Pacaya is one of the most active volcanoes in Guatemala, with activity largely consisting of frequent lava flows and Strombolian activity at the Mackenney crater. This report summarizes continued activity during February through July 2019 based on reports by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) and Sistema de la Coordinadora Nacional para la Reducción de Desastres (CONRED), visiting scientists, and satellite data.

At the beginning of February activity included Strombolian explosions ejecting material up to 5 to 30 m above the Mackenney crater and a degassing plume up to 300 m. Multiple lava flows were observed throughout the month on the N, NW, and W flanks, reaching 350 m from the crater and resulting in avalanches from the flow fronts. Strombolian activity continued with sporadic to continuous explosions ejecting material 5-75 m above the Mackenney crater. Degassing produced plumes up to 300 m above the crater, and incandescence from the crater and lava flows were seen at night. Daniel Sturgess of Bristol University observed activity on the 24th, noting a 70-m-long lava flow with individual blocks from the front of the flow rolling down the flanks (figure 108). He reported that mild Strombolian explosions occurred every 10-20 minutes and ejected blocks, up to approximately 4 m in diameter, as high as 5-30 m above the crater and towards the northern flank.

Figure 108. An active lava flow on the NW flank of Pacaya on 24 February 2019 with incandescence visible in lower light conditions. Courtesy of Daniel Sturgess, University of Bristol.

Similar activity continued through March with multiple lava flows reaching a maximum of 200 m N and NW, and avalanches descending from the flow fronts. Ongoing Strombolian explosions expelled material up to 75 m above the Mackenney crater. Degassing produced a white-blue plume to a maximum of 900 m above the crater (figure 109) and incandescence was noted some nights.

Figure 109. A degassing plume at Pacaya reaching 350 m above the crater and dispersing to the S on 19 March 2019. Courtesy of CONRED.

During April lava flows continued on the N and NW flanks, reaching a maximum length of 300 m, with avalanches forming from the flow fronts. Degassing formed plumes up to 600 m above the crater that dispersed with various wind directions. Strombolian activity continued with explosions ejecting material up to 40 m above the crater. On the 2nd and 3rd weak rumbles were heard at distances of 4-5 km. Similar activity continued through May with lava flows reaching 300 m to the N, degassing producing plumes up to 600 m above the crater, and Strombolian explosions ejecting material up to 15 m above the crater.

Lava flows continued out to 300 m in length to the N and NW during June (figures 110 and 111). Strombolian activity ejected material up to 30 m above the crater and degassing resulted in plumes that reached 300 m. During July there were multiple active lava flows that reached a maximum of 300 m in length on the N and NW flanks (figure 112). Avalanches generated by the collapse of material at the front of the lava flows were accompanied by explosions ejecting material up to 30 m above the crater.

Figure 110. An active lava flow on Pacaya on 9 June 2019 with incandescent blocks rolling down the flank from the flow front. Courtesy of Paul Wallace, University of Liverpool.

Figure 111. Activity at Pacaya on 22 June 2019 with a degassing plume dispersed to the W and a 300-m-long lava flow. Photos by Miguel Morales, courtesy of CONRED.

Figure 112. Two lava flows were active to the N and NW at Pacaya on 20 July 2019. Photos courtesy of CONRED.

During February through July multiple lava flows and crater activity were detected in Sentinel-2 satellite thermal images (figures 113 and 114) and relatively constant thermal energy was detected by the MIROVA system with a slight decrease in the energy and frequency of anomalies during June (figure 115). The thermal anomalies detected by the MODVOLC system for each month from February through July spanned 6-30, with six during June and 30 during April.

Figure 113. Sentinel-2 thermal satellite images of Pacaya show lava flows to the N and NW during February through April 2019. There was a reduction in visible activity in early March. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 114. Sentinel-2 thermal satellite images of Pacaya showing lava flow and hot avalanche activity during June and July 2019. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 115. MIROVA log radiative power plot of MODIS thermal infrared at Pacaya during October 2018 through July 2019. Detected thermal energy is relatively stable with a decrease through June and subsequent increase during July. Courtesy of MIROVA.

Geologic Background. Eruptions from Pacaya, one of Guatemala's most active volcanoes, are frequently visible from Guatemala City, the nation's capital. This complex basaltic volcano was constructed just outside the southern topographic rim of the 14 x 16 km Pleistocene Amatitlán caldera. A cluster of dacitic lava domes occupies the southern caldera floor. The post-caldera Pacaya massif includes the ancestral Pacaya Viejo and Cerro Grande stratovolcanoes and the currently active Mackenney stratovolcano. Collapse of Pacaya Viejo between 600 and 1500 years ago produced a debris-avalanche deposit that extends 25 km onto the Pacific coastal plain and left an arcuate somma rim inside which the modern Pacaya volcano (Mackenney cone) grew. A subsidiary crater, Cerro Chino, was constructed on the NW somma rim and was last active in the 19th century. During the past several decades, activity has consisted of frequent strombolian eruptions with intermittent lava flow extrusion that has partially filled in the caldera moat and armored the flanks of Mackenney cone, punctuated by occasional larger explosive eruptions that partially destroy the summit of the growing young stratovolcano.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Daniel Sturgess, School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, United Kingdom (URL: http://www.bristol.ac.uk/earthsciences/); Paul Wallace, Department of Earth, Ocean and Ecological Sciences, University of Liverpool, 4 Brownlow Street, Liverpool L69 3GP, United Kingdom (URL: https://www.liverpool.ac.uk/environmental-sciences/staff/paul-wallace/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

Frequent historical eruptions at Volcán de Colima date back to the 16th century and include explosive activity, lava flows, and large debris avalanches. The most recent eruptive episode began in January 2013 and continued through March 2017. Previous reports have covered activity involving ash plumes with extensive ashfall, lava flows, lahars, and pyroclastic flows (BGVN 41:01 and 42:08). In late April 2019, increased seismicity related to volcanic activity began again. This report covers activity through July 2019. The primary source of information was the Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC).

On 11 May 2019, CUEIV-UdC reported an explosion that was recorded by several monitoring stations. A thermal camera located south of Colima captured thermal anomalies associated with the explosion as well as intermittent degassing, which mainly consisted of water vapor (figure 131). A report from the Unidad Estatal de Protección Civil de Colima (UEPCC), and seismic and infrasound network data from CUEIV-UdC, recorded about 60 high-frequency events, 16 landslides, and 14 low-magnitude explosions occurring on the NE side of the crater during 11-24 May. Drone imagery showed fumarolic activity occurring on the inner wall of this crater on 22 May (figure 132).

Figure 131. Gas emissions from Colima during the 11 May 2019 eruption as seen from the Naranjal station. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 17 mayo 2019 no 121).

Figure 132. A drone photo showing fumarolic activity occurring within the NE wall of the crater at Colima on 22 May 2019. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 24 mayo 2019 no 122).

Small explosions and gas-and-steam emissions continued intermittently through mid-July 2019 concentrated on the NE side of the crater. An overflight on 9 July 2019 revealed that subsidence from the consistent activity slightly increased the diameter of the vent; other areas within the crater also showed evidence of subsidence and some collapsed material on the outer W wall (figure 133). During the weeks of 19 and 26 July 2019, monitoring cameras and seismic data recorded eight lahars.

Figure 133. A drone photo of the crater at Colima on 8 July 2019 shows continuing fumarolic activity and evidence of a collapsed wall on the W exterior side. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 12 julio 2019 no 129).

Geologic Background. The Colima volcanic complex is the most prominent volcanic center of the western Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4320 m high point of the complex) on the north and the 3850-m-high historically active Volcán de Colima at the south. A group of cinder cones of late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima complex. Volcán de Colima (also known as Volcán Fuego) is a youthful stratovolcano constructed within a 5-km-wide caldera, breached to the south, that has been the source of large debris avalanches. Major slope failures have occurred repeatedly from both the Nevado and Colima cones, and have produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions date back to the 16th century. Occasional major explosive eruptions (most recently in 1913) have destroyed the summit and left a deep, steep-sided crater that was slowly refilled and then overtopped by lava dome growth.

Information Contacts: Centro Universitario de Estudios e Investigaciones de Vulcanologia, Universidad de Colima (CUEIV-UdC), Colima, Col. 28045, Mexico; Centro Universitario de Estudios Vulcanologicos y Facultad de Ciencias de la Universidad de Colima, Avenida Universidad 333, Colima, Col. 28045, Mexico (URL: http://portal.ucol.mx/cueiv/); Unidad Estatal de Protección Civil, Colima, Roberto Esperón No. 1170 Col. de los Trabajadores, C.P. 28020, Mexico (URL: http://www.proteccioncivil.col.gob.mx/).

Masaya, in Nicaragua, contains a lava lake found in the Santiago Crater which has remained active since its return in December 2015 (BGVN 41:08). In addition to this lava lake, previous volcanism included explosive eruptions, lava flows, and gas emissions. Activity generally decreased during March-July 2019, including the number and frequency of thermal anomalies, lava lake levels, and gas emissions. The primary source of information for this report comes from the Instituto Nicareguense de Estudios Territoriales (INETER).

On 21 July 2019 a small explosion in the Santiago Crater resulted in some gas emissions and an ash cloud drifting WNW. In addition to the active lava lake (figure 77), monthly reports from INETER noted that thermal activity and gas emissions (figure 78) were decreasing.

Figure 77. Active lava lake visible in the Santiago Crater at Masaya on 27 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

Figure 78. Gas emissions coming from the Santiago Crater at Masaya on 29 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

On 15 May and 22 July 2019, INETER scientists used a FLIR SC620 thermal infrared camera to measure temperatures of fumaroles on the Santiago Crater. In May 2019 the temperature of fumaroles had decreased by 48°C since the previous month. Between May and July 2019 fumarole temperatures continued to decline; temperatures ranged from 90° to 136°C (figure 79). Compared to May 2019 these temperatures are 3°C lower. INETER reports that the level of the lava lake has been slowly dropping during this reporting period.

Figure 79. FLIR (forward-looking infrared) and visible images of the Santiago Crater at Masaya showing fumarole temperatures ranging from 90° to 136°C. The scale in the center shows the range of temperatures in the FLIR image. Courtesy of INETER (March 2019 report).

According to MIROVA (Middle InfraRed Observation of Volcanic Activity) data from MODIS satellite instruments, frequent thermal anomalies were recorded from mid-March through early May 2019, with little to no activity from mid-May to July 2019 (figure 80). Sentinel-2 thermal images show high temperatures in the active lava lake on 10 March 2019 (figure 81). Thermal energy detected by the MODVOLC algorithm showed 14 hotspot pixels with the most number of hotspots (7) occurring in March 2019.

Figure 80. Thermal anomalies were relatively constant at Masaya from early September 2018 through early May 2019 and then abruptly decreased until mid-June 2019 as recorded by MIROVA. Courtesy of MIROVA.

Figure 81. Sentinel-2 thermal satellite image showing a detected heat signature from the active lava lake at Masaya on 10 March 2019. The lava lake is visible (bright yellow-orange). Approximate diameter of the crater containing the lava lake is 500 m. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Geologic Background. Masaya is one of Nicaragua's most unusual and most active volcanoes. It lies within the massive Pleistocene Las Sierras pyroclastic shield volcano and is a broad, 6 x 11 km basaltic caldera with steep-sided walls up to 300 m high. The caldera is filled on its NW end by more than a dozen vents that erupted along a circular, 4-km-diameter fracture system. The twin volcanoes of Nindirí and Masaya, the source of historical eruptions, were constructed at the southern end of the fracture system and contain multiple summit craters, including the currently active Santiago crater. A major basaltic Plinian tephra erupted from Masaya about 6500 years ago. Historical lava flows cover much of the caldera floor and have confined a lake to the far eastern end of the caldera. A lava flow from the 1670 eruption overtopped the north caldera rim. Masaya has been frequently active since the time of the Spanish Conquistadors, when an active lava lake prompted attempts to extract the volcano's molten "gold." Periods of long-term vigorous gas emission at roughly quarter-century intervals cause health hazards and crop damage.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Sheila DeForest (URL: https://www.facebook.com/sheila.deforest).

The acid lake of Rincón de la Vieja's active crater has generated intermittent weak phreatic explosions regularly since 2011, continuing during the past year through at least August 2019. The volcano is monitored by the Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), and the information below comes from its weekly bulletins between 4 March and 2 September 2019. Clouds often prevented webcam and satellite views. The current report describes activity from March through July 2019.

OVSICORI-UNA reported that weak events occurred on 19 March at 1851 and on 29 March 2019 at 2043. A two-minute-long phreatic explosion on 1 April at 0802 produced a plume that rose 600 m above the crater rim. Continuous emissions were visible during 3-4 April, rising 200 m above the crater rim. On 3 April, at 1437, a small explosion was detected. An explosion on 10 April at 0617 produced a gas-and-steam plume that rose 1 km above the crater rim and drifted SE. On 12 April at 0643, a plume rose 500 m. Another event took place at 0700 on 13 April, although poor weather conditions prevented visual observations. On 14 April, OVSICORI-UNA noted that aerial photographs showed a milky-gray acid lake at a relatively low water level with convection cells of several tens meters of diameter in the center and eastern parts of the lake.

According to an OVSICORI-UNA bulletin, a small phreatic explosion occurred on 1 May. Another explosion on 11 May at 0720 produced a white gas-and-steam plume that rose 600 m above the crater rim. Phreatic explosions were recorded on 14 May at 1703 and on 17 May at 0357, though dense fog prevented visual confirmation of both events with webcams. On 15 May a local observer noted a diffuse plume of steam and gas, material rising from the crater, and photographed milky-gray deposits on the N part of the crater rim ejected from the event the day before. A major explosion occurred on 24 May.

OVSICORI-UNA recorded a significant phreatic 10-minute-long explosion that began on 11 June at 0343, but plumes were not visible due to weather conditions. No further phreatic events were reported in July.

Seismic activity was very low during the reporting period, and there was no significant deformation. Short tremors were frequent toward the end of April, but were only periodic in May and June; tremor almost disappeared in July. A few long-period earthquakes were recorded, and volcano-tectonic earthquakes were even less frequent.

Geologic Background. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge that was constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of 1916-m-high Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide crater. A plinian eruption producing the 0.25 km3 Río Blanca tephra about 3500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/, https://www.facebook.com/OVSICORI/).

Sakurajima rises from Kagoshima Bay, which fills the Aira Caldera near the southern tip of Japan's Kyushu Island. Frequent explosive and occasional effusive activity has been ongoing for centuries. The Minamidake summit cone has been the location of persistent activity since 1955; the Showa crater on its E flank has also been intermittently active since 2006. Numerous explosions and ash-bearing emissions have been occurring each month at either Minamidake or Showa crater since the latest eruptive episode began in late March 2017. This report covers ongoing activity from January through June 2019; the Japan Meteorological Agency (JMA) provides regular reports on activity, and the Tokyo VAAC (Volcanic Ash Advisory Center) issues tens of reports each month about the frequent ash plumes.

From January to June 2019, ash plumes and explosions were usually reported multiple times each week. The quietest month was June with only five eruptive events; the most active was March with 29 (table 21). Ash plumes rose from a few hundred meters to 3,500 m above the summit during the period. Large blocks of incandescent ejecta traveled as far as 1,700 m from the Minamidake crater during explosions in February and April. All the activity originated in the Minamidake crater; the adjacent Showa crater only had a mild thermal anomaly and fumarole throughout the period. Satellite imagery identified thermal anomalies inside the Minamidake crater several times each month.

Table 21. Monthly summary of eruptive events recorded at Sakurajima's Minamidake crater in Aira caldera, January-June 2019. The number of events that were explosive in nature are in parentheses. No events were recorded at the Showa crater during this time. Data courtesy of JMA (January to June 2019 monthly reports).

There were eight eruptive events reported by JMA during January 2019 at the Minamidake summit crater of Sakurajima. They occurred on 3, 6, 7, 9, 17, and 19 January (figure 76). Ash plume heights ranged from 600 to 2,100 m above the summit. The largest explosion, on 9 January, generated an ash plume that rose 2,100 m above the summit crater and drifted E. In addition, incandescent ejecta was sent 800-1,100 m from the summit. Incandescence was visible at the summit on most clear nights. During an overflight on 18 January no significant changes were noted at the crater (figure 77). Infrared thermal imaging done on 29 January indicated a weak thermal anomaly in the vicinity of the Showa crater on the SE side of Minamidake crater. The Kagoshima Regional Meteorological Observatory (KRMO) (11 km WSW) recorded ashfall there during four days of the month. Satellite imagery indicated thermal anomalies inside Minamidake on 7 and 27 January (figure 77).

Figure 76. Incandescent ejecta and ash emissions characterized activity from Sakurajima volcano at Aira during January 2019. Left: A webcam image showed incandescent ejecta on the flanks on 9 January 2019, courtesy of JMA (Explanation of volcanic activity in Sakurajima, January 2019). Right: An ash plume rose hundreds of meters above the summit, likely also on 9 January, posted on 10 January 2019, courtesy of Mike Day.

Figure 77. The summit of Sakurajima consists of the larger Minamidake crater and the smaller Showa crater on the E flank. Left: The Minamidake crater at the summit of Sakurajima volcano at Aira on 18 January 2019 seen in an overflight courtesy of JMA (Explanation of volcanic activity in Sakurajima, March 2019). Right: Two areas of thermal anomaly were visible in Sentinel-2 satellite imagery on 27 January 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

Activity increased during February 2019, with 15 eruptive events reported on days 1, 3, 7, 8, 10, 13, 14, 17, 22, 24, and 27. Ash plume heights ranged from 600-2,300 m above the summit, and ejecta was reported 300 to 1,700 m from the crater in various events (figure 78). KRMO reported two days of ashfall during February. Satellite imagery identified thermal anomalies at the crater on 6 and 26 February, and ash plumes on 21 and 26 February (figure 79).

Figure 78. An explosion from Sakurajima at Aira on 7 February 2019 sent ejecta up to 1,700 m from the Minamidake summit crater. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, February 2019).

Figure 79. Thermal anomalies and ash emissions were captured in Sentinel-2 satellite imagery on 6, 21, and 26 February 2019 originating from Sakurajima volcano at Aira. Top: Thermal anomalies within the summit crater were visible underneath steam and ash plumes on 6 and 26 February (closeup of bottom right photo). Bottom: Ash emissions on 21 and 26 February drifted SE from the volcano. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

The number of eruptive events continued to increase during March 2019; there were 29 events reported on numerous days (figures 80 and 81). An explosion on 14 March produced an ash plume that rose 3,500 m above the summit and drifted E. It also produced ejecta that landed 800-1,100 m from the crater. During an overflight on 26 March a fumarole was the only activity in Showa crater. KRMO reported 14 days of ashfall during the month. Satellite imagery identified an ash plume on 13 March and a thermal anomaly on 18 March (figure 82).

Figure 80. A large ash emission from Sakurajima volcano at Aira was photographed by a tourist on the W flank and posted on 1 March 2019. Courtesy of Kratü.

Figure 81. An ash plume from Sakurajima volcano at Aira on 18 March 2019 produced enough ashfall to disrupt the trains in the nearby city of Kagoshima according to the photographer. Image taken from about 20 km away. Courtesy of Tim Board.

Figure 82. An ash plume drifted SE from the summit of Sakurajima volcano at Aira on 13 March (left) and a thermal anomaly was visible inside the Minamidake crater on 18 March 2019 (right). "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

A decline in activity to only ten eruptive events on days 7, 13, 17, 22, and 25 was reported by JMA for April 2019. An explosion on 7 April sent ejecta up to 1,700 m from the crater. Another explosion on 13 April produced an ash plume that rose 2,200 m above the summit. Most of the eruptive events at Sakurajima last for less than 30 minutes; on 22 April two events lasted for almost an hour each producing ash plumes that rose 1,400 m above the summit. Ashfall at KRMO was reported during seven days in April. Two distinct thermal anomalies were visible inside the Minamidake crater on both 12 and 27 April (figure 83).

Figure 83. Two thermal anomalies were present inside Minamidake crater at the summit of Sakurajima volcano at Aira on 12 (left) and 27 (right) April 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

There were 15 eruptive events during May 2019. An event that lasted for two hours on 12 May produced an ash plume that rose 2,900 m from the summit and drifted NE (figure 84). The Meteorological Observatory reported 14 days with ashfall during the month. Two thermal anomalies were present in satellite imagery in the Minamidake crater on both 17 and 22 May.

Figure 84. An ash plume rose 2,900 m above the summit of Sakurajima at Aira on 12 May 2019 (left); incandescent ejecta went 1,300 m from the summit crater on 13 May. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, May 2019).

During June 2019 five eruptive events were reported, on 11, 13, and 24 June; the event on 11 June lasted for almost two hours, sent ash 2,200 m above the summit, and produced ejecta that landed up to 1,100 m from the crater (figure 85). Five days of ashfall were reported by KRMO.

Figure 85. A large ash plume on 11 June 2019 rose 2,200 m above the summit of Sakurajima volcano at Aira. Courtesy of Aone Wakatsuki.

Geologic Background. The Aira caldera in the northern half of Kagoshima Bay contains the post-caldera Sakurajima volcano, one of Japan's most active. Eruption of the voluminous Ito pyroclastic flow accompanied formation of the 17 x 23 km caldera about 22,000 years ago. The smaller Wakamiko caldera was formed during the early Holocene in the NE corner of the Aira caldera, along with several post-caldera cones. The construction of Sakurajima began about 13,000 years ago on the southern rim of Aira caldera and built an island that was finally joined to the Osumi Peninsula during the major explosive and effusive eruption of 1914. Activity at the Kitadake summit cone ended about 4850 years ago, after which eruptions took place at Minamidake. Frequent historical eruptions, recorded since the 8th century, have deposited ash on Kagoshima, one of Kyushu's largest cities, located across Kagoshima Bay only 8 km from the summit. The largest historical eruption took place during 1471-76.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Mike Day, Minnesota, Twitter (URL: https://twitter.com/MikeDaySMM, photo at https://twitter.com/MikeDaySMM/status/1083489400451989505/photo/1); Kratü, Twitter (URL: https://twitter.com/TalesOfKratue, photo at https://twitter.com/TalesOfKratue/status/1101469595414589441/photo/1); Tim Board, Japan, Twitter (URL: https://twitter.com/Hawkworld_, photo at https://twitter.com/Hawkworld_/status/1107789108754038789); Aone Wakatsuke, Twitter (URL: https://twitter.com/AoneWakatsuki, photo at https://twitter.com/AoneWakatsuki/status/1138420031258210305/photo/3).

After a large, deadly explosive and effusive eruption during 1963-64, Indonesia's Mount Agung on Bali remained quiet until a new eruption began in November 2017 (BGVN 43:01). Lava emerged into the summit crater at the end of November and intermittent ash plumes rose as high as 3 km above the summit through the end of the year. Activity continued throughout 2018 with explosions that produced ash plumes rising multiple kilometers above the summit, and the slow effusion of the lava within the summit crater (BGVN 43:08, 44:02). Information about the ongoing eruptive episode comes from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), the Darwin Volcanic Ash Advisory Center (VAAC), and multiple sources of satellite data. This report covers the ongoing eruption from February through May 2019.

Intermittent but increasingly frequent and intense explosions with ash emissions and incandescent ejecta characterized activity at Agung during February through May 2019. During February, explosions were reported three times; events on seven days in March were documented with ash plumes and ashfall in surrounding villages. Five significant events occurred during April; two involved incandescent ejecta that traveled several kilometers from the summit, and ashfall tens of kilometers from the volcano. Most of the five significant events reported in May involved incandescent ejecta and ashfall in adjacent villages; air traffic was disrupted during the 24 May event. Ash plumes in May reached altitudes over 7 km multiple times. Thermal activity increased steadily during the period, according to both the MIROVA project (figure 44) and MODVOLC thermal alert data. MAGMA Indonesia reported at the end of May 2019 that the volume of lava within the summit crater remained at about 25 million m³; satellite information indicated continued thermal activity within the crater. Alert Level III (of four levels) remained in effect throughout the period with a 4 km exclusion radius around the volcano.

Figure 44. Thermal activity at Agung from 4 September 2018 through May 2019 was variable. The increasing frequency and intensity of thermal events was apparent from February-May. Courtesy of MIROVA.

Steam plumes rose 30-300 m high daily during February 2019. The Agung Volcano Observatory (AVO) and PVMBG issued a VONA on 7 February (UTC) reporting an ash plume, although it was not visible due to meteoric cloud cover. Incandescence, however, was observed at the summit from webcams in both Rendang and Karangasem City (16 km SE). The seismic event associated with the explosion lasted for 97 seconds. A similar event on 13 February was also obscured by clouds but produced a seismic event that lasted for 3 minutes and 40 seconds, and ashfall was reported in the village of Bugbug, about 20 km SE. On 22 February a gray ash plume rose 700 m from the summit during a seismic event that lasted for 6 minutes and 20 seconds (figure 45). The Darwin VAAC reported the plume visible in satellite imagery moving W at 4.3 km altitude. It dissipated after a few hours, but a hotspot remained visible about 10 hours later.

Figure 45. An ash plume rose from the summit of Agung on 22 February 2019, viewed from the Besakih temple, 7 km SW of the summit. Courtesy of PunapiBali.

Persistent steam plumes rose 50-500 m from the summit during March 2019. An explosion on 4 March was recorded for just under three minutes and produced ashfall in Besakih (7 km SW); no ash plume was observed due to fog. A short-lived ash plume rose to 3.7 km altitude and drifted SE on 8 March (UTC) 2019. The seismic event lasted for just under 4 minutes. Ash emissions were reported on 15 and 17 March to 4.3 and 3.7 km altitude, respectively, drifting W (figure 46). Ashfall from the 15 March event spread NNW and was reported in the villages of Kubu (6 km N), Tianyar (14 km NNW), Ban, Kadundung, and Sukadana. MAGMA Indonesia noted that two explosions on the morning of 17 March (local time) produced gray plumes; the first sent a plume to 500 m above the summit drifting E and lasted for about 40 seconds, while the second plume a few hours later rose 600 m above the crater and lasted for 1 minute and 16 seconds. On 18 March an ash plume rose 1 km and drifted W and NW. An event on 20 March was measured only seismically by PVMBG because fog prevented observations. An eruption on 28 March produced an ash plume 2 km high that drifted W and NW. The seismic signal for this event lasted for about two and a half minutes. The Darwin VAAC reported the ash plume at 5.5 km altitude, dissipating quickly to the NW. No ash was visible four hours later, but a thermal anomaly remained at the summit (figure 47). Ashfall was reported in nearby villages.

Figure 46. Ash plumes from Agung on 15 (left) and 17 (right) March 2019 resulted in ashfall in communities 10-20 km from the volcano. Courtesy of PVMBG and MAGMA Indonesia (Information on G. Agung Eruption, 15 March 2019 and Gunung Agung Eruption Press Release March 17, 2019).

Figure 47. A thermal anomaly was visible through thick cloud cover at the summit of Agung on 29 March 2019 less than 24 hours after a gray ash plume was reported 2,000 m above the summit. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

The first explosion of April 2019 occurred on the 3rd (UTC); PVMBG reported the dense gray ash plume 2 km above the summit drifting W. A few hours later the Darwin VAAC raised the altitude to 6.1 km based on infrared temperatures in satellite imagery. The seismic signal lasted for three and a half minutes and the explosion was heard at the PGA Post in Rendang (12 km SW). Incandescent material fell within a radius of 2-3 km, mainly on the S flank (figure 48). Ashfall was reported in the villages of Telungbuana, Badeg, Besakih, Pempatan, Teges, and Puregai on the W and S flanks (figure 49). An explosion on 11 April also produced a dense gray ash plume that rose 2 km above the summit and drifted W. A hotspot remained about six hours later after the ash dissipated.

Figure 48. Incandescent ejecta appeared on the flanks of Agung after an eruption on 4 April 2019 (local time) as viewed from the observation post in Rendang (8 km SW). Courtesy of Jamie Sincioco.

Figure 49. Ashfall in a nearby town dusted mustard plants on 4 April 2019 from an explosion at Agung the previous day. Courtesy of Pantau.com (Photo: Antara / Nyoman Hendra).

PVMBG reported an eruption visible in the webcam early on 21 April (local time) that rose to 5.5 km altitude and drifted SW. The ash spread W and S and ash fell around Besakih (7 km SW), Rendang (8 km SW), Klungkung (25 km S), Gianyar (20 km WSW), Bangli (17 km WNW), Tabanan (50 km WSW), and at the Ngurah Rai-Denpasar Airport (60 km SW). About 15 hours later a new explosion produced a dense gray ash plume that rose to 3 km above the summit and produced incandescent ejecta in all directions as far as 3 km away (figure 50). The ash spread to the S and ashfall was reported in Besakih, Rendang, Sebudi (6 km SW), and Selat (12 km SSW). Both of the explosions were heard in Rendang and Batulompeh. The incandescent ejecta from the explosions remained within the 4-km exclusion zone. A satellite image on 23 April showed multiple thermal anomalies within the summit crater (figure 51). A dense gray plume drifted E from Agung on 29 April (30 April local time) at 4.6 km altitude. It was initially reported by ground observers, but was also visible in multispectral satellite imagery for about six hours before dissipating.

Figure 50. An explosion at Agung on 21 April 2019 sent incandescent eject 3,000 m from the summit. Courtesy of MAGMA Indonesia (Gunung Agung Eruption Press Release April 21, 2019).

Figure 51. Multiple thermal anomalies were still present within the summit crater of Agung on 23 April 2019 after two substantial explosions produced ash and incandescent ejecta around the summit two days earlier. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG reported an eruption on 3 May 2019 that was recorded on a seismogram with a signal that lasted for about a minute. Satellite imagery reported by the Darwin VAAC showed a growing hotspot and possible ash near the summit at 4.3 km altitude moving NE. A few days later, on 6 May, a gray ash plume rose to 5.2 km altitude and drifted slowly W before dissipating; it was accompanied by a seismic signal that lasted for about two minutes. Explosions on 12 and 18 May produced significant amounts of incandescent ejecta (figure 52). The seismic signal for the 12 May event lasted for about two minutes; no plume was observed due to fog, but incandescent ejecta was visible on the flanks and the explosion was heard at Rendang. The Darwin VAAC reported an ash plume from the explosion on 17 May (18 May local time) at 6.1 km altitude in satellite imagery moving E. They revised the altitude a short while later to 7.6 km based on IR temperature and movement; the plume drifted N, NE, and E in light and variable winds. A few hours after that it was moving NE at 7.6 km altitude and SE at 5.5 km altitude; this lasted for about 12 hours until it dissipated. Ashfall was reported in villages downwind including Cutcut, Tongtongan, Bonyoh (20 km WNW), and Temakung.

Figure 52. Explosions on 12 (left) and 18 (right) May (local time) 2019 produced substantial ejecta on the flanks of Agung visible from a distance of 10 km or more in PVMBG webcams. The ash plume from the 18 May event resulted in ashfall in numerous communities downwind. Courtesy of PVMBG (Information Eruption G. Agung, May 13, 2019, Information Eruption G. Agung, May 18, 2019).

The initial explosion on 18 May was captured by a webcam at a nearby resort and sent incandescent ejecta hundreds of meters down the NE flank within 20 seconds (figure 53). Satellite imagery on 3, 8, 13, and 18 May indicated multiple thermal anomalies growing stronger at the summit. All of the images were captured within 24 hours of an explosive event reported by PVMBG (figure 54).

Figure 53. The 18 May 2019 explosion at Agung produced an ash plume that rose to over 7 km altitude and large bombs of incandescent material that traveled hundreds of meters down the NE flank within the first 20 seconds of the explosion. Images taken from a private webcam located 12 km NE. Courtesy of Volcanoverse, used with permission.

Figure 54. Satellite images from 3, 8, 13, and 18 May 2019 at Agung showed persistent and increasing thermal anomalies within the summit crater. All images were captured within 24 hours of explosions reported by PVMBG. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

PVMBG issued a VONA on 24 May 2019 reporting a new ash emission. They indicated that incandescent fragments were ejected 2.5-3 km in all directions from the summit, and the seismic signal lasted for four and a half minutes (figure 55). A dense gray ash plume was observed from Tulamben on the NE flank rising 2 km above the summit. Satellite imagery indicated that the plume drifted SW and ashfall was reported in the villages of Besakih, Pempatan, Menanga, Sebudi, Muncan, Amerta Bhuana, Nongan, Rendang, and at the Ngurah Rai Airport in Denpassar. Additionally, ashfall was reported in the districts of Tembuku, Bangli, and Susut (20 km SW). The Darwin VAAC reported an ash plume visible in satellite imagery at 4.6 km altitude along with a thermal anomaly and incandescent lava visible in webcam imagery. The remains of the ash plume were about 170 km S of the airport in Denpasar (60 km SW) and had nearly dissipated 18 hours after the event. According to a news article several flights to and from Australia were cancelled or diverted, though the International Gusti Ngurah Rai (IGNR) airport was not closed. On 31 May another large explosion produced the largest ash plume of the report period, rising more than 2 km above the summit (figure 56). The Darwin VAAC reported its altitude as 8.2 km drifting ESE visible in satellite data. It split into two plumes, one drifted E at 8.2 km and the other ESE at 6.1 km altitude, dissipating after about 20 hours.

Figure 55. A large explosion at Agung on 24 May 2019 produced incandescent ejecta that covered all the flanks and dispersed ash to many communities to the SW. Courtesy of PVMBG (Gunung Agung Eruption Press Release 24 May 2019 20:38 WIB, Kasbani, Ir., M.Sc.).

Figure 56. An explosion at Agung on 31 May 2019 sent an ash plume to 8.2 km altitude, the highest for the report period. Courtesy of Sutopo Purwo Nugroho, BNPB.

Geologic Background. Symmetrical Agung stratovolcano, Bali's highest and most sacred mountain, towers over the eastern end of the island. The volcano, whose name means "Paramount," rises above the SE caldera rim of neighboring Batur volcano, and the northern and southern flanks extend to the coast. The summit area extends 1.5 km E-W, with the high point on the W and a steep-walled 800-m-wide crater on the E. The Pawon cone is located low on the SE flank. Only a few eruptions dating back to the early 19th century have been recorded in historical time. The 1963-64 eruption, one of the largest in the 20th century, produced voluminous ashfall along with devastating pyroclastic flows and lahars that caused extensive damage and many fatalities.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); The Jakarta Post, Mount Agung eruption disrupts Australian flights, (URL: https://www.thejakartapost.com/news/2019/05/25/mount-agung-eruption-disrupts-australian-flights.html); PunapiBali (URL: http://punapibali.com/, Twitter: https://twitter.com/punapibali, image at https://twitter.com/punapibali/status/1098869352588288000/photo/1); Jamie S. Sincioco, Phillipines (URL: Twitter: https://twitter.com/jaimessincioco. Image at https://twitter.com/jaimessincioco/status/1113765842557104130/photo/1); Pantau.com (URL: https://www.pantau.com/berita/erupsi-gunung-agung-sebagian-wilayah-bali-terpapar-hujan-abu?utm_source=dlvr.it&utm_medium=twitter); Volcanoverse (URL: https://www.youtube.com/channel/UCi3T_esus8Sr9I-3W5teVQQ); Sutopo Purwo Nugroho, BNPB (Twitter: @Sutopo_PN, URL: https://twitter.com/Sutopo_PN ).

Frequently active, Indonesia's Mount Kerinci on Sumatra has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838. Intermittent explosions with ash plumes, usually multiple times per month, have characterized activity since April 2018. Similar activity continued during February-May 2019, the period covered in this report with information provided primarily by the Indonesian volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, notices from the Darwin Volcano Ash Advisory Center (Darwin VAAC), and satellite data. PVMBG has maintained an Alert Level II (of 4) at Kerinci for several years.

On 13 February 2019 the Kerinci Volcano Observatory (KVO), part of PVMBG, noted a brownish-white ash emission that was drifting NE about 400 m above the summit. The seismicity during the event was dominated by continuous volcanic tremor. A brown ash emission was reported on 7 March 2019 that rose to 3.9 km altitude and drifted NE. Ash also drifted 1,300 m down the SE flank. Another ash plume the next morning drifted W at 4.5 km altitude, according to KVO. On 10, 11, and 13 March KVO reported brown ash plumes drifting NE from the summit at about 4.0-4.3 km altitude. The Darwin VAAC observed continuous ash emissions in satellite imagery on 15 March drifting W at 4.3 m altitude that dissipated after about 3 hours (figure 10). A gray ash emission was reported on 19 March about 600 m above the summit drifting NE; local news media noted that residents of Kayo Aro reported emissions on both 18 and 19 March (figure 11). An ash emission appeared in satellite imagery on 25 March (figure 10). On 30 March the observatory reported two ash plumes; a brown emission at 0351 UTC and a gray emission at 0746 UTC that both drifted NE at about 4.4 km altitude and dissipated within a few hours. PVMBG reported another gray ash plume the following day at a similar altitude.

Figure 10. Sentinel-2 satellite imagery of Kerinci from 15 (left) and 25 (right) March 2019 showed evidence of ash plumes rising from the summit. Kerinci's summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Figure 11. Dense ash plumes from Kerinci were reported by local news media on 18 and 19 March 2019. Courtesy of Nusana Jambi.

Activity continued during April with a brown ash emission reported on 3 April by several different agencies; the Darwin VAAC and PVMBG daily reports noted that the plume was about 500 m above the summit (4.3 km altitude) drifting NE. KVO observed two brown ash emissions on 13 April (UTC) that rose to 4.2 km altitude and drifted NE. Satellite imagery showed minor ash emissions from the summit on 14 April; steam plumes 100-500 m above the summit characterized activity for the remainder of April (figure 12).

Figure 12. A dilute ash emission rose from the summit of Kerinci on 14 April 2019 (left); only steam emissions were present on a clear 29 April in Sentinel-2 imagery (right). "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Ashfall on the NE and S flanks within 7 km of the volcano was reported on 2 May 2019. According to a news article, at least five villages were affected late on 2 May, including Tanjung Bungo, Sangir, Sangir Tengah, Sungai Rumpun, and Bendung Air (figures 13 and 14). The smell of sulfur was apparent in the villages. Brown ash emissions were observed on 3 and 4 May that rose to 4.6 and 4.1 km altitude and drifted SE. The Darwin VAAC reported an emission on 5 May, based on a pilot report, that rose to 6.7 km altitude and drifted NE for about an hour before dissipating. A brown ash emission on 10 May rose 700 m above the summit and drifted SE. Satellite imagery captured ash emissions from the summit on 14 and 24 May (figure 15). For the remainder of the month, 300-700-m-high dense steam plumes were noted daily until PVMBG reported white and brown plumes on 26 and 27 May rising 500-1,000 m above the summit. Although thermal anomalies were not reported during the period, persistent weak SO₂ emissions were identified in TROPOMI instrument satellite data multiple times per month (figure 16).

Figure 13. Ashfall was reported from five villages on the flanks of Kerinci on 2 May 2019. Courtesy of Uzone.

Figure 14. An ash plume at Kerinci rose hundreds of meters on 2 May 2019; ashfall was reported in several nearby villages. Courtesy of Kerinci Time.

Figure 15. Ash emissions from Kerinci were captured in Sentinel-2 satellite imagery on 14 (left) and 24 (right) May 2019. The summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.

Figure 16. Weak SO2 anomalies from Kerinci emissions were captured by the TROPOMI instrument on the Sentinel-5P satellite multiple times each month from February to May 2019. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Gunung Kerinci in central Sumatra forms Indonesia's highest volcano and is one of the most active in Sumatra. It is capped by an unvegetated young summit cone that was constructed NE of an older crater remnant. There is a deep 600-m-wide summit crater often partially filled by a small crater lake that lies on the NE crater floor, opposite the SW-rim summit. The massive 13 x 25 km wide volcano towers 2400-3300 m above surrounding plains and is elongated in a N-S direction. Frequently active, Kerinci has been the source of numerous moderate explosive eruptions since its first recorded eruption in 1838.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Nuansa Jambi, Informasi Utama Jambi: (URL: https://nuansajambi.com/2019/03/20/gunung-kerinci-semburkan-asap-tebal/); Kerinci Time (URL: https://kerincitime.co.id/gunung-kerinci-semburkan-abu-vulkanik.html); Uzone.id (URL: https://news.uzone.id/gunung-kerinci-erupsi-5-desa-tertutup-abu-tebal).

Suwanosejima is an active volcanic island south of Japan in the Ryuku islands with recent activity centered at Otake crater. The current eruption began in October 2004 and activity has mostly consisted of small ash plumes, ballistic ejecta, and visible incandescence at night. This report summarizes activity during January through June 2019 and is based on reports by the Japan Meteorological Agency (JMA), and various satellite data.

Thermal activity recorded by the MIROVA system was low through January and February after a decline in November (figure 36), shown in Sentined-2 thermal infrared imagery as originating at a vent in the Otake crater (figure 37). During January an explosive event was observed at 1727 on the 3rd, producing a gray plume that rose 600 m above the crater. A white gas-and-steam plume rose to 1.5 km above the crater and nighttime incandescence was observed throughout the month. Reduced activity continued through February with no reported explosive eruptions and light gray plumes up to 900 m above the crater. Incandescence continued to be recorded at night using a sensitive surveillance camera.

Figure 36. MIROVA log radiative power plot of MODIS thermal infrared data at Suwanosejima during September 2018 through June 2019. There was reduced activity in 2019 with periods of more frequent anomalies during March and June. Courtesy of MIROVA.

Figure 37. A Sentinel-2 thermal satellite image shows Suwanosejima with the active Otake crater in the center with elevated temperatures shown as bright orange/yellow. There is a light area next to the vent that may be a gas plume. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

There was an increase in thermal energy detected by the MIROVA system in mid-March and there was a MODVOLC thermal alert on the 15th. Occasional small explosions occurred but no larger explosive events were recorded. A white plume was noted on the 27th rising to 900 m above the crater and an event at 1048 on the 30th produced a light-gray plume that rose to 800 m. Incandescence was only observed using a sensitive camera at night (figure 38).

Figure 38. Incandescence from the Suwanosejima Otake crater reflecting in clouds above the volcano. Courtesy of JMA (Volcanic activity of Suwanosejima March 2019).

No explosive events were observed through April. A white gas-and-steam plume rose to 1,200 m above the crater on the 19th and incandescence continued intermittently. Minor explosions were recorded on 5, 30, and 31 May, but no larger explosive events were observed during the month. The event on the 30th produced ash plume that reached 1.1 km above the crater. Similar activity continued through June with one explosive event occurring on the 2nd. Overall, there was a reduction in the number of ash plumes erupted during this period compared to previous months (figure 39).

Figure 39. Observed activity at Suwanosejima for the year ending in July 2019. The black vertical bars represent steam, gas, or ash plume heights (scale in meters on the left axis), yellow diamonds represent incandescence observed in webcams, gray volcano symbols along the top are explosions accompanied by ash plumes, red volcano symbols represent large explosions with ash plumes. Courtesy of JMA (Volcanic activity of Suwanosejima June 2019).

Geologic Background. The 8-km-long, spindle-shaped island of Suwanosejima in the northern Ryukyu Islands consists of an andesitic stratovolcano with two historically active summit craters. The summit of the volcano is truncated by a large breached crater extending to the sea on the east flank that was formed by edifice collapse. Suwanosejima, one of Japan's most frequently active volcanoes, was in a state of intermittent strombolian activity from Otake, the NE summit crater, that began in 1949 and lasted until 1996, after which periods of inactivity lengthened. The largest historical eruption took place in 1813-14, when thick scoria deposits blanketed residential areas, and the SW crater produced two lava flows that reached the western coast. At the end of the eruption the summit of Otake collapsed forming a large debris avalanche and creating the horseshoe-shaped Sakuchi caldera, which extends to the eastern coast. The island remained uninhabited for about 70 years after the 1813-1814 eruption. Lava flows reached the eastern coast of the island in 1884. Only about 50 people live on the island.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The Great Sitkin volcano is located about 40 km NE of Adak Island in the Aleutian Islands and has had a few short-lived eruptions over the past 100 years. Prior to the latest activity in early June 2019 described below, small phreatic explosions occurred in June and August 2018 (BGVN 43:09). An eruption in 1974 produced a lava dome in the center of the crater. The Alaska Volcano Observatory (AVO) is the primary source of information for this September 2018-June 2019 reporting period.

Low-level unrest occurred from September 2018 through February 2019 with slightly elevated seismic activity (figure 6). Small explosions were seismically detected by AVO on 30 October, 5 and 16 November, and 11 December 2018, but they were not seen in regional infrasound data and satellite data did not show an ash cloud.

On 1, 7, and 9 June 2019, AVO reported small steam explosions as well as slightly elevated seismic activity. Steam plumes and surficial evidence of an explosion were not observed during these events. On 18 June 2019 weakly elevated surface temperatures were recorded, field crews working on Adak observed some steam emissions, and a gas flight was conducted. Elevated concentrations of carbon dioxide detected above the lava dome were likely associated with the steam explosions earlier in the month (figures 7 and 8). From 23 June through the end of the month seismicity began to decline back to background levels.

Figure 6. A steam plume was seen at the summit of Great Sitkin on 7 December 2018. Photo by Andy Lewis and Bob Boyd; courtesy of AVO/USGS.

Figure 7. Some degassing was observed on the southern flank of the Great Sitkin during an overflight on 18 June 2019. Photo by Laura Clor; image courtesy of AVO/USGS.

Figure 8. View of Great Sitkin with white plumes rising from the summit on 20 June 2019. Photo by Laura Clor, courtesy of AVO/USGS.

Geologic Background. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667 USA (URL: https://avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA (URL: http://dggs.alaska.gov/).

Ibu volcano on Halmahera island in Indonesia began the current eruption episode on 5 April 2008. Since then, activity has largely consisted of small ash plumes with less frequent lava flows, lava dome growth, avalanches, and larger ash plumes up to 5.5 km above the crater. This report summarizes activity during December 2018 through June 2019 and is based on Volcano Observatory Notice for Aviation (VONA) reports by MAGMA Indonesia, reports by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and Badan Nasional Penanggulangan Bencana (BNPB), and various satellite data.

During December PVMBG reported ash plumes ranging from 200 to 800 m above the crater. There were 11 MODVOLC thermal alerts that registered during 1-12 December. An explosion on 12 January 2019 produced an ash plume that reached 800 m above the crater and dispersed to the S (figure 15). A report released for this event by Sutopo at BNPB said that Ibu had erupted almost every day over the past three months; an example given was of activity on 10 January consisting of 80 explosions. There were four MODVOLC thermal alerts through the month.

Figure 15. An eruption at Ibu at 1712 on 21 January 2019 produced an ash plume that rose to 800 m above the crater. Courtesy of BNPB (color adjusted).

Throughout February explosions frequently produced ash plumes as high as 800 m above the crater, and nine MODVOLC thermal alerts were issued. Daily reports showed variable plume heights of 200-800 m most days throughout the month. Wind directions varied and dispersed the plumes in all directions. A VONA released at 1850 on 6 February reported an ash plume that rose to 1,925 m altitude (around 600 m above the summit) and dispersed S. Activity continued through March with the Darwin VAAC and PVMBG reporting explosions producing ash plumes to heights of 200-800 m above the crater and dispersing in various directions. There were ten MODVOLC alerts through the month.

Similar activity continued through April, May, and June, with ash plumes reaching 200-800 m above the crater. There were 12, 6, and 15 MODVOLC Alerts in April, May, and June, respectively.

Planet Scope satellite images show activity at a two vents near the center of the crater that were producing small lava flows from February through June (figure 16). Thermal anomalies were frequent during December 2018 through June 2019 across MODVOLC, MIROVA, and Sentinel-2 infrared data (figures 17 and 18). Sentinel-2 data showed minor variation in the location of thermal anomalies within the crater, possibly indicating lava flow activity, and MIROVA data showed relatively constant activity with a few reductions in thermal activity during January and February.

Figure 16. Planet Scope natural color satellite images showing activity in the Ibu crater during January through June 2019, with white arrows indicating sites of activity. One vent is visible in the 21 February image, and a 330-m-long (from the far side of the vent) lava flow with flow ridges had developed by 24 March. A second vent was active by 12 May with a new lava flow reaching a maximum length of 520 m. Activity was centered back at the previous vent by 23-27 June. Natural color Planet Scope Imagery, copyright 2019 Planet Labs, Inc.

Figure 17. Examples of thermal activity in the Ibu crater during January through May 2019. These Sentinel-2 satellite images show variations in hot areas in the crater due to a vent producing a small lava flow. Sentinel-2 false color (urban) images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 18. MIROVA log radiative power plot of MODIS thermal infrared at Ibu from September 2018 through June 2019. The registered energy was relatively stable through December, with breaks in January and February. Regular thermal anomalies continued with slight variation through to the end of June. Courtesy of MIROVA.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/).

The Ebeko volcano, located on the northern end of the Paramushir Island in the Kuril Islands, consists of many craters, lakes, and thermal features and has been frequently erupting since late February 2017. Typical activity includes ash plumes, explosive eruptions, and gas-and-steam activity. The previous report through November 2018 (BGVN 43:12) described frequent ash explosions that sometimes caused ashfall in Severo-Kurilsk (7 km E). The primary source of information is the Kamchatka Volcanic Eruptions Response Team (KVERT). This report updates the volcanic activity at Ebeko for December 2018 through May 2019.

Frequent moderate explosive activity continued after November 2018. Volcanologists in Severo-Kurilsk observed explosions sending up ash, which drifted N, NE, and E, resulting in ash falls on Severo-Kurilsk on 28 different days between December 2018 and March 2019. On 25 December 2018 an explosion sent ash up to a maximum altitude of 4.5 km and then drifted N for about 5 km. Explosions occurring on 8-10 March 2019 sent ash up to an altitude of 4 km, resulting in ashfall on Severo-Kurilsk on 9-10 March 2019. An ash plume from these explosions rose to a height of 2.5 km and drifted to a maximum distance of 30 km ENE.

Satellite data analyzed by KVERT registered 12 thermal anomalies from December 2018 through May 2019. According to satellite data analyzed by MIROVA (Middle InfraRed Observation of Volcanic Activity), only one thermal anomaly was recorded from December 2018-May 2019, and no hotspot pixels were recognized using satellite thermal data from the MODVOLC algorithm.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

Klyuchevskoy has had alternating eruptive and less active periods since August 2015. Activity has included lava flows, a growing cinder cone, thermal anomalies, gas-and-steam plumes, and ash explosions. Though some eruptions occur near the summit crater, major explosive and effusive eruptions have also occurred from flank craters (BGVN 42:04 and 43:05). Intermittent moderate gas-and-steam and ash emissions were previously reported from mid-February to mid-August 2018. The Kamchatka Volcanic Eruptions Response Team (KVERT) is the primary source of information for this September 2018-June 2019 reporting period.

KVERT reported that moderate gas-and-steam activity, some of which contained a small amount of ash, and weak thermal anomalies occurred intermittently from the beginning of September 2018 through mid-April 2019. On 21-22 April 2019 webcam data showed a gas-and-steam plume extending about 160 km SE (figure 31). Moderate Strombolian-type volcanism began late April 2019 and continued intermittently through June 2019. On 11-12 June webcam data showed explosions that sent ash up to a maximum altitude of 6 km, with the resulting ash plume extending about 200 km WNW.

Figure 31. Gas-and-steam plume containing some amount of ash rising from the summit of Klyuchevskoy on 22 April 2019. Photo by A. Klimova, courtesy of Institute of Volcanology and Seismology (IVS FEB RAS).

Thermal anomalies were noted by KVERT during two days in September 2018, six days in April 2019, eleven days in May 2019, and six days in June 2019. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed infrequent weak thermal anomalies December 2018 through early May 2019.

Geologic Background. Klyuchevskoy (also spelled Kliuchevskoi) is Kamchatka's highest and most active volcano. Since its origin about 6000 years ago, the beautifully symmetrical, 4835-m-high basaltic stratovolcano has produced frequent moderate-volume explosive and effusive eruptions without major periods of inactivity. It rises above a saddle NE of sharp-peaked Kamen volcano and lies SE of the broad Ushkovsky massif. More than 100 flank eruptions have occurred during the past roughly 3000 years, with most lateral craters and cones occurring along radial fissures between the unconfined NE-to-SE flanks of the conical volcano between 500 m and 3600 m elevation. The morphology of the 700-m-wide summit crater has been frequently modified by historical eruptions, which have been recorded since the late-17th century. Historical eruptions have originated primarily from the summit crater, but have also included numerous major explosive and effusive eruptions from flank craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/).

We report Akutan non-eruptive seismic activity after our mid-1996 report (BGVN 21:06) through December 2010. AVO (Alaska Volcano Observatory) reporting emphasized seismicity in 2000, 2007, 2008, 2009, and 2010, including seismicity during 2007 triggered by an M 8.2 earthquake in the Kurile islands.

Background. Akutan Island is home to indigenous people located in several coastal villages, and the base of a large fish processing facility. The island resides in the Aleutian arc, a string of islands projecting ~2,000 km into the Bering Sea from the Alaskan Peninsula (figure 2).

Figure 2. Akutan, an island ~32 km by ~20 km, lies on the E Aleutian arc in the Bering Sea near the coast of Alaska. Courtesy of Neal and McGimsey (1996), revised by GVP.

Akutan Island (figure 3) has a vegetated coast line dotted with spectacular bridges and caves created by the erosion of numerous lava tubes. Waythomas and others (1998) presented a map showing that much of the coastline is susceptible to rockfall avalanches and points out that these may trigger local tsunamis. The authors also analyzed the likely path of lava flows.

Figure 3. Akutan Island and its volcanic features, including fumaroles, hot springs, and a new steaming area. A cindercone resides in the NE quadrant of the generally circular caldera. The fumarole field, shown in red, is down slope on the E flank of the summit. The Trident seafood plant, shown as a yellow star, lays along the E coast. Courtesy of AVO, revised by GVP.

A 2 km diameter caldera atop the 1,303 m high volcano is breached to the NW, and elsewhere encircled by crater walls 60 to 365 m high. The caldera contains a ~200 m high cinder cone, and a small lake. Fumeroles lay along the summit flank toward the E (Miller and others, 1998). The cinder cone has been the site of all historical eruptive activity (Richter and others, 1998; Waythomas and others, 1998).

The village of Akatan ( figure 4), ~ 13 km E of the volcano, hosts the Trident seafood plant, the largest such plant in North America, employing up to 900 seasonal workers (McGimsey, 2011). Akutan villagers and seafood plant employees fled the island during the 1996 seismic events (Li and others, 2000). The cited references provide many details omitted here.

Figure 4. Akutan coastal image with seafood plant in foreground adjacent to Akutan village. Image courtesy of AVO, created by Helena Buurman.

According to Diefenbach and others (2009), Akutan has been the most active of the volcanoes monitored by AVO, having over 20 eruptions since 1790; more than any other Alaskan volcano.

A 2009 report by AVO noted that 11 eruptions occurred at Akutan during 1980-1992, many lasting several months (table 5). The most recent eruption started in December 2009 but the eruption's end was not clearly constrained (table 5). A seismic swarm took place in 1996, an episode without a corresponding eruption.

Table 5. Akutan eruptions tabulated from January 1980 to 2009. Courtesy of Diefenbach and others (2009).

From 1980 to 2009, Alaskan eruptions made up to 77% of the total reported in the United States (Diefenbach and others, 2009). Note that, even though during 1980-2009 Akutan erupted more times than other US volcanoes, this distinction is only one of many that can be used for comparisons. For example, in the course of that interval and the 11 recorded eruptions at Akutan, it clearly emitted less material and the eruptive intervals spanned much less time than eruptions at either Kilauea or Mt. St. Helens.

1996 seismicity. In March 1996, two strong earthquake swarms struck the island, causing minor damage and prompting some residents and dozens of plant employees to leave the island. The seismicity, reported in BGVN 21:06, was probably the result of a magmatic intrusion (Lu and others, 2000). They stated the following:

"In March 1996 an intense swarm of volcano-tectonic earthquakes (~3,000 felt by local residents, M max = 5.1, cumulative moment of 2.7 × 10¹⁸ N m) beneath Akutan Island in the Aleutian volcanic arc, Alaska, produced extensive ground cracks but no eruption of Akutan volcano. Synthetic aperture radar interferograms that span the time of the swarm reveal complex island-wide deformation: the western part of the island including Akutan volcano moved upward, while the eastern part moved downward. The axis of the deformation approximately aligns with new ground cracks on the western part of the island and with Holocene normal faults that were reactivated during the swarm on the eastern part of the island. The axis is also roughly parallel to the direction of greatest compressional stress in the region. No ground movements greater than 2.83 cm were observed outside the volcano's summit caldera for periods of 4 years before or 2 years after the swarm. We modeled the deformation primarily as the emplacement of a shallow, E-W trending, north dipping dike plus inflation of a deep, Mogi-type [spherical] magma body beneath the volcano. The pattern of subsidence on the eastern part of the island is poorly constrained. It might have been produced by extensional tectonic strain that both reactivated preexisting faults on the eastern part of the island and facilitated magma movement beneath the western part. Alternatively, magma intrusion beneath the volcano might have been the cause of extension and subsidence in the eastern part of the island."

The 11 March 1996 swarm involved more than 80 earthquakes of M 3.0 or greater with the largest measuring M 5.2. The 13 March swarm involved more than 120 events of M 3.0 or greater with the largest measuring M 5.3 (Waythomas and others, 1998).

As a result, new ground cracks developed ( figure 5) and Waythomas and others (1998) described them as follows: "Numerous fresh, linear ground cracks were discovered in three areas on Akutan Island during field studies in the summer of 1996. Ground breaks and cracks likely formed during the strong seismic swarms in March. The ground cracks extend discontinuously from the NE side of the island near Lava Point to the island's SE side [figure 5].

"The most extensive ground cracks are between Lava Point and the volcano summit [ figure 6]. In this area, the cracks are confined to a zone 300 to 500 m wide and 3 km long. Vertical displacement of the ground surface along individual cracks is 30 to 80 cm. The ground cracks probably formed as magma moved toward the surface between the two most recently active vents on the volcano. Ground cracks on the SE side of the island occur on known faults, indicating that they probably formed in response to motion along these preexisting structures. No ground cracks were found at the head of Akutan Harbor even though this was an area where numerous earthquakes occurred from March through July, 1996."

Figure 5. Location of ground cracks and seismometers on Akutan, as published in 1998. Three sets of ground cracks, shown as black lines, presumably formed during the March 1996 earthquake swarm. The most extensive breaks occurred on the NW flank of the volcano near Lava Point with the other two shorter sets to the SE in line with the first. On the map, the green triangles locate seven monitoring stations, one at the summit, and others spread throughout the island as well as one at the village. Courtesy of AVO, Waythomas and others (1998), annotated by GVP.

Figure 6. Ground breaks like this were found at Akutan in a zone about 300-500 m wide and ~ 3,000 m long on the NW flank of the volcano. Surface deposits offset by the cracks consist of course tephra and colluvium. The backpack in the lower left delineates scale (distant figures removed for clarity). Courtesy of AVO, Waythomas and others (1998).

A permanent seismic network was installed during the summer of 1996 which currently consists of seven short-period stations and five broadband stations (figure 5).

Akutan seismicity, 2000 to 2010. According to AVO annual reports covering the interval 1997-2011, noteworthy seismicity occurred during the years 2000, 2007, 2008, 2009, and 2010.

On 19 January 2000, five earthquakes occurred in less than 30 minutes with epicenters 10-11 km E of the summit at hypocentral depths of ~5-6 km. This was the same region as the March 1996 volcanic swarm.

Akutan was one of several Alaska volcanoes with behavioral anomalies triggered by the M 8.2 earthquake generated in the Kurile Islands on 12 January 2007 at 0423 UTC (McGimsey, 2011). Seismologists located four of the seven largest triggered M 0.0-0.5 earthquakes at Akutan and found their depths in the range from +0.86 to -2.17 km (figure 7). The locations fell along the trend of intense seismicity and ground breakage that occurred in March 1996 at Akutan (Neal and others, 1997; Waythomas and others, 1998; Lu and others, 2005). The AVO Akutan seismic network recorded the triggered seismicity.

Figure 7. Epicenters at Akutan triggered by the 13 January 2007, M 8.2 Kurile Islands earthquake (the event occurred at 0423 UTC, 12 January 2007). The four largest events (red dots) lie along the same trend (blue line) as that of intense seismicity with accompanied ground breakage that occurred during dike intrusion in March 1996 (Waythomas and others, 1998). Open triangles mark locations of seismic stations. Plot of earthquake locations by John Power. Courtesy of AVO, McGimsey and others (2011).

In early October 2007, AVO remote sensors detected signs of renewed inflation of the W flank during the previous month using GPS time series. This inflation was in the same area that inflated during the 1996 seismic crisis. A few days later, on 8 October 2007, the manager of the Trident seafood processing plant called to alert AVO of strong steaming near Hot Springs Bay (figure 8) at a spot significantly up slope from established hot springs in the valley. This plume location was considered "new" by local observers. The established lower-valley thermal springs rarely emit a concentrated, vertically rising steam plume and most earlier reports of steaming arose from the prominent fumarole field located at the 460 m elevation of the E flank at the headwaters of Hot Springs Bay valley. This is also the area of maximum deflation following the 1996 seismic swarms. No unusual seismic activity was noted for the period of W-flank inflation or the location of this steaming episode (McGimsey and others, 2011).

Figure 8. Midway up Akutan's Hot Springs Bay valley on the E flank of Akutan from a point well upslope of the previously active hot springs area, a steam column rises from a new site. AVO photo taken 8 October 2007 by David Abbasian.

In 2008, over 100 seismic events were recorded. During the next two years, Akutan seismic events decreased to about half that number. During 2010 low frequency earthquakes doubled compared to 2009 (Table 6).

Table 6. Akutan seismic activity for 2008-2010 compiled from AVO/USGS annual reports. Total earthquakes (in the second column) summed those in the Volcano-tectonic and Low frequency columns. '--' indicates data not reported. Courtesy of AVO.

According to AVO, Akutan seismic events during the years 2009 and 2010 were temporally spread roughly throughout the months except for a tight cluster of M 2 earthquakes reported at depths of between ~5 km to ~10 km during the first weeks of January 2010. The majority of earthquakes in 2010 were located within ~5 km of the crater along a N-trending line spanning 10 km. In 2009 the spread was longer, over 20 km.

References. Diefenbach, A.K., Guffanti, M., and Ewert, J.W., 2009, Chronology and references of volcanic eruptions and selected unrest in the United States, 1980-2008: U.S. Geological Survey Open-File Report 2009-1118, 85 p. [http://pubs.usgs.gov/of/2009/1118/].

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, C.K., 2010, Catalog of Earthquake Hypocenters at Alaskan Volcanoes: January 1 through December 31, 2009: U.S. Geological Survey Data Series 531.

Dixon, J.P., Stihler, S.D., Power, J.A., and Searcy, C.K., 2011, Catalog of earthquake hypocenters at Alaskan Volcanoes: January 1 through December 31, 2010: U.S. Geological Survey Data Series 645.

Kent, T., 2011, Hydrothermal Alteration of Open Fractures in Prospective Geothermal Drill Cores, Akutan Island, Alaska, Fall Meeting of the American Geophysical Union, 2011, Abstract ##V13D-2637.

Lu, Z., Wicks Jr., C., Power, J.A., and Dzurisin, D., 2000, Ground deformation associated with the March 1996 earthquake swarm at Akutan volcano, Alaska, revealed by satellite radar interferometry, J. Geophys. Res., 105(B9), 21,483-21,495 (DOI:10.1029/2000JB900200).

Miller, T.P., McGimsey, R.G., Richter, D.H., Riehle, J.R., Nye, C.J., Yount, M.E., and Dumoulin, J.A., 1998, Catalog of the historically active volcanoes of Alaska: U.S. Geological Survey Open-File Report 98-582, 104 p. (Also available at http://www.avo.alaska.edu/downloads/catalog.php.)

McGimsey, R.G., Neal, C.A., Dixon, J.P., Malik, Nataliya, and Chibisova, M., 2011, 2007 Volcanic activity in Alaska, Kamchatka, and the Kurile Islands: Summary of events and response of the Alaska Volcano Observatory: U.S. Geological Survey Scientific Investigations Report 2010-5242, 110 p.

Neal, C.A. and McGimsey, R.G., 1997, 1996 Volcanic Activity In Alaska And Kamchatka: Summary Of Events And Response Of The Alaska Volcano Observatory: U.S. Geological Survey Open-File Report 97-433.

Richter, D.H., Waythomas, C.F., McGimsey, R.G., and Stelling, P.L., 1998, Geologic map of Akutan Island, Alaska: U.S. Geological Survey Open-File Report 98-135, 22 p., 1 plate.

Waythomas, C.F., Power, J.A., Richter, D.H., and McGimsey, R.G., 1998, Preliminary volcano-hazard assessment for Akutan Volcano east-central Aleutian Islands, Alaska: U.S. Geological Survey Open-File Report 98-0360, 36 p., 1 plate.

Geologic Background. One of the most active volcanoes of the Aleutian arc, Akutan contains 2-km-wide caldera with an active intracaldera cone. An older, largely buried caldera was formed during the late Pleistocene or early Holocene. Two volcanic centers are located on the NW flank. Lava Peak is of Pleistocene age, and a cinder cone lower on the flank produced a lava flow in 1852 that extended the shoreline of the island and forms Lava Point. The 60-365 m deep younger caldera was formed during a major explosive eruption about 1600 years ago and contains at least three lakes. The currently active large cinder cone in the NE part of the caldera has been the source of frequent explosive eruptions with occasional lava effusion that blankets the caldera floor. A lava flow in 1978 traveled through a narrow breach in the north caldera rim almost to the coast. Fumaroles occur at the base of the caldera cinder cone, and hot springs are located NE of the caldera at the head of Hot Springs Bay valley and along the shores of Hot Springs Bay.

Information Contacts: Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA, b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys.

Our last Bulletin report (BGVN 35:03) covered eruptive activity through the last eruptive episode, which ended 12 January 2010.

Beginning 14 August and through 10 September 2010, the Observatoire Volcanologique du Piton de la Fournaise (OVPDLF) recorded a slow but steady increase in the number and magnitude of earthquakes from Piton de la Fournaise. Inflation of the summit area began in late August. The following report is based on data received from OVPDLF. It discusses eruptions and related behavior as late as 10 December 2010.

On 13 September 2010, localized deformation W of the Dolomieu crater and a small number of landslides in the crater was observed. On 20 September instruments recorded a significant increase in the number of earthquakes located at the W and S of the Dolomieu crater, although their average magnitude was low.

On 24 September, OVPDLF reported the possibility of an impending eruption. During the night, a seismic crisis began with a series of several tens of earthquakes localized under the Dolomieu crater, which was associated with inflation (approximately 3 cm), especially close to the summit. The most significant deformations were measured on the rim and the N and S sides of the volcano, indicating a shallow magma body was distributed directly below the Dolomieu crater. After decreasing on 27 September, seismicity rose again by 29 September. Earthquakes were located at the base of the volcano, and inflation was noted particularly in the E. A significant number of landslides were detected in the crater. The Alert level remained at 1 ("probable or imminent eruption").

Beginning 7 October 2010, there was a steady increase in the number and magnitude of volcano-tectonic (VT) earthquakes. During 10-11 October the summit area inflated 3-7 cm, and an increase in the number of landslides in the crater was detected. The Alert level remained at 1.

Increased seismicity was again recorded on 14 October 2010, with a new seismic crisis of more than several hundred earthquakes. During this phase, significant ground deformation occurred near the summit, which generated numerous rockfalls inside the Dolomieu crater. At 1411, the seismicity moved toward the SE part of the volcano (Château Fort), and at 1910 an eruption began within the Enclos Fouqué, about 1.5 km SE of the Dolomieu crater rim. Lava fountaining occurred from four vents along a fissure. The Alert level was raised to 2 ("eruption in progress in the Fouqué caldera").

Eruptive activity continued on 15-16 October 2010, developing along a fissure. This eruption included low lava fountains and fed a lava flow moving to the ESE. Lava issued from an area close to the old Château Fort crater at the base of the SE flank of Dolomieu crater and remained within the Enclos Fouqué. Four small cones were active along the eruptive fissure; lava fountaining occured from three of them. A lava flow moved slowly about 1.6 km to the E and SE and approached the break in slope at the Grandes pentes. OVPDLF measured lava temperatures of ~1,100°C.

On 17 October 2010 explosions and degassing accompanied lava emissions. These explosions and degassing decreased on 18 October. The volcanic tremor also decreased to one-seventh compared to the beginning of the eruption. The number of VT events remained low (7/day); the strongest event occurred at 2323, a M 1.4 earthquake localized at about 1,600 m depth under the Bory summit crater. The base and the summit of the volcano remained in inflation. Preliminary estimation of the lava volume erupted was 600,000 m³.

During 19-21 October consistent eruptive activity continued, with weak emissions and small lava fountains at the main eruptive vents located along the eruptive fissure. Explosive activity and degassing decreased, and tremor remained stable. Lava flows extended ESE to ~2 km. Gas emissions decreased, but concentrated to the S and W of the fissure.

On 22 October 2010 eruptions continued, located close to the Château Fort area, in the southern portion of the Enclos Fouqué. During 22-26 October lava fountains and gas emissions originated from one vent, and lava traveled ESE. Gas emissions decreased significantly. At this point, only one cone was active and only a few lava fountains were observed. Volcanic tremor was stable. No earthquakes had been reported since the previous day. GPS ground deformation showed a weak deflation under the volcano.

A sudden increase in activity and tremor began on 27 October 2010 and continued on 28 October. On 29 October, observation made during a flight disclosed that a part of summit cone 3 (the only active cone) had collapsed. Some lava ejecta and gas emissions occurred from this cone, which also contained a small active lava pond. Lava from this cone fed a small, slow moving lava flow. This new lava field remained upstream of the cone named Gros Benard. On 31 October, OVPDLF reported that the eruption had ended.

On 9 December 2010, following a seismic crisis and inflation, a new eruption began from an eruptive fissure oriented N-S, just above the Mi-Côte peak, at ~2,500 m elevation, characterized by lava fountaining and two lava flows. Many small landslides occurred in the Dolomieu crater. Later that day lava flows from two fissures on the N flank of Piton de la Fournaise, ~1 km NW of the Dolomieu crater rim, traveled about 1.5 km N and NW. On 10 December 2010, seismicity and deformation measurements indicated that eruption of lava had stopped.

Geologic Background. The massive Piton de la Fournaise basaltic shield volcano on the French island of Réunion in the western Indian Ocean is one of the world's most active volcanoes. Much of its more than 530,000-year history overlapped with eruptions of the deeply dissected Piton des Neiges shield volcano to the NW. Three calderas formed at about 250,000, 65,000, and less than 5000 years ago by progressive eastward slumping of the volcano. Numerous pyroclastic cones dot the floor of the calderas and their outer flanks. Most historical eruptions have originated from the summit and flanks of Dolomieu, a 400-m-high lava shield that has grown within the youngest caldera, which is 8 km wide and breached to below sea level on the eastern side. More than 150 eruptions, most of which have produced fluid basaltic lava flows, have occurred since the 17th century. Only six eruptions, in 1708, 1774, 1776, 1800, 1977, and 1986, have originated from fissures on the outer flanks of the caldera. The Piton de la Fournaise Volcano Observatory, one of several operated by the Institut de Physique du Globe de Paris, monitors this very active volcano.

Information Contacts: Laurent Michon and Patrick Bachélery, Laboratoire GéoSciences Réunion, Institut de Physique du Globe de Paris, Université de La Réunion, CNRS, UMR 7154-Géologie des Systèmes Volcaniques, La Réunion, France; Guillaume Levieux, and Thomas Staudacher, and Valérie Ferrazzini, Observatoire Volcanologique du Piton de la Fournaise (OVPDLF), Institut de Physique du Globe de Paris, 14 route nationale 3, 27ème km, 97418 La Plaine des Cafres, La Réunion, France (URL: http://www.ipgp.fr/fr/ovpf/actualites-ovpf/).

[NOTE: The location shown on the summary page is that for the main summit of Hierro volcano on El Hierro Island. The location of the submarine vent of Hierro that erupted beginning in October 2011 was found to be at latitude 27°37.18' N and longitude 17° 59.58' W.]

In BGVN 36:10 we discussed a submarine eruption of a vent of Hierro volcano that began in early October 2011 S of La Restinga, a town at the southermost tip of El Hierro Island (figure 7). The eruption was preceded by increased seismicity, although this seismicity declined significantly by mid-November 2011 (figures 8 and 9). Based on seismic activity monitored by the Instituto Geográfico Nacional (IGN-National Geographic Institute), authorities for the Canary Islands decided in late March 2012 to shut down the web cameras at La Restinga. Volcanic tremor was still present, although at minimal levels, and some seismicity continued beneath the island. The patch of brown water over the submarine vent (location shown in figure 8) continued to be observed throughout both March and April (figure 10).

Figure 7. Location maps showing the Canary Islands, with volcanoes, and their intra-plate location with respect to plate boundaries. Information on the locations and latest eruptions of the volcanoes is found in table 1. El Hierro Island (and its volcano of the same name) appears on the SW margin of the archipelago. (a) Geographic and geodynamic setting of the NW African continental margin with the Canary Islands; numbers on the Canary Islands show the ages of the oldest surface volcanism, in millions of years before present (Ma). The Canary Islands developed in a geodynamic setting characterized by Jurassic oceanic lithosphere formed during the first stage of opening of the Atlantic at 180-150 Ma and lying close to a passive continental margin on the African plate. The archipelago lies adjacent to a region of intense deformation comprising the Atlas mountains, a part of the Alpine orogenic belt. The intraplate Canary Islands archipelago is within the African plate, bounded by the Azores-Gibralter fault on the north and the mid-Atlantic ridge on the west. (b) Close-up view of the Canary Islands, showing the names of the islands, and the ages of the oldest surface volcanism for each island. Courtesy of Viñuela (2012) and Carracedo and others (2002).

Table 1. Background information on the six main Canary Islands and their volcanoes. Latest eruption dates are from Siebert and others (2010) and Smithsonian's Global Volcanism Program website. The volcano age indicates date of oldest volcanic rocks of each island (Carracedo and others, 2002).

Figure 8. Topographic map of El Hierro Island showing the locations of IGN seismic monitoring stations. A small red triangle offshore of the southernmost tip of the island locates the submarine vent of Hierro that began erupting in October 2011. The pronounced curved form on the N side of the island resulted from lateral collapse; see figure 11b. Courtesy of IGN.

Figure 9. Cumulative energy (in joules) based on daily seismic monitoring at El Hierro island from 18 July 2011 through 19 March 2012. The sharp upturn in the curve occurred ~27 September 2011, leveled out ~9 October 2011, resumed to a sharp upturn on ~29 October 2011 to level out again ~21 November 2011. Since that time, the seismic energy has not increased measureably. Courtesy of IGN.

Figure 10. A natural-color satellite image collected on 10 February 2012 showed the site of the Hierro submarine vent eruption, offshore from the fishing village of La Restinga. Bright aquamarine-colored water indicated high concentrations of volcanic material in the water above the vent, which lies at a water depth of between 200 and 300 m. A patch of turbulent light brown water on the sea surface indicated the area most strongly affected. This image was acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite. NASA Earth Observatory image prepared by Jesse Allen and Robert Simmon, using EO-1 ALI data.

Bathymetry and water chemistry. For 4 months following the eruption (a period from 22 October 2011 through 26 February 2012), the Instituto Oceanográfico Español (IOE-Spanish Oceanographic Institute) conducted 12 oceanographic cruise legs (called La Campaña Bimbache-Bimbache Campaign; Bimbache refers to native inhabitants of El Hierro), documenting the submarine morphology and water chemistry changes resulting from the eruption. Reports of these cruises on board the research vessel Ramon Margalef are found on the IEO web site; some highlights follow.

During the 7th leg, 8-12 January 2012, IEO scientists found that the volcano's summit was ~130 m below the water surface, 30 m more since its last survey on 2 December 2011. The diameter of the volcano's base was about 800 m, and its height ~200 m above the ocean floor. The total volume of material emitted since the eruption onset in October 2011 to the date of this cruise leg, calculated by bathymetry compared to 1998, was 145 x 10⁶ m³. This volume included a new eruptive cone and associated lava flows. This new material nearly completely covered the W escarpment of the submarine canyon where the eruption was located. It was also found that a split in the top of the cone recorded in the bathymetric survey of 30 November 2011 no longer existed.

During the 9th leg, 6-8 February 2012, Hierro volcano was found to have grown somewhat more in height. The most significant differences between this and the 7th leg (January 2012) occurred at the top of the cone, including a slight increase in the elevation of its summit, which now reached to ~120 m below the water surface, and the emergence of a secondary cone, ~23 m high, attached to the side of the main cone, with a summit depth of 200 m. The emergence of the secondary cone and the greater mass of material on the volcano flank had caused a flattening of the structure. The slope ranged between 25° and 30° on the N flank, with slopes of up to 35° on the E and W flanks.

The 10th leg, 9-13 February 2012, was dedicated to water sampling. Observers found very high levels of hydrogen sulfide (H₂.S), with a below normal pH, and very high partial pressure of CO₂.

The IEO report of the 11th leg, 23-24 February 2012, notes that the coordinates of the main summit of the new volcano were: latitude 27°37.18' N and longitude 17° 59.58' W.

During a cruise from 5 to 9 April 2012 by researchers from IEO and the University of Las Palmas de Gran Canaria (ULPGC), 19 hydrographic stations were occupied. Data was collected on the physical-chemical properties of the water around the volcano (including temperature, salinity, depth, fluorescence, turbidity, dissolved oxygen, pH, alkalinity, total inorganic carbon, and CO₂ partial pressure). The researchers intend to quantify the environmental impact caused by the volcano 7 months after the beginning of the eruption. The physical-chemical properties of the water column in an area of 500 m radius around the submarine volcanic cone where found to be still significantly affected. At this stage, the degassing of the volcano was fundamentally of CO₂, with complete absence of sulfur compounds.

Remote submarine vessel observations. The University of Las Palmas de Gran Canaria (ULPGC) web site on 16 March 2012 reported initial filming of the submarine vent using the robot submarine vessel Atlantic Explorer. They reported particles of tephra in the mouth of the still-active vent. At a depth of 120 m, hot jets emerged from a vent, forming converging water convection cells reaching upwards to depths of ~40-60 m. From the same depths, some pyroclastic ejecta were seen in the form of large volcanic bombs. The SW flank of the main volcanic vent cone sloped steeply and was the resting place of many large pyroclastics, some of which are similar to the hollow volcanic bombs (lava balloons) that reached the ocean surface during November and December 2011. Marine life had returned to near the vent, and at a depth of ~170 m and under a rain of ash they observed a school of fish (possibly amberjack).

Geologic setting. Carracedo and others (2012a) provided further details on the geologic setting of El Hierro island and the 2011 vent eruption. They state that "As early as 1793, administrative records of El Hierro indicate that a swarm of earthquakes was felt by locals; fearing a greater volcanic catastrophe, the first evacuation plan of an entire island in the history of the Canaries was prepared. The 1793 eruption was probably submarine . . . over the next roughly 215 years the island was seismically quiet. Yet seismic and volcanic activity are expected on this youngest Canary Island due to its being directly above the presumed location of the Canary Island hot spot, a mantle plume that feeds upwelling magma just under the surface, similar to the Hawaiian Islands." Currently, roughly 10,000 people live on the island of El Hierro.

The report continued (references have been removed): "El Hierro, 1.12 million years old, is the youngest of the Canary Islands and rests on a nearly 3,500-m-deep ocean bed (figure 11a). According to stratigraphic data, two eruptions are known to have occurred on El Hierro, one ~4,000 years ago at Tanganasoga volcano complex and one 2,500 ± 70 years ago at Montaña Chamuscada cinder cone (figure 11b). The principal configuration of El Hierro is controlled by a three-armed rift zone system. The last stage of growth of El Hierro started some 158,000 years ago, characterized by volcanism that concentrated mainly at the crests of the three-armed rift system."

Figure 11. El Hierro maps and diagrams to illustrate the setting and context of the 2011 eruption. (a) Location of the submarine vent (red star); image from Masson and others (2002); inset shows the island's location within the Canary Islands archipelago. (b) Simplified geological map of El Hierro, showcasing two recent eruptions. (c) Epicenter distribution migrating southward, 19 July to 8 October 2011 (data from IGN). (d) Hypocenter depths increased during 3 August to 9 October 2011, and then they became shallower (

Carracedo and others (2012a) described the pattern of earthquakes detected by IGN's permanent seismic network. The pattern consisted of an event every few minutes and an average short-period body wave magnitude of about M 1-2. Though the most of these quakes were largely insignificant in terms of seismic hazards, they initially focused N of the island (figure 11c), concentrated within the lower oceanic crust at depths of 8 and 14 km, in agreement with petrological evidence of previous eruptions. The seismic and petrological data are thus in line with a scenario of a magma batch becoming trapped as an intrusion horizon near the base or within the oceanic crust. Shifting seismic foci suggested that magma progressively accumulated and expanded laterally in a southward direction along the southern rift zone, which caused a vertical surface deformation of ~40 mm based on GPS measurements.

The report continues: "Soon after the initial earthquake swarm was observed by the permanent seismometers associated with IGN, efforts were made to mobilize a more complete monitoring seismic and GPS array spaced roughly 2,000 m apart throughout the island. This expanded network, completely installed by September 2011, allowed scientists to follow the progress of the recent activity at El Hierro."

"The new instruments revealed that earthquakes and magma transport remained active but as of the beginning of October 2011 showed no sign of having breached the oceanic crust. Instead, magma continued to move south until, on 9 October, the magma apparently progressed rapidly toward the surface, as indicated by the first-time occurrence of shallow earthquakes (at depths of

"The eruption continued through 15 October, with the appearance of submarine volcanic 'bombs' with cores of white and porous pumice-like material encased in a fine coating of basaltic glass [figure 12; see figure 4 in BGVN 36:10 showing a cross-section view of a bomb]. These bombs are probably xenoliths from pre-island sedimentary rocks that were picked up and heated by the ascending magma, causing them to partially melt and vesiculate." According to Carracedo and others (2012b), "the interiors of these floating rocks are glassy and vesicular (similar to pumice), with frequent mingling between the pumice-like interior and the enveloping basaltic magma. These floating rocks have become known locally as 'restingolites' after the nearby village of La Restinga." Some 'restingolite' samples contain quartz crystals, jasper fragments, gypsum aggregates and carbonate relicts, materials more compatible with sedimentary rocks than with a purely igneous origin for the cores of the floating stones. Figure 13 shows one explanation for the formation these bombs.

Figure 12. Lava fragments ('restingolites') floating on the sea surface about 2 km offshore from La Restinga village on 27 November 2011. At some times a few hundreds of these fragments were present. They arrived at the sea surface at high temperature and, while cooling, they vaporized sea water, suffered intense degassing, and, in some cases broke into small pieces. Courtesy of Alicia Rielo, IGN.

Figure 13. Sketch summarizing the inferred structure of El Hierro Island and the 2011 intrusive and extrusive events. Ascending magma that, according to the distribution of seismic events prior to eruption, moved sub-horizontally from N to S in the oceanic crust and contacted pre-volcanic sedimentary rocks. The floating blocks were attributed to magma-sediment interaction beneath the volcano. These blocks, called 'restingolites', were carried toward the ocean floor during eruption, being melted and vesiculated while immersed in magma. Once erupted onto the ocean floor, they separated from the erupting lava and floated on the sea surface due to their high vesicularity and low density (from Troll and others, 2011). Courtesy of Carracedo and others (2012b).

2012 El Hierro Conference. A conference on the 2011-2012 submarine eruption will take place in the Canary Islands on 10-15 October 2012. The scientific program will cover a broad variety of topics related to volcanic risk management at oceanic island volcanoes and the balance between short-term hazards posed by volcanoes and benefits of volcanism over geologic time.

References. Carracedo, J-C., Perez-Torrado, F-J., Rodriguez-Gonzalez, A., Fernandez-Turiel, J-L., Klügel, A., Troll, V.R., and Wiesmaier, S., 2012a, The ongoing volcanic eruption of El Hierro, Canary Islands, Eos, Transactions, American Geophysical Union, v. 93, no. 9, pp. 89-90.

Carracedo, J.C., Torrado, F.P., González, A.R., Soler, V., Turiel, J.L.F., Troll, V.R., and Wiesmaier, S., 2012b, The 2011 submarine volcanic eruption in El Hierro (Canary Islands), Geology Today, v. 28, issue 2, pp. 53-58.

Carracedo, J.C., 2008, Canarian Volcanoes: La Palma, La Gomera and El Hierro, 213 pp., Editorial Rueda, Madrid.

Carracedo, J.C., Pérez, F.J., Ancochea, E., Meco J., Hernán, F., Cubas C.R., Casillas, R., Rodriguez, E., and Ahijado, A., 2002, Cenozoic volcanism II: The Canary Islands, in: The Geology of Spain, Gibbons, W., and Moreno, T., eds, The Geological Society of London, pp. 439-472.

Carracedo, J.C., Badiola, E.R., Guillou, H.J., de La Nuez, J., and Torrado, F.J.P., 2001, Geology and volcanology of La Palma and El Hierro, western Canaries, Estudios Geológicos, v. 57, no. 5-6, pp. 171-295.

Guillou, H., Carracedo, J.C., Torrado, F.P., and Badiola, E.R., 1996, K-Ar ages and magnetic stratigraphy of a hotspot-induced, fast grown oceanic island: El Hierro, Canary Islands, Journal of Volcanology and Geothermal Research, v. 73, no. 1-2, pp. 141-155.

Masson, D.G., Watts, A.B., Gee, M.J.R., Urgeles, R., Mitchell, N.C., Le Bas, T.P., and Canals, M., 2002, Slope failures on the flanks of the western Canary Islands, Earth-Science Reviews, v. 57, no. 1-2, pp. 1-35.

Siebert, L., Simkin, T., and Kimberly, P., 2010, Volcanoes of the World, Third Edition, Smithsonian Institution, Washington, D.C., and University of California Press, Berkeley, 551 pp.

Troll, V.R., Klügel, A., Longpré, M.-A., Burchardt, S., Deegan, F.M., Carracedo, J.C., Wiesmaier, S., Kueppers, U., Dahren, B., Blythe, L.S., Hansteen, T., Freda, C.D., Budd, A., Jolis, E.M., Jonsson, E., Meade, F., Berg, S., Mancini, L., and Polacci, M., 2011, Floating sandstones off El Hierro (Canary Islands, Spain): the peculiar case of the October 2011 eruption. Solid Earth Discussion, v. 3, pp. 975-999.

Viñuela, J.M., 2012, (online) The Canary Islands Hot Spot, www.mantleplumes.org/Canary.html, updated 21 December 2007, accessed 27 March 2012.

Geologic Background. The triangular island of Hierro is the SW-most and least studied of the Canary Islands. The massive shield volcano is truncated by a large NW-facing escarpment formed as a result of gravitational collapse of El Golfo volcano about 130,000 years ago. The steep-sided scarp towers above a low lava platform bordering 12-km-wide El Golfo Bay, and three other large submarine landslide deposits occur to the SW and SE. Three prominent rifts oriented NW, NE, and south at 120 degree angles form prominent topographic ridges. The subaerial portion of the volcano consists of flat-lying Quaternary basaltic and trachybasaltic lava flows and tuffs capped by numerous young cinder cones and lava flows. Holocene cones and flows are found both on the outer flanks and in the El Golfo depression. Hierro contains the greatest concentration of young vents in the Canary Islands. Uncertainty surrounds the report of an historical eruption in 1793.

Information Contacts: Alicia Felpeto Rielo, Instituto Geográfico Nacional (IGN), General Ibáñez de Ibero, 3. 28003, Madrid, España (URL: http://www.ign.es/); Volcano Discovery (URL: http://www.volcanodiscovery.com); Earthquake Report (URL: http://www.earthquake-report.com); University of Las Palmas de Gran Canaria (ULPGC) (URL: http://www.ulpgc.es); Canaries News (URL: http://www.canariesnews.com); Instituto Oceanográfico Español (IEO) (URL: htp://www.ieo.es).

A memorable eruption at Kelut began in August 2007 injecting what became a substantial lava dome in the midst of a crater lake. The process was devoid of large violent steam explosions of the kind often associated with molten lava extruding into a lake. The passively emplaced lava dome evaporated and displaced most or all of the crater lake. Dome extrusion had clearly stopped by April 2008 (BGVN 33:07) or perhaps by May 2008 (De Bélizal and others, 2012). Since then and as late as April 2012, the Center of Volcanology and Geological Hazard Mitigation (CVGHM), has noted ongoing quiet, at times broken by the emergence of diffuse white plumes. Those plume were seen in June 2009 rising 50-150 m above the crater and the new dome was still emitting steam in February 2012. As of 30 March 2012, the Alert Level remained Green, although CVGHM recommended that people not approach the lava dome due to instability of the area and the presence of potentially high temperatures and poisonous gases.

Three short subsections follow. The first discusses uplift at Kelut during 2007-2008 as part of a larger survey of volcanic deformation on Java (Philibosian and Simons, 2011). The next subsection discusses a paper that provides an overview on the unexpectedly tranquil eruption, which, though of substantial size, was one of Kelut's few substantial yet passive eruptions in the historic record (De Bélizal and others, 2012). The authors surveyed residents to assess how they felt about how authorities had managed the crisis. The third subsection below discusses the dome's declining thermal output in early 2008, and presents a photo taken in February 2011 showing the steaming dome's spiny upper surface.

2007-2008 deformation. Philibosian and Simons (2011) discussed satellite-borne (Japanese ALOS) L-band synthetic aperture radar used to conduct a comprehensive survey of volcanic deformation on Java during 2007-2008. For Kelut, the authors found a possible 15 cm line-of-sight change in late 2008, an uplift. The area of uplift was limited to the very top of Kelut and was only a few hundred meters wide. However, the authors state that, given there were only two radar acquisitions after this late 2008 uplift, it was "difficult to judge whether this was permanent, real deformation rather than a short-term atmospheric effect." According to the authors, "the volcano did not exhibit a significant deformation before or during the dome extrusion in our time series" (figure 13).

Figure 13. Time series of Kelut's deformation during October 2006-January 2009 (summing all the time steps and for satellite track 428). The plot shows the 15-cm line-of-sight change consistent with an uplift peaking during late 2008. The period of observed lava dome extrusion (shown in red) corresponded with a minor uplift (under 5 cm along the line of sight). Taken from Philibosian and Simons (2011).

2007 eruption and crisis management revisited. De Bélizal and others (2012) discuss a survey conducted shortly after the end of an evacuation process triggered by Kelut's eruption that started in 2007.

The authors summarized Kelut's unrest that started prior to the extrusions first seen in August by noting that earlier, on 1 November 2007, CVGHM recorded a new peak of seismicity with signals having reached shallow depths beneath the crater floor. The crater lake temperature recorded by a thermal camera increased significantly by 6 November. A steam plume developed, reaching 550 m above the crater lake. A new lava dome extruded through the ~350 m diameter crater lake (BGVN 33:03). Progressively, nearly all the lake water vaporized as the lava dome grew to a diameter of 400 m and a height of 260 m representing a volume of ~35 x 10⁶ m³.

According to De Bélizal and others (2012), "recorded volcanic seismicity decreased shortly after the onset of dome growth. Tiltmeter records also showed the absence of any significant deformation on the flanks of the volcano. These data suggested that the magmatic pressure decreased within the volcano therefore greatly reducing the likelihood of a violent explosion. Thus, on 8 November 2007, Indonesian authorities decided to end the emergency phase. The volcano Alert Level was lowered to Level 3 'Siaga' until 30 November, when it was then lowered to Level 2 'Waspada' until August 2008."

The passively extrusive and unexpectedly non-explosive eruption was the first here in recent historical times. This called for careful monitoring of both the eruptive behavior of the volcano and the stability of a lake-bound dome plugging the vent. Tourism and agriculture ceased on its flanks for many months in anticipation of potential sudden signs of renewed activity.

The article stated that the crisis management team ordered an evacuation, which followed the rise to Alert Level 4 on 16 October 2007 (BGVN 33:03), but it noted that many residents disregarded the order because they did not consider that an eruption was imminent. The authors conducted interviews with members of the crisis management team, and undertook a questionnaire-based survey in the settlement nearest to the crater to determine how residents reacted to the crisis and how they thought authorities managed the crisis. The survey was carried out while Kelut was still under surveillance for fear of an explosive phase. According to the authors, the crisis management team "was well organized and strategic"; however, the results "showed that crisis management was not fully integrated with the way of life of the local communities at risk, and that information, communication and trust were lacking."

Decreasing thermal alerts in 2008 and an early 2011 photo. During November and December 2007, there were numerous days with MODVOLC thermal alerts. This number decreased in January 2008 to only six days that month. After January 2008, thermal alerts had been absent as late as 27 April 2012. The probable cause was the cooling of the dome to the point where the levels of thermal radiation emitted dropped below the threshold values needed to create MODVOLC alerts.

A photo of Kelut taken by Daniel Quinn in early 2011 shows the steaming, rough-surfaced lava dome in the crater (figure 14). The photo only showed a small portion of the entire crater floor, but on the N side of the dome, the crater floor contained a dark brown, muddy-colored patch of water the photographer considered a large puddle. Some 2010 photos on the Picassa website showed a small body of water on the crater floor at that time.

Figure 14. A late January or early February 2011 photo taken of Kelut's new dome from a high spot on the NNW rim. Apparent are both the dome's spiny upper surface, and many areas of the dome still emitting small amounts of steam. The photo appeared on the Picassa website and is used with the permission of the photographer, Daniel Quinn.

According to Daniel Quinn, the photo in figure 14 was taken on the rim at a spot accessed via a small pavilion he passed walking from the car parking area. He took the photo having walked clockwise about as far around the rim as he could travel before reaching vertical cliffs. Pungent odors were absent during his visit.

References. De Bélizal, É., Lavigne, F., Gaillard, J., Grancher, D., Pratomo, I., and Komorowski, J. , 2012. The 2007 eruption of Kelut volcano (East Java, Indonesia): Phenomenology, crisis management and social response, Geomorphology, v. 136, issue 1, p. 165-175.

Philibosian, B., and Simons, M., 2011. A survey of volcanic deformation on Java using ALOS PALSAR interferometric time series, Geochemistry Geophysics Geosystems, v. 12, no. 11, 8 November 2011, Q11004, 20 pp. (DOI:10.1029/2011GC003775).

Geologic Background. The relatively inconspicuous Kelut stratovolcano contains a summit crater lake that has been the source of some of Indonesia's most deadly eruptions. A cluster of summit lava domes cut by numerous craters has given the summit a very irregular profile. Satellitic cones and lava domes are also located low on the E, W, and SSW flanks. Eruptive activity has in general migrated in a clockwise direction around the summit vent complex. More than 30 eruptions have been recorded from Gunung Kelut since 1000 CE. The ejection of water from the crater lake during the typically short but violent eruptions has created pyroclastic flows and lahars that have caused widespread fatalities and destruction. After more than 5000 people were killed during an eruption in 1919, an ambitious engineering project sought to drain the crater lake. This initial effort lowered the lake by more than 50 m, but the 1951 eruption deepened the crater by 70 m, leaving 50 million cubic meters of water after repair of the damaged drainage tunnels. After more than 200 deaths in the 1966 eruption, a new deeper tunnel was constructed, and the lake's volume before the 1990 eruption was only about 1 million cubic meters.

Information Contacts: Center of Volcanology and Geological Hazard Mitigation (CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://vsi.esdm.go.id/); Daniel P. Quinn (URL: http://bubbingtondump.com/).

This report on Long Valley caldera, California, summarizes USGS reports for 2009. The volcano remained non-eruptive. Long Valley Observatory (LVO) is now part of the California Volcano Observatory (CalVO). A tectonic earthquake sequence during 2011 in nearby Hawthorne, Nevada, is also discussed.

Long Valley caldera entered relative quiescence in the spring of 1999 (BGVN 26:07) following unrest that began in 1980 (SEAN 07:05); this relative quiescence continued through 2009.

Seismicity during 2009 was characterized by a low level of seismicity within the caldera, and a typical higher level of seismicity in the surrounding Sierra Nevada range (figure 41). Three recorded earthquakes were larger than M 3.0, yet none of them occurred within the region of Long Valley caldera as delimited by LVO. The largest earthquakes within Long Valley caldera were an M 2.7 on 9 January in the S moat, and a pair of M 2.3 earthquakes on 10 December that were located beneath the resurgent dome.

Figure 41. Seismicity in the region of Long Valley caldera and the surrounding Seirra Nevada range. The upper red dashed outline indicates volcanic areas associated with Long Valley caldera (including Mammoth Mountain and Inyo Craters), and the red dashed and dotted outline indicates the adjacent Sierra Nevada range. Earthquake epicenters are shown with symbols proportional to earthquake magnitudes, according to the scale at top-right. Modified from USGS-LVO.

Deep seismic swarm at Mammoth Mountain.At Mammoth Mountain, increased seismicity began in late May, and a deep seismic swarm occurred on 29 September. The 29 September seismic swarm included over 50 M ≥0.5 high-frequency earthquakes that occurred at depths of 20-25 km, depths inferred to be in the mafic lower crust (figure 42). The high frequencies of these earthquakes indicated brittle-rock failure similar to shallow earthquakes that typically occur at <10 km depth, and were distinctly different than the long-period earthquakes that occur within the silicic upper crust, at depths of 10-25 km. The increased seismicity at Mammoth Mountain during 2009 produced more earthquakes there than occurred within Long Valley caldera (figures 41, 42, and 43).

Figure 42. Map (left) and cross-section (right) views focusing on Mammoth Mountain seismicity during 2009. Note the two main clusters of earthquakes at ~0-7 km and ~20-25 km depth. Earthquakes are shown by symbols proportional to earthquake magnitude, shown by the scale at left. The line A-A' on the map indicates the plane of projection of the cross-section. The inferred mafic lower crust and silicic upper crust regions are indicated to the right of the cross-section. The cross-section also indicates interpreted brittle and plastic zones and the typical source area for deep, long-period (LP) earthquakes. Modified from USGS-LVO.

Figure 43. Plot of the cumulative number of earthquakes within Long Valley caldera (dashed line) and beneath Mammoth Mountain (solid line, highlighted in orange) during 2009. The 29 September deep earthquake swarm took place within a longer episode of enhanced seismicity at Mammoth Mountain that lasted from mid-2009 through at least the end of the year. Mammoth Mountain's cumulative 2009 seismicity surpassed that at the rest of the Long Valley caldera area. Courtesy of USGS-LVO.

Slow inflation of the caldera's resurgent dome. Deformation trends during 2007-2009 highlighted slow inflation of the resurgent dome. At the end of 2009, the height of the resurgent dome remained ~75 cm higher than prior to the onset of unrest in 1980. Measurements since 2007 indicated horizontal displacement rates of ~5 mm/year, mostly in a pattern radiating away from the resurgent dome (figure 44).

Figure 44. Horizontal displacement rates determined by GPS at different measurement sites in and around Long Valley caldera during the start of 2007 to early 2010, which highlight a trend of expansion away from the resurgent dome. Displacement rate vectors are relative to two reference sites located off the map in the Sierra Nevada range. Ellipses around arrows represent standard 2σ errors on the measurements. Light gray arrows represent insignificant displacement rates. The black dashed outline indicates the extent of Long Valley caldera, the gray dashed outline labeled "inflation source" indicates the resurgent dome, and the gray dashed outline at the SW edge of Long Valley caldera indicates Mammoth Mountain. From S to N, the brown dashed outlines indicate the Inyo Domes, Mono Craters, and Mono Lake islands. Modified from USGS-LVO.

During 2009, soil CO₂ emission measurements revealed variations typical of most previous years. The increase in seismicity at Mammoth Mountain on 29 September did not produce a corresponding increase in CO₂ emissions.

2011 Hawthorne, Nevada, earthquake sequence. In March 2011, an earthquake sequence (mentioned in LVO weekly activity updates) began in Hawthorne, Nevada (~100 km NNE of the center of Long Valley caldera) that, according to Smith and others (2011), initially sparked brief concerns of unrest at Mud Springs volcano (figure 45). Mud Springs volcano is a probable Pleistocene volcano of the Aurora-Bodie volcanic field, Nevada (Wood and Kienle, 1992). The Hawthorne earthquakes did not show volcanic signatures in near-source seismograms (Smith and others, 2011), and the sequence was quickly identified as tectonic in origin.

Figure 45. Mapped epicenters and magnitudes (legend, bottom right) of the 2011 Hawthorne, Nevada, earthquake sequence through 19 May 2011. Hawthorne is ~10 km to the NE of the top right margin of the image. Green triangles mark the locations of three temporary seismometers (TVH1-3) installed during 17-19 April 2011. Mud Springs volcano and its associated lava flows are labeled at the bottom of the image. Modified from the Nevada Seismological Laboratory, University of Nevada, Reno.

According to Smith and others (2011), "An additional concern, as the sequence . . . proceeded, was a clear progression eastward toward the Wassuk Range front fault. The east dipping range bounding fault is capable of M 7+ events, and poses a significant hazard to the community of Hawthorne and local military facilities. The Hawthorne Army Depot is an ordinance storage facility and the nation's storage site for surplus mercury."

Earthquakes of the March 2011 sequence were as strong as M 4.6 (figure 46); the largest earthquakes may have been felt in Bridgeport, CA (~60 km SW of Hawthorne, and ~70 km NNW from the center of Long Valley caldera), according to LVO. The earthquakes occurred along at least two shallow faults, originating at 2-6 km depth (Smith and others, 2011). The earthquake sequence "slowly decreased in intensity through mid-2011" (Smith and others, 2011).

Figure 46. Mapped areas of felt responses to the M 4.6 earthquake that occurred on 16 April 2011 (see scale at bottom). The hypocenter is indicated by the red star (center). This was the strongest earthquake of the 2011 Hawthorne, Nevada earthquake sequence. The red triangle near the bottom of the map shows the location of Long Valley caldera. Modified from the Nevada Seismological Laboratory, University of Nevada, Reno.

References. Smith, K.D., Johnson, C., Davies, J.A., Agbaje, T., Antonijevic, S.K., and Kent, G., 2011. The 2011 Hawthorne, Nevada, Earthquake Sequence; Shallow Normal Faulting. American Geophysical Union, Fall Meeting 2011, Abstract ##S53B-2284.

Wood, C.A. and Kienle, J., 1992. Volcanoes of North America: United States and Canada, Cambridge University Press, 354 p., pgs. 256-262.

Geologic Background. The large 17 x 32 km Long Valley caldera east of the central Sierra Nevada Range formed as a result of the voluminous Bishop Tuff eruption about 760,000 years ago. Resurgent doming in the central part of the caldera occurred shortly afterwards, followed by rhyolitic eruptions from the caldera moat and the eruption of rhyodacite from outer ring fracture vents, ending about 50,000 years ago. During early resurgent doming the caldera was filled with a large lake that left strandlines on the caldera walls and the resurgent dome island; the lake eventually drained through the Owens River Gorge. The caldera remains thermally active, with many hot springs and fumaroles, and has had significant deformation, seismicity, and other unrest in recent years. The late-Pleistocene to Holocene Inyo Craters cut the NW topographic rim of the caldera, and along with Mammoth Mountain on the SW topographic rim, are west of the structural caldera and are chemically and tectonically distinct from the Long Valley magmatic system.

Information Contacts: Dave Hill, California Volcano Observatory (CalVO), formerly theLong Valley Observatory (LVO), U.S. Geological Survey, Menlo Park, CA (URL: http://volcanoes.usgs.gov/observatories/calvo/); Nevada Seismological Laboratory, Laxalt Mineral Engineering Building, Room 322, University of Nevada-Reno, Reno, NV 89557 (URL: http://www.seismo.unr.edu/).

In this report we present seismicity at Maderas from 1998 through 2011, highlight the 2005 earthquake swarm, describe the "Tomography Under Costa Rica and Nicaragua" (TUCAN) Broadband Seismometer Experiment and the subsequent analysis of an M_w 6.3 event also from 2005, and summarize results from fieldwork conducted in 2009 with new age dates from Kapelancyzk and others (2012).

The 2009 field investigation also characterized two distinct phases of volcanism at Maderas, as recent as the Upper Pleistocene (70.4 ± 6.1 ka before present). Despite this interval without documented eruptions, it is plausible that the volcano could erupt again, but risk of a future eruption from Maderas is considered low (Kapelancyzk, 2011). More likely are hazards associated with non-eruptive processes such as seismically triggered mass wasting and gas emissions. A deadly lahar in 1996 (BGVN 21:09) emphasized that non-eruptive processes still offer considerable hazards and justify efforts to watch for and catalog non-eruptive events.

Maderas and Concepción volcanoes sit at opposite ends of the dumbbell-shaped Ometepe Island (figure 1). The population on the island is estimated at 30,000 however seasonal tourism increases that number during the year. These volcanoes are monitored by the Instituto Nicaragüense de Estudios Territoriales (INETER) with seismic stations and regular field investigations by staff volcanologists.

Figure 1. This map of Central America focuses on Maderas volcano; the inset zooms in on Lake Nicaragua and Ometepe Island. Dashed lines represent the large-scale geologic features, the Nicaraguan depression (ND) to the S and the Median Trough (MT) to the N; triangles represent volcanic centers (Kapelanczyk and others, 2012).

Seismicity. One seismic station is located on Ometepe Island within a network of ~32 stations in Nicaragua. From 1998 to 2011, INETER reported that seismicity was irregular although in most years, they located fewer than four earthquakes (table 1). Earthquakes were frequently M_L < 3.5 (M_L= Local earthquake magnitude) with focal depths ranging between the surface and 179 km.

Table 1. Earthquakes located near Maderas volcano from 1998 through 2011. For each year, the table also lists the range of the earthquakes' local magnitudes (M_L), the range of their focal depths, and their average focal depths. INETER did not comment on earthquakes that were anomalously deep (e.g. 179 km below sea level). Courtesy of INETER.

During 2005, INETER's network registered a total of 2,785 earthquakes throughout Nicaragua; 2,629 of these events were located by seismologists, 78 caused shaking that was strong enough to be reported by local populations, and 406 were located near Maderas volcano. Many of these events were located beneath Lake Nicaragua and S of Maderas volcano (figure 2). According to an interview presented in a La Prensa news article, 71% of the events were attributed to strain release along the subduction zone while 27% were associated with the volcanic chain. INETER reported that a significant number of earthquakes also occurred offshore in the Pacific Ocean with magnitudes greater than 5.0.

Figure 2. (Left) A map of epicenters for the entire year of 2005 plotted for Nicaragua and the surrounding region. (Right) A map of epicenters for the month of September 2005 plotted for the Lake Nicaragua region. On both maps, note the concentration of epicenters around Maderas at the SE portion of Ometepe Island. Courtesy of INETER.

Large regional earthquake. In their monthly bulletins, INETER reported that the earthquake swarm from August through September 2005 included an M_L 5.7 earthquake that occurred on 3 August. The USGS National Earthquake Information Center reported this event as M_s 6.2 (M_s = surface-wave magnitude). This earthquake was located ~15 km S of Maderas volcano (figure 3) and INETER reported that many homes on Ometepe Island were destroyed. Shaking was felt by local residents on the Pacific coast of Nicaragua as well as the interior of the country and in Costa Rica. INETER noted that this was the first time in memory that an event of this magnitude occurred near Maderas. Aftershocks continued for several weeks after the event (La Prensa).

Figure 3. Map views of initial (left) and double-difference (right) relocated hypocenters. The green and red stars correspond to the Mw 5.3 and 6.3 fore and main shock, respectively (Mw = moment magnitude). The initial hypocenters were cataloged by INETER except for the main shock, which was located separately using TUCAN P and S phase data (horizontal plane 95% confidence ellipse shown). The red inverted triangle represents the INETER catalog location of the main shock. Note that contour intervals are inconsistent with those elsewhere in the literature. Map is modified from French and others (2010).

This major seismic event was also captured by the "Tomography Under Costa Rica and Nicaragua" (TUCAN) Broadband Seismometer Experiment. This array of instruments was in the field from July 2004 to March 2006 (French and others, 2010). Project collaborators conducted a relocation and directivity analysis based on data from 16 of the 48 TUCAN stations. They determined the rupture was on a vertical, N60°E striking main shock plane; a secondary fault, with a strike of N350°E-N355°E, was also activated during the 5 hours following the main event.

The seismic analysis provided important insight into the regional tectonic setting while also characterizing activity that was independent from the coincident volcanism at Concepción Volcano. Just six days prior to the 3 August 2005 M_w 6.3 event, INETER reported high local seismicity and an ash explosion from Concepción (BGVN 30:07). Explosive activity had begun on 28 July but they lacked any other local diagnostic signatures at Maderas or Concepción related to the M_w 6.3 event. French and others (2010) conclude that "the eruption was not triggered at short time scales by stress transfer from slip on this fault. No earthquakes in [the] analysis relocated beneath Concepción either before or after the eruption."

These were also significant findings as they correlate well with the larger interpretation of the region's tectonic setting, supporting the "bookshelf model" (LaFemina and others, 2002). This model addresses the complexities of Nicaragua's deforming tectonic blocks that include clockwise rotation and slip on NE-striking left-lateral faults.

Volcanic history. In 2009, field investigations by Michigan Technological University student Lara Kapelanczyk yielded new age dates and geologic mapping for Maderas. Previous investigators had characterized Maderas as a small-volume (~30 km³) stratovolcano (Carr and others, 2007), lacking historic volcanic activity (Borgia and others, 2000), and having unique structural characteristics variously attributed to gravitational spreading (van Wyk de Vries and Borgia, 1996) and localized faulting (Mathieu and others, 2011).

Geologic mapping and rock sampling during field campaigns in 2009 contributed to new insight about the eruptive history of Maderas as well as the geologic hazards of the area. Geomorphologic characteristics also distinguish Maderas as an older volcanic site compared to its frequently active neighbor, Concepción (figure 4). Satellite remote sensing also distinguishes deep ravines that cut through the edifice of Maderas, features that suggest long-term, uninterrupted erosion. As recent as March 2010 (BGVN 36:10), Concepción has erupted ash and tephra.

Figure 4. A view across Lake Nicaragua in March 2010 toward the twin volcanoes on Ometepe Island, Concepción (left) and Maderas (right). Intermittent ash explosions characterized Concepción's activity in 2010. In this view, a diffuse ash plume covered Concepción's summit and was dissipating at a low altitude, spreading toward the shoreline. Courtesy of Lara Kapelanczyk, Michigan Technological University.

Geochemical data and ⁴⁰Ar/³⁹Ar dating determined that Maderas is an andesitic volcano with lava flows dating from 179.2 ± 16.4 ka to 70.4 ± 6.1 ka. These ages are significant in that, for the first time, quantitative data shows that Maderas has not been active for tens of thousands of years.

Kapelanczyk (2011) concluded that, during its lifespan, edifice construction at Maderas was marked by fault displacements that cross the major sectors of the volcano (figure 5). These major events led to the formation of a central graben and distinguish two phases of activity at Maderas: cone growth with pre-graben lava flows and post-graben lava flows. Pre-graben activity included the formation of a lateral vent and two littoral maars to the NE while post-graben activity included a lateral vent to the NW. Maar structures were also described in this research as well as structural information about the summit crater which includes a small lake, Laguna de Maderas (figure 6).

Figure 5. Geologic map of Maderas volcano (Kapelancyzk and others, 2012). Note the normal faults (heavy black lines) bounding the NNW-trending graben crossing the structure, an extension of the San Ramon fault zone (Funk and others, 2009). Pre- and post-graben lithologies and structures were recognized by Kapelancyzk (2011). Laguna de Maderas appears as the gray area within the summit crater.

Figure 6. View inside of the Maderas summit crater looking SE toward Laguna de Maderas, the summit crater lake. Courtesy of Lara Kapelanczyk, Michigan Technological University.

Based on the new information about Maderas's volcanic history, the risk associated with eruptions is considered low (Kapelanczyk, 2011). However, geophysical monitoring is important due to processes such as occasional, significant earthquakes and the potential for debris flows on the steep flanks.

In 1996 a deadly lahar occurred on the E flank (BGVN 21:09). This event was triggered during a heavy rainstorm and released a significant volume of material, enough to destroy the town of El Corozal and other settlements nearby. Deep, steep-sided ravines have cut through the slopes, especially on the lower NE and SW flanks (figure 7).

Figure 7. This satellite image of Ometepe Island was processed by GVP using near-, mid-infrared, and infrared bands (4,5,7). Water-poor soils appear cyan; brown-to-red areas indicate moist soils; water is black. A small pond is located within the circular crater of Maderas (Laguna de Maderas) and deep erosional features radiate from the summit, distinguishing the relatively older edifice from the neighboring volcano, Concepción. Recent lava flows on Concepción appear black/blue and have distinctive terminal lobes. Landsat acquired this ETM+ image on 27 January 2000 (NASA Landsat Program, 2003).

References. Borgia, A., Delaney, P.T. and Denlinger, R.P., 2000. Spreading volcanoes. Annual Review of Earth and Planetary Sciences, 28, 539-570.

Carr, M.J., Saginor, I., Alvarado, G.E., Bolge, L.L., Lindsay, F.N., Milidakis, K., Turrin, B.D., Feigenson, M.D. and Swisher, C.C., 2007. Element fluxes from the volcanic front of Nicaragua and Costa Rica. Geochemistry, Geophysics, Geosystems (G3), 8, 6.

French, S.W., Warren, L.M., Fischer, K.M., Abers, G.A., Strauch, W., Protti, J.M., and Gonzalez, V., 2010. Constraints on upper plate deformation in the Nicaraguan subduction zone from earthquake relocation and directivity analysis, Geochemistry, Geophysics, Geosystems (G3), 11, 3.

Funk, J., Mann, P., McIntosh, K., and Stephens, J., 2009. Cenozoic tectonics of the Nicaraguan depression, Nicaragua, and Median Trough, El Salvador, based on seismic-reflection profiling and remote-sensing data, GSA Bulletin 121, 11-12, 1491-1521.

Kapelanczyk, L.N., 2011. An eruptive history of Maderas Volcano using new ⁴⁰Ar/³⁹Ar ages and geochemical analyses [Master's thesis]: Houghton, MI, Michigan Technological University, 118 p.

Kapelanczyk, L.N., Rose, W.I., and Jicha, B.R., 2012. An eruptive history of Maderas volcano using new ⁴⁰Ar/³⁹Ar ages and geochemical analyses. Bulletin of Volcanology, In Review.

LaFemina, P.C., Dixon, T.H., and Strauch, W., 2002. Bookshelf faulting in Nicaragua, Geology, 30, 751-754.

Mathieu, L., van Wyk de Vries, B., Pilato, M. and Troll, V.R., 2011. The interaction between volcanoes and strike-slip, transtensional and transpressional fault zones: Analogue models and natural examples. Journal of Structural Geology, 33, 898-906.

NASA Landsat Program, 2003, Landsat ETM+ scene 7dx20000127, SLC-Off, USGS, Sioux Falls, Jan. 27, 2000.

van Wyk de Vries, B. and Borgia, A., 1996. The role of basement in volcano deformation. Geological Society Special Publication, 110, 95-110.

Geologic Background. Volcán Maderas is a roughly conical stratovolcano that forms the SE end of the dumbbell-shaped Ometepe island in Lake Nicaragua. The basaltic-to-trachydacitic edifice is cut by numerous faults and grabens, the largest of which is a NW-SE-oriented graben that cuts the summit and has at least 140 m of vertical displacement. The small Laguna de Maderas lake occupies the bottom of the 800-m-wide summit crater, which is located at the western side of the central graben. The SW side of the edifice has been affected by large-scale slumping. Several pyroclastic cones, some of which may have originated from littoral explosions produced by lava flow entry into Lake Nicaragua, are situated on the lower NE flank down to the level of Lake Nicaragua. The latest period of major growth was considered to have taken place more than 3000 years ago, but later detailed mapping has shown that the most recent dated eruptive activity took place about 70,000 years ago and that it has likely been inactive for tens of thousands of years (Kapelanczyk et al., 2012). A lahar in September 1996 killed six people in an E-flank village, but associated volcanic activity was not confirmed.

Information Contacts: Instituto Nicaragüense de Estudios Territoriales (INETER), Apartado Postal 2110, Managua, Nicaragua (URL: http://www.ineter.gob.ni/); Global Land Cover Facility (URL: http:// http://www.glcf.umiacs.umd.edu/); National Earthquake Information Center (NEIC), US Geological Survey, Geologic Hazards Team Office, Colorado School of Mines, 1711 Illinois St., Golden, CO 80401, USA (URL: https://earthquake.usgs.gov/); La Prensa (URL: http://archivo.laprensa.com.ni).

Until 4 June 2011, the volcanic complex named Puyehue-Cordón Caulle had been quiet since its last major eruption in 1960. This report summarizes an increase in seismicity in early 2011 and the ensuing eruption that began on 4 June 2011. Our previous and only reports on the complex were in March and April 1972, which offered and then dismissed a report of a 1972 eruption (CSLP Cards 1362 and 1371). Information here goes through 2011 but omits some remote sensing observations. The eruption continued through at least April 2012, but in March and again in April 2012 the eruption's diminished vigor resulted in successively lowered alert statuses. During the height of the eruption the vent emitted ash plumes and generated significant ashfall, and flights were cancelled as far away as Australia and New Zealand. Pyroclastic flows occurred, with runout distances up to 10 km.

The Puyehue-Cordón Caulle complex includes Puyehue volcano at the SE end and the Cordillera Nevada caldera at the NW end. The current eruption discussed here vented at a location roughly between these two features, along the same fissure complex that had been active in the 1960 eruption. Available information failed to disclose any other eruptive sites during the reporting interval. Although the eruption continues as this report goes to press in March 2012, the report discusses activity only during 2011. A subsequent report will discuss further details, including satellite data on eruptive plumes, and updates since the end of the 2011 reporting period. This report also contains a table that condenses reporting from the Buenos Aires Volcanic Ash Advisory Center (VAAC).

Precursory seismicity. The Southern Andes Volcanological Observatory-National Geology and Mining Service (SERNAGEOMIN) reported that on 26 April 2011 an overflight of the volcano was conducted in response to recent increased seismicity and observations of fumarolic activity by nearby residents. Scientists confirmed fumarolic activity, but did not observe any other unusual activity.

On 27 April a seismic swarm (with about 140 events under M_L 3.0) was detected at depths of 4-6 km below the complex. Most were hybrid earthquakes, the largest being M 3.9. Lower levels of seismicity continued through 29 April. That day the Alert Level was raised to Yellow (on a scale from Green to Yellow to Red).

According to SERNAGEOMIN, between 2000 on 2 June and 1959 on 3 June 2011, about 1,450 earthquakes occurred at Puyehue-Cordón Caulle (~60 earthquakes/hour, on average). More than 130 earthquakes occurred with magnitudes greater than 2.0. The earthquakes were mostly hybrid and long-period, and located in the SE sector of the Cordón Caulle rift zone at depths of 2-5 km. A flight over the volcano revelaed no significant changes. Area residents reported feeling earthquakes during the evening of 3 June through the morning of 4 June.

For a six-hour period on 4 June, seismicity increased to an average of 230 earthquakes/hour, with hypocenter depths of 1-4 km. About 12 events were of magnitudes greater than 4.0, and 50 events were of magnitudes greater than 3.0. As a result of the increased seismicity, the Alert Level was raised from Yellow to Red on 4 June.

Eruption. On 4 June 2011, an explosion from Cordón Caulle produced a set of plumes, including an ash plume described as 5 km wide and with its top at ~12 km altitude. Portions of the plume bifurcated; at ~5 km altitude a part of the plume drifted S, and at ~10 km altitude parts drifted W and E. A news account (Agency France-Presse) around this time, quoting a government official, said the eruption would lead to the evacuation of 4,270 residents.

According to the Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), SERNAGEOMIN had noted the presence of pyroclastic flow deposits, but not lava. Residents reported a strong sulfur odor and significant ash and pumice fall. According to the BBC, the number of evacuees rose to 3,500-4,000 during the next several days.

According to SERNAGEOMIN, the eruption from the Cordón Caulle rift zone, although somewhat diminished, continued on 5 June. At least five pyroclastic flows were generated from partial collapses of the eruptive column and traveled N in the Nilahue River drainage. These pyroclastic flows extended up to 10 km from the vent.

Figures 1-3 show scenes of the volcano from various perspectives, including a natural color January 2012 image from space.

Figure 1. Puyehue-Cordón Caulle's eruption seen in a long-exposure photo taken during 4-6 June 2011. The photo depicts molten material discharging over a wide area near the eruption column's base. Above the glowing, molten material there grew a substantial, rapidly rising ash plume. Much of the scene is lit by numerous bolts of lightning. Courtesy of Daniel Basualto, European Pressphoto Agency.

Figure 2. A long-exposure photograph of the eruption at the Puyehue-Cordón Caulle complex taken on 5 June 2011. The complex scene shows a wide eruption column aglow with prominent lightning strikes branching across its surface. The long exposure is evidenced by the long star trails (with stars forming streaks due to the Earth's rotation) and the superimposition of many distinct bolts of lightning. Courtesy of Franscisco Negroni, Agencia Uno/European Pressphoto Agency.

Figure 3. Satellite photo acquired on 26 January 2012 of the Puyehue-Cordón Caulle area. The natural color image was taken by the Advanced Land Imager aboard the Earth Observing (EO-1) satellite. The emissions, which blow in a narrow band toward the SE, can clearly be observed emanating from the Cordón Caulle fissure complex and not from the Puyehue volcano itself. According to a NASA Earth Observatory report, after 8 months of ceaseless activity, the landscape around the Puyehue-Cordón Caulle complex was covered in ash. The light-colored ash appears most clearly on the rocky, alpine slopes surrounding the active vent and the Puyehue caldera. Within the caldera, the ash appears slightly darker, possibly because it may be resting on wet snow that is melting and ponding during the South American summer. NASA also noted that evergreen forests on the E side of the volcano complex have been damaged by months of nearly continuous ashfall, and are now an unhealthy brown, while forests to the W had only received intermittent coatings of ash and appeared relatively healthy. Courtesy of NASA (Robert Simmon, Mike Carlowicz, and Jesse Allen).

Eruptive plumes were dense, oftentimes continuous, and extended E over Argentina and then the Atlantic Ocean (table 1). Ashfall reached up to about 15 cm thick in Argentina and adjacent parts of Chile (figures 4-6). Numerous flights were cancelled as far away as Australia and New Zealand, and many airports were forced to close temporarily (see section below).

Table 1. The Puyehue-Cordón Caulle ash plume altitudes and drift distances and directions documented by aviation authorities between 4 June 2011 and 3 January 2012. A plume on any particular date may be a continuation of a plume on the previous day(s). All maximum plume heights are stated in altitudes (a.s.l.). '-' indicates data not reported. Cloud cover often prevented video camera and satellite observations. Data from the Buenos Aires Volcanic Ash Advisory Center (VAAC) and SERNAGEOMIN.

Figure 4. Photograph published on 6 June 2011 of workers using earth-moving equipment to remove the ash that fell 100 km SE of the Puyehue-Cordón Caulle in San Carlos de Bariloche, Argentina. As discussed in a subsection below, the ash led to the cancellation of numerous public activities, and flights were suspended. Courtesy of Alfredo Leiva, Associated Press.

Figure 5. Photograph of an Air Austral jet stranded at the airport at San Carlos de Beriloche, Argentina, on 7 June 2011 after being covered with ash that blew over the Andes from the Puyehue-Cordón Caulle complex. Courtesy of Alfredo Leiva, Associated Press.

Figure 6. A member of the media walks along a road covered with ash from the Puyehue-Cordón Caulle complex that crossed Cardenal Samoré pass, a major linkage along the border between Argentina and Chile. Courtesy of Ivan Alvarado, Reuters.

According to news accounts (BBC, MailOnline, Merco Press), the Nilahue river, which runs off the N slopes of the volcano, became clogged with ash and overflowed its banks. The press reports said that the river water was steaming, having been locally heated up to 45°C by hot volcanic material, and more than four million salmon and other fish died.

During 4-5 June, ashfall several centimeters thick was reported in San Carlos de Bariloche, Argentina (about 100 km SE of the volcano) and in surrounding areas (figures 4-6). ONEMI reported that the Cardenal Samoré mountain pass border crossing between Argentina and Chile had temporarily closed on 4 June due to poor visibility caused by the heavy ashfall. According to a press report (EMOL), the road crossing the border was covered with ash that locally reached 10-15 cm thick. According to MailOnline and Boston.com, ash covered Lake Nahuel Huapi, Argentina's largest lake, which lies in the eastern foothills of the Andes. Videos documenting the eruption are abundant on the YouTube website (a search there using "Puyehue volcano" brings up over 400 hits. See several examples in the Reference list below).

By 9 June 2011, pumice and vitreous tephra had accumulated in many area lakes and rivers, darkening the color or their waters (figure 7).

Figure 7. Photo of ash-clogged Nilahue River (Chile) with steam hanging above the river. Courtesy of Reuters.

A government observation flight on 11 June revealed that the vent was located at the head of the Nilahue River's basin, a spot immediately N of the 1960 eruption fissure. Observers found that abundant amounts of ash had accumulated around the vent, as well as to the E and SW.

Scientists aboard an observation flight on 13 June reported that the eruption formed a cone located in the center of a crater ~300 to ~400 m in diameter. Gas-and-steam plumes rose from two or three locations along the same fissure as the eruptive vent. Scientists watching a strong ash emission saw the lower part of the ash column collapse. Dark gray ash plumes that rose to an altitude of ~11 km. Instrumental records around that time registered pulses of tremor. At other points on 13 June, plume heights oscillated.

On 20 June, a news article (Agency France-Presse) reported that authorities had ended the evacuation, enabling residents to return home.

SERNAGEOMIN personnel along with regional authorities flew over the Puyehue-Cordón Caulle complex on 20 June. They observed a viscous lava flow, confirming speculation of magma ascent based on seismic data from the previous few days. A 50-m-wide lava flow had traveled 200 m NW and 100 m NE from the point of emission, filling a depression. A white plume with a gray base rose 3-4 km above the crater. Devastated vegetation from pyroclastic flows was observed near the Nilahue and Abutment rivers. Pulses of tremor were detected by the seismic network.

Plumes continued through at least the end of 2011. Although there were no new aerial observations, the seismic signals indicated that the lava flow remained active. Ashfall was periodically reported in areas downwind, including on 22 June in Riñinahue (5-10 mm of ash), Llifen, Futrono, and Curarrehue, and on 25 June in Riñinahue, Pucón, and Melipeuco (in the region of Araucanía).

Decline in seismicity. By the end of June, seismic activity had decreased further. During July through at least 31 December 2011, the eruption continued at a low level. Numerous plumes (mostly white, but sometimes containing ash) were noted during this period, often rising as high as 2.5 km above the crater (4.7 km altitude) and occasionally higher. Cloudy weather often prevented satellite and camera observations. Some of the ash plumes dropped ash in nearby communities, and some ash plumes extended for hundreds of kilometers, continuing to disrupt air traffic. Occasional incandescence and lava flows were noted.

During 18-19 August 2011, a period of harmonic tremor lasted about 25 minutes and may have indicated lava emission. Incandescence was observed at night. An observation flight on 19 August showed that solidified lava had filled up a depression around the cliffs of the Cordón Caulle area; no active lava flows were noted.

On 30 October 2011 seismicity indicated a possible minor lava effusion. Ashfall was reported in Río Bueno (80 km WNW).

During the night of 11-12 November 2011, crater incandescence and small explosions were observed. Satellite imagery showed ash plumes drifting 90 km NE on 11 November and 400 km SE on 12 November. Ash fell in areas on the border of Chile and Argentina, and at Paso Samore on 12 November. As of 31 December 2011, the Alert Level remained at Red.

Disruption of airline traffic. Based upon a review of news accounts on the Internet, the massive ash plumes resulting from the eruption caused major delays and cancellations of air traffic worldwide. Between 4-14 June, numerous flights were cancelled or disrupted in Paraguay, Chile, southern Argentina, Uruguay, and Brazil. News accounts (Reuters, CBS News, Global Media Post) reported that the two major airports serving Buenos Aires, Argentina, and the international airport in Montevideo, Uruguay, closed for several days as did many airports in southern Argentina, including those in Patagonia. One of the worst hit airports serves the ski resort city of San Carlos de Bariloche, Argentina. On 9 June alone, workers removed about 15,000 tons of volcanic ash (600 truckloads) from the airport's main runway.

According to news accounts (Sydney Morning Herald, Agency France-Presse, Stuff, Australian Associated Press), by the middle of June, the ash plume that had been drifting mostly E since the beginning of the eruption had reached Australia and New Zealand. This caused flight disruptions and airport closures in Australia.

By the third week in June, according to the Associated Press, plumes from the eruption had circumnavigated the globe, arrived in the W part of Chile (in Coyhaique, 550 km S of the volcano), and again caused the cancellation of domestic flights. During the last week of June, numerous flights in and around Argentina and Chile were again cancelled, as well as some flights in Uruguay. According to Stuff, Associated Press, and South Africa To, ash from the second circumnavigation of the ash plume again disrupted flights at Capetown and Port Elizabeth, South Africa, as well as in Australia.

During the first two weeks of July, numerous flights in and around Argentina and Uruguay were cancelled and some airports remained closed. According to Merco, the first private plane landed around 17 July at the airport in Bariloche, Argentina, since the airport had closed on 4 June. On 17 September, the first commercial flights resumed at Bariloche.

Ash clouds remained a problem for months after the eruption. According to news articles, several domestic and international flights in Argentina, Brazil, Chile and Uruguay were cancelled on 16 October due to re-suspended ash kicked up by high winds in the region. Flights resumed the next day. According to the Agency France-Presse, airborne ash again disrupted or cancelled flights in Uruguay and Argentina on 22 and 26 November.

References (sample of videos available on Youtube):

1. !!Rock, ash fill overflowing river in Chile (Cordon Caulle)!!; MSNBC.com, uploaded by ThisisMotherNature on 10 June 2011. URL: http://www.youtube.com/watch?v=Mw3132MPfvE [Lahar scenes; MSNBC newscast in English]

2. Chile Volcano Erupts (Breathtaking Raw Video) 4th June 2011; (original author uncertain), uploaded by horrificStorms on 14 June 2011. URL: http://www.youtube.com/watch?feature=fvwp&NR=1&v=ZIq0tlYVb9U [Umbrella cloud forms above rising ash plume, seen from the ground; a yet-unidentified newscast]

3. Dormant Puyehue volcano in Chile erupts after lying dormant for decades; SkyNews, 2011, uploaded by TruthTube451 on 5 June 2011. URL: http://www.youtube.com/watch?NR=1&feature=endscreen&v=xhANgMJdvsk Source: SkyNews (URL: http://news.sky.com) [Newscast showing rising plumes, ashfall, and scenes of mitigation efforts]

4. Buzo intentando nadar en el lago Nahuel Huapi, el cuál se encuentra cubierto por una gruesa capa de cenizas volcánicas emitidas por volcán Puyehue. Uploaded by SonyOficial on 14 June 2011. URL: http://www.youtube.com/watch?v=4_cXUVZJxP8&feature=fvsr [An amusing attempt to enter Nahuel Huapi Lake to scuba dive beneath a thick mat of floating tephra. This video exceeded 1 million views on 16 November 2011.]

Geologic Background. The Puyehue-Cordón Caulle volcanic complex (PCCVC) is a large NW-SE-trending late-Pleistocene to Holocene basaltic-to-rhyolitic transverse volcanic chain SE of Lago Ranco. The 1799-m-high Pleistocene Cordillera Nevada caldera lies at the NW end, separated from Puyehue stratovolcano at the SE end by the Cordón Caulle fissure complex. The Pleistocene Mencheca volcano with Holocene flank cones lies NE of Puyehue. The basaltic-to-rhyolitic Puyehue volcano is the most geochemically diverse of the PCCVC. The flat-topped, 2236-m-high volcano was constructed above a 5-km-wide caldera and is capped by a 2.4-km-wide Holocene summit caldera. Lava flows and domes of mostly rhyolitic composition are found on the E flank. Historical eruptions originally attributed to Puyehue, including major eruptions in 1921-22 and 1960, are now known to be from the Cordón Caulle rift zone. The Cordón Caulle geothermal area, occupying a 6 x 13 km wide volcano-tectonic depression, is the largest active geothermal area of the southern Andes volcanic zone.

Information Contacts: Southern Andes Volcanological Observatory-National Geology and Mining Service (SERNAGEOMIN), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); 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/productos.php); Robert Simmon, Mike Carlowicz, and Jesse Allen, NASA Earth Observatory (URL: http://earthobservatory.nasa.gov); Agency France-Presse (URL: http://www.afp.com/afpcom/en/); Associated Press (URL: http://www.ap.org/); Australian Associated Press (AAP) (URL: http://aap.com.au/); BBC News (URL: http://www.bbc.co.uk/); Big Pond News (URL: http://bigpondnews.com); Boston.com (URL: http://www.boston.com); CBS News (URL: https://www.cbsnews.com/); EMOL (URL: http://www.emol.com/); europaPress (URL: http://www.europapress.es); European Pressphoto Agency (URL: http://wn.com/european_pressphoto_agency); Flight Global (URL: http://www.flightglobal.com); Global Media Post (URL: http://www.globalmediapost.com; La Mañana Neuquén (URL: http://www.lmneuquen.com.ar/); Mail Online (URL: http://www.dailymail.com.uk); MercoPress (URL: http://en.mercopress.com); Reuters (URL: http://www.reuters.com); Sky News (URL: news.sky.com); Stuff (URL: http://www.stuff.co.nz); South Africa To (URL: http://www.southafrica.to); Sydney Morning Herald (URL: http://news.smh.com.au/); The Telegraph (URL: http://bigpondnews.com).

Reventador discharged a series of small eruptions and lava flows during 2007-2009 (BGVN 33:04; 33:08; 34:03; and 34:09). Our last report (BGVN 34:09) discussed events through 26 October 2009. Since then seismicity generally remained moderate to low through at least April 2012, and ash emissions accompanying lava-dome growth intermittently occurred. Much of this report stems from work by the Instituto Geofísico-Escuela Politécnica Nacional (IG). The andesitic volcano contains a 4-km summit caldera that opens to form a large U-shaped scarp that funnels material SE (see map in BGVN 28:06). A VEI 4 eruption on 3 November 2002 (BGVN 27:11) occurred unexpectedly after a 26-year repose.

During this reporting interval, October 2009-April 2012, small plumes with occasional ash emissions accompanied dome growth (table 5). In August 2011, the top of the growing lava dome first reached the same height as the highest part of the rim. MODVOLC thermal alerts, which are satellite based using the MODIS instrument, were absent during 2011, possibly due to masking effects of cloud cover. The two tallest plumes noted in table 5 rose to approximately 7 km altitude. In addition, as discussed below in text, pyroclastic flows were also seen during the reporting interval. Lahars were common, including one that destroyed a bridge over a river on the SE flank on 25 May 2010.

Table 5. Summary of behavior and plumes at Reventador between mid-October 2009 and 18 April 2012. Some aspects of the October 2009 activity were previously reported (BGVN 34:09). Cloud cover frequently prevented observations of the volcano, and minor plumes may not have been recorded or were omitted. Heights above crater were converted to altitude by adding the summit elevation of 3.6 km. '-' indicates data not reported. Data provided by the Instituto Geofísico-Escuela Politécnica Nacional (IG), the Guayaquil Meteorolgical Watch Office (MWO) in Ecuador, and the Washington Volcanic Ash Advisory Center (VAAC).

On 20 April 2010, IG scientists flying over Reventador saw an explosion that generated a pyroclastic flow. It traveled ~200 m down the S flank. Recent deposits from earlier pyroclastic flows were also seen on the same flank. Steam-and-gas emissions also continued. On 8 May 2010, IG noted a small lahar inside the caldera.

On 25 May a destructive lahar took place that was detected for 90 minutes by the seismic network. It traveled down the SE flank and destroyed a bridge over the Marker River, ~8 km SE of the summit area. The loss of the bridge disrupted travel along Route E45 between Baeza (~34 km SSW) to Lago Agrio (also called Nueva Loja, ~121 NE).

On 28 September 2010, IG recorded three seismic episodes from Reventador. Cloud cover prevented observations during the first episode. The second seismic episode was accompanied by a steam plume containing a small amount of ash that rose 400-500 m above the crater. The third episode occurred in conjunction with a steam-and-ash plume that rose 2 km above the crater. Ash fell on the flanks.

In May 2011, seismicity began to increase and became more pronounced by early July.

During an overflight on 14 July 2011, IG scientists noted that the lava dome at the top of the 2008 cone had continued to grow (figures 37 and 38). The dome had reached the same height, or higher, as the highest part of the crater rim formed during 2002 (figures 37 and 38). Intense fumarolic activity produced continuous plumes.

Figure 37. Annotated photo of Reventador taken looking NW on 14 July 2011. The green lines trace the topographic margin of the summit caldera initially formed in the sudden 2002 eruption. The conical structure outlined in orange is a scoria or tephra cone (which includes some lavas) and spills out of the breach toward the viewer. The red line outlines the dome, initially seen in 2004, that grew substantially in 2011. Courtesy of J. Bustillos/Instituto Geofísico-Escuela Politécnica Nacional.

Figure 38. Thermal image of Reventador crater for comparison with the visual image (figure 37), also taken 14 July 2011. The measured temperature of the growing dome was ~150°C. Courtesy of S. Vallejo/Instituto Geofísico-Escuela Politécnica Nacional.

During 3-9 August cloud cover prevented observations of the lava dome, but the seismic network detected long-period and explosion-type earthquakes.

During a field trip on 6-7 January 2012, IG staff observed constant emissions of gas and steam that originated from the growing lava dome. At this point in time the dome had broadened and stood a few ten's of meters above the crater rim.

During 10-13 February 2012, IG detected new activity, including a thermal anomaly, an ash plume, and crater incandescence. This elevated activity continued during 15-21 February. Incandescence near the summit was again observed during 25-26 March but seismicity decreased around this time.

In accordance with these other observations, occasional MODVOLC thermal alerts were posted. Between 1 November 2009-1 April 2012, there were 12 days with MODVOLC thermal alerts. No thermal alerts were detected in 2011. As of 26 April 2012, six days in 2012 had thermal alerts (10, 13, 22, 26 February, 18 March, and 26 April).

Geologic Background. Reventador is the most frequently active of a chain of Ecuadorian volcanoes in the Cordillera Real, well east of the principal volcanic axis. The forested, dominantly andesitic Volcán El Reventador stratovolcano rises to 3562 m above the jungles of the western Amazon basin. A 4-km-wide caldera widely breached to the east was formed by edifice collapse and is partially filled by a young, unvegetated stratovolcano that rises about 1300 m above the caldera floor to a height comparable to the caldera rim. It has been the source of numerous lava flows as well as explosive eruptions that were visible from Quito in historical time. Frequent lahars in this region of heavy rainfall have constructed a debris plain on the eastern floor of the caldera. The largest historical eruption took place in 2002, producing a 17-km-high eruption column, pyroclastic flows that traveled up to 8 km, and lava flows from summit and flank vents.

Information Contacts: Instituto Geofísico-Escuela Politécnica Nacional (IG), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Guayaquil Meteorological Watch Office (MWO); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP), MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).

In discussing the week ending on 12 September, "Earthweek" (Newman, 1997) incorrectly claimed that a volcano named "Mount Pinukis" had erupted. Widely read in the US, the dramatic Earthweek report described terrified farmers and a black mushroom cloud that resembled a nuclear explosion. The mountain's location was given as "200 km E of Zamboanga City," a spot well into the sea. The purported eruption had received mention in a Manila Bulletin newspaper report nine days earlier, on 4 September. Their comparatively understated report said that a local police director had disclosed that residents had seen a dormant volcano showing signs of activity.

In response to these news reports Emmanuel Ramos of the Philippine Institute of Volcanology and Seismology (PHIVOLCS) sent a reply on 17 September. PHIVOLCS staff had initially heard that there were some 12 alleged families who fled the mountain and sought shelter in the lowlands. A PHIVOLCS investigation team later found that the reported "families" were actually individuals seeking respite from some politically motivated harassment. The story seems to have stemmed from a local gold rush and an influential politician who wanted to use volcanism as a ploy to exclude residents. PHIVOLCS concluded that no volcanic activity had occurred. They also added that this finding disappointed local politicians but was much welcomed by the residents.

PHIVOLCS spelled the mountain's name as "Pinokis" and from their report it seems that it might be an inactive volcano. There is no known Holocene volcano with a similar name (Simkin and Siebert, 1994). No similar names (Pinokis, Pinukis, Pinakis, etc.) were found listed in the National Imagery and Mapping Agency GEOnet Names Server (http://geonames.nga.mil/gns/html/index.html), a searchable database of 3.3 million non-US geographic-feature names.

The Manila Bulletin report suggested that Pinokis resides on the Zamboanga Peninsula. The Peninsula lies on Mindanao Island's extreme W side where it bounds the Moro Gulf, an arm of the Celebes Sea. The mountainous Peninsula trends NNE-SSW and contains peaks with summit elevations near 1,300 m. Zamboanga City sits at the extreme end of the Peninsula and operates both a major seaport and an international airport.

[Later investigation found that Mt. Pinokis is located in the Lison Valley on the Zamboanga Peninsula, about 170 km NE of Zamboanga City and 30 km NW of Pagadian City. It is adjacent to the two peaks of the Susong Dalaga (Maiden's Breast) and near Mt. Sugarloaf.]

References. Newman, S., 1997, Earthweek, a diary of the planet (week ending 12 September): syndicated newspaper column (URL: http://www.earthweek.com/).

Manila Bulletin, 4 Sept. 1997, Dante's Peak (URL: http://www.mb.com.ph/).

Simkin, T., and Siebert, L., 1994, Volcanoes of the world, 2nd edition: Geoscience Press in association with the Smithsonian Institution Global Volcanism Program, Tucson AZ, 368 p.

Information Contacts: Emmanuel G. Ramos, Deputy Director, Philippine Institute of Volcanology and Seismology, Department of Science and Technology, PHIVOLCS Building, C. P. Garcia Ave., University of the Philippines, Diliman campus, Quezon City, Philippines.

Xinhua News Agency filed a news report on 27 February under the headline "Volcano erupts in Somalia" but the veracity of the story now appears doubtful. The report disclosed the volcano's location as on the W side of the Gedo region, an area along the Ethiopian border just NE of Kenya. The report had relied on the commissioner of the town of Bohol Garas (a settlement described as 40 km NE of the main Al-Itihad headquarters of Luq town) and some or all of the information was relayed by journalists through VHF radio. The report claimed the disaster "wounded six herdsmen" and "claimed the lives of 290 goats grazing near the mountain when the incident took place." Further descriptions included such statements as "the volcano which erupted two days ago [25 February] has melted down the rocks and sand and spread . . . ."

Giday WoldeGabriel returned from three weeks of geological fieldwork in SW Ethiopia, near the Kenyan border, on 25 August. During his time there he inquired of many people, including geologists, if they had heard of a Somalian eruption in the Gedo area; no one had heard of the event. WoldeGabriel stated that he felt the news report could have described an old mine or bomb exploding. Heavy fighting took place in the Gedo region during the Ethio-Somalian war of 1977. Somalia lacks an embassy in Washington DC; when asked during late August, Ayalaw Yiman, an Ethiopian embassy staff member in Washington DC also lacked any knowledge of a Somalian eruption.

A Somalian eruption would be significant since the closest known Holocene volcanoes occur in the central Ethiopian segment of the East African rift system S of Addis Ababa, ~500 km NW of the Gedo area. These Ethiopian rift volcanoes include volcanic fields, shield volcanoes, cinder cones, and stratovolcanoes.

Information Contacts: Xinhua News Agency, 5 Sharp Street West, Wanchai, Hong Kong; Giday WoldeGabriel, EES-1/MS D462, Geology-Geochemistry Group, Los Alamos National Laboratory, Los Alamos, NM 87545; Ayalaw Yiman, Ethiopian Embassy, 2134 Kalorama Rd. NW, Washington DC 20008.

Following the Ms 7.8 earthquake in Turkey on 17 August (BGVN 24:08) an Email message originating in Turkey was circulated, claiming that volcanic activity was observed coincident with the earthquake and suggesting a new (magmatic) volcano in the Sea of Marmara. For reasons outlined below, and in the absence of further evidence, editors of the Bulletin consider this a false report.

The report stated that fishermen near the village of Cinarcik, at the E end of the Sea of Marmara "saw the sea turned red with fireballs" shortly after the onset of the earthquake. They later found dead fish that appeared "fried." Their nets were "burned" while under water and contained samples of rocks alleged to look "magmatic."

No samples of the fish were preserved. A tectonic scientist in Istanbul speculated that hot water released by the earthquake from the many hot springs along the coast in that area may have killed some fish (although they would be boiled rather than fried).

The phenomenon called earthquake lights could explain the "fireballs" reportedly seen by the fishermen. Such effects have been reasonably established associated with large earthquakes, although their origin remains poorly understood. In addition to deformation-triggered piezoelectric effects, earthquake lights have sometimes been explained as due to the release of methane gas in areas of mass wasting (even under water). Omlin and others (1999), for example, found gas hydrate and methane releases associated with mud volcanoes in coastal submarine environments.

The astronomer and author Thomas Gold (Gold, 1998) has a website (Gold, 2000) where he presents a series of alleged quotes from witnesses of earthquakes. We include three such quotes here (along with Gold's dates, attributions, and other comments):

(A) Lima, 30 March 1828. "Water in the bay 'hissed as if hot iron was immersed in it,' bubbles and dead fish rose to the surface, and the anchor chain of HMS Volage was partially fused while lying in the mud on the bottom." (Attributed to Bagnold, 1829; the anchor chain is reported to be on display in the London Navy Museum.)

(B) Romania, 10 November 1940. ". . . a thick layer like a translucid gas above the surface of the soil . . . irregular gas fires . . . flames in rhythm with the movements of the soil . . . flashes like lightning from the floor to the summit of Mt Tampa . . . flames issuing from rocks, which crumbled, with flashes also issuing from non-wooded mountainsides." (Phrases used in eyewitness accounts collected by Demetrescu and Petrescu, 1941).

(C) Sungpan-Pingwu (China), 16, 22, and 23 August 1976. "From March of 1976, various large anomalies were observed over a broad region. . . . At the Wanchia commune of Chungching County, outbursts of natural gas from rock fissures ignited and were difficult to extinguish even by dumping dirt over the fissures. . . . Chu Chieh Cho, of the Provincial Seismological Bureau, related personally seeing a fireball 75 km from the epicenter on the night of 21 July while in the company of three professional seismologists."

Yalciner and others (1999) made a study of coastal areas along the Sea of Marmara after the Izmet earthquake. They found evidence for one or more tsunamis with maximum runups of 2.0-2.5 m. Preliminary modeling of the earthquake's response failed to reproduce the observed runups; the areas of maximum runup instead appeared to correspond most closely with several local mass-failure events. This observation together with the magnitude of the earthquake, and bottom soundings from marine geophysical teams, suggested mass wasting may have been fairly common on the floor of the Sea of Marmara.

Despite a wide range of poorly understood, dramatic processes associated with earthquakes (Izmet 1999 apparently included), there remains little evidence for volcanism around the time of the earthquake. The nearest Holocene volcano lies ~200 km SW of the report location. Neither Turkish geologists nor scientists from other countries in Turkey to study the 17 August earthquake reported any volcanism. The report said the fisherman found "magmatic" rocks; it is unlikely they would be familiar with this term.

The motivation and credibility of the report's originator, Erol Erkmen, are unknown. Certainly, the difficulty in translating from Turkish to English may have caused some problems in understanding. Erkmen is associated with a website devoted to reporting UFO activity in Turkey. Photographs of a "magmatic rock" sample were sent to the Bulletin, but they only showed dark rocks photographed devoid of a scale on a featureless background. The rocks shown did not appear to be vesicular or glassy. What was most significant to Bulletin editors was the report author's progressive reluctance to provide samples or encourage follow-up investigation with local scientists. Without the collaboration of trained scientists on the scene this report cannot be validated.

References. Omlin, A, Damm, E., Mienert, J., and Lukas, D., 1999, In-situ detection of methane releases adjacent to gas hydrate fields on the Norwegian margin: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Yalciner, A.C., Borrero, J., Kukano, U., Watts, P., Synolakis, C. E., and Imamura, F., 1999, Field survey of 1999 Izmit tsunami and modeling effort of new tsunami generation mechanism: (Abstract) Fall AGU meeting 1999, Eos, American Geophysical Union.

Gold, T., 1998, The deep hot biosphere: Springer Verlag, 256 p., ISBN: 0387985468.

Gold, T., 2000, Eye-witness accounts of several major earthquakes (URL: http://www.people.cornell.edu/ pages/tg21/eyewit.html).

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

In December 2002 information appeared in Mongolian and Russian newspapers and on national TV that a volcano in Central Mongolia, the Har-Togoo volcano, was producing white vapors and constant acoustic noise. Because of the potential hazard posed to two nearby settlements, mainly with regard to potential blocking of rivers, the Director of the Research Center of Astronomy and Geophysics of the Mongolian Academy of Sciences, Dr. Bekhtur, organized a scientific expedition to the volcano on 19-20 March 2003. The scientific team also included M. Ulziibat, seismologist from the same Research Center, M. Ganzorig, the Director of the Institute of Informatics, and A. Ivanov from the Institute of the Earth's Crust, Siberian Branch of the Russian Academy of Sciences.

Geological setting. The Miocene Har-Togoo shield volcano is situated on top of a vast volcanic plateau (figure 1). The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Pliocene and Quaternary volcanic rocks are also abundant in the vicinity of the Holocene volcanoes (Devyatkin and Smelov, 1979; Logatchev and others, 1982). Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Figure 1. Photograph of the Har-Togoo volcano viewed from west, March 2003. Courtesy of Alexei Ivanov.

Observations during March 2003. The name of the volcano in the Mongolian language means "black-pot" and through questioning of the local inhabitants, it was learned that there is a local myth that a dragon lived in the volcano. The local inhabitants also mentioned that marmots, previously abundant in the area, began to migrate westwards five years ago; they are now practically absent from the area.

Acoustic noise and venting of colorless warm gas from a small hole near the summit were noticed in October 2002 by local residents. In December 2002, while snow lay on the ground, the hole was clearly visible to local visitors, and a second hole could be seen a few meters away; it is unclear whether or not white vapors were noticed on this occasion. During the inspection in March 2003 a third hole was seen. The second hole is located within a 3 x 3 m outcrop of cinder and pumice (figure 2) whereas the first and the third holes are located within massive basalts. When close to the holes, constant noise resembled a rapid river heard from afar. The second hole was covered with plastic sheeting fixed at the margins, but the plastic was blown off within 2-3 seconds. Gas from the second hole was sampled in a mechanically pumped glass sampler. Analysis by gas chromatography, performed a week later at the Institute of the Earth's Crust, showed that nitrogen and atmospheric air were the major constituents.

Figure 2. Photograph of the second hole sampled at Har-Togoo, with hammer for scale, March 2003. Courtesy of Alexei Ivanov.

The temperature of the gas at the first, second, and third holes was +1.1, +1.4, and +2.7°C, respectively, while air temperature was -4.6 to -4.7°C (measured on 19 March 2003). Repeated measurements of the temperatures on the next day gave values of +1.1, +0.8, and -6.0°C at the first, second, and third holes, respectively. Air temperature was -9.4°C. To avoid bias due to direct heating from sunlight the measurements were performed under shadow. All measurements were done with Chechtemp2 digital thermometer with precision of ± 0.1°C and accuracy ± 0.3°C.

Inside the mouth of the first hole was 4-10-cm-thick ice with suspended gas bubbles (figure 5). The ice and snow were sampled in plastic bottles, melted, and tested for pH and Eh with digital meters. The pH-meter was calibrated by Horiba Ltd (Kyoto, Japan) standard solutions 4 and 7. Water from melted ice appeared to be slightly acidic (pH 6.52) in comparison to water of melted snow (pH 7.04). Both pH values were within neutral solution values. No prominent difference in Eh (108 and 117 for ice and snow, respectively) was revealed.

Two digital short-period three-component stations were installed on top of Har-Togoo, one 50 m from the degassing holes and one in a remote area on basement rocks, for monitoring during 19-20 March 2003. Every hour 1-3 microseismic events with magnitude <2 were recorded. All seismic events were virtually identical and resembled A-type volcano-tectonic earthquakes (figure 6). Arrival difference between S and P waves were around 0.06-0.3 seconds for the Har-Togoo station and 0.1-1.5 seconds for the remote station. Assuming that the Har-Togoo station was located in the epicentral zone, the events were located at ~1-3 km depth. Seismic episodes similar to volcanic tremors were also recorded (figure 3).

Figure 3. Examples of an A-type volcano-tectonic earthquake and volcanic tremor episodes recorded at the Har-Togoo station on 19 March 2003. Courtesy of Alexei Ivanov.

Conclusions. The abnormal thermal and seismic activities could be the result of either hydrothermal or volcanic processes. This activity could have started in the fall of 2002 when they were directly observed for the first time, or possibly up to five years earlier when marmots started migrating from the area. Further studies are planned to investigate the cause of the fumarolic and seismic activities.

At the end of a second visit in early July, gas venting had stopped, but seismicity was continuing. In August there will be a workshop on Russian-Mongolian cooperation between Institutions of the Russian and Mongolian Academies of Sciences (held in Ulan-Bator, Mongolia), where the work being done on this volcano will be presented.

References. Devyatkin, E.V. and Smelov, S.B., 1979, Position of basalts in sequence of Cenozoic sediments of Mongolia: Izvestiya USSR Academy of Sciences, geological series, no. 1, p. 16-29. (In Russian).

Logatchev, N.A., Devyatkin, E.V., Malaeva, E.M., and others, 1982, Cenozoic deposits of Taryat basin and Chulutu river valley (Central Hangai): Izvestiya USSR Academy of Sciences, geological series, no. 8, p. 76-86. (In Russian).

Geologic Background. The Miocene Har-Togoo shield volcano, also known as Togoo Tologoy, is situated on top of a vast volcanic plateau. The 5,000-year-old Khorog (Horog) cone in the Taryatu-Chulutu volcanic field is located 135 km SW and the Quaternary Urun-Dush cone in the Khanuy Gol (Hanuy Gol) volcanic field is 95 km ENE. Analysis of seismic activity recorded by a network of seismic stations across Mongolia shows that earthquakes of magnitude 2-3.5 are scattered around the Har-Togoo volcano at a distance of 10-15 km.

Information Contacts: Alexei V. Ivanov, Institute of the Earth Crust SB, Russian Academy of Sciences, Irkutsk, Russia; Bekhtur andM. Ulziibat, Research Center of Astronomy and Geophysics, Mongolian Academy of Sciences, Ulan-Bator, Mongolia; M. Ganzorig, Institute of Informatics MAS, Ulan-Bator, Mongolia.

An eruption at Mount Elgon was mistakenly inferred when fumes escaped from this otherwise quiet volcano. The fumes were eventually traced to dung burning in a lava-tube cave. The cave is home to, or visited by, wildlife ranging from bats to elephants. Mt. Elgon (Ol Doinyo Ilgoon) is a stratovolcano on the SW margin of a 13 x 16 km caldera that straddles the Uganda-Kenya border 140 km NE of the N shore of Lake Victoria. No eruptions are known in the historical record or in the Holocene.

On 7 September 2004 the web site of the Kenyan newspaper The Daily Nation reported that villagers sighted and smelled noxious fumes from a cave on the flank of Mt. Elgon during August 2005. The villagers' concerns were taken quite seriously by both nations, to the extent that evacuation of nearby villages was considered.

The Daily Nation article added that shortly after the villagers' reports, Moses Masibo, Kenya's Western Province geology officer visited the cave, confirmed the villagers observations, and added that the temperature in the cave was 170°C. He recommended that nearby villagers move to safer locations. Masibo and Silas Simiyu of KenGens geothermal department collected ashes from the cave for testing.

Gerald Ernst reported on 19 September 2004 that he spoke with two local geologists involved with the Elgon crisis from the Geology Department of the University of Nairobi (Jiromo campus): Professor Nyambok and Zacharia Kuria (the former is a senior scientist who was unable to go in the field; the latter is a junior scientist who visited the site). According to Ernst their interpretation is that somebody set fire to bat guano in one of the caves. The fire was intense and probably explains the vigorous fuming, high temperatures, and suffocated animals. The event was also accompanied by emissions of gases with an ammonia odor. Ernst noted that this was not surprising considering the high nitrogen content of guano—ammonia is highly toxic and can also explain the animal deaths. The intense fumes initially caused substantial panic in the area.

It was Ernst's understanding that the authorities ordered evacuations while awaiting a report from local scientists, but that people returned before the report reached the authorities. The fire presumably prompted the response of local authorities who then urged the University geologists to analyze the situation. By the time geologists arrived, the fuming had ceased, or nearly so. The residue left by the fire and other observations led them to conclude that nothing remotely related to a volcanic eruption had occurred.

However, the incident emphasized the problem due to lack of a seismic station to monitor tectonic activity related to a local triple junction associated with the rift valley or volcanic seismicity. In response, one seismic station was moved from S Kenya to the area of Mt. Elgon so that local seismicity can be monitored in the future.

Information Contacts: Gerald Ernst, Univ. of Ghent, Krijgslaan 281/S8, B-9000, Belgium; Chris Newhall, USGS, Univ. of Washington, Dept. of Earth & Space Sciences, Box 351310, Seattle, WA 98195-1310, USA; The Daily Nation (URL: http://www.nationmedia.com/dailynation/); Uganda Tourist Board (URL: http://www.visituganda.com/).