Nicaragua's Volcan Masaya has an intermittent lava lake that has attracted visitors since the time of the Spanish Conquistadores; tephrochronology has dated eruptions back several thousand years. The unusual basaltic caldera has had historical explosive eruptions in addition to lava flows and actively circulating magma at the lava lake. An explosion in 2012 ejected ash to several hundred meters above the volcano, bombs as large as 60 cm fell around the crater, and ash fell to a thickness of 2 mm in some areas of the park. Brief incandescence and thermal anomalies of uncertain origin in April 2013 were followed by very little activity until the reemergence of the lava lake inside Santiago crater was reported in December 2015. By late March 2016 the lava lake had grown and intensified enough to generate a significant thermal anomaly signature (BGVN 41:08, figure 49) which persisted at a constant power level through April 2017 (BGVN 42:09, figure 53) with an increase in the number of thermal anomalies from November 2016 through April 2017. Although the MIROVA thermal anomaly signal decreased slightly in intensity during May 2017, INETER scientists reported continued strong convection at the lava lake. Similar activity continued throughout July 2017-April 2018 and is covered in this report with information provided by the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite thermal data.

A persistent thermal signature in the MIROVA data during July 2017-April 2018 supported the visual observations of the active lava lake at the summit throughout this period (figure 58). MODVOLC thermal alerts were also issued every month, with the number of alerts ranging from a high of 17 in November 2017 to a low of six in April 2018.

Figure 58. MIROVA thermal data for Masaya for the year ending on 11 May 2018 showed a persistent and steady level of heat flow consistent with the observations of the active lava lake inside Santiago crater. Courtesy of MIROVA.

INETER made regular visits to the summit most months in coordination with specialists from several universities to gather SO₂ data; CO₂, H₂S and gravity measurements were also taken during specific site visits. Thermal measurements around the lava lake inside Santiago crater taken on 24 February 2018 indicated temperatures ranging from 210-389°C. Seismicity remained very low throughout the period. The lava lake was actively convecting each time it was visited, and Pele's hair was abundant around the summit area (figures 59-64).

Figure 59. The lava lake at Masaya was actively convecting on 22 August 2017 when observed by INETER scientists. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Agosto, 2017).

Figure 60. Pele's hair near the summit of Masaya on 22 August 2017. Scale is likely a few tens of centimeters. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Agosto, 2017).

Figure 61. The summit crater (Santiago) of Masaya with an active lava lake and fumarole plume (white circle) during 8-16 January 2018. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Enero, 2018).

Figure 62. Thermal measurements of the lava lake inside Santiago crater at the summit of Masaya on 24 February 2018 indicated temperatures in the 210-389°C range. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Febrero, 2018).

Figure 63. Nindiri plateau, the broad, flat area inside the summit crater of Masaya, was covered with Pele's hair and basaltic tephra on 6 March 2018. Courtesy of Carsten ten Brink.

Figure 64. The lava lake inside Santiago crater at Masaya was actively convecting on 1 April 2018. Courtesy of Alexander Schimmeck.

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/); Alexander Schimmeck, flickr (URL: https://www.flickr.com/photos/alschim/), photo used under Creative Commons license Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0) (URL: https://creativecommons.org/licenses/by-nc-nd/2.0/); Carsten ten Brink, flickr (URL: https://www.flickr.com/photos/carsten_tb/), photo used under Creative Commons license Attribution-NonCommercial-NoDerivs 2.0 Generic (CC BY-NC-ND 2.0) (URL: https://creativecommons.org/licenses/by-nc-nd/2.0/).

Nevados de Chillán is a complex of late-Pleistocene to Holocene stratovolcanoes constructed in the Chilean Central Andes. The Nuevo and Arrau craters are adjacent vents on the NW flank of the cone of the large stratovolcano referred to as Volcán Viejo. An eruption started with a phreatic explosion and ash emission on 8 January 2016 from a new crater on the E flank of Nuevo. Explosions continued through September 2017 with ash plumes rising several kilometers and Strombolian activity sending ejecta hundreds of meters (BGVN 42:10). This report covers continuing activity from September 2017-May 2018. Information for this report is provided by Chile's Servicio Nacional de Geología y Minería (SERNAGEOMIN)-Observatorio Volcanológico de Los Andes del Sur (OVDAS), Oficina Nacional de Emergencia-Ministerio del Interior (ONEMI), and by the Buenos Aires Volcanic Ash Advisory Center (VAAC).

About 150 ash-bearing explosions were recorded during September and October 2017, with plumes rising almost 2 km above the summit. Activity decreased during the second half of October, and no ash plumes were recorded during November. A significant increase in activity in early December led to over 200 explosions with ash emissions. An overflight on 21 December 2017 produced images of a fissure at the bottom of the new crater. The presence of a growing lava dome in the crater was confirmed in early January 2018. Frequent Strombolian explosions produced nighttime incandescence at the summit and down the flanks. Hundreds of ash-bearing explosions occurred during February 2018; the largest plume rose 2.5 km above the summit, and many smaller pulses produced ash and steam that rose 1.5 km. Sporadic incandescence at night and continued explosions of magmatic gases were typical during March 2018. A large explosion on 31 March coincided with the first appearance of a low-level MODIS thermal anomaly in the MIROVA data, and incandescence from explosions at night indicated that the dome continued to grow during April and May. SERNAGEOMIN reported that the top of the lava dome was visible from the E flank for the first time at the end of May 2018.

Activity during September-December 2017. SERNAGEOMIN reported 117 ash-bearing explosions between 16 and 30 September 2017 (figure 17). The one that released the most energy occurred on 19 September. The plumes of steam and ash rose up to 1,800 m above the crater. The Buenos Aires VAAC observed a narrow plume of ash in satellite imagery moving N at 3.9 km altitude and dissipating rapidly on 15 September, and a similar plume moving SE near the summit on 26 September 2017.

Figure 17. Over 100 ash-bearing explosions were reported at Nevados de Chillán during late September 2017, including ones on 15 September (upper left), 20 September (upper right), 23 September (lower left) and 24 September (lower right). Courtesy of SERNAGEOMIN.

During the first two weeks of October 2017 there were 30 ash-bearing explosions recorded. The Buenos Aires VAAC reported small sporadic puffs of ash on 6 October 2017 that were visible in the webcam (figure 18), but not in satellite data, and a similar dense but short-lived plume on 14 October. SERNAGEOMIN reported a series of pulsating low-energy explosions visible in the webcam that drifted SW on 11 and 12 October 2017, and rose no more than 1 km above the summit.. Only two ash-bearing explosions were recorded during the second half of the month. The volcano was much quieter during November; plumes of steam were observed rising only 100 m above the summit throughout the month, with no ash-bearing plumes reported.

Figure 18. Ash plumes at Nevados de Chillán on 6 (left) and 11 (right) October 2017 were two of the 30 plumes recorded during the first half of October. Courtesy of SERNAGEOMIN.

A significant increase in activity in early December 2017 resulted in 245 explosions associated with ash emissions during the first two weeks, some rising as high as 3,000 m above the summit. The Buenos Aires VAAC reported a puff of ash on 1 December that rose to 3.7 km altitude and drifted S, dissipating rapidly. The next day another plume rose slightly higher, to 4.3 km. A dense emission on 4 December rose to 4.9 km and drifted SE before dissipating in a few hours and was not visible in satellite data. On 11 and 14 December, short-lived emissions rose to 4.3 km (figure 19). A yellow cloud of sulfur formed on 11 December within 300 m of the active crater. The webcams also recorded sporadic nighttime incandescence during increased explosions in the early morning of 14 December. Continuous steam emissions with pulses of minor ash were first noted on 16 December; they were visible in satellite imagery the next day at 3.9-4.3 km altitude drifting NE, and by 18 December, consisted only of water vapor.

Figure 19. An increase in explosive activity at Nevados de Chillán in December 2017 resulted in numerous explosions with ash plumes including on 1 December (upper left), 2 December (upper right), 4 December (lower left), and 11 December (lower right). Courtesy of SERNAGEOMIN.

In a special report released on 19 December, OVDAS-SERNAGEOMIN reported an increase in surface activity over the previous three days, recording minor explosions averaging four per hour, and seismic pulses lasting 5-10 minutes; they also noted harmonic tremor with the increase in explosion frequency. A detailed review of images taken during an overflight on 21 December revealed a fissure 30-40 m long trending NW at the bottom of the crater. Incandescence at night was regularly observed after 20 December (figure 20), and ash emissions rose to 3,000 m above the summit during the second half of the month.

Figure 20. Phreatic explosions with steam and minor ash were common at Nevados de Chillán during the last two weeks of December 2017. Ash emissions and pyroclastic flows (top image) were noted during 12-19 December, and numerous incandescent blocks accompanied the explosions on 28 December (bottom image). Courtesy of SERNAGEOMIN.

Activity during January-April 2018. SERNAGEOMIN volcanologists identified a growing lava dome within the new crater during two overflights on 9 and 12 January 2018 (figures 21); it was emerging from the fissure first identified on 21 December. During the first two weeks of January SERNAGEOMIN reported 1,027 pulsating explosions associated primarily with magmatic gases, and very little ash that rose up to 1,000 m above the summit. Confirmed ash emissions were reported on 11 January at 4.3 km altitude faintly visible moving SE in satellite imagery, according to the Buenos Aires VAAC. Nighttime incandescence from the growing dome was periodically observed (figure 22). Based on the overflight data and satellite imagery, they calculated a growth rate for the dome of 1,360 m³ per day. They estimated the size at 37,000 m³ by mid-month.

Figure 21. During an overflight at Nevados de Chillán on 9 January 2018, SERNAGEOMIN scientists observed the growing dome within the crater. Courtesy of SERNAGEOMIN.

Figure 22. Incandescence at night increased from the growing dome at Nevados de Chillán on 13 January 2018. Courtesy of SERNAGEOMIN.

Overflights on 23 and 31 January measured temperatures of 305-480°C over the surface of the dome, with the highest values at the fissure. The growth rate calculated after these overflights was 2,540 m³ per day. The webcam revealed emissions of ash and water vapor during the second half of the month that rose less than 1,000 m above the summit crater.

An explosion on 2 February 2018 sent an ash plume to 2,500 m above the summit (figure 23). Vibrations from the explosion were reported in Las Trancas (10 km) and at the Gran Hotel Termas de Chillan (5 km). SERNAGEOMIN began referring to the active crater as Nicanor, and the dome was named Gil-Cruz. During the first two weeks of February, 840 explosions associated with plumes of magmatic gases were reported. The plumes generally rose as high as 1,500 m above the summit and were often accompanied by incandescence at night. Two overflights on 7 and 14 February recorded temperatures of 500 and 550°C. SERNAGEOMIN determined a dome growth rate of 1,389 m³ per day, and a total volume of 82,500 m³ by mid-month. At least four explosions on 14 February were characterized by two simultaneous plumes, one of white steam and the other darker with a higher ash content according to SERNAGEOMIN. The highest plume that day reached 1,200 m above the summit crater. The Buenos Aires VAAC also reported a small pulse of ash on 14 February that rose to 4.6 km altitude and drifted SE. The dome continued to grow slowly during the rest of February, with a small increase in size noted during a 22 February flyover. Plumes of mostly water vapor with minor ash rose a maximum of 1,080 m above the summit during the hundreds of small explosions that took place.

Figure 23. A substantial explosion on 2 February 2018 at Nevados de Chillán sent an ash plume 2,500 m above the summit and generated vibrations that were felt 10 km from the summit. Courtesy of SERNAGEOMIN.

Sporadic incandescence at night and continued explosions of magmatic gases were typical during March 2018, with plume heights reaching 2,000 m over the Nicanor crater. During an overflight on 11 March, a temperature of 330°C was measured around the Gil-Cruz dome, which had grown to a volume of about 100,000 m³ but still remained below the crater rim. Morphological changes in the still-slowly growing dome included fracture lines and unstable large vertical blocks. A significant decrease in seismic energy was noted beginning on 24 March that ended when two larger explosions occurred on 30 and 31 March (figure 24).

Figure 24. A substantial explosion on 31 March 2018 at Nevados de Chillán generated distinct ash and steam plumes (top) and sent several large blocks down the flanks (bottom). Courtesy of SERNAGEOMIN.

During an overflight on 3 April 2018, scientists observed energetic pulses of steam and minor ash from the central NW-SE trending fissure inside the crater. They noted that lapilli from explosions had been ejected as far as 1 km from the fissure, and that the Gil-Cruz dome had increased in volume since 11 March; they also observed an area of subsidence on the top of the growing dome (figure 25). The dome was expanding toward the E side of the crater, and the top of the dome rose above the crater rim. They measured a maximum temperature of 670°C on the surface of the dome. The decrease in daily seismicity, the larger explosions of the previous days, and the increased size of the dome with greater risk of collapse, pyroclastic flows, and lahars, all led SERNAGEOMIN to raise the alert level at Chillan to Orange on 5 April 2018.

Figure 25. The growing lava dome at Nevados de Chillán, referred to as Gil-Cruz, had an active steam plume at the center when photographed by SERNAGEOMIN during an overflight on 3 April 2018. Courtesy of SERNAGEOMIN.

The Buenos Aires VAAC reported continuous emissions of steam and gas with minor ash along with a small pulse of ash on 2 April 2018. Low-altitude plumes of mostly water vapor were common throughout April 2018. Incandescence from explosions was visible on clear nights during the month, and ejecta rose as high as 250 m above the crater and was scattered around the crater rim. Seismicity remained constant at moderate levels related to the repeated explosions and the growth of the dome. A faint ash plume could be seen in visible satellite imagery on 18 April at 3.7 km altitude drifting E.

Observations reported on 1 May 2018 from the previous flyover indicated that the rate of growth of the dome had slowed to about 690 m³ per day, and the estimated volume had grown to about 150,000 m³. Activity remained at similar levels throughout May 2018. Seismic instruments recorded long-period seismicity and tremor episodes similar to previous months that corresponded with surface explosions and the extrusion of the lava dome. Seismic energy levels were moderate but fluctuated at times. Plumes of predominantly water vapor with minor gas rose a few hundred meters above the summit drifting generally S or SE before dissipating. Incandescence was often observed on clear nights, accompanied by ejection of incandescent blocks that were observed generally 100 to 150 m above the active crater. A larger explosive event took place on 7 May. Occasional plumes with minor ash were reported on 11 May. SERNAGEOMIN reported on 24 May 2018 that the top of the lava dome was visible from the E flank.

Geologic Background. The compound volcano of Nevados de Chillán is one of the most active of the Central Andes. Three late-Pleistocene to Holocene stratovolcanoes were constructed along a NNW-SSE line within three nested Pleistocene calderas, which produced ignimbrite sheets extending more than 100 km into the Central Depression of Chile. The largest stratovolcano, dominantly andesitic, Cerro Blanco (Volcán Nevado), is located at the NW end of the group. Volcán Viejo (Volcán Chillán), which was the main active vent during the 17th-19th centuries, occupies the SE end. The new Volcán Nuevo lava-dome complex formed between 1906 and 1945 between the two volcanoes and grew to exceed Volcán Viejo in elevation. The Volcán Arrau dome complex was constructed SE of Volcán Nuevo between 1973 and 1986 and eventually exceeded its height.

Information Contacts: Servicio Nacional de Geología y Minería, (SERNAGEOMIN), Observatorio Volcanológico de Los Andes del Sur (OVDAS), Avda Sta María No. 0104, Santiago, Chile (URL: http://www.sernageomin.cl/); Oficina Nacional de Emergencia - Ministerio del Interior (ONEMI), Beaucheff 1637/1671, Santiago, Chile (URL: http://www.onemi.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/inicio.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/).

The Marapi volcano on Sumatra (not to be confused with the better known Merapi volcano on Java) previously erupted on 4 June 2017, generating dense ash-and-steam plumes that rose as high as 700 m above the crater and caused minor ashfall in a nearby district (BGVN 42:10). The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Centre for Volcanology and Geological Hazard Mitigation or CVGHM).

On 27 April 2018, a phreatic explosion produced an ash plume that rose 300 m above the crater rim (figure 8); a thin ash deposit was reported in the Cubadak area (Tanah Datar Regency), about 12 km SE. Another explosion at 0703 on 2 May 2018 (figure 9) produced a voluminous dense gray ash plume that rose 4 km above the crater rim and drifted SE; seismic data recorded by PVMBG indicated that the event lasted just over 8 minutes (485 seconds).

The Alert Level has remained at 2 (on a scale of 1-4), where it has been since August 2011. Residents and visitors have been advised not to enter an area within 3 km of the summit.

Figure 8. Ash plume from a phreatic explosion at Marapi on 27 April 2018. Courtesy of Sutopo Purwo Nugroho (BNPB).

Figure 9. An explosion from Marapi on 2 May 2018 sent an ash plume to a height of 4 km. Courtesy of PVMBG.

Geologic Background. Gunung Marapi, not to be confused with the better-known Merapi volcano on Java, is Sumatra's most active volcano. This massive complex stratovolcano rises 2000 m above the Bukittinggi plain in the Padang Highlands. A broad summit contains multiple partially overlapping summit craters constructed within the small 1.4-km-wide Bancah caldera. The summit craters are located along an ENE-WSW line, with volcanism migrating to the west. More than 50 eruptions, typically consisting of small-to-moderate explosive activity, have been recorded since the end of the 18th century; no lava flows outside the summit craters have been reported in historical time.

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/).

As has been the case since at least 1971, the active lava lake in the summit crater of Nyiragongo was present during a tourist visit in June 2017, and seismicity was recorded in the crater in October 2017 (BGVN 42:11). Thermal data from satellite-based instruments shows that an open lava lake remained through 23 May 2018. MIROVA analysis of MODIS satellite thermal data (figure 64) shows nearly daily strong thermal anomalies. Similarly, MODVOLC alerts for the same time period shows a consistently frequent number of anomalies (figure 65).

Figure 64. Thermal anomaly MIROVA plot of log radiative power at Nyiragongo for the year ending 23 May 2018. Courtesy of MIROVA.

Figure 65. Map showing MODVOLC alert pixels at Nyiragongo, reflecting MODIS satellite thermal data, for the year ending 23 May 2018. Each pixel shows a thermal alert for a ground area of about 1.5 km2. Nyiragongo (many pixels) is in the center of the map, and Nyamuragira volcano (fewer pixels) is about 13 km to the NNW. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Geologic Background. One of Africa's most notable volcanoes, Nyiragongo contained a lava lake in its deep summit crater that was active for half a century before draining catastrophically through its outer flanks in 1977. In contrast to the low profile of its neighboring shield volcano, Nyamuragira, 3470-m-high Nyiragongo displays the steep slopes of a stratovolcano. Benches in the steep-walled, 1.2-km-wide summit crater mark levels of former lava lakes, which have been observed since the late-19th century. Two older stratovolcanoes, Baruta and Shaheru, are partially overlapped by Nyiragongo on the north and south. About 100 parasitic cones are located primarily along radial fissures south of Shaheru, east of the summit, and along a NE-SW zone extending as far as Lake Kivu. Many cones are buried by voluminous lava flows that extend long distances down the flanks, which is characterized by the eruption of foiditic rocks. The extremely fluid 1977 lava flows caused many fatalities, as did lava flows that inundated portions of the major city of Goma in January 2002.

Information Contacts: 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/).

The most recent eruption at Ebeko, a remote volcano in the Kuril Islands, began in October 2016 (BGVN 42:08) with explosive eruptions accompanied by ashfall. Frequent ash explosions were observed through November 2017 and the eruption remained ongoing at that time (BGVN 43:03). Activity consisting of explosive eruptions, ash plumes, and ashfalls continued during December 2017 through May 2018 (table 6). Eruptions were observed by residents in Severo-Kurilsk (about 7 km E), by volcanologists, and based on satellite imagery. The Kamchatkan Volcanic Eruption Response Team (KVERT) is responsible for monitoring Ebeko, and is the primary source of information. The Aviation Color Code (ACC) remained at Orange throughout this reporting period. This color is the second highest level of the four color scale.

Table 6. Summary of activity at Ebeko volcano from December 2017 to May 2018. Aviation Color Code (ACC) is a 4-color scale. Data courtesy of KVERT

Minor ash explosions were reported throughout the period from December 2017 through May 2018 (figure 17). Minor amounts of ash fell in Severo-Kurilisk at the end of 2017 and into 2018. Ash was reported on 2-4, and 7 December 2017; 15, 16, 18, and 29 January 2018; 8, 17, and18 February; 17 and 21 March; and 6 April. Ash plume altitudes during this reporting period ranged from 1.5 to 3.5 km (table 6); the summit is at 1.1 km.

Figure 17. Explosions from Ebeko sent ash up to an altitude of 1.5 km, or about 400 m above the summit, on 6 February 2018. Courtesy of T. Kotenko (IVS FEB RAS).

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/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/).

Langila, one of the most active volcanoes of New Britain (figure 7), has been intermittently ejecting ash since April 2016 (BGVN 42:09). Volcanic ash warnings continue to be issued by the Darwin Volcanic Ash Advisory Centre (VAAC). Recent ash plume altitudes (table 5) are in the range of 1.5-2.5 km, but several in mid-April to mid-May 2018 reached up to twice that level. Thermal anomaly data acquired by satellite-based MODIS instruments showed a gradual decrease in power level and occurrence through mid- to late-2017, followed by significantly fewer alerts and anomalies in the first half of 2018. Rabaul Volcano Observatory (RVO) data indicates the activity during 2017 was primarily located in Crater 2 (northern-most crater).

Figure 7. Satellite imagery showing Langila volcano at the far NW end of New Britain island. The brown color of recent lava flows and other volcanic deposits are easily noticeable compared to green vegetated areas. The volcano is about 9 km due south of the community labeled Poini. Imagery in this view is from sources listed on the image; courtesy of Google Earth.

Table 5. Reported data by Darwin Volcanic Ash Advisory Centre (VAAC) on ash plume altitude and drift from Langila based on analyses of satellite imagery and wind model data between 21 June 2017 and 28 May 2018.

MIROVA analysis of thermal anomalies measured by MODIS satellite sensors show a gradual decline of radiative power from early June 2017 to the end of the year (figure 8). Sporadic low-power anomalies occurred in January, April, and May 2018.

Figure 8. Thermal anomalies from MODIS data analyzed by MIROVA, plotted as log radiative power vs time for the year ending 6 June 2018. Courtesy of MIROVA.

Thermal alerts from MODVOLC analyses were concentrated between early June 2017 and late September 2017 (figure 9), with only one pixel being measured in 2018 through early June, that alert being on 5 January 2018.

Figure 9. Map showing thermal anomalies from MODIS data analyzed by MODVOLC for the year ending 6 June 2018. Courtesy of HIGP - MODVOLC Thermal Alerts System.

Geologic Background. Langila, one of the most active volcanoes of New Britain, consists of a group of four small overlapping composite basaltic-andesitic cones on the lower eastern flank of the extinct Talawe volcano. Talawe is the highest volcano in the Cape Gloucester area of NW New Britain. A rectangular, 2.5-km-long crater is breached widely to the SE; Langila volcano was constructed NE of the breached crater of Talawe. An extensive lava field reaches the coast on the north and NE sides of Langila. Frequent mild-to-moderate explosive eruptions, sometimes accompanied by lava flows, have been recorded since the 19th century from three active craters at the summit of Langila. The youngest and smallest crater (no. 3 crater) was formed in 1960 and has a diameter of 150 m.

Information Contacts: 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/); Rabaul Volcano Observatory (RVO), Geohazards Management Division, Department of Mineral Policy and Geohazards Management (DMPGM), PO Box 3386, Kokopo, East New Britain Province, Papua New Guinea.

Extensive lava flows, bomb-laden Strombolian explosions, and ash plumes emerging from MacKenney crater have characterized persistent activity at Pacaya since 1961. The latest eruptive episode began with intermittent ash plumes and incandescence in June 2015; the growth of a new pyroclastic cone inside the summit crater was confirmed in mid-December 2015. Strombolian activity from the cone continued during 2016 and it grew sporadically through September 2017 (BGVN 42:12). Lava flows first emerged from fissures around the summit during January-April 2017. Explosions from the cone summit caused growth and destruction of the top of the cone; by the end of September it was about 10 m above the elevation of the crater rim. This report describes the continued growth of the pyroclastic cone and the increasing emergence of lava flows around the summit during October 2017-March 2018. Information was provided primarily by the Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH) and satellite thermal data.

Thermal activity was relatively quiet at Pacaya during October and November 2017. The pyroclastic cone inside MacKenney crater continued to grow as material from Strombolian explosions sent ejecta a few tens of meters above the cone and onto its flanks, slowly filling the area within the crater. In late November, small lava flows began to emerge from the crater. Material flowed from the 2010 fissure on the NW side of the crater, and also appeared from new lateral fissures on the W and SW flanks. Multiple small short-lived lava flows traveled a few hundred meters down the flanks with increasing frequency during January through March 2018. Strombolian activity from the summit of the cone occasionally reached over 100 m; by the end of March, the summit of the cone remained about 25 m above the crater rim, and much of the crater was filled with ejecta (figure 84).

Figure 84. A satellite image of Pacaya dated 7 March 2018 shows MacKenney crater at the summit nearly full of ejecta from the growing pyroclastic cone, and at least two small steam plumes on the SW flank from fissures that show dark traces of recent fresh lava. Courtesy of DigitalGlobe and Google Earth.

Activity during October-December 2017. Activity during October 2017 consisted primarily of degassing with small plumes of steam and gas rising 100 m above the summit, and weak Strombolian explosions. . By the end of the month, the cone inside MacKenney crater rose about 10 m above the crater rim. At night, incandescent ejecta could be seen 25-100 m above the summit of the cone. During the last week of October strong winds dispersed the plumes SW and SE, and ashfall was reported 2 km from the crater in El Rodeo.

Steam and gas plumes generally rose no more than 25 m above the summit for the first 20 days of November 2017. Beginning on 21 November, more substantial steam and gas plumes, rising 500 m, were observed in the webcam (figure 85). An increase in tremor activity on 28 November coincided with an increase in explosive activity, a gray ash plume, and the appearance of a small lava flow on the NW flank that extended about 30 m. By the end of the month the cone had reached about 25 m above the rim of MacKenney crater and continued to grow from the accumulation of tephra fragments ranging in size from one millimeter to 50 cm that were ejected 25-100 m above the summit (figure 86). Explosions could be heard up to 1 km from the cone.

Figure 85. A steam plumes rises about 500 m above the summit of Pacaya on 21 November 2017. Courtesy of Michigan Technological University and INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, novembre 2017).

Figure 86. The pyroclastic cone at Pacaya had nearly filled MacKenney Crater by 17 November 2017 (upper photo). An explosion from the summit of the cone with ash and ejecta was captured by the thermal camera on 17 November (lower image). Courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, novembre 2017).

Strombolian explosions rising to 25 m continued in early December. On 10 December 2017, INSIVUMEH noted that there were two lava flows, one flowing on the SE flank with a length of 50-75 m and a second flowing NW towards Cerro Chino for 75-100 m. Strombolian explosions were reported 100 m above the summit of the cone on 15 December, and 25-50 m high on 25 December. The flow on the NW flank was about 100 m long on 26 December.

Activity during January-March 2018. Weak Strombolian activity continued from the cone during January 2018 with ejecta reaching 50 m above the summit. Small lava flows on the NW flank, generally only a few tens of meters long, were visible as incandescence at night (figure 87). While the height of the cone inside MacKenney crater remained about 25 m above the crater rim, material from the continuing low-level explosions had filled a large area of the crater by the end of the month. Blocks up to 1 m in diameter were also dislodged by the tremors and flow activity on the SW flank of MacKenney crater (figure 88). An increase in explosive activity beginning on 20 January resulted in audible explosions heard 2 km from the cone and fine ash deposited on the flanks. A new, larger flow also emerged from the crater early on 20 January and descended about 400 m down the SW flank, with material spalling off the front as it cooled. The following day, low-level Strombolian activity continued, and the flow remained active 200 m down the SW flank. During the last few days of January, the flow rate decreased, and the active flow was only 25 m long (figure 89).

Figure 87. Incandescence from the summit of Pacaya on 8 January 2018, viewed from the SW flank, was caused by Strombolian activity and lava flows. Photo by Instagram user @cesiasocoy, courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, enero 2018).

Figure 88. Low-level Strombolian activity sent ejecta up to 50 m above the summit of the cone at MacKenney crater on Pacaya during most of January 2018. The top of the cone inside the crater was just visible above the crater rim at the summit in this view from the NW flank taken on 17 January 2018. White blocks at the base of the SW slope on the right of the image are recently dislodged, 1-m-diameter blocks. Courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, enero 2018).

Figure 89. Lava flows on the SW flank of Pacaya on 25 January 2018, photographed by Instagram user @Carolinegod1. Courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, enero 2018).

Low-level steam and occasional gas plumes rising up to 300 m above the summit were typical during February 2018 (figure 90). In addition, intermittent lava flows continued to travel tens to a few hundred meters down the S, SW, and W flanks. A 25-m-long flow was observed on the SW flank on 2 February. On 8 February, a 150-m-long flow was noted, also on the SW flank. INSIVUMEH reported a 300-m-long lava flow from the NW area of crater on 9 February in the region of the 2010 fissure; it traveled NW towards Cerro Chino crater. A flow 75-100 m long was observed on the SW flank on 10 February; the next day 150-m-long flows were visible on both the SW and W flanks. Flows on both flanks were 100 m long on 12 February. A 30-m-long flow appeared on the SW flank on 13 February. The flow on the NW flank that began on 9 February was 20-m-wide and only 50 m long during the afternoon of 14 February. A flow was also visible on 14 February extending 250 m down the SW flank (figure 91).

Figure 90. A vigorous steam plume rose 300 m from the summit of the pyroclastic cone inside MacKenney crater at Pacaya during February 2018. The top of the cone was just visible above the crater rim in this view from the NW. Courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, febrero 2018).

Figure 91. Steaming lava flowed on the SW flank of Pacaya on 14 February 2018 and dislodged loose debris on the slope. Courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, febrero 2018).

Multiple lava flows on the SW flank ranged from 50-200 m long during 15-20 February. A flow on the W flank grew from 25 to 150 m during 17-23 February (figure 92). A flow reached 500 m down the SW flank on 25 February and after flow-front collapses was still 300 m long by the end of the month. A new surge of lava on 27 February emerged from the fissure on the NW flank of MacKenney crater and traveled 150 m towards Cerro Chino crater. Explosive activity remained constant; weak explosions, generally 3-5 times per hour, scattered ejecta on the flanks of the cone and created incandescence at night that often reached 15-35 m above the cone. The explosions also generated weak avalanches that sent material up to 1 m in diameter down the S and SW flanks to an area frequented by park visitors. Explosions were sometimes heard up to 3 km from the crater. Strombolian explosions increased in height towards the end of the month; they were reported at 150 m above the summit on 26 February.

Figure 92. A lava flow emerged from a fissure on the W flank of Pacaya on 18 February 2018 and was imaged with a thermal camera as it traveled 150 m down the flank. Courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, febrero 2018).

Strombolian activity and persistent lava flows throughout March 2018 resulted in continued growth of the pyroclastic cone within the MacKenney crater. Low-level steam and gas plumes generally rose a few tens of meters above the summit; occasional plumes rose as high as 500 m. Small lateral fissures near the crater rim produced repeated small lava flows that generally flowed less than 250 m SW and W. Weak explosions averaging 3-5 per hour sent ejecta 10-50 m above the pyroclastic cone.

During the first week of March, flows on the SW flank were active as far as 500 m down the flank. A flow on 4 March was 65 m long, and one on 5 March ranged from 50-200 m long (figure 93). During the second week, two flows were active to 300 m down the W flank, and two others on the SW flank were 150-200 m long. A flow was reported 200 m down the E flank on 16 March. Multiple lava flows were visible during 17-23 March; one traveled 250 m down the SW flank, two others went 150 m down the W flank and remained active through the end of the month.

Figure 93. Landsat satellite imagery from 5 March 2018 shows a thermal anomaly from a SW-directed lava flow at Pacaya, about 250 m long. Landsat 8 image processed by Rudiger Escobar (Michigan Technological University), courtesy of INSIVUMEH (Departamento de Investigación y servicios Geofísicos, Informe mensual de la actividad volcánica, marzo 2018).

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/); Google Earth (URL: https://www.google.com/earth/).

Historical records of eruptions at Ecuador's Volcán El Reventador date back to 1541 and include numerous lava flows and explosive events (figure 74). The largest historical eruption took place in November 2002 and generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. Eruptive activity has been continuous since 2008. Persistent ash emissions and incandescent block avalanches characterized activity during January-September 2017 with large pyroclastic and lava flows during June and August (BGVN 43:01). Explosions that produced ash plumes and incandescent blocks continued throughout October 2017-March 2018. Information is provided primarily by the Instituto Geofisico-Escuela Politecnicia Nacional (IG-EPN) of Ecuador, the Washington Volcanic Ash Advisory Center (VAAC), and also from satellite-based MODIS infrared data.

Figure 74. Aerial image of Reventador's inner caldera with its pyroclastic cone emitting a plume of steam and ash. View is looking to the W. Photograph taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Persistent, near-daily ash emissions were typical for Reventador during October 2017-March 2018 (figure 75). In general, the plumes drifted W and NW over sparsely populated nearby areas, but occasional wind-direction changes resulted in ashfall in larger communities within 30 km to the S and SW. The plume heights were commonly 1,000 m above the summit, with the highest plume rising 5 km (to 8.5 km altitude) in October. Most days that the summit and slopes were not obscured by weather clouds, there were observations of incandescent blocks falling at least 300-500 m down the flanks. Larger explosions generated Strombolian fountains and incandescent blocks that traveled 800 m down the flanks every week, even farther on occasion (figure 76). Heavy rains caused one lahar in late November; no damage was reported. Small pyroclastic flows on the flanks were observed once or twice each month (figure 77). The lava flows of June and August 2017 continued to cool on the flanks (figure 78). Thermal activity was somewhat higher during October 2017 with 19 MODVOLC thermal alerts issued, but it remained constant throughout the rest of the period with 8-11 alerts each month. The MIROVA radiative power data showed a similar pattern of moderate, ongoing activity during this time.

Figure 75. A dense ash plume rose from Reventador during the first week of December 2017, viewed from a shelter 3.5 km E of the summit. Photograph taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Figure 76. Incandescent blocks rolled hundreds of meters down the flanks of Reventador during the first week of December 2017. Photograph taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Figure 77. A small pyroclastic flow traveled down the flank of Reventador during the first week of December 2017 while an ash plume rose about 1 km above the summit. Photograph taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Figure 78. The lava flows from June and August 2017 were still cooling on the flanks of Reventador during the first week of December 2017. Photograph taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Activity during October-December 2017. The Washington VAAC issued ash advisories every day but one during October 2017. IGEPN reported near-daily emissions of ash, with plumes rising over 1,000 m many days of the month and rising to 500-800 m the other days. Plume drift directions were generally W or NW. Incandescence at the summit crater was visible on most nights, and incandescent block avalanches were seen rolling 400-800 m down the flanks during 15 nights of the month. Explosive activity intensified for several days near the end of the month (figure 79). A possible pyroclastic flow traveled down the SE flank in the morning of 24 October.

Figure 79. Strombolian explosions from two vents at the summit and incandescence on the SE flank of Reventador were captured on 24 October 2017 by B. Bernard. Photo taken from the Hosteria Reventador, 7.2 km SE from the summit. Courtesy of IGEPN (Informe Especial del Volcán El Reventador – 2017 – No. 5, Actualización de la actividad del volcán, 30 de octubre del 2017).

IGEPN scientists in the field during 23-25 October 2017 noted a high level of explosive activity with loud noises and vibrations felt in the vicinity of Hostería Reventador, about 7.2 km SE of the volcano. Thermal imaging data gathered during their trip indicated that the maximum temperatures of the explosions were over 500°C and that the lava flows of June and August were much cooler with temperatures ranging between 100 and 150°C (figure 80). A dense ash plume rose to more than 2,800 m above the summit and drifted N and E on 25 October (figure 81).

Figure 80. Thermal imaging at Reventador on 24 October 2017 indicated that the temperatures of explosions were over 500°C, and that the lava flows of June and August 2017 were much cooler, around 100-150°C. Image taken by M. Almeida from the Hosteria Reventador, 7.2 km SE from the summit. Courtesy of IGEPN (Informe Especial del Volcán El Reventador – 2017 – No. 5, Actualización de la actividad del volcán, 30 de octubre del 2017).

Figure 81. A dense ash plume rose at least 2,800 m above the summit of Reventador on 25 October 2017 and drifted NE. Photo by B Bernard, courtesy of IGEPN (Informe Especial del Volcán El Reventador – 2017 – No. 5, Actualización de la actividad del volcán, 30 de octubre del 2017).

The Washington VAAC reported numerous ash emissions during 24-26 October 2017 at altitudes of 5.8-6.1 km, drifting N and NE from the summit about 35 km. IGEPN reported continuing ash emissions beginning on 27 October that lasted for several days, including observations that day of a plume that rose to 4,900 m above the summit. The Washington VAAC reported the plume at 8.5 km altitude, the highest for the period of this report. During the last few days of October, the wind changed to the S, resulting in reports of moderate ashfall in Napo province in the towns of San Luis, San Carlos (9 km S), El Salado (14 km S), El Chaco (33 km SW), and Gonzalo Díaz de Pineda (El Bombón, 26 km SW).

Persistent ash emissions continued during November 2017 along with observations of incandescence at the summit crater. Plumes of steam, gas, and ash were reported over 600 m above the summit throughout the month; the Washington VAAC issued multiple daily aviation alerts with plume heights averaging 4.3-4.9 km altitude, usually drifting W. Higher altitude plumes over 6.0 km were reported a few times with the highest during 11-12 November rising to 6.7 km. There were reports in the morning of 1 November of ashfall in Borja and San Louis (SE) and on 4 November of minor ashfall in the communities adjacent to the volcano. Incandescent blocks were seen rolling 300 m down the flanks during 7-9 November. Heavy rains on 20 November resulted in a lahar on the E flank. During 22-27 November blocks rolled as far as 800 m down all the flanks, with many on the S and SE flanks (figure 82).

Figure 82. Steam, gas, and ash plumes, and incandescent blocks rolling down the flanks were common occurrences at Reventador throughout November 2017. Top: An ash and steam plume on 22 November 2017 rose over 600 m and drifted W. Bottom: Incandescent blocks rolled as far as 800 m down the flanks on 23 November 2017, mostly on the S and SE flanks. Courtesy of IGEPN webcam (Informe Diario del Estado del Volcán Reventador Nos. 2017-326, and 2017-327).

Although multiple daily aviation alerts continued throughout December 2017 from the Washington VAAC, weather clouds often prevented satellite observations of the ash plumes. When visible, plume heights were generally 4-5 km altitude, drifting W or NW; the highest plume on 17 December reached 5.5 km and drifted WNW before dissipating. IGEPN noted incandescence at the summit on almost all nights it was visible; incandescent blocks traveled as far as 900 m down all the flanks on 11 December, and 400-800 m most nights. They also reported ash plumes rising more than 600 m above the summit 24 days of the month. A video of typical activity at Reventador was taken by Martin Rietze during 1-7 December 2017, along with numerous excellent photographs (figures 83-85).

Figure 83. Strombolian explosions at Reventador during the first week of December 2017 sent showers of incandescent debris skyward (upper photo) before sending larger incandescent blocks hundreds of meters down the flanks of the cone (lower photo) while a dense ash plume rose from the summit area. Photographs taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Figure 84. Lightning strikes were photographed within the dense ash plumes that rose from the summit of Reventador during the first week of December 2017. Photograph copyright by Martin Rietze and used with permission.

Figure 85. Explosions at Reventador during the first week of December 2017 produced dense ash plumes and small pyroclastic flows down multiple flanks. The flanks were bare at the beginning of the ash emission event (upper photo) but small pyroclastic flows can be seen descending the flanks a few moments later (lower photo). Photograph taken during 1-7 December 2017, copyright by Martin Rietze and used with permission.

Activity during January-March 2018. Except for several cloudy days during the third week of January 2018 when no observations were possible, IGEPN reported recurring emissions of steam, gas, and ash rising over 600 m and drifting mostly W or NW throughout the month. During 11-12 January ash plumes briefly drifted E. Incandescent block avalanches were reported most often traveling 200-400 m down the S and SE flanks; a few times they travelled up to 800 m down all the flanks. Other than the cloudy days of 20-24 January, the Washington VAAC issued multiple daily aviation alerts. When ash plumes were visible in satellite imagery, plume altitudes ranged from 4.3-4.9 km, except for 30-31 January when they were reported at 5.2 km (figure 86).

Figure 86. Ash plumes and incandescent blocks were reported numerous times at Reventador during January 2018. Top left: Steam, gas, and ash were reported rising over 600 m and drifting NW and E on 2 January. Top right: on 3 January, the drift directions of the steam, gas, and ash plumes were W and NE. Lower left: Incandescent blocks were reported travelling 800 m down all the flanks on 12 January. Lower right: Ash plumes on 30 January were reported by the Washington VAAC at 5.2 km altitude, the highest during the month; they drifted N and W. Courtesy of IGEPN (Informe Diario del Estado del Volcán Reventador, Nos. 2018-2, 2018-3, 2018-12, and 2018-30).

Multiple daily aviation alerts continued from the Washington VAAC throughout February 2018. While daily plume heights mostly averaged 4.3-4.9 km altitude, there were a greater number of higher-altitude ash plumes than during recent months. A plume on 5 February was reported at 6.1 km drifting 15 km N and a plume the following day drifted 30 km ENE at 7.6 km altitude. A plume on 16 February rose to 5.5 km and drifted 55 km NW; one on 22 February rose to 7.0 km and drifted almost 100 km SE before dissipating. The next day, a plume rose to 5.5 km and drifted 35 km SE. Two separate plumes were observed in satellite imagery drifting NE on 25 February, the first rose to 5.5 km and drifted 110 km and the second rose to 6.4 km and drifted 45 km before dissipating. IGEPN reported a plume of steam, gas, and ash on 27 February that rose over 1,000 m above the summit and drifted NE. Although IGEPN only reported incandescent avalanche blocks on 11 days in February, more likely occurred because the view was obscured by weather clouds for 14 days of the month.

Minor ashfall in the vicinity of the volcano was reported by IGEPN on 1 March 2018. They also noted steam and gas plumes containing moderate amounts of ash that rose over 2,000 m above the summit and drifted SW and S that day (figure 87). IGEPN reported ash emissions around 600 m or higher above the summit on 21 days during the month. In addition to persistent incandescent activity at the summit, avalanche blocks rolled down all the flanks 800 m numerous times. A pyroclastic flow was reported 400 m down the S flank on 13 March (figure 88). Incandescent blocks rolled 1,000 m down all the flanks on 22 March. Other than a plume reported in satellite imagery at 5.8 km moving E on 26 March, all of the ash plumes reported by the Washington VAAC during March ranged from 3.9-4.9 km altitude and generally drifted NW or W.

Figure 87. A plume of steam, gas, and ash rose from Reventador on 1 March 2018; IGEPN reported it as rising over 2,000 m above the summit and drifting SW and S. A small pyroclastic flow also appeared to descend the flank. Courtesy of IGEPN (Informe Diario del Estado del Volcán Reventador, No. 2018-60).

Figure 88. Continued explosions at Reventador during March 2018 produced abundant incandescent avalanche blocks, ash plumes, and a few pyroclastic flows. Top: Abundant incandescent blocks rolled 800 m down all the flanks on 6 March 2018. Bottom: An ash plume rose over 600 m above the summit and drifted NW while a pyroclastic flow traveled 400 m down the S flank on 13 March 2018. Courtesy of IGEPN (Informe Diario del Estado del Volcán Reventador, Nos. 2018-65 and 2018-72).

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 (IGEPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.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/); Martin Rietze (URL: http://mrietze.com/web16/Ecuador17.htm).

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing since 1922. The youngest of the four vents in the complex, Caliente, has been actively erupting with ash explosions, pyroclastic, and lava flows for more than 40 years. During January-October 2017 (BGVN 42:12), daily weak ash emissions sent ash plumes to altitudes around 3.3 km, and ashfall was frequent in villages and farms within 12 km S and SW. The lava dome that appeared within the summit crater of Caliente in October 2016 continued to grow, increasing the frequency of block avalanches moving down the flanks. Several lahars affected the major drainages during May-October. Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center) provided regular updates on the continuing activity during the time period of this report from November 2017-April 2018.

Activity at Santa Maria was very consistent with little variation during November 2017-April 2018. Plumes of steam with minor magmatic gases rose continuously from the Caliente crater 300-500 m above the summit, drifting SW or SE before dissipating. In addition, tens of daily explosions with varying amounts of ash rose to altitudes of around 3.5-4.0 km and usually traveled short distances of 20-30 km before dissipating. The longest-lived plume, on 22 March 2018 drifted 100 km before dispersing. Almost all of the plumes drifted SW or SE; minor ashfall occurred in the mountains and was reported at the fincas up to 15 km away in those directions several times each month. Continued growth of the lava dome at Caliente resulted in block avalanches descending its flanks every day. The MIROVA plot of thermal energy during this time shows a consistent level of heat flow with minor variations. The spike of strongest heat flow in late March 2018 corresponds with the largest ash plume reported (figure 70) for the period.

Figure 70. MIROVA plot of thermal energy from Santa Maria for the year ending 12 July 2018 shows persistent low levels of heat flow. The spike at the end of March 2018 corresponds to the largest reported ash plume for the period. Courtesy of MIROVA.

Activity during November 2017-January 2018. During November 2017, persistent steam plumes rose 100-500 m above the summit crater at Caliente, and generally drifted SE. Tens of weak explosions daily created ash plumes that rose to about 3.2 km altitude and drifted usually SE. These resulted in ashfall reported near Finca San José on 9, 26, and 28 November, and in the mountains around Finca la Florida on 27 November. The Washington VAAC reported an ash emission seen in satellite imagery on 18 November drifting S about 15 km from the summit at 4.3 km altitude. Block avalanches were reported daily, they usually extended down the SE flank, occasionally making it to the base of the dome.

Characteristic steam plumes rising 100-500 m continued daily throughout December 2017. Numerous daily weak to moderate explosions generated ash plumes that rose to around 3.0-3.3 km altitude and drifted most often to the SW. Weak to moderate, and occasionally strong block avalanches descended the SE flank of the dome most days.

The Caliente dome maintained constant degassing with mostly steam plumes and occasional magmatic gas throughout January 2018 (figure 71). The plumes rose 50-300 m above the dome; most plumes came from the crater, but a few rose from fissures on the flanks. Explosions with ash plumes rose to 2.8-3.5 km altitude and generally drifted W or SW (figure 72). The seismic station registered 15-21 weak to moderate explosions per day. Ash generally drifted to the E or SE and caused ashfall in the regions around the fincas of San José, Patzulin, La Quina and others. Finca San José reported ashfall in the vicinity on 6, 7, and 9 January, and El Faro noted nearby ashfall on 9 January. A small plume with minor ash content was noted in satellite imagery by the Washington VAAC on 10 January drifting E at 4.3 km altitude. Ash emissions extended about 35 km SW before dissipating on 12 January, also at 4.3 km. Weak and moderate-size block avalanches occurred daily with blocks generally descending the SE or E flank of the dome.

Figure 71. A typical plume of steam and magmatic gas rose from the Caliente vent at Santa Maria on 8 January 2018. Courtesy of INSIVUMEH (Informe mensual de actividad volcánica enero 2018, Volcán Santiaguito, 1402-03).

Figure 72. An explosion at the Caliente dome of Santa Maria on 7 January 2018 sent ash a few hundred meters above the summit crater. Courtesy of INSIVUMEH (Informe mensual de actividad volcánica enero 2018, Volcán Santiaguito, 1402-03).

Activity during February-April 2018. Plumes of steam and gas continued rising daily to a few hundred meters above Caliente during February 2018. Weak and moderate explosions with steam and ash rose to 2.6-3.2 km altitude and drifted variably S, SE, W, or SW during the month (figure 73). Explosions averaged about 14 per day. Ashfall was reported in the fincas to the E and SE during the first week, including at Finca San José on 5 February, and la Florida on 10 February; they occurred in the mountainous areas W and SW during the rest of the month. Ashfall was also reported around the perimeter of the volcano several times during the last week of the month. The Washington VAAC reported an ash plume at 4.6 km altitude on 12 February drifting rapidly W, and a thin veil of gas and minor ash on 28 February extending about 15 km SW from the summit at 4.3 km altitude. Observations of repeated block avalanches down the SE flank throughout the month concurred with thermal measurements on 28 February that showed the hottest areas of the dome at the summit and on the SE flank (figure 74).

Figure 73. An explosion of steam and ash rose from Caliente at Santa Maria on 18 February 2018. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 17 al 23 de febrero de 2018).

Figure 74. Material inside the summit crater of Caliente at Santa Maria measured about 140°C on 28 February 2018, and showed the warmest region on the SE flank where most of the block avalanches occurred. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo:, Volcán Santiaguito (1402-03), Semana del 24 de febrero al 02 de marzo de 2018).

Block avalanches down the SE and S flanks of Caliente from the growing summit dome persisted at weak to moderate levels throughout March 2018 (figure 75). Ten to twenty daily ash-bearing explosions usually rose to about 3.2 km altitude and drifted SW or SE causing ashfall around the perimeter. Ashfall was reported in the mountains around Finca San José on 4-6, 9, 20, and 23 March, and in the Palajunoj area on 11 March. Steam plumes rising from the summit of Caliente to 2.9-3.1 km altitude drifting SE or SW were a daily feature of activity (figure 76). The Washington VAAC reported an ash plume on 5 March that rose to 4.6 km altitude and drifted SW before dissipating within 15 km of the summit. On 21 March, an emission was observed in satellite imagery that extended about 35 km SW from the summit at 4.6 km altitude. Another ash plume the following day also rose to 4.6 km altitude and extended almost 100 km SW before dissipating. That same day, 22 March, MODVOLC issued four thermal alerts for Santiaguito, and the MIROVA system showed a spike in thermal activity as well (figure 70).

Figure 75. Block avalanches descended the SE flank of Caliente at Santa Maria on 6 March 2018. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo:, Volcán Santiaguito (1402-03), Semana del 03 al 09 de marzo de 2018).

Figure 76. A typical steam plume rose from Caliente summit during the last week of March 2018. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 17 al 23 de marzo de 2018).

Multiple daily explosions with ash rose up to 3.2 km altitude during April 2018. The plumes drifted SW or SE, spreading fine-grained ash over the nearby hills. Finca San José reported ashfall on 2 April and the Palajunoj area reported ashfall on 10, 13, 15, and 17 April. Abundant degassing of mostly steam plumes at the Caliente crater continued throughout the month, as did the constant descent of block avalanches down the SE flank.

Geologic Background. Symmetrical, forest-covered Santa María volcano is one of the most prominent of a chain of large stratovolcanoes that rises dramatically above the Pacific coastal plain of Guatemala. The 3772-m-high stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a large, 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank and was formed during a catastrophic eruption in 1902. The renowned plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four westward-younging vents, the most recent of which is Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

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/ ); 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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html).

An eruption at Sheveluch has been ongoing since 1999, and volcanic activity was previously described through January 2018 (BGVN 43:02). Ongoing activity has consisted of pyroclastic flows, explosions, and lava dome growth with a viscous lava flow in the N. According to the Kamchatka Volcanic Eruption Response Team (KVERT), moderate emissions of gas-and-steam have continued, and ash explosions up to 10-15 km in altitude could occur at any time. The Aviation Color Code remained at Orange (the second highest level on a four-color scale) throughout this reporting period from February through April 2018.

KVERT reported continuous moderate gas-and-steam plumes from Sheveluch during February-April 2018 (figure 49). Satellite imagery interpreted by KVERT showed a thermal anomaly over the volcano on 13 days during February, 21 days in March, and 15 days in April. Cloud cover obscured satellite imagery the remainder of the time during this reporting period.

Figure 49. Photo of the lava dome at Sheveluch on 25 March 2018. Courtesy of Yu. Demyanchuk (IVS FEB RAS, KVERT).

The MIROVA system detected intermittent low-power thermal anomalies from February through April 2018. Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were not detected during this period.

Geologic Background. The high, isolated massif of Sheveluch volcano (also spelled Shiveluch) rises above the lowlands NNE of the Kliuchevskaya volcano group. The 1300 km3 volcano is one of Kamchatka's largest and most active volcanic structures. The summit of roughly 65,000-year-old Stary Shiveluch is truncated by a broad 9-km-wide late-Pleistocene caldera breached to the south. Many lava domes dot its outer flanks. The Molodoy Shiveluch lava dome complex was constructed during the Holocene within the large horseshoe-shaped caldera; Holocene lava dome extrusion also took place on the flanks of Stary Shiveluch. At least 60 large eruptions have occurred during the Holocene, making it the most vigorous andesitic volcano of the Kuril-Kamchatka arc. Widespread tephra layers from these eruptions have provided valuable time markers for dating volcanic events in Kamchatka. Frequent collapses of dome complexes, most recently in 1964, have produced debris avalanches whose deposits cover much of the floor of the breached caldera.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far East Division, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); 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/).

Heightened activity at Kikai (also known as Satsuma Iwojima) was reported during January 2013-July 2014 (BGVN 3907), which included one eruption with intermittent explosions, occasional ash and steam plumes, and sporadic weak seismic tremor. Subsequently, seismicity remained at background levels, and plume activity was low. A short-lived period of heightened activity occurred in March 2018, with increased daily plume heights, sulfur dioxide output, and seismicity. Activity returned to background levels by 26 April. This report is based on information supplied by the Japanese Meteorological Agency (JMA).

JMA reported that one small-amplitude short-duration volcanic tremor was detected on 16 March 2018. The number of volcanic earthquakes increased on 19 March, with 93 occurrences, prompting JMA to raise the Alert Level from 1 (active volcano) to 2 (restricted area around the crater), on a 5-level scale. The report noted increased thermal activity since February, with occasional visual observations of incandescence. Plume heights and volcanic earthquakes briefly increased during 22-23 March (figure 8, plot 4).

Figure 8. Plots showing multi-year records of measured plume heights (1 and 4) and volcanic earthquakes (2 and 5) during January 1998-April 2018 from Kikai. Explosive events are indicated by the small volcano icons along the top of plot 1. Plot 3 indicates measured sulfur dioxide in tons/day since 2012. The orange diamonds on plot 4 indicate observations of incandescence. Plume heights are measured in meters above the crater. This record is from a seismic station located less than 1 km from the summit. Courtesy of Japan Meteorological Agency (JMA).

The number of volcanic earthquakes was low during 27 March-2 April. A white plume at the Iwo-dake summit crater rose to 1,800 m above the crater rim in late March (figure 8, plot 4), the highest seen in many years. At the same crater a highly sensitive surveillance camera revealed incandescence at night on 27 and 28 March due to increased thermal activity. No incandescence was observed after 12 April (figure 8, plot 4).

In its report for 20-26 April, JMA noted a white plume at the Iwo-dake summit crater that rose to 700 m above the rim. A field survey conducted on 25 and 26 April confirmed the slight expansion of a thermal anomaly area when compared to 24 and 25 March, but the release amount of sulfur dioxide was slightly less than 300 tons per day (compared with 600 tons on March 24) (figure 8, plot 3).

On 27 April 2018, with volcanic earthquakes being small in number and no observed volcanic tremor, JMA determined that activity had decreased and reduced the warning level from 2 to 1.

Geologic Background. Kikai is a mostly submerged, 19-km-wide caldera near the northern end of the Ryukyu Islands south of Kyushu. Kikai was the source of one of the world's largest Holocene eruptions about 6300 years ago. Rhyolitic pyroclastic flows traveled across the sea for a total distance of 100 km to southern Kyushu, and ashfall reached the northern Japanese island of Hokkaido. The eruption devastated southern and central Kyushu, which remained uninhabited for several centuries. Post-caldera eruptions formed Iodake lava dome and Inamuradake scoria cone, as well as submarine lava domes. Historical eruptions have occurred in the 20th century at or near Satsuma-Iojima (also known as Tokara-Iojima), a small 3 x 6 km island forming part of the NW caldera rim. Showa-Iojima lava dome (also known as Iojima-Shinto), a small island 2 km east of Tokara-Iojima, was formed during submarine eruptions in 1934 and 1935. Mild-to-moderate explosive eruptions have occurred during the past few decades from Iodake, a rhyolitic lava dome at the eastern end of Tokara-Iojima.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/).

Dieng has had a history of intermittent phreatic explosions. In 2017, explosions occurred on 30 April, 24 May, and 2 July (BGVN 42:10). Another phreatic explosion occurred on 1 April 2018. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Centre for Volcanology and Geological Hazard Mitigation or CVGHM).

PVMBG reported that a phreatic explosion at the Sileri Crater lake (Dieng Volcanic Complex) occurred at 1342 on 1 April 2018, ejecting mud and material 150 m high, and up to 200 m in multiple directions. The event was preceded by black emissions that rose 90 m, and then diffuse white emissions that rose 150 m. The report noted that few tourists were in the area due to rainy weather; visitors are not permitted within 200 m of the crater rim.

According to a news report (The Jakarta Post) that cited an official of the National Disaster Management Agency (BNPB), no toxic gases such as carbon dioxide, hydrogen sulfide, or sulfur dioxide were detected in the explosion.

Geologic Background. The Dieng plateau in the highlands of central Java is renowned both for the variety of its volcanic scenery and as a sacred area housing Java's oldest Hindu temples, dating back to the 9th century CE. The Dieng volcanic complex consists of two or more stratovolcanoes and more than 20 small craters and cones of Pleistocene-to-Holocene age over a 6 x 14 km area. Prahu stratovolcano was truncated by a large Pleistocene caldera, which was subsequently filled by a series of dissected to youthful cones, lava domes, and craters, many containing lakes. Lava flows cover much of the plateau, but have not occurred in historical time, when activity has been restricted to minor phreatic eruptions. Toxic gas emissions are a hazard at several craters and have caused fatalities. The abundant thermal features and high heat flow make Dieng a major geothermal prospect.

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/); The Jakara Post (URL: http://www.thejakartapost.com).

The Kamchatka Volcanic Eruptions Response Team (KVERT) characterized Bezymianny as having weak activity from mid-June 2014 through the end of 2015, including weak or moderate gas-and-steam emissions (figures 17 and 18) and, when not obscured by clouds, weak thermal anomalies (BGVN 41:01). Observations here through May 2017 come from KVERT reports and Tokyo Volcanic Ash Advisory Center (VAAC) advisories.

Figure 17. View of the summit showing fumarolic activity at Bezymianny on 16 September 2014. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

Figure 18. Moderate gas-and-steam activity at Bezymianny on 15 April 2015. Photo by Yu. Demyanchuk; courtesy of IVS FEB RAS, KVERT.

Activity during 2016. KVERT reported that weak volcanic activity continued into January 2016, with moderate gas-and-steam activity through 12 December 2016. During this time, satellite data by KVERT showed a weak thermal anomaly over the volcano on most days, although on some days KVERT described the volcano as "quiet." Often the volcano was obscured by clouds.

The Tokyo VAAC reported that on 30 July an ash plume rose to an altitude of 3 km and drifted E, an observation based on information from the Yelizovo Airport (UHPP). Weak fumarolic activity continued in late August (figure 19).

Figure 19. A small, weak, fumarolic plume could be seen rising from Bezymianny on 24 August 2016. Photo by O. Girina; courtesy of IVS FEB RAS, KVERT.

Based on KB GS RAS (Kamchatka Branch of Geophysical Services, Russian Academy of Sciences) data, KVERT noted that seismicity began to increase on 18 November. The thermal anomaly temperature detected in satellite images also increased on 5 December, and then significantly increased on 13 December, probably caused by lava-dome extrusion. This activity prompted KVERT to raise the Aviation Color Code from Yellow, where it had been since 17 July 2014, to Orange (second highest level).

According to KVERT, a gas-and-steam plume containing a small amount of ash drifted about 118 km W on 15 December. The Tokyo VAAC noted that ash plumes rose as high as 6.1 km that same day. KVERT reported strong gas-and-steam emissions during 16-31 December (figure 20); a gas-and-steam plume drifted about 60 km SW on 18 December. A daily thermal anomaly was detected over the volcano.

Figure 20. A strong gas-and-steam plume was seen rising from Bezymianny on 19 December 2016. Photo by V. Buryi; courtesy of IVS FEB RAS, KVERT.

Activity during January-May 2017. According to KVERT, lava-dome extrusion likely continued into January 2017. Strong gas-and-steam emissions continued through 19 January 2017 and a thermal anomaly was detected over the volcano during most days. On 12 January, KVERT noted that activity had gradually decreased after an intensification during 5-24 December 2016, and thus the Aviation Color Code was lowered to Yellow. Thereafter, KVERT characterized the volcano as having moderate gas-steam activity. On 23 February, KVERT reported that the effusive eruption continued and that lava was flowing on the S flank of the lava dome.

On 9 March at about 1330, an explosive eruption occurred (figure 21). Based on webcam observations, at 1454 an ash plume rose to altitudes of 6-7 km and drifted 20 km NE. The Aviation Color Code was raised to Orange. About 30 minutes later, at 1523, an ash plume rose to altitudes of 7-8 km and drifted 60 km NW. KVERT raised the Aviation Color Code to Red, the highest level. Satellite data showed a 14-km-wide ash plume drifting 112 km NW at an altitude of 7 km. Later that day a 274-km-long ash plume identified in satellite images drifted NW at altitudes of 4-4.5 km; the majority of the leading part of the plume contained a significant amount of ash. Lava flowed down the NW part of the lava dome. The Aviation Color Code was lowered to Orange. Ash plumes drifted as far as 500 km NW.

Figure 21. The start of an explosive eruption from Bezymianny was captured in this image taken from a webcam video on 9 March 2017. Video from KB GS RAS; courtesy of IVS FEB RAS, KVERT.

KVERT reported that lava continued to advance down the NW flank of the lava dome during 10 March-21 April, and gas-and-steam plumes rose from the crater. A thermal anomaly was visible most days in satellite images. The Aviation Color Code was lowered to Yellow on 25 May. According to a KVERT report on 26 May, the volcano became quiet after the 9 March episode, although strong gas-and-steam emissions and daily thermal anomalies continued.

Thermal anomalies. Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were almost daily events during January through 2 November 2016, except none were reported in March through 19 May 2016. On many days, multiple pixels were reported (13 pixels on 1 September). The number of events diminished in December (only six days), and except for a brief period during 9-12 March 2017, none were reported after 20 December through at least 26 May 2017.

The Mirova (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, reported several hotspots each month during May-August 2016, with a significant increase in September through early November (figure 22). Numerous hotspots were again reported in December, but only a few in January and February, except for a narrow cluster during the middle of February. In contrast to the MODIS/MODVOLC data, numerous hotspots were reported in March, April, and May 2017. The vast majority of hotspots during the past 12 months were within 5 km of the volcano and were of low power.

Figure 22. Thermal anomalies at Bezymianny recorded by the MIROVA system (log radiative power) for the year ending 5 May 2017. Note stronger frequent activity in the second half of December 2016 and the stronger anomalies associated with the March 2017 activity. Courtesy of MIROVA.

Geologic Background. Prior to its noted 1955-56 eruption, Bezymianny had been considered extinct. The modern volcano, much smaller in size than its massive neighbors Kamen and Kliuchevskoi, was formed about 4700 years ago over a late-Pleistocene lava-dome complex and an ancestral edifice built about 11,000-7000 years ago. Three periods of intensified activity have occurred during the past 3000 years. The latest period, which was preceded by a 1000-year quiescence, began with the dramatic 1955-56 eruption. This eruption, similar to that of St. Helens in 1980, produced a large horseshoe-shaped crater that was formed by collapse of the summit and an associated lateral blast. Subsequent episodic but ongoing lava-dome growth, accompanied by intermittent explosive activity and pyroclastic flows, has largely filled the 1956 crater.

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/); Institute of Volcanology and Seismology, Far Eastern Branch, Russian Academy of Sciences (IVS FEB RAS), 9 Piip Blvd., Petropavlovsk-Kamchatsky 683006, Russia (URL: http://www.kscnet.ru/ivs/eng/); Kamchatka Branch of the Geophysical Service, Russian Academy of Sciences (KB GS RAS) (URL: http://www.emsd.ru/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); 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/).

The remote island of Chirinkotan is in the Northern Kuril Islands at the southern end of the Sea of Okhotsk, about 320 km SW of the tip of Kamchatka, Russia. It is an outlier about 40 km NW of the main Kuril Islands Arc. There have been very few historical observations of activity at Chirinkotan, although there is at least one confirmed 19th century observation of lava flows. A short-lived event that resulted in a small, low-level ash plume-and-gas plume was seen in satellite imagery on 20 July 2004 (Neal et al., 2005). Volcanic activity resumed in mid-2013, with intermittent ash plumes, thermal anomalies, and block lava flows reported through April 2017. The volcano is monitored by the Sakhalin Volcanic Eruption Response Team (SVERT) of the Institute of Marine Geology and Geophysics (Far Eastern Branch, Russian Academy of Science), and aviation alerts are issued by the Tokyo Volcanic Ash Advisory Center (VAAC).

A new eruptive phase began with a likely ash emission on 11 June 2013. Intermittent thermal anomalies and gas-and-steam emissions were reported for the next 12 months, sometimes drifting up to 100 km, usually SE. Renewed thermal anomalies and gas emissions were recorded during clear weather beginning on 21 November 2014. Two ash plumes observed in late July 2015 were the likely sources of fresh ashfall and block lava flows sampled during a visit by Russian geoscientists on 9 August 2015. A gas-and-steam plume on 17 November 2015 was the last activity observed, except for low-level thermal anomalies, until a substantial ash plume was captured in satellite data at 8.8 km altitude over a year later on 29 November 2016. Additional ash plumes were observed in satellite data once in late January, and twice each in March and April 2017.

Activity during May 2013-June 2014. After no reports of activity since July 2004, SVERT observed gas-and-steam emissions in satellite imagery beginning in late May 2013. They raised the Alert Level from Green to Yellow (on the four level Green-Yellow-Orange-Red scale) sometime between 27 May and 10 June. The first likely ash emission was reported on 11 June, followed by a thermal anomaly detected on 13 June. Thermal anomalies continued to be detected by SVERT during June and July 2013. The first MODVOLC thermal alert was reported on 22 July; they were reported monthly after that through 11 December 2013, with several days of multiple-pixel alerts. SVERT also noted thermal anomalies and gas-and-steam emissions during August through December, including plumes drifting 30-60 km SE during 17-19 October, 55-100 km SE during 5-6 November, and more than 50 km SE on 25 November.

From the beginning of January 2014 through early June, persistent thermal anomalies were observed in clear imagery nearly every week by SVERT, along with intermittent steam-and-gas emissions. Several times during March, plumes were observed drifting 80-170 km SE. MODVOLC thermal alerts were reported on 8 February, 4 days in March (four pixels on 8 March), and twice on 27 May. SVERT reported that beginning on 24 May, gas emissions containing ash were detected in satellite images. A decrease in thermal anomalies observed by SVERT led them to lower the Alert Level to Green on 5 June 2014.

Activity during November 2014-July 2015. SVERT raised the Alert Level back to Yellow in late November 2014, citing new thermal anomalies beginning on 21 November followed by intermittent steam-and-gas emissions. A plume was observed drifting 40 km SE on 27 November. A new MODVOLC thermal alert appeared on 4 December. SVERT reported thermal anomalies and diffuse gas-and-steam plumes during December 2014 and January-February 2015. Emissions were detected 3 km above Chirinkotan drifting SE on 5 January 2015. MODVOLC reported two thermal alert pixels on 7 January and one on 10 January.

SVERT briefly lowered the Alert Level to Green between 4 and 20 March when no activity was detected. Thermal anomalies were reported again beginning on 19 March; they were noted weekly along with intermittent gas-and-steam emissions through mid-May when the Alert Level was lowered back to Green again on 19 May.

MODVOLC reported a three-pixel thermal alert on 20 July 2015 (local time). The Tokyo VAAC reported an eruption on 21 July (local time) with an ash plume rising to 3.7 km altitude drifting SE. The plume was observed in satellite imagery for about 2 hours before dissipating. SVERT reported a thermal anomaly and steam-and-gas emissions on 22 July, and the Alert Level was raised to Yellow. Another ash plume was reported by the Tokyo VAAC on 26 July rising to an altitude of 4.6 km and drifting NW for several hours before dissipating.

Expedition during August 2015. Scientists from the Institute of Marine Geology and Geophysics (IMGiG) of the Far Eastern Branch of the Russian Academy of Sciences visited Chirinkotan on 9 August 2015. While there, they observed steaming from a recent blocky lava flow near the coast (figure 3), hiked to the summit, and collected data about volcanic and biological activity on the island. A group of researchers climbed to the edge of the summit crater at 600 m elevation, where clouds prevented clear views of the crater (figure 4), however the strong odor of sulfur and noise from fumarolic activity was noted. The scientists sampled the fresh pyroclastic rocks. When the visibility improved, the depth of the crater was observed to be about 150 m; an extrusive dome in the center had a vent on the top emitting gas.

Figure 3. Steam rising from recent lava flow at Chirinkotan that reached the coastline, 9 August 2015. Courtesy of IMGiG (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

Figure 4. Fieldwork at the summit crater rim of Chirinkotan, 9 August 2015. Courtesy of IMGiG. (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

The upper flank of the volcano was strewn with ash and bombs (from 2-3 cm to several meters in diameter). Scientists observed recently buried and charred living vegetation, and nesting birds freshly killed by volcanic ash and bombs, indicating a very recent event (figure 5). The botanists in the research group noted that all of the vegetation on the upper and middle flanks had been killed 2-3 years ago in a major event, likely during the start of the 2013 eruptive cycle. Ash deposits ranged in thickness from a few centimeters near the coast to 8-15 cm near the summit. During a survey of a pyroclastic flow on the SW coast, scientists noted that it was still hot on the surface (40-60°?) and consisted of block lava, bombs, and volcanic ash (figure 6).

Figure 5. Evidence of recent explosive activity at Chirinkotan. Top: recently burned vegetation from a volcanic bomb on the flank. Bottom: living vegetation buried in recent volcanic ash, 9 August 2015. Courtesy of IMGiG (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

Figure 6. Still-hot debris from a block lava flow on Chirinkotan, 9 August 2015. Courtesy of IMGiG (Diary of the Kurils 2015 Expedition, 7-9 August 2015, http://imgg.ru/ru/news/111 ).

Activity during November 2015-April 2017. As a result of the direct observations of the recent eruption on the island, SVERT raised the Alert Level to Orange on 11 August 2015. There were no further reports available from SVERT until 17 November when gas-and-steam emissions were detected, and the Aviation Color Code was reported as Yellow. SVERT reported on 7 December 2015 that the ACC had been lowered to Green. Although SVERT did not report renewed activity from Chirinkotan until it issued a VONA on 29 November 2016 and raised the Alert Level to Yellow, the MIROVA thermal anomaly detection system indicated intermittent low-level anomalies between late May and early October 2016 (figure 7), indicating a heat source on the island.

Figure 7. MIROVA data of Log Radiative Power at Chirinkotan for the year ending on 31 January 2017 showing a weak but persistent thermal anomaly between late May and early October 2016. Courtesy of MIROVA.

The Tokyo VAAC issued a report of a volcanic ash plume from an eruption on 29 November (local time) 2016. The plume rose to 8.8 km altitude and drifted N. It was observed in satellite imagery for about 9 hours before dissipating. SVERT briefly raised the ACC to Yellow between 29 November and 2 December. They noted that the ash plume was observed drifting 39 km N. A new report of ash emissions came from the Tokyo VAAC on 26 January 2017, with an ash plume at 3.7 km drifting SE observed in the Himawari-8 satellite imagery. SVERT raised the alert level to Yellow on 27 January (UTM) 2017 and also noted ash emissions on 29 January drifting SE to a maximum distance of 105 km. They lowered the Alert Level to Green on 1 February 2017.

A new ash plume was observed by the Tokyo VAAC on 1 March (local time) 2017 at an altitude of 5.5 km. When SVERT raised the Aviation Color Code to Yellow on 2 March, they noted that the plume had drifted 165 km E. They lowered the ACC back to Green on 6 March. The Tokyo VAAC reported a new ash plume at 6.1 km extending SE early on 21 March 2017. SVERT reported the emission at 15 km E of the volcano when they raised the ACC to Yellow a short while later. They noted on 24 March, when they lowered the ACC to Green, that the maximum extent of the ash cloud had been about 50 km SE.

On 31 March 2017, the Tokyo VAAC issued an advisory for an ash plume at 6.7 km altitude drifting E, and SVERT raised the Alert Level to Yellow the next day. They reported the ash plume drifting 165 km NE before dissipating. Another plume on 7 April was observed by the Tokyo VAAC at 3.7 km altitude drifting SE. SVERT reported the plume at 5 km altitude drifting NE. SVERT lowered the ACC to Green on 24 April 2017.

Reference: Neal C A, McGimsey R G, Dixon J, Melnikov D, 2005. 2004 volcanic activity in Alaska and Kamchatka: summary of events and response of the Alaska Volcano Observatory. U S Geol Surv, Open-File Rpt, 2005-1308: 1-67.

Geologic Background. The small, mostly unvegetated 3-km-wide island of Chirinkotan occupies the far end of an E-W volcanic chain that extends nearly 50 km W of the central part of the main Kuril Islands arc. It is the emergent summit of a volcano that rises 3000 m from the floor of the Kuril Basin. A small 1-km-wide caldera about 300-400 m deep is open to the SW. Lava flows from a cone within the breached crater reached the shore of the island. Historical eruptions have been recorded since the 18th century. Lava flows were observed by the English fur trader Captain Snow in the 1880s.

Information Contacts: Sakhalin Volcanic Eruption Response Team (SVERT), Institute of Marine Geology and Geophysics, Far Eastern Branch, Russian Academy of Science, Nauki st., 1B, Yuzhno-Sakhalinsk, Russia, 693022 (URL: http://www.imgg.ru/en/, http://www.imgg.ru/ru/svert/reports); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/); Institute of Marine Geology and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, (FEB RAS IMGiG), 693 022 Russia, Yuzhno-Sakhalinsk, ul. Science 1B (URL: http://imgg.ru/ru); 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/).

Eruptive activity at Dukono has continued since 1933. As previously reported, ash explosions were frequently observed, and thermal anomalies were intermittent, from September 2011 through July 2014 (BGVN 39:06). Similar activity has continued through March 2017. Monitoring is conducted by the Indonesian Center for Volcanology and Geological Hazard (PVMBG, also known as CVGHM) from an observation post 11 km away. The Alert Level has remained at 2 (on a scale of 1-4), with residents and tourists advised to not approach the crater within a radius of 2 km.

PVMBG reported that in March-April 2015 seismicity remained high and consisted of explosion signals, volcanic earthquakes, and tremor, accompanied by roaring heard at the observation post. A powerful explosion on 23 May 2015 was followed by minor ashfall in areas to the E. During 1-5 July 2015 white-and-gray plumes rose as high as 600 m; minor ashfall was reported in northern areas on 1 July. Ashfall was reported in areas from the Galela District to Tobelo town (NNW) in August 2015 and at the observation post in September. Seismicity fluctuated at high levels, with elevated periods during 15-22 August, 28 August-5 September, and 15-25 October 2015.

As summarized by PVMBG, the period from 1 January to 19 December 2016 exhibited white-and-gray plumes rising as high as 1.2 km above the rim of the Malupang Warirang crater, accompanied by roaring heard at the observation post. The eruption plume height generally fluctuated though, was higher during periods in May and from late November into December; ashfall increased during the periods of higher plume heights, and was noted in villages within 11 km N, NE, and SW. Seismicity remained high.

Nearly daily aviation advisories from the Darwin VAAC (Volcanic Ash Advisory Centre) since July 2014 confirmed the PVMBG reports. As identified in satellite imagery, white and gray ash plumes were seen rising to altitudes of 1.5-4 km from the Malupang Warirang crater, and drifting in various directions for tens to hundreds of kilometers. Data compiled from VAAC reports and summarized by month for April 2016-March 2017 (table 15) reveal plume altitudes between 1.5 and 3.7 km with visible drift distances up to 300 km away.

Table 15. Monthly summary of reported ash plumes from Dukono for April 2016-March 2017. The direction of drift for the ash plume was highly variable. Data from Darwin VAAC and PVMBG.

Intermittent thermal anomalies, typically single pixels, were recorded by MODVOLC (table 16) in the months of April and June 2014, January-March 2015, December 2015, and November 2016. MODIS thermal data recorded by the MIROVA system during the year of April 2016-March 2016 (figure 6) showed intermittent low-power anomalies in May and August 2016, and then in every month from October 2016 through March 2017. It should be noted that the MODIS satellite thermal sensors cannot penetrate cloud cover, which is frequent over Dukono much of the year.

Table 16. Thermal anomalies at Dukono based on MODIS data processed by MODVOLC, August 2014-March 2017. Courtesy of Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System.

Figure 6. Thermal anomalies (Log Radiative Power) detected by MODIS and recorded by the MIROVA system for year ending 5 April 2017. Courtesy of MIROVA.

Vistors to the crater in March 2016 photographed ash rising form an incandescent vent (figure 7). Patrick Marcel reported that "the vents at the bottom of the crater emitted a sustained, extremely noisy jet of gas, steam and ash, and ejected incandescent bombs to up to 500 m height. Some of them landed outside the crater rim." The "You&MeTraveling2" blog posted a trip journal that described a late-August 2016 visit to Dukono, including photos and a video looking down into the crater that showed activity similar to that seen by Marcel in March 2016.

Figure 7. View into Dukono's crater on 12 March 2016. Photo by Patrick Marcel (color adjusted from original); courtesy of Volcano Discovery.

Geologic Background. Reports from this remote volcano in northernmost Halmahera are rare, but Dukono has been one of Indonesia's most active volcanoes. More-or-less continuous explosive eruptions, sometimes accompanied by lava flows, occurred from 1933 until at least the mid-1990s, when routine observations were curtailed. During a major eruption in 1550, a lava flow filled in the strait between Halmahera and the north-flank cone of Gunung Mamuya. This complex volcano presents a broad, low profile with multiple summit peaks and overlapping craters. Malupang Wariang, 1 km SW of the summit crater complex, contains a 700 x 570 m crater that has also been active during historical time.

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/); 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/); Volcano Discovery (URL: http://www.volcanodiscovery.com/); You&MeTraveling2 (URL: http://youandmetraveling2.com/).

The existence of an anorthoclase phonolite lava lake in the summit crater of Mount Erebus was first reported in 1972, and it has been thought to be continuously active since that time. Antarctica's best known volcano is located on Ross Island, 90 km E of the continent, offshore of the Scott Coast. McMurdo station, run by the United States Antarctic Program, is about 40 km S on the tip of Ross Island (figure 16). During the history of observations, lava lake(s) have generally persisted, although changes in size and shape over time reflect variations in volcanic activity.

Figure 16. On 31 December 2013, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite acquired visible near-infrared images of the western end of Ross Island in austral mid-summer. McMurdo Station is about 40 km S of the summit of Mount Erebus. Courtesy of NASA Earth Observatory.

This report briefly summarizes research activity at Mount Erebus, and volcanic activity observed since 1972. Photographs from expeditions between 2010 and 2016 show more recent activity at the volcano. Observations from MODVOLC data collected from 2000 through 2016 are also discussed.

Summary of research activity. For most years since the 1970's, scientists have visited Erebus during the austral summer (November-February) and gathered samples, taken SO₂ and other geochemical measurements, collected GPS data, and made observations and overflights to evaluate the condition of the volcano.

Seismometers were initially installed by a joint project of United States, New Zealand, and Japanese scientists in 1980-1981. Between 1980 and 2016 as many as 10 seismic stations were recording activity at Erebus; they were monitored by the Mount Erebus Volcano Observatory (MEVO) run by the New Mexico Institute of Mining and Technology (New Mexico Tech). During the early 2000s MEVO also used infrasonic recordings to capture data on the frequency of eruptions. Researchers from New Mexico Tech, the University of Cambridge, and University College London made yearly expeditions there between 2003 and 2016.

The Mount Erebus Volcano Observatory closed in 2016. A final report was submitted to the National Science Foundation (NSF) on the past research and ideas for future research (Mattioli and LaFemina, 2016), and includes a comprehensive list of scientific publications about Erebus. One area of ongoing volcanology research relates to studying the behavior of the lava lake with a variety of on-site monitoring equipment (figure 17).

Figure 17. Radar altimeter installed at the crater rim of Erebus in December 2016. There are two dishes, to both transmit and receive data. Several other devices are seen in the background, all trained on the lava lake on the floor of the crater. Courtesy of the University of Cambridge Department of Geography.

Summary of activity, 1972-2009. During the 1970's, the lava lake was observed to be about 130 m long and oval shaped, producing occasional Strombolian explosions. Bombs up to 10 m in in diameter were ejected near the vent, and ones up to 30 cm in diameter were thrown out over the main crater. Oscillations of the lake level of up to 2 m were observed.

During a period of increased activity between September 1984 and January 1985, several large explosions were recorded by the seismic network, and there were reports of mushroom-shaped clouds rising as much as 2 km above the summit. During September 1984, numerous large explosions sent ejecta as high as 600 m above the summit, and incandescence was visible from 70 km away. Ash also covered the NW flank down to 3,400 m elevation. Observations in October 1984 indicated that much of the lava lake had solidified, and that the surface was covered with ejecta from the recent explosions. Seismicity remained above average through January 1985. During this period of increased activity, bombs averaging 2 m in diameter (but some as large as 10 m in diameter) were ejected up to 1.2 km from within the inner crater. The eruptions were witnessed from 60 km away and explosions could be heard up to 2 km from the volcano (SEAN 11:03). A small lava lake about 15 m in diameter reappeared late in 1985.

Two primary lakes of phonolitic lava, and a third transient lake, were present inside the crater during the late 1980s (see figure 9, SEAN 13:02), and infrequent Strombolian eruptions with small bombs were captured by a remote video camera mounted on the crater rim. Small ash eruptions were observed from an active vent near the lava lakes in January 1991. On 19 October 1993, two moderate phreatic eruptions created a new crater ~80 m in diameter on the main crater floor and ejected debris over the northern crater rim. These were the first known phreatic eruptions at Erebus, and probably resulted from steam build-up associated with melting snow in the crater (BGVN 20:11).

Vent and lava lake eruptions were recorded by MEVO during the late 1990s and early 2000s. The largest peaks in terms of numbers of eruptions were during 1995, 1997, 1998, 2000, and a broad peak beginning in late 2005 that continued into late 2006 (BGVN 31:12).

Activity during 2010-2016. The two primary lava lakes remained active at Erebus. The one in the NE sector of the inner crater has been persistent almost continuously since first reported in 1972. The second lake is more in the center of the main crater and is intermittently active. During a visit in 2010, only the NE sector lake was active (BGVN 36:09). During clear weather, a steady steam plume is often observed (figure 18).

Figure 18. Mount Erebus with a steam plume rising from the summit crater, viewed from the Lower Erebus Hut (LEH), 6 December 2010. Courtesy of Mount Erebus Volcano Observatory.

Visits during 2011-2016 have confirmed the ongoing Strombolian activity and convection at the lava lakes nearly every year. During 2011 the glowing lava lake emitted steam and magmatic gases from the bottom of a vent at the main crater (figure 19). An eruption on 2 January 2012 at the lava lake was captured by the remote video cameras managed by MEVO (figure 20). Several bombs were ejected on 18 December 2013 and landed close to monitoring equipment run by MEVO. Researchers were able to open a hot bomb and see the molten interior (figure 21).

Figure 19. The lava lake at Erebus, photographed in December 2011. Image by Clive Oppenheimer/Volcanofiles; courtesy of Erik Klemetti.

Figure 20. An eruption from the lava lake at Erebus, captured on the MEVO video cameras on 2 January 2012. Courtesy of MEVO and Volcano Discovery.

Figure 21. Several bombs erupted from Erebus on 18 December 2013 and landed close to monitoring equipment run by MEVO. Researchers were able to open a hot bomb and see the molten interior. Images courtesy of Aaron Curtis, MEVO, 18 December 2013 (posted on Facebook).

When UNAVCO (a non-profit university-governed consortium) flew over Erebus in December 2015, steam and magmatic gas plumes indicated that both lava lakes were active (figure 22). The two incandescent crater vents at were observed in greater detail during January 2016 by researchers associated with the University of Cambridge (figure 23).

Figure 22. The crater of Erebus, with active steam plumes from two lava lakes on 7 December 2015, photographed during an overflight by UNAVCO (a non-profit university-governed consortium). Photo by Annie Zaino, UNAVCO (posted on Facebook).

Figure 23. Two lava lakes at Erebus were observed on 14 January 2016 by researchers associated with the University of Cambridge. Lower image is a close-up of the right vent in the upper image. Courtesy of Kayla Iacovino and Tehnuka Ilanko (posted on Facebook).

MODVOLC data, 2000-2016. With the remoteness of Erebus, satellite imagery serves as one of the few year-round tools currently available to assess longer-term activity. The University of Hawaii's MODVOLC thermal alert system has been processing MODIS infrared satellite data since 2000. Mount Erebus has had a strong and nearly continuous MODVOLC signature throughout 2000-2016 (table 3), confirming its ongoing eruptive activity.

Table 3. Number of MODVOLC thermal alert pixels recorded per month from 1 January 2000 to 31 December 2016 by the University of Hawaii's thermal alert system for Erebus. Table compiled by GVP from data provided by MODVOLC. Spurious data from 25 October 2014 was omitted.

The MODVOLC thermal alert data show that thermal activity at Erebus has waxed and waned several times during the 2000-2016 interval (figure 24). Activity was very low during 2000, but increased steadily through mid-2005 to more than 20 times as many annual thermal alert pixels since 2000. Activity dropped off substantially from late 2005 and remained low through early 2007, when another increase began that peaked at an even higher level (2514 pixels during 2009) in mid-2009. Another drop in activity occurred during 2010, and since 2011 there have been fewer than 300 pixels per year, with numbers below 200 for 2015 and 2016.

Figure 24. The number of MODVOLC thermal alert pixels per year, colored by month, reported for Erebus from 2000 through 2016. Activity was very low during 2000, but increased steadily through mid-2005. Activity dropped off substantially from late 2005 through early 2007, when another increase began that peaked at an even higher level in mid-2009. Another drop in activity occurred during 2010, and since 2011, there have been fewer than 300 pixels per year. Data courtesy of MODVOLC.

Another trend in the MODVOLC data is also apparent when the number of pixels are plotted by month, as opposed to year, for this time period (figure 25). From November through February, during the austral summer, the number of pixels per month never exceeds 150 (see table 3, highest value is 125). From March through October, during the Austral winter, the number of pixels recorded per month can be much higher (the highest value is 458). The average number of 'summer' pixels per month (November-February, 2000-2016) is 30. The average number of 'winter' pixels per month for the same period (March-October) is 108, more than three times greater.

Figure 25. The number of MODVOLC thermal alert pixels per month for the period 2000-2016, colored by year. The total average number of pixels per month from 1 March through 31 October (1732) is three times the average total number of pixels per month from 1 November through 28 February (480). Data courtesy of MODVOLC.

References: Mattioli, G.S., and LaFemina, P.C., 2016, Final Report submitted to the National Science Foundation, Community Workshop: "Scientific Drivers and Future of Mount Erebus Volcano Observatory (MEVO)" (URL: https://www.unavco.org/community/meetings-events/2016/mevo/2016-MEVO-Final-Report.pdf)

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. The 3794-m-high Erebus is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: Mt. Erebus Volcano Observatory (MEVO), New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA; 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/); The University of Cambridge Department of Geography (URL: http://www.geog.cam.ac.uk/research/projects/lavalakes/); Erik Klemetti, Eruptions Blog, Wired (URL: https://www.wired.com/author/erikvolc/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301-5394 (URL: http://www.unavco.org/); Kayla Iacovino and Tehnuka Ilanko, The Volcanofiles (URL: http://www.volcanofiles.com/).

Volcán de Fuego has been erupting continuously since 2002. Historical observations of eruptions date back to 1531, and radiocarbon dates are confirmed back to 1580 BCE. These eruptions have resulted in major ashfalls, pyroclastic flows, lava flows, and damaging lahars. Fuego was continuously active from June 2014-December 2015. Ash plumes rose to 6 km altitude, ashfall was reported in communities as far as 90 km away, pyroclastic flows descended multiple drainages at least four times, Strombolian activity rose to 800 m above the summit, lava flows descended a few kilometers down five different drainages numerous times, and three different lahars damaged roadways (BGVN 42:05). This report continues with a summary of similar activity during January-June 2016. In addition to regular reports from INSIVUMEH, the Washington Volcanic Ash Advisory Center (VAAC) provides aviation alerts. Locations of towns and drainages are listed in table 12 (BGVN 42:05).

Daily weak and moderate explosions generating ash plumes to about 800 m above the summit (4.6 km altitude) that dissipated within about 10 km were typical activity for Fuego during January-June 2016. In addition, ten eruptive episodes were recorded during this time. Each episode lasted 24-72 hours, with all but one including incandescent material rising 200-400 m above the summit feeding lava flows down the larger drainages for several kilometers. Most also included pyroclastic flows down the larger drainages. One of the episodes consisted of only large pyroclastic eruptions (with an accompanying ash plume) that issued directly from the summit crater and down the ravines; all included ash plumes rising over 5 km in altitude. Several lahars were reported during late April-June.

Activity during 30 December 2015. INSIVUMEH reported a significant increase in activity on 30 December 2015. A series of pyroclastic flows descended the Las Lajas and El Jute drainages on the SE flank, and a dense ash plume rose to 5 km altitude and drifted 20 km W. Ashfall was reported in multiple communities on the flanks, including Panimache I and II (8 km SW), Morelia (9 km SW), and Santa Sofía (12 km SW).

Activity during January 2016. Two eruptive episodes with explosions that generated ash plumes, pyroclastic flows, Strombolian activity, lava flows, and ashfall were documented by INSIVUMEH during January 2016. The first eruption began with an increase in seismicity early in the morning of 3 January. Moderate to strong explosions were accompanied by an ash plume that rose to 4.8 km altitude (about 1 km above the summit) and drifted W and SW. Two lava flows emerged from the summit crater and traveled down the Las Lajas and Trinidad ravines. Moderate to strong explosions continued during 3 January. By the afternoon, dense plumes of ash were reported at 6 km altitude drifting SW and SE more than 40 km. Ashfall was reported in the villages of Panimaché I and II, Morelia, Santa Sofia, El Porvenir, La Rochela, Osuna, El Zapote and Rodeo. Also later in the day, incandescence was observed 400 m above the crater; it fed three lava flows in the Santa Teresa, Trinidad, and Las Lajas canyons that reached 2.5 km in length. Eruptive activity diminished after about 37 hours with weak bursts of ash rising to 4.6-4.7 km altitude on 5 January that drifted S, SW, and SE.

A smaller explosive event during 15-17 January produced block avalanches and created ash plumes that rose 450-750 m above the crater and drifted up to 12 km N and NE; four to five explosions per hour were detected. The second eruptive episode began with increased activity on 19 January; incandescent material was ejected 400-500 m above the summit, generating new lava flows to the same three canyons as the earlier eruption (Santa Teresa, Trinidad and Las Lajas) (figure 36). Ash emissions rose to 4.9 km altitude and drifted NE. Pyroclastic flows also descended the Las Lajas and El Jute canyons (figure 37).

Figure 36. Lava flows towards Las Lajas Canyon on 19 January 2016 as viewed from the SE flank. Courtesy of INSIVUMEH-OVFGO (Informe Mensual De La Actividad Del Volcán Fuego, January 2016).

Figure 37. A pyroclastic flow descends towards the Las Lajas and El Jute ravines on the SE flank of Fuego on 19 January 2016 in this thermal image captured by INSIVUMEH. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, January 2016).

The second episode continued throughout 20 January 2016 when the largest ash plume rose to 6.7 km altitude and drifted NE more than 90 km according to the Washington VAAC. Ashfall was reported in San Miguel, Las Dueñas, Alotenango, Acatenango, and Antigua. Ash plumes from the pyroclastic flows also generated ashfall on the S and SW flanks (figure 38). By the morning of 21 January, the lava flows had ceased advancing at about 3 km length, although a hot spot was still clearly visible in satellite imagery. Weak explosions generated ash plumes that rose only a few hundred meters above the summit and drifted NNE. During January, the Observatorio del Volcan de Fuego installed a second webcam on the SE side of Fuego at the Finca La Reunión, a resort about 8 km from the summit. The first webcam is located about 10 km SW of the summit at the Observatorio del Volcan de Fuego in the community of Panimache.

Figure 38. A pyroclastic flow on 20 January 2016 travels down the SE flank of Fuego, creating an ash cloud in the ravine. Additional ash emissions drifted in multiple directions. A recent lava flow is also visible in the ravine. View is from the La Reunión webcam, 8 km SE of the summit. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, January 2016).

Activity during February-March 2016. Explosions increased in number and energy on 5 February 2016, classified by INSIVUMEH as the 3rd episode of the year. Six moderate to strong explosions per hour were reported, sending ash emissions to 4.5 km altitude, drifting W, NW, and N more than 12 km, and avalanche blocks down the flanks to the base. The third eruptive episode of the year began with moderate explosions on 9 February 2016; it generated ash plumes which rose to 4.7 km altitude and dispersed up to 35 km NNW. Ashfall was reported in Chimaltenango, Zaragoza, Ciudad Vieja, San Pedro las Huertas, San Miguel Las Dueñas, San Juan Alotenango, Antigua Guatemala and the Capital City as far as 35 km N and NE. The explosions were accompanied by incandescent material rising to 300 m above the summit and feeding lava flows that traveled towards the Trinidad, Las Lajas, and Santa Teresa canyons, reaching lengths of 800 to 3,000 meters (figure 39).

Figure 39. Incandescence rises 300 m above the crater at Fuego, generating lava flows down the Trinidad, Las Lajas and Santa Teresa canyons on 9 February 2016. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Febrero 2016).

The following day (10 February 2016), pyroclastic flows descended the El Jute and Las Lajas ravines (figure 40) while ash plumes rose to 5.2 km altitude and incandescent material was ejected 400 m above the crater. Although activity decreased throughout the day, explosions continued to generate ash plumes to 4.9 km altitude that dispersed ash up to 45 km N and NE. Minor ash emissions were reported by the Washington VAAC on 17 February at 4.6-4.9 km altitude drifting SE about 40 km, and on 24 February at 4.6 km drifting about 25 km SW.

Figure 40. Pyroclastic flows descend the Las Lajas and El Jute ravines at Fuego on 10 February 2016 as viewed from the webcam at Finca la Reunión, 8 km SE. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Febrero 2016).

On 29 February 2016, moderate to strong explosions at a rate of 6-10 per hour were heard more than 14 km away. They were accompanied by an ash plume that rose to 4.8 km and drifted 12 km E, and a lava flow that traveled 500 m towards Las Lajas ravine. This 4th eruptive episode (according to INSIVUMEH) lasted more than 72 hours (figure 41). On 2 March, several ash plumes rose to different altitudes and dispersed in different directions. The largest ash plume, was observed by the Washington VAAC at 7.3 km altitude; it was visible 400 km N before it dissipated into weather clouds. Lower altitude plumes rose to 4.6 km and drifted 75 km SW before dissipating. Ash fell in the communities of Morelia, Santa Sofia, La Rochela, Panimaché I and II, Sangre de Cristo, La Soledad and Yepocapa. The incandescent activity fed two lava flows; the first in the direction of Las Lajas reached 3 km, the second flowed towards El Jute ravine and reached 2 km in length. Pyroclastic flows also travelled down these two canyons and block avalanches descended the Honda Canyon. Explosive activity diminished during 3-6 March; ash emissions rose to 550 m above the summit and drifted 8-10 km W, SE, and SE.

Figure 41. RSAM values spiked at Fuego during 29 February-3 March 2016 during eruptive episode 4. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

During 10 March 2016, moderate to strong Vulcanian explosions generated an ash plume that rose to 4.4 km altitude and drifted E. The Washington VAAC observed ash emissions in multispectral satellite imagery on 15 March at 4.3 km altitude extending about 80 km SW from the summit as well as hot spots and pyroclastic flows visible in the INSIVUMEH webcam. An increase in activity on 21 March generated weak and moderate explosions that produced ash plumes that rose to 4.3-4.7 km and drifted W. This activity was recorded as an increase in RSAM tremor amplitude and duration at the FG3 seismic station, but was not considered an eruptive episode by INSIVUMEH (figure 42).

Figure 42. Increases in RSAM tremor amplitude and duration at Fuego were recorded during 21 and 22 March, and eruptive episode 5 was recorded during 26 and 27 March 2016. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

Eruptive episode 5 began on 26 March 2016 and lasted more than 24 hours (figure 42). Strombolian eruptions rose up to 500 m above the crater (figure 43), feeding three lava flows that traveled 2 km down Las Lajas, 1.3 km down the Santa Theresa, and 1 km down the Trinidad ravines. Ash plumes rose to 6.1 km altitude and drifted up to 150 km W (figure 44); ash fell on the villages of Morelia, Santa Sofia, San Predro Yepocapa, Panimaché I and II. By the end of 27 March, eruptive activity had diminished to background conditions, which included weak and moderate explosions generating ash plumes to about 800 m above the summit (4.6 km altitude) that dissipated within about 10 km WSW. On 29 March ashfall was reported Sangre de Cristo and Panimaché I and II.

Figure 43. Strombolian activity rises 300 m above the crater at Fuego on 26 March 2016. Photo by Gustavo Chigna, courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

Figure 44. An ash plume at Fuego rose to over 6 km altitude on 26 March 2016 and drifted 150 km W before dissipating. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Marzo 2016).

Activity during April-May 2016. The Washington VAAC reported diffuse volcanic ash emissions in satellite and webcam imagery on 2 April 2016. The ash plume drifted W at 4.3 km altitude, and extended 75 km from the summit before dissipating. Increased eruptive activity during 6-7 April 2016 resulted in moderate and strong explosions which produced ash plumes rising to 4.6-4.8 km altitude that drifted W and SW 15 km. The explosions were audible more than 20 km from the volcano; roofs and windows vibrated within 12 km. INSIVUMEH received reports of ashfall from the villages of Morelia, Sangre de Cristo, and Panimche I and II.

An explosion on 8 April created an ash plume that rose to 5.8 km and drifted SSW about 35 km. Successive bursts of ash on 9 April rose to 4.9 km altitude and drifted W. Emissions on 11 April were reported at 4.3 km altitude about 15 km SW from the summit; the next day they rose to 4.9 km and drifted SW to a distance of 45 km. INSIVUMEH reported variable activity beginning on 11 April with high levels of explosive activity on 12 April marking the beginning of the sixth eruptive episode of the year, which lasted for three days. An incandescent fountain persisted 100-300 m above the crater and fed two lava flows during the event; one traveled 2 km down the Las Lajas ravine, and the other reached 1 km in length in the Santa Teresa ravine. Avalanches were constant along the flanks during this episode. Continuous ash emissions were observed as well; plumes generally rose no higher than 5.8 km (2 km above the summit). Ashfall was reported in La Rochela, Ceylon, Morelia, Hagia Sophia, Sangre de Cristo, Panimaché I and II. On 13 April the ash plume extended 185 km SW from the summit. A brilliant hotspot was observed in satellite imagery on 14 April after which no further VAAC reports were issued until early May. On 29 April, after more than a week of rain, a lahar descended the Las Lajas drainage but no damage was reported.

Activity at Fuego increased significantly during May 2016, and included three eruptive episodes that generated ash plumes, pyroclastic and lava flows, and increased rainfall that resulted in lahars. Ash plumes rose above 5.5 km altitude (more than 2 km above the summit) and dispersed to the S, SW, and SE. Seismic activity increased on 5 May in the form of internal vibrations caused by lava which flowed more than 1.2 km down the Las Lajas ravine, and moderate to strong explosions that produced ash plumes which rose to 4.8 km altitude and drifted S for 12 km. The Washington VAAC reported diffuse ash extending 65 km SE from the summit.

The 7th eruptive episode of the year began on 6 May 2016 with incandescent material rising 300 m above the summit crater, causing two lava flows. One traveled down Las Lajas ravine more than 3 km; the second descended the Trinidad ravine for 1.5 km. Block avalanches were constant around the crater rim. The episode lasted for more than 32 hours (figure 45); the moderate to strong explosions ejected ash to altitudes above 5.5 km that drifted S and SW. Ashfall was reported in Escuintla and its surroundings. There were no pyroclastic flows during this episode. The Washington VAAC reported emissions extending 65 km SE of the summit at 5 km altitude on 6 May.

Figure 45. RSAM values during 2 May-6 June 2016 helped INSIVUMEH to define eruptive episodes for 2016 at Fuego, along with observed activity. Eruptive episode 7, consisting of Strombolian activity, lava flows, and ash plumes, occurred during 6-7 May 2016. Episode 8 comprised ash plumes and several large pyroclastic flows that descended the S flank during 18 and 19 May, but no seismic explosive activity. Increases in explosive activity on 21 May marked the beginning of episode 9, which lasted through 23 May 2016 and included incandescent fountains, lava flows, and ash plumes. Courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Mayo 2016).

The next eruptive episode (8) did not involve seismic explosive activity (figure 45). Instead, several large pyroclastic flows overflowed the crater rim on 18 and 19 May 2016 and descended the flanks towards Las Lajas and Honda ravines (figure 46) resulting in ashfall reported to the S, SW, and W, in villages more than 30 km away. A large ash plume reached more than 5.5 km altitude and drifted 15 km SSW on 19 May (figure 47). Ashfall was reported in the villages of El Rodeo, La Rochela, Osuna, Panimaché, Morelia, Sangre de Cristo and Yepocapa. By late in the day, the Washington VAAC noted that the plume was centered about 90 km SW at 5.8 km altitude.

Figure 46. A pyroclastic flow descends Las Lajas ravine on the S flank of Fuego on 18 May 2016 in these images taken from Finca La Reunión. Lower photo by Basilo Sul, both images courtesy of INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Mayo 2016).

Figure 47. An ash plume drifts SW from Fuego on 19 May 2016 after a series of pyroclastic flows and ash emissions sent ash plumes to over 5 km altitude. The Operational Land Imager instrument on Landsat 8 captured this image. Courtesy of NASA Earth Observatory.

The ninth eruptive episode of 2016 generated incandescent fountains 200-300 m above the summit; they fed a 2-km-long lava flow down the Las Lajas ravine (figure 48). Seismic activity began to increase on 21 May and lasted through 23 May (see figure 45). Moderate and strong explosions created an ash plume that rose to 5.5 km altitude and drifted SW and W. The Observatory reported ashfall in Morelia, El Porvenir, Santa Sofia, Los Yucales, Panimaché I and II. The Washington VAAC reported an ash plume visible in satellite imagery at 5.5 km altitude, drifting 75 km S beyond the coast on 23 May 2016. A lahar descended the Las Lajas ravine on 20 May and was recorded by the seismic station FG3, but no damage was reported.

Figure 48. Landsat band 7 (top) and band 10 (bottom) images of the still-cooling lava flow in Las Lajas ravine at Fuego on 26 May 2016. Courtesy of Rudiger Escobar, Michigan Technological University and INSIVUMEH (Informe Mensual De La Actividad Del Volcán Fuego, Mayo 2016).

Activity during June 2016. A significant rainfall combined with the plentiful ash from recent pyroclastic flows, resulted in lahars descending Las Lajas and El Jute ravines on 5 June 2016. They transported blocks, branches, and tree trunks, and a strong sulfur smell was reported by nearby residents. Another lahar was reported on 18 June that was 15 m wide and had a 1.5-m-high front. An increase in seismic activity during the afternoon of 24 June signaled the beginning of eruptive episode 10. This was followed by about 30 hours of moderate to strong explosive activity that could be heard and felt as far as 12 km away. A dense ash plume on 25 June rose to 5.5 km altitude and drifted S, SW, and W more than 40 km. Ashfall was reported in San Pedro Yepocapa, Sangre de Cristo, Morelia, Santa Sofia, Panimaché I and II. The Washington VAAC observed the ash plume in multispectral imagery on 25 June extending 120 km WSW from the summit. NASA Goddard Space Flight Center captured a small but distinct SO₂ plume from Fuego on 25 June as well (figure 49). Incandescent material rose 300 m above the summit crater during this episode and fed three lava flows; the first descended Las Lajas ravine 2.5 km, the second traveled 2.3 km down El Jute ravine, and the third flowed down Taniluyá ravine for 600 meters. Seismic activity from episode 10 decreased on 26 June.

Figure 49. A small but distinct SO2 anomaly was measured from Fuego on 25 June 2016. INSIVUMEH reported the 10th eruptive episode of the year during that time with a dense ash plume and lava flows emerging from the summit crater. Courtesy of NASA Goddard Space Flight Center.

Geologic Background. Volcán Fuego, one of Central America's most active volcanoes, is one of three large stratovolcanoes overlooking Guatemala's former capital, Antigua. The scarp of an older edifice, Meseta, lies between 3763-m-high Fuego and its twin volcano to the north, Acatenango. Construction of Meseta dates back to about 230,000 years and continued until the late Pleistocene or early Holocene. Collapse of Meseta may have produced the massive Escuintla debris-avalanche deposit, which extends about 50 km onto the Pacific coastal plain. Growth of the modern Fuego volcano followed, continuing the southward migration of volcanism that began at Acatenango. In contrast to the mostly andesitic Acatenango, eruptions at Fuego have become more mafic with time, and most historical activity has produced basaltic rocks. Frequent vigorous historical eruptions have been recorded since the onset of the Spanish era in 1524, and have produced major ashfalls, along with occasional pyroclastic flows and lava flows.

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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).

The Virunga Volcanic Province (VVP) in the Democratic Republic of the Congo (DRC) is part of the western branch of the East African Rift System (EARS). Nyamuragira (or Nyamulagira), a high-potassium basaltic shield volcano on the W edge of VVP, includes a lava field that covers over 1,100 km² and contains more than 100 flank cones in addition to a large central crater (see figure 54, BGVN 40:01). A large lava lake that had been active for many years emptied from the central crater in 1938. Numerous flank eruptions have been observed since that time, the last during November 2011-March 2012 on the NE flank. This report covers the substantial SO₂ emissions from both Nyamuragira and nearby Nyiragongo (15 km SE) between November 2011 and April 2016, and the onset of eruptive activity, including a new lava lake, at the summit crater beginning in May 2014. Activity is described through April 2017.

On-the-ground information about Nyamuragira is intermittent due to the unstable political climate in the region, but some information is available from the Observatoire Volcanologique de Goma (OVG), MONUSCO (the United Nations Organization working in the area), geoscientists who study Nyamuragira, and travelers who visit the site. The most consistent data comes from satellite – thermal data from the MODIS instrument processed by the MODVOLC and MIROVA systems, SO₂ data from the AURA instrument on NASA's OMI satellite, and NASA Earth Observatory images from a variety of satellites.

A substantial flank eruption took place from November 2011 through March 2012. This was followed by a period of degassing with SO₂-rich plumes, but no observed thermal activity, from April 2012 through April 2014. Increased seismicity and minor thermal activity was observed at the central crater during April 2014; lava fountains first seen in early July 2014 continued through September. A lava lake in the crater was confirmed on 6 November 2014, and it produced a consistent and strengthening thermal anomaly through the first week of April 2016, when it stopped abruptly. Thermal activity suggesting reappearance of the lava lake began again in early November 2016, and strengthened in both frequency and magnitude into early January 2017, continuing with a strong signal through April 2017.

Activity during November 2011-March 2012. Nyamuragira erupted from cones and fissures on the NE flank between early November 2011 and mid-March 2012 (BGVN 39:03). The vent area, 12 km ENE of the central crater, was an E-W fissure 500-1,000 m long. Lava fountains up to 300 m high produced flows that advanced nearly 12 km N in the first 10 days. Three scoria cones formed adjacent to the fissure during the eruption, and a small lava lake appeared in the center of the largest cone. During January 2012, lava flowed from the vent area and from numerous small breakouts within 2 km of the cones (figures 58, 59). Dario Tedesco reported that the eruptions ceased in March 2012 after a series of explosion earthquakes recorded by the OVG had ended; the last MODVOLC thermal alert in the area of the eruption was captured on 14 March 2012, and none were reported again until 2014.

Figure 58. Lava fountain and active lava flow emerging from the breach of the erupting flank cone of Nyamuragira volcano on 8 January 2012. Courtesy of Volcano Discovery.

Figure 59. Lava fountains around 150 m high erupt on 8 January 2012 from the active flank vent during the 2011-2012 eruption of Nyamuragira. Photo by Lorraine Field, courtesy of Volcano Discovery.

Activity during April 2012-May 2014. Periodic field surveys at Nyamuragira have been carried out since 2009 by helicopter, thanks to the support of the United Nations Organization Stabilization Mission in the DR Congo (MONUSCO). Since 2013, observations of the crater have also been done once or twice a month by helicopter. The team has included researchers from the OVG, Dario Tedesco, and other international scientists. This area is a high-risk sector due to the presence of armed groups, and it is impossible, due to the lack of security, to make detailed field surveys (Coppola et al., 2016).

Dario Tedesco reported SO₂-rich fumaroles in Nyamuragira's central crater beginning in early March 2012, shortly before the NE-flank fissure eruptions ended (BGVN 40:01). A progressive collapse of the 400-m-wide, 50-80 m deep pit crater located in the NE part of the caldera began as soon as the eruptions ended. They noted that during the second half of April, large SO₂ plumes continuously emerged from the pit crater.

NASA's Global Sulfur Dioxide Monitoring program captured major SO₂ plumes from the area for an extended period between November 2011 and February 2014. The plumes represent combined emissions from both Nyamuragira and Nyiragongo, which are too close together to distinguish the source in the satellite data. Campion (2014), however, noted that SO₂ emissions from the VVG increased several fold after the end of the 2011-2012 Nyamuragira eruption; they interpreted that 60-90 % of these emissions should be attributed to Nyamuragira.

Significant areas of SO₂ plumes with DU > 2 (shown as red pixels on the Aura/OMI images, figure 60) were captured by the OMI instrument at the beginning of the November 2011 eruption and continued through February 2012. Beginning in April 2012 elevated values occurred more than 20 days per month through December 2012. Values were more variable in both frequency and magnitude during 2013 with a notable surge of activity during 6-19 June 2013 that resulted in daily SO₂ plumes. Details of monthly SO₂ values are given in the last section of this report (see table 3).

Figure 60. Large SO2 plumes from Nyamuragira and Nyiragongo between November 2011 and December 2013. Four of the dates correspond to the Maximum DU days for that month (see table 3), and two represent other days of the month with substantial plumes. Courtesy of NASA/GSFC.

Activity during June 2014-April 2017. Incandescence at the summit and increased seismicity was reported again in April 2014, along with increasing SO₂ values. A strong MODVOLC thermal alert signal appeared on 22 June 2014, and a satellite image from 30 June showed clear hotspots at both Nyamuragira and Nyiragongo (figure 61).

Figure 61. Hot spots from both Nyamuragira and Nyiragongo on 30 June 2014. This false-color image combines shortwave-infrared, near-infrared, and green light as red, green, and blue, respectively. Since shortwave- and near- infrared light penetrates hazy skies better than visible light, more surface detail is visible in this image than would be in natural-color. Because very hot surfaces glow in shortwave-infrared, the lava within both summit craters appear bright red. The dark lava flows spreading from Nyamuragira were erupted within the past 50 years, some as recently as 2012. Vegetation is bright green. The image was collected by Landsat 8. Courtesy of NASA Earth Observatory.

An extended series of MIROVA thermal anomaly data beginning in May 2014 clearly shows the episodic periods of active heat flow at Nyamuragira from late May 2014 through April 2017 (figure 62). During the first episode, from late May to early September 2014, lava fountains were observed in early July, and reported to be active through September (BGVN 40.01). Campion (2014) and Smets and others (2014) debated whether the lava lake first appeared in April or not until November. On 6 November 2014 a small lava lake was confirmed at the base of the summit pit when sighted during an OVG helicopter survey. Both MODVOLC and MIROVA thermal anomalies appeared again in early November and persisted through the end of the year.

Figure 62. MIROVA thermal anomaly data from Nyamuragira from May 2014 through April 2017. Vertical black bar on each chart show the ending date of the previous chart. Chart "A" was previously published (BGVN 40:01, figure 57); other charts were captured via Volcano Discovery, Erik Klemetti, and Culture Volcan. Courtesy of MIROVA.

Thermal anomalies were persistent throughout 2015, with a noted increase in both frequency and magnitude during July (figure 62 C). A NASA Earth Observatory image from 9 February 2015 clearly shows active plumes venting from both Nyamuragira and Nyiragongo (figure 63). MONUSCO-supported summit crater visits by researchers on 2 April 2015, and photographer Oliver Grunwald on 10 July 2015, confirmed the presence of an active lava lake during both visits (figure 64, and video link in Information Contacts).

Figure 63. On 9 February 2015, clear skies afforded an unobstructed view from space of plumes venting from both Nyamuragira (north) and Nyiragongo (south) volcanoes in the Democratic Republic of the Congo. The lower image shows a close-up view of Nyamuragira, which is topped with a small caldera with walls about 100 m high. In 1938, a lava lake within the caldera drained during a large, long-lasting fissure eruption that sent lava flows all the way to Lake Kivu. Satellite observations and helicopter overflights in 2014 confirmed that the caldera again contained a small but vigorous lava lake. Courtesy of NASA Earth Observatory.

Figure 64. An active lava lake at Nyamuragira crater on 2 April 2015. Courtesy of MONUSCO/Abel Kavanagh (URL: https://www.flickr.com/photos/monusco/17118082715/).

The MIROVA and MODVOLC thermal anomaly data suggest that the lava lake at Nyamuragira was active until 4 April 2016 when the signals abruptly ended (figure 62 D). This also corresponds closely in time to when the major SO₂ emissions captured by NASA also ceased. Observations by Dario Tedesco at the summit on 6 April 2016, during a UNICEF and MONUSCO-sponsored helicopter overflight, showed only an incandescent vent releasing hot gases, and no active lava lake. A small lava lake was again visible in the pit crater on 27 April 2016 when observed by Sebastien Valade of the University of Florence on another MONUSCO-sponsored flight (figure 65).

Figure 65. Nyamuragira's pit crater with a small lava lake observed on 27 April 2016; volcanologist Sebastien Valade takes thermal measurements from the rim. Photo by Abel Kayanagh/MONUSCO. Courtesy of MONUSCO via Culture Volcan.

Thermal anomaly data from MIROVA suggest a pulse of activity during late April through early June 2016 (figure 62 D). This was followed by a period from early June through early November 2016 with no record of activity at Nyamuragira. The MIROVA signal reappeared in early November, followed by intermittent MODVOLC thermal alerts beginning on 27 November. A new pulse of thermal activity, with values similar to those observed during July 2015-April 2016, reappeared in early January 2017 (figure 62 E) and continued through April 2017. On an OVG-sponsored visit to the summit crater on 11 March 2017, independent journalist Charly Kasereka photographed the summit crater with incandescent lava covering the crater floor (figure 66).

Figure 66. Effusive activity at the bottom of the summit crater of Nyamuragira on 11 March 2017. Additional image available at https://laculturevolcan.blogspot.fr/2017/04/quelques-nouvelles-des-volcans.html shows minor spattering of molten lava near the vent on the crater floor. Photo by Charly Kasereka; courtesy of Cultur Volcan.

Sulfur dioxide and thermal anomaly data. Abundant sulfur dioxide emissions at Nyamuragira during November 2011-April 2017 show large variations in both magnitude and frequency during the period (table 3). A plot of the SO₂ data (figure 67) reveals a sharp increase in both the number of days per month with DU greater than 2 and the actual maximum DU value during the active flank eruption between November 2011 and February 2012. After lower values during March 2012, they rise steadily and remain significantly elevated for all of 2013. Values drop briefly in early 2014 and then rise again during April 2014, remaining elevated through February 2016 before dropping off significantly.

Figure 67. Sulfur dioxide data for Nyamuragira and Nyiragongo, October 2011 through April 2017. Blue bars represent the number of days each month where DU > 2 was captured in the Aura/OMI data (left axis). The orange points represent the highest DU value for the months where SO2 emissions had DU values > 2 for at least one day. See table 3 for details of Dobson Units (DU), and text for discussion of values. The two volcanos are less than 20 km apart, and thus the individual sources of SO2 cannot be distinguished in the satellite data.

A similar plot of the number of monthly MODVOLC thermal alert pixels for Nyamuragira from November 2011 through April 2017 (figure 68) shows that there were no thermal alerts for the period from April 2012-February 2014 when SO₂ emissions were large and frequent. In contrast, there were frequent thermal alerts from June 2014-April 2016 when SO₂ emissions were also high.

Figure 68. Number of MODVOLC thermal alert pixels per month at Nyamuragira from October 2011 through April 2017. Data courtesy of MODVOLC.

Table 3. Days per month that SO₂ values over the Nyamuragira and Nyiragongo area exceeded 2 Dobson Units (DU), October 2011-April 2017, and maximum DU values for each month. Data represent minimum values due to OMI row anomaly missing data (gray stripes), and missing days. SO₂ is measured over the entire earth using NASA's Ozone Monitoring Instrument (OMI) on the AURA spacecraft. The gas is measured in Dobson Units (DU), the number of molecules in a square centimeter of the atmosphere. If you were to compress all of the sulfur dioxide in a column of the atmosphere into a flat layer at standard temperature and pressure (0 C and 1013.25 hPa), one Dobson Unit would be 0.01 millimeters thick and would contain 0.0285 grams of SO₂ per square meter.

References: Campion, R., 2014, New lava lake at Nyamuragira volcano revealed by combined ASTER and OMI SO₂ measurements, 7 November 2014, Geophysical Research Letters (URL: http://onlinelibrary.wiley.com/doi/10.1002/2014GL061808/full).

Coppola, D., Campion, R., Laiolo, M., Cuoco, E., Balagizi, C., Ripepe, M., Cigolini, C., Tedesco, D., 2016, Birth of a lava lake:Nyamulagira volcano 2011-2015. Bull Volcanol (2016) 78: 20. doi:10.1007/s00445-016-1014-7.

Smets, B., d'Oreye, N., Kervyn, F., 2014, Toward Another Lava Lake in the Virunga Volcanic Field?, 21 October 2014, EOS, Transactions American Geophysical Union (URL: http://onlinelibrary.wiley.com/doi/10.1002/2014EO420001/pdf)

Smets, B., d'Oreye, N., Kervyn, F., Kervyn, M., Albino, F., Arellano, S., Bagalwa, M., Balagizi, C., Carn, S.A., Darrah, T.H., Fernández, J., Galle, B., González, P.J., Head, E., Karume, K., Kavotha, D., Lukaya, F., Mashagiro, N., Mavonga, G., Norman, P., Osodundu, E., Pallero, J.L.G., Prieto, J.F., Samsonov, S., Syauswa, M., Tedesco, D., Tiampo, K., Wauthier, C., Yalire, M.M., 2014. Detailed multidisciplinary monitoring reveals pre- and co-eruptive signals at Nyamulagira volcano (North Kivu, Democratic Republic of Congo). Bull Volcanol 76 (787): 35 pp.

Smets, B., Kervyn, M., Kervyn, F., d'Oreye, N., 2015. Spatio-temporal dynamics of eruptions in a youthful extensional setting: Insights from Nyamulagira volcano (D.R. Congo), in the western branch of the East African Rift. Earth-Science Review 150, 305-328. doi:10.1016/j.earscirev.2015.08.008

Geologic Background. Africa's most active volcano, Nyamuragira, is a massive high-potassium basaltic shield about 25 km N of Lake Kivu. Also known as Nyamulagira, it has generated extensive lava flows that cover 1500 km2 of the western branch of the East African Rift. The broad low-angle shield volcano contrasts dramatically with the adjacent steep-sided Nyiragongo to the SW. The summit is truncated by a small 2 x 2.3 km caldera that has walls up to about 100 m high. Historical eruptions have occurred within the summit caldera, as well as from the numerous fissures and cinder cones on the flanks. A lava lake in the summit crater, active since at least 1921, drained in 1938, at the time of a major flank eruption. Historical lava flows extend down the flanks more than 30 km from the summit, reaching as far as Lake Kivu.

Information Contacts: Observatoire Volcanologique de Goma (OVG), Departement de Geophysique, Centre de Recherche en Sciences Naturelles, Lwiro, D.S. Bukavu, DR Congo; NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); 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/); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/); Erik Klemetti, Eruptions Blog, Wired (URL: https://www.wired.com/author/erikvolc/); Cultur Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.com/); MONUSCO, United Nations Organization Stabilization Mission in the DR Congo (URL: https://monusco.unmissions.org/en/); Oliver Grunewald, Video filmed on 10 July 2015 (URL: https://laculturevolcan.blogspot.fr/2015/07/le-lac-de-lave-du-volcan-nyamuragira.html).

The andesitic Volcán El Reventador lies well east of the main volcanic axis of the Cordillera Real in Ecuador and has historical observations of eruptions of numerous lava flows and explosive events going back to the 16th century. The largest historical eruption took place in November 2002 and generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. This report briefly summarizes activity between 2002 and June 2014, and covers details of activity from July 2014 through December 2015. The volcano is monitored by the Instituto Geofisico-Escuela Politecnicia Nacional (IG) of Ecuador, and the Washington Volcanic Ash Advisory Center (VAAC).

Summary of 2002-2014 activity. Intermittent activity including pyroclastic flows, ash plumes, lava flows and explosive events took place between 2003 and 2008. Since July 2008 there have been persistent gas-and-ash plumes, dome growth, and both pyroclastic and lava flows. Lahars are also very common in this high-rainfall area, and cause damage to infrastructure on a regular basis. A lava dome was first observed growing in September 2009 within the crater that formed during the 2002 eruption. By July 2011, it had reached the height of the highest part of the crater rim; by January 2013 it filled the crater and formed a new summit, 100 m above the E rim. This led to lava blocks travelling down the flanks, in addition to the lava flows and pyroclastic flows traveling down the flanks of the cone inside the crater during 2012-2014. A summary of thermal anomalies compiled from MIROVA data (figure 46) demonstrates the ongoing but intermittent nature of heat flow between 2002 and 2014.

Figure 46. Thermal activity detected by the MIROVA system at Reventador, January 2002-January 2014. Courtesy of IG (Informe Especial del Volcan Reventador No. 3, 7 July 2014).

Summary of June 2014-December 2015 activity. Activity was very consistent throughout the period of June 2014 through December 2015. The thermal webcam captured images of lava flows, pyroclastic flows and ejected incandescent blocks nearly every month. MODVOLC thermal alerts were reported every month except March 2015. Satellite imagery of hot spots were common as well. The Washington VAAC reported observations of ash plumes every month, although they generally rose only to altitudes below 5.6 km (2 km above the summit). IG reported seismicity as varying between moderate and high during the period.

Activity during June-December 2014. Activity during June 2014 was characterized by numerous explosions and small pyroclastic flows that descended the flanks of the cone. The Washington VAAC issued two series of reports on 11-12 and 19-20 June. A pilot reported an ash plume on 11 June rising 2.8 km above summit at 6.4 km altitude and drifting W, and the next day ash was observed 1.8 km above the summit. Weather generally obscured satellite views. On 19 June, multiple small emissions of volcanic ash were seen in the observatory webcam along with incandescent material on the flanks. MODVOLC thermal alerts were issued on 5, 21, and 30 June.

IG reported a new lava flow on 2 July 2014 descending 400 m on the SSW flank. A pyroclastic flow was also reported on 2 July (figure 45, BGVN 39:07) extending 1,500 m down the S flank. IG noted ash emissions on 2, 4, 9-12, 18, 22-24, and 27 July rising 800 m to 2 km above the summit. MODVOLC reported multi-pixel thermal alerts on 2, 16, and 27 July, and single pixel alerts on 10 and 25 July. In addition to the ash plumes reported by IG, the Washington VAAC reported on-going ash emissions and detected hotspots at the crater on 31 July.

The Washington VAAC issued a report of hot spots visible in satellite imagery on 1 August 2014 and a pilot report of an ash plume at 6.1 km altitude (2.5 km above the summit) on 25 August. The only MODVOLC thermal alerts were issued on 31 August. IG reported lower level plumes (300-800 m above the summit) with minor ash on 6 other days during the month.

Activity increased during September 2014. The Washington VAAC issued reports during 2-4, 18, and 23 September. On 2 September, ash plumes were observed extending about 45 km W of the summit at 5.5 km altitude. Another faint plume of volcanic ash was observed within 20 km of the summit the next day. An ongoing hotspot with possible small ash emissions was noted on 4 September. IG reported an explosion on the morning of 5 September that generated a plume and ejected blocks from the crater that fell ~500 m below the summit on the W flank. A thermal camera detected an explosion on the following day that also included ballistics. MODVOLC thermal alerts were issued on eight days during September. Steam plumes with minor ash rose to around 1 km above the summit and dispersed generally W several times during the month.

A single MODVOLC thermal alert was reported on 6 October 2014. The Washington VAAC reported short 2-3 minute bursts of minor volcanic ash on 19 October which was seen drifting WNW and dispersing within 16 km of the summit below 5.8 km altitude. An additional single pixel thermal alert was issued on 25 October, and a three-pixel alert appeared on 29 October.

IG reported steam-and-ash plumes rising up to 1 km above the summit a few times during the month, which were visible on the rare clear-weather days (figure 47). Only two days in November, 5 and 21, had MODVOLC thermal alerts. The Washington VAAC, however, issued reports during 11-12, 18-19, and 27 November of possible low-level ash-bearing plumes. The IG webcam LAVA on the SE flank captured images of pyroclastic flows on 20 and 25 November (figure 48).

Figure 47. The active cone at Reventador on 9 November 2014 with a low-level steam plume. Image taken from the IG Webcam LAVA on the SE flank. Courtesy of IG via La Culture Volcan.

Figure 48. Pyroclastic flows at Reventador, 20 (left) and 25 (right) November 2014 taken from the IG LAVA webcam on the SE flank. Courtesy of IG via Culture Volcan.

On 5 December 2014 a webcam recorded a steam-and-gas emission associated with an incandescent lava flow on the E flank. MODVOLC thermal alert pixels appeared on four days in December 2014 (3, 7, 14, and 23), and VAAC reports of ash plumes were issued on 5, 13-14, 21-22, and 30 December. The largest plume, on 14 December, rose to 6.1 km (2.5 km above the summit) and drifted NE. IG reported moderate seismicity and low-level steam plumes with minor ash content on several occasions.

Activity during 2015. Moderate seismic activity continued during January 2015 with low-level steam-and-ash plumes from explosions rising a few hundred meters above the summit, according to IG. A larger explosion reported by IG on 16 January generated an ash plume that rose 2 km and drifted SE. The Washington VAAC reported activity from 14-18 January, and again on 26 January. Their reports were of small puffs of ash within a kilometer of the summit drifting for a few hours before dissipating. MODVOLC thermal alerts were issued on 15 and 29 January.

Steam plumes containing minor amounts of ash were recorded a few times during February 2015 during periods of moderate seismicity. The Washington VAAC issued several reports, during 7-9, 13-17, 19-21, 24, and 26-28 February, noting occasional plumes with ash rising to less than one km above the summit, and hot-spots seen in satellite imagery on 13-14, 17, 19, and 27 February. An aircraft reported volcanic ash on 19 February at 6.1 km altitude. A new lava flow first observed on the SW flank on 11 February had advanced 1 km by 19 February. This is consistent with the four-pixel MODVOLC thermal alert issued on 18 February. Single pixel alerts were issued on 7, 19, and 23 February as well.

No MODVOLC thermal alerts were issued during March 2015, but the Washington VAAC continued to note low-level small bursts of ash emissions several times a week within 15 km of the summit, as reported by IG. The webcam captured a hotspot at the summit on 11 March. A thermal camera image of a lava flow taken on 13 March showed the visible part of it to be over 500 m long (figure 49), and IG noted in their 13 March report that is was actually about 1.5 km long that day.

Figure 49. Annotated thermal camera image at Reventador of an 11 March 2015 lava flow. Camera is located SE of the volcano. Courtesy of IG (Informe especial del Volcan Reventador No. 1, 13 March 2015).

Activity during April 2015 included moderate seismicity and incandescence at the crater reported by IG. A lava flow on the SW flank was visible with the infrared camera during the first week; this agrees with the 5-pixel MODVOLC thermal alert recorded on 5 April and the bright hotspot observed in both satellite imagery and the webcam during 3-5 April. Hot spots were observed via satellite and webcam several additional times during the month. Additional thermal alerts also appeared on 10 and 21 April. Steam-and-ash plumes rising to 1 km above the summit were intermittent throughout the month, mostly observed from the webcam.

Multi-pixel MODVOLC thermal alerts appeared during 2-3, 20, and 30 May, indicating continued sources of heat from lava flows. In a special report issued on 19 May, IG noted a new lava flow during the previous week that descended the S flank, forming a fan with three lobes on the SE and SW flanks. The length was greater than 1,000 m from the summit on 19 May, although the flows remained on the flanks of the summit cone within the caldera (figure 50). IG noted an increase in emission tremor on 17 May which may have been related to the extrusion of the lava, but weather conditions prevented visual confirmation. During 17-30 May, intermittent low-level gas-and-ash plumes within 15 km of the summit were reported on most days.

Figure 50. Annotated thermal image of the summit cone of Reventador on 19 May 2015 showing a 3-lobed lava flow descending the S flank of the cone for more than 1 km. Courtesy of IG (Informe especial del Volcan Reventador No. 2, 19 May 2015).

MODVOLC thermal alerts diminished during June 2015, occurring only on 8 and 15 June. Nonetheless, thermal images showed lava flows down the SW and S flanks of the cone several times, and hot spots were observed in satellite images and on the webcam when the weather permitted. Steam-and-ash plumes were generally reported to rise to 1 km or less above the summit and drift usually NW or SW within 15 km of the volcano. A pilot reported volcanic ash on 30 June at 6.7 km, but no ash was seen in satellite imagery under cloudy conditions. IG issued a special report on 24 June noting increased seismicity in the form of increased tremor signal and explosions on 23 June. The thermal camera located in the area of El Copete, 5 km S of the crater, showed an increase in surface activity characterized by several lava flows on the SW, S, and SE flanks exceeding one km in length (figure 51).

Figure 51. Thermal image of Reventador taken on 23 June at 1950 by the webcam near El Copete. Courtesy of IG (Informe especial del Volcan Reventador No. 3, 24 June 2015).

Seismic activity was reported as high during July 2015 by IG, and included explosions, tremor, long-period earthquakes, harmonic tremor, and emission signals. During the first week, incandescent material was visible more than 1 km down the SE flank in thermal images. On 17 July, light gray deposits possibly from a pyroclastic flow were observed; on 21 July explosions again ejected incandescent material onto the flanks. Steam and ash emissions were intermittent and generally remained below 5.1 km altitude. MODVOLC thermal alerts appeared on 1, 3, 15, and 17 July.

High levels of seismic activity continued during August 2015. The Washington VAAC reported possible ash plumes on 14 days during the month, and MODVOLC thermal alerts were issued on six dates, including four-pixel alerts on 4 and 27 August suggestive of lava flows and/or incandescent material on the flanks of the cone. A discrete volcanic ash emission on 6 August was reported by the Washington VAAC at 7 km altitude (3.4 km above the summit) with a plume extending about 25 km NW of the summit. Other plumes that were reported by pilots (on 25 August at 8.8 km altitude moving NW, and on 26 August at 6.7 km moving W) were not observed in cloudy satellite imagery.

Ash-and-gas emissions were reported by the Washington VAAC during 14 days in September 2015, generally drifting N and W at altitudes less than 2 km above the crater (5.6 km altitude); high levels of seismicity also continued, according to IG. The Guayaquil MWO reported volcanic ash at 6.1 km on 19 September. Puffs of ash seen in the webcam were reported at 7.3 km altitude on 25 September and thought to have quickly dissipated. MODVOLC thermal alerts appeared on seven days during the month; five of them were two- or three-pixel alerts. An SO₂ plume drifting WNW from Reventador was captured by NASA's OMI instrument on 22 September (figure 52).

Figure 52. An SO2 plume drifting W from Reventador on 22 September 2015. Reventador is represented by the triangle south of the NW-SE trending Ecuador/Columbia border in the bottom center of the image near longitude 78 W just south of the equator. A small plume in the top half of the image is likely SO2 from Nevado del Ruiz. Courtesy of NASA/GSFC.

A series of VAAC reports of low-level minor ash emissions were issued during 1-5 October 2015. After two weeks of no activity, multi-pixel MODVOLC thermal alerts and VAAC reports increased during 20-30 October. The peak MODVOLC activity included 4-6 daily pixels during 26-28 October, and the VAAC reports noted a bright hotspot on the satellite images beginning on 20 October and present for most of the rest of the month. Continuous emissions were observed in the webcam during 22-26 October, generally below 4.6 km, moving NW, and extending up to 40 km from the summit. Continuous emissions appeared again on 30 October at 5.1 km moving W.

During the last two weeks of November 2015, steam, gas, and ash emissions rose to less than 2 km above the summit and incandescent blocks rolled 500 m down the flanks of the cone. MODVOLC thermal alerts were reported for five days between 15 and 29 November. Similar activity was reported during December, although the Washington VAAC only issued reports on four different days, and MODVOLC thermal alerts were recorded only on 6 and 24 December. VAAC reports noted hotspots in satellite imagery on 7 December. The VAAC reports on 11 and 16 December indicated ash plumes at 5.5 km moving W and SW.

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 (IG), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Culture Volcan, Journal d'un volcanophile (URL: https://laculturevolcan.blogspot.fr/).

A February 2012 ash explosion of Columbia's Nevado del Ruiz volcano was the first confirmed ash emission in over 20 years. The broad, glacier-capped volcano has an eruption history documented back 8,600 years, and historical observations since 1570. Notably, a large explosion at night in heavy rain on 13 November 1985 generated large lahars that washed down 11 flank valleys, inundating most severely the town of Armero where over 20,000 residents were killed. It remains the second deadliest volcanic eruption of the 20th century after Mt. Pelee in 1902 killed 28,000.

This report summarizes and concludes the February 2012-April 2014 eruption (BGVN 37:08, 39:07), and then describes details of new activity beginning in November 2014, through December 2015. The volcano is monitored by the Servicio Geologico Colombiano (SGC) and aviation reports are provided by the Washington Volcanic Ash Advisory Center (VAAC).

Summary of activity, November 1985-June 2012. After the large explosions and deadly lahars of November 1985, activity at Ruiz continued with intermittent ash emissions and significant seismic activity through July 1991. Seismicity, deformation, and SO₂ emissions have been closely monitored since the 1985 eruption. Between 1991 and February 2012 intermittent high-frequency seismic events (earthquake swarms) were recorded, but no ash emissions were observed. In September 2010, seismicity notably increased in frequency and diversity of event type until early 2012 when fresh ashfall was observed. INGEOMINAS (Instituto Colombiano de Geología y Minería, precursor to SGC) also noted an inflationary trend in the geodetic data from October 2010 through 2011.

A March 2012 overflight by INGEOMINAS noted minor amounts of ash-covered snow on the E flank, which they surmised came from an explosion on 22 February (BGVN 37:08). During March, long-period seismicity underwent a 20-fold increase. SO₂ emissions also dramatically increased between March and June 2012. Several ash emissions from the summit were observed during April-June 2012 (BGVN 37:08). An ash plume that rose to 11 km altitude on 29 May caused ashfall in over 20 communities to the NW and closures at three nearby airports. Widespread ashfall during June covered solar panels on field equipment. An EO-1 satellite image from 6 June 2012 shows a plume and significant ashfall around the summit (figure 71).

Figure 71. Satellite image of Nevado del Ruiz taken on 6 June 2012 showing an active ash plume from the Arenas crater and ash deposits NW of the summit. It was acquired by the Advanced Land Imager (ALI) aboard the Earth Observing-1 (EO-1) satellite. Courtesy NASA Earth Observatory.

Summary of activity, July 2012-December 2015.Explosions and seismic tremor with ash emissions continued during July and August 2012. Ashfall was reported within 30 km on numerous occasions. From September 2012 through early July 2013 minor amounts of ashfall were reported a few times each month, mostly in the immediate vicinity of the volcano. After a larger explosion on 11 July 2013, sparse and intermittent ash emissions were reported between August 2013 and April 2014. Between May and October 2014 there were no reports of ash emissions or thermal anomalies.

A significant increase in seismicity occurred during the second week of November 2014, and ash was seen at the summit during an overflight on 19 November. Ash fell in communities within 30 km several times each month through December 2015. Seismic evidence suggesting possible lava dome extrusion first appeared in August 2015, and stronger signals were recorded on 22 October. Thermal anomalies around the summit crater increased in frequency and magnitude during the last three months of 2015.

Activity during July 2012-October 2014.A large ash plume on 30 June 2012 prompted evacuation warnings to several communities within 30 km and closed three nearby airports for the second time within 30 days. On 2 July the Washington VAAC reported a 7.5-km-wide ash plume at 6.1 km altitude drifting 75 km W (BGVN 37:08). Additional VAAC reports were issued on 8, 9, and 10 July for SO₂ emissions containing minor volcanic ash. SGC noted that explosions and ash emissions continued throughout the month in spite of a decrease in seismicity. Ashfall was reported near the volcano, and in municipalities in the departments of Caldas (W) and Risaralda (SW), steadily throughout the month.

Tremors associated with continuing gas and ash emissions occurred throughout August 2012; ash plumes were observed rising 200-800 m above the summit crater. During 3-6 August, gas and ash emissions were seen from Manizales (30 km NW) and Chinchiná (30 km WNW). On 12 August, a gas-and-ash plume observed with a webcam rose 1 km above the crater and drifted W, and ashfall was reported in Brisas (50 km SW). A layer of ash was deposited at the Observatorio Vulcanológico y Sismológico de Manizales (OVSM) on 13 August; they also reported ash emissions associated with seismic signals the next evening. Webcams showed gas-and-ash plumes rising 400 m and drifting W and NW during 15-16 August.

Minor amounts of ashfall were reported by SGC in areas around the volcano each month during September 2012 through 11 July 2013 (table 4), when a larger ash emission occurred. A noted increase in seismicity beginning on 13 April 2013 was also reported by SGC. The ash emission on 11 July was captured by the webcam in the Parque Nacional Natural Los Nevados (PNNN) (figure 72), and fine ash fell in Manizales. The Washington VAAC reported the ash plume at 6.1 km altitude. Multispectral imagery showed the plume extending 55 km NW. After 12 July 2013 there were no further reports from the Washington VAAC until December 2014.

Table 4. Ash emission events at Ruiz during September 2012-July 2013. Data compiled from various sources as shown.

Figure 72. Ash emission at Ruiz on 11 July 2013 at 1143. The column of gases and gray ash stands out among the white clouds. Photo by Julián Peña, courtesy of SGC (Informe-Technico, July 2013).

Evidence for ash emissions between August 2013 and April 2014 is sparse and intermittent. The SGC Monthly reports during this time mention pulses of low-energy tremor associated with emissions of gases, steam, and small amounts of ash every month except November, when they reported only steam and gas, but no specific dates are given. SGC's Technical Information Monthly reports mention occasional grayish coloration, suggesting ash in the gas-and-steam plumes during August-October 2013. Tremors associated with small amounts of ash and grayish coloration in the plumes are again noted from January through April 2014 without describing specific events.

The weekly activity reports issued by SGC make no mention of ash from August through November 2013. They note in weekly reports for 2-8 and 9-15 December that gray emissions possibly associated with ash in plumes of mostly water vapor and gases were observed. During the week of 16-23 December they recorded low-energy tremors associated with the output of small amounts of ash, which were reported in trace quantities in Manizales. In their 31 December 2013-6 January 2014 and 10-16 February 2014 weekly reports they noted the occurrence of tremors associated with ash and gas. There is no mention of ash in their March or April 2014 weekly reports. There is also no mention of ash emission in SGC monthly reports during May-October 2014. The MIROVA thermal anomaly data do show minor thermal anomalies in latest August and more persistent anomalies at the beginning of October 2014 (figure 73) prior to the reports of ash emissions during November.

Figure 73. MIROVA signal of MODIS data for the year ending on 15 May 2015. Persistent thermal anomalies are present between late October 2014 and mid-April 2015. Courtesy of the MIROVA project supported by the Centre for Volcanic Risk of the Italian Civil Protection Department via SGC (Informe de Actividad, April 2015).

Activity during November 2014-December 2015.A significant change in seismicity occurred beginning in the second week of November 2014. There was an increase in the number of long-period (LP) earthquakes, pulses of volcanic tremor, and several periods of continuous tremor (lasting for hours or even days) associated with fluid movement, and with emissions of gas and ash (table 5). Several of these periods were preceded by an LP event. The first significant pulse of volcanic tremor began on the evening of 18 November following an LP event and lasted more than 12 hours.

Table 5. Periods of continuous tremor associated with ash emissions at Ruiz during November 2014. Some of the tremor episodes were preceded by long-period (LP) events. Courtesy of SGC (Informe de Actividad, November 2014).

The Unidad Nacional de Gestion de Riesgo de Desastres (UNGRD, National Disaster Risk Management Unit) coordinated an overflight during 19-21 November 2014 and observed fresh ash deposits on the S flank. Ash emissions were also verified in satellite imagery (figure 74) and by reports from nearby communities. The ash dispersed generally SE and SW during 18-21 November. Ash was again observed on the N side of the Arenas crater on 29 November in the early morning after a lengthy period of continuous tremor was recorded the previous day (see table 5).

Figure 74. Image of Ruiz on 24 November 2014 taken by the OLI-TIRS sensor on the Landsat 8 Satellite at 1018 local time. Ash deposits are dispersed SE and SW of the summit crater, and the steam plume is drifting W. Courtesy of SGC (Informe de Actividad, November 2014).

During the second half of December 2014, SGC reported significant concentrations of ash in the emissions that were associated with continuous tremor episodes. On 15 December seismic signals indicating ash emissions were detected, and then confirmed by a local webcam and nearby residents. The Washington VAAC also noted an ash emission based on a pilot observation extending 16 km S at 7.6 km altitude. The next day they reported a narrow plume of minor volcanic ash extending 22 km SW of the summit at 6.1 km altitude. On 18 and 19 December the Washington VAAC reported ash plumes to altitudes of 7.9 and 9.1 km, respectively, that drifted SSW and dissipated within a few hours. A faint thermal anomaly was also detected. A satellite image taken on 26 December 2014 clearly shows ash deposits in nearly all directions from the Arenas crater (figure 75). Ashfall was reported during this time in the Caldas (W) and Risaralda (SW) departments.

Figure 75. An ASTER image from the OLI-TIRS Sensor on the Landsat 8 satellite taken on 26 December 2014 of Ruiz (N is to the top) showing fresh ash deposits covering the summit glacier in nearly all directions. Courtesy of SGC (Informe de Actividad, December 2014).

According to the news source Prensa Latina, increased ash emissions at Ruiz prompted closure of the La Nubia airport (22 km NW) on 7 January 2015. On 14 January, the Washington VAAC reported an ash plume visible in satellite imagery extending 16 km SW of the summit at 6.7 km altitude. SGC reported seven episodes of continuous tremor on 4, 7, 14, 24, 26, 28, and 29 January, almost all of which were associated with ash emissions (figures 76). Ashfall was reported several times after these episodes in the Eje Cafetero area to the W of Ruiz.

Figure 76. Ash emissions on six different dates during January 2015 at Ruiz. Photographs taken by the webcam located in the Azufrado sector (NW). Courtesy of SGC (Informe de Actividad, January 2015).

Occasional minor ash emissions were reported during February 2015 during periods of continuous tremor, but most of the emissions were steam and gas. On 9 February, ashfall was reported in El Libano (29 km E), El Oso (10 km SE), and Murillo (17 km E). Although seismic tremors were diminished during March from the previous month, emissions associated with these tremors contained gases and minor amounts of ash from 8 March through the end of the month. Ashfall was reported after a tremor in the evening on 8 March by personnel from the Parque Nacional Natural Los Nevados (PNNN), the Observatorio Vulcanológico y Sismológico de Manizales (OVSM), and from the municipalities of Manizales and Villamaria (27 km NW).

An increase in several types of seismicity was observed by SGC during April 2015. Volcanic tremor, associated with gas and ash emissions, were confirmed through photographs taken by the webcams (figure 77), and by officials at PNNN and SGC. Ashfall was reported on 20 April in the municipalities of Manizales and Villamaría. The Washington VAAC reported a small puff of gas and minor amounts of ash visible in satellite imagery on 22 April at 7.3 km altitude drifting W about 40 km before dissipating. The MIROVA signal from the MODIS thermal anomaly data shows persistent thermal activity from late October 2014 through mid-April 2015 (figure 73).

Figure 77. Plumes of ash-and-gas from Ruiz during April 2015. Confirmed ash emissions were observed on 9, 22, 27, and 29 April. Courtesy of SGC (Informe de Actividad, April 2015).

Ash emissions were photographed by the webcams located in the Azufrado and Cerro Guali regions on at least eleven dates during May 2015. The Washington VAAC reported possible emissions on 19 and 26 May, but extensive weather clouds prevented satellite observations. Most of the frequent episodes of volcanic tremor during June were also associated with ash emissions which were photographed at least six times during the month. The Observatory at Manizales reported ash moving WNW on 6 June at about 800 m above the summit; weather clouds obscured satellite observations by the Washington VAAC.

A significant increase in ashfall was reported during July 2015 (figure 78), including in the regions of Caldas, Tolima, and Risaralda, as well as by officials in the Park (PNNN). The Observatory at Manizales (OVSM) reported an ash plume on 6 July at about 7.3 km altitude, but it was not observed in satellite data due to weather. The Washington VAAC noted ash emissions visible in satellite data and the webcam on 13 July, with a plume at 7 km altitude drifting NW a few tens of kilometers before dissipating. OVSM reported plumes at about 6 km moving S and W during 18-20 July. Seismic signals indicating emissions were reported on 23 July and observed in the webcam, according to the Washington VAAC. SGC noted seismic tremors and a plume on the morning of 26 July that rose to 3 km above the summit (8.2 km altitude) (figure 79); near summit-level emissions were also observed via the webcam on 26 and 27 July. Seismic data indicated continued occasional bursts of ash drifting W to WSW during the next few days. Ashfall was reported downwind in the municipalities of Chinchina (33 km NW), Palestina (35 km NW), Santa Rosa de Cabal (33 km W), Dosquebradas (40 km WSW), and Pereira (40 km WSW). A bright thermal anomaly was reported in satellite imagery on 31 July, but no ash was observed.

Figure 78. Gas, steam, and ash plumes from the Arenas crater at Ruiz during July 2015. Photographs captured by the cameras located in the area of Azufrado, Cerro Gualí, and in the OVSM. Courtesy of SGC (Informe de Actividad, July 2015).

Figure 79. Seismic and visual images of tremors that produced ash emissions at Ruiz between 0800 and 1559 on 26 July 2015. The digital seismogram and spectrogram are from station BIS (2 km W of Arenas Crater) and show a characteristic spasmodic tremor (1, 2, and 3) that was associated with ash emissions recorded on the Piranha-Azufrado webcamera in the lower images. Courtesy of SGC (Informe de Actividad, July 2015).

SGC reported greater instability at Ruiz compared with previous months during August 2015. Seismicity related to fracturing and fluid flow both increased during the month. Energy levels for spasmodic tremor related to gas and ash emissions were also generally higher. The Washington VAAC reported ash visible in satellite imagery on 6 August at 7.3 km altitude moving NW as far as 20 km for about 10 hours before dissipating. They noted another possible plume with minor ash on 12 August at 6.7 km drifting 55 km NW from the summit. Ashfall was reported on 23 August from officials of PNNN and residents of Pereira. A brief emission containing minor ash on 28 August, observed in a webcam, was reported by the Washington VAAC as extending about 35 km W. Ongoing emissions rising a few hundred meters above the summit with occasional small bursts of ash continued for the next two days.

The tremor event on 31 August 2015 was the largest since 18 November 2014; ashfall affected numerous cities and municipalities, including Manizales (30 km NW) (with the largest particle sizes towards the E side of the city), La Linda, La Cabaña (36 km NW), and trace amounts in Santagueda (40 km NW), Arauca (48 km NW), Kilómetro 41, Villamaría (27 km NW), Chinchiná, Palestina, and Neira (36 km NW) (figure 80). A news article reported that the La Nubia airport closed that day due to ash emissions. Most ash emissions during the month affected the regions of Caldas and Risaralda NW of the volcano.

Figure 80. Ashfall was recorded in a number of cities during the 31 August 2015 emission event at Ruiz. The four left images are from the city of Manizales. The six right images are from different towns in the department of Caldas. Courtesy of SGC (Informe de Actividad, August 2015).

The Washington VAAC issued advisory reports on 3, 12-15, 17, 23-24, 27, and 29-30 September 2015. Most reports were based on observations from the webcams near the volcano and/or seismic activity, but many events were not visible in satellite imagery due to weather clouds. Plume altitudes ranged from 5.5 to 7.9 km. Incandescence observed in a webcam on 4 September was followed by a high-energy tremor. The ash plumes reported by the Washington VAAC on 12 and 13 September rose to 7.9 km and drifted in several directions. Ash was moving to the NW below 5.2 km and extended for over 90 km; between 5.2 and 7.9 km altitude it extended about 80 km SW. Ongoing emissions with small bursts of ash continued through 15 September with a new emission to 7.6 km around 1600 that day.

The OVSM reported a strong seismic signal at 0728 on 17 September, but weather clouds blocked observation from satellite imagery of the potential ash plume. The largest tremor of the month occurred in the afternoon of 18 September and ash emissions were verified in the webcams as well as by SGO officials doing fieldwork in the area; ash emissions were also observed in the webcam on 19 September at 1556. SGO reported a seismic event on 22 September that produced water-vapor, gas, and ash plumes that rose 2 km above the crater and drifted mainly NW. An ash plume was confirmed by the Washington VAAC in a satellite image on 27 September extending about 70 km WNW at 6.1 km altitude. An advisory issued on 29 September noted ash to 8.5 km within 16 km of the summit. SGO noted that the 29 September emissions were observed both E and W of the volcano.

The Washington VAAC confirmed continuous ash emissions on 5 October 2015 at 7 km altitude extending about 25 km W of the summit. A gas, steam, and ash plume rose 1.7 km and drifted NW on 8 October. Another report of volcanic ash early on 9 October was not visible in satellite imagery, although a thermal anomaly persisted and seismicity was elevated. A small ash emission was spotted in imagery data drifting WNW late on 9 October. A gas, steam, and ash plume rose 1.8 km and drifted NW on 17 October. A discrete emission of ash rose to 9.1 km altitude on 22 October and drifted N. SGO reported ash emissions observed in webcams on 26 October, but weather clouds prevented satellite observation by the Washington VAAC. A gas, steam, and ash plume rose 1.7 km and drifted NW on 30 October.

SGC first noticed an unusual pattern of seismicity known as a "drumbeat" signal, for which they issued a special report on 20 August 2015. The "drumbeat" signal is characterized by discrete episodes of short duration (about 30 minutes each) that repeat at regular time intervals and show similar waveforms and energy. They are interpreted by volcanologists to represent phenomena associated with the ascent of high-viscosity magma to the surface and thus are an indicator of near-surface extrusion or dome building. SGC recorded the same signal on 8 September, and then again on 22 October (figure 81). Thermal anomalies near the Arenas crater were observed by SGO on 26, 28, and 30 September, and were again recorded on 7, 9, and 10 October 2015.

Figure 81. Episodes of seismic "drumbeats" at Ruiz recorded on 22 October 2015. The top box is the vertical component seismic record from station BIS, the larger yellow shaded box highlights the entire 'drumbeat' episode. The seismogram from the OLLETA station (lower left) shows a clearer view of the first episode (1). The lower right images show details of the signal at three different time intervals highlighted in smaller boxes in the top image. This signal is interpreted to represent phenomena associated with the ascent of high-viscosity magma to the surface and thus are an indicator of near-surface extrusion or dome building over the emission conduit. Courtesy of SGC (Informe de Actividad, October 2015).

Seismic activity decreased slightly during November 2015, but there still were episodes of volcanic tremor associated with gas and ash emissions that were recorded by the webcams and personnel at PNNN. Continuous tremor signal was recorded on 1 and 4 November. The "drumbeat" signal was again briefly recorded on 13 November. Thermal anomalies increased in frequency and were observed on 4, 18, 20, 22, 26, and 27 November. SGC confirmed ash emissions on 5, 10, 14, 27, and 29 November. The Washington VAAC reported an ash plume on 14 November at 6.4 km altitude moving SW. SGC captured images of the ash plume from two different webcams (figure 82).

Figure 82. Photographs of the ash emission at Ruiz of 14 November 2015 at 0537 from two different webcams. Top image is from the Azufrado webcam (5 km NE) and the lower image is from the Pitayo webcam. Courtesy of SGC (Informe de Actividad, November 2015).

Thermal alerts captured by the University of Hawai'i's MODVOLC system appeared in December 2015 for the first time in several years. They were recorded on 3, 22, 26, and 31 December. Additionally, the MIROVA thermal anomaly system showed significant increases in anomalies at Ruiz during the last three months of 2015 (figure 83).

Figure 83. MIROVA data for the year ending 2 January 2016 showing the substantial increase in frequency and magnitude of thermal anomalies at Ruiz during the last three months of 2015. Courtesy of MIROVA via SGC (Informe de Actividad, December 2015).

Minor episodes of volcanic tremor with ash emissions were reported by SGC during the first two weeks of December 2015. A significant volcanic tremor with ash emissions occurred on 20 December, and ashfall was reported by SGC officials, PNNN personnel, and residents near the volcano and in the city of Manizales. The Washington VAAC noted the ash plume at 6.1 km altitude with 25 km of the summit. A gas, steam and ash plume rose 1.7 km and drifted NW on 28 December.

Sulfur Dioxide emissions, June 2012-2015. Persistent, large SO₂ plumes were captured from Ruiz many times during June 2012-December 2015 (figure 84 and 85). Every month during this period the OMI (Ozone Measuring Instrument) on the Aura satellite recorded days with SO₂ emissions exceeding 2 DU (Dobson Units); many months had more than half of the recording days with values > 2 DU. Dobson Units are the number of molecules in a square centimeter of the atmosphere. If you were to compress all of the sulfur dioxide in a column of the atmosphere into a flat layer at standard temperature and pressure, one Dobson Unit would be 0.01 millimeters thick and contain 0.0285 grams of SO₂ per square meter.

Figure 84. Select Aura/OMI images of SO2 plumes from Ruiz, 2012-2013. Top left: 14 June 2012, the SO2 plume drifts NW. Top right: 18 August 2012, the SO2 plume from Ruiz drifts W. An SO2 plume is also visible drifting W from Ecuador's Cotopaxi in the lower left corner of the image. Bottom left: A 10.26 DU (Dobson Unit) SO2 plume sits directly over Ruiz on 7 December 2012. Bottom right: The SO2 plume drifts south on 19 December 2013. See text above for description of Dobson Units. Courtesy of NASA Goddard Space Flight Center (NASA/GSFC).

Figure 85. Select Aura/OMI images of SO2 plumes from Ruiz, 2014-2015. Top left: On 3 February 2014 an SO2 plume from Ruiz drifts due W while another plume drifts NE from Guagua Pichincha in northern Ecuador. Top right: A 24 September 2014 SO2 plume drifts NW from Ruiz as far as the coastline. Bottom left: On 5 March 2015, a plume drifts slightly W from Ruiz. Bottom right: A W-drifting SO2 plume from Ruiz on 4 October 2015 is visible along with W-drifting plumes from both Cotopaxi and Tungurahua in Ecuador. Courtesy of NASA/GSFC.

Geologic Background. Nevado del Ruiz is a broad, glacier-covered volcano in central Colombia that covers more than 200 km2. Three major edifices, composed of andesitic and dacitic lavas and andesitic pyroclastics, have been constructed since the beginning of the Pleistocene. The modern cone consists of a broad cluster of lava domes built within the caldera of an older edifice. The 1-km-wide, 240-m-deep Arenas crater occupies the summit. The prominent La Olleta pyroclastic cone located on the SW flank may also have been active in historical time. Steep headwalls of massive landslides cut the flanks. Melting of its summit icecap during historical eruptions, which date back to the 16th century, has resulted in devastating lahars, including one in 1985 that was South America's deadliest eruption.

Information Contacts: Servicio Geologico Colombiano (SGC), Observatorio Vulcanologico Y Sismologico Manizales, Diagonal 53 N0. 34 - 53 - Bogotá D.C. Colombia (URL: http://www2.sgc.gov.co/Manizales.aspx); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/, archive at: http://www.ssd.noaa.gov/VAAC/archive.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/); NASA Goddard Space Flight Center (NASA/GSFC), Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); 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/); Prensa Latina, Agencia Informativa Latinoamericana (URL: http://www.plenglish.com/).

Strong fumarolic activity characterized activity at Costa Rica's Turrialba for several decades before a phreatic eruption in January 2010 resulted in ashfall tens of kilometers from the volcano. Since the January-March 2010 eruption, there have been one or two brief eruptive episodes with ash emissions each year, generally lasting days to weeks. An episode from 29 October through 8 December 2014 began with an ash explosion, followed by continuous emissions on 30 and 31 October. Several additional explosions with ash emissions occurred during November, followed by a strong Strombolian explosion on 8 December that included ashfall up to 1 cm thick in places, and ballistics deposited 300 m from the vent (BGVN 40:04). This report covers the increasing ash-emission activity during 2015 and 2016. Information comes primarily from the Observatorio Vulcanologico y Sysmologico de Costa Rica-Universidad Nacional (OVSICORI-UNA). Aviation alerts are issued by the Washington Volcanic Ash Advisory Center (VAAC).

Turrialba began a new eruptive episode with an ash plume on 8 March 2015. Frequent, intermittent ash-bearing events continued through mid-May, and tapered off during June, with a final event reported on 22 June 2015. The larger plumes rose 2-2.5 km above the vent rim and drifted in many different directions, leading to ashfall throughout the region as far as 40 km from the volcano. A 'bubble of magmatic gas' dispersed accumulated ash from the vent on 15 August 2015. An eruption on 16 October 2015 was the largest in a year, and the start of a new series of emissions that persisted through the end of October, dispersing ash for tens of kilometers in most directions. A brief period of ash emissions between 2 and 8 February 2016 deposited ash within a few kilometers of the summit crater. Ash emissions and frequent small explosions between 28 April and 7 May preceded a longer series of emissions that began with a significant explosion on 16 May, included significant ashfall in regions within 30 km, and lasted until late July 2016. Strombolian activity and pyroclastic flows were also reported during late May; ashfall was reported up to 100 km SW. A new series of explosions and ash emissions began on 13 September that continued nearly uninterrupted through the end of the year, although ashfall reports were greatest in October 2016.

Activity during 2015. Little activity was reported during January and February 2015. Seismicity slowly increased from short-duration, low-amplitude, higher-frequency events in January to more lower-frequency events in February. Very-long-period earthquakes (VLP's) began to register in February and became more pronounced during March, when some were associated with explosions and ash emissions. The first, short, effusive emissions with low ash content occurred on 8 March. The largest events with prolonged ash emissions occurred on 12 (figure 43) and 15 March.

Figure 43. Eruption at Turrialba on 12 March 2015. Webcam image courtesy of OVSICORI (Boletín de Vulcanología Estado de los Volcanes de Costa Rica, January, February, March 2015).

Based on webcam views, weather models, and OVSICORI-UNA updates, the Washington VAAC reported that on 8 March diffuse ash emissions rose from the Cráter Oeste (West Crater) and seismicity increased. OVSICORI-UNA reported more ash emissions on 11 and 12 March. Almost continuous ash emissions were observed in the afternoon of 12 March punctuated by two noticeable explosions. Ash plumes rose as high as 2 km above the crater and drifted NW. Ashfall also occurred in the Valle Central and in the capital of San José (30 km WSW), and caused the closure of the Juan Santamaria International Airport (48 km W), which reopened during the evening on 13 March. The local Tobias Bolanos airport (40 km WSW) closed intermittently. On 13 March three short-duration explosions were reported. According to the Washington VAAC, ash plumes that day drifted 45 km NE at an altitude of 9.1 km, and drifted over 35 km W at an altitude of 6.1 km.

On 18 March, OVSICORI-UNA reported that gas, vapor, and ash plumes rose from Cráter Oeste and seismicity remained high. Observers in Finca La Central (2 km SW) noted gas-and-steam emissions. On 19 March two gas-and-water-vapor emissions were observed; one from Cráter Central contained a small amount of ash. At 1400 the webcam recorded strong emissions of gas, vapor, and tephra from Cráter Oeste. On 23 March a gas, vapor, and ash plume rose from Cráter Oeste, causing ashfall in areas E and SE of the crater including in the Cráter Central and El Mirador. In addition, a dense and vigorous gas-and-vapor plume caused Parque Nacional Volcán Turrialba authorities to recommend masks for protection against gas inhalation.

There were 11 gas-and-ash eruptions and 10 additional smaller ash emissions during April 2015. OVSICORI-UNA reported that a small ash eruption occurred on 3 April, causing ashfall in nearby areas including Silvia and La Central. On 5 April, an eruption generated a plume that rose 500 m and caused ashfall in Curridabat (31 km WSW), Granadilla (29 km WSW), San Pedro, Desamparados (35 km WSW), Aserrí (40 km SW), San Sebastián (37 km WSW), and Escazú (42 km WSW). The eruption of 7 April was the largest of the month (figure 44), and although it occurred at night, the visible ash plume rose to about 2.5 km above the summit. Ash and sulfur odors were reported in many areas of the city of San José (30-40 km WSW). The largest quantities of ash fell in the La Picada and La Silvia communities a few kilometers NNE of the volcano, and affected several hundred cows and other animals at dairy farms. Small ash emissions occurred on 8, 16, and 18 April, and every day during 20-24 April. The ash on 20 April dispersed N and affected Guápiles (20 km N). On 23 and 24 April, ash dispersed NW and affected the inhabitants of the Valle Central, and was reported at Tobias Bolanos and San Juan Santamaria international airports.

Figure 44. Nightime eruption of ash and hot volcanic blocks from Turrialba on 7 April 2015 that began at 0205 and lasted until 0241. Webcam image courtesy of OVSICORI-UNA, (Boletín de Vulcanología, Estado de los Volcanes de Costa Rica, April 2015)

During May 2015, OVSICORI-UNA recorded 39 eruptions with ash emissions. In general, the plumes did not rise more than 500 m above the crater, and a few were accompanied by small pyroclastic flows. The largest events were on 1 and 4 May when emissions lasted for 4 and 23 minutes, respectively. The 4 May event produced an ash plume that rose 2.5 km and drifted SW. The eruption ejected ballistics 1 km from the crater. Most of the ashfall occurred around the crater. Reports of minor ashfall and sulfur odors came from communities 30-40 km WSW around the city of San José (Moravia, Coronado, Mata de Plátano, La Uruca, Guadalupe, Tibás, Calle Blancos, San Pedro Montes de Oca, Sabanilla Montes de Oca, Pavas, Zapote, Escazú, Paso Ancho, Curridabat, Santa Ana), and a few localities in the eastern region of Heredia (40 km W). Additional ash emissions were reported on 6, 11, 14, and 18 May. Although the multiple emissions on 18 May lasted as long or longer than earlier events (23 and 25 minutes), they were lower energy, and the plumes rose only 400-500 m above the summit crater.

OVSICORI-UNA reported that ash emissions occurred on 1, 4, 7, and 22 June 2015. The eruption on 1 June was the largest, and the small ash eruption on the afternoon of 22 June deposited ash mainly in the vicinity of the volcano to the SW (figure 45). They also reported a significant decrease in the seismic activity, such that by late June, the RSAM values had returned to levels similar to October 2014, prior to the start of the most recent eruptive events. Significant rains after April 2015 led to a shallow lake forming in the Cráter Oeste. Images taken in July of the Cráter Central showed deposits of eruptive material more than 2 m thick compared with May 2014.

Figure 45. Eruption at Turrialba on 22 June 2015. Webcam image courtesy of OVSICORI-UNA (Boletín de Vulcanología, Estado de los Volcanes de Costa Rica, June 2015).

Seismicity continued to decrease during August 2015. However, an event on 15 August comprised nine hours of tremor associated with the ascent and escape of a bubble of magmatic gas, according to OVSICORI-UNA. The resulting ash ejection was believed to be material that had accumulated at the bottom of the crater. Seismicity remained low during September, with no reported ash emissions.

An increase in seismicity began on 1 October 2015, and until a large eruption on 16 October (figure 46). This was followed on 23 October by a lengthy sequence of ash emissions that continued until 31 October. The 16 October eruption was the largest in terms of energy since the 30 October 2014 eruption. Most of the ash fell on the summit, but a plume headed NW and minor ashfall was reported in parts of the Valle Central such as la Unión, Concepción de Tres Ríos, Montes de Oca (30 km WSW), San Rafael de Coronado (26 km WSW), and Moravia (27 km W). A strong odor of sulfur was reported in Tierra Blanca (18 km SW), Pacayas (12 km SSW), Moravia, and Guadalupe (32 km WSW).

Figure 46. A Google Earth image of Turrialba annotated with images from the 16 and 26 October 2015 eruptions. a) 20-cm- diameter impact from volcanic ejecta. b) Solar panel destroyed by impacts. c) Ash deposit. d) Pyroclastic flow deposit. e) Hot material deposited by the pyroclastic flow. f) Thermal image of an eruption on 26 Of October (Photos: G.Avard). Courtesy of OVSICORI-UNA (Boletín de Vulcanología, Estado de los Volcanes de Costa Rica, October 2015).

Seismicity increased between 16 and 23 October, when new ash emissions began and were accompanied by pyroclastic flows. Between 23 and 31 October, OVSICORI-UNA reported 57 small emissions and 120 explosions of varying size and characteristics. The Washington VAAC was unable to see most of the emissions in satellite imagery due to weather clouds, however the plumes on 31 October were reported at 4.3 km altitude moving W. Both seismic and eruptive activity declined considerably during November 2015. OVSICORI-UNA reported one small eruption on 27 November and a small explosion on 30 November; they did not mention ash related to either event.

Activity during 2016. OVSICORI-UNA reported a brief emission of gases and volcanic ash to 500 m above the crater on 2 February 2016. Residents of La Silva (2 km NW) reported a sulfur odor and ashfall on 5 February, and additional emissions above Cráter Oeste on 6 February. The Washington VAAC noted gray emissions on 8 February. The next report, on 3 April, described an explosion lasting less than one minute that generated a small gas-and-ash plume. Seismicity increased on 28 April, followed by ash emissions and frequent small explosions on 30 April and 1 May from Cráter Oeste. Gas-and-tephra emissions increased on 1 May with minor amounts of ash deposited in La Central (4 km SW) and La Pastora (6 km SSE). A larger ash plume on 2 May rose 2 km above the summit, and was followed by frequent explosions producing 1-km-high ash plumes the next day. Frequent explosions were again recorded during 3-5 May with ash plumes rising up to 1 km above Cráter Oeste. Small lahars were reported on 7 May, and small, frequent ash emissions accompanied spasmodic tremor on 8 May.

A significant explosion on 16 May 2016, that caused abundant ashfall on farms 2.5 km WNW, was the start of a new episode that lasted for more than two months. Frequent ash emissions continued the next day, although seismic tremor amplitude decreased substantially from the initial explosion. Numerous gas-and-ash emissions were reported during 17-19 May. Ashfall was reported in areas of Valle Central (30-40 km W), including Coronado, Guadalupe, and Heredia (38 km W). On 20 May a Strombolian phase began, producing an ash-and-gas plume that rose 3 km and drifted W. The eruptive column collapsed, generating pyroclastic flows that reached the nearby ranches of La Silva and La Picada, and the Cráter Central. According to a news article, some airlines canceled or delayed flights into the Juan Santamaría International Airport (48 km W).

Gas-and-ash emissions continued during 21-22 May; plumes rose as high as 600 m above the summit. Villagers reported ashfall in areas of San José (40 km WSW), Cartago (25 km SW), Alajuela (49 km W), Heredia (38 km W), Puriscal (65 km WSW), and Jaco (100 km SW). Ash plumes rose as high as 1 km and drifted W and SW on 23 May, causing ashfall in areas downwind including Tapezco (Zarcero-Alfaro Ruíz, 70 km WNW), Guácima de Alajuela (55 km WSW), Barva (39 km W), Finca Lara (17 km W), Finca Laguna (23 km WNW), Grecia, and Naranjo. A strong explosion on 24 May generated new ash plumes that rose 3.5 km and drifted SW. This event ejected large rocks around the crater and led to ashfall in multiple areas including Santa Rosa de Oreamuno, Santa Cecilia de Heredia, and San Francisco de Heredia, tens of kilometers to the W. Large amounts of ash (deposits 2-7 mm thick) fell in Carthage, Heredia (38 km W), San José (40 km W), and Alajuela (49 km W) from more explosions on 25 May that also ejected incandescent material.

A small explosion on 1 June 2016 began a new sequence of ash emissions, with plumes rising 1-2 km, that lasted until 4 June. Ashfall was reported in a number of communities including San Rafael de Moravia (31 km WSW), Sabana (38 km WSW), Buenos Aires (17 km N), and Pococí (45 km N) during 2-3 June. Ash emissions and explosions on 10 June caused ashfall and/or a sulfur odor in multiple areas of Valle Central including San Luis, Santo Domingo, Moravia, San Francisco, and Coronado. OVSICORI-UNA reported increased seismic activity on 16 June; the webcam showed areas of incandescence. Morning satellite imagery showed a diffuse ash plume extending 45 km WNW of the summit that dissipated by mid-afternoon. Tremor increased on 23 June, followed by a lengthy sequence of tremor episodes and ash emissions that lasted through 26 June; ashfall was reported in several neighborhoods in San José and Heredia. Increased tremor on 28 June was likely accompanied by ash emissions, but darkness and clouds obscured views from the webcam.

Strong tremor on 7 July 2016 was followed by an ash plume that rose 1 km above the crater and likely drifted WNW and WSW. Ashfall was recorded in many neighborhoods downwind, in San José, Heredia, and Turrubares. Emissions of large amounts of ash were visible in the webcam the next day, and ashfall was reported in many of the same areas as the day before. The Washington VAAC issued daily reports from 7 to 15 July of diffuse ash emissions observed in the webcam, generally rising less than 500 m above the summit. A new series of explosions during 22-25 July were recorded seismically, but visual observations were difficult due to fog. Hot rock fragments, gas, and ash were noted as high as 500 m above the crater on 24 July. Ash plumes rose to 3 km above the crater and drifted NW, W, and SW the next day. OVSICORI-UNA reported possible volcanic ash again on 29 July and 1 August, but weather clouds prevented views in satellite imagery.

Another new series of explosions and ash emissions began on 13 September 2016. They were reported daily from 15 September to the end of the month. Most plumes rose less than 1 km above the crater, but explosions on 19 September generated ash plumes that rose as high as 4 km and resulted in ashfall in many communities in the Valle Central, including those in San José (35 km WSW), Heredia (38 km W), Alajuela, and Cartago (25 km SW). According to news articles, flights in and out of the Juan Santamaría International Airport were canceled; the airport remained closed at least through the morning of 20 September. The Pavas San José Tobías Bolaños Airport in San José was also temporarily closed. Plumes that rose as high as 2 km were reported on 22, 26, and 27 September.

During a 22-24 September field visit OVSICORI-UNA scientists observed a significant lahar in the Rio Toro Amarillo which flows NW from Turrialba, that mobilized logs and large rocks in a 1.5-m-deep flow (figure 47). They had observed 3 cm of fresh ash in the drainage prior to the start of the rainfall on 22 September.

Figure 47. The abrupt change in flow conditions was observed by OVSICORI-UNA scientists on 22 September 2016 when heavy rains generated a lahar in the Rio Toro Amarillo at Turrialba. The inset photo shows the same area about an hour before the flooding. Photo by E. Duarte, courtesy of OVSICORI-UNA (Algunos Efectos Proximales y Distales por Acumulación de la Ceniza: Volcán Turrialba, Reporte de campo: 22-24 de setiembre de 2016).

From 26 September through 24 November 2016 multiple reports were issued by the Washington VAAC virtually every day, usually reporting minor emissions of gas and ash. OVSICORI reported intermittent steam, gas, and ash emissions rising 500-1,000 m during all of October 2016. Ashfall was reported in Guadeloupe on 11 October. On 16 October OVSICORI-UNA noted that the almost constant ash emission in the previous few days affected the operation and communication of various scientific instruments installed at the top of the volcano and surrounding areas; communication with two seismic stations located near the summit was lost. Webcams showed continuing ash emissions rising as high as 1 km during 16-18 October. During 18-25 October, passive ash emissions continued, causing ashfall in Siquirres (30 ENE), Guacimo (23 km NNE), Guapiles (21 km N), Moravia (27 km W), San José (36 km WSW), Tibás (35 km WSW), Guadalupe (32 km WSW), Curridabat (32 km WSW), Tres Ríos (27 km SW), San Pedro (32 km WSW), and various areas of the Valle Central. Ashfall was reported in Nubes de Coronado (25 km W) on 28 October.

There were fewer reports of ashfall during November, although many areas of the Valle Central reported ashfall during 9-13 November. A small quantity of ash fell in Cartago and Paraiso de Cartago (25 km SE) on 20 November. The Washington VAAC again issued near-daily reports of ash and gas plumes between 6 December and the end of 2016. The weak and sporadic emissions generally rose only a few hundred meters, drifting in multiple directions, and there were few reports of ashfall in the surrounding communities.

Geologic Background. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Information Contacts: Observatorio Vulcanologico Sismologica de Costa Rica-Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica (URL: http://www.ovsicori.una.ac.cr/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/).

Murray Ford, a coastal geomorphologist from New Zealand's Auckland University, reported in a Radio New Zealand story on 1 February 2017 that satellite imagery showed a large plume of discolored water between Tongatapu and the volcanic Hunga Tonga-Hunga Ha'apai islands. The activity seen by Murray was on a Landsat 8 OLI (Operational Land Imager) satellite image acquired on 27 January 2017 (figure 2). which showed a bright area of discolored water above the summit and a broader area of discolored water immediately NW, likely from previous events. According to volcanologist Brad Scott (GNS Science) there are additional satellite images from 23, 26, 28, and 29 January 2017, indicating that the eruption had been ongoing for over a week. His colleagues in Tonga indicated a possible associated steam plume, but cloud cover made observations uncertain.

Figure 2. Landsat 8 OLI satellite image a submarine plume from an unnamed seamount in Tonga on 27 January 2017, about 33 km NW of Tongatapu island. A small bright area of discolored water is directly over the summit (bottom center), with a small plume immediately N, and a broad area of discolored water to the NW, likely from previous eruptive events. The larger plume to the NW measures 30 km long and 20 km wide. Courtesy of NASA Earth Observatory (https://earthobservatory.nasa.gov/IOTD/view.php?id=89565).

A report prepared by Taylor (2000) noted that there had been four previous reports of activity from this location: submarine activity in August 1911, a steam plume in July 1923, discolored water in 1970, and an ephemeral island near the end of an eruptive episode during 27 December 1998-14 January 1999 (also see BGVN 24:03). In a blog post about the latest eruption, Brad Scott (GNS Science) also stated that there had been discolored water and felt earthquakes sometime in 2007.

Reference: Taylor, P., 2000, A volcanic hazards assessment following the January 1999 eruption of Submarine Volcano III, Tofua Volcanic Arc, Kingdom of Tonga, Australian Volcanological Investigations (AVI) Occasional Report No. 99/01, 5 August 2000, 7 p.

Geologic Background. An unnamed submarine volcano is located 35 km NW of the Niu Aunofo lighthouse on Tongatapu Island. Tongatapu is a coral island at the southern end of an island chain paralleling the Tofua volcanic arc to the E. The volcano was constructed at the S end of a submarine ridge segment of the Tofua volcanic arc extending NNE to Falcon Island. The first documented eruptions took place in 1911 and 1923; an ephemeral island was formed in 1999.

Information Contacts: NASA Earth Observatory, EOS Project Science Office, NASA Goddard Space Flight Center, Goddard, Maryland, USA (URL: http://earthobservatory.nasa.gov/); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, http://www.geonet.org.nz/news/1usjOmF4LqaI64qScMocuW); Radio New Zealand (URL: http://www.radionz.co.nz/international/pacific-news/323569/scientist-discovers-underwater-eruption-in-tonga).

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/).