Copahue

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  • Country
  • Volcanic Region
  • Primary Volcano Type
  • Last Known Eruption
  • 37.856°S
  • 71.183°W

  • 2953 m
    9686 ft

  • 357090
  • Latitude
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9 July-15 July 2014

SERNAGEOMIN reported that a phreatic explosion from Copahue occurred at 2023 on 4 July that deposited bombs (less than 12 cm in diameter), lapilli (less than 4 cm), ash, and gray clay smelling strongly of sulfuric acid along the E flank of the crater. During an overflight on 7 July, OVDAS officials observed the deposit and measured a moderate amount of gas emissions (an average of 4,000 tons per day of SO2), a relatively low level of water in the crater, and low temperatures of the fumaroles within El Agrio crater. DOAS stations had measured up to 18,000 tons/day of SO2 on the day of the explosion. An anomalous tremor signal was detected at 0823 on 5 July that was associated with an explosion from El Agrio crater; a microphone installation 13 km E also detected an acoustic signal. The explosion generated a plume 1,000 m above the crater. The Alert Level remained at Yellow.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)

Index of Weekly Reports


2014: March | April | July
2013: January | March | May | June | November
2012: December

Weekly Reports


9 July-15 July 2014

SERNAGEOMIN reported that a phreatic explosion from Copahue occurred at 2023 on 4 July that deposited bombs (less than 12 cm in diameter), lapilli (less than 4 cm), ash, and gray clay smelling strongly of sulfuric acid along the E flank of the crater. During an overflight on 7 July, OVDAS officials observed the deposit and measured a moderate amount of gas emissions (an average of 4,000 tons per day of SO2), a relatively low level of water in the crater, and low temperatures of the fumaroles within El Agrio crater. DOAS stations had measured up to 18,000 tons/day of SO2 on the day of the explosion. An anomalous tremor signal was detected at 0823 on 5 July that was associated with an explosion from El Agrio crater; a microphone installation 13 km E also detected an acoustic signal. The explosion generated a plume 1,000 m above the crater. The Alert Level remained at Yellow.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


2 April-8 April 2014

On 4 April OVDAS-SERNAGEOMIN reported that activity at Copahue continued to fluctuate at an elevated level however did not indicate an impending eruption. The Alert Level was lowered to Yellow.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


26 March-1 April 2014

OVDAS-SERNAGEOMIN reported that cameras installed around Copahue recorded white gas plumes rising 100-600 m above the crater during 25-29 March; clouds prevented observations on 30 March. Sulfur dioxide measurements in tons per day were 270 on 26 March, 1,400 on 27 March, 2,000 on 28 March, 1,400 on 29 March, and 920 on 30 March. The Alert Level remained at Orange.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


19 March-25 March 2014

OVDAS-SERNAGEOMIN reported that a gradual increase of volcanic tremor was detected at Copahue starting at 0230 on 20 March; from 0230 to 1100 the signal fluctuated and intense periods lasted up to 3 hours. Cameras showed minimal activity at the surface while concentrations of sulfur dioxide increased. The Alert Level was raised to Orange. Residents and visitors were prohibited within a 3-km radius of the active crater. During 21-24 March gas plumes rose at most 500 m and drifted E. Seismicity continued to increase.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


20 November-26 November 2013

Based on satellite images, the Buenos Aires VAAC reported that on 21 November a 5-km-wide steam plume possibly containing ash extended over 35 km SE of Copahue. A few hours later the webcam recorded a possible ash plume drifting SE at low altitudes.

Source: Buenos Aires Volcanic Ash Advisory Center (VAAC)


13 November-19 November 2013

Based on ODVAS webcam views and satellite images, the Buenos Aires VAAC reported that on 15 November a low-level diffuse plume from Copahue drifted almost 40 km NW. Later that night a thermal anomaly was detected by satellite and light from a full moon allowed webcam views of a possible ash emission. The next day steam-and-gas emissions were observed with the webcam. The Alert Level remained at Yellow.

Source: Buenos Aires Volcanic Ash Advisory Center (VAAC)


6 November-12 November 2013

OVDAS-SERNAGEOMIN reported that during 16-31 October the webcam installed 18 km SW of Copahue recorded steady fumarolic activity from Del Agrio Crater, which produced plumes that rose 1.8 km above the crater rim. On 28 October the plume changed color, suggesting ash content, and was accompanied by a small explosion recorded at 1252. The Alert Level remained at Yellow.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


19 June-25 June 2013

Based on web camera views, the Buenos Aires VAAC reported that on 26 June steam-and-gas emissions from Copahue possibly contained ash. Ash was not detected in clear satellite images.

Source: Buenos Aires Volcanic Ash Advisory Center (VAAC)


12 June-18 June 2013

OVDAS-SERNAGEOMIN reported that during 11-12 June seismicity at Copahue had significantly decreased with respect to the previous 24-hour period; the majority of the signals were low-magnitude hybrid events, detected at an average rate of one per hour. White plumes recorded by a web camera rose at most 100 m and drifted E. Seismicity remained low during 12-13 June; an average of one event per hour continued to be detected. Meteorological cloud cover prevented views of the crater. The Alert Level remained at Orange.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


5 June-11 June 2013

OVDAS-SERNAGEOMIN reported that during 4-11 June white plumes recorded by a web camera rose at most 200 m above Copahue and drifted N and E. During 4-5 June seismicity had decreased with respect to the previous 24-hour period; the majority of the signals were low-magnitude hybrid events, detected at an average rate of 42 per hour. During 5-6 June seismicity was similar to the previous period, with an average of 50 events per hour being detected. Seismicity increased during 6-7 June; an average of 84 events per hour was detected. During 7-8 June seismicity fluctuated with a high average of 124 events per hour then decreased to a low average of 8 events per hour; the overall average was 62 events per hour. Seismicity decreased during 8-9 June; only 5 events per hour were detected. On 9 June OVDAS-SERNAGEOMIN scientists aboard an overflight to locate sites for the installation of three additional seismic stations observed fumaroles inside Del Agrio Crater, and gas emissions that rose at most 200 m and drifted NE. They noted that no lava dome was present. During 9-10 June the number of earthquakes increased to an average of 20 events per hour. The Alert Level remained at Orange.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


29 May-4 June 2013

OVDAS-SERNAGEOMIN reported that during 28-29 May seismicity at Copahue had decreased with respect to the previous 24-hour period; the majority of the signals were low-magnitude hybrid events, detected at an average rate of 127 per hour. Meteorological cloud cover prevented visual observations. During 29-30 May seismicity again decreased; earthquakes were detected at a rate of 40 events per hour. A camera near the volcano recorded a white plume that rose 100-200 m and drifted SE. The seismic network continued to record a downward trend during 30-31 May, with 120 events per hour detected during the night. By the time of the release of the report at 1700 on 31 May about 20 events per hour were being detected. Visual observations were again inhibited due to weather conditions. About 42 events per hour were recorded during 31 May-1 June, about 52 events per hour were detected during 1-2 June, and about 102 events per hour were detected during 2-3 June. A small plume rose 80 m above the crater during 2-3 June. ONEMI reported on 3 June that about 280 people, of 2,440 people, remained within the 25-km evacuation zone. That same day SERNAGEOMIN lowered the Alert Level to Orange.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN); Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI)


22 May-28 May 2013

OVDAS-SERNAGEOMIN reported that a gradual increase of seismicity at Copahue had been detected since 15 May. A camera recorded periodic small explosions and corresponding ash emissions, along with nighttime incandescence. On 19 May satellite images detected increased sulfur dioxide emissions, which produced a plume that rose 300 m above the crater and drifted SE. Images from 20 and 22 May showed large plumes drifting 100 km SE that appeared translucent gray, suggesting a significant presence of volcanic gases. On 23 May the Alert Level was raised to Orange.

On 24 May cameras recorded white plumes that mostly rose 250-400 m; at 1900 a plume rose 1.9 km, and another drifted NE. Seismicity increased sharply during 24-25 May. The seismic network detected 8,556 low-magnitude earthquakes with an average of 356 events per hour, and a gap of a few seconds between events. Seismicity increased again during 25-26 May, with an average of 455 events per hour, and then decreased to 269 events per hour during 26-27 May. An explosion on 26 May generated crater incandescence and a plume that rose 400 m. Weather conditions often prevented views during 25-27 May.

On 27 May OVDAS-SERNAGEOMIN noted that the intensity and type of seismicity observed in recent days, in conjunction with the deformation data, suggested the rise of a magmatic body to shallow depths. The Alert Level was raised to Red. According to ONEMI, the government ordered a precautionary evacuation of the 2,440 people living within a radius of 25 km. During 27-28 May seismic signals were detected at an average rate of 130 events per hour. Cloud cover prevented visual observations. ONEMI noted that 44 people had evacuated by 28 May.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN); Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI)


8 May-14 May 2013

OVDAS-SERNAGEOMIN reported that an explosion from Copahue at 1015 on 7 May recorded by a webcam produced a gas, steam, and ash plume that rose 350 m and drifted SE. Incandescence from the crater was visible at night. The Alert Level was raised to Yellow.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


27 March-2 April 2013

Based on analysis of satellite imagery and a pilot observation, the Buenos Aires VAAC reported that on 28 March steam-and-gas emissions with small amounts of ash rose from Copahue.

Source: Buenos Aires Volcanic Ash Advisory Center (VAAC)


30 January-5 February 2013

OVDAS-SERNAGEOMIN reported that during 29 January-4 February the web camera near Copahue recorded white gas plumes rising 350-1,550 m above the crater and drifting E and SE. Seismicity fluctuated but mostly remained at low levels. The Alert Level was lowered to Yellow on 4 February.

The Buenos Aires VAAC noted that although a pilot reported an ash plume between the altitudes of 3-4.6 km (10,000-15,000 ft) a.s.l., no ash was detected in mostly clear satellite images. The VAAC also noted that steam with possible diffuse ash was recorded by the OVDAS webcam.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN); Buenos Aires Volcanic Ash Advisory Center (VAAC)


23 January-29 January 2013

OVDAS-SERNAGEOMIN reported that during 22-28 January the web camera near Copahue recorded white gas plumes rising 100-800 m above the crater and drifting E and SE. Seismicity remained at low levels. An explosion at 2355 on 22 January produced a gas plume (with no ash) that rose 1.45 km above the crater. The Alert Level remained at Orange.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


16 January-22 January 2013

OVDAS-SERNAGEOMIN reported that the web camera near Copahue recorded white gas plumes rising 250-1,300 m above the crater during 15-18 January and drifting W and NW. Seismicity remained at low levels. The Alert Level was lowered from Orange to Yellow on 18 January.

A seismic swarm of long-period earthquakes started at 1420 on 22 January. The earthquakes were initially deep but became shallower, and volcano-tectonic events were more frequently detected, until the next report posted at 2200. Web camera and satellite images did not show any changes. The Alert Level was raised to Orange.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


9 January-15 January 2013

OVDAS-SERNAGEOMIN reported that the web camera near Copahue recorded white gas plumes rising 0.9-1.5 km above the crater during 9-15 January and drifting NNE, E, ESE, and SSE. Incandescence from the crater was observed on some nights. Satellite images showed plumes drifting 10 km E and SSE during 10-12 January. The Alert Level remained at Orange.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


2 January-8 January 2013

OVDAS-SERNAGEOMIN reported that seismicity at Copahue during 31 December, and 2 and 4-5 January indicated magma movement focused at 4 km below the crater and moving to shallower depths. On 5 January seismicity increased as well as gray emissions observed with a web camera. The Alert Level was raised to Orange. Incandescence on the crater was noted during 5-6 January, and plumes rose 200 m above the crater and drifted E during 5-7 January.

Based on analysis of satellite imagery, the Buenos Aires VAAC reported that on 2 January a diffuse gas-and-ash plume drifted 93 km NE and E. During 2-3 January web cameras near the volcano recorded steam-and-gas plumes drifting E and dissipating near the summit.

Sources: Servicio Nacional de Geología y Minería (SERNAGEOMIN); Buenos Aires Volcanic Ash Advisory Center (VAAC)


26 December-1 January 2013

OVDAS-SERNAGEOMIN reported that during 25-29 December white plumes observed with a web camera installed near Copahue rose 450-850 m and drifted NE and E. Plumes detected in satellite imagery drifting 16 km NE on 26 December. Incandescence from the crater was observed at night during 26-28 December; explosions were detected during 27-28 December. Seismicity had decreased during the reporting period. The Alert Level was lowered to Yellow on 29 December.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


19 December-25 December 2012

OVDAS-SERNAGEOMIN reported increased seismicity at Copahue on 22 December. Seismicity fluctuated but was high and indicated that emissions from what was thought to be a phreatic eruption varied between white gas and dark ash plumes. The plumes rose 1-1.5 km above the crater and were observed in satellite imagery drifting 400 km SE. The Alert Level was raised to Orange.

Scientists aboard an overflight observed a low plume rising 1.5 km above a vent in Del Agrio Crater, in the same area as the previous eruption in 2000, and drifting SE. The scientists noted that at 1600 the emissions changed from ash to gas. Later that day web cameras showed incandescence from the crater reflecting in the clouds. The Alert Level was raised to Red, and people within a 15-km-radius and along drainages were warned about potential increases in activity or lahars.

On 23 December incandescence from the crater increased with explosions, as high as 450 m. Strombolian activity ejected incandescent blocks, and mostly white plumes turned dark during explosions. The plumes rose 1 km and drifted SE. On 24 December seismicity decreased. The camera recorded crater incandescence which increased to heights of 200 m with explosions. Incandescent blocks were again ejected with Strombolian explosions. Plumes rose 300 m and drifted SE; they were mostly white, but turned dark with ash during explosions. The Alert Level was lowered to Orange. On 25 December seismicity decreased to low values and tremor was not detected. Cloud cover obscured web camera views. Diffuse plumes visible in satellite images drifted 70 km SE.

Source: Servicio Nacional de Geología y Minería (SERNAGEOMIN)


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.

07/1992 (BGVN 17:07) Small explosions and mudflows; strong sulfur odors

10/1992 (BGVN 17:10) Small explosions; earthquakes and tremor; pyroclastic sulfur ejected

03/1997 (BGVN 22:03) Crater lake lies several meters below drainage notch

06/2000 (BGVN 25:06) Frequent ash explosions and acidic mudflows starting on 1 July

09/2000 (BGVN 25:09) Continued ash explosions and tremor during August-October

10/2012 (BGVN 37:10) Crater lake geochemical study suggests recent magma intrusion

09/2013 (BGVN 38:09) Small ash eruptions during 2012-2013


Contents of Monthly Reports

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

All times are either Chile (UTC - 4 hours) or Argentina (UTC - 3 hours) local time, as noted

07/1992 (BGVN 17:07) Small explosions and mudflows; strong sulfur odors

A series of explosions started [at Copahue (figure 1)] on 31 July at about 0900 and continued until 1133 [all times are Chile local time]. Photographs taken 10 km NE of the volcano (at Los Copahues thermal springs, Argentina) show small, cauliflower-shaped columns emerging from the E (Del Agrio) crater. Ash clouds were rapidly dispersed by SW winds, and a strong sulfur smell was noted in the area. Renewed explosions began at around 1800 and continued until about 0300 the next morning, also producing ash columns and a sulfur smell. Earthquakes had begun to be felt in the area on 30 July.

Figure 1. Schematic view of the Copahue complex, showing the position of the historically active summit crater with respect to the Del Agrio and Trapa-Trapa calderas. Adapted from a map by O. González-Ferrán.

Hugo Moreno overflew the summit on 1 August at 1700. Solfataric activity was intense in the E crater, and snow had melted on the inner crater walls and rim. Pyroclastic-fall deposits covered ~ 1.5 km2 of the upper NE flank, and light ashfall extended 4-5 km NE. The bottom of the active crater had previously been filled by a green, highly sulfuric, acid lake (pH about 1.5), which appeared to be covered by a grayish, cracked ash blanket. Small debris-flow deposits could be seen for 3-4 km along Del Agrio stream, which drains the crater lake through a small notch in the E rim.

An explosion occurred on 2 August at 0330, and fine lapilli-fall (2-16 mm diameter) was reported 30 minutes later at Caviahue village, 15 km SE of the volcano, where hotels were filled with tourists. Small phreatic explosions occurred at 15-minute intervals during the morning. Field observations by Daniel Delpino revealed that lapilli-sized pumice to 7 mm in diameter had fallen on the volcano's snow-covered flanks. About 90% of the ejecta were accessory fragments, including rounded sulfur-rich vesicular particles. Only ~ 10% were believed to be juvenile. Four small debris flows were identified, one toward the E (Del Agrio stream), the other three toward the S (into Chile). These coalesced into one flow that turned SW along the Lomín river, which flows into one of Chile's major rivers, the Bíobío. The debris-flow deposits were a mixture of snow, ice, and pyroclastic material up to 1 m deep. Earthquakes were felt for the first time at Caviahue on 2 August between 2230 and 2245, when three had intensities of about MM II-III. An intense sulfur smell was noted throughout the area within the Del Agrio caldera that contains Caviahue and several lakes.

Some of the 300 tourists at a hotel in Caviahue suffered from headaches, and they were advised to leave the area. A 20-km restricted zone around the volcano was recommended by Hugo Moreno. Additional visitors were prevented from entering the Caviahue area. There are few towns near the volcano in Chile. Guallalí is 20 km SW and Trapatrapa is 17 km NW, but many houses and small settlements are distributed along the Lomín/Bíobío and Queco rivers. The Chilean electricity enterprise (ENDESA) was warned of potential hazards because the Pangue and Ralco hydroelectric projects have camps along the Bíobío river, 45 and 35 km from the volcano, respectively.

Univ de la Frontera seismologists installed two MEQ-800 seismic stations at the E foot of the volcano on 5 August, one 9 km from the active crater (near Caviahue), the other 18 km away (in Cajón Chico). During the first 8 hours, 150 harmonic tremor events were recorded (figure 2), with frequencies of 0.9-1.3 Hz. The next day, 815 events were recorded, including a 2.5-minute long-period earthquake at 1858 associated with a phreatomagmatic explosion that generated a mushroom-shaped column 700 m high. Strong winds rapidly carried the column NE, leaving a dark-gray deposit on the recent NE-flank snowfall. No eruptive activity had been reported since the 2 August explosion, but bad weather had obscured the volcano until 30 minutes before the 6 August ash ejection.

Figure 2. Number of tremor episodes per hour recorded by a seismic station (Caviahue), 9 km from the active crater at Copahue, 5-9 August 1992. Courtesy of the SAVO seismological team.

Daniel Delpino, Luís Mas, and Hugo Moreno overflew the volcano by helicopter during the late morning of 7 August. An elliptical airfall deposit 11 km long and 2 km wide covered the NE flank. Several secondary, gravitationally generated, flows had occurred on steep unstable talus slopes near the crater. Ballistic blocks had produced numerous impact craters to ~ 1 m in diameter in this area. Moderate fumarolic activity was occurring in the crater. S of the v-shaped notch in the crater rim, very narrow red-brownish mudflows, probably overflows of muddy crater-lake water, extended no more than 150 m. The geologists landed ~ 2.5 km NE of the crater near the tephra-dispersion axis. The dominant airfall material was accretionary lapilli 0.3-1 cm in diameter, composed of very fine sulfur-rich dust spherulites. Most of the remainder of the deposit was also accessory material, including angular volcanic lithic fragments up to 3 cm across. Small globular to ribbon-shaped vesicular glassy fragments were also found, and were interpreted as juvenile hydroclastites. A new, less-voluminous debris-flow deposit had been emplaced along the Del Agrio stream, on top of the earlier deposit. Pale-brown muddy material extended about 200 m beyond the previous flow front, ~ 4.2 km from the crater. Another overflight late on 8 August showed small fumaroles in Del Agrio crater, but no other visible activity within the 2-km-long, ENE-WSW row of summit craters, or elsewhere outside of the Termas de Copahue area.

Seismicity declined after the 6 August explosion, remaining at low levels until tremor began to increase on 9 August at 0230. Between 0330 and 1230, 176 episodes of harmonic tremor were recorded, and 5 high-frequency events were detected during the same period. A 2.9-minute long-period earthquake occurred at 1057, probably marking a phreatic or phreatomagmatic explosion. However, the volcano was obscured by weather clouds, and the explosion could not be confirmed.

O. González-Ferrán visited the volcano on 12-13 August, with the support of the Chilean Air Force. The source of the explosions was a new vent, 100 m in diameter at the rim and 30 m across at the base, on the outer SW flank of the active crater (figure 3). Ash deposits evident during his fieldwork extended ENE and SE, to maximum distances of 4 and 6 km, respectively. Partial melting of the glacier, 5-40 m thick, that covers the older inactive summit craters and the SSW flank, had generated at least three jökulhlaups and a small lahar that extended ~ 6 km down the S flank toward the Lomín/Bíobío river system. An ~ 60-m-long fracture (f on figure 3) below the outflow of the crater lake was the source of another small mudflow that descended the Del Agrio river toward Del Agrio lake. The crater lake, ~ 300 m in diameter with 5-6 x 105 m3 of acid water, continues to drain to the E at 2,716 m altitude. Lake level had dropped 8-10 m since the previous visit by González-Ferrán in 1990. Solfataras were active on the crater's S interior wall, and fresh landslides were visible on the SE interior wall. The glacier's headwall, 30-50 m high, is 80 m above the lake, and is the lake's main source of water.

Figure 3. Sketch of the summit area (top) and locations of 1992 eruption deposits (bottom) at Copahue, 13 August 1992. The 60-m fracture that spawned a small mudflow in the Del Agrio river is marked with an "f". The approximate area shown by the summit-area sketch is enclosed by a box on the bottom drawing. Courtesy of O. González-Ferrán.

Small earthquakes at 3.7 and 6.3 km depth were recorded at 0222 and 0226 on 14 August. A light-gray gas cloud extending 10 km SE from Del Agrio crater was seen at 0700. Daniel Delpino, Alberto Andolino, and Mario Deza reported strong effervescence and waves on the crater lake, which also showed strong fumarolic activity, at 1500. An explosion signal lasting 10 seconds was recorded at 1731. Four minutes later, a dense, light-gray gas cloud with dimensions of about 2 x 0.6 x 0.5 km descended ~ 4 km ESE, remaining there until about 0615 the next morning. A series of explosions and a strong increase in tremor, to 30-40 episodes/hour, began at 2100 on 14 August. During the night, the entire volcano was covered by a gaseous fog. Tremor activity was lower on 15 August, with about 20-25 episodes per hour between 0700 and 1700. Earthquakes were recorded at Caviahue at 0538, 0558, and 0645.

Information Contacts: D. Delpino, A. Bermudez, and M. Pérez, Dirección Provincial de Minería, Zapala, Argentina; H. Moreno, SERNAGEOMIN-SAVO, Temuco, Chile; G. Fuentealba and J. Cayupi, SAVO-Univ de la Frontera, Temuco, Chile; Oscar González-Ferrán, Univ de Chile.

10/1992 (BGVN 17:10) Small explosions; earthquakes and tremor; pyroclastic sulfur ejected

Explosive activity at Copahue began on 31 July. Tephra from repeated moderate explosions was generally carried eastward, and mudflows extended several kilometers down streams draining the glaciated summit area. Airfall from the largest explosion, on 2 August, covered ~ 88 km2 and debris flows were generated within the valleys of the Agrio (Argentina) and Lomin (Chile) rivers. Tephra from the 6 August explosion covered ~ 23 km2, from the 31 July explosion ~ 1 km2 (figure 4). [All times are Chile local time.]

Figure 4. Preliminary geologic map of Copahue, showing outlines of Pliocene and Pleistocene calderas, post-caldera lava flows, faults, and fumaroles (not including the one in Del Agrio crater). Distribution of airfall tephra from the 3 main 1992 explosions is also shown. Contour interval, 100 m. Courtesy of A. Bermúdez and D. Delpino.

Eruptive activity and seismicity, 15 August-20 October. Fumarolic activity was continuous through mid-October, occasionally accompanied by rhythmic explosions. Roaring noise typically preceded the rise of a vapor cloud by some minutes. Fumarolic activity and explosions originated from the same area in the S part of the crater lake. The entire lake was obscured by an intense vapor cloud on some days. The level of water in the lake remains unchanged. Successive explosions have melted the ice on the crater walls, leaving them completely ice-free (unusual at this time of year), and covered the walls with ejecta. Experienced mountaineers often climbed to the crater, reporting an intense sulfur smell and rapid development of eye irritation (perhaps from hydrochloric acid vapor).

The following is from the Grupo de Estudios Vulcanológicos, Proyecto Riesgo Volcánico de Neuquen.

Emission of the light-gray gas cloud reported 15 August was accompanied by increasing harmonic tremor activity (~ 40 episodes/hour) and three high-frequency shocks. Between 18 and 21 August, 80 long-period events were recorded, some of which coincided with phreatic and phreatomagmatic explosions. Material from some of the explosions remained inside Del Agrio crater, but on 19 August, mushroom-shaped columns ~20 and 50 m high were seen. At 1700, a phreatomagmatic explosion from Del Agrio crater fed a gray column ~100 m high. The column rapidly drifted SE, covering the flank with a dark-gray airfall deposit. A heavy snowstorm obscured the volcano 20-23 August, but when weather cleared on the 23rd, dark gray material was visible on the flank. Tremor episodes became increasingly frequent (~ 80/hour) 24-26 August, and nine new long-period events coincided with explosions that ejected dark-gray material. Event durations ranged to 2 minutes 10 seconds. Tremor was harmonic with some high-frequency activity, particularly on 25 August, when high-frequency tremor alternated with harmonic episodes at rates of ~100/hour. Fumarolic activity from Del Agrio crater was accompanied by a light-gray gas cloud on 24 August. Three high-frequency shocks and two long-period events were recorded on 27 August, as intense fumarolic activity formed a dense cloud that covered the crater and appeared to flow toward the E.

A strong increase in tremor episodes (to around 200/hour) characterized the period 28 August-3 September. Ten small high-frequency shocks were recorded 28-30 August. The largest, on 29 August at 1117, had an amplitude of 34 mm and a duration of 35 seconds. It was felt in Caviahue (15 km SE of the volcano) and was accompanied by an explosion sound. Intense fumarolic activity occurred inside the crater 1-2 September. Dense, white, mushroom-shaped clouds sometimes formed within the crater, and others rose 50 m above the summit. Some were light-gray, suggesting the presence of gases other than water vapor. On 3 September, two high-frequency shocks were detected, with a maximum amplitude of 21 mm. Intense tremor activity continued 4-9 September, including some high-frequency episodes.

Tremor decreased somewhat and became banded 10-17 September, with bands of less-frequent episodes (40-50/hour) of low amplitude alternating with those of more-frequent (100-150/hour) stronger tremor. Four small high-frequency shocks were recorded on 16 September (maximum amplitude, 17 mm) but no long-period events were detected. Tremor decreased in amplitude and duration 17-24 September, but was present on all seismograms. Some tremor was banded, and other episodes alternated with quiet periods. Three high-frequency events were recorded on 23 Spetember, one of which (at 0247) was felt at MM II in Caviahue. Four long-period events were registered during the period, but cloud cover and persistent snowfall prevented visual observations. The number of tremor episodes diminished drastically 25 September-11 October. Two patterns were evident, one with isolated periods of tremor on otherwise quiet records, the other (less common) in which weak harmonic tremor covered the seismogram, followed by quiet intervals of 2-5 minutes, then high-frequency tremor. A long-period event lasting 3 minutes on 1 October accompanied an explosion that ejected material. Tremor increased slightly 12-20 October, and five small high-frequency shocks were recorded.

Preliminary information from the Copahue geothermal field, 4 km NNE of Del Agrio crater, indicates no substantial changes. Snow continues to prevent road access to the geothermal field.

Petrology. Samples obtained from debris flows are composed of: lithics; rounded fragments of argillaceous white material; black, shiny fragments of uncertain composition; and small, globular to ribbon-shaped greenish particles. Proportions and size distributions of each component are still being determined. X-ray diffraction shows that the greenish particles are composed entirely of sulfur. Morphology and grain size resemble scoriae, with vesiculated surfaces and interiors. Some show elongation and separation into branches with ball-like terminations. Others are tiny spheres, sometimes deformed and flattened, or Pele's tears. Geologists proposed an eruptive mechanism producing pyroclastic sulfur scoriae similar to those at Poás (Bennett and Raccichini (1978) and Francis and others (1980).

Monitoring. An MEQ-800 seismograph owned by INPRES (Argentina's National Institute of Seismic Warning) and operated by residents of Caviahue municipality is positioned 7.5 km ESE of the active E (Del Agrio) crater. Seismic data and visual observations are telephoned daily to volcanologists Adriana Bermúdez and Daniel Delpino. After 1 September, Delpino left his monitoring post in Caviahue, but he and Bermúdez visit the volcano when activity warrants. Seismograms are sent once a week for reading by the volcanologists, and monthly to INPRES for final interpretation. The provincial government has established the Technical Group for Volcanological Studies to work on the Volcanic Risk Project of Neuquen Province, covering all active volcanoes in the province. A program of volcanological monitoring, detailed mapping, and preparation of a risk map for Copahue has the support of the provincial government. The limited seismic and volcanological monitoring have not revealed a consistent pattern of eruptive behavior at Copahue. For example, no relationship is apparent between increases in fumarolic and tremor activity, or between explosions and high-frequency shocks.

References. Bennett, F.D., and Raccichini, S.M., 1978, Subaqueous sulphur lake in Volcán Poás: Nature, v. 271, p. 342-344.

Francis, P., Thorpe, R., and Brown, G., 1980, Pyroclastic sulphur eruption at Poás volcano, Costa Rica: Nature, v. 283, p. 754-756.

Information Contacts: D. Delpino and A. Bermúdez, Dirección Provincial de Minería, Neuquen, Argentina.

03/1997 (BGVN 22:03) Crater lake lies several meters below drainage notch

A late-March overflight made after a prolonged dry season enabled scientists to see Copahue with relatively low snow levels. The lake level was some meters below the prominent notch through which drainage occurs on the ESE side of the crater.

Light-gray mud deposits from recent overflow events extended halfway down the E flank. Deposits were also observed to the S and formed a small laharic fan of highly altered material near the head of the Río Lomín.

A pH of 2 was measured in Río Lomín in 1995; in contrast, during March the pH was neutral in the headwaters draining off the lahar fan. However, farther downstream the Río Lomím captures the Estero Turbío, which drains the S flank of the volcano and ran orange, presumably due to high acidity. After capturing Estero Turbío, Río Lomín reportedly became acidic and remained so all the way to its confluence with the Río Biobío, ~33 km from the volcano.

Information Contacts: Jose Antonio Naranjo, Servicio Nacional de Geología e Minería (SERNAGEOMIN), Av. Santa María 0104, Casilla 10465, Santiago, Chile (Email: sernageo@reuna.cl); Hugo Moreno Roa, Observatorío Volcanogía de los Andes del Sur (OVDAS), Manantial 1710-Carmino del Alba, Temuco, Chile (Email: hmoreno.pillan@lazos.cl); Simon R. Young, British Geological Survey (BGS), Murchison House, West Mains Road, Edinburgh EH9 3LA, United Kingdom (Email: sry@bgs.ac.uk).

06/2000 (BGVN 25:06) Frequent ash explosions and acidic mudflows starting on 1 July

An eruption of Copahue (figure 5) began on 1 July 2000. Ash-and-gas emissions, which have continued into late July, are considered to be Copahue's most vigorous activity in the past century. Reports were received from geologists in Argentina and Chile. Except where otherwise noted, Argentine geologists Adriana Bermúdez (CONICET) and Daniel Delpino (Civil Defense of Neuquén Province) reported information for 1-9 July, and Chilean geologists José Naranjo and Gustavo Fuentealba (both of SERNAGEOMIN) reported information from 10-13 July. The scientists submitted joint reports beginning on 13 July. All time references are to Argentina local time; Chilean time is one hour earlier (GMT - 4 hours).

Figure 5. Preliminary geologic map of Copahue, showing outlines of Pliocene and Pleistocene calderas and post-caldera lava flows. Contour interval, 100 m. Modified from a previous map in BGVN 17:10. Courtesy of A. Bermúdez and D. Delpino.

Initial explosions, 1-2 July. Although visibility was poor in late June, at 0030 and at 0430 on 1 July local Argentine police and gendarmerie (National Guard) reported ash mixed with heavy snowfall, as well as a strong sulfur smell. At around 1145, lapilli and ashfall became heavier, eventually covering the snow and the products of previous eruptions around the summit. At 1200 the gendarmerie reported lapilli falling 7.5 km NE of the volcano, in the village of Copahue, Argentina. The alert status was set at yellow; the village's emergency committee restricted tourist access and helped to evacuate 200 people.

Explosions continued throughout 2 July with increasing intensity. Lapilli, ash, and sporadic bombs (15 cm in diameter) fell 8-9 km E on the town of Caviahue, Argentina, with up to 15 cm of materials from the day's explosions eventually being deposited in some areas (figure 6). Until 2345 there were explosions of varying intensities. Preliminary results of an examination of the deposits revealed that they were composed of a very fine silica, sulfur particles, accidental rock fragments from the conduit, and juvenile materials. In Caviahue, visibility was practically zero due to ash particles in the air, and heavy ashfall cut off power for several hours. By midday, eruption plumes blowing SE reached Loncopué, a small village 50 km from the volcano.

Figure 6. Ashfall from the frequent eruptions that began [1 July] at Copahue and heavy snowfall have affected the reliability of power and potable water resources in the town of Caviahue, a popular ski area 8-9 km E of the volcano. Although the town is no longer under official evacuation, many inhabitants have not returned to battle current conditions. Courtesy of A. Bermúdez and D. Delpino.

Alert status was raised to orange on 2 July when ash was dispersed as far as 100 km away from the crater and the plume covered a total area of 2,000 km2. Maximum ash accumulation of 3-5 cm occurred over an area of 6 km2, including the town of Caviahue and the W sector of Lake Caviahue. Due to the ashfall, the surface of Lake Caviahue changed color from its normal deep blue to gray-green, and a water sample taken had a pH of 2.l.

Tests by Argentine geologists on ash samples deposited in Caviahue revealed a grain-size distribution of 15% coarse ash (> 1 mm), 80% fine ash (0.5-1.0 mm), and 5% fine ash dust (< 0.5 mm). The coarse ash contained a small quantity of juvenile and lapilli-sized (3-6 mm) accidental fragments; the juvenile materials were dark gray vitric scoria. Non-juvenile accessory materials accounted for 7-10% of the coarse ash and consisted primarily of white-gray silica from the bottom of the crater lake. The fine ash-sized particles had similar components and characteristics.

Irregularly shaped dark gray scoriae, 3-8 cm in size, were found as far as 12 km N of the crater; scoriae completely covered the area within a 1.0-1.5 km radius around the crater. The scoriae contained spherical vesicles 3-5 mm in diameter. Cooling cracks marked the scoriae's surfaces and their shapes had been modified during flight.

Ashfall was also reported 60 km SE of the volcano in the town of Loncopué, where the stream closest to the volcano had cloudy brown-gray waters.

Continuing activity through 25 July. Activity decreased after 2345 on 2 July. The only explosion of 3 July, at 1720 in the main crater, deposited tephra on the flanks and generated a dense, dark gray ash plume that blew NW and produced a local ashfall. According to the Buenos Aires Volcanic Ash Advisory Center, the ash plume reached an altitude of 10.6 km and blew NE. On 4 July there were explosions at 1030, 1830, and 2000. In the town of Caviahue, Delpino noted a strong sulfur smell and great booming sounds that caused windows to shake. A dark gray ash plume rose 2 km above the summit. Bermúdez and Delpino reported that at 0020 on 5 July a new cycle of rhythmic explosions began; by 1325 a total of 37 explosions had occurred. The biggest explosion, at 0515, generated a pyroclastic surge down the E and N slopes.

A report was received on 5 July from Ralco-Lepoy, a town 30 km SW of the volcano, indicating that dead fish had washed up along the banks of the Lomín river. The Lomín, as well as the Agrio river, which drain the acidic, active crater, were marked by a deep, dark-colored gully but there was no evidence of lahars. However, it is possible that ashfall covered up the evidence. The dead fish found along the Lomín River on 5 July confirmed that acidic mudflows from the crater had been channeled down this river. Chilean geologists Naranjo and Fuentealba recommended that states bordering the Lomín river (to the SW) and Queuco to Trapa-Trapa (to the N) be alerted that an acidic mudflow was moving down the river. Accordingly, authorities noted that inhabitants should be evacuated outside of an enforced safety radius. It was also recommended that professionals regularly measure the pH of affected Lomín drainages, meteorological reports be kept up to date, and that town officials periodically reevaluate the yellow alert.

Naranjo and Fuentealba also noted that at 2030 on 5 July a patrol of carabineros (Chilean National Guard) approached the volcano on horseback and observed small dark ash emissions moving SE from the volcano.

Observers in Argentina during the night of 5-6 July reported an incandescent pyroclastic emission flowing down the cone and, at one point, a white light emanating from the crater for ~15 seconds. In the same time interval, gendarmerie officers from Copahue village described "an orange-red light coming up from the crater." It is thought that the light was produced when magma rose to the surface but did not spill over the crater walls. They also noted the vertical ejection of large incandescent blocks that fell back into the crater, as well as smaller incandescent fragments that fell onto the volcano's slopes, rolled downhill, and broke up into smaller pieces.

On 6 July, Delpino reported to Naranjo and Fuentealba from Caviahue that the eruption was Strombolian with explosion pulses every 1-2 hours. Winds blew ash S of Caviahue without any ashfall in the town. There was no evidence of lahars or floods. Throughout the morning of 6 July snow continued, and there was zero visibility of the volcano.

Bermúdez and Delpino reported that during 0100-1020 on 7 July, loud explosions and ash emissions occurred at 15-minute intervals. At about 2000, the wind changed, blowing W, and ash began falling over Caviahue. About 1 mm of ashfall was observed from 20 km W of the crater.

The same day, ice blocks 15-20 cm in diameter, as well as ash and lapilli, were carried down the swollen Agrio river from the volcano's permanent ice cap. At 1300, a sample of the river water taken at the bridge near Caviahue had a pH of 2, and at 2000 a sample from the same location had a pH of 1.5. The Dulce stream source lies 4.5 km E of the cone and it flows 5.5 km W of the cone into Lake Caviahue. Ashfall altered the stream's typical pH of 7 to a pH of 2.5. Preliminary investigations by Argentina's Provincial Water Division also indicated an increased iron content.

A loud explosion summit at 0300 on 8 July awakened citizens of Caviahue; a day-long ash emission moved SE through clear skies. On 9 July at 0100 a glowing light was seen over the crater, but cloud cover obscured visual observations throughout the day.

Naranjo and Fuentealba reported that on 10 July, explosions were gray to dark brown and it is thought that the ash fell over a 25 km2 area to the W, in the direction of Chile. Ash reached the summit of neighboring Callaqui volcano, covering it in gray ash. Samples from this ashfall taken 4 km W of the active crater were found to contain juvenile volcanic glass fragments, 0.3-0.5 mm in diameter.

During 1200-1230 on 12 July, a Chilean overflight revealed that explosions inside the active crater (El Agrio) occurred at 1- to 3-minute intervals, ejecting fine material up to 500 m above the crater. This material was dispersed via a plume of fine ash and gases moving NNE for more than 250 km. Observers reported that 1-2 mm of fine ash was deposited in the village of Copahue. Throughout the day, activity increased and, at 2300, there was an explosion heard in Caviahue that was thought to have deposited 1-2 cm of ash 5 km NNE of Copahue. On 12 July, scientists noted that Copahue was in an eruptive phase of lower intensity (a Volcano Explosivity Index, VEI, of 1) compared to that seen on 1-2 July (an inferred VEI of 2).

At 1100 on 13 July, explosions generated white-gray to bluish gas emissions rising 200-300 m over the crater. A gas cloud with a strong sulfur odor remained trapped in the Agrio valley over a 10 km2 area; it later descended, and strong winds spread it over a 20 km2 area. At 2310, an explosion produced a 1-km-high plume and incandescent fragments were ejected onto the flanks of the cone reaching up to 1 km from the crater. The plume covered Caviahue, obscuring the moon, but there was no ashfall on the town.

A Chilean helicopter flight on the morning of 13 July observed explosions emitting pale gray ash columns up to 300 m above the crater rim. Winds dispersed the ash ENE to Caviahue. Carabineros sampling water at the source of the Lomín river found it slightly acidic (pH = 5-6).

At 1250 on 13 July, an eruption plume that rose 3-5 km over the crater was reported by military and civilian pilots. The column dispersed to the NE and was a reddish-brown color. Reports from Caviahue stated that on 15 July the eruption stayed at the same intensity as previous days, and fine ash was dispersed to the N. Ash samples from 13 July were found to have an andesitic composition and to include juvenile fragments, the presence of which indicates the volcano's potential to produce even larger explosions. Water samples from the Lomín river on the same date revealed high fluorine and sulfate levels.

At 1700-1730 on 16 July, and also between 0300 and 0400 on 17 July, a dusting of ash fell over Caviahue and there was a strong sulfur smell in the air. At 0905 on 18 July, a civilian pilot reported a pale gray ash column at 3.5-4 km above sea level (just over the top of the cordillera) dispersed over 10 km to the volcano's NNW. At this time, the ongoing eruptions were considered to be of VEI 1. Ash from the weak explosions was dispersed by low winds as it escaped from the crater.

At 2206 on 19 July, members of the gendarmerie reported that a series of explosions continued to generate columns of ash and water vapor 0.5-1.0 km above the crater. The plumes dispersed to the NE depositing a fine dusting of ash over the village of Copahue. A strong sulfurous odor was reported at 2100 in Caviahue. On 20 July activity remained low, and no noises or odors were detected. Winds carried the gas-and-ash plume NNE, depositing a light ashfall over the N sector of Caviahue.

On 21 July, light ashfall dusted Caviahue and, although the crater was obscured, ash columns were sighted rising above the summit and through the clouds to heights of 700-1,000 m. At 1048 (Argentina), Caviahue residents heard a series of rhythmic explosions occurring every 2-5 minutes for one hour. The plume carried ash NNE toward Trapa-Trapa. The volcano was obscured by cloud cover on 22 July but intermittent explosions continued emitting ash plumes carried NE toward Trapa-Trapa.

A seismological team from the Southern Andes Volcanological Observatory (OVDAS) installed a portable seismic station on 21 July at a spot ~2 km NNW of the active crater in the vicinity of Trapa-Trapa, Chile. After taking 15 hours of readings, the team left on 23 July after cold temperatures had prematurely reduced battery power. These readings were fortunately during a time of elevated activity, and registered seismic events generally correlated with visual observations. Despite this similarity, it was impossible to establish an exact correlation between the periodicity of the explosions (occurring every 1-3 minutes) and their microseismic signals at distance.

During the stay of the seismic team, no ashfall was reported in the Queco river region and no correlation was established between seismicity and sporadic thundering sounds reported by villagers in the area. These sounds have been attributed to chunks of the ice cap breaking off and rolling down Copahue's flanks. Due to over 3 m of snowfall, access to the area is difficult.

Explosions of low to intermediate intensity continued emitting ash-and-gas plumes on 23 July. The clouds continued to partially obscure the volcano, but at 1930 an ash column blew E toward Caviahue. On 24 July, the active crater was producing small explosions and dark gray ash emissions; a dusting of ash fell over Caviahue. When the Argentina gendarmerie and the Chilean carabineros compared respective observations no discrepancies were found.

Two pilots reported a strong sulfur odor at 1.8-2.1 km altitude, ~250 km WSW of Copahue on 25 July. At 1000 another pilot reported an ash plume extending 200 km WNW from the summit; plume height was ~2 km and width was 10-15 km. Although this explosion was not seen from Caviahue, a light ashfall fell over the town.

Due to the continued frequent ashfalls over Caviahue, town officials decided to reestablish a yellow alert. The prolonged fall of fluorine-rich ash has posed a possible problem for grazing animals in the affected fields, but heavy snowfall has made it less likely that vegetation will absorb the fluorine.

Background. Volcan Copahue is a composite cone constructed along the Chile-Argentina border. The cone lies within an 8-km-wide caldera formed 0.6 million years ago at a spot near the NW rim of the Pliocene, 20 x 15 km Del Agrio caldera. Copahue's eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains an acidic crater lake (also referred to as Del Agrio) and displays intense fumarolic activity. Infrequent explosive eruptions have been recorded since the 18th century. Eruptions in 1992 and 1995 produced several phreatic and phreatomagmatic explosions and emissions that contained higher levels of water vapor but lower ash particle content than the current eruption. The current eruption has been of longer duration than either of the previous two.

The Agrio river emerges from a crack in the edifice of the volcano 50 m below the active El Agrio crater. The river water is highly acidic and has a yellow color. Near Caviahue, the Agrio river enters the Caviahue lake basin. The lake is formed by 2 glacial finger lakes over a 9.2 km2 area and is a reservoir of acidic water.

Most residents of Copahue village leave each winter, but Caviahue's population of 400 can grow to 10,000 during the ski season. Eruption-related damage has cut off power and potable water, and there remains an inability to keep ski slopes cleared of ash. In late July there were reportedly only about 419 people staying in Caviahue.

Information Contacts: Adriana Bermúdez, National Council of Scientific and Technical Research (CONICET) and the National University of Comahue, Buenos Aires 1400, Neuquén Capital, Argentina; Daniel Delpino, Advisor to the Civil Defense of Neuquén Province, Argentina and the National University of Comahue, Buenos Aires 1400, Neuquén Capital, Argentina (Email: delpinus@neuquen.com.ar); José Naranjo, National Geology and Mining Service (SERNAGEOMIN), P.O. Box 10465, Avda. Santa Maria 0104, Providencia, Santiago, Chile (Email: jnaranjo@sernageomin.cl); Gustavo Fuentealba, Southern Andes Volcanological Observatory (OVDAS), SERNAGEOMIN, P.O. Box 10465, Avda. Santa Maria 0104, Providencia, Santiago, Chile (Email: ovdassis@chilesat.net); Buenos Aires Volcanic Ash Advisory Center, Argentina (URL: http://www.ssd.noaa.gov/ VAAC/OTH/AG/messages.html).

09/2000 (BGVN 25:09) Continued ash explosions and tremor during August-October

The most vigorous eruptive activity at Copahue in the last century began on 1 July 2000 (BGVN 25:06). Lapilli, ash, and sporadic bombs fell within 9 km of the crater, and ash was dispersed as far as 100 km away on the second day of eruptions. Frequent explosions throughout July generated ash columns that often caused ashfall over the villages of Copahue to the N and Caviahue to the E.

Between 0700 and 1200 on 4 August, Ramon Ortíz and technician Erwin Medel (OVDAS) installed a portable seismic station in the Queuco river valley, 16 km N of Copahue. The instrument detected a fracture-type earthquake that probably originated from the volcano, but the depth could not be determined. During 3-5 August, explosions were not noted in the Trapatrapa sector, and acidic rainfall in the Queuco river valley has not occurred since mid-July. According to residents of Caviahue, on 5 August gray spots were observed on the snow, possibly caused by fine ashfall. Apparently, eruptive activity during the previous two weeks included a greater amount of steam as a result of melting snow. A strong sulfur odor was detected in Caviahue on the night of 7 August, but there was no ashfall.

Seismic data and observations from Caviahue indicated increased activity starting on 9 August. Explosions that morning generated columns up to 4,500 m altitude that dispersed W over Chilean territory, into the Trapatrapa valley area, and during afternoon towards the Lomín river valley. The elevated activity continued through at least 1600 on 10 August, with small explosions at intervals of 5-10 or more minutes. On the night of 15 August incandescence in the crater was observed from Caviahue. Up to fist-sized fragments ejected during explosions fell back into the crater. People who approached the crater reported steam explosions composed of white clouds alternating with dark-gray ash emissions. Explosions occurred every 4-5 minutes.

A ski instructor from Caviahue, Daniel Maniero, observed the volcano under clear conditions on the evening of 17 August. Around 2100 that night intermittent incandescence in the crater was followed by thundering noises at intervals of 5 minutes. Clouds reflected crater incandescence on the night of 19 August. Maniero also reported that loud explosions every 8-10 seconds were heard near the crater on 20 August. During 20-21 August intermittent black ash clouds rose not more than 300 m, causing local ashfall around the crater.

Scientists from SERNAGEOMIN-OVDAS, Eliza Calder and Ramon Ortiz, monitored seismicity in the Trapatrapa area, ~16 km NNW of the volcano, from the afternoon of 18 August to 1100 on 19 August. They observed low and weak gray clouds. Between 1839 on 18 August and 0940 on 19 August one long-period earthquake was detected at 0036 on 19 August. According to the Argentina Gendarmerie, during that night there was a strong explosion. Seismic registries showed low-level seismicity without high-frequency earthquakes.

On 19, 21, and 23 August there were strong explosions with dark ash clouds. On the morning of 22 August an observer using binoculars on a commercial flight noted steam clouds extending 5 km N and S of the crater area as well as explosions that rose up to 500 m above the cloud layer located at ~3,000 m altitude. Direct observations carried out at 1000 on 1 September indicated the development of small explosions in the interior of the crater, where an increase in both ash accumulation and the diameter of the explosion crater were observed. The crater measured ~50 m across. Another eruptive cloud was observed from a commercial aircraft (LAN flight 991) on the morning of 2 September; it dispersed toward the N at a height of 700-1,000 m above the crater (3,700-4,000 m altitude).

Data registered by the MEQ-800 seismic station maintained by Instituto Nacional de Prevención Sísmica (INPRES) of San Juan, Argentina during 11 August-4 September, and registries obtained by a digital seismic station at the Volcanólogico Observatory (OVDAS) of SERNAGEOMIN, Chile, in the locality of Caviahue, Argentina, were used to correlate seismic and volcanic activity. Correlations were made between some periods of tremor, or periods of intense tremor separated by quiescent periods, that corresponded with later ash emissions. On 15 August rockfall events were detected. Long-period events were registered on 20 (140 seconds) and 21 August (120 and 104 seconds).

The new OVDAS station consists of an L4C seismometer with an analog-digital card converter, and a portable HP 2000 XL computer. The station was installed in Caviahue, 7 km from the crater, and buried to a depth of 70 cm to protect it from wind effects. The registered microseismic activity in Caviahue was significantly better than data obtained in Trapatrapa, over 15 km NW of the volcano in Chile. Data collection began at 0900 on 26 September. The activity consisted of short-period events associated with volcanic activity. Some events were associated with small crater explosions. A long-period event at 1946 on 23 September was followed approximately 4 hours later by a small ash emission. Although it is not always possible to directly correlate the recorded seismicity with eruptive events, it is evident that there is a close correlation between long-period events and later ash emissions. The appearance of tremor bands is also important and considered precursory to ash emission.

At dawn on 23 September, observers in Caviahue saw intense gaseous emissions in pulses of 30-60 seconds that rose up to 150 m above the crater and dispersed NNE. During that night the crater appeared incandescent. On 24 September the presence of snow was verified in the crater interior, indicating a reduction in temperature. Activity with similar characteristics occurred during the first half of October. Seismographs installed in the area detected microseismic tremors on 17 October. Between 1145 and 1245 of 18 October, constant steam emission occurred along with some denser emanations of brown color and fine ash. The inner crater diameter had not changed noticeably since mid-September, except for a new levee that resulted from wall collapse. On 19 October a thermal anomaly was detected by the GOES satellite, but there were no explosions.

Information Contacts: José Antonio Naranjo, Jefe, Departamento Geología Aplicada, Servicio Nacional de Geología y Minería (URL: http://www.sernageomin.cl/, Email: jnaranjo@sernageomin.cl); Gustavo Fuentealba, Paola Peña, Eliza Calder, and Ramón Ortíz, Servicio Nacional de Geología y Minería, OVDAS (URL: http://www.dgf.uchile.cl/salsa/ovdas/ovdas.html, Email: ovdassis@chilesat.net); Adriana M. Bermúdez, Investigadora Científica, CONICET, Argentina; Daniel H. Delpino, Asesor Dirección Provincial de Defensa Civil de la Provincia del Neuqué (Email: delpinus@neuquen.com.ar).

10/2012 (BGVN 37:10) Crater lake geochemical study suggests recent magma intrusion

The following summary describes Copahue’s crater lake activity during 1992-2000 as presented by Varekamp and others (2001). Copahue erupted sporadically in the 1990’s with a series of explosions, and later in July 2000. The 1992 and 1995 eruptions were phreatic and ejected fragmented, hydrothermally altered rocks, and copious amounts of liquid sulfur. In contrast, the July 2000 eruption (BGVN 25:06, 25:09) was phreato-magmatic and was characterized by explosions that ejected incandescent juvenile material and chilled sulfur fragments; dark ash covered an area up to 50 km from the source.

Data gathered during 1997-2000 by Varekamp and others (2001) suggested that Copahue acts as a “beehive” volcano, meaning that void spaces were generated by near-congruent rock dissolution, and these spaces were subsequently filled by accumulating liquid sulfur and precipitated silica. During the phreatic eruptions of 1992 and 1995, much of that liquid sulfur was ejected; in contrast the phreato-magmatic eruptions of 2000 left the hydrothermal system largely intact. The RFE/Cl ratio (RFE = rock-forming elements = Ca + Na + Mg + K + Al + Fe) measured in the crater lake water increased dramatically in July 2000. This spike was interpreted by Varekamp and others (2001) to be a result of a recent intrusion of fresh magma and therefore more interaction between water and newly solidified rock.

Varekamp and others (2001) concluded that “Integration of [data from the Upper Rio Agrio river] and the modeled volcanic fluxes into the crater lake provide the following parameters for the whole Copahue system in November 1999: an energy flux of ~32 MW, an equivalent sulfur gas input of ~344 t SO2/d, a net rock removal rate of about 12,000 m3/yr, and an elemental sulfur accumulation rate of about 11,600 m3/yr.” The eruption of large amounts of liquid sulfur in 1992 and 1995 strongly supported inferences about gradual elemental sulfur accumulation inside the volcano. Analyses also suggested that the eruptions of Copahue during 2000 were preceded by a dramatic increase of volcanically-derived elements into the crater lake. The authors further concluded that “The evolution of the crater lake fluids during the twentieth century suggest a gradual awakening of Copahue volcano”. Continued monitoring of crater lake temperature and composition would be useful to assess future volcanic activity.

Other studies. Varekamp and others (2004) concluded that Copahue represented “a rare example of the occurrence of hydrothermal fluids on the surface of the earth from a deep source with a strong magmatic signal.” Varekamp (2004) noted that Copahue “has a volcanic spring-fed acid river with deposits of red hematite in the streambed and abundant gypsum mineralization, and these fluids are saturated with K-jarosite. This riverbed may be a modern terrestrial analog of the Opportunity Rover landing site on the planet Mars.” Another paper (Varekamp and others, 2006) described the geochemistry and isotopic characteristics of the Caviahue-Copahue volcanic complex; they discuss the roles of crust and sediments from the subducting slab as contributions to the magma systems.

According to the Chilean National Service of Geology and Mining (SERNAGEOMIN), Copahue had been quiet since its last major eruption in 2000 until recently. A new eruption took place in mid-2012; subsequent reports will discuss this event.

References. Varekamp, J.C., 2004, Copahue Volcano: A Modern Terrestrial Analog for the Opportunity Landing Site?, Eos, v. 85, no. 41, p. 401 and 407.

Varekamp, J.C., Ouimette, A.P., Hermán, S.W., Bermúdez, A., and Delpino, D., 2001, Hydrothermal element fluxes from Copahue, Argentina: A “beehive” volcano in turmoil, Geology, v. 29, no. 11, p. 1059-1062.

Varekamp, J.C., Ouimette, A.P., and Kreulen, R., 2004, The magmato-hydrothermal system of Copahue volcano, Argentina, in Wanty, R.B., and Seal, R.R., (eds), Water Rock Interaction: Proceedings of the Eleventh International Symposium on Water Rock Interaction, WRI-11, 27 June-2 July 2004, Saratoga Springs, NY, v. 1, p. 215-218, Taylor and Francis Group, London.

Varekamp, J.C., deMoor, J.M., Merrill, M.D., Colvin, A.S., Goss, A.R., Vroon, P.Z., and Hilton, D.R., 2006, Geochemistry and isotopic characteristics ofthe Caviahue-Copahue volcanic complex, Province of Neuquen, Argentina, Geological Society of America Special Papers 2006, v. 407, pp. 317-342.

Information Contacts: J.C. Varekamp, Department of Earth & Environmental Sciences, 265 Church St., Wesleyan University, Middletown CT 06459-0139 USA (E-mail: jvarekamp@wesleyan.edu); Servicio Nacional de Geología e Minería (SERNAGEOMIN), Av. Santa María 0104, Casilla 10465, Santiago, Chile (URL: http://www.sernageomin.cl/).

09/2013 (BGVN 38:09) Small ash eruptions during 2012-2013

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Volcán Copahue is an elongated composite cone constructed along the Chile-Argentina border within the 6.5 x 8.5 km wide Trapa-Trapa caldera that formed between 0.6 and 0.4 million years ago near the NW margin of the 20 x 15 km Pliocene Caviahue (Del Agrio) caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains a briny, acidic 300-m-wide crater lake (also referred to as El Agrio or Del Agrio) and displays intense fumarolic activity. Acidic hot springs occur below the eastern outlet of the crater lake, contributing to the acidity of the Río Agrio, and another geothermal zone is located within Caviahue caldera about 7 km NE of the summit. Infrequent mild-to-moderate explosive eruptions have been recorded at Copahue since the 18th century. Twentieth-century eruptions from the crater lake have ejected pyroclastic rocks and chilled liquid sulfur fragments.

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

Start Date Stop Date Eruption Certainty VEI Evidence Activity Area or Unit
2012 Dec 22 2013 Dec 10 Confirmed 2 Historical Observations Del Agrio Crater
2000 Jul 1 2000 Oct 18 Confirmed 2 Historical Observations Del Agrio crater
1995 Sep Unknown Confirmed 2 Historical Observations Del Agrio crater
1994 Dec Unknown Confirmed 2 Historical Observations Del Agrio crater
1992 Jul 22 1993 Confirmed 2 Historical Observations Del Agrio crater
1961 Unknown Confirmed 2 Historical Observations
1960 Unknown Confirmed   Historical Observations
1944 Unknown Confirmed   Historical Observations
1937 Unknown Confirmed 2 Historical Observations
1867 (?) Unknown Confirmed 2 Historical Observations
[ 1759 (?) ] [ Unknown ] Uncertain    
1750 (?) Unknown Confirmed 2 Historical Observations
0250 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected)
6820 BCE (?) Unknown Confirmed   Radiocarbon (uncorrected)

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.



Synonyms
Copahues, Los | Cupahue | Notuco | Trolope | Trilope


Craters
Feature Name Feature Type Elevation Latitude Longitude
Caviahue
    Agrio, del
Caldera 2306 m 37° 51' 0" S 71° 10' 0" W
Trapa-Trapa Caldera 2306 m 37° 51' 0" S 71° 10' 0" W


Thermal
Feature Name Feature Type Elevation Latitude Longitude
Chanchoco, Termas de Thermal
Copahue, Baños Thermal
Volcán Copahue is a composite volcano constructed along the Chile-Argentina border within an 8-km-wide Pleistocene caldera. The eastern summit crater, part of a 2-km-long, ENE-WSW line of nine craters, contains the briny El Agrio crater lake and displays intense fumarolic activity. Infrequent explosive eruptions have been recorded since the 18th century from the 2965-m-high volcano.

Photo by Hugo Moreno (University of Chile).
The broad glacier-covered summit of Volcán Copahue along the Chile/Argentina border is seen from the SE with conical Callaqui volcano in the distance. The lake-filled active crater of Copahue (lower center) has been the site of historical eruptions. The composite cone was constructed along the Chile/Argentina border within an 8-km-wide caldera formed 0.6 million years ago. The eastern summit crater is part of a 2-km-long, ENE-WSW line of nine craters that cuts across the western rim of the caldera.

Photo by Oscar González-Ferrán, 1992 (University of Chile).

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.

Bruggen J, 1950. Fundamentals of the Geology of Chile. Santiago: Editado por el Instituto Geografico Militar, p 1-374.

Casertano L, 1963a. Chilean Continent. Catalog of Active Volcanoes of the World and Solfatara Fields, Rome: IAVCEI, 15: 1-55.

Gonzalez-Ferran O, 1995. Volcanes de Chile. Santiago: Instituto Geografico Militar, 635 p.

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

Katsui Y (ed), 1971. List of the World Active Volcanoes. Volc Soc Japan draft ms, (limited circulation), 160 p.

Moreno H, 1974. Airplane flight over active volcanoes of central-south Chile. Internatl Symp Volc Andean & Antarctic Volc Problems Guidebook, Excur D-3, 56 p.

Moreno H, Naranjo J A, 1991. The southern Andes volcanoes (33°-41° 30' S), Chile. 6th Geol Cong Chile, Excur PC-3, 26 p.

Naranjo J A, Polanco E, 2004. The 2000 AD eruption of Copahue volcano, southern Andes. Rev Geol Chile, 31: 279-292.

Newhall C G, Dzurisin D, 1988. Historical unrest at large calderas of the world. U S Geol Surv Bull, 1855: 1108 p, 2 vol.

Varekamp J C, Maarten deMoor J, Merrill M D, Colvin A S, Goss A R, Vroon P Z, Hilton D R, 2006. Geochemistry and isotopic characteristics of the Caviahue-Copahue volcanic complex, province of Neuquen, Argentina. In: Kay S M, Ramos V A (eds) Evolution of an Andean margin: a tectonic and magmatic view from the Andes to the Neuquen Basin (35°-39° S lat), {Geol Soc Amer Spec Pap}, 407: 317-342.

Varekamp J C, Ouimette A P, Herman S W, Bermudez A, Delpino D, 2001. Hydrothermal element fluxes from Copahue, Argentina: a "beehive" volcano in turmoil. Geology, 29: 1059-1062.

Volcano Types

Stratovolcano
Caldera(s)

Tectonic Setting

Subduction zone
Continental crust (> 25 km)

Rock Types

Major
Trachybasalt / Tephrite Basanite
Andesite / Basaltic Andesite
Trachyte / Trachyandesite
Rhyolite

Population

Within 5 km
Within 10 km
Within 30 km
Within 100 km
88
555
3,042
138,414

Affiliated Databases

Large Eruptions of Copahue 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.