Increased seismicity February 2013; explosive events in August 2014

Although historical records of eruptive activity at Peru's Sabancaya volcano go back to 1750, there have only been a handful of eruptions documented since the 1980s; activity that began in 1986 was the first recorded in over 200 years. Weak solfataric activity from vents within and outside the 350-m-wide summit crater since then has created a persistent risk of ash plumes, Vulcanian explosions, and glacial melting causing mudflows. Reports of fresh ashfall on snow-covered slopes in 2003 (BGVN 29:01) indicated that some level of eruptive activity was continuing into the early 2000's. An increase in seismic and fumarolic activity in late 2012 and 2013 led to increased monitoring at the volcano, located 72 km NW of Arequipa. IGP-OVS (Instituto Geofisico del Peru, Observatoria Vulcanologico del Sur) and OVI-INGEMMET (Observatorio Volcanologico del INGEMMET, Instituto Geológical Minero y Metalúrgico) installed a number of seismic stations after significant seismic events in February 2013 (reported on in BGVN 38:02) caused damage to numerous homes in the area.

While the data reported by Peru's IGP-OVS and OVI-INGEMMET indicate ongoing seismic activity beginning in February 2013, and two phreatic-type explosions on 9 and 25 August 2014, no substantial eruption of ash was reported between February 2013 and February 2016. Numerous VAAC (Volcanic Ash Advisory Center) reports of ash were reported by pilots, but the Buenos Aires VAAC noted that no ash plume was visible either on satellite images or from the web camera located near the volcano. Occasional references to "possible light volcanic ash" are mentioned in some VAAC reports, but generally not corroborated with visual or satellite information. A few photographs from the area appear to show trace amounts of fine ash or particulates from magmatic gases in the snow around the crater, but such deposits were not confirmed by fieldwork. Throughout the period, Sabancaya emitted significant water vapor plumes occasionally as high as 3,000 m, and SO₂-rich magmatic gases that were blue in color and possibly contained trace amounts of ash.

Activity during 2013 and 2014. After a decade of quiet, a significant increase in fumarolic emissions was observed in late 2012 (BGVN 38:02). Throughout 2013 earthquakes were concentrated in areas NE, N and NW of the crater up to 25 km away; much of this seismicity was later interpreted by IGP-OVS to be related to regional tectonism and not to volcanic activity. An increase in SO₂ emissions, seen as bluish gas emitting from the fumaroles, was observed in March 2013, but a field visit in May noted no fresh lava or ash in the area.

White, gray, and bluish SO₂-rich fumarolic emissions increased in June 2014. VT (volcano-tectonic) earthquakes were recorded within 1.7 km of the crater in early July; IGP-OVS seismologists identified hybrid-type seismic events that they associated with the rise of magmatic material near the crater in early July. By mid-July, VT earthquakes were averaging over 200 per day, and the foci were located 12 km NNE of the crater. During late July, seismic events decreased, and the foci moved to 8 km N of the crater. Persistent off-white and bluish fumaroles rose 500-600 m above the crater during July 2014.

Fumarolic emissions intensified markedly on 5 August 2014, rising to 3 km above the crater; whitish water vapor, bluish magmatic gases, and gray emissions were observed, suggesting a "possible release of minor volcanic ash", as reported by IGP-OVS. The VT seismic events also began to increase in magnitude, ranging between 2.5 and 4.6 ML, including two located very close to the crater, between 4 and 14 km deep. Both LP and Hybrid seismic events, increased to hundreds of events per day in the early days of August. At 0429 local time on 9 August 2014 a large explosion was recorded; it was not observed due to darkness and cloud cover. After the explosions, VT events dropped back to tens per day, and emissions rose to between 500 and 1,000 m above the crater. Many of the earthquakes were located within 1.5 km of the crater at depths between 4 and 14 km. On 25 August beginning at 2039 local time four consecutive explosions lasting a total of 82 seconds were recorded (figure 14). Again, due to darkness, there was no visual confirmation of the explosion.

Figure 14. Seismograph from 25 August 2014 at SAB seismic station, located 3 km from the top of Sabancaya. Four explosive events occurred in the crater area at 2039 local time, followed by numerous small earthquakes. The energy calculated by IGP-OVS for this sequence of events was 1,151 MJ, with a total duration of 82 seconds. Courtesy of IGP-OVS (2014 Annual Report, Sabancaya).

In the days between the 9 and 25 August explosions, observed emissions from the fumaroles were water vapor and bluish magmatic gases rising to heights between 500 and 1,500 m above the crater (figure 15).

Figure 15. Emissions from Sabancaya on 13 August 2014. White vapor plumes and bluish SO2-rich magmatic gases are emitting from the crater. Courtesy of IGP-OVS (2014 Annual report, Sabancaya).

Water vapor and magmatic gas plume heights in September 2014 rose between 500 and 2,000 m above the crater. OVI-INGEMMET daily reports noted grayish plumes containing "possible ash" on 26 and 29 September 2014.

In October 2014, fumarolic emission heights were below 1 km above the crater; they were generally white steam plumes but also showed significant bluish SO₂ content. Constant emissions of water vapor and SO₂ to heights of 1,400 m above the floor of the crater continued into November along with intermittent seismic activity at constant levels since August. Seismicity increased slightly in early December and fumaroles of water vapor and SO₂ were observed rising to heights between 500 and 1,600 m above the crater floor. Seismic signals characteristic of a mudflow were recorded in mid-December 2014 in the ravine between Sabancaya and Ampato, the large volcano immediately SW.

Buenos Aires VAAC reports in 2014 were all ambiguous as to the presence of ash from Sabancaya. A "faint ash cloud" was detected in visible imagery on 14 July 2014. Numerous pilot reports of ash between August and December were not verified by satellite imagery under clear skies, and the webcam usually revealed water vapor emissions or cloud cover at the summit at the time of most of the reports. VAAC reports that do mention "possible minor volcanic ash" were given on 16 September, 23 October, 10 November, and 27 December 2014.

Activity during 2015 and early 2016. A similar level of activity continued during 2015. Neither OVI-INGEMMET nor IGP-OVA reported explosions with ash emissions during the year. Constant emissions of steam and bluish magmatic gases were observed from the fumaroles within the crater. Plumes of water vapor and magmatic gases rose to 1 km above the crater in January and to 1.2 km in February. From March through May seismic activity remained steady and fumarolic plumes were consistently below 1 km above the crater.

Seismicity increased during June 2015. Fumarolic plume heights also increased to 2.4 km above the crater, and bluish SO₂-rich gases were frequently observed. During July, some seismic events were located within 3 km of the crater, and fumarolic plumes rose to 2 km. Volcanologists from OVI-INGEMMET visited on 10 July 2015 and observed trace amounts of ashfall or particulates from SO₂ emissions in the vicinity of the crater (figure 16). IGP-OVS scientists who visited in late July to make temperature measurements observed constant water vapor and magmatic gas emissions. The temperature at the side of the dome was measured at 81°C, and the hottest points at the bottom of the crater were 391° and 280°C.

Figure 16. Crater inspection of Sabancaya on 10 July 2015 where trace amounts of ash or particulates from SO2 emissions were observed. Courtesy of OVI-INGEMMET.

During late August 2015 and the first week of September seismicity increased significantly, and was located within 6 km of the crater at depths between 6 and 9 km. Fumarolic emissions ranged between 600 and 1,600 m above the crater. Seismicity was low during October. An IGP-OVS visit on 1 October obtained temperature data similar to that collected in late July. The expedition reported the absence of recently deposited solid material in the vicinity of the crater, and also observed the constant emission of steam and magmatic gases (figure 17).

Figure 17. Emissions of white steam and bluish magmatic gases from Sabancaya in the early hours of 1 October 2015. Courtesy of IGP-OVA (2015 Annual report, Sabancaya).

VT seismicity remained low in November 2015, but an increase in the second week in December included two events (4.0 and 3.6) located within 2 km of the volcano. Constant emissions of water vapor and magmatic gases rising to 1,100 m were observed.

Buenos Aires VAAC reports for 2015 were again ambiguous about the presence of ash. Many reports note that pilot observations of ash clouds were not corroborated by satellite or webcam images. However, on several occasions, the VAAC reports indicated that the webcam showed continuous emission of steam, gases, and "possible light volcanic ash" (8 March, 19 May, 15 and 21 June, 18 and 21 July, 26 August, 10 October, 6 November and 12 December).

Sabancaya maintained a similar level of seismic and fumarolic unrest through February 2016 that was monitored and reported by both OVI-INGEMMET and IGP-OVS. OVI-INGEMMET reported plume heights of water vapor in early January as high as 2,000 m above the crater, gradually decreasing to below 1,000 m in early February. The intermittent presence of magmatic gases was also noted during this time.

While there have not been substantial ash emissions since renewed seismic activity began in 2013, there have been measurable SO₂ emissions observed by IGP-OVS and recorded by NASA's OMI instrument (figure 18). Emissions of SO₂ recorded on 27 December 2014 (0.937 kT), 3 April 2015 (0.750 kt), 28 November 2015 (0.773 kt), 25 February 2016 (0.365 kt) appear most likely to have originated at Sabancaya.

Figure 18. Four different images from the OMI instrument satellite data from NASA's Goddard Space Flight Center showing SO2 anomalies possibly attributable to Sabancaya (upper left triangle). The image dates are 27 December 2014 (top left), 3 April 2015 (top right), 28 November 2015 (bottom left), and 25 February 2016 (bottom right). Courtesy of NASA Goddard Space Flight Center.

Information Contacts: Instituto Geofisico del Peru, Observatoria Vulcanologico del Sur (IGP-OVS), Arequipa Regional Office, Urb La Marina B-19, Cayma, Arequipa, Peru (URL: http://ovs.igp.gob.pe/); Observatorio Volcanologico del INGEMMET, (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, (URL: http://ovi.ingemmet.gob.pe); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php?lang=es); NASA Goddard Space Flight Center, Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, (URL: http://so2.gsfc.nasa.gov/index.html).

Information is preliminary and subject to change. All times are local (unless otherwise noted)

June 1988 (SEAN 13:06) Cite this Report

Increased fumarolic activity

Sabancaya reportedly began strong fumarolic activity in December 1986 [see also 15:05]. Interviews with area residents indicated that glowing tephra ejections from the crater were visible at night. Seismicity was felt on the flanks but was not noticed at a distance of 15 km.

A summit photograph was taken 10 August 1987, 8 months after initial reports of activity, during a civil defense helicopter reconnaissance in response to requests from residents and local authorities. Light to dense steam emerged from several sources in a moat surrounding the central plug of the middle (of at least three) summit cone. The dome, moat, and surrounding pyroclastic cone were covered with thick ice and snow except in areas adjacent to steam emission.

Geologists observed the volcano 22-24 June 1988.

22 June (Banks, Hall, Salas, Mothes, and Huaman; at 40 km distance with binoculars.) Every 0.5-2 minutes, voluminous steam pulses, some with dark, basal "rooster-tails," rose 0.5-1 km above the summit. A yellowish plume streamed horizontally 10-15 km E. A dark area of several tens to hundreds of square meters was prominent on the NE slope adjacent to the source of the steam emission.

23 June (Hall, Salas, Mothes, and Huaman; at 15 km.) Activity was similar to 22 June with perhaps slightly decreased plume heights. Strong sulfurous fumes were reported by flank inhabitants. Some cattle had died in these areas, either directly from the fumes or after eating contaminated foliage.

24 June (Banks, Lazo, Portillo, Salas, Huaman, and Tejada; from a fixed-wing flight supported by the Fuerza Aérea del Perú in coordination with the Defensa Civil. Observations are preliminary and will be improved by analysis of photographs and geological investigations on the ground.) A continuous annular crack encircled the outer flanks of an old pyroclastic cone. Weak to moderate fumarolic activity emitted vapor along the annular crack and the dome's edges. Frequent steam emissions (every 1-2 minutes) rose 0.3-5 km and originated from a vent in the moat on the SE side of the dome. Emission energy was substantially less than on 22 June. Some ejection events were lightly colored with ash but no "rooster-tail" forms were noted. Initial white steam pulses dissipated 500 m above the crater, but a yellowish plume streamed more than 10 km E. There was ~ 20-50 x 10⁶ m³ of ice and snow on Sabancaya, a substantial decrease since the August 1987 observations. A bare area, devoid of snow and ice, surrounded the annular crack at variable distances averaging 50 m. Snow beyond this bare area was lightly dusted with ash, particularly on the SE side nearest the pulsing steam vent. Fresh sulfur surrounded many of the fumaroles. Several tens of meters in the bare area, S of the summit, were yellow. No crater lake was observed in the moat between the central dome and the surrounding pyroclastic cone. No new lava or bomb craters were observed. Sabancaya appeared to be built on a pile of young, thick, blocky lava flows and domes erupted from a vent on the mid-NE flanks of the larger Ampato volcano (figure 1). No thick pyroclastic deposits were obvious on Sabancaya or Ampato.

Figure 1. Map of Sabancaya and Ampato showing the plateau, drainage system, and villages to the SE. Contour interval, 50 m. From the Chivay sheet (1:100,000), Instituto Geográfico Militar, 1980.

25 June (at 30 km from Aeroperú flight.) Activity was greatly diminished relative to that of 24 June.

Information Contacts: N. Banks, CVO; M. Hall, Instituto Geofísico, and P. Mothes, Defensa Civil liaison, Quito, Ecuador; M. Lazo, G. Salas Alvarez, and H. Portillo, Univ Nacional de Arequipa; D. Huaman, Instituto Geofísico del Perú, Lima; M. Tejada, Tercera Region Defensa Civil, Arequipa.

May 1990 (BGVN 15:05) Cite this Report

Ash eruption; plume to 7 km

Sabancaya is the youngest of a group of four stratovolcanoes . . . (figures 2 and 3). Weak solfataric activity from vents within and outside the summit crater has continued at Sabancaya for many years, . . . . Increased fumarolic activity began in 1985, and a September 1986 helicopter overflight by Alberto Parodi revealed that part of the ice cap had melted and sulfur was being precipitated by the fumaroles. According to area residents (roughly 4,000 people live on or near the volcano, and many more in valleys draining the edifice), strong fumarolic activity and ejection of glowing tephra began in December 1986. Frequent pulses of steam, minor ash emission, and a strong sulfur odor (noted by area residents) were reported by visiting scientists in June 1988 (13:6). By April 1989 the plume had reached 800 m height and the ice cover was significantly reduced (Guido Salas estimated in June 1990 that the ice cover was 20-40 x 10⁶ m³). Activity then gradually increased through May 1990.

Figure 2. Sketch map of SE Perú (box on inset map) showing the locations of Sabancaya and nearby volcanoes (triangles), and towns and rivers in the region. Pilots were warned of eruption cloud hazard along high-altitude routes UB677 and UB679 in the 5 June Notice to Airmen (NOTAM). Low-altitude air routes (W23, W25, and W26) and reporting points (ATIPA, VUGAL, and NEVDO) covered by the 5 June NOTAM are not shown.

Figure 3. Portion of the Chivay 1:250,000 sheet (SD 19-13, Instituto Geográfico Nacional, Lima, Perú, 1988), showing Sabancaya, Ampato, Hualca-Hualca, and Ahuashune volcanoes, nearby towns, and the upper Colca river valley. Contour interval, 100 m.

Eruption begins, 29 May. A loud sonic boom on 29 May signalled the onset of periodic explosions at the volcano. From 29 May to 3 June, 2-3 explosions occurred/day with 700-800-m column heights. The eruption plume had a strong sulfur odor. A 1 June press report noted that residents of Maca, 18 km NE of the volcano on the Río Colca, heard underground noises and smelled sulfur (see also 6 June). Two additional seismographs were installed on 3 June and increased seismic monitoring was begun (one seismograph had been installed ~ 10 km SW of the crater in 1989). By 3 June, the plume's height had increased to 1 km and it was blowing SSE (figure 4).

Figure 4. Tephra cloud from Sabancaya, viewed from the E on 3 June 1990. Ampato volcano is at left. Photo by Ch. Pattry, courtesy of Alberto Parodi.

Intensity increases, 4 June. Residents at the base of the volcano reported that explosions had increased to 1 every 20 minutes with a strong sulfur odor and higher noise levels. Ash emission was reported to be continuous, with a column height of 2 km and pulses every few minutes. The plume appeared water-rich, dark gray, and blew NE and ENE, with dense ashfall to 5 km and light ashfall as far as 10 km downwind. Frequent earthquakes were reported.

5 June. The eruption intensity continued to increase, becoming essentially continuous with column heights of 3-6 km. Glowing tephra ejection was reported. The continued ash emission reportedly was seriously affecting grazing land within 10 km of the volcano. Residents in scattered settlements were advised to evacuate at once and remove livestock (llamas and alpacas); many people were reported to have already left. A NOTAM was issued at 1730 stating that routes in the Sabancaya area were affected by the plume, just over 9 km asl (roughly 3 km above the summit).

7 June. The Corporation for Airports and Commercial Aviation requested airlines regularly flying over south Perú to modify routes and issued specific warnings to Perúvian airlines flying to Arequipa. They reported a column to 7 km above the summit. The press reported that the plume headed toward Arequipa and Puno with ash continuing to fall up to 20 km away, destroying pastures and crops, and contaminating the Río Sihuas to the south. Earthquakes were felt at 3-minute intervals in the towns of Chivay (30 km NE of Sabancaya), Maca (18 km NE), Lari (20 km NNE), and Achoma (22 km NE). The press also reported that "crevices with sulfur emanations opened on the ground" in Maca.

8 June. Violent explosions occurred every 5-10 minutes, ejecting pyroclastic material, mainly fine ash, to 1 km height. Ash was reported to cover an area with a radius of 20 km at accumulations up to 1 cm thick. No new lava or juvenile material had been identified. The explosions were accompanied by felt shocks and dull rumbling. The seismic network measured 5-6 microearthquakes/day. Satellite wind data on 11 June indicated that surface winds were from the S, winds at ~ 8 km altitude (372 mbars) were from the NW (298°) at 32-38 m/s (60-70 knots), and winds at >10 km (200 mbars) were from the WNW at 40 m/s (75 knots). As of 17 June, eruptive activity appeared to be continuing to increase.

Information Contacts: A. Parodi, Arequipa; N. Banks, CVO; M. Casaverde, A. Rodriguez, and E. Deza, Instituto Geofísico del Perú, Lima; R. Kosaka, G. Salas Alvarez, and M. Lazo, Univ Nacional de San Agustín, Arequipa; A. Giesecke, CERESIS, Lima; N. Krull, FAA; S. Hamerla, SAB; EFE network, Madrid, Spain; Agence France-Presse; Reuters.

June 1990 (BGVN 15:06) Cite this Report

Ash emission continues; plume to 3-5 km

Sabancaya continued to eject ash through late June. Pulses of volcanic gas and ash were emitted at roughly 30-minute intervals, reaching 1-3 km above the summit. Ashfall appeared to be limited to a 10-km radius. Accumulations of several tens of centimeters were reported on the ice/snow cap that covers ~ 4 km² of the summit area. No juvenile material was evident in a preliminary petrographic examination of the ash. An average of 15 high-frequency (A-type) events were recorded daily. The seismic network consisted of two seismometers 22 km NE and NW of Sabancaya, with an additional seismometer being installed on the S side of the volcano. A 1:100,000 scale hazard map was produced by the Univ Nacional de San Agustín and Civil Defense officials. Towns in the 1,500-m-deep Colca Valley, 20 km N of the volcano, are perched above the valley floor and not at much apparent risk from lahars or other volcano related flows. Although between 8,000 and 10,000 people were living in other drainages in the area, all were at least 25 km away. Field geology showed one old lava flow to be hornblende-rich high-Si andesite/dacite in composition. Pits dug at the volcano's E base yielded only alluvium, with no recent volcanic deposits.

Information Contacts: M. Hall, Instituto Geofísico, Quito, Ecuador; N. Banks, CVO.

July 1990 (BGVN 15:07) Cite this Report

Ash emissions decreasing in intensity; more information on June activity

A joint mission by Minard Hall, Escuela Politécnica Nacional, Quito, Ecuador, and scientists from the Instituto Geofísico del Perú (IGP) and the Univ Nacional, San Agustín (UNSA) in Arequipa, was conducted 16-24 June to evaluate the status of activity at Sabancaya. The following is Hall's report on the mission (translated by John Ewert) which supplements information in 15:5-6.

"The first indication of the reactivation . . . began in December 1986 with the appearance of summit crater fumarolic activity, which increased during 1988. In June and July 1987, a swarm of felt earthquakes was reported in the region but could not be confirmed. During a visit to the area by the [USGS] Volcano Disaster Assistance Program and the author in June 1988, the inhabitants of Huanca (25 km S from Sabancaya) reported that nothing new had occurred at the volcano other than an increase in summit fumarolic activity.

"On 28 May 1990, the inhabitants of the region informed Civil Defense of an eruption . . . consisting of a steam and ash plume that ascended several kilometers above the volcano. IGP and UNSA were informed at the same time. More intense activity was reported 2-4 June, leaving a thin (1 mm) deposit of ash in the valley E of the volcano. From 12 June until this writing (23 June) the volcano has apparently shown the same level of activity, consisting of violent emission of gases and ash forming a light-gray to medium-gray cloud that rose 2-3 km above the summit. Emissions lasted less than a minute before stopping and typically occurred every 20-30 minutes. Between emissions the volcano maintained a vapor plume several hundred meters high.

"During the mission a trace of gray ash fell over an extensive area to the N, NE, and E of Sabancaya, causing considerable worry among the inhabitants. Nevertheless, the quantity of ash that has fallen since 12 June is not significant and we confirmed that only 1 cm of ash had accumulated at the E foot of the cone since that date. All of the cone, including its snow and ice, is covered with several centimeters of ash. The two neighboring volcanoes are also covered with a trace of gray ash. It should be noted that neither of these neighboring volcanoes are displaying abnormal activity."

Since the time of Hall's report, there has been a gradual decrease in activity (column height and frequency of explosive events) at Sabancaya.

Information Contacts: M. Hall, Instituto Geofísico, Quito, Ecuador; N. Banks, CVO.

May 1991 (BGVN 16:05) Cite this Report

Vigorous Vulcanian activity; mudflows force daily clearing of river channel

Strong Vulcanian explosions were observed during a visit on 13-19 April. The explosions, occurring every 20-30 minutes, lasted ~ 1 minute and produced 3-4-km-high, medium-gray ash clouds. Small avalanches were produced by falling blocks at the base of the eruptive columns. Quiet degassing continued between explosions. Light-gray ashfall was frequent during the visit, depositing 2 mm one night ~9.5 km SE of the summit (at Cajamarcana).

The volcano began erupting in late May 1990, reportedly ejecting ash to 7 km. By late June 1990 (15:7), activity had decreased to periodic explosions with weak ash columns 2-3 km high, but then increased slowly through November. High-frequency seismicity (>122 events recorded over one 2-week period) was usually centered ~ 10 km NE, although two earthquakes occurred under the crater. Several tremor episodes were recorded, starting in October.

The plume was black and heavy with ash during an overflight on 10 November, rising an estimated 5-8 km in distinct, but almost continuous pulses. Ash deposited on Hualca Hualca (4 km N) caused increased melting of the glaciers (estimated 20 cm of snow above the ice and berm) producing numerous mudflows. These moved down the N flank nightly, dumping an estimated 13,000 m³ of debris/day into the Majes River drainage system ~ 5 km N of the volcano. Construction crews cleared the channel daily. Airfall deposits were composed of 80% lithics and 20% glassy fragments and breadcrusted material. At one outcrop, the 1990 ash accumulations were 1 cm thick, overlying at progressively greater depth 30 cm soil, 2 cm ash, 40 cm soil, and another 2 cm ash. Eruptive activity observed on 22 December appeared about the same as it was on 10 November.

Information Contacts: P. Vetsch and R. Haubrichs, SVG, Switzerland; N. Banks, CVO; Instituto Geofísico del Perú, Lima.

July 1991 (BGVN 16:07) Cite this Report

Earthquake swarm damages towns and triggers mudslides; 20 people reported dead

A swarm of earthquakes, reported on 23-24 July, triggered mudslides that partly buried four villages. In towns within 20 km N of the volcano, the earthquakes caused many houses to collapse, especially in Maca (15 km N) which was almost completely destroyed. The press reported that 20 people were killed, 80 were injured, and 3,000 were left homeless. More than 20 earthquakes/day were reported felt (MM <=V) 75 km SE (in Arequipa). The largest of the shocks (Ms [4.7]), detected at [1444] on 23 July by the WWSSN, was centered [35] km [ENE] from the volcano at shallow depth.

Information Contacts: NEIC; EFE network, Madrid, Spain; Agence France-Presse; Reuters; UPI; AP.

January 1992 (BGVN 17:01) Cite this Report

Increased activity prompts official alert; ashfalls force evacuation of nearby towns

The press reported that the Instituto Geofísico del Perú and Civil Defense officials declared an "alert" on 19 February, following increased activity at the volcano. Gas and ash from the 4.5-km-high plume had reportedly caused respiratory problems and covered homes and crops during the previous several months, prompting people to evacuate several towns within a 14-km radius of the volcano. The press also reported that several small streams of "lava" had moved downslope during the previous few days. Seismicity at the volcano had increased to as many as 50 earthquakes recorded daily. Vulcanian activity has continued at varying intensity (ash clouds 2-7 km high) since the start of the eruption in late May 1990.

Information Contacts: A. Giesecke, CERESIS, Lima; N. Banks, CVO; AP.

March 1994 (BGVN 19:03) Cite this Report

Moderate Vulcanian activity continues; hazard maps completed

Fieldwork was conducted on 4-8 March by scientists from the Univ Blaise Pascal (Clermont-Ferrand, France), the Instituto de Geofisico del Perú (Arequipa, Perú), and the Univ de Liège (Belgium). The purpose of the visit was to observe current activity, assess eruptive hazards, and collect samples of juvenile material. The joint mission investigations included the geology and geomorphology of the summit domes and block-lava flows, the role played by explosions on the morphology of the summit, crater, and ice cap (fracturing, gullying, tephra-fall cover, and mudflows), and analysis of tephra, lavas, and ice.

An ash explosion was observed early in the morning on 5 March from Sallili (8 km E at the base of the volcano). The eruption column rose for 30 seconds to a height of 2.5 km and generated a dark gray plume that was blown W. A vapor-rich explosion ~ 2.5 hours later produced a dominantly white plume that rose 1.5 km. Between these explosion there was a discrete vapor plume above the crater. Another early morning explosion on 7 March lasted for about 60 seconds and fed a dark gray plume 1.5 km high. Dominantly white plumes later that morning rose 1-2 km.

Activity of a similar nature has been exhibited since December 1992, with strong explosions of gas, ash, and blocks forming a gray or light-gray plume rising 1-3 km above the summit. Explosions have occurred every 1-2 hours (20-30 minutes in late 1992), and generally lasted <1 minute. Residents of Sallili have seen glowing projections at night since autumn 1993. Observations in December 1992 (Salas and Thouret) indicated that the crater had widened.

The 1990-92 tephra represent a small bulk volume (0.025 km³), but are widely dispersed around the crater; ballistic blocks reached a few hundred meters, and ash as far as 20 km. The juvenile component belongs to a K-rich calc-alkaline series and is compositionally variable from andesite (58% SiO₂) to dacite (63% SiO₂). The mineral assemblage of 1990-93 juvenile magma consists of plagioclase, green pyroxene, brown amphibole, biotite, destabilized olivine, and Fe-Ti oxides. Since 1990 the juvenile component has increased from 15 to ~50% by volume. Ejecta consist of black, vitreous, slightly vesicular andesitic fragments and gray dacitic fragments. Glassy black blocks with radial fractures dominate the 1994 tephra. Although the geochemical difference between the andesite and dacite is small, mineralogical disequilibrium suggests an interaction between two magma batches. One was more felsic than the dacite and included oligoclase and hypersthene; the other was more mafic than the andesite and included labradorite, bronzite, and olivine.

Hazard assessment and hazard-zone mapping has been done based on geological and geomorphological data, photo interpretation, remote sensing, and models of tephra dispersion (Thouret and others, 1994). Hazard zones are defined for tephra-fall, pyroclastic flows, lahars, and potential catastrophic events. These zones are portrayed for moderate Vulcanian activity (1990-94), growth of a dome and/or emission of a blocky lava flow, possible increase of Vulcanian activity (including small-scale pyroclastic flows), and a potential large Plinian event. Geological study and remote sensing of the current activity have provided a sound basis for evaluating and mapping hazards at and around Sabancaya. Holocene block-lava flows cover as much as 40 km² around the summit domes. Thin Plinian tephra-fall deposits from historical eruptions are found as far as 11 km from the crater, and block-and-ash pyroclastic-flow deposits as far as 7 km from the source. Recent lahars have traveled ~25 km downstream.

Unstable lava domes pose a threat for ~35,000 people living in the Rio Colca and Siguas valleys. Sabancaya is still ice-clad (currently estimated to be 3.5 km² of glacial ice) despite its recent 4-year period of activity. The Majes River irrigation canal project is also at potential risk should a moderate-to-large eruption melt the ice and snow on Sabancaya and Ampato.

Reference. Thouret, J-C., Guillande, R., Huaman, D., Gourgaud, A., Salas, G., and Chorowicz, J., 1994, L'activité actuelle du Nevado Sabancaya (Sud-Pérou): reconnaissance géologique et satellitaire, évaluation et cartographie des menaces volcaniques: Bull. Soc. Geol. France, v. 165, no. 1, p. 49-63.

Information Contacts: A. Gourgaud, F. Legros, and J-C. Thouret, Univ Blaise Pascal, Clermont-Ferrand, France; G. Salas, Univ San Augustine, Arequipa; A. Rodriguez and M. Uribe, Instituto de Géofisico del Perú, Arequipa; E. Juvigné, Univ de Liège, Belgium.

May 1995 (BGVN 20:05) Cite this Report

Continuing activity, eleven eruptions observed during 9-10 May

During a 2-day visit to Sabancaya, 11 eruptions were witnessed, 5 on 9 May and 6 on 10 May. The repose periods varied in duration from 35-160 minutes, with a mean of 125 minutes on both days. All of the eruptions started with the quiet emission of a white vapor plume followed tens of seconds later by a rapidly rising cloud of vapor and ash. Each eruption progressed from the S vent to the two N vents, and typically lasted 5-15 minutes.

Throughout the eruptions only a few blocks were ejected from the crater as seen from the foot of the cone, ~500 m from the crater rim. No "cannon-like" explosions were seen or heard. The talus apron at the foot of the cone consisted mainly of dense blocks with abundant thermal cracks, and minor amounts of poorly vesiculated scoria.

Plume height varied between 1 and 4 km above the crater, though usually the plumes rose ~2-2.5 km. Eruptions were typically followed by emission of a quiet, slowly rising white-blue plume; these plumes drifted to the SW and S on 9 May and S and E on 10 May. The presence of ash on Sabancaya and the adjacent Ampato volcano caused enhanced ice-melting during daytime hours, creating continuous small mudflows.

Although observations were not as detailed, activity on 11 May was apparently much less than on 9-10 May with only three reported eruptions, one being purely phreatic (white vapor).

Vulcanian activity has persisted at varying intensity levels since ash emission began in late May 1990 (BGVN 15:05, 15:06, 16:05, and 17:01). During the previous visit to the volcano in March 1994 (BGVN 19:03), scientists observed explosions, classified tephra layers, and carried out hazard-zone mapping. Unstable lava domes continue to threaten the 35,000 inhabitants living in the Rio Colca and Siguas valleys. Sabancaya remains ice-covered and poses a potential risk to the Majes River irrigation canal project if a moderate-to-large eruption were to occur. Of particular concern is an eruption that might melt the ice on both Sabancaya and Ampato volcanoes.

Information Contacts: Jean-Luc Le Pennec, Centre ORSTOM de Brest, BP 70, 29 280 Plouzane, France (Email: jlpennec@ifremer.fr); Francois Legros, Universite Blaise Pascal, Departement des Sciences de la Terre, 5 rue Kessler, 63038 Clermont-Ferrand, France; Anibal Rodriguez and Miguel Uribe, Instituto Geofísico del Perú, Arequipa, Perú; Jean-Claude Thouret and Alain Gourgaud, Centre de Recherches Volcanologiques, 5 rue Kessler, 63038 Clermont-Ferrand, France.

July 1997 (BGVN 22:07) Cite this Report

Quiet on 19 July; ash-bearing plumes on 1-2 May

During a mid-[July] visit, Sabancaya displayed only fumarolic activity. Visiting scientists also examined the area well to Sabancaya's N along the Colca river. They determined that previous reports of destructive, seismically triggered mudslides in 1991 (BGVN 16:07) had been incorrect.

On 19 July scientists flew over Sabancaya and the two adjacent volcanoes Ampato and Hualca Hualca (figure 5) while taking slides and Super VHS images. Ice fields and snow cover were observed only on the summit regions of Ampato (6,288 m) and Hualca Hualca (6,025 m). Thus, the ice fields that existed on Sabancaya prior to the most recent eruption (29 May 1991, BGVN 15:05) had not returned.

Figure 5. Map of the region around Sabancaya showing adjacent stratovolcanoes and the Colca river. This segment of the Colca river flows westwards. Courtesy of M. Bulmer, F. Engle, and A. Johnston, CEPS.

As the photo (figure 6) reveals, Sabancaya's cone remains nearly symmetrical with slopes of 30-40 degrees. The cone is roughly 1 km in diameter and contains a central crater with a diameter of approximately 400 m. Slope failure occurred along a ~600-m-long arcuate scarp seen on the cone's NE flank. This could prove to be a zone of weakness in any future eruption. An active fumarole was located at the summit cone in a spot on the wall of the southern crater rim; it vented rapidly. Less active fumaroles were seen on the western crater wall and sulfur deposits occurred on the upper crater walls. When the cone was viewed from a distance of 1 km, observers saw significant atmospheric aberrations that implied gas emissions.

Figure 6. Aerial photo of Sabancaya taken on 19 July 1997 looking W. The crater is approximately 400 m in diameter. The surface of the cone is mantled in young ash deposits (not snow). Courtesy of M. Bulmer, F. Engle, and A. Johnston, CEPS.

In the Colca Valley scientists saw extensive damage from the 23-24 July 1991 earthquake swarm including abandoned, damaged buildings, and slope failures; what they failed to find, however, was evidence that mudslides had ravaged local villages. This was important because BGVN 16:07 briefly described seismic damage from the earthquakes but also stated that they ". . . triggered mudslides that partly buried four villages." Based on this latest visit, this latter statement was clearly incorrect; it may have stemmed from the cited press accounts.

The scientists visited the villages of Maca, Achoma, Yanque, Lari, and Chivay. The earthquake damage was greatest in Maca, which lies in the Colca valley below the NNE flank of Hualca Hualca, a spot 15 km N of Sabancaya. Particularly in Maca, there was abundant evidence of seismically induced damage to structures. It should be noted that most buildings in the region had been constructed with walls made of loose stone without the benefit of concrete mortar or steel reinforcing.

On the NW side of Maca the group found evidence for a series of rotational and translational slides and slumps triggered by 2 m of throw along a normal fault. There was a series of well defined backscarps delineating different slope failures (figure 7) that extended ~1 km from the NW margin of Maca down to the Colca river. No houses were located on the failed surfaces; instead, this area had been terraced for agricultural use, but it was fallow when visited. The failure "complex" remained mobile and its toe was being undercut by the river. The village of Maca was being rebuilt gradually as people returned to the area. Some of the new housing includes concrete structures but most are made of adobe (clay and straw) brick with corrugated sheet-metal roofing.

Figure 7. Aerial photo of Sabancaya taken on 19 June 1997 looking SE; it shows slope failures located NW of the village of Maca. The Rio Colca is visible in the lower part of the image. Note the road running across the upper third of the photo (trending E-W); it had to be realigned near Maca. Maca's market square can be seen in the upper left side of photo. Courtesy of M. Bulmer, F. Engle, and A. Johnston, CEPS.

Prior to the visit, on 1 and 2 May, aviation reports described ash-bearing plumes. The plume on 1 May reportedly reached ~5.5-km altitude; the one on 2 May, ~7.3-km altitude.

Information Contacts: M.H. Bulmer, F. Engle, and A. Johnston, Center for Earth and Planetary Studies (CEPS), National Air and Space Museum, Smithsonian Institution, Washington, DC 20560 USA (Email: mbulmer@ceps.nasm.edu); Guido Salas, Universidad de San Agustin, Casilla 1203, Arequipa, Perú; A. Seimon, Department of Geography, University of Colorado, Boulder, CO 80309-0260 USA; NOAA/NESDIS Satellite Analysis Branch (SAB), Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA; Tom Fox, Air Navigation Bureau, International Civil Aviation Organization (ICAO), 999 University St., Montreal H3C 5H7, Canada (URL: http://www.cam.org/~icao/).

May 1998 (BGVN 23:05) Cite this Report

Summit activity, ice observed on visit in May

Sabancaya was observed by scientists of the National Air and Space Museum's Colca Valley Geohazard Project during a four-day visit (18-21 May) made in preparation for field work later in the year. Continuous fumarolic activity at the E side of the crater rim was observed during this visit. Seasonal snow patches were visible on the SE flank that were not present when the team made an aerial observation in July 1997 (BGVN 22:07).

On 18 May a seismic event was noted by observers traveling in a vehicle on the Pampa Lliullipampa, SE of the volcano. The disturbance produced a dust cloud that spanned the entire Ampato-Sabancaya-Hualca Hualca complex along its E slopes, a distance of 15 kilometers. A video camera recorded the disturbance at 1525 on 18 May. Roughly concurrently, scientists at the Instituto Geofísico in Arequipa detected a deep focus M 6 earthquake centered 250 km to the N near Ayacucho. Tremors occurred at this time in the pueblo of Cabana Conde located 15 kilometers NW of Hualca Hualca.

On 20 May A. Seimon of the University of Colorado ascended Sabancaya's SE flank and recorded a video of the fumarolic activity inside the crater rim, including the steady emission of gas from the crater floor (figure 8). He noticed ice along the route up the E flank. The ice lies beneath a layer of ash 5 to 10 cm thick, a depth that seemed sufficient to insulate it from higher surface temperatures. Ice was also observed filling a breach in the N side of the crater rim.

Figure 8. Video frame showing the inside of the S rim of Sabancaya's crater. The fumarole was continuous during the observation period (18-21 May). Snow-covered Nevado Ampato is visible beyond the crater rim. Courtesy of A. Seimon.

Sabancaya is the youngest of the three adjacent stratovolcanoes located 75 km NW of Arequipa. The volcano's 29 May 1990 eruption produced a plume reaching a maximum height of 7 km (BGVN 15:05). The plume traveled NE and carried fine ash that fell up to 20 km away. Extensive mudflows (not mudslides) had occurred in the area in the months after the Sabancaya eruptions that began in late May 1990. These mudflows resulted from fallen ash and the subsequent melting of snow and ice on Hualca Hualca (BGVN 16:05; v. 15, no. 5).

Information Contacts: F. Engle, Center for Earth and Planetary Studies (CEPS), National Air and Space Museum, Smithsonian Institution, Washington, D.C. 20560 USA (Email: engle@ceps.nasm.edu); A. Seimon, Department of Geography, University of Colorado, Boulder, CO 80309-0260 USA; S.O. Brooks, Department of Geography, University of Wisconsin, Madison, WI USA 53706-1491.

August 1998 (BGVN 23:08) Cite this Report

Increases in August gas emissions

Activity was monitored during 13-31 August using satellite remote sensing data and detailed field observations. During this time, the amount of gas being emitted from the central crater increased. At the height of emission, gas clouds from the crater rose over 1 km. Most frequently, plumes attained heights of 300-500 m before dissipating due to strong winds. However, on several occasions cumulo-type clouds formed and moved over the surrounding Pampa. Gas emissions were predominantly white in color but occasionally gray, yellow, and brown. During active phases new plumes emerged on average every 2-3 minutes. Nearly continuous venting occurred from two fumaroles on the N and S sides of the crater.

At 0640 on 16 August a pronounced increase in gas emission was observed. Dense white clouds filled the crater and formed a plume rising over 300 m. At 0645 material was seen falling from a gray/brown cloud onto the S flank of the cone. This small ash ejection lasted for a few minutes (figure 9). A noticeable decline in the emission rate occurred from 0726 until 0847, when gas clouds became infrequent. Activity continued at this reduced level into the next day. At 1355 on the 18th a yellow/brown and gray cloud rose ~800 m above the crater. Following this, activity returned to faint gas emissions. Increased activity was observed again at 1019 on the 20th when dense yellow and brown clouds were emitted. Another thick brown gas cloud emerged at 1044, after which there was a return to white emissions. Activity decreased noticeably from 1100 to 1200, by which time the gas was only faintly visible. On the 22nd at 1420 dense white clouds rose 500 m over the crater. Plumes emerged predominantly from the S side of the crater every 2-3 minutes.

Figure 9. A ground view of one of the small ash eruptions at Sabancaya on 16 August at 0700 looking to the NW. Ash fell on the S side of the upper slopes of the cone. Courtesy of Mark Bulmer.

No emissions were seen on 23 August until 1325; a large dense gas cloud emerged from the whole crater at 1510. At 1524 the cloud on the S side of the crater formed a brown plume that rose straight upwards more than 400 m. Gas clouds descended the upper S slopes of the cone at 1530. Five minutes later a light brown-white and yellow gas plume formed on the N side of the crater. Emissions continued until dusk when observations ceased. On the morning of the 24th at 0740 dark gray clouds rose slowly from the crater. At 0756 gas from the lower portion of an ascending plume moved down the upper slopes of the cone on the N side. By 0804 the color of the plumes emerging from the crater altered to white. However, at 0816 a gray/brown gas cloud emerged and dispersed <100 m above the crater. After this no further emissions were seen until 1359 when white emissions commenced, forming cumulo-type clouds that sat over Ampato. At 0700 on the 25th, dark gray and brown clouds were emitted from the center of the crater. At 0714 a white, brown, and gray cloud emerged from the middle of the crater. Emissions were light for the rest of the day.

On 26 August at 0757 a light brown-and-gray cloud emerged. Only faint emissions were noted until 0804 when a new brown and white cloud rose 300 m. The amount of gas released then diminished to very small clouds every 2-3 minutes. At 1430 gas was rising from the whole crater; activity remained at a similar level for the rest of the afternoon. At dusk, a brown haze sat over the crater. Only limited observations were possible on 28 August. Activity was first noted at 0857 when a gray cloud emerged from the S side of the crater. Gas emission was observed at 1430 but not at 1630. The next observation was at 1447 on the 31st, at which time white clouds were being emitted from the center of the crater. At 1625 the amount of gas being released appeared to increase and became grayer. Evening sunlight was seen refracted in gas clouds ~1 km above the crater, producing a rainbow effect.

Information Contacts: Mark Bulmer, Frederick Engle, and Andrew Johnston, Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington DC 20560-0315 (Email: mbulmer@ceps.nasm.edu).

October 1998 (BGVN 23:10) Cite this Report

Intermittent gas plumes in early September, some with ash

Activity was monitored during 1-9 September using detailed field observations combined with satellite and aerial remote sensing data. Activity was generally similar to that reported in August. On 6 September a large eruption began. In the preceding days activity had fluctuated. On 1 September, the only activity observed was a small white gas cloud at 0944. Gas clouds were emitted from 0748 until 0942 on 2 September. These predominantly white and gray clouds rose only 200 m above the crater before dissipating. The only exception was a period of ten minutes when brown and dark gray clouds issued from the crater. The sole emission the following day was a small white gas cloud at 1506. On 4 and 5 September small gas emissions were observed from the fumarole on the S side of the cone.

Activity on 6 September was first noted at 0702 when large white and gray gas clouds rose from the whole crater. At 0704 part of the gas column began to sink and move down the upper flanks, obscuring the E-flank ice walls. The gray and brown gas cloud was densest on the S side of the crater and appeared to be expanding as it rose. At 0711, the whiter part of the cloud rose upward while the dark gray portion dropped ash on the N side of the cone. Wind speeds at the summit appeared to increase, and the 400-m-high column began to be pushed N. At 0716 more gas descended the flanks. At 0735 observers on the edge of the easternmost lava flow could smell sulfur.

The main gas emission continued to be from the S side of the crater and at 0740 another cloud descended over halfway down the flanks. At 0743 a large white and dark gray gas cloud emerged from the crater. Ash fell from it onto the upper and mid-slopes. Another large gray, white, and brown plume filled the whole crater at 0746 and billowing to 400 m. At 0749 the plume color changed to brown, yellow, and dark gray. Ash was blown N. New gas clouds emerged from the crater on average every 30 seconds. At 0824 the cloud color returned to white and light gray for a few minutes before it once again became brown, gray, and yellow. The brown portion seemed to contain the ash. Gas once again descended the upper slopes at 0846. Winds at the summit began to pull the top of the plumes apart and by 0854 they were almost flat across the crater.

There was a reduction in gas emission at 1143. Gas continued to periodically descend the upper slopes and ashfall appeared to be mainly on the N slopes. At 1155 a gas cloud descended to mid-slope. The interval between gas emissions grew during the afternoon. After three hours of white- and gray-colored gas clouds, yellow, white, and brown clouds emerged again at 1604. This marked renewal of activity was similar to that in the early morning. Gas originated mainly from the southern fumarole and occasionally descended the upper slopes. Gas clouds rose 500 m and formed a cumulo-like mass. At 1737 there was a big gas release, part of which descended the cone slope while the main cloud rose and curled N over the crater. After this the intensity of the activity from the cone diminished and gas clouds became light gray.

On 7 September a faint brown haze was noted over Sabancaya at 0630. Dust in the atmosphere obscured viewing. Gas clouds were observed at 0643, 0704, 0719, and 1210. Visibility improved around mid-day, and ashfall was observed on the S side of the cone at 1243. At 1652 a small gas cloud descended the upper slopes. From 1740 until dark, gas emissions were continuous, but none were seen the following day. On 9 September observers on a morning flight around the volcano observed light emissions from fumaroles on the N and S crater rims. Fresh sulfur deposits existed on the crater walls. The crater itself was deeper than the year before and the floor could not be seen. Recent ash eruptions had covered the ice walls on the E side.

Information Contacts: Mark Bulmer, Frederick Engle, and Andrew Johnston, Center for Earth and Planetary Studies, National Air and Space Museum, Smithsonian Institution, Washington DC 20560-0315 USA (Email: mbulmer@ceps.nasm.edu); Guido Salas, Departamento Academico de Geoloia y Geofisica, Universidad Nacional de San Augustin, Arequipa, Perú; Elian Perea, Universidad Nacional de San Augustin, Arequipa, Perú.

May 2000 (BGVN 25:05) Cite this Report

During 28 April-10 May observers saw continuous gas plumes, some containing ash

A team of geologists monitored Sabancaya from the settlement of Sallalli on the E flank of the volcano during the daylight hours from 28 April to 10 May. In this period, gas emissions from the active crater fluctuated but were less than those observed in 1998 (BGVN 23:08 and 23:09).

During much of the current visit, a continual background emission was observed rising from the whole crater. Vigorous activity also occurred from three fumaroles located on the S, E, and N rims of the crater. The fumarole on the S rim was most active, with emissions every 1-3 minutes, while the fumarole on the N rim was the most sporadic.

During periods of calm air, gas clouds the width of the crater rose 1,000 m before dissipating, but summit level winds often sheared gas clouds 200-300 m above the vent. Emissions were predominantly white in color, but occasionally were gray or brown and appeared to contain ash. Localized fresh ash deposits were observed on the S flank of the cone. Material was also observed cascading from the ice wall on the E side of the cone forming small talus aprons.

Strong sulfurous smells were noted on five separate days while observers conducted topographic surveys on the lava flows. These coincided with winds blowing downslope from the summit.

While in the town of Arequipa, the group visited the Universidad San Augustin and reviewed the seismic records for Sabancaya and the Colca Valley over the period 1987 to the present. These data failed to reveal any direct correlation between eruptions of Sabancaya and the succession of earthquakes that occurred in the Colca Valley during 1990-1991 (BGVN 16:07).

Frequent seismic swarms have occurred in the Colca Valley around the towns of Lari and Cabana Conde but have shown no correlation with the low level eruptions at Sabancaya. In 1991, the local press (El Correo, 3 May, 1991) reported a correlation between a rise in the geothermal water temperature in the Colca Valley and the activity at Sabancaya but no geophysical data can be provided to support this correlation. Examination of the seismic records for Sabancaya suggests that the magma chamber is isolated.

Information Contacts: Mark Bulmer, Center for Earth and Planetary Studies, National Air and Space Museum, Washington DC 20560-0315 (Email: mbulmer@ceps.nasm.edu); Tracy Gregg, Department of Geological Sciences, SUNY Buffalo, NY 14260-3050; Stephen Metzger, Department of Geology, University of Nevada Reno, NV 89557; Steve Schubring, Department of Geography, Geology, and Anthropology, Indiana State University, IN 47802 USA; Jeff Byrnes, Department of Geology and Planetary Sciences, University of Pittsburgh, PA 15260 USA; Guido Salas, Departamento de Geología y Geofísica, Universidad Nacional de San Agustín, Arequipa, Perú.

May 2003 (BGVN 28:05) Cite this Report

Inflation at Hualca Hualca detected by satellite surveys from June 1992 to April 1996

A satellite-based interferometric synthetic aperture radar (InSAR) survey of the remote central Andes volcanic arc (Pritchard and Simons, 2002) revealed deformation in the Sabancaya area during June 1992-mid 1997. Inflation was detected ~2.5 km E of the Hualca Hualca cone and 7 km N of Sabancaya (figure 16), with the maximum deformation rate in the radar line-of-sight being ~2 cm/year. While not temporally well-constrained, this inflation seems to have stopped in 1997, perhaps related to the large eruption of Sabancaya in May 1997 (BGVN 22:07). No deformation was observed between mid 1997-December 2001. The inferred source depth was 11-13 km below sea level. Additional details about the study and analysis are available in Pritchard and Simons (2002).

Reference. Pritchard, M., and Simons, M., 2002, A satellite geodetic survey of large-scale deformation of volcanic centres in the Central Andes: Nature, v. 418, p. 167-170.

Information Contacts: Matthew Pritchard and Mark Simons, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA (Email: matt@gps.caltech.edu, URL: http://www.gps.caltech.edu/).

January 2004 (BGVN 29:01) Cite this Report

New ashfall during July 2003

As previously reported in BGVN 28:05 no deformation had been observed during mid-1997 through December 2001. In mid-2003 observers saw evidence of recent ash emissions.

On 31 July 2003, during a commercial flight from Cusco to Arequipa, Mike Sheridan observed ashfall deposits on fresh snow at Sabancaya volcano. The flight path was S of the volcano on a cloud-free day, and fresh snowfall had occurred a day or two before. Ashfall deposits blanketed the cone's summit and, on the NE side, extended to the volcano's base. Two days later, when traveling by car, Sheridan and Jean-Claude Thouret observed the ash from the E. They saw ash down to ~ 5,000 m elevation. The ash blanket appeared comparable to those observed at Sabancaya in the 1990s.

Information Contacts: Michael F. Sheridan, SUNY at Buffalo, Dept. of Geology, Buffalo, NY 14260 (mfs@acsu.buffalo.edu); Jean-Claude Thouret, Centre de Recherches Volcanologiques, 5 rue Kessler, 63038 Clermont-Ferrand, France (Email: thouret@opgc. univ-bpclermont.fr).

February 2013 (BGVN 38:02) Cite this Report

Increased seismic and fumarolic activity in late 2012 and early 2013

Sabancaya volcano, located 72 km NW of Arequipa city, is one of the most active volcanoes of the Central Andes (figure 10). Our last report of Sabancaya described ashfall during July 2003 (BGVN 29:01). This report describes an increase in anomalous seismic and fumarolic activity, beginning in late 2012 and continuing through the end of March 2013. The restlessness spurred increased monitoring of the volcano.

Figure 10. A map illustrating hazards at the Ampato-Sabancaya volcanic complex (high danger, red; moderate danger, orange; and low danger, yellow). Types of volcanic hazards include pyroclastic flows (including debris flows), mudflows, lava flows, and avalanches. The overall thickness of ash deposits from eruptions during 1990-1998 is indicated by 1 and 0.1 cm isopachs. Major roads and highways are shown as thick, dark red lines; thin lighter red lines are elevation contours. The map shown is featured on a poster with more details. From Mariño and others (2013).

Between 1988 and 1997, activity at Sabancaya was intermittent and characterized by low to moderate Vulcanian eruptions (VEI 2) and mainly modest eruption columns (less than 5 km above the summit) with local ashfall (e.g., SEAN 13:06; BGVN 19:03). After this eruptive episode, between 1998 and 2012, minor and intermittent fumarolic emissions rose from the active crater. During the last months of 2012, a slight increase of fumarolic activity was observed during a field campaign by Peru’s Instituto Geológico Minero y Metalúrgico (INGEMMET) volcanologists and their counterparts from the Laboratoire Magmas et Volcans (Clermont-Ferrand, France).

The Instituto Geofisico del Peru (IGP) reported that inhabitants from Sallalli hamlet, ~ 11 km S of Sabancaya, observed an increase in fumarolic emissions beginning 5 December 2012. Meteorological conditions prevented IGP scientists from visiting the area during the rainy season.

In mid-February 2013, local residents reported an increase in fumarolic activity, which was confirmed by INGEMMET scientists that visited the volcano on 15 and 22-23 February (figure 11). Scientists also reported a strong sulfur odor within an 8-km radius, and felt several strong earthquakes probably associated with the volcano’s unrest.

Figure 11. Photograph taken of a gas plume above the active vent of Sabancaya, as seen from the SE flank on 17 February 2013. Courtesy of Pablo Samaniego, IRD.

IGP reported that within a span of 95 minutes on 22 February 2013, three earthquakes, of M 4.6, 5.2, and 5.0 respectively, were registered at Sabancaya (figure 12). This activity prompted IGP to install a network of close proximity seismic stations. Earthquakes continued through the following day (23 February) and caused damage at Maca village, 20 km NE of the crater.

Figure 12. The principal earthquakes (red dots) registered at Sabancaya on 22 February 2013. Of these, three earthquakes of M 4.6, 5.2, and 5.0 occurred within a span of 95 minutes. Courtesy of IGP.

During 22-23 February, a seismic station installed by INGEMMET registered more than 500 small volcano tectonic (VT) seismic events at Sabancaya. On 23 February IGP separately reported 560 events at the Cajamarcana seismic station (CAJ on figure 13b) on the SE flank. According to a Reuters article from 27 February, 80 homes were damaged by the seismicity during 22-23 February, leading to some evacuations. During that seismicity, a plume rose ~100 m above Sabancaya. After 24 February, VT, long period (LP), and hybrid seismicity continued (figure 13).

Figure 13. (a) Plot of daily earthquakes at Sabancaya, showing the number of volcano tectonic, long period, and hybrid events that occurred during 24 February-27 March 2013. (b) The locations of earthquake epicenters on 27 March 2013 (red dots) and the seismic stations that were monitoring the volcano as of that date (yellow triangles). Courtesy of IGP.

Reference. Mariño J., Samaniego P., Rivera M., Bellot N., Manrique N., Macedo L., Delgado R., 2013, Mapa de peligros del Complejo Volcánico Ampato-Sabancaya, Esc. 1:50.000. Edit. INGEMMET-IRD.

Information Contacts: Instituto Geológico Minero y Metalúrgico (INGEMMET), Av. Dolores (Urb. Las Begonias B-3), J.L. Bustamante y Rivero, Arequipa, Perú (URL: http://www.ingemmet.gob.pe); Pablo Samaniego Eguiguren, Laboratoire Magmas et Volcans, Université Blaise Pascal, Le Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Casilla 18-1209, Calle Teruel 357 - Miraflores, Lima 18 - PERU (URL: wwwobs.univ-bpclermont.fr/lmv/pperm/samaniego_p/index.php); Reuters, report by Lima Newsroom; Orlando Macedo, PhD, Chief of Volcanology Research Department, Instituto Geofisico del Peru, (IGP), Arequipa Volcano Observatory, Urb. La Marina B-19, Cayma, Arequipa, Peru.

May 2016 (BGVN 41:05) Cite this Report

Increased seismicity February 2013; explosive events in August 2014

Although historical records of eruptive activity at Peru's Sabancaya volcano go back to 1750, there have only been a handful of eruptions documented since the 1980s; activity that began in 1986 was the first recorded in over 200 years. Weak solfataric activity from vents within and outside the 350-m-wide summit crater since then has created a persistent risk of ash plumes, Vulcanian explosions, and glacial melting causing mudflows. Reports of fresh ashfall on snow-covered slopes in 2003 (BGVN 29:01) indicated that some level of eruptive activity was continuing into the early 2000's. An increase in seismic and fumarolic activity in late 2012 and 2013 led to increased monitoring at the volcano, located 72 km NW of Arequipa. IGP-OVS (Instituto Geofisico del Peru, Observatoria Vulcanologico del Sur) and OVI-INGEMMET (Observatorio Volcanologico del INGEMMET, Instituto Geológical Minero y Metalúrgico) installed a number of seismic stations after significant seismic events in February 2013 (reported on in BGVN 38:02) caused damage to numerous homes in the area.

While the data reported by Peru's IGP-OVS and OVI-INGEMMET indicate ongoing seismic activity beginning in February 2013, and two phreatic-type explosions on 9 and 25 August 2014, no substantial eruption of ash was reported between February 2013 and February 2016. Numerous VAAC (Volcanic Ash Advisory Center) reports of ash were reported by pilots, but the Buenos Aires VAAC noted that no ash plume was visible either on satellite images or from the web camera located near the volcano. Occasional references to "possible light volcanic ash" are mentioned in some VAAC reports, but generally not corroborated with visual or satellite information. A few photographs from the area appear to show trace amounts of fine ash or particulates from magmatic gases in the snow around the crater, but such deposits were not confirmed by fieldwork. Throughout the period, Sabancaya emitted significant water vapor plumes occasionally as high as 3,000 m, and SO₂-rich magmatic gases that were blue in color and possibly contained trace amounts of ash.

Activity during 2013 and 2014. After a decade of quiet, a significant increase in fumarolic emissions was observed in late 2012 (BGVN 38:02). Throughout 2013 earthquakes were concentrated in areas NE, N and NW of the crater up to 25 km away; much of this seismicity was later interpreted by IGP-OVS to be related to regional tectonism and not to volcanic activity. An increase in SO₂ emissions, seen as bluish gas emitting from the fumaroles, was observed in March 2013, but a field visit in May noted no fresh lava or ash in the area.

White, gray, and bluish SO₂-rich fumarolic emissions increased in June 2014. VT (volcano-tectonic) earthquakes were recorded within 1.7 km of the crater in early July; IGP-OVS seismologists identified hybrid-type seismic events that they associated with the rise of magmatic material near the crater in early July. By mid-July, VT earthquakes were averaging over 200 per day, and the foci were located 12 km NNE of the crater. During late July, seismic events decreased, and the foci moved to 8 km N of the crater. Persistent off-white and bluish fumaroles rose 500-600 m above the crater during July 2014.

Fumarolic emissions intensified markedly on 5 August 2014, rising to 3 km above the crater; whitish water vapor, bluish magmatic gases, and gray emissions were observed, suggesting a "possible release of minor volcanic ash", as reported by IGP-OVS. The VT seismic events also began to increase in magnitude, ranging between 2.5 and 4.6 ML, including two located very close to the crater, between 4 and 14 km deep. Both LP and Hybrid seismic events, increased to hundreds of events per day in the early days of August. At 0429 local time on 9 August 2014 a large explosion was recorded; it was not observed due to darkness and cloud cover. After the explosions, VT events dropped back to tens per day, and emissions rose to between 500 and 1,000 m above the crater. Many of the earthquakes were located within 1.5 km of the crater at depths between 4 and 14 km. On 25 August beginning at 2039 local time four consecutive explosions lasting a total of 82 seconds were recorded (figure 14). Again, due to darkness, there was no visual confirmation of the explosion.

Figure 14. Seismograph from 25 August 2014 at SAB seismic station, located 3 km from the top of Sabancaya. Four explosive events occurred in the crater area at 2039 local time, followed by numerous small earthquakes. The energy calculated by IGP-OVS for this sequence of events was 1,151 MJ, with a total duration of 82 seconds. Courtesy of IGP-OVS (2014 Annual Report, Sabancaya).

In the days between the 9 and 25 August explosions, observed emissions from the fumaroles were water vapor and bluish magmatic gases rising to heights between 500 and 1,500 m above the crater (figure 15).

Figure 15. Emissions from Sabancaya on 13 August 2014. White vapor plumes and bluish SO2-rich magmatic gases are emitting from the crater. Courtesy of IGP-OVS (2014 Annual report, Sabancaya).

Water vapor and magmatic gas plume heights in September 2014 rose between 500 and 2,000 m above the crater. OVI-INGEMMET daily reports noted grayish plumes containing "possible ash" on 26 and 29 September 2014.

In October 2014, fumarolic emission heights were below 1 km above the crater; they were generally white steam plumes but also showed significant bluish SO₂ content. Constant emissions of water vapor and SO₂ to heights of 1,400 m above the floor of the crater continued into November along with intermittent seismic activity at constant levels since August. Seismicity increased slightly in early December and fumaroles of water vapor and SO₂ were observed rising to heights between 500 and 1,600 m above the crater floor. Seismic signals characteristic of a mudflow were recorded in mid-December 2014 in the ravine between Sabancaya and Ampato, the large volcano immediately SW.

Buenos Aires VAAC reports in 2014 were all ambiguous as to the presence of ash from Sabancaya. A "faint ash cloud" was detected in visible imagery on 14 July 2014. Numerous pilot reports of ash between August and December were not verified by satellite imagery under clear skies, and the webcam usually revealed water vapor emissions or cloud cover at the summit at the time of most of the reports. VAAC reports that do mention "possible minor volcanic ash" were given on 16 September, 23 October, 10 November, and 27 December 2014.

Activity during 2015 and early 2016. A similar level of activity continued during 2015. Neither OVI-INGEMMET nor IGP-OVA reported explosions with ash emissions during the year. Constant emissions of steam and bluish magmatic gases were observed from the fumaroles within the crater. Plumes of water vapor and magmatic gases rose to 1 km above the crater in January and to 1.2 km in February. From March through May seismic activity remained steady and fumarolic plumes were consistently below 1 km above the crater.

Seismicity increased during June 2015. Fumarolic plume heights also increased to 2.4 km above the crater, and bluish SO₂-rich gases were frequently observed. During July, some seismic events were located within 3 km of the crater, and fumarolic plumes rose to 2 km. Volcanologists from OVI-INGEMMET visited on 10 July 2015 and observed trace amounts of ashfall or particulates from SO₂ emissions in the vicinity of the crater (figure 16). IGP-OVS scientists who visited in late July to make temperature measurements observed constant water vapor and magmatic gas emissions. The temperature at the side of the dome was measured at 81°C, and the hottest points at the bottom of the crater were 391° and 280°C.

Figure 16. Crater inspection of Sabancaya on 10 July 2015 where trace amounts of ash or particulates from SO2 emissions were observed. Courtesy of OVI-INGEMMET.

During late August 2015 and the first week of September seismicity increased significantly, and was located within 6 km of the crater at depths between 6 and 9 km. Fumarolic emissions ranged between 600 and 1,600 m above the crater. Seismicity was low during October. An IGP-OVS visit on 1 October obtained temperature data similar to that collected in late July. The expedition reported the absence of recently deposited solid material in the vicinity of the crater, and also observed the constant emission of steam and magmatic gases (figure 17).

Figure 17. Emissions of white steam and bluish magmatic gases from Sabancaya in the early hours of 1 October 2015. Courtesy of IGP-OVA (2015 Annual report, Sabancaya).

VT seismicity remained low in November 2015, but an increase in the second week in December included two events (4.0 and 3.6) located within 2 km of the volcano. Constant emissions of water vapor and magmatic gases rising to 1,100 m were observed.

Buenos Aires VAAC reports for 2015 were again ambiguous about the presence of ash. Many reports note that pilot observations of ash clouds were not corroborated by satellite or webcam images. However, on several occasions, the VAAC reports indicated that the webcam showed continuous emission of steam, gases, and "possible light volcanic ash" (8 March, 19 May, 15 and 21 June, 18 and 21 July, 26 August, 10 October, 6 November and 12 December).

Sabancaya maintained a similar level of seismic and fumarolic unrest through February 2016 that was monitored and reported by both OVI-INGEMMET and IGP-OVS. OVI-INGEMMET reported plume heights of water vapor in early January as high as 2,000 m above the crater, gradually decreasing to below 1,000 m in early February. The intermittent presence of magmatic gases was also noted during this time.

While there have not been substantial ash emissions since renewed seismic activity began in 2013, there have been measurable SO₂ emissions observed by IGP-OVS and recorded by NASA's OMI instrument (figure 18). Emissions of SO₂ recorded on 27 December 2014 (0.937 kT), 3 April 2015 (0.750 kt), 28 November 2015 (0.773 kt), 25 February 2016 (0.365 kt) appear most likely to have originated at Sabancaya.

Figure 18. Four different images from the OMI instrument satellite data from NASA's Goddard Space Flight Center showing SO2 anomalies possibly attributable to Sabancaya (upper left triangle). The image dates are 27 December 2014 (top left), 3 April 2015 (top right), 28 November 2015 (bottom left), and 25 February 2016 (bottom right). Courtesy of NASA Goddard Space Flight Center.

Information Contacts: Instituto Geofisico del Peru, Observatoria Vulcanologico del Sur (IGP-OVS), Arequipa Regional Office, Urb La Marina B-19, Cayma, Arequipa, Peru (URL: http://ovs.igp.gob.pe/); Observatorio Volcanologico del INGEMMET, (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, (URL: http://ovi.ingemmet.gob.pe); Buenos Aires Volcanic Ash Advisory Center (VAAC), Servicio Meteorológico Nacional-Fuerza Aérea Argentina, 25 de mayo 658, Buenos Aires, Argentina (URL: http://www.smn.gov.ar/vaac/buenosaires/inicio.php?lang=es); NASA Goddard Space Flight Center, Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, (URL: http://so2.gsfc.nasa.gov/index.html).