Cotopaxi

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  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 0.677°S
  • 78.436°W

  • 5911 m
    19388 ft

  • 352050
  • Latitude
  • Longitude

  • Summit
    Elevation

  • Volcano
    Number

7 September-13 September 2005

During 29 August to 4 September, the number of long-period and hybrid earthquakes at Cotopaxi decreased slightly, and the number of volcano-tectonic earthquakes increased, in comparison to the previous week. No changes in deformation were recorded, and no surficial changes were seen at the volcano.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)

Index of Weekly Reports


2005: August | September
2004: January
2003: November | December

Weekly Reports


7 September-13 September 2005

During 29 August to 4 September, the number of long-period and hybrid earthquakes at Cotopaxi decreased slightly, and the number of volcano-tectonic earthquakes increased, in comparison to the previous week. No changes in deformation were recorded, and no surficial changes were seen at the volcano.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


31 August-6 September 2005

During 22-28 August, a large number of long-period (LP) and hybrid earthquakes continued to be recorded at Cotopaxi. Increased seismicity was first recorded in late July. Most of the events recorded during the report period were small, and were recorded mainly at stations nearest to the crater. Also, several LP earthquakes correlated with increased activity at fumaroles in the crater. No deformation or surficial changes were observed at the volcano.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


17 August-23 August 2005

A seismic anomaly that began at Cotopaxi in late July continued through 14 August. During this period, there was an increase in the number of long-period earthquakes in comparison to previous months. The earthquakes were less than M 3 and occurred at depths between 1 and 2 km below the volcano. Several of the earthquakes correlated with increases in the volume of fumarole emissions in the crater. No carbon dioxide was detected when measurements were made during 8-14 August.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


7 January-13 January 2004

During 29 December to 4 January, the number of earthquakes at Cotopaxi slightly increased in comparison to the previous week. On 2 January a strong smell of sulfur was reported in the Yanasacha area.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


24 December-30 December 2003

During 15-21 December, there was a slight reduction in the level of seismicity at Cotopaxi in comparison to the previous week. The number of long-period earthquakes increased around 20 December. No volcano-tectonic earthquakes were recorded. Only fumarolic activity was observed at the volcano.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


17 December-23 December 2003

Seismicity at Cotopaxi during 8-14 December was above background levels, much like the previous week. During the report period, there was an increase in high-frequency tremor, but it remained within "normal" limits. A weak scent of sulfur was reported and steam columns rose to low levels.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


26 November-2 December 2003

During 10-16 November, seismicity at Cotopaxi was at moderate levels, although it had increased in comparison to previous weeks. During the report period, seismicity was dominated by long-period earthquakes. Since late October volcano-tectonic earthquakes occurred beneath the zone of Pita and beneath the volcano's edifice. These events were less than M 3 and were not felt by the local population.

Source: Instituto Geofísico-Escuela Politécnica Nacional (IG)


Index of Monthly Reports

Reports are organized chronologically and indexed below by Month/Year (Publication Volume:Number), and include a one-line summary. Click on the index link or scroll down to read the reports.

10/1975 (SEAN 01:01) Vapor plumes rising above the crater in September and October

11/1975 (SEAN 01:02) Continued vapor emanations in November

12/1975 (SEAN 01:03) Activity declines

12/2002 (BGVN 27:12) First anomalous seismicity since 1975 begins in October 2001

11/2003 (BGVN 28:11) Low seismicity and emission signals January-May 2003; March earthquake clusters

12/2003 (BGVN 28:12) During May-December 2003 seismicity moderate, degassing and inflation variable

11/2004 (BGVN 29:11) Seismically quiet in January-April 2004; planning for emergency water supplies


Contents of Monthly Reports

All information contained in these reports is preliminary and subject to change.

All times are local (= UTC - 5 hours)

10/1975 (SEAN 01:01) Vapor plumes rising above the crater in September and October

On 23 July 1975 small grayish puffs of smoke were observed emanating from the crater. In mid-September a 300-m vapor plume rose above the crater, and a small earthquake shook the volcano on 24 September. In mid-October vapor plumes were reported to be increasing in volume and frequency. Cotopaxi last erupted in 1944.

Information Contact: M. Hall, Escuela Politécnica, Quito.

11/1975 (SEAN 01:02) Continued vapor emanations in November

The activity continued during November. The amount of vapor was about the same as in October, but daily cloud activity was observed. There was increased fumarolic activity on the W side, just below the crater. Earthquakes were felt in the town of Mulaló around 0000, 11 November, and at 0431, 12 November, and again on 14 November. Three portable seismographs were placed around the volcano, and were gathering valuable seismic data by the end of the month.

Information Contact: M. Hall, Escuela Politécnica, Quito.

12/1975 (SEAN 01:03) Activity declines

Activity declined during December. The crater steam clouds of previous months were observed only once, on 12 December, since 28 November. Seismic activity was not strong and focal depths were at least 20 km below the volcano. Relevelling of dry tilt stations installed 7 November showed no inflation of the volcano. However, a USGS team including Donal Mullineaux and C. Dan Miller reached Ecuador in late December to assess volcanic hazards and assist the local authorities in contingency planning.

Information Contact: M. Hall, Escuela Politécnica, Quito.

12/2002 (BGVN 27:12) First anomalous seismicity since 1975 begins in October 2001

The last Cotopaxi report (SEAN 01:03) described a decline in activity during December 1975. Beginning in October 2001, anomalous seismic activity was registered. Seismicity increased further during November 2001-January 2002, and at times was up to seven times the normal level (tables 1 and 2). During this period, other seismic signals were registered that were distinct from those during the 13 previous years of monitoring, including: tornillos, explosion events, bands of harmonic tremor sometimes lasting a few minutes, and deep, high-energy long-period (LP) events registered away from the volcano (at the Antisana and Guagua Pichincha stations). Seismic observations and statistics were compiled using station "VCl," located ~4 km NE of the volcano. Earthquake locations were determined using records from the seven seismic stations on different flanks of Cotopaxi, and for higher-energy events with stations of the National network.

Table 1. Seismicity at Cotopaxi during 2001-2002. Courtesy IG.

    Date       Long-period        Hybrid             Volcano-tectonic
               Total Daily avg.   Total Daily avg.   Total Daily avg.

    Jan 2001    336    10.8          0     0.0         18     0.6
    Feb         185     6.6          0     0.0          4     0.1
    Mar         319    10.3          1     0.0         10     0.3
    Apr         280     9.3          0     0.0         26     0.9
    May         241     7.8          7     0.2         10     0.3
    Jun         243     8.1         11     0.4         53     1.8
    Jul         262     8.5          2     0.1          9     0.3
    Aug         241     7.8          0     0.0          9     0.3
    Sep         394    13.1          9     0.3          9     0.3
    Oct         555    17.9          0     0.0          7     0.2
    Nov         432    14.4         57     1.9        400    13.3
    Dec         516    16.6        169     5.5        729    23.5
    Jan 2002    595    19.2          5     0.2        363    11.7
    Feb         532    19.0          4     0.1        157     5.6
    Mar         504    16.3          1     0.0        191     6.2
    Apr         310    10.3          7     0.2         63     2.1
    May         431    13.9          8     0.3         53     1.7
    Jun         429    14.3         41     1.4         45     1.5
    Jul         445    14.4        181     5.8         92     3.0
    Aug         455    14.7         91     2.9         32     1.0
    Sep         509    17.0        184     6.1        140     4.7
    Oct         322    10.4        219     7.1         62     2.0
    Nov         295     9.8        142     4.7         64     2.1
    Dec         233     9.0        120     4.6         48     1.5

    Date       Tornillo           Total earthquakes
               Total Daily avg.   Total Daily avg.

    Jan 2001      0     0.0        354    11.4
    Feb           0     0.0        189     6.8
    Mar           0     0.0        320    10.3
    Apr           0     0.0        306    10.2
    May           0     0.0        248     8.0
    Jun           0     0.0        307    10.2
    Jul           0     0.0        273     8.8
    Aug           0     0.0        250     8.1
    Sep           0     0.0        412    13.7
    Oct           0     0.0        562    18.1
    Nov           4     0.1        893    29.8
    Dec           0     0.0       1423    45.9
    Jan 2002      3     0.1        966    31.2
    Feb           0     0.0        693    24.8
    Mar           0     0.0        696    22.5
    Apr           0     0.0        380    12.7
    May           0     0.0        453    14.6
    Jun           3     0.1        474    15.8
    Jul           2     0.1        720    23.2
    Aug          12     0.4        590    19.0
    Sep          19     0.6        852    28.4
    Oct          13     0.4        616    19.9

    Nov           2     0.1        503    16.8
    Dec           1     0.0        402    16.1

Table 2. Comparison of average seismicity at Cotopaxi during 2001 and 2002. Courtesy IG.

    Year    Daily average    Monthly average    Total

    2001       15.4              461.4           5537
    2002       20.4              612.1           7345

On 5 and 29 January 2002, two seismic clusters lasted an average of 2 hours and were composed mainly of LP and VT earthquakes. Most of the earthquakes were located at depths of 1-10 km beneath the summit. On 5 and 13 January small fumaroles were reported in the crater, and visible defrosting occurred on the upper E flank. A visit to the summit on 13 January revealed increased fumarolic activity compared to previous months. On 19 and 20 January observers reported gray plumes rising as high as 1,000 m.

During February and March activity diminished, and no seismic clusters were registered. Most of the earthquakes were located 1-10 km beneath the volcano. On 5 February roaring noises were heard from Mulaló and the refuges located on the flanks of the volcano. Strong fumarolic activity was also reported. On 6 February steam plumes rose ~300 m above the summit. On 27 February a small steam plume was reported exiting from the NW side of the crater. On 7 and 10 March small steam plumes originated from the W side of the crater. On 28 March harmonic tremor lasted for ~10 minutes.

Activity remained low during April-June. On 17 April a band of harmonic tremor lasted ~6 minutes with a maximum frequency of 4.3 Hz. During the first days of April small steam plumes were reported. During May LP earthquakes lasted up to a minute and saturated the seismometer for several seconds. On 20 May a seismic cluster of LP earthquakes lasted ~2 hours. On 8 and 14 May a white steam plume from the NE side of the volcano reached up to 200 m high. During June VT events mostly occurred ~10 km N of the crater. On 30 June a band of harmonic tremor lasted ~7 minutes with a maximum frequency of 1.7-5.2 Hz. Visits to the summit on 1 and 2 June revealed that fumarolic activity had diminished ~40% since January.

During July seismicity was at a moderate level with respect to the rest of 2002. During the first days of the month a series of LP events were registered that were large enough to be detected at distant stations, such as Antisana and Guagua Pichincha. The earthquakes had maximum frequencies of ~2.1 Hz and were generally 1-2 km beneath the summit. However, some events were located at depths of ~10 km. On 18 July at 2000 a band of low-frequency tremor lasted ~4 minutes. About 5 hours later a seismic cluster began that lasted for ~8 hours. The cluster consisted of ~110 total events, mostly hybrid (HB) and volcano-tectonic (VT). The earthquakes were located 1-4 km beneath the summit, and 2 LP events were located ~10 km deep.

Visitors to the summit on 6 July reported fumarolic activity in the zone of Yanasacha, a slight sulfur smell on the NE side, and noise generated by an avalanche on the E side. At the end of July reports indicated defrosting in the W zone. During August moderate seismicity was dominated by LP events at a depth of ~10 km.

Seismicity was again high in September 2002. A small cluster of VT earthquakes on 15 September lasted ~7 hours. During the first days of the month a visit to the crater revealed new fumaroles in the E and S zones. Defrosting continued in the W zone and left 40% of the W wall open.

During October seismic activity was low but the number of hybrid events increased compared to the previous months. Tectonic events were registered in the S and N zones up to ~7 km from the summit. Deep LP events decreased by ~50% compared to previous months.

Seismicity remained low during November and December. Less than 10% of VT events were registered in the N sector. No fumarolic or other surface activity was observed. During December seismic events were located 1-7 km beneath the summit. On 7 December people in Yanahurco reported dark brown plumes rising from the crater.

Seismicity since 1989 clearly shows an increase in recent months (figure 1). The 2001 seismic events were registered at 1-10 km beneath the volcano, but ~90% occurred at 2-4 km and showed little migration. The 2002 activity was variable, from a high of 966 events in January to a low of 420 events in April. Mostly LP events occurred with some VT events during the first half of the year, and later mostly LP events with hybrids during the second half of the year. On the basis of 2002 seismic activity, a new injection of magma did not occur, and the anomalies in July and September were the result of the movement of gas from magma intrusion that occurred during the last months of 2001.

Figure 1. Graph of the total registered monthly events at Cotopaxi during 1989-2002. The activity increased beginning in November 2001 and has since remained above background levels. Courtesy of IG.

Information Contact: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.

11/2003 (BGVN 28:11) Low seismicity and emission signals January-May 2003; March earthquake clusters

This report contains details of seismicity at Cotopaxi during January through 2 May 2003. The seismicity was generally low (averaging ~20 earthquakes per day), as it has been since 24 November 2001. Despite the low seismicity, during January seismic signals suggestive of emissions registered, although these lacked visual confirmations at the volcano. Moreover, a cluster composed of a variety of kinds of shallow earthquakes took place in mid-March. This was the first such cluster since 19 July 2002.

Activity during January-February 2003. Seismicity was generally low in January 2003 and located earthquakes commonly had focal depths down to 5 km below the summit. During the first week of January one volcano-tectonic (VT) event occurred N of the volcano. Around this time the rate of energy release was very low and no unusual observations were reported. Seismicity decreased after the first week of January, although some long-period (LP) events occurred, including one of high frequency (10 Hz) on 9 January that was followed immediately by another with a slowly decaying coda or tail (a so-called "tornillo" event, with a dominant frequency of 2.7 Hz). Two LP events were located at depths of 1 km. The rate of energy release remained very low, with some peaks on 8 January. Seismicity stayed low through the next week; some hybrid and LP events did occur. Some signals characteristic of emissions were received, although these were not visually confirmed.

During 20-26 January the number of hybrid events increased slightly, to above average. Emission signals were again received, similar to the previous week. No LP earthquakes were recorded this week, but a small group of earthquakes were located at the headwaters of the Pita river. Events such as these were also noted in November 2001. During the last week of January, seismicity remained low, on a par with activity seen since 24 November 2001. However, the low number of events registered or located was partly because arrivals were not clear at many stations.

Seismicity remained low in February, particularly for the first week. During 10-16 February it rose slightly due to larger numbers of hybrid events. No other changes in the volcano were noted. Although the third week of February brought no important variations in seismicity, beginning in late February LP events dominated the record. Still, the number of LP event stayed below the 2002 average.

Activity during March-April 2003. Although low seismicity generally prevailed throughout this interval, there was some variations in the abundance of earthquake types and a mid-March cluster of earthquakes occurred. During early March hybrid earthquakes increased to slightly higher than the 2002 average; in addition another LP-type tornillo was recorded on 6 March. On 7 March LP earthquakes were common.

On 16 March a cluster of hybrid, VT, and LP earthquakes was located 1-3 km below the volcano. Following eight months of low seismicity (averaging ~20 events per day), this was the first seismic swarm registered at Cotopaxi since 19 July 2002. However, the energy released per number of events was similar to earlier activity.

Seismicity increased after 16 March. Clusters similar to that of the 16th continued, but with lower magnitudes. By the beginning of April seismicity decreased to within the base level, although on 4, 7, and 8 April VT events were recorded to the S and SE, approximately 3 km below the summit. No significant changes were noted at the volcano, although the usual smell of sulfur was noted on a visit to the summit. During 14-20 April, the number of LP events decreased from the previous week, but VT events of M 2.5-M 3.4 continued to the N. VT events persisted through the rest of April, particularly in late April, which on 23 April included an M 3.6 event. VT events occurred on the N, NE, and S sides of the volcano up to 15 km from the summit at depths between 3 and 15 km. The VT events were interpreted as related to rock fracturing.

On the morning of 2 May a VT event registered on the S flank, located ~3 km deep. It was M 3.2, moderate for Cotopaxi. Later that day an event registered at the seismic stations at Cotopaxi, Antisana, and Guagua Pichincha. This event had a duration of 180 seconds and was made up of an LP earthquake followed by a tremor-like signal with a duration of 150 seconds that was of low frequency (1.6 Hz).

Information Contact: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/).

12/2003 (BGVN 28:12) During May-December 2003 seismicity moderate, degassing and inflation variable

This report contains details of seismicity at Cotopaxi during May through December 2003. In general, seismicity was low and within normal levels, occasionally punctuated by increased activity. Fumarolic and inflationary activity varied throughout the period.

Seismicity during the first week of May was characterized by a high number of fracture-related volcano-tectonic events in the N, NE, and S zones, up to 15 km from the summit. These events were located at depths between 3 and 15 km below the summit. On 2 May at 0949 a volcano-tectonic event on the S flank occurred at ~ 3 km depth. Based on the coda, the event was calculated as M 3.2, a value considered moderate at this volcano. At 1918 on 2 May a long-period event was recorded at the Cotopaxi, Antisana, and Guagua Pichincha seismic stations. It lasted about 180 seconds. The earthquake was followed by a low-frequency (1.6 Hz) tremor signal lasting about 150 seconds.

Between 2 and 4 May deflation was recorded, with slight variations. On 2 May staff at the Refuge felt earthquakes. On 3 May the staff saw steam plumes at heights of 400-800 m above the crater, which blew W. On 3 and 4 May observations were made at the Refuge and the summit. Staff smelled sulfur halfway to the summit; and found new fumaroles in the Yanasacha area. On 4 May these fumaroles generated white steam plumes up to 50 m above the summit. Fumarole temperatures were 29-31°C.

A tectonic earthquake was recorded on 8 May, but although tremor episodes increased, volcano-tectonic earthquakes were fewer during 5-11 May than the previous week. Seismicity continued to drop during the week of 12-18 May. Although some low-amplitude tremor occurred during that interval, activity was dominated by long-period earthquakes. Earthquakes increased slightly the following week, but seismicity remained lower than average for the year. Low-frequency tremor lasting under 10 minutes was recorded on 23 May; tectonic activity on 24 May occurred in the zone of Saquisili and was determined to be unrelated to Cotopaxi. During the final week of May, long-period events and tremor signals increased slightly but seismicity continued to remain within the normal parameters established as of November 2001, when Cotopaxi entered a period of unusual seismic and fumarolic activity.

Activity remained generally constant through June, with episodes of harmonic tremor increasing slightly between 9 and 15 June and again on 23 June. White steam plumes reached 300 m high on 4 June, but later they were under 100 m high. At the end of June there was a slight tendency toward deflation; tremor events increased slightly and usually had fundamental frequencies of ~ 1.7 Hz.

Between 7 and 13 July the number of long-period events increased, as did the number of hybrid events. However, tremor decreased, and the average number of earthquakes per day (8) was lower than in recent periods of increased activity. The average number of earthquakes per day decreased again the following week. Notable tremor occurred on 20 July, with episodes lasting between 80 and 125 seconds and reduced displacement varying from 0.5 to 11 cm2. During the week of 21-27 July activity increased slightly, from 6.6 to 8.3 events per day, but in general seismic data indicated a state of low activity during July.

In early August seismicity rose to an average of 20 events per day, and tremor signals increased, especially on 8-10 August. However, the released energy remained low throughout August. Earthquakes registered that month were generally small, and tremor signals were constant except for two periods of harmonic tremor on 28 August.

Although seismicity remained low in early September, on 6 September instruments registered a low-frequency (0.9 Hz), low-amplitude tremor lasting more than 3 hours. On 18 September a cluster of earthquakes (characterized by long-period events and hybrid events) began around 1300 and lasted ~ 4 hours. A second cluster occurred the next day, lasting ~ 6 hours. The earthquakes associated with these clusters were located between 1 and 4 km below the summit. Fumarolic activity was normal for most of September, although a gas discharge was reported on 21 September. After 21 September seismicity returned to normal levels, and continued to decrease through the following week.

Seismicity generally remained low for the next few months. Volcano-tectonic earthquakes and tremor increased slightly during 13-19 October. Three distinct episodes of tremor on 15, 17, and 18 October consisted of similar events with dominant frequencies of 0.8-0.9 Hz. Seismicity into November remained low, with no significant episodes of tremor and only small events.

By mid-December seismicity increased and although activity remained within normal levels, the occurrence of high-frequency tremor was noteworthy. Also through mid-December, a slight odor of sulfur was reported, as well as occasional columns of steam no higher than 300 m.

Correction: A brown plume mentioned on 7 December 2002 (BGVN 27:12) might be misinterpreted as evidence of an ash-bearing emission. Gorki Ruiz, a colleague of Pete and Patty Hall, clarified events and interpretations from that date. He interviewed guards at the Cotopaxi refugio, who stated that neither they nor others at the refugio that day had observed emissions. They discounted observations of ash emissions and noted that although fumarolic plumes frequently reach 300 m above the summit, no phreatic explosions had occurred. That time interval was also one of low seismicity.

Information Contact: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/).

11/2004 (BGVN 29:11) Seismically quiet in January-April 2004; planning for emergency water supplies

Seismicity at Cotopaxi during December 2003 through December 2004 yielded averages that generally remained within normal levels (table 3). Steam emissions continued, and sulfurous odors were occasionally reported. A plot of total seismicity each week during 2001-July 2004 portrayed numerous peaks and valleys in the range 50-200 events per week. Occasional excursions took the weekly totals to several hundred events in late 2001 and early 2002 (peaking at over 700 events per week during mid-October 2001). The 2004 data lacked such dramatic excursions.

Table 3. Annual summaries showing typical daily averages of various kinds of seismicity at Cotopaxi during 2001-2004. Courtesy of IG (shown on their website in the January 2005 report).

    Year    Volcano-tectonic    Hybrid    Long-period    Tornillo    Tremor    Total

    2001          3.1            1.0         10.2          0.1        0.2      11.3
    2002          2.9            3.0         14.6          0.1        0.4      18.2
    2003          1.2            3.7          9.3          0.0        1.4      14.2
    2004          0.41           3.59        11.10         0.0        1.56     15.11

Planning for emergency water supplies. Although seismicity and other monitored parameters were moderate to low during most of 2003 (BGVN 28:11 and 28:12), local authorities worked on a contingency plan for emergency drinking water in the event of a crisis at Cotopaxi.

The Quito metropolitan sanitation and drinking water company (EMAAP-Q) prepared a contingency plan for residents around Cotopaxi. The challenge was to provide for sufficient amounts of potable and sanitation water for some half a million people in the event of an eruption that contaminates their normal water supplies. This contingency plan was drawn up using experience gained from the operational emergency plan used to recover from the eruption in 1998-99 and the Reventador eruption in 2002.

During the Guagua Pichincha eruption, pyroclastic material impacted Quito, and ash fell into the water treatment plants and threatened the water supply systems. EMAAP-Q developed an operational and emergency plan. The plan was tested in 1999 when the volcano had two major eruptions that heat dropped ash on Quito and its infrastructure.

Information Contact: Geophysical Institute (IG), Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/).

Symmetrical, glacier-clad Cotopaxi stratovolcano is Ecuador's most well-known volcano and one of its most active. The steep-sided cone is capped by nested summit craters, the largest of which is about 550 x 800 m in diameter. Deep valleys scoured by lahars radiate from the summit of the andesitic volcano, and large andesitic lava flows extend as far as the base of Cotopaxi. The modern conical volcano has been constructed since a major edifice collapse sometime prior to about 5000 years ago. Pyroclastic flows (often confused in historical accounts with lava flows) have accompanied many explosive eruptions of Cotopaxi, and lahars have frequently devastated adjacent valleys. The most violent historical eruptions took place in 1744, 1768, and 1877. Pyroclastic flows descended all sides of the volcano in 1877, and lahars traveled more than 100 km into the Pacific Ocean and western Amazon basin. The last significant eruption of Cotopaxi took place in 1904.

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
[ 1942 Feb 17 ] [ 1942 Feb 19 ] Uncertain 3  
1940 Unknown Confirmed 2 Historical Observations
1939 Feb 2 Unknown Confirmed 2 Historical Observations
1931 Unknown Confirmed 2 Historical Observations
1926 Unknown Confirmed 2 Historical Observations
1922 Unknown Confirmed 2 Historical Observations
1908 1914 Confirmed 1 Historical Observations
1907 Jun Unknown Confirmed 2 Historical Observations
1906 Aug 21 1906 Sep 19 Confirmed 2 Historical Observations
1905 Unknown Confirmed 2 Historical Observations
1903 Sep 26 1904 Dec Confirmed 3 Historical Observations
1895 Unknown Confirmed 2 Historical Observations
1886 Jan Unknown Confirmed 2 Historical Observations
1885 Jul 23 Unknown Confirmed 2 Historical Observations
1883 Dec Unknown Confirmed 2 Historical Observations
1883 Aug Unknown Confirmed 2 Historical Observations
1882 Jan 1882 Mar Confirmed 2 Historical Observations
1880 Feb 1880 Jul Confirmed 3 Historical Observations
1879 Feb 26 1879 Jun 19 Confirmed 2 Historical Observations
1878 Aug 23 1878 Aug 24 Confirmed 2 Historical Observations
1877 Jan 1877 Sep 2 Confirmed 4 Historical Observations
1870 1876 Confirmed 2 Historical Observations
1869 Jul 1869 Aug Confirmed 3 Historical Observations
1868 Aug 15 1868 Aug 16 Confirmed 2 Historical Observations
1867 Unknown Confirmed 2 Historical Observations
1866 Sep 21 1866 Sep 26 Confirmed 2 Historical Observations
1863 Unknown Confirmed 2 Historical Observations
1860 1862 Confirmed 2 Historical Observations
1859 Unknown Confirmed 2 Historical Observations
1858 Nov 1858 Dec Confirmed 2 Historical Observations
1857 Unknown Confirmed 2 Historical Observations
1856 Oct 1856 Dec Confirmed 2 Historical Observations
1856 May Unknown Confirmed 2 Historical Observations
1855 Nov Unknown Confirmed 2 Historical Observations
1854 Sep 14 Unknown Confirmed 2 Historical Observations
1854 Apr 3 Unknown Confirmed 2 Historical Observations
1853 Sep 13 1853 Sep 15 Confirmed 3 Historical Observations
1852 Unknown Confirmed 2 Historical Observations
1851 Jun Unknown Confirmed 2 Historical Observations
1850 Unknown Confirmed 2 Historical Observations
1845 Apr Unknown Confirmed 2 Historical Observations
1844 Unknown Confirmed 2 Historical Observations
1803 Jan 4 1803 Jan 5 Confirmed 3 Historical Observations
1768 Apr 4 Unknown Confirmed 4 Historical Observations
1766 Feb 10 1766 Dec Confirmed 3 Historical Observations
1750 Sep 2 ± 1 days 1750 Sep 4 ± 1 days Confirmed 2 Historical Observations
1747 1749 Confirmed 2 Historical Observations
1746 Feb Unknown Confirmed 2 Historical Observations
1744 May 1744 Dec Confirmed 4 Historical Observations
1743 Sep 27 1743 Oct 4 Confirmed 2 Historical Observations
1743 Apr Unknown Confirmed 3 Historical Observations
1742 Dec 9 Unknown Confirmed 3 Historical Observations
1742 Jun 15 1742 Jul Confirmed 3 Historical Observations
1740 1741 Confirmed 2 Historical Observations
1738 Unknown Confirmed 2 Historical Observations
1698 Unknown Confirmed 3 Historical Observations
1534 Jun 1534 Jul Confirmed 4 Historical Observations Tephra set MZ
1533 Oct 1533 Nov Confirmed 2 Historical Observations
1532 Nov 15 Unknown Confirmed 4 Historical Observations
1350 (?) Unknown Confirmed 4 Tephrochronology Tephra layer Y4
1260 ± 150 years Unknown Confirmed   Tephrochronology
1130 ± 75 years Unknown Confirmed 5 Radiocarbon (uncorrected) Tephra layer X
0950 (?) Unknown Confirmed 3 Tephrochronology Tephra layer L2
0770 ± 75 years Unknown Confirmed 4 Radiocarbon (uncorrected) Tephra layer L1
0740 ± 75 years Unknown Confirmed 4 Radiocarbon (uncorrected) Tephra layer Kb2
0550 ± 200 years Unknown Confirmed   Tephrochronology Tephra layer 10
0370 ± 200 years Unknown Confirmed   Tephrochronology Tephra layer 11
0180 ± 100 years Unknown Confirmed 4 Radiocarbon (uncorrected) Tephra layer Kb2
0150 (?) Unknown Confirmed 4 Tephrochronology Tephra layer Ka2
0070 ± 150 years Unknown Confirmed 4 Radiocarbon (uncorrected) Tephra layer Ka1
0050 BCE (?) Unknown Confirmed 3 Tephrochronology Tephra layer JK
0230 BCE ± 200 years Unknown Confirmed 4 Radiocarbon (uncorrected) Tephra layer JJ
0400 BCE (?) Unknown Confirmed 4 Tephrochronology Tephra layer J
1050 BCE (?) Unknown Confirmed 4 Tephrochronology Tephra layer I2
1510 BCE ± 150 years Unknown Confirmed   Radiocarbon (uncorrected)
2050 BCE (?) Unknown Confirmed 5 Tephrochronology Tephra layers I1
2220 BCE ± 100 years Unknown Confirmed   Radiocarbon (uncorrected) Tephra set H
2250 BCE Unknown Confirmed   Tephrochronology
2640 BCE ± 200 years Unknown Confirmed 5 Radiocarbon (uncorrected) Colorado Canyon tephra set
3280 BCE ± 500 years Unknown Confirmed 5 Tephrochronology Tephra set F-5
3880 BCE ± 75 years Unknown Confirmed 5 Radiocarbon (uncorrected) Tephra set F-4
4350 BCE ± 75 years Unknown Confirmed 5 Radiocarbon (uncorrected) Tephra set F-3
5820 BCE ± 75 years Unknown Confirmed 5 Radiocarbon (uncorrected) Tephra set F-2
7690 BCE ± 75 years Unknown Confirmed 2 Radiocarbon (uncorrected) Tephra set F-1

This compilation of synonyms and subsidiary features may not be comprehensive. Features are organized into four major categories: Cones, Craters, Domes, and Thermal Features. Synonyms of features appear indented below the primary name. In some cases additional feature type, elevation, or location details are provided.



Cones
Feature Name Feature Type Elevation Latitude Longitude
Callo, Cerrito del Cone 3183 m 0° 43' 0" S 78° 35' 0" W


Domes
Feature Name Feature Type Elevation Latitude Longitude
Morucu Dome
Santa Barbara Dome
This massive rounded boulder on the SW side of Cotopaxi volcano was carried in a lahar, or volcanic mudflow, possibly during a major eruption in 1877. Scale is provided by volcanologists Minard Hall and Patty Mothes of Ecuador's national university, who have spent many years assessing hazards from Ecuador's volcanoes. More than 130,000 persons live in areas subject to lahar risk from Cotopaxi. The 1877 eruption produced lahars that covered this valley, swept into the Amazon basin, and reached the Pacific Ocean along valleys to the NW.

Photo by Tom Pierson, 1992 (U.S. Geological Survey).
The foreground of this flat valley north of Cotopaxi volcano is the top of the deposit produced by a massive lahar from the volcano in 1877. During this eruption, one of the largest from Cotopaxi during historical time, pyroclastic flows descended all sides of the volcano, creating devastating lahars. The lahar that produced this deposit eventually traveled north down the Guayllabamba River past Quito to reach the Pacific Ocean at Esmeraldas, 225 km NW of Cotopaxi. Mudflows also swept down valleys south and east into the western Amazon basin.

Photo by John Ewert, 1987 (U.S. Geological Survey).
Symmetrical Cotopaxi is one of the most prominent volcanoes that line both sides of the Interandean valley along Ecuador's "Avenue of Volcanoes." Cotopaxi, one of Ecuador's most active volcanoes, has produced more than 50 eruptions since the 16th century. Glaciers cover the upper part of the cone from 4700 m altitude on the west flank, seen here, to the 5911-m-high summit. Devastating lahars in historical time swept this valley before turning south and then east into the Amazon basin. Lahars to the NW reached the Pacific Ocean.

Photo by Lee Siebert, 1978 (Smithsonian Institution).
The glacier-capped summit of Ecuador's Cotopaxi volcano is truncated by two nested craters. The outer crater, seen here from the SE, is 800 x 550 m wide. A cone that grew inside this crater is cut by a smaller crater that is 250 m wide and 120 m deep. Frequent explosive eruptions during historical time have modified the shape of the summit crater. In 1903, prior to growth of a broad central cone, it was 450 m deep.

Photo by Tom Simkin (Smithsonian Institution).

The following references have all been used during the compilation of data for this volcano, it is not a comprehensive bibliography. 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.

Barberi F, Coltelli M, Frullani A, Rosi M, Almeida E, 1995. Chronology and dispersal characteristics of recently (last 5000 years) erupted tephra of Cotopaxi (Ecuador): implications for long-term eruptive forecasting. J Volc Geotherm Res, 69: 217-239.

Hall M L, 1977. El Volcanismo en El Ecuador. Quito: Biblioteca Ecuador, 120 p.

Hall M L, 1987. Peligros potenciales de las erupciones futuras del volcan Cotopaxi. Rev Politecnica, Quito, 12: 41-80.

Hall M L, 1992. . (pers. comm.).

Hall M, Mothes P, 2008. The rhyolitic-andesitic eruptive history of Cotopaxi volcano, Ecuador. Bull Volc, 70: 675-702.

Hantke G, Parodi I, 1966. Colombia, Ecuador and Peru. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 19: 1-73.

IAVCEI, 1973-80. Post-Miocene Volcanoes of the World. IAVCEI Data Sheets, Rome: Internatl Assoc Volc Chemistry Earth's Interior..

Miller C D, Mullineaux D R, Hall M L, 1978. Reconnaissance map of potential volcanic hazards from Cotopaxi volcano, Ecuador. U S Geol Surv Map, I-1072.

Mothes P A, Hall M L, Janda R J, 1998. The enormous Chillos Valley Lahar: an ash-flow-generated debris flow from Cotopaxi volcano, Ecuador. Bull Volc, 59: 233-244.

Mothes P, Hall M L, Andrade D, Samaniego P, Pierson T C, Ruiz A G, Yepes H, 2004. Character, stratigraphy and magnitude of historical lahars of Cotopaxi volcano (Ecuador). Acta Vulc, 16: 85-108.

Paulo A, Narebski W, Bakun-Czubarow N, Prochazka K, Wichrowoski Z, 1979. Geology, geochemistry and petrogenesis of volcanics of Cotopaxi (Ecuador). Prace Mineralalogiczne, 61: 1-62.

Volcano Types

Stratovolcano
Caldera
Lava dome(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Andesite / Basaltic Andesite
Dacite
Rhyolite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
251
7,299
152,139
3,631,492

Affiliated Databases

Large Eruptions of Cotopaxi Information about large Quaternary eruptions (VEI >= 4) is cataloged in the Large Magnitude Explosive Volcanic Eruptions (LaMEVE) database of the Volcano Global Risk Identification and Analysis Project (VOGRIPA).
WOVOdat WOVOdat is a database of volcanic unrest; instrumentally and visually recorded changes in seismicity, ground deformation, gas emission, and other parameters from their normal baselines. It is sponsored by the World Organization of Volcano Observatories (WOVO) and presently hosted at the Earth Observatory of Singapore.
EarthChem EarthChem develops and maintains databases, software, and services that support the preservation, discovery, access and analysis of geochemical data, and facilitate their integration with the broad array of other available earth science parameters. EarthChem is operated by a joint team of disciplinary scientists, data scientists, data managers and information technology developers who are part of the NSF-funded data facility Integrated Earth Data Applications (IEDA). IEDA is a collaborative effort of EarthChem and the Marine Geoscience Data System (MGDS).
Smithsonian Collections Search the Smithsonian's NMNH Department of Mineral Sciences collections database. Go to the "Search Rocks and Ores" tab and use the Volcano Name drop-down to find samples.