatures in cracks near the base of the spine were near 700 degrees C. Thermal data from 15 June suggested that much of the western part of the dome was moving upward, as well as southward. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


8 June-14 June 2005

During 8-13 June, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismic and deformation data continued trends similar to the previous few weeks, with small earthquakes every ~5 minutes, little to no movement of the old lava dome, minor movement of the N end of the new lava dome, and continued growth of the lava spine. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


1 June-7 June 2005

During 1-6 June, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismicity remained unchanged during the report period. Around 4 June the rate of motion of a GPS unit on the N end of the new dome slowed slightly, continuing to creep eastward and northward at a rate of several centimeters per day, but it no longer rose vertically. The lava spine, however, continued to grow. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


25 May-31 May 2005

During 25-31 May, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Lava extrusion continued at the N end of the new lava dome, while the high spines continued to crumble. Other parts of the lava dome moved at the relatively low velocity of about 0.3 m per day or remained stagnant. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


18 May-24 May 2005

During 18-24 May, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismicity and ground deformation continued at rates similar to those of the previous few weeks. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


11 May-17 May 2005

Images from a camera at the mouth of the crater showed the new spine of lava at the N end of the dome continuing to grow during 11-12 May. Data from seismic and GPS instruments in the crater and on the outer flanks of the volcano show no significant changes from readings of the past few weeks. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


4 May-10 May 2005

Poor weather obscured the volcano during most of this period. VolcanoCam detected intermittent glow from the growing lava dome through much of the night of 4-5 May. Seismic and ground-deformation activity remained unchanged. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


27 April-3 May 2005

During 27 April to 3 May, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. On the morning of 28 April there were reports of minor amounts of ashfall in the eastern part of the Portland metropolitan area. There was no evidence of a new explosion. CVO scientists determined that large convective storms over the Cascades on 27 April entrained ash generated by the frequent hot rockfalls from the growing lava dome and kept it in suspension to fall out as far away as Portland.

CVO corrected the volume of the new lava dome measured on 10 March, with the new estimate at 45 million cubic meters. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 April-26 April 2005

During 20-25 April, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Analysis of aerial photographs indicated that as of 10 March the topographic changes in the crater resulting from growth of the new dome and consequent glacier deformation had a combined volume of about 47.4 million cubic meters. The current eruption had thus far caused a total topographic change in the crater equivalent to about two-thirds the volume of the old lava dome. Qualitative analysis of recent photographs suggested that the rate of extrusion at the N end of the new lava dome continued at about 2-3 meters per day. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 April-19 April 2005

During 13-19 April, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. GPS instruments showed that displacement of the old lava dome had slowed for several days around 18 April. CVO reported that such relative quiescence has been observed previously at the volcano during the current eruption, and should not be taken to mean that the eruption was ending. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


6 April-12 April 2005

During 6-11 April, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Observations on 6 April revealed that the smooth whaleback-shaped portion of the growing lava dome was broken by numerous fractures, and the edges had crumbled greatly. Several deep gashes on the E, N, and W sides frequently produced rockfalls and accompanying ash clouds. On 10 April the new dome continued to fracture and spread laterally. As a consequence, the dome's summit has dropped by a few tens of meters during the previous 2-3 weeks, except for isolated high-standing remnants.

Earthquakes steadily decreased in magnitude and number over the week. A GPS receiver 200 m N of the new dome crept steadily NNW about 10 cm per day. The combination of the GPS measurements adjacent to the lava dome and the qualitative estimate of lateral spreading suggested that extrusion of new lava continued during the report week. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


30 March-5 April 2005

Growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. As has happened on several occasions during the lava-dome-building phase of the eruption, a series of large (equal to or greater than M 3) earthquakes occurred during 3-4 April, in addition to the typical array of smaller events. CVO warned that during such eruptions, episodic changes in the level of activity can occur over days to months.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


23 March-29 March 2005

During 23-29 March, growth of the new lava dome inside the crater of Mount St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. CVO noted that during such eruptions, episodic changes in the level of activity can occur over days to months. During about 26-27 March, a group of M 2 to M 3 earthquakes occurred beneath the volcano, a level of activity considered normal during dome-emplacing volcanism.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 March-22 March 2005

During 16-21 March, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. CVO noted that during such eruptions, episodic changes in the level of activity can occur over days to months.

Results from a digital elevation model produced from imagery taken on 21 February showed that the highest part of the new lava dome was 12 m (~40 ft) higher than on 1 February and that the volume of dome and surrounding uplift had increased by 3 million cubic meters (4 million cubic yards) during that 3-week period. The average rate of growth continued at about 2 cubic meters (2.7 cubic yards) per second. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


9 March-15 March 2005

A small but significant explosion that occurred at St Helens on 8 March at 1725 produced a fine dusting of ash in Ellensberg, Yakima, and Toppenish, Washington during 1900-2100. By 0200 on 9 March, the leading edge of the faint, diffuse plume had reached western Montana. Scientists found that St. Helens' lava dome was intact after the explosion and that ballistics up to ~1 m in diameter were hurled as far as the northern flank of the old lava dome. No ballistics were found along, or beyond the crater rim. The source of the explosion was from the NNW side of the new lava dome and was very near the source of the 1 October 2004 and 16 January 2005 explosions.

After the 8 March explosion, St. Helens only emitted steam, and seismicity returned to a level similar to that during the several hours prior to the explosion. Gas emissions were very low, essentially unchanged from those measured in late February. During 9-15 March, St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


2 March-8 March 2005

A small explosive event began at St. Helens at approximately 1725 on 8 March. Pilot reports indicated that the resulting steam-and-ash plume reached a height of about 11 km a.s.l. within a few minutes and drifted downwind ENE. The principal event lasted about 30 minutes with intensity gradually declining throughout. There were no reports of deaths or injuries. This was one of the largest steam-and-ash emissions to occur since renewed activity began at St. Helens in October 2004. CVO lost radio signals from three monitoring stations in the crater soon after the event started. The event followed a few hours of slightly increased seismic activity that was noted, but was not interpreted as precursory. There were no other indications of an imminent change in activity.

Prior to the explosion, during 2-7 March, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismic data indicated that parts of the growing lava dome continued to crumble, forming rockfalls and generating small ash clouds that drifted out of the crater. The bulging ice on the deformed E arm of the glacier in the volcano's crater continued to rapidly move northward about 1.2 m per day.

CVO stated that the current hazard assessment for the ongoing eruption mentions the possibility of events like the 8 March explosion occurring without warning, and the assessment remained unchanged. The eruption could intensify suddenly and with little warning and produce explosions that cause hazardous conditions within several miles of the crater and farther downwind. Small lahars could suddenly descend the Toutle River if triggered by heavy rain or by interaction of hot rocks with snow and ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS) but could pose a hazard along the river channel upstream.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


23 February-1 March 2005

During 23 February to 1 March, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismic data indicated that parts of the growing lava dome continued to crumble, forming rockfalls and generating small ash clouds that drifted out of the crater. Photographs taken on 28 February showed that the W and E margins of the new lava dome were crumbling and that the smooth whaleback form of the lava dome was disintegrating. According to CVO, this process also occurred in December 2004 and in that case several weeks later lava-dome extrusion again manifested a whaleback form. GPS measurements on the bulging E arm of the glacier within St. Helens' crater showed that rapid northward movement of 1.2 m per day continued. St. Helens remained at Volcano Advisory (Alert Level 2); aviation code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


16 February-22 February 2005

During 16-22 February, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. A GPS unit deployed on 16 February on the E arm of the glacier within the volcano's crater moved northward about 1.2 m per day. This rapid rate of flow was consistent with the thickening of the glacier that resulted from its compression between the growing lava dome and E crater wall. A thermal imaging flight on the 16th suggested that a longitudinal crack was developing along the top of the new lava dome.

On the afternoon of 18 February, a rockfall off of the lava dome produced an ash plume that rose several hundred meters above the crater rim. CVO reported that extensive cracking on the long, smooth, whaleback-shaped lava dome suggested that increased rockfall activity and similar small plumes could occur in the coming weeks. Analysis of recent airphotos showed that as of 1 February the high point on the whaleback-shaped extrusion was 2,330 m (nearly 425 m above the 1980 crater floor and 150 m above the top of the old lava dome). The extrusion was about 470 m long, and 150 m wide. The new lava dome, uplifted area of crater floor, and deformed glacier ice grew to a combined volume of about 38 million cubic meters, almost one-half the volume of the old lava dome. St Helens remained at Volcano Advisory (Alert Level 2); aviation code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


9 February-15 February 2005

During 9-15 February, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Gas emissions were unchanged in comparison to recent measurements. On 14 and 15 February, the GPS instrument installed on the new lava dome moved an average of 6 m per day mostly southeastward with an upward component of about 1 m per day. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


2 February-8 February 2005

During 2-7 February, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. On the afternoon of 2 February several small ash clouds rose from the lava dome, cleared the volcano's rim, and drifted E. Bursts of small ash clouds from the base of the lava dome continued on 3 February. By 7 February only steam was emitted from the volcano. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


26 January-1 February 2005

During 26 January to 1 February, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Seismicity continued at roughly the same rate as that of mid-December. Small earthquakes (M less than 1.5) occurred 2-3 times per minute beneath the new lava dome. The GPS receiver located on new lava-dome rock continued its steady ESE progression. GPS receivers on the 1980-86 lava dome, which lies to the N, continued their trifling northward travel. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


19 January-25 January 2005

During 19-25 January, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. On 19 January, crews investigated the effects of an eruption that occurred on 16 January around 0300. During a 17-minute period, there were explosive emissions of ash and volcanic blocks from the vent area at the N end of the growing lava dome. A shower of ballistic fragments pockmarked a snow-covered area up to several hundred meters NE of the lava dome with craters up to 1 m in diameter. Ash fell thickly in E and W parts of the crater and drifted eastward over the rim depositing a thin layer of gray ash on the E flank outward for at least 3 kilometers. The scale and impact of the explosion was similar to that of 1 October 2004.

Analysis of a digital-elevation model made from photographs taken on 3 January provided new information about the size of the lava dome. Since last measured on 11 December 2004, the lava dome had maintained its 475-meter length, which was constrained by the old lava dome and crater wall, but widened from 310 to 410 m. Its highest point was 7 m higher. The entire lava dome increased in volume from 30 to 34 million cubic meters, an average rate of about 2 cubic meters per second. Based on these results CVO suggested that the rate of lava extrusion had decreased from autumn 2004 rates. St Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


12 January-18 January 2005

Lava-dome growth continued at St. Helens during 12-18 January. Seismicity continued at a very low level. A large slab on the west side of the dome collapsed and generated a small rock avalanche and ash cloud that drifted over the south crater rim. A bright glow on the VolcanoCam seen the night of 13 January was likely caused by this event.

New instrumentation packages installed on and near the new lava dome on 14 January, including a video camera, gas sensor, GPS, and seismometer, stopped transmitting data early on 16 January. Analysis of seismic and other data from about 0300 on 16 January, when two instruments on and near the new dome ceased functioning, suggests that a steam and ash emission occurred, perhaps accompanied by ejection of ballistic fragments. The event lasted about 18 minutes. During that time radio-telemetry signals from a few other instruments in the crater were interrupted temporarily, probably as the result of ash in the air. In the 24 hours prior to the event, the GPS on the north end of the new dome moved southward and upward more than 8 m, showing that dome extrusion continues at a vigorous pace. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


5 January-11 January 2005

Lava-dome growth continued at St. Helens during 5-11 January. Low seismicity also continued - interspersed with a few earthquakes per day as large as about magnitude 1.5. Photographs revealed that the N end of the new dome emerged at a rate similar to that observed over the past several weeks, and that movement of this part of the dome was somewhat decoupled from the fractured bulk of the dome farther S. Thus, during the past several weeks different parts of the dome moved and shifted at different rates. In regard to the issue of the overall (longer-term) rate of dome growth, photographs suggested this had slowed since late November. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


29 December-4 January 2005

Lava-dome growth continued at St. Helens during 28 December to 4 January. Observations on 3-4 January indicated that the new dome, with the exception of the northern-most portion, was becoming heavily fractured and faulted. GPS data showed that expansion of the rear part of the dome had slowed to a rate of only a few meters per day. Seismicity decreased dramatically during 29-30 December, reaching the lowest levels recorded since dome building began. This lull continued through 4 January. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 December-28 December 2004

During 22-28 December, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Analysis of gas emissions sampled during the previous week revealed that no significant change had occurred. On 27 December, field instruments indicated that the lava dome continued to grow at a rapid rate. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


15 December-21 December 2004

During 16-20 December, growth of the new lava dome inside the crater of St. Helens continued, accompanied by low rates of seismicity, low emissions of steam and volcanic gases, and minor production of ash. Observations on 16 December revealed that the lava dome had noticeably widened, the prominent fracture system along its top continued to widen, and ash was intermittently emitted from hot cracks.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


8 December-14 December 2004

During 8-14 December, growth of the new lava dome inside the crater of St. Helens continued and was accompanied by intermittent emissions of steam and ash. Overall seismicity remained at low levels compared to that observed early in this unrest, consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggested that the lava reaching the surface was gas poor, thereby reducing the probability of highly explosive eruptions in the near term.

A reading on 8 December from a single GPS (global positioning system) station high on the outer SE flank of the volcano showed about 2 cm of progressive southeastward movement over the previous 3 weeks. According to CVO, this minimal movement was apparently in response to new lava impinging on the SE crater wall and is an expected consequence of the nature of the dome growth occurring in the crater. Aerial views of the crater on 11 December showed that the new lava dome was becoming increasingly fractured as a new, ambiguous, pattern of growth began to emerge. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


1 December-7 December 2004

During 1-7 December, growth of the new lava dome inside the crater of St. Helens continued and was accompanied by intermittent emissions of steam and ash. Overall seismicity remained at low levels compared to that observed early in this unrest, consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term. During the report period, a steam plume rose above the S crater rim. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


24 November-30 November 2004

During 24-30 November, growth of the new lava dome inside the crater of St. Helens continued and was accompanied by intermittent emissions of steam and ash. Overall seismicity remained at low levels compared to that observed early in this unrest, consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.

A shallow M 3.1 earthquake that occurred in the volcano's crater on 27 November around 0500 was the first earthquake greater than M 3 that had been recorded since the new lava dome emerged in mid-October. This and other similar-sized earthquakes during the report period represented nothing unusual in the expected sequence of events accompanying lava-dome growth.

Good weather conditions on 29 November allowed photographs to be taken of the new lava dome in the S part of the crater with a welt, or broad area of uplift. The dome was smooth and elongated due to ongoing extrusion from a vent on its N end, which lies at the S margin of the 1980-86 lava dome. The lava emerged from the vent with enough strength that it pushed earlier-extruded lava S toward the crater wall. The leading edge of the extruded lava reached the crater wall. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


17 November-23 November 2004

Growth of the new lava dome inside the crater of St. Helens continued and was accompanied by intermittent emissions of steam and ash. When weather permitted during the report period, a plume was observed rising passively and drifting out of the crater. The plume occasionally contained minor ash, which fell out in the crater and on the flanks of the volcano, darkening the snow.

Seismicity remained at low levels compared to that observed early in this unrest. The current seismicity is consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding the extrusion of lava onto the surface, where it builds a dome. The overall low rates of seismicity and gas emission suggest that the lava reaching the surface is gas poor, thereby reducing the probability of highly explosive eruptions in the near term.

A new GPS site installed 20 November near the top of the new lava dome showed that the highest point on the new lava dome is at an altitude of 2256 m a.s.l, or about 76 m higher than the summit of the 1980-86 lava dome. In its first 24 hours near the top of the new lava dome, this GPS site moved about 10 m to the SE and 2 m vertically, confirming visual and photographic observations that the new lava dome is moving at an impressive rate.

Gas measurements taken on 20 November show that daily gas emissions remain at a more or less constant rate of around 180 metric tons of sulfur dioxide, about 900 metric tons of carbon dioxide, and several metric tons of hydrogen sulfide.

St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


10 November-16 November 2004

Growth of the new lava dome inside the crater of St. Helens continued and was accompanied by intermittent emissions of steam and ash. When weather permitted during the report period, a plume was observed rising passively and drifting out of the crater. The plume occasionally contained minor ash, which fell on both the crater and flanks, darkening the snow.

Seismicity remained low compared to that observed early in this episode of unrest, consistent with continued slow uplift of the crater floor and surface extrusion of lava. Overnight on 16 November, three earthquakes in the M 2.5-2.8 range shook the crater floor, behavior considered typical during an episode of dome growth. The overall low rates of seismicity and gas emission suggested that the lava reaching the surface was gas-poor and unlikely to generate highly explosive eruptions in the near term.

Recent extrusion-rate estimates of ~4 cubic meters per second were slightly lower than those in mid-October. These rates, which are based on the volume of deformed crater floor and the amount of airborne sulfur dioxide measured during gas-monitoring flights, have uncertainties associated with their calculation. Volcanoes like St. Helens are expected to undergo slight variations in their extrusion rates during eruptive cycles. This change is small and does not indicate a notable change in the eruptive process.

Good viewing conditions on 10 November revealed continued growth of the lava dome. Current estimates are that the welt, the broad area of deformation, is about 600 m in diameter. The new lava dome, which occupies the central and western parts of the welt, is about 400 by 180 m. The highest point on the new lava dome is about 250 m above the former surface of the glacier that occupied that point in mid-September. Maximum surface temperatures on the new dome remain at about 700 degrees Celsius. GPS instruments on the welt show rates of movement of up to several meters per day, while GPS instruments on the 1980-86 lava dome show movements of up to 1-2 cm per day northward, away from the growing welt and new dome.

St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


3 November-9 November 2004

According to CVO, during 3-8 November, seismicity at St. Helens remained at a low level compared to early in the unrest. The seismicity during the report period was consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggested that the lava reaching the surface was gas poor, thereby reducing the probability of highly explosive eruptions in the near term.

Fieldwork conducted on 4 November revealed that the elongated new lava dome, which extends S from the 1980-1986 lava dome, had undergone substantial vertical growth since 27 October. A new mass of dacite extruded upward as much as 100 m. Exposed rock faces had temperatures between 400 and 500 degrees Celsius, creating incandescence that could be seen from the N on clear nights. Samples of the dome were similar to those collected on 27 October and to lava erupted in the 1980s. Most dome growth was vertical, with only about 30 m of outward growth in some directions. Hot rockfalls and avalanches occurred from the steep new faces on the dome. The finer particulates from these deposits roiled upward within the steam plume to about 800 m above the crater rim. Consequently, the near S and SW flanks of the volcano received a notable dusting of ash. The thick glacial ice that forms a buttress on the S and E sides of the dome remained largely intact. All dome growth was contained within the St. Helens crater. A continuous GPS (Global Positioning System) station N of the volcano had moved to the S by about 2 cm since late September or early October. Aerial observations on 7 November revealed that the new lava dome continued to expand and move upward. Small aprons of rockfall debris accumulated at several sites around the new dome. CVO stated that some ash emissions may be caused by these rockfalls as collapsing hot dome lava disintegrates into smaller fragments. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


27 October-2 November 2004

According to CVO, during 28 October to 1 November, seismicity at St. Helens remained at a low level compared to early in the unrest. The seismicity during the report period was consistent with a continuing, slow rise of magma driving uplift of the crater floor and feeding a surface extrusion of lava. The overall low rates of seismicity and gas emission suggested that the lava reaching the surface was gas poor, thereby reducing the probability of highly explosive eruptions in the near term. Field work conducted on 27 October revealed several new observations. A new GPS (Global Positioning System) station on the southern part of the new lava dome moved downward and SE. A GPS station near the summit of the old lava dome had moved northward about 7 cm since 20 October. Thermal imaging showed an elongate band of elevated surface temperature, locally as great as 775° C along the W face of the new lava dome coincident with the area of exposed newly extruded lava. Gas-emission rates measured that day were similar to recent previous measurements (SO2 at about 250 tons per day, CO2 at about 300 tons per day, H2S at about 2 tons per day). In addition, samples of lava-dome rock similar in appearance to the rock of the older lava dome were collected from two localities in the vicinity of the exposed new lava. Overall, the results indicated that the character and rise of magma continued as it has over the past few weeks. CVO reported on 29 October that GPS, LIDAR (LIght Detection and Ranging), and photogrammetric measurements, in combination with visual observations over several days suggested that the lava-dome complex was spreading outward at its margins, similar to the expected behavior of a viscous lava flow. St. Helens remained at Volcano Advisory (Alert Level 2); aviation color code Orange.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


20 October-26 October 2004

During 21-26 October, the new lava dome inside the emerging dome of St Helens continued to grow, and seismicity remained at low levels compared to early in the unrest. Geological and thermal-imaging observations on 20 October confirmed that both the area of uplift, and the new lava extrusion increased in size noticeably since last seen on 14 October. In addition, the area of uplift and intense deformation continued to move southward and was nearing the crater wall. About 0.3 m of new snow with a light dusting of ash covered much of the uplift, except for the new lava extrusion, which was steaming heavily. The new lava extrusion, which occupies the western part of the uplift, was about 275 m long by 75 m wide, 70 m high, and had a volume of almost 1.5 million cubic meters. Its maximum temperature was about 600 degrees C. Low levels of carbon dioxide, sulfur dioxide, and hydrogen sulfide were recorded on the 20th, an observation which did not rule out the continued rise of magma from depth. On 21 October a new protrusion that had a maximum temperature of about 650 degrees C.

Analyses of samples from the new lava dome collected on 20 October suggested that since lava first appeared on 11 October it has been rising more rapidly from depth and not spending much more than a few days at shallow levels before being extruded onto the surface. Reviews of several lines of evidence confirmed that the average rate of volume change for the deformed area and new lava dome between late September and mid-October was about 8 cubic meters (a typical dump-truck full) per second. According to CVO, a substantial part of that change must be magma, which suggests a rate similar to that for many other lava-dome-building eruptions.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


13 October-19 October 2004

During 13-18 October, seismicity was at low levels at St. Helens and growth of the new lava dome inside the volcano's crater continued. Gas-sensing flights on 13 October detected low levels of sulfur dioxide and hydrogen sulfide, but no carbon dioxide. Measurements of flow rate and temperatures in streams draining the crater showed no significant change from late September values. On 14 October, visual observations and thermal imaging of the crater showed enlargement of both the section of intense deformation and uplift on the S side of the 1980-86 lava dome, and the new lobe of lava in the W part of that area. Temperatures of almost 700 degrees C were measured in parts of the new lobe from which ash-rich jets rose tens of meters. Abundant steam continued to rise from the area of lava extrusion to the crater rim, where it dispersed southwestward in strong winds. On the 14th only sulfur-dioxide flux was detected, and there was no detectable carbon dioxide or hydrogen sulfide. Thermal imaging showed slow extrusion of lava continuing on the 14th. Global Positioning System (GPS) measurements on 15 October continued to indicate only minor deformation of the northern part of the 1980-86 dome and no deformation of the volcano's outer flanks. Parts of the area of uplift and new lava dome were higher than when previously seen on 14 October. On the evening of 16 October, rainfall triggered a small debris flow that traveled N from the crater and changed rapidly into a muddy stream flow within 5 km of the volcano. Through 18 October, the level and character of seismicity was consistent with a continuing rise of magma driving uplift of the crater floor and feeding the surface extrusion of lava. According to CVO, low rates of seismicity and gas emission suggested that the lava reaching the surface was gas poor.

CVO stated on 18 October that as long as this eruption is in progress, episodic changes in the level of activity can occur over days, weeks, or even months. Increase in the intensity of eruption could occur suddenly or with very little warning and may include explosive events that produce hazardous conditions within several kilometers of the volcano. Small lahars (volcanic debris flows) could suddenly descend the Toutle River valley if triggered by heavy rain or by interaction of hot rocks with snow or glacier ice. These lahars pose a negligible hazard below the Sediment Retention Structure (SRS), but could pose a hazard to people along the river channel upstream of the SRS. At this time of year, it is not unusual for rivers draining the volcano to contain high concentrations of sediment that turn the water murky. Although considered less likely at this time, the current eruptive activity could evolve into a more explosive phase that affects areas farther from the volcano and sends significant ash thousands of feet above the crater where it could be a hazard to aircraft and to downwind communities.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


6 October-12 October 2004

Following a steam-and-ash emission at St. Helens on 5 October, seismicity dropped to low levels and CVO reduced the warning from Volcano Alert (Alert Level 3: aviation color code Red), to Volcano Advisory (Alert Level 2: aviation color code Orange). During 6-12 October, seismicity was at low-to-moderate levels, with the highest magnitude earthquakes (M 2.4) occurring at a rate of one every 2 minutes on 8 October.

On 6 October only weak steam puffs were emitted from the volcano and CVO scientists confirmed that the top of the area of intense uplift was at or slightly above the highest point on the lava dome, which suggested that some uplift occurred during the period of low seismicity. Scientists also confirmed that small lahars spilled out of the crater and onto the Pumice Plain during a rainstorm the evening of 5 October. Lahars traveled a short distance toward Spirit Lake and the North Fork Toutle River. CVO received reports that a light dusting of ash from the emission on 5 October affected the eastern part of Mount Rainier National Park, ~110 km NNE of St. Helens. A new steam vent opened during the evening of 6 October, joining two that had been present for several days.

Measurements from recent photographs and LIDAR (LIght Detection And Ranging) showed that as of 7 October the intensely deformed and uplifted area on the S side of the 1980-86 lava dome was ~400 m (N-S) by ~490 m (E-W) with a maximum uplift of about 90-120 m. Additional analysis revealed that the total volume change represented by the deformation between late September and 6 October was ~16 million cubic meters. The average rate of change was ~2 million cubic meters per day. On 11 October, thermal imaging of the western part of the uplifting area revealed temperatures of 500 to 600 degrees C on a large pinkish-gray fin of rock and in nearby fumaroles and cracks. These observations are consistent with new lava having reached the surface of the uplift. A gas-sensing flight on 11 October measured fluxes of sulfur dioxide and carbon dioxide that were similar to, or slightly smaller than, those measured on 7 October.

CVO reported on 13 October, "As a result of the intense unrest of the past two and one-half weeks and recent observations, we infer that magma is at a very shallow level and is extruding onto the surface. Incandescence from hot rock or gases reflects off steam clouds and is visible from north of the volcano. During times of unrest, Mount St. Helens and similar volcanoes elsewhere typically go through episodic changes in level of unrest over periods of days to weeks, or even months. Such changes are in part driven by variations in the rate of magma movement. We expect fluctuations in the level of unrest to continue during coming days. Escalation in the degree of unrest could occur suddenly or with very little warning. There may be little time to raise the alert level before a hazardous event occurs."

Source: US Geological Survey Cascades Volcano Observatory (CVO)


29 September-5 October 2004

Shortly before noon on 1 October, Mount St. Helens emitted a plume of steam and minor ash from an area of new crevasses that had opened in a portion of the crater glacier between the headwall of the 1980 crater and the lava dome. This marked the first eruption from Mount St. Helens since a series of phreatic explosions during 1989-1991. The area of the new vent, located at the southern base of the lava dome, had become increasingly crevassed and uplifted over the previous few days. The event lasted from 11:57 to 12:21 PDT and created a pale-gray cloud that reached an altitude of about 9700 ft (from pilot reports) and drifted SW. USGS scientists making thermal measurements witnessed the emission and noted that the clouds were not particularly hot. Blocks of rock and ice ejected by the event fell in the crater and rim areas. The emission was accompanied by an abrupt drop in seismicity, which remained at low levels.

Prior to the eruption, on 29 September CVO raised the Alert level to 2 (out of 3) due to a significant increase in seismicity overnight. The Volcano Alert was raised to the highest level on 2 October due to a change in the type of seismic signals (50-minute-long tremor) that occurred immediately after a small steam emission at 1215 that day. A small 2-minute-long eruption occurred around noon on 4 October from the vent just S of the lava dome, sending a steam and minor ash plume to an altitude of about 3 km. It drifted SW accompanied by minor ashfall in areas close to the volcano.

During the evening of 3 October, seismicity increased until a steam (and possibly ash) emission around 2240. The plume barely rose to the crater rim. On 4 October, there were 30- and 10-minute-long steam-and-ash emissions at 0943 and 1410, respectively. The larger emission dusted roads SE of the volcano with ash. The maximum thickness of the ash at 8 km distance was 0.2 mm. Neither event generated earthquakes or an explosion signal. CVO scientists inferred that the eruption occurred because hot rock was pushed up into the glacier, melted ice, and generated the steam. On 5 October earthquake energy slowly increased to previous high values.

Shortly after 9:00 a.m. PDT on 5 October, the most vigorous steam and ash emission of the current period of activity began. The emission originated from the same vent as have others this past week, as well as from another nearby new vent in the intensely deforming area on the south side of the 1980-86 lava dome. Steam clouds billowed from the crater for more than one hour. Ash content varied with intensity of steam jetting from the vent, and ash plumes at times billowed above the 1980 crater rim. For the first time, ash content was sufficient that it was detected by National Weather Service Doppler Radar. Steam and ash clouds reached about 12,000 feet and drifted NNE. Media reports indicated that a light dusting of ash fell in Morton, Randle, and Packwood, Washington, towns ~30 miles N of the volcano. There were no reports of ash falling at greater distances.

Following the 5 October steam-and-ash eruption, seismicity dropped to a low level and remained low. Low-level tremor observed following the eruption also gradually declined. Lack of earthquake and rockfall signals suggested that deformation of the uplift area on the south side of the 1980-86 lava dome had slowed. Brief visual observations the morning of 6 October from Coldwater Visitor Center showed weak steam emissions from the crater. Because the USGS inferred that the vigorous unrest of the past few days had lessened and that the probability of an imminent eruption that would endanger life and property was significantly less than at any time since 2 October, the alert level was lowered to Volcano Advisory (Alert Level 2).

Source: US Geological Survey Cascades Volcano Observatory (CVO)


22 September-28 September 2004

CVO issued a Notice of Volcanic Unrest for Mount St. Helens on 26 September. They reported that increased activity started when a swarm of very small, shallow earthquakes (less than M 1) began on the morning of 23 September. The swarm peaked by about mid-day on 24 September and slowly declined through the morning of the 25th. The character of the swarm then changed to include more than 10 larger earthquakes (M 2-2.8), the most in a 24-hour period since the last eruption in October 1986. In addition, the character of some of the earthquakes suggested the involvement of pressurized fluids (water and steam) or magma. The events continued through 27 September at shallow depths (less than 1.6 km) below the lava dome that formed in the crater between 1980 and 1986.

As of the 27th, seismicity had slowly increased throughout the day and the largest earthquake recorded was about M 1.5. CVO crews installed global positioning system (GPS) equipment to monitor any ground movement on the lava dome, the crater floor, and the volcano's slopes. Preliminary results from a gas flight on the 27th revealed that no magmatic gas was recorded around the lava dome.

Source: US Geological Survey Cascades Volcano Observatory (CVO)


7 November-13 November 2001

The swarm of tiny earthquakes that began at Mount St. Helens on the evening of 2 November ended by noon of 4 November. During this period ~2,000 earthquakes occurred that may have been related to increasing ground water levels due to autumn rain. Most of the earthquakes had magnitudes less than 0. The largest event, M 1.9, occurred shortly before noon on the 4th. All located events were shallow (< 2 km) and in or below the lava dome or crater floor near the dome. Most of the events were too small to locate accurately. After the main swarm, during 4 November to at least 10 November, about 10 small, shallow earthquakes occurred per day.

Sources: US Geological Survey Cascades Volcano Observatory (CVO), Associated Press


31 October-6 November 2001

Beginning on 2 November at about 1800 a swarm of approximately 200 very small, shallow earthquakes was detected for at least 24 hours beneath Mount St. Helens. The earthquakes had magnitudes less than 0, occurred at depths less than 1 km, and were mostly in or under the lava dome's N flank. Such earthquakes are common at Mount St. Helens, but a swarm with so many earthquakes had not been recorded for several years. Cascades Volcano Observatory (CVO) scientists were uncertain what caused the earthquakes, but they suggested that increasing ground water levels due to autumn rain could have caused slippage on fractures in and below the lava dome and crater floor. CVO stated that the probability of small landslides, debris flows in the crater, and steam explosions is enhanced during these periods. Larger-scale eruptions are unlikely without significant additional precursory activity.

Sources: US Geological Survey Cascades Volcano Observatory (CVO), Seattle Post-Intelligencer


Summary of eruption dates and Volcanic Explosivity Indices (VEI).

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2004 Oct 1 2008 Jan 27 ± 10 days Confirmed 2 Historical Observations South of 1980-1986 lava dome
1990 Nov 5 1991 Feb 14 Confirmed 3 Historical Observations North side of lava dome
1989 Dec 7 1990 Jan 6 Confirmed 2 Historical Observations North side of lava dome
1980 Mar 27 1986 Oct 28 ± 3 days Confirmed 5 Historical Observations Summit and north flank
[ 1921 Mar 18 ] [ Unknown ] Uncertain    
[ 1903 Sep 15 ] [ Unknown ] Uncertain    
[ 1898 Apr 5 ] [ Unknown ] Uncertain    
1857 Apr Unknown Confirmed 2 Historical Observations
1854 Feb 1854 Apr Confirmed 2 Historical Observations North flank
1853 Mar 15 ± 5 days 1853 Aug (?) Confirmed 2 Historical Observations North flank
1850 Mar 1850 May (?) Confirmed 2 Historical Observations North flank
[ 1849 ] [ Unknown ] Uncertain 2   North flank
1848 Apr 1 (in or before) Unknown Confirmed 2 Historical Observations
1847 Mar 26 1847 Mar 30 Confirmed 2 Historical Observations North flank (Goat Rocks)
1842 Nov 22 1845 Sep 18 (?) Confirmed 3 Historical Observations North flank (Goat Rocks)
1835 Mar (?) Unknown Confirmed 2 Historical Observations North flank (Goat Rocks area)
1831 Aug Unknown Confirmed 3 Historical Observations North Flank (Goat Rocks area)
1800 Jan 15 ± 120 days Unknown Confirmed 5 Dendrochronology N flank--Goat Rocks area, Layer T
1610 ± 40 years Unknown Confirmed   Radiocarbon (corrected) Pre-1980 summit dome, Tephra layer z
1525 ± 25 years Unknown Confirmed   Dendrochronology tephra set X
1482 Jan 15 ± 120 days Unknown Confirmed 5 Dendrochronology Tephra layer We
1480 Jan 15 ± 120 days Unknown Confirmed 5 Dendrochronology tephra Wn
0780 ± 300 years Unknown Confirmed   Radiocarbon (uncorrected) NE flank (Sugar Bowl)
0420 (?) Unknown Confirmed   Radiocarbon (corrected)
0270 (?) Unknown Confirmed   Radiocarbon (corrected) Tephra layer Bu
0230 (?) Unknown Confirmed 0 Tephrochronology
0190 (?) Unknown Confirmed   Radiocarbon (corrected) Lower E flank (East Dome), Layer Bi
0100 (?) Unknown Confirmed 0 Radiocarbon (corrected) SW flank (Cave basalts)
0100 BCE (?) Unknown Confirmed   Radiocarbon (corrected)
0220 BCE (?) Unknown Confirmed   Radiocarbon (corrected) NNE flank (Dogs Head), Layer Bd
0250 BCE (?) Unknown Confirmed   Tephrochronology Tephra layer Bo
0280 BCE (?) Unknown Confirmed   Radiocarbon (corrected)
0530 BCE (?) Unknown Confirmed 5 Radiocarbon (corrected) Pine Creek tephra layers Ps and Pu
0800 BCE (?) Unknown Confirmed   Radiocarbon (corrected)
0830 BCE ± 75 years Unknown Confirmed   Radiocarbon (uncorrected)
1010 BCE (?) Unknown Confirmed   Radiocarbon (corrected)
1100 BCE (?) Unknown Confirmed   Radiocarbon (corrected)
1180 BCE (?) Unknown Confirmed   Radiocarbon (corrected) Pm layer
1610 BCE (?) Unknown Confirmed   Radiocarbon (corrected)
1680 BCE (?) Unknown Confirmed   Radiocarbon (corrected) Tephra layer ya
1770 BCE ± 100 years Unknown Confirmed 5 Tephrochronology Tephra layer Ye
1860 BCE (?) Unknown Confirmed 6 Radiocarbon (corrected) Tephra layer Yn
2100 BCE ± 300 years Unknown Confirmed   Tephrochronology Tephra layer Yd
2340 BCE (?) Unknown Confirmed 5 Radiocarbon (corrected) Yb layer

The following references are the sources used for data regarding this volcano. References are linked directly to our volcano data file. Discussion of another volcano or eruption (sometimes far from the one that is the subject of the manuscript) may produce a citation that is not at all apparent from the title. Additional discussion of data sources can be found under Volcano Data Criteria.

Anderson S W, Fink J H, Rose W I, 1995. Mount St. Helens and Santiaguito lava domes; the effect of short-term eruption rate on surface texture and degassing processes. J Volc Geotherm Res, 69: 105-116.

Belousov A, Voight B, Belousov M, 2007. Directed blasts and blast-generated pyroclastic density currents: a comparison of the Bezymianny 1956, Mount St Helens 1980, and Soufriere Hills, Montserrat 1997 eruptions and deposits. Bull Volc, 69: 701-740.

Carey S, Gardner J, Sigurdsson H, 1995. The intensity and magnitude of Holocene plinian eruptions from Mount St. Helens volcano. J Volc Geotherm Res, 66: 185-202.

Coombs H A, Howard A D, 1960. United States of America. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 9: 1-68.

Crandell D R, 1987. Deposits of pre-1980 pyroclastic flows and lahars from Mount St. Helens volcano, Washington. U S Geol Surv Prof Pap, 1444: 1-93.

Crandell D R, Mullineaux D R, 1978. Potential hazards from future eruptions of Mount St. Helens volcano, Washington. U S Geol Surv Bull, 1383-C: 1-26.

Crandell D R, Mullineaux D R, Rubin M, 1975. Mount St. Helens volcano: recent and future behavior. Science, 187: 438-441.

Evarts R C, Ashley R P, Smith J G, 1987. Geology of the Mount St. Helens area: record of discontinuous volcanic and plutonic activity in the Cascade Arc of southern Washington. J Geophys Res, 92: 10,155-10,169.

Gardner J E, Carey S, Sigurdsson H, 1998. Plinian eruptions at Glacier Peak and Newberry volcanoes, United States: implications for volcanic hazards in the Cascade Range. Geol Soc Amer Bull, 110: 173-187.

Green J, Short N M, 1971. Volcanic Landforms and Surface Features: a Photographic Atlas and Glossary. New York: Springer-Verlag, 519 p.

Hildreth W E, 2007. Quaternary magmatism in the Cascades--geologic perpectives. U S Geol Surv Prof Pap, 1744: 1-125.

Hoblitt R P, Crandell D R, Mullineaux D R, 1980. Mount St. Helens eruptive behavior during the past 1500 years. Geology, 8: 555-559.

Hopson C A, Melson W G, 1990. Compositional trends and eruptive cycles at Mount St. Helens. Geosci Can, 17: 131-141.

Kashman K V, Cronin S J, 2008. Welcoming a monster to the world: myths, oral tradition, and modern societal response to volcanic disasters. J Volc Geotherm Res, 176: 407-418.

Lipman P W, Mullineaux D R (eds), 1981. The 1980 eruptions of Mount St. Helens, Washington. U S Geol Surv Prof Pap, 1250: 1-844.

Mullineaux D R, 1986. Summary of pre-1980 tephra-fall deposits erupted from Mount St. Helens, Washington State, USA. Bull Volc, 48: 17-27.

Pringle P T, 1993. Roadside geology of Mount St. Helens National Volcanic Monument and vicinity. Wash Dept Nat Resour, Div Geol Earth Resour Inf Circ, 88: 1-119.

Sherrod D R, Scott W E, Stauffer P H (eds), 2008. A volcano revisted: the renewed eruption of Mount St. Helens, 2004-2006. U S Geol Surv Prof Pap, 1750: 1-856.

Sherrod D R, Smith J G, 1990. Quaternary extrusion rates of the Cascade Range, northwestern United States and southern British Columbia. J Geophys Res, 95: 19,465-19,474.

Shevenell L, Goff F, 1995. Evolution of hydrothermal waters at Mount St. Helens, Washington, USA. J Volc Geotherm Res, 69: 73-94.

Sisson T, 1995. Blast ashfall deposit of May 18, 1980 at Mount St. Helens, Washington. J Volc Geotherm Res, 66: 203-216.

Williams D A, Kadel S D, Greeley R, Lesher C M, Clynne M A, 2004. Erosion by flowing lava: geochemical evidence in the Cave Basalt, Mount St. Helens, Washington. Bull Volc, 66: 168-181.

Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.