This file contains all of the reports for this month. Select "Table of Contents" for links containing all Smithsonian reports for each volcano.
Michael (South Sandwich Islands)
Eruption from ‘new’ vent
Increased seismic and fumarolic activity in late 2012 and early 2013
Non-eruptive activity: swarms and increased emissions during 2011-2012
Turrialba (Costa Rica)
Decreased seismicity and emissions in 2012
Degassing continues in 2012; increased micro-earthquake activity in March 2013
2009 highlights: Waikupanaha ocean entry ceases, lava enters Halema`uma`u
Minor tremor and small earthquakes during 2011-2012
Quiet prevails despite the Tohoku megathrust of March 2011
Editors: Rick Wunderman, Julie Herrick, Robert Dennen, and Sally Kuhn Sennert
Volunteer Staff: Paul S. Berger, Robert Andrews, Russell Ross, Kenneth Brown, Jacquelyn Gluck, Hugh Replogle, Serenity Purcell, and Casey Karch
Matthew Patrick (USGS-HVO) notified Bulletin editors that in late 2012 images from thermal sensing satellites showed a ‘new’ active vent on Mount Michael on Saunders Island in the South Sandwich Islands (see location map, figure 1 in BGVN 28:02). This prompted scrutiny of the same vent in earlier images. Patrick noted that, although the vent was first identified in the 2012 images, it also appeared as activity in satellite images starting in 2006. The South Sandwich Islands are generally devoid of vegetation and habitants, and are largely ice-bound. Thus, satellite thermal alerts are strong evidence of volcanism.
Patrick shared with us the following information from a paper by Patrick and Smellie (in review) about the vent, labeled as Old Crater (SE and outside of main crater, see figure 2 in BGVN 28:02). ASTER [Advance Spaceborne Thermal Emission and Reflection Radiometer] imagery provided “new information on the small subordinate crater, marked as ‘Old Crater’ by Holdgate and Baker (1979), presumably because it was inactive at the time of their observations.” An ASTER image on 28 October 2006 showed an apparent SWIR [short-wave infrared] anomaly at Old Crater. The crater itself appeared to be snow-free and was approximately 150 m in diameter. An ASTER image from 5 January 2008, showed a steam plume coming from this vent, which appeared to be about 190 m wide, as well as a TIR [thermal infrared] anomaly. A very high resolution image from November 2009 available on Google Earth showed a small steam plume emanating from the crater, which is about 190 m wide (figure 1). An ASTER image from 17 November 2010, showed apparently recent eruptive activity in Old Crater, evidenced by tephra fallout emanating from the crater and a small TIR anomaly (at the time there was also a TIR anomaly in the main crater). According to Patrick and Smellie, the plume, tephra fall, SWIR anomalies, and crater enlargement (from 150 to 190 m) indicated that this vent had reactivated by late 2006.
|Figure 1. Annotated Google Earth imagery of Michael volcano (Saunders Island) acquired on 19 November 2009. (a) Saunders Island is mostly glacier covered, and steam plumes rose from the summit area. The scale bar indicates a distance of ~2.4 km. (b) A close up of the summit area that clearly shows steam plumes emanating from both the summit crater as well as the snow-filled ‘Old Crater’ (as termed by Holdgate and Baker, 1979). The scale bar indicates a distance of ~0.5 km. Courtesy of Google Earth.|
MODVOLC satellite thermal alerts measured from the volcano since our last Bulletin report (BGVN 33:04, activity through May 2008) and to 4 April 2013 are shown in Table 1. A solitary alert appeared 25 October 2008, followed by a four year period of apparent inactivity. Then, another solitary alert was measured in late June 2012, followed by alerts for two days in October 2012 and two days in November 2012. Patrick noted that occasional and sporadic alerts are very typical for Michael.
Date Time Pixels MODIS (UTC) Satellite 25 Oct 2008 0100 1 Terra 30 Jun 2012 0100 1 Terra 2 Oct 2012 0110 1 Terra 28 Oct 2012 0200 2 Aqua 28 Oct 2012 1125 2 Terra 14 Nov 2012 0055 3 Terra 22 Nov 2012 1120 2 Terra
References. Patrick, M.R., and Smellie, J.L., (in review), A spaceborne inventory of volcanic activity in Antarctica and southern oceans, 2000-2010, Antarctic Science, in review in 2013.
Holdgate, M.W., and Baker, P.E., 1979. The South Sandwich Islands: I. General description, British Antarctic Survey Scientific Reports, No. 91, pp. 1-76.
Geologic Summary. The young constructional Mount Michael stratovolcano dominates glacier-covered Saunders Island. Symmetrical 990-m-high Mount Michael has a 700-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a north-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the N coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Vapor emission is frequently reported from the summit crater. Recent AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater of Mount Michael.
Information Contacts: Matthew Patrick, Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/; Email: firstname.lastname@example.org); MODVOLC, Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
Sabancaya volcano, located 72 km NW of Arequipa city, is one of the most active volcanoes of the Central Andes (figure 2). Our last report of Sabancaya described ashfall during July 2003 (BGVN 29:01). This report describes an increase in anomalous seismic and fumarolic activity, beginning in late 2012 and continuing through the end of March 2013. The restlessness spurred increased monitoring of the volcano.
|Figure 2. A map illustrating hazards at the Ampato-Sabancaya volcanic complex (high danger, red; moderate danger, orange; and low danger, yellow). Types of volcanic hazards include pyroclastic flows (including debris flows), mudflows, lava flows, and avalanches. The overall thickness of ash deposits from eruptions during 1990-1998 is indicated by 1 and 0.1 cm isopachs. Major roads and highways are shown as thick, dark red lines; thin lighter red lines are elevation contours. The map shown is featured on a poster with more details. From Mariño and others (2013).|
Between 1988 and 1997, activity at Sabancaya was intermittent and characterized by low to moderate Vulcanian eruptions (VEI 2) and mainly modest eruption columns (less than 5 km above the summit) with local ashfall (e.g., SEAN 13:06; BGVN 19:03). After this eruptive episode, between 1998 and 2012, minor and intermittent fumarolic emissions rose from the active crater. During the last months of 2012, a slight increase of fumarolic activity was observed during a field campaign by Peru’s Instituto Geológico Minero y Metalúrgico (INGEMMET) volcanologists and their counterparts from the Laboratoire Magmas et Volcans (Clermont-Ferrand, France).
The Instituto Geofisico del Peru (IGP) reported that inhabitants from Sallalli hamlet, ~ 11 km S of Sabancaya, observed an increase in fumarolic emissions beginning 5 December 2012. Meteorological conditions prevented IGP scientists from visiting the area during the rainy season.
In mid-February 2013, local residents reported an increase in fumarolic activity, which was confirmed by INGEMMET scientists that visited the volcano on 15 and 22-23 February (figure 3). Scientists also reported a strong sulfur odor within an 8-km radius, and felt several strong earthquakes probably associated with the volcano’s unrest.
|Figure 3. Photograph taken of a gas plume above the active vent of Sabancaya, as seen from the SE flank on 17 February 2013. Courtesy of Pablo Samaniego, IRD.|
IGP reported that within a span of 95 minutes on 22 February 2013, three earthquakes, of M 4.6, 5.2, and 5.0 respectively, were registered at Sabancaya (figure 4). This activity prompted IGP to install a network of close proximity seismic stations. Earthquakes continued through the following day (23 February) and caused damage at Maca village, 20 km NE of the crater.
|Figure 4. The principal earthquakes (red dots) registered at Sabancaya on 22 February 2013. Of these, three earthquakes of M 4.6, 5.2, and 5.0 occurred within a span of 95 minutes. Courtesy of IGP.|
During 22-23 February, a seismic station installed by INGEMMET registered more than 500 small volcano tectonic (VT) seismic events at Sabancaya. On 23 February IGP separately reported 560 events at the Cajamarcana seismic station (CAJ on figure 5b) on the SE flank. According to a Reuters article from 27 February, 80 homes were damaged by the seismicity during 22-23 February, leading to some evacuations. During that seismicity, a plume rose ~100 m above Sabancaya. After 24 February, VT, long period (LP), and hybrid seismicity continued (figure 5).
|Figure 5. (a) Plot of daily earthquakes at Sabancaya, showing the number of volcano tectonic, long period, and hybrid events that occurred during 24 February-27 March 2013. (b) The locations of earthquake epicenters on 27 March 2013 (red dots) and the seismic stations that were monitoring the volcano as of that date (yellow triangles). Courtesy of IGP.|
Reference. Mariño J., Samaniego P., Rivera M., Bellot N., Manrique N., Macedo L., Delgado R., 2013, Mapa de peligros del Complejo Volcánico Ampato-Sabancaya, Esc. 1:50.000. Edit. INGEMMET-IRD.
Geologic Summary. Sabancaya, located on the saddle between 6,288-m-high Ampato and 6,025-m-high Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three volcanoes, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. Both Nevado Ampato and Nevado Sabancaya are only slightly affected by glacial erosion and consist of a series of lava domes aligned along a NW-SW trend. The name of 5,967-m-high Sabancaya (meaning “tongue of fire” in the Quechua Indian language) first appeared in records in 1595 AD, suggesting activity prior to that date. Holocene activity has consisted of plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions of Sabancaya date back to 1750.
Information Contacts: Instituto Geológico Minero y Metalúrgico (INGEMMET), Av. Dolores (Urb. Las Begonias B-3), J.L. Bustamante y Rivero, Arequipa, Perú (URL: http://www.ingemmet.gob.pe); Pablo Samaniego Eguiguren, Laboratoire Magmas et Volcans, Université Blaise Pascal, Le Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Casilla 18-1209, Calle Teruel 357 - Miraflores, Lima 18 - PERU (URL: wwwobs.univ-bpclermont.fr/lmv/pperm/samaniego_p/index.php); Reuters, report by Lima Newsroom; Orlando Macedo, PhD, Chief of Volcanology Research Department, Instituto Geofisico del Peru, (IGP), Arequipa Volcano Observatory, Urb. La Marina B-19, Cayma, Arequipa, Peru.
Our last report on Cumbal volcano (BGVN 19:07) highlighted fumarolic activity from the NE craters, and monitoring efforts by scientists collaborating with the Servicio Geológico Colombiano (SGC). The SGC (formerly known as Instituto Colombiano de Geología y Minería, “INGEOMINAS”) monitors the volcano from Pasto, ~72 km NE of Cumbal (figure 6). In this report we describe field observations during 2005-2012, significant new monitoring instruments installed during 2008-2012, and episodes of seismic unrest. Earthquake swarms during 2011 and 2012 accompanied increased fumarolic activity.
|Figure 6. This 2008 map of the Cumbal region indicates locations of telemetered monitoring instruments (see legend), major towns (black labels), and nearby volcanoes (yellow text; red text for Cumbal). Yellow text is also used for the radio repeater at “Cruz de Amarillo” ~65 km ENE of Cumbal volcano. More instruments were added to the system later. Courtesy of SGC.|
SGC maintained Alert Level Green (Level IV, the lowest status on a 4-step system; figure 7) with two exceptions. Reduced monitoring during May-July 2010 caused the status to be unassigned during that time. Elevated seismicity and emissions noted in June 2012 raised the status from Green (Level IV) to Yellow (Level III) signifying detected “changes in behavior of the volcanic system.”
|Figure 7. This pictogram describes the volcano Alert Levels used for communicating hazards in Colombia (translated from original in Spanish). This is a four-step system similar to the USGS volcanic activity alert-notification system (Gardner and Guffanti, 2006), except that each step is numbered in addition to having a color code: Green (Level IV), Yellow (Level III), Orange (Level II), and Red (Level I). All SGC observatories (based in Pasto, Popayán, and Manizales) apply this qualitative system. Courtesy of SGC.|
Local hazard map. SGC published a hazard map in 1988 for the region surrounding Cumbal (figure 8). The three asymmetrical hazard zones, high (red), medium (orange), and low (yellow), are at risk for ashfall and pyroclastic flows.
|Figure 8. This hazard map for Cumbal volcano was developed in 1988 by Ricardo Méndez and María Luisa Monsalve of INGEOMINAS (now the Servicio Geológico Colombiano). Three major zones delineate high, medium, and low risk. Note that ashfall could occur in any of the three zones. Courtesy of SGC.|
Areas at highest risk, in the red zone, could be affected by lava and pyroclastic flows, especially within the narrow valleys of Chiquito, Blanco, and Río Grande. Ashfall, ballistics, mudflows, and gas emissions could also occur as far away as ~8 km from the summit. Areas at medium risk, the orange zone, could also be affected by pyroclastic flows, ashfall, and mudflows over an area extending up to 14 km SE from the summit, encompassing the town of Cumbal. Areas at lowest risk, yellow zone, is located primarily downwind of the volcano where pyroclastic flows and ashfall could occur; this zone extends beyond the view of the map.
Monitoring efforts. Aerial investigations conducted since 2005 revealed persistent plumes rising from Cumbal’s NE craters, El Verde and La Plazuela (figure 9; see also figure 2 in BGVN 19:07 for an annotated sketch map of the summit craters). In their online Technical Bulletins, SGC emphasized the frequency of plumes from this region that were documented since at least 1988.
|Figure 9. Cumbal is an elongate volcano with multiple peaks. In 2005 and 2007, clear conditions provided views of plumes rising from Cumbal’s summit craters, El Verde and La Plazuela. (top) On 29 January 2007, white plumes rose from the fumaroles El Verde and Rastrojo; the look direction is N. (bottom) On 29 December 2005, discrete plumes were visible from the fumaroles El Verde (1), El Tábano (2), and La Desfondada (3); the look direction is NNW. Some snow had collected along the ridges and a small pond of water was visible within La Plazuela crater that day. Courtesy of SGC.|
To help understand Cumbal’s state, SGC installed seismic and electronic tilt equipment in late 2008 (figure 6). The La Mesa (2.5 km ESE) and Limones (2 km SE) stations had electronic tilt and short-period seismic instrumentation (figure 10). During installation on 24 September 2008, technicians observed steam plumes rising from the fumarolic areas El Verde and La Plazuela (figure 11).
|Figure 10. This satellite image-based map includes upgrades in Cumbal’s monitoring network as of 2012. Courtesy of SGC.|
|Figure 11. Clear conditions revealed the pale, fumarolic summit area of Cumbal during the mornings of two days in September 2008. (top) Two white plumes seen at 0704 on 24 September 2008; the smaller plume (center) rose from La Plazuela crater while the larger plume (to the right) rose from El Verde. Emissions from these sites have been noted since the late 1980s. This photograph was taken from a location ~6.5 km SE from the summit. (bottom) From the center of town, near the Cumbal Nariño Temple, the view NW toward Cumbal’s summit and fumarolic sites was clear on 25 September 2008. Courtesy of SGC.|
In June 2009, SGC installed a broadband seismometer at Limones station, upgrading from the short-period sensor. Unfortunately, monitoring capabilities were significantly reduced when, in December 2009, vandals stole station instrumentation at this site.
Data from the remaining station, La Mesa, was only acquired intermittently during January-June 2010 owing to radio repeater problems. From May to July, the Alert Level status went unassigned, but upon repair of the system, later returned back to Green (Level IV).
In August 2010 a short-period seismic station (CUMZ) came online (figure 10). This station was maintained by the National Seismological Network of Colombia (RSNC). The electronic tiltmeter at La Mesa was offline during August-November 2010 due to electronic malfunctions.
In November and December 2011, SGC collaborated with the Colombia Air Force (FAC) to conduct overflights of the volcanic complex. In addition to aerial photos and observations, a thermal camera was used to determine the hotspot distribution and measure temperatures for those sites (figure 12).
|Figure 12. This thermal image was taken during an overflight of Cumbal’s summit on 27 November 2011. The look direction was approximately S with El Verde (43.6°C) and the highest part of La Plazuela’s rim (34.5°C) showing the highest temperatures. Steam plumes rising from the craters partly obscured the view. Courtesy of FAC and SGC.|
Monitoring capabilities were expanded when SGC installed an infrasound sensor at the La Mesa monitoring site in March 2012 and a webcamera was installed in the town of Cumbal (~11 km SE) in May (figure 13). During March-December 2012, white plumes were frequently observed rising from Cumbal’s fumarolic sites.
|Figure 13. An image taken by the new Cumbal webcamera on 23 May 2012. The black arrow points to the source of the strongest plumes, El Verde crater. Courtesy of SGC.|
The Limones short-period seismometer was back online in October 2012. Additionally, two new stations, Nieve and Punta Vieja (figure 10), were added to the network in December; these stations had broadband seismic and electronic tilt equipment.
Summit fumarole monitoring. During 2010-2012, SGC conducted field campaigns to monitor Cumbal’s summit fumarolic sites. Three fumaroles (Desfondada, El Verde, and El Rastrojo) were visited during this time period with repeat observations and measurements. Lab analyses were conducted at the Manizales Volcanological and Seismological Observatory.
The Desfondada fumarole, located near the W rim of La Plazuela crater (see the sketch map in figure 2 in BGVN 19:07), was visited only once for sampling with the Giggenbach bottle method in August 2010; this site had a relatively high temperature, 278.4°C. The other sites were visited frequently and also sampled to determine gas species and condensates (table 2).
Site Date Temperature (°C) Desfondada Aug 2010 278.4 El Rastrojo Aug 2010 177.6 El Rastrojo Sep 2011 153.3 El Rastrojo Dec 2011 178.9 El Rastrojo Mar 2012 148.5 El Rastrojo Apr 2012 104.0 El Verde Aug 2010 313.0 El Verde Mar 2012 122.3 El Verde Apr 2012 115.6
The earliest measured temperature from El Verde (in August 2010) yielded the highest value of the three fumaroles (313°C). Compared with temperatures measured in 1994 (378°C, BGVN 19:07), El Verde’s values were slightly lower; however, the three available temperatures from 2010 and 2012 were within the measured range determined by SGC field campaigns conducted during previous years (BGVN 19:07).
The El Rastrojo site was located ~1.6 km SW of the summit (figure 14); this fumarolic area, on the outer edge of Mundo Nuevo crater regularly emitted plumes and had temperatures in the range 104-178.9°C.
|Figure 14. On 27 November 2011, white plumes were visible rising from fumarolic features along the ridge of Cumbal volcano. (top) This oblique view of Cumbal is centered on Mundo Nuevo crater, the SW crater of the ~2 km-long volcanic complex. The area highlighted in red shows the location of El Rastrojo, an active fumarolic site that frequently emitted white plumes and was monitored by SGC. White plumes also emerge from La Plazuela and El Verde craters in the middle-ground (near the right edge of the image). (bottom) In this zoomed image (clipped from the top image), a short column of white vapor rises from El Rastrojo fumarole. This area is a scree slope where several large boulders are discolored by yellow sulfur deposits. Courtesy of SGC.|
Hot spring investigations. Inferred magmatic compositions were detected from hot springs during 1988-1996 (Lewiki and others, 2000). Field investigators sampled from sites located within the central crater and from sites along the SE flank, up to 10 km from the summit and towards the town of Cumbal (figure 15). However, they concluded that “from 1995 to 1996, geochemical data show increasing hydrothermal signatures, suggesting a decline in magmatic volatile input.”
|Figure 15. This sketch map of Cumbal and the surrounding area highlights the locations of hot springs. During 2010-2012, SGC monitored four of these sites: El Salado (“S”), Cuetial (“C”), El Zapatero (“Z”), and Hueco Grande (also known as Quebrada el Corral, “QC”). Note that the generalized name “Cumbal Crater” is assigned to the area of La Plazuela and El Verde craters. Modified from Lewiki and others (2000).|
During 2010, SGC monitored four hot springs for temperature and chemical changes. Results from sampling during May, August, and November 2010 determined chemical classifications for the springs El Salado, Cuetial, El Zapatero, and Hueco Grande (figure 16).
|Figure 16. Based on geochemical results from investigations in May (triangles), August (squares), and November 2010 (circles), SGC scientists classified four of Cumbal’s hot springs. Within this ternary diagram, the datapoints were generally well within the “Periferal Water” (Aguas Periféricas, significant HCO3) class. Datapoints from Hueco Grande, approached the “Volcanic Water” (translated from Spanish “Aguas Calentadas por Vapor,” significant SO4) class than the others. No datapoints were within the “Mature Water” (Aguas Maduras, significant Cl) class. Courtesy of SGC.|
Sampling and analysis of the four hot springs continued during 2011-2012. SGC maintained a growing database of characteristics from these springs and released the results in online bulletins. In particular pH, temperature, conductivity, and concentrations of carbonates were repeatedly measured. During this time period, pH values measured from the hot springs were in the range of 5.9-7.3; temperatures were 26.4-34.4°C (the highest values were from Cuetial spring); conductivity values (Oxidation-Reduction Potential, “ORP”) ranged from 7.7-42.2 mV (highest values were from Cuetial and the lowest was from Hueco Grande springs); bicarbonate (HCO3) concentrations were 271.7-1,008.0 mg/L (the highest value was obtained from El Zapatero spring).
Cumbal seismicity. When the seismic stations Limones and La Mesa came online in late 2008, SGC began characterizing Cumbal’s seismicity based on the following interpretive scheme:
• Hybrid (HYB): Seismicity associated with signals characterizing fracturing and fluid movement.
• Long period (LPS): Seismicity associated with unsteady fluid movement (magma or hydrothermal fluids, for example).
• Tremor (TRE): Seismicity associated with fluid movement in which the source behaves in a sustained manner.
• Tornillo (TOR): Seismicity associated with fluid movement in which subterranean structures are linked with special conditions in such a manner that makes the cavities resonate. In their January 2009 online bulletin, SGC acknowledged that tornillo earthquakes have been an important indicator of eruptive activity at Galeras volcano, but the occurrence of the same signature at Cumbal volcano required additional analysis before associating specific unrest with this seismicity.
• Volcano-tectonic (VT): Earthquakes associated with brittle failure events caused by magma movement.
• Unclassified volcanic (VOL): Earthquakes from the region of Cumbal that do not correspond with the other classes; SGC stated that these events will be analyzed in more detail after more baseline data is collected. This category was also applied to seismic analyses of Doña Juana, a volcano that was instrumented around the same time (see report on Doña Juana in BGVN 38:01).
Seismicity in 2009. During 2009, as SGC began to establish baseline data for Cumbal’s seismicity, a wide range of earthquake classes was detected (figure 17). LPS and VT events dominated the records and TRE, HYB, and TOR earthquakes were also detected (in order of decreasing occurrence). TOR earthquakes occurred more frequently during August to early December. Due to vandalism, the 2009 record ended on 13 December 2009.
|Figure 17. The daily seismicity detected from Cumbal during 2009 in three plots that display January-August, August-November, and 1-13 December. Five different classes of earthquakes were tallied daily (VT, HYB, TRE, LPS, and TOR). Data gaps are attributed to station outages and time periods requiring re-processing; gray regions signify the reporting period in which the plots appear. Courtesy of SGC.|
Seismicity in 2010. From January to July 2010, La Mesa station detected earthquakes intermittently and the Limones seismic station remained offline. When the network connection was re-established for La Mesa in late July, LPS earthquakes again dominated the records through the end of December (figure 18).
|Figure 18. Daily seismicity from Cumbal during 1 September-31 December 2010 was dominated by LPS events. Six different classes of earthquakes were tallied daily (VT, LP, TRE, HYB, TOR, and VOL); the gray region highlights the month when the plot was released online. Courtesy of SGC.|
Seismicity in 2011. LPS, VT, and HYB events dominated seismicity at Cumbal for most of 2011; more VOL events occurred than HYB, but this category was described as temporary until more analysis is possible (table 3 and figure 19). Data quality enabled some events to be located and some swarms were apparently driving a several-fold increase in monthly counts. Until November 2011, TOR events were occurring ~5 times per month and TRE were occurring ~13 times per month. In November, seismicity increased significantly and SGC reported that several earthquake swarms had occurred; in particular, one event occurred on 18 November. A swarm of LPS earthquakes also occurred during 20-21 and on 31 December. Epicenters could not be calculated from the data and there were no reports of felt earthquakes.
Date VT LPS TRE HYB TOR VOL Total Notes 2011 Jan 165 906 14 109 8 111 1313 - Feb 188 453 5 5 5 104 760 - Mar 96 743 9 76 12 136 1072 - Apr 52 476 3 45 1 76 653 - May 80 575 10 37 5 38 745 - Jun 88 659 2 31 2 36 818 - Jul 76 726 9 29 4 30 874 - Aug 53 560 7 40 2 9 671 - Sep 75 524 8 70 7 47 731 - Oct 64 678 61 65 0 90 958 - Nov 300 1967 385 279 4 326 3261 Swarms Dec 160 2028 453 228 4 130 3003 Swarms 2012 Jan 103 1657 252 159 2 8 2181 Swarms Feb 176 758 73 167 1 6 1181 - Mar 78 678 47 105 5 0 913 - Apr 80 619 32 60 0 1 792 - May 54 625 35 45 0 0 759 Swarms Jun 56 858 29 34 5 0 982 - Jul 98 1306 29 54 5 0 1492 Swarms, 13 EQs located Aug 101 855 46 42 4 0 1048 Swarms, 11 EQs located Sep 117 1344 31 60 4 0 1556 Swarms, 3 EQs located Oct 135 1080 62 51 14 0 1342 Swarms, 92 EQs located Nov 235 1017 15 99 2 1 1369 Swarms, 89 EQs located Dec 260 1001 10 180 3 24 1478 Swarms, 97 EQs located
|Figure 19. Cumbal earthquakes tallied by month based on event class during 2011-2012. Elevated seismicity persisted during November 2011-January 2012, particularly VT, LPS, and TRE. The “TOTAL” class is the sum of VT, LPS, TRE, HYB, TOR, and VOL earthquakes for each month (see table 3 for values). Courtesy of SGC.|
Seismicity in 2012. SGC reported that seismic swarms continued to occur in January 2012. The swarm that began at 2200 on 31 December 2011 continued until 1 January 2012 and a total of 211 LPS events were detected. Two more swarms occurred later that month, amounting to a total of 274 earthquakes. Seismicity declined during February-April but swarms reappeared: in May, one; in July, five; in August, two; in September, six; in October, six; in November, seven.
Due to elevated seismicity, persistent swarms, and observations of increased emissions from El Verde and La Plazuela, SGC announced on 10 July that the Alert Level was raised to Yellow (Level III). This status was maintained through December 2012. In their online July 2012 Activity Report, SGC noted that residents in the area had also reported notable gas emissions, seismicity, and possible noises associated with earthquakes.
Epicenters of Cumbal’s VT earthquakes were calculated during July-December 2012 and located on regional maps (table 4). Earthquake locations tended to be dispersed throughout the region, although some clustering was notable between 2 and 6 km of the summit region and at depths less than 12 km (as measured from the summit elevation) (figure 20).
Date Location Magnitude Depth 31 Jul SW <2.1 ≤10 6 Aug N, S, Disp. <1.3 ≤6 16 Oct ≤10 km N <1.3 ≤9 23 Oct ≤2 km SE <1 ≤3 30 Oct ≤4 km E <1.2 ≤4 6 Nov ≤5 km SE <0.2 ≤9 13 Nov ≤3 km E <0.6 ≤2 20 Nov ≤3 km E <1.9 ≤6 4 Dec ≤13 km Disp. <1.6 ≤12 11 Dec ≤5 km Disp. <0.6 ≤10 18 Dec ≤6 km Cent. na <1 26 Dec Cent. <1.1 <2 26 Dec N <1.1 ≤9
|Figure 20. A total of 97 volcano-tectonic earthquakes were located during December 2012 within the region of Cumbal volcano. Five seismic stations (dark red squares) were online near the volcano: LIMC (Limones), MEVZ (La Mesa), NIEV (Nieve), VIEZ (Punta Vieja), and CUMZ (the RSNC Cumbal station). Earlier in the month, VTs were primarily dispersed in the region while later in the month, they were more clustered around the edifice and N (table 4). Courtesy of SGC.|
In September, October, and November 2012, during field investigations at various locations around Cumbal’s flanks, SGC scientists also noted increased emissions from the summit fumaroles. In particular, white plumes were strong from El Verde and El Rastrojo fumaroles.
Geodetic monitoring during 2009-2010. Electronic tilt data available during 2009 showed oscillations within the expected range of the instruments. During 2010, while instrumentation was reduced and electronic problems persisted, tilt records continued to show minor variations. In July, a decreasing trend was observed from the tangential component of La Mesa tiltmeter (figure 21). Unfortunately, the instrument was offline from August through November. When monitoring resumed in December, no deformation trends were noted.
|Figure 21. The two components of the La Mesa electronic tiltmeter recorded stable conditions from Cumbal’s SW flank (in the Mundo Nuevo region) during 1 January-31 July 2010. The four plots, from top to bottom, contain radial tilt component (in µrad), tangential tilt component (in µrad), temperature (°C), and voltage (V) data. Note that minor variations in temperature and daily variations in the voltage correspond to the recharging cycle controlled by the solar panels and consequent voltage drain at night. The gray shaded section represents the reporting period when the data was published online. Courtesy of SGC.|
Geodetic monitoring during 2011-2012. In their April 2011 Technical Bulletin, SGC highlighted the onset of a decreasing trend in La Mesa’s tangential data; the trend began on 30 April and continued to 30 June for a total decrease of ~25 µrad (figure 22); this trend ended in July. A period of increasing tilt began on 29 September and ended on 30 November 2011 (total increase was ~35 µrad). The signal from La Mesa station (effecting electronic tilt as well as seismic records) was intermittent in August. From December 2011 through December 2012, fluctuations persisted in the tilt data; however, stable conditions were characteristic of 2012 deformation.
|Figure 22. Tilt record of Cumbal during 2011 (tangential component on top plot, radial on bottom). In their Technical Bulletins, SGC highlighted several trends that became apparent in the tangential data from La Mesa station; a decreasing event began at the end of April reaching a total decrease of ~25 µrad by late June. The station detected an increase in tilt of equal magnitude in late September and ending by late November. Courtesy of SGC.|
References. Gardner, C.A., and Guffanti, M.C., 2006, U.S. Geological Survey’s Alert Notification System for Volcanic Activity, U.S. Geological Survey, Fact Sheet 2006-3139, Version 1.0.
Lewiki, J.L., Fischer, T., and Williams, S.N., 2000, Chemical and isotopic compositions of fluids at Cumbal Volcano, Colombia: evidence for magmatic contribution, Bulletin of Volcanology, 62: 347-361.
Geologic Summary. Many youthful lava flows extend from the glacier-capped Cumbal volcano, the southernmost historically active volcano of Colombia. The volcano is elongated in a NE-SW direction and is composed primarily of andesitic-dacitic lava flows. Two fumarolically active craters occupy the summit ridge; the main crater on the NE side and Mundo Nuevo crater on the SW side. A young lava dome occupies the 250-m-wide summit crater, and eruptions from the upper E flank produced a 6-km-long lava field. The oldest crater lies NNE of the summit crater, suggesting SW-ward migration of activity. Explosive eruptions in 1877 and 1926 are the only known historical activity from Cumbal. Fumarole fields are found in the two summit craters, and thermal springs are located on the SE flanks.
Information Contact: Servicio Geológico Colombiano (SGC), Observatorio Vulcanológico y Sismológico de Pasto, Pasto, Colombia (URL: http://www.SGC.gov.co/Pasto.aspx).
As noted by our previous report (BGVN 37:06), on 12 January 2012 Turrialba emitted ash for a few hours due to the opening of a vent, named 2012 Vent, on the SW inside slope of Central Crater. Since then, 2012 Vent has been an active contributor to the regular plume generation at the volcano. Our previous report noted activity through May 2012. This report primarily highlights activity through December 2012, based on online documents from the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA) showing a diminution in activity during 2012 compared to 2010 and 2011.
Seismicity. According to OVSICORI-UNA, the seismic activity at Turrialba in 2012 was characterized primarily by shallow and volcano-tectonic events concentrated in the upper part of the edifice, and minor seismicity in nearby faults. In general, seismicity was lower in 2012 than in 2011, and notably lower than that in 2010. Seismic activity climbed slightly during September-October 2012 (from about 20/day, peaking at 150/day on 13 October, and then declining back to normal values after 1 November; figure 23). OVSICORI-UNA noted that seismic activity in 2012 was caused by water and heat interactions causing gas pressure.
|Figure 23. The number of seismic events registered per day at Turrialba during 2012. Courtesy of OVSICORI-UNA.|
Deformation. OVSICORI-UNA reported that during 2012 the distances between the Electronic Distance Measurement (EDM) station “Pilar” and several nearby reflectors contracted from 2 to 7 cm/year, with the highest value at the N reflector and lowest at the ENE and NE reflectors (see figure 24 for EDM station locations).
|Figure 24. The location of geodetic monitoring stations at Turriabla during 2012. Red circles are reflectors of the EDM network, and measurements were made from the Pilar station (red square). Blue circles are permanent GPS stations (CAPI and GIBE). Courtesy of OVSICORI-UNA.|
Emissions. According to OVSICORI-UNA, the opening of the 2012 vent was not associated with new magmatic activity. Vent temperatures measured with a thermocouple were similar during 2010-2012, suggesting to OVSICORI-UNA a sustained and common magmatic source. Measured vent temperatures also correlated with CO2 and H2S gas emissions (figure 25).
|Figure 25. (Background image) Thermal image of Turrialba’s W wall in Cráter Central (Central Crater) on 27 October 2012. Two vents are indicated, Boca 2012 (2012 Vent) and Cráter Oeste (West Crater). (Plots) For the measurement locations indicated by arrows, plots compare CO2 flux measurements (black) to both H2S flux measurements (blue) and thermal measurements acquired at 10-cm depth (red). Courtesy of OVSICORI-UNA; thermal photo taken by G. Avard.|
OVSICORI-UNA noted that gas emissions during 2012 had decreased considerably compared to those during 2010 and 2011. OVSICORI-UNA suggested that this decrease might be due to various factors, including a decline in rainfall that resulted in less water vapor, the primary component of the emissions. In a report discussing activity during January-February 2013, OVSICORI-UNA noted that the emissions from 2012 Vent had decreased, even though nighttime incandescence could be observed. Emissions drifted primarily NW during 2012.
Figures 26 and 27 summarize SO2 measurements from both miniature Differential Optical Absorption Spectrometer (mini-DOAS, fluxes) and OMI satellite data (masses). SO2 fluxes were lower than those in 2010-2011 when fluxes often reached above 1,000 tons/day (and in one case, nearly 4,000 tons/day; figure 27).
|Figure 26. (Left) Daily SO2 flux (metric tons/day) at Turrialba measured by a mini-DOAS station at La Central school, ~2.2 km SW of West Crater, between 1 May 2012 and 1 January 2013. (Right) SO2 mass (uncorrected for any noise) emitted by Turrialba as recorded by NASA’s Ozone Monitoring Instrument (OMI) aboard the AURA satellite during 2012. The SO2 mass corresponds to the total mass detected by the OMI sensor in the Central America area at 1800-1900 UTC. According to OVSICORI, both mini-DOAS and OMI measurements were consistent and of the same magnitude. The red-shaded area in the satellite data represents the time period corresponding to that of the mini DOAS data. Courtesy of OVSICORI-UNA and NASA-OMI.|
|Figure 27. SO2 mass emitted by Turrialba as recorded by NASA’s OMI instrument aboard the AURA satellite between 1 October 2008 and 6 November 2012. These represent masses in the atmospheric column that are thought to have roughly 1 day residence times. Courtesy of NASA-OMI.|
As in previous years, rain and fog absorbed volcanic gases in 2011 and 2012, producing acid rain with consequent damage and destruction to vegetation, especially in downwind areas in the sector sweeping clockwise from SW to N from the vents (figure 28).
|Figure 28. Annotated photo of Turrialba taken on 26 August 2012. The vegetation on the top and on the flanks of the edifice (zone 1) showed severe effects such as necrosis. The pasture vegetation (zone 2), used for milk production, turned yellowish (chlorosis). Interestingly, part of the native vegetation such as the tall trees (Quercus species) showed a stronger resistance to environmental acidification. Courtesy of OVSICORI-UNA; photo taken by G. Avard.|
OVSICORI-UNA observed that hydrothermal activity modified the mineralogy and decreased the cohesion of the rocks in contact with the fluids, which alter and reduce the stability of the slopes of the volcanic edifice, triggering gravitational collapses, rockfalls, and strong erosion during the main rain events. These phenomena were especially observed after storms on 15 August and in November 2012, when coarse and fine material was transported from the walls to the bottom of Central Crater, deepening the W and NW gullies.
In an M.S. thesis, Rivera (2011) compared SO2 concentrations in Turriabla’s volcanic plume using a ground-based mini-DOAS and three new data analysis techniques using NASA’s OMI instrument. The three new techniques were the MODIS smoke estimation, OMI SO2 lifetime, and OMI SO2 transect techniques. All four techniques involve UV sensor analysis. She found that the OMI SO2 lifetime technique provided qualitative agreement between the ground-based and satellite-based data, while the OMI transect technique provided occasional quantitative agreements with the mini-DOAS measurements. The MODIS smoke estimation technique was inaccurate in estimating SO2 emission rates.
Reference. Rivera, A.M., 2011, Comparisons between OMI SO2 data and ground-based SO2 measurements at Turrialba volcano, M.S. Thesis, Michigan Technological University.
Geologic Summary. Turrialba, the easternmost of Costa Rica’s Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive 3,340-m-high Turrialba is exceeded in height only by Irazú, covers an area of 500 sq km, and is one of Costa Rica’s most voluminous volcanoes. Three well-defined craters occur at the upper SW end of a broad 800 x 2,200 m wide summit depression that is breached to the NE. Most activity at Turrialba originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred at Turrialba during the past 3,500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.
Information Contact: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/).
Degassing that followed the May 2011 explosive eruption of Telica (figure 29; see also BGVN 36:11) continued through 2012 and into 2013. The following information summarizes observations by the Nicaraguan Institute of Territorial Studies (INETER) for 2012 and through March 2013.
|Figure 29. A location map of Telica, Nicaragua, in Central America. Telica (red triangle) is located ~105 km NW of the capitol, Managua. It last erupted in May 2011 (BGVN 36:11), but no major damage was reported. Gases emitted by Telica normally affect communities in the nearby provinces of Leon and Chinandega. Small black triangles in the figure depict other known Holocene volcanos in the region. Courtesy of USGS.|
INETER issues a monthly bulletin, Boletín mensual Sismos y Volcanes de Nicaragua (Newsletter, Earthquakes and Volcanoes in Nicaragua), reporting on monitoring of Nicaraguan volcanoes including San Cristóbal, Telica, Cerro Negro, Momotombo, Masaya, and Concepcion (figure 30). In the Boletín, INETER presents monitoring data for Telica crater and adjacent fumarol temperatures, seismic activity, and sulfur dioxide (SO2) fluxes. In addition, visual observations are made during periodic field trips. Generally, the time difference between the arrival of P (primary) and S (secondary) waves from local earthquakes ranges from 0.5 to 2 sec, suggesting a source depth of 4 to 10 km.
|Figure 30. An oblique view of a schematic map of Nicaragua with high vertical exaggeration highlights the locations of Nicaraguan volcanoes. Courtesy of INETER.|
As an example of normal ongoing activity at Telica, INETER reported that during 10-11 September 2012, ‘jet’ sounds were heard from the volcano, and two incandescent fumaroles were observed, along with gas-and-steam plumes rising 100-200 m above the crater. On 11 September two small explosions occurred in the crater. During 12-14 and 17 September gas plumes rose 30-150 m and incandescence from the crater was observed. Gas measurements on 14 and 17 September showed normal levels of SO2 flux.
2012 Sulfur dioxide flux. Average daily SO2 flux measurements made using the Mini-DOAS (differential optical absorption spectroscopy) mobile technique in 2012 were 303 metric tons per day in April, 627 metric tons per day in June, 377 metric tons per day in August, and 130 metric tons per day in October.
2012 Seismic Events. INETER has developed some novel ways for grouping seismic events at Telica. The types of seismic events monitored at Telica and activity during 2012 are shown in tables 5 and 6, respectively.
Activity type Frequency Duration Possible explanation nomenclature range/peak for events during 2012 (abbreviations) (Hz) Long period (LP) 1.0-4.5/4.0 20-40 sec Magma movement at 6-10 km depth Tremor 5.0-7.0 short Degassing and magma movement Volcano-tectonic 10.0-20.0+/ 1+ min Rupture of rock at 6-10 km depth (VT; VTA + VTB) 12 Double earthquake 4.0-7.0/ 40-60 sec Brittle fracture followed by (SDO) 4.0 and 7.0 magma displacement Gas eplosion (EG) 4.0-10.0 1-2 min Release of gas in volcanic conduit Swarms of seismic 5.0-7.0 1-3 min Breaking rocks combined with LP-type events (TS) events (avg. of 10 events per swarm) Degasification 5.0-10.0 1 min - signal (SD)
Activity type 18-31 March April May June July Total events 1,986 3,222 3,544 5,754 4,112 LP 535 (27%) 953 (30%) 1,077 (30%) 827 (14%) 332 (8 %) Tremor 0 (0%) 72 (2%) 78 (2%) 0 (0%) 125 (3%) VT (VTA+VTB) 168 (8%) 299 (9%) 315 (9%) 2,418 (42%) 997 (24%) SDO 658 (33%) 638 (20%) 635 (18%) - - EG 625 (32%) 609 (19%) 686 (19%) - - TS - - - 2,519 (44%) 2,658 (65%) SD - 651 (20%) 753 (21%) - -
2012 Temperature measurements. Figure 31 shows INETER staff members measuring crater and fumarole vent temperatures at Telica; temperatures are measured approximately once per month (figure 32). Temperatures measured during 2012 at the 4 fumaroles (figure 33), vents located E and outside of Telica crater, ranged between 52° and 79°C.
|Figure 31. INETER staff measuring temparatures at the Telica crater using a thermal imaging camera (left) and one of the fumarole vents using an IR thermometer (right). Courtesy of INETER.|
|Figure 32. (a) Maximum monthly temperatures for Telica crater during January 2011-February 2012, and (b) average monthly temperatures during 2012. Courtesy of INETER.|
|Figure 33. A W looking Google Earth view of Telica showing the approximate location of the fumarole vents E of Telica crater (lower arrow) and the location of temperature measurements in the crater (upper arrow). Courtesy of INETER.|
2013 activity. The Costa Rica News reported on 24 March 2013 that Virginia Tenorio of INETER announced that Telica was experiencing increased micro-earthquakes. According to the INETER report, dozens of micro-earthquakes had occurred per day since 17 March. The increase continued to at least 24 March; 20 earthquakes occurred on 22 March, but only one reached as high as M 2.1. Tenorio was reported to state that, although earthquakes were located within the volcano’s structure, an imminent eruption was not indicated. She further stated that while some changes may occur in the magmatic system and in the expulsion of gases, conditions were stable. Local observers reported elevated vapor and gas emissions associated with the spike in seismicity and incandescence in a fissure at the bottom of the active crater. Since 21 March 2013, the member institutions of the National System for Prevention, Mitigation and Attention to Disasters (SINAPRED), have been ordered to monitor Telica’s activity and keep it under close observation.
Geologic Summary. Telica, one of Nicaragua’s most active volcanoes, has erupted frequently since the beginning of the Spanish era. The Telica volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the Telica group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of 1,061-m-high Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately SE of Telica, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.
Information Contacts: Virginia Tenorio, Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni); Costa Rica News, San Jose, Costa Rica (URL: http://thecostaricanews.com); Sistema Nacional para la Prevención, Mitigación y Atención de Desastres (SINAPRED), Managua, Nicaragua (URL:http://www.sinapred.gob.ni/); MODVOLC, Hawai'i Institute of Geophysics and Planetology (HIGP) Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://hotspot.higp.hawaii.edu/).
This report discusses eruptive highlights at Kilauea during 2009, with occasional reference to earlier and later events. Within the E rift zone, Pu`u `O`o crater was relatively quiet during 2009, while lava flows escaping from the Thanksgiving Eve Breakout (TEB) tube system continued to feed emissions along the SE coast. Along the E portion of the TEB system, the Waikupanaha ocean entry remained active for up to 363 days during 2009 before ceasing altogether on 4 January 2010. Along the W branches and ocean entries of the TEB tube system, lava emissions halted in July 2009.
At Kilauea‘s summit, lava returned to the active vent within Halema`uma`u crater in January 2009, ending a pause in lava emissions there that began in December 2008. The active vent’s shape was explored using Lidar, and in mid-2009 the lava lake’s surface sat ~200 m below the floor of Halema`uma`u crater. The active vent underwent numerous cycles of lava rise, surface cooling, and collapse. Unless otherwise noted, all information in this report is from USGS Hawaiian Volcano Observatory (HVO) reports.
Pu`u `O`o crater quiescence. During the first four months of 2009, heavy fuming at Pu`u `O`o prevented visual observation of areas within the crater. HVO reported gas-rushing noises, but nothing unusual in available views from Forward Looking Infrared Radiometer (FLIR) thermal imaging. FLIR instruments detect infrared radiation, and produce calibrated thermal videos and still images.
On 15 May, favorable wind directions provided clear views of the crater floor. Observers reported patches of less broken, ponded surfaces near locations previously observed as spattering vents, as well as a V-shaped trough that ran SW-NE traversing the length of the crater (figure 34). They also observed an incandescent, fuming vent emitting puffing sounds in the NE part of the crater (also heard during a later visit in June), and an unseen vent distinguished by sounds on the W end of the crater floor (figure 34). Until October, further observation was limited to FLIR imagery, showing a few small, hot vents on the crater floor.
|Figure 34. Map of Pu`u `O`o crater (dark gray) and vicinity showing active vents during 2009 (red dots) and the V-shaped trough (dashed line) that was observed on 15 May 2009. The webcam (POcam) location on the crater’s rim is indicated by the yellow triangle. Other mapped units correspond to previous flow fields emplaced in 1983-1986 (light gray), 1992-2007 (tan and orange), and 2008 (pink, top right); during 1986-1992, lava flows were emplaced outside of the mapped area. A small lithic debris field observed on the NE rim on 2 December 2009 is also indicated. Courtesy of USGS-HVO.|
Crater glow at Pu`u `O`o was observed via webcam on most nights during the last three months of 2009. Ground observation on 2 December revealed a small (estimated <1 m3) surficial deposit of lithic lapilli and small blocks on the NE rim from a small explosion estimated to have occurred as early as 23 September (figure 34). The lithic debris was most likely sourced from one of the nearby vents on the NE crater wall.
During 2009 (and possibly since August 2007), a series of collapses removed a significant portion of the N crater rim. HVO reported that the series of collapses removed some of the highest points of the summit of the Pu`u `O`o rim, thus lowering the local elevation by a few meters.
Flow field and coastal plain breakouts and changes. Lava flows emplaced during 2009 covered an area of 6.5 km2, most of which covered previous lava flows; only 0.8 km2 of vegetated land (chiefly forested kipukas within the flow field) was overrun by lava (2009 flow field changes are shown in figure 35).
|Figure 35. Map of the changes to Pu`u `O`o’s 21 July 2007 eruption flow field during 2009. The pre-existing (July 2007-2008) extent of the flow field is shown in pink, and the 2009 flow field additions are shown in red. Note that the portions of 2009 lava flows that overran the 2008 flow field extent are not represented, only changes to the extent of the July 2007-2008 flow field in 2009. The TEB tube system is shown in yellow with points where lava escaped to the surface, breakout points, indicated (‘B/O points’). Ocean entries are indicated and labeled along the coast. Pool 1 (green) indicates the location of a lava lake roof collapse (discussed in text). Flow fields active during 1983-86 are shown in light gray, 1986-92 shown in light yellow, and 1992-2007 shown in orange. Courtesy of USGS-HVO.|
The TEB vent and rootless shields (a pile of lava flows built over a known lava tube rather than over a conduit feeding magma; explained in BGVN 27:03) showed little change in early 2009, with small (most <300 m long) breakout-fed lava flows occurring occasionally during February and March on the fault scarp and cliffs (pali) in the Royal Gardens subdivision (figure 35) and the upper flow field. In early March, a breakout-fed lava flow reached the ocean, establishing the Kupapa`u ocean entry, which was active for a few months (discussed below) and consisted of several points where lava entered the sea (entry points). The long-lived Waikupanaha ocean entry (active since 5 March 2008) frequently produced littoral explosions and underwent delta collapses.
Other short-lived ocean entries occurred during this time, stemming from coastal plain breakouts from the W branch of the TEB tube system. These breakouts often slowed or stopped in harmony with deflation-inflation (DI) events at the summit. DI events, measured by tiltmeters at Kilauea’s summit, are thought to result from changes in magma supply to a storage reservoir less than 1 km deep and just E of Halema`uma`u crater. These fluctuations often propagate through the magmatic system, and are usually measured by another tiltmeter at Pu`u `O`o crater a few hours later. Typically occurring over weekly timescales during 2009 (up to a few days of deflation, followed by up to a few days of inflation; figure 36), DI events often correlate to pulses and/or pauses in lava emission at E rift zone vents.
|Figure 36. Radial deformation recorded by tiltmeters at Kilauea’s summit (blue) and Pu`u `O`o crater (pink) during 2009. The sawtooth patterns delineate what have come to be called deflation-inflation (DI) events, which typically occurred over weekly timescales during 2009. The timing and behavior of DI events often coincided with vent collapses at Kilauea’s summit and decreases or pauses in lava effusion along the E rift zone. Courtesy of USGS-HVO.|
On 8 March 2009, the pool 1 lava lake roof (labeled in figure 35, feeding a perched lava channel - a lava channel with walls built up from previous overflows - from the 21 July 2007 fissure eruption, BGVN 34:03) collapsed. Subsequent cooling and further collapses during 11-19 March caused the channel to seal. No further active lava was observed in pool 1.
By 29 April, surface lava flows leading to the Kupapa`u ocean entry were no longer visible. This observation was taken to indicate that a tube branch leading to the Kupapa`u entry had been established. Later, during May-June, the multiple entries at Kupapa`u coalesced into one entry point. This entry was weaker and less persistant than the Waikupanaha entry and never formed a significant delta. Lava flows at the Kupapa`u entry pulsated in a manner closely correlated to DI events, unlike flows at the Waikupanaha entry, and the Kupapa`u ocean entry ceased by 21 July.
The onset of a strong DI event correlated with a breakout on June 1 from the Waikupanaha branch of the TEB tube system. Although beginning slowly, it remained active through mid-August. As is common, the flows slowed during deflation stages of DI events, and advanced further during inflation stages.
The Waikupanaha entry underwent common delta collapses throughout the year. The vigor of lava effusion at the entry, however, made up for the area lost to collapses, and the size of the delta continued to increase. The only known pause in lava entering the sea at Waikupanaha during 2009 occurred during a DI event, when the entry stopped for two days during 28-29 September.
On 31 October, surface lava flows reached the ocean ~700 m W of Waikupanaha, and established the W Waikupanaha entry. The new entry point was fed by an inferred secondary lava tube crossing over the main Waikupanaha tube branch (see the dashed portion of the yellow line labeled 'E Tube Branch', figure 35). Following the termination of the W Waikupanaha entry on 17 December, HVO concluded that its feeder tube had eroded down into the main Waikupanaha tube, thus tapping off its supply. Breakouts and surface flows during the end of the year continued to be affected by DI events.
Second longest ocean entry ceases. A large and prolonged DI event at Kilauea’s summit in December correlated with a brief pause in lava effusion at the E rift zone. As a result, by 4 January 2010, lava ceased entering the ocean at Waikupanaha after 22 months of near-continuous lava entry. This was the second longest ocean entry in the history of the eruption, being about half a month shorter than the 2005-2007 E Lae`apuki entry.
Lava lake returns to Kilauea’s summit. A lull in activity at Halema`uma`u crater began in mid-December 2008; on 14 January 2009, rockfall sounds returned to the summit, attributed to rising lava digesting talus slopes along the steep walled vent. Four days later, gas-rushing sounds, increased temperature, and collapses of the vent rim (figure 37) occurred, dusting nearby areas with ash and further marking the summit’s re-awakening.
|Figure 37. Time lapse photographs of a collapse of a portion of the Halema`uma`u vent rim, Kilauea, taken one minute apart (at 1528 and 1529) on 18 January 2009. The black line in the left frame indicates the area of collapse, which is absent in the right frame. Courtesy of USGS-HVO.|
Vent glow, temperature increases, gas-rushing noises, and production of vitric ash continued during early 2009, indicating fresh lava had ascended to a shallow level in the vent. These eruption related processes fluctuated in a manner that suggested that they were moderated by in-falling crater walls burying the vent bottom.
Onset of a DI event on 3 February correlated with the retreat of the lava within the vent, removing support for the rubble clogging the vent cavity and collapsing the rubble into the cavity. This disturbance was accompanied by an ash plume that was sustained for 8 minutes. FLIR images captured the following day disclosed a lava lake situated deep within the vent (the rubble clogging the vent cavity was gone). HVO noted upwelling on the lake’s E side, draining and filling events (figure 38) and spattering from the lake. Similar fluctuations at Halema`uma`u occurred in concert with DI events through late April.
|Figure 38. Observational and geophysical data highlight filling (pink) and draining (gray) cycles at Kilauea’s summit vent within Halema`uma`u crater. (a) Filling and draining cycles over 3 hours on 6 February 2009 were observed with FLIR, and compared with seismicity (Realtime Seismic Amplitude Measurement - RSAM - , top) and infrasound (sound at lower than audible frequencies, bottom). RSAM provides rapid analysis of ground-motion amplitudes across multiple stations; measurements are unitless and usually reported as 'RSAM units'. (b) Filling and draining cycles over ~1 hour on 7 February 2009 were observed via acoustic noises and compared with tilt (top), seismicity (middle, reported in instrument counts, here representing the seismometer response to the vertical component of ground motion velocity), and infrasound (bottom). Courtesy of USGS-HVO.|
On 28-29 April 2009, a series of collapses at the vent within Halema`uma`u dislodged rubble and tephra covering the lava surface within the vent. As a result, for the next two months, particle emissions became > 50% juvenile (figure 39). Tephra emissions (juvenile, or glassy, and lithic components) have been measured nearly daily at Halema`uma`u since April 2008 by collecting passively emitted tephra (i.e. derived from non-explosive activity) in an array of buckets deployed around the vent. The resulting assessments led to the compilation of isomass maps and calculations of the total mass emitted (Swanson and others, 2009). By 6 May, bubbling and churning at the lava lake surface was visible with the naked eye.
|Figure 39. Calculated monthly ejected mass of tephra from Kilauea’s summit during April 2008-January 2010. The histogram excludes any explosive eruptions during that period. Collected tephra were assigned to one of two components: juvenile (glass, shown in black) and lithic (lava, shown in gray). Note that more than half of the mass ejected during May-June 2009 was juvenile, following a series of collapses on 28-29 April. See text or Swanson and others (2009) for a description of the daily tephra emission measurement technique. Courtesy of USGS-HVO.|
A strong DI event in early June (reflected in the E rift zone by breakouts on the pali on 1 June, see above) marked the peak of lava activity within Halema`uma`u crater during 2009. The vent’s lava lake showed strong upwelling in the NE, at times forming a dome-shaped fountain. The surface of the lava lake was circulating rapidly enough to prevent any significant crust from forming. The lava lake’s circulation and activity slowed near the end of June and its surface appeared almost completely crusted over. A tripod mounted Lidar (T-Lidar) survey of the vent during 10-12 June indicated that the lava surface was ~207 m below the floor of Halema`uma`u crater (figure 40).
|Figure 40. 2-D projection of 3-D reconstruction of the Halema`uma`u crater vent as measured by a T-Lidar survey on 10-12 June 2009. The reconstruction (gray) is shown on a black background. The T-Lidar was shot from the Halema`uma`u crater rim, adjacent to the active vent. The plane projected here trends approximately NNE-SSW. The lava surface (indicated in purple at the bottom) was measured to be ~207 m below the floor of Halema`uma`u crater (indicated in green). Various other dimensions of the vent’s geometry are shown. Image by Todd Ericksen, University of Hawaii-Manoa; courtesy of USGS-HVO.|
On 30 June, a series of significant collapses of the vent wall again clogged the vent with rubble. For the following several days, lava appeared through the rubble and established a ponded surface. The lava retreated during a DI event on 4 July, and the vent became very quiet until mid-August. On the night of 9 August, the vent emitted a faint glow. Areas of degassing appeared within days, but the vent floor lacked visible molten material.
On 13 September, lava reappeared briefly, but a DI event a few days later coincided with another vent-wall collapse, again covering the lava surface. The vent floor collapsed further on 26 September, and two days later, lava had re-entered the vent and webcam videos confirmed the filling and draining behavior of the lava surface. This collapse coincided with a strong hybrid earthquake with large very-long-period waveforms. Hybrid earthquakes at Kilauea typically begin as high-frequency earthquakes (similar to local earthquakes or rockfalls), then transition to long- and sometimes very-long-period oscillations. During 2009, hybrid earthquakes (i.e. the 26 September event) and ongoing very-long-period tremor at Kilauea’s summit suggested a source location beneath the summit, and within ~500 m above or below sea level.
The lava level within the vent fluctuated until the lava surface froze and sealed shut. It collapsed again on 18 November, revealing a fresh and mobile lava surface. Similar fluctuations and crusting of the lava surface continued through the end of 2009, when the lava level again dropped out of view deep below the Halema`uma`u crater floor.
2009 deformation trends. Satellite based radar interferometry determined that broad-scale deformation at Kilauea during 2009 was marked by subsidence of the summit and E rift zone (figure 41; see the report on Mauna Loa, BGVN 37:05, for an explanation of the technique). This pattern was interpreted as deflation of the magma system, with displacement of the S flank towards the sea. Deflation also occurred in the E rift zone, but ceased by September. 64 DI events were recorded during 2009, a record number of short-lived DI events since they have been monitored. The largest and longest DI events tended to coincide with decreases or pauses in lava effusion in the E rift zone, and vent collapses at the summit (discussed above, figure 36).
|Figure 41. Subsidence and deflation of Kilauea and the E rift zone during 2009, as seen in an ENVISAT interferrogram spanning 12 January 2009 to 3 February 2010. Approximately 8 cm of subsidence occurred at Kilauea’s summit (Halema`uma`u crater, which is labeled), and ~6 cm of subsidence occurred in the E rift zone near Pu`u `O`o crater. Colored stripes indicate offsets as shown in the scale, top right (see Mauna Loa report in BGVN 37:05 for an explanation of the technique). The image was acquired with an incidence angle of 18° with the ground, looking W to E. Courtesy of USGS-HVO.|
Hexahydrite spherules discovered at Kilauea’s summit. While collecting Pele’s hair on 30 March, HVO scientists discovered and collected small (<3 mm diameter), extremely fragile, white spherules that were stuck into wads of Pele’s hair (figure 42).
|Figure 42. Hexahydrite (MgSO4·6H2O) spherules discovered and collected from just S of Kilauea’s summit vent in 2009. Photomicrographs (a, b) with scales show surface and textural details of the spherules. An in-situ photograph (c, key for scale) shows the spherules as they were found, within wads of Pele’s hair. From Hon and Orr (2011).|
X-ray diffraction revealed that the spherules were nearly pure magnesium-sulfate hexahydrite (MgSO4·6H2O). Hon and Orr (2011) proposed that the spherules form from the percolation of rainwater through vesicular vent rocks, enriching the water in soluble sulfates. Magnesium sulfate resists precipitation owing to its higher solubility, and most other hydrothermal minerals would precipitate from the enriched fluid sooner. Hon and Orr (2011) suggested that boiling of the residual magnesium sulfate enriched fluids formed a foam of magnesium sulfate-coated bubbles, which formed the spherules when the bubbles were subsequently entrained into the eruptive plume.
Petrologic trends, shallow magma mixing. Through long-term petrologic monitoring and analysis of Kilauea’s summit and E rift zone lavas, HVO scientists noted that the weight percent MgO (an indicator of the temperature of tapped magmas) of E rift zone lavas indicated well-buffered, shallow magma conditions that were maintained by “near-continuous recharge and eruption.” Similarly, textural and compositional evidence highlighted pre-eruptive magma mixing between a shallow, cooler, degassed component and a gaseous, hotter, recharge magma component. Combined, the two components are erupted as a hybrid lava at the E rift zone.
Interestingly, since 2001, increased magma supply (interpreted from cross-summit extension distance) has correlated with an increase in the shallower, degassed magma component in the E rift zone lavas (interpreted from MgO weight percent; figure 43). HVO reported that this inverse relationship (higher magma supply coincident with cooler erupted lavas) is explained by more efficient flushing of the shallow edifice during times of increased magma supply.
|Figure 43. MgO weight percent (green points and blue trend, left axis) plotted versus Kilauea’s cross-summit extension distance (red, right axis) during 2000-2009 shows an inverse relationship between magma supply (i.e. variations in cross-summit extension) and the temperature of erupted lavas (i.e. variation in MgO weight percent). Courtesy of USGS-HVO.|
Summit gas emissions exceed health standards. Based on Flyspec measurements, the total SO2 emissions from Kilauea in 2009 (~0.72 x 106 tons) were 35% less than in 2008 (the highest annual SO2 emissions since measurements began in 1979, correlating to the opening of a new vent in Halema`uma`u crater; BGVN 35:01). Of the total 2009 emissions, ~60% and ~40% were attributed to the E rift and the summit, respectively (figure 44). Although 2009 emissions were down from the previous year, a record number of Ambient Air Quality exceedences occurred at the summit during 2009 (figure 45).
|Figure 44. Daily average SO2 emissions from Kilauea’s summit (green) and from the E rift (pink) during 1992-2009. The total daily average emissions are shown in blue. 2008 marked an increase in emissions from the summit (and the highest annual SO2 emissions since measurements began in 1979) correlating with the opening of a new vent in Halema`uma`u crater (BGVN 35:01). In 2009, although total emissions were down 35% from 2008, summit emissions remained elevated. Courtesy of USGS-HVO.|
|Figure 45. Histograms show the number of days per year that the Ambient Air Quality standard was exeeded, as monitored at the HVO building (left) and at the Kilauea Visitor Center (right) since 2001. Since air quality monitoring began, the standard was exceeded most often in 2009. Courtesy of USGS-HVO.|
Vog health concerns. A recent clinic study by Longo and others (2010) highlighted the health effects of increased volcanic air pollution (volcanic smog, or ‘vog’) exposure at Kilauea, and identified population subgroups who are more susceptible to the effects of vog. They found that periods of increased vog emission and exposure coincide with increases in medical visits for “cough, headache, acute pharyngitis, and acute airway problems.” Among previously identified population subgroups with increased susceptibility to health problems from exposure to vog, Longo and others (2010) found a specific correlation with Pacific Islander children living in exposed rural communities. The native children showed higher rates of acute respiratory effects both in times of low- and high-vog emissions. Longo and others (2010) suggested that this unique population showed the highest vulnerability due to physiological and genetic contributions, as well as the built environment and a lack of prevention efforts for vog exposure.
References. Hon, K., and Orr, T., 2011, Hydrothermal hexahydrite spherules erupted during the 2008-2010 summit eruption of Kilauea Volcano, Hawai`i, Bulletin of Volcanology, 73(9), pgs. 1369-1375.
Longo, B.M., Yang, W., Green, J.B., Crosby, F.L., and Crosby, V.L., 2010, Acute health effects associated with exposure to volcanic air pollution (vog) from increased activity at Kilauea in 2008, Journal of Toxicology and Environmental Health, Part A, 73(20), pgs. 1370-1381.
Swanson, D., Wooten, K., and Orr, T.R., 2009, Mass flux of tephra sampled frequently during the ongoing Halema'uma'u eruption [abs.], Eos, Transactions, American Geophysical Union, v. 90, no. 52 (fall meeting supplement), abstract no. V52B-01.
Geologic Summary. Kilauea volcano, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii’s most active volcano during historical time. Eruptions of Kilauea are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halema`uma`u crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1,500 years ago and during the 18th century; eruptions have also originated from the lengthy E and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1,100 years old; 70% of the volcano’s surface is younger than 600 years. A long-term eruption from the E rift zone that began in 1983 has produced lava flows covering more than 100 sq km, destroying nearly 200 houses and adding new coastline to the island.
Information Contacts: Michael Poland, Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawai'i National Park, HI 96718, USA (URL: http://hvo.wr.usgs.gov/; Email: email@example.com).
On 7 February 1996, hydrophone data and water level changes suggested that a small hydrothermal ejection may have occurred at Kusatsu-Shirane (also known as Kusatsu-Shiranesan) at Yugama crater’s pond (BGVN 21:02). Several months later, on 8 July, numerous small earthquakes were detected by the Kusatsu-Shirane Volcano Observatory (BGVN 21:07). The volcano is about 150 km NW of Tokyo (figures 46 and 47; also refer to the sketch map in figure 1, SEAN 07:10). This report summarizes seismicity between May 2011 and February 2013 based on available reports from the Japan Meteorological Agency (JMA).
|Figure 46. A sketch map showing the location of Kusatsu-Shirane (Kusatsu-Shiranesan) in Honsho, Japan. Courtesy of JMA.|
|Figure 47. An aerial photo of Kusatsu-Shirane, as viewed from the S. The photo, taken on 29 May 2008, shows the overlapping pyroclastic cones and two of the three crater lakes. Courtesy of Flickr user rangaku1976.|
On 27 May 2011, tremor was detected at Kusatsu-Shirane; no further information was provided. During 5-7 June 2011, an elevated number of microearthquakes with low amplitude occurred around Yugama crater (the main crater). No volcanic tremor or significant deformation was detected during this time. Thereafter, activity gradually diminished to background levels.
Field surveys during 27-29 June and 12-13 July 2011 revealed that elevated thermal anomalies persisted inside Yugama crater’s N flank, the N fumarole area, and the slope located N to NE of Mizunuma crater. Ground temperatures around fumaroles remained high.
On 18 July 2011, a short period of tremor (duration 2.5 min) was detected. No change in fumarole activity was observed.
On 10 August 2011, an aerial survey was conducted in cooperation with Gunma prefecture. The survey found that the distribution of thermal anomalies and fumaroles in Yugama crater and the N fumarole area had not changed.
During 16-18 August, an elevated number of microearthquakes with low amplitude occurred near and to the S of Yugama crater. Significant deformation was not detected. Seismicity remained at background levels during the other days in August. High temperatures persisted on the N flank inside the main crater.
A field survey on 8 March 2012 found that the high temperatures on the N slope of Mizugama crater and the N fumarole area were the same as those found during a previous survey conducted during 27-29 June 2011. Very weak steam plumes at the N fumarole area of Yugama were sometimes observed by a camera at Okuyamada, though bad weather and mechanical trouble prevented their observation for long periods. The ground temperature in the fumarole area NE of Yugama crater remained elevated since its rapid rise in May 2009, despite occasional fluctuations.
According to JMA, the occurrence of small amplitude volcanic earthquakes occasionally increased during March 2012. The hypocenters were located just beneath the S part of Yugama crater. No tremor or significant crustal change was noted in GPS data.
During 1-2 April 2012, seismicity increased slightly, then subsided. No tremor, change in fumarole activity, or crustal change was observed, and no further reports have been issued on activity at Kusatsu-Shirane as of February 2013.
Geologic Summary. The summit of Kusatsu-Shirane volcano, located immediately N of Asama volcano, consists of a series of overlapping pyroclastic cones and three crater lakes. The andesitic-to-dacitic volcano was formed in three eruptive stages beginning in the early to mid Pleistocene. The Pleistocene Oshi pyroclastic flow produced extensive welded tuffs and non-welded pumice that covers much of the E, S and SW flanks. The latest eruptive stage began about 14,000 years ago. All historical eruptions have consisted of phreatic explosions from the acidic crater lakes or their margins. Fumaroles and hot springs that dot the volcano’s flanks have strongly acidified many rivers draining from the volcano. The crater was the site of active sulfur mining for many years during the 19th and 20th centuries.
Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); rangaku1976, Flickr (URL: http://www.flickr.com/photos/rangaku1976/).
Our previous report on Izu-Tobu (BGVN 23:04) summarized the elevated seismicity that began on 20 April 1998 in the eastern Izu Peninsula and started declining around 10 May. The activity included crustal deformation, indicating inflation likely linked to shallow magmatic activity. Izu-Tobu is located 100 km SW of Tokyo and just inland from the coast on the Izu peninsula.
Recent reports from the Japan Meteorological Agency (JMA) noted the Tohoku megathrust of March 2011, centered 400 km to the NE of Izu-Tobu, and that Izu-Tobu lacked any signs of correlated behavior as a result of that M 9.0 earthquake event and the numerous aftershocks.
Izu-Tobu had been quiet since March 2011 until 17 July when seismicity increased and small earthquakes with epicenters around Ito city (8.5 km N) were detected. Earthquakes on 18 July were M 2.5 and M 2.8 (interim values). A maximum seismic intensity of 1 on the JMA scale was observed in Ito-city and Higashi-Izu town (15 km SSW). Seismicity declined to the usual background level the following day. Ground deformation was observed around seismically active areas.
Seismicity along an area from Arai (8 km N) through offshore Shiofuki-zaki (2 km E of Ito-city), increased during 18-23 August 2011, then declined after 24 August. No earthquakes were observed until 22 September when the number of earthquakes temporarily increased at a shallower area around Usami; this activity was interpreted as not being directly related to magma intrusion.
Prior to the 22 September 2011 seismic activity, the volumetric strainmeter at Higashi-Izu town (15 km SSW) showed continuous contraction; the tiltmeter at Ito-city showed an apparent change on 18 September. The trend slowed as seismicity decreased; no change was observed after 23 September. GPS measurements did not exhibit remarkable changes and low-frequency earthquakes and tremor were not observed. The Alert Level at Izu-Tobu remained at 1.
Geologic Summary. The Izu-Tobu volcano group (Higashi-Izu volcano group) is scattered over a broad, plateau-like area of more than 400 sq km on the east side of the Izu Peninsula. Construction of several stratovolcanoes continued throughout much of the Pleistocene and overlapped with growth of smaller monogenetic volcanoes beginning about 300,000 years ago. About 70 subaerial monogenetic volcanoes formed during the last 140,000 years, and chemically similar submarine cones are located offshore. These volcanoes are located on a basement of late-Tertiary volcanic rocks and related sediments and on the flanks of three Quaternary stratovolcanoes: Amagi, Tenshi, and Usami. Some eruptive vents are controlled by NW-SE- or NE-SW-trending fissure systems. Thirteen eruptive episodes have been documented during the past 32,000 years. Kawagodaira maar produced pyroclastic flows during the largest Holocene eruption about 3,000 years ago. The latest eruption occurred in 1989, when a small submarine crater was formed NE of Ito City.
Information Contact: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html).