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Bulletin of the Global Volcanism Network

All reports of volcanic activity published by the Smithsonian since 1968 are available through a monthly table of contents or by searching for a specific volcano. Until 1975, reports were issued for individual volcanoes as information became available; these have been organized by month for convenience. Later publications were done in a monthly newsletter format. Links go to the profile page for each volcano with the Bulletin tab open.

Information is preliminary at time of publication and subject to change.

Recently Published Bulletin Reports

Kirishimayama (Japan) Ash plumes and lava flows at Shinmoedake starting in March 2018; explosion at Iwo-yama

Sabancaya (Peru) Strong, sporadic explosions with ash plumes throughout December 2017-May 2018

Masaya (Nicaragua) Lava lake persists during July 2017-April 2018

Chillan, Nevados de (Chile) Hundreds of ash-bearing explosions; dome appears in crater in mid-December 2017

Marapi (Indonesia) Two explosions during April-May 2018 cause ashfall to the southeast

Nyiragongo (DR Congo) Thermal anomalies show that lava lake remains active through May 2018

Ebeko (Russia) Ash explosions remained frequent through May 2018, with plumes typically rising more than 1 km

Langila (Papua New Guinea) Gradual decline in activity after July 2017, but continuing through May 2018

Pacaya (Guatemala) Pyroclastic cone fills MacKenney crater; lava flows emerge from fissures around the crater rim

Reventador (Ecuador) Near-daily explosions produce 1-km-high ash plumes and incandescent blocks on all flanks, October 2017-March 2018.

Santa Maria (Guatemala) Daily explosions with minor ash and block avalanches at Caliente, November 2017-April 2018

Sheveluch (Russia) Intermittent thermal anomalies along with gas and steam emissions continue through April 2018



Kirishimayama (Japan) — June 2018 Citation iconCite this Report

Kirishimayama

Japan

31.934°N, 130.862°E; summit elev. 1700 m

All times are local (unless otherwise noted)


Ash plumes and lava flows at Shinmoedake starting in March 2018; explosion at Iwo-yama

Kirishimayama is a large group of more than 20 Quaternary volcanoes located N of Kagoshima Bay, Japan (figure 22). For the last 1,000 years, repeated eruptions have taken place at two locations in the complex: the Ohachi crater on the W flank of the Takachihomine stratovolcano, and the Shinmoedake stratovolcano 4 km NW of Ohachi. A single eruption was reported in 1768 from the Iwo-yama (Ebino Kogen) dome located on the NW flank of the Karakunidake stratovolcano, about 5 km NW of Shinmoedake.

Figure (see Caption) Figure 22. Subfeatures of the Kirishimayama volcanic complex showing the three areas with activity discussed in this report: Ohachi, Shinmoedake, and Iwo-yama (Ebino Kogen). View is to the SE. Image taken by the Japan Maritime Self Defense Force on 7 October 2014. Courtesy of JMA (Volcanic activity report on Kirishimayama, October, Heisei 26 [2014]).

The last confirmed eruption at the Ohachi crater was in July 1923. Intermittent steam plumes have been observed since then, including in December 2003 (BGVN 33:09), but the Japan Meteorological Agency (JMA) noted that it had been quiet since 1 December 2007. Shinmoedake has been the site of several short-lived eruptive events since 2008. Most of the events were single-day explosions with ash emissions (BGVN 35:12). A more protracted event from January to September 2011 included numerous explosions with ash plumes, which produced ashfall tens of kilometers away, the growth of a lava dome, ejecta of large blocks, and small pyroclastic flows (BGVN 36:07). Shinmoedake remained quiet until seismicity increased on 23 September 2017, followed by several explosions during October 2017 (BGVN 43:01). Seismic unrest was first reported from the area around Iwo-yama in December 2013, and it has been regularly monitored since that time. This report covers activity from November 2017 through May 2018 and includes new explosive events at Shinmoedake during March-May 2018, an explosive event at Iwo-yama in April 2018, and a brief increase in seismicity at Ohachi in February 2018. Information is provided primarily by the JMA and the Tokyo Volcanic Ash Advisory Center (VAAC), with additional satellite data and news media reports.

Summary of activity during November 2017-May 2018. After steam plumes disappeared at Ohachi in mid-2006, only minor intermittent seismicity was reported through 2017. A sudden increase in earthquakes and tremor activity on 9 February 2018 led JMA to raise the 5-level Alert Level system from 1 (potential for increased activity) to 2 (do not approach the crater) for about a month. Activity diminished after the middle of February and Ohachi remained quiet through May 2018, with only a continuing modest thermal anomaly at the crater.

The latest eruptive episode at Shinmoedake, during 11-17 October 2017, generated an SO2 plume recorded by NASA satellites, caused ashfall up to 100 km away, and created a new vent about 80 m in diameter on the E side of the crater. Intermittent earthquakes and tremors along with low-level steam plumes characterized activity during November 2017-February 2018. A new eruptive episode began on 1 March 2018 with near-constant explosive activity that lasted until 10 March. A new lava flow at the summit was first observed by JMA on 6 March and began to overflow the NW rim of the crater on 9 March. The Tokyo VAAC reported ash plumes over 6 km altitude on 10 March. An explosion on 5 April produced the largest ash plume of the period; it rose to 10.1 km altitude, was visible drifting E for 24 hours, and resulted in significant ashfall in the region. The lava flow had ceased advancing down the NW flank by the end of April. Another explosion on 14 May 2018 generated an ash plume that rose to 7.3 km altitude and caused ashfall 30 km S that covered the roadways.

An increase in seismicity at Iwo-yama in December 2013, followed by a 7-minute-period of tremor activity in August 2014 was the first recorded at the site since 1768. Thermal anomalies and weak fumarolic activity first appeared in December 2015. Seismicity, including intermittent tremor events and larger amplitude earthquakes, gradually increased during 2016 and 2017. Intermittent fumarolic activity and temperature anomalies began to increase measurably in mid-2017. Jets of sediment-laden hot water emerged from several vents early in 2017. A further increase in fumarolic activity and the temperature of the thermal anomalies in February 2018 led JMA to raise the Alert Level at Iwo-yama. Large amplitude earthquakes and a tremor event accompanied an ash-bearing explosion on 19 April 2018 from a vent on the S side of Iwo-yama. The following day, a vent opened 500 m to the W and produced vigorous steam emissions. On 26 April 2018 an explosion from the new vent sent ash 200 m high. Jets of hot water continued at the Iwo-yama vents through May 2018.

Activity at Ohachi during 2003-2018. JMA reported tremor activity with epicenters near Ohachi in mid-December 2003 (BGVN 33:09) that was followed by fumarolic activity for a few weeks. Intermittent steam plumes were observed during 2004; on 26 March 2004 a tremor event lasted for four hours and a steam plume rose 800 m above the crater (figure 23). A few periods of microtremor were recorded, and intermittent fumarolic activity was observed with webcams until March 2006, after which most activity ceased. JMA lowered the 5-level Alert Level from 2 (Do not approach the crater) to 1 (Potential for increased activity) on 22 May 2006. Fumarolic activity was not observed after July 2006, and no new thermal activity was reported during a field visit in October 2006. Minor seismicity was reported for a few days during July 2007, and small-amplitude, short-duration tremor activity was occasionally recorded during 2008-2014.

Figure (see Caption) Figure 23. Steam plumes were visible on the NW side of the Ohachi crater at Kirishimayama on 31 March 2004. Courtesy of JMA (JMA Kirishimayama annual report, Heisei 16 (2004)).

Although earthquake activity increased slightly in July 2015, the warning level was not raised, and no surface fumarolic activity was observed during field visits in August and September 2015 (figure 24). Seismic activity remained elevated at Ohachi through February 2016 and then gradually decreased during March. Although tremors were recorded in May and December 2016, there was no change in condition at the site and seismicity continued to decrease; no tremors were recorded during 2017.

Figure (see Caption) Figure 24. No fumarolic activity was visible at the Ohachi crater at Kirishimayama on 18 September 2015 during a site visit. View is to the NW. Courtesy of JMA (JMA Kirishimayama annual report, Heisei 27 (2015)).

Earthquake frequency on the SW side of Ohachi increased during 9-16 February 2018, resulting in 199 seismic events, and tremor activity was also recorded on 9 February. This activity led JMA to increase the Alert Level to 2 on 9 February 2018. In spite of the increased seismic activity, the thermal activity remained unchanged from previous months with continued minor thermal anomalies in the same areas as before (figure 25). Seismicity decreased significantly during March 2018 to only 13 volcanic earthquakes, and no microtremor activity was recorded. Inspections carried out on 11 and 14 March showed no surface changes (figure 26) and resulted in JMA lowering the Alert Level back to 1 on 15 March 2018. Ohachi remained quiet through May 2018.

Figure (see Caption) Figure 25. Thermal anomalies at the Ohachi crater of Kirishimayama were unchanged compared with previous months when measured on 9 February 2018 in this view to the NW. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, February, Heisei 30 (2018)).
Figure (see Caption) Figure 26. An overview looking W of the Ohachi crater at Kirishimayama on 2 March 2018 showed no surface activity after the increased seismicity of February. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).

Activity at Shinmoedake during August 2008-October 2017. An explosion on 22 August 2008 lasted for about six hours and produced ashfall in Kobayashi City (10 km NE) (BGVN 33:09). Seismicity had increased rapidly a few days prior to the explosion, and then decreased gradually for the remainder of 2008. Other than a brief increase in seismicity in May the following year, only steam plumes rising about 100 m from the crater were reported for 2009.

Seven small ash-bearing explosive events were reported during March-July 2010. Small-amplitude tremor activity on 30 March 2010 was accompanied by a plume that rose 400 m above the crater rim; a small amount of ash fell 400 m to the W of the fumarole within the crater. The webcam on the S rim of the crater captured a grayish plume rising 300 m after a small explosion on 17 April 2010. Another small explosion on 27 May produced a grayish-white plume that rose 100 m above the crater rim and resulted in minor ashfall NE in Kobayashi City. Officials noted a new fumarole on the W flank after this event. Two more explosions on 27 and 28 June 2010 resulted in a small amount of ash deposited 10 km E of Shinmoedake. A small explosion was reported on 5 July. On 10 July, a grayish-white plume, observed in the webcam, rose 100 m above the crater rim after an explosion, and a small low-temperature pyroclastic surge flowed 300 m down the SW slope. GPS instruments recorded minor inflation from December 2009 through September 2010.

A new, more substantial, eruption began at Shinmoedake on 19 January 2011. Activity increased on 26 January with an explosion that released a large volume of ash and pumice and included the growth of a new lava dome (BGVN 35:12, 36:07). Thirteen additional explosions occurred through 1 March 2011. Activity became more intermittent after mid-February, and the last emission was reported on 7 September 2011. Seismicity declined significantly in March 2012 and had returned to background levels by May 2012. With no surface changes and very low seismicity, JMA reduced the Alert Level from 3 to 2 on 22 October 2013, and the only reported activity was steam plumes rising 50-200 m above the crater rim during 2013. The lava dome in the crater remained about 600 m in diameter. Inflation had slowed and stopped after December 2011 but began again around December 2013. Shallow, low-level seismicity during 2014 with epicenters near Shinmoedake was distributed within a few kilometers below the summit; there were no surface changes observed at the crater during several overflights conducted by the Japan Maritime Self Defense Force throughout the year.

Occasional steam plumes rising 400 m above the crater rim were reported during 2015. Volcanic earthquakes were intermittent, with brief increases in activity during March-May and October- December with roughly the same number as the previous year. Inflationary deformation that began around December 2013 ceased in January 2015. A very brief tremor on 1 March 2015 was the first recorded since 1 February 2012. During 2016, occasional steam plumes rose 300 m above the crater. In spite of a seismic swarm on 23 February 2016, and a general increase in seismicity throughout the year, no eruptions occurred, and no surface changes were observed. JMA kept the Alert Level at 2 throughout the year. A small tremor event on 17 September was the only recorded during 2016. Very little activity was reported from January to September 2017; occasional steam plumes were reported rising 400 m above the crater rim. JMA lowered the Alert Level from 2 to 1 on 26 May 2017.

A minor increase in seismicity was observed beginning in July 2017, and was followed by a marked increase on 23 September. After a further increase in frequency and amplitude of earthquakes on 4 October, JMA raised the Alert Level to 2 for Shinmoedake on 5 October 2017. This was followed by an eruption that began on 11 October 2017. A new vent was observed on the E side of the crater during an overflight that same day, and ashfall was reported in numerous communities as far as 90 km NE (BGVN 43:01). A significant SO2 plume was measured by the OMI instrument on the Aura satellite the following day (figure 27). After raising the Alert Level to 3 on 11 October, JMA expanded the restricted area radius from 2-3 km during 15-31 October.

Figure (see Caption) Figure 27. A significant SO2 plume from the explosion at the Shinmoedake crater of Kirishimayama was measured on 12 October 2017 by NASA's OMI instrument on the Aura satellite. Courtesy of NASA Goddard Space Flight Center.

Explosions on 14 October 2017 resulted in confirmed ashfall in Kagoshima city (50 km SW), Takahara Town (15 km E), Kobayashi city (25 km NE), Saito city (55 km NE), Hyuga city (90 km NE), and Misato town (75 km NE). Ongoing explosions continued until 17 October, after which persistent steam plumes were observed rising as high as 600 m above the crater. In an overflight conducted on 23 October JMA scientists noted the new vent was about 80 m in diameter, and ejecta from the vent had formed a small cone around the vent. (figure 28).

Figure (see Caption) Figure 28. Two vents were visible on the E side of the crater in this view to the WNW taken on 23 October 2017 of Shinmoedake crater at Kirishimayama. The left vent (center front) had formed during the 2011 eruption, and the right vent formed during the 11-17 October 2017 eruption earlier in the month. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, October, Heisei 29 (2017)).

Activity at Shinmoedake during November 2017-March 2018. After the eruption of 11-17 October 2017 seismicity decreased significantly, and no morphological changes were observed for the remainder of the year. Steam plumes rose 300-500 m above the crater during November and December. Short-duration tremors were detected during 25-29 November, along with a slight increase in the number of volcanic earthquakes. A small earthquake swarm recorded during 2-4 December was the only significant seismic activity that month.

Infrequent, large-amplitude earthquakes were recorded during 15-17 January 2018, along with a few short-duration tremor events, the first since 29 November 2017. The earthquakes were located within a 1 km radius of Shinmoedake, around 2-4 km deep. Steam plumes at the crater rose no more than 100 m most days; occasional plumes rising as high as 200 m were noted. An earthquake swarm on 25 February was the first notable event of the month; the steam plumes remained under 100 m above the crater, except for a 500-m-high plume on 21 February. Thermal imaging surveys in late February indicated a modest increase in heat flow from fractures inside the crater and on the W slope compared with previous measurements.

Earthquakes with shallow epicenters below Shinmoedake increased in number early on 1 March 2018 and a new eruptive episode followed a few hours later, leading JMA to increase the restricted zone to 3 km around the crater (figure 29). SO2 emissions also increased sharply. By the afternoon of 1 March an ash plume rose 1,500 m above the crater, emerging from the vent on the E side and drifting SE. Ashfall was confirmed on 1 March in the area up to 18 km E of the crater. Large blocks of ejecta were observed within the crater on 5 March.

Figure (see Caption) Figure 29. A new eruptive episode at the Shinmoedake crater of Kirishimayama began around 1100 on 1 March 2018 with ash emissions emerging from the new vent on the E side of the crater. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, February, Heisei 30 (2018)).

During an overflight on 6 March 2018, JMA witnessed a new lava flow covering a large area on the E side of the crater floor (figure 30). Eighteen explosive eruptions occurred on 6 March and JMA reported that the ash plume rose 2,800 m above the crater (figure 31). Ashfall was confirmed SW of Shinmoedake in Shibushi city (50 km SSE), Tarumizu City (50 km SSW) and Aira City (30 km SW). NASA 's Aqua satellite captured a false color image of the eruption on 6 March showing the ash plume drifting SE and SW from Shinmoedake (figure 32). About 80 flights in and out of nearby Kagoshima airport were canceled.

Figure (see Caption) Figure 30. Lava emerged from the new vent on the E side of the Shinmoedake crater at Kirishimayama on 6 March 2018 in this view to the W. Plumes of both ash and steam rose from the center and N sides of the crater. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, February, Heisei 30 (2018)).
Figure (see Caption) Figure 31. Ash and steam rose from newly emergent lava inside the summit crater of Shinmoedake at Kirishimayama on 6 March 2018, and disrupted air traffic for most of the day. Courtesy of Kyodo News via AP.
Figure (see Caption) Figure 32. NASA 's Aqua satellite captured a false color image of the eruption from Shinmoedake crater at Kirishimayama on 6 March 2018 with an ash plume drifting SE and SW. Courtesy of NASA Earth Observatory.

Tremor events occurred continuously over 1-8 March; forty-seven explosions were recorded between 6 and 8 March; they decreased in frequency after the middle of the month. The OMI instrument on the NASA Aura satellite recorded a significant SO2 plume on 7 March 2018 (figure 33). Geospatial data that had shown a gradual inflation of the Kirishimayama complex since July 2017 showed a sharp deflation during 6-7 March 2018, after which inflation resumed.

Figure (see Caption) Figure 33. An SO2 plume with a density of almost ten Dobson Units (DU) was recorded by the OMI instrument on the Aura satellite on 7 March 2018. Courtesy of NASA Goddard Space Flight Institute.

During an overflight on 9 March 2018, a staff member from the Geographical Survey Institute observed the lava flow beginning to overflow the NW side of the crater (figure 34). Explosions resulted in ejecta traveling 800 m from the crater on 9 March and an ash plume rising 3,200 m. An increase in the intensity of activity the following day sent ejecta 1,800 m from the vent and generated an ash plume that rose 4,500 m (figure 35); this led JMA to increase the restricted area around the crater to 4 km between 10 and 15 March.

Figure (see Caption) Figure 34. The new lava flow began to overtop the NW side of Shinmoedake crater (left side of crater with steam) at Kirishimayama on 9 March 2018. Photographed by a staff member from the Geographical Survey Institute during a helicopter overflight by the Kyushu Regional Development Bureau. Courtesy of the Geographical Survey Institute (Correspondence on the eruption of Kirishimayama (Shinmoedake) in Heisei 30 (2018), 29 March 2018).
Figure (see Caption) Figure 35. An increase in explosive activity at the Shinmoedake crater of Kirishimayama on 10 March 2018 sent an ash plume 4,500 m above the crater (left), and incandescent ejecta 1,800 m from the vent (right). Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).

A thermal image taken on 11 March showed that the lava was moving very slowly down the NW flank, advancing only a few tens of meters since 9 March (figure 36). JMA confirmed during an overflight on 14 March that the lava flowing down the NW flank was about 200 m wide. Two explosions on 25 March produced plumes that rose 3,200 and 2,100 m, ejecta that traveled 800 m, and a small pyroclastic flow that advanced about 400 m down the W flank (figure 37). Although analysis of satellite data by Japan's Geographical Survey Institute suggested that the eruption of lava into the crater had ceased by 9 March, it continued to flow slowly down the NW flank for several weeks. The diameter of the flow inside the crater was about 700 m, and it had traveled about 85 m down the NW flank by 28 March (figure 38).

Figure (see Caption) Figure 36. A thermal image taken on 11 March 2018 of the new lava flow in the Shinmoedake crater at Kirishimayama showed the slow movement of the flow over the NW rim and down the flank a few tens of meters in two days. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).
Figure (see Caption) Figure 37. Two explosions on 25 March 2018 from Shinmoedake crater at Kirishimayama produced plumes that rose 3,200 and 2,100 m, ejecta that traveled 800 m, and a small pyroclastic flow that advanced about 400 m down the W flank (foreground). Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).
Figure (see Caption) Figure 38. Lava was still slowly moving down the NW flank of the Shinmoedake crater at Kirishimayama on 26 March 2018, and gray ash covered much of the adjacent flank, possibly from a pyroclastic flow the previous day. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).

The Tokyo VAAC issued multiple daily reports from 1-15 March 2018, and a few intermittent reports during the rest of the month. JMA usually reports plume heights in meters above the crater and the Tokyo VAAC reports them as altitudes above sea level; conversions are noted where the height or altitude of a plume is exceptional. They reported an ash plume drifting SE on 1 March at 1.5 km altitude; the plume had risen to 2.4 km by the end of the day. The following day a plume was visible in satellite images at 2.1 km altitude drifting E. Continuous emissions drifting NE above 2.4 km altitude were reported on 3 and 4 March. Several explosions generated plumes that were visible in satellite imagery during 5-7 March drifting S, SW, and W at altitudes between 3.0 and 4.6 km. Plumes from larger explosions during 9 and 10 March rose to altitudes between 4.3 and 6.1 km and drifted SE, finally dissipating after about 24 hours. Explosions on 12 and 13 March drifted NE and E at 3.4-4.9 km altitude, with continuous emissions visible in satellite imagery during those days. Two explosions on 24 March produced plumes that drifted SE at 3.7 and 4.9 km altitude, and were visible in satellite imagery until they dissipated the next day.

A strong MIROVA thermal anomaly signal appeared at the beginning of March and slowly tapered off into April. The signal is consistent with the reports of the eruption of lava from the summit of Shinmoedake and its gradual cooling (figure 39). The MODVOLC thermal alert signals also closely match the reports of the eruption of the lava. The first six alerts were issued on 6 March, four each on 9 and 10 March, three each on 11 and 12 March, and one each on 13, 14, 16, 23, and 30 March, matching a gradual cooling pattern for the lava after the main eruptive event.

Figure (see Caption) Figure 39. A strong MIROVA thermal anomaly signal appeared at Kirishimayama at the beginning of March and slowly tapered off into April 2018. The signal is consistent with the reports of the eruption of lava from the summit of Shinmoedake, and its gradual cooling. A thermal image of the lava flow at Shinmoedake from 28 March 2018 (inset) shows significant cooling from two weeks earlier (see figure 36). Courtesy of MIROVA and JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).

Activity at Shinmoedake during April and May 2018. A new explosion on 5 April 2018 generated a large ash plume that rose 5,000 m above the crater; a small pyroclastic flow traveled 400 m down the SE flank, and ejecta was thrown 1,100 m from the vent (figure 40). The Tokyo VAAC reported an explosion, and an ash plume at 6.7 km altitude drifting E visible in satellite imagery early in the day. A few hours later, the plume was visible at 10.1 km altitude, or more than 8,000 m above the crater. Incandescent tephra was ejected hundreds of meters high, and lightning was observed within the large ash plume (figures 41 and 42). The plume was observed continuously in satellite images for almost 24 hours before dissipating; a significant SO2 plume was also recorded (figure 43).

Figure (see Caption) Figure 40. Ejecta was thrown 1,100 m from the vent in an explosion at the Shinmoedake crater of Kirishimayma on 5 April 2018 (farthest right incandescence). A large ash plume (to the right of the main incandescence) eventually rose to over 8,000 m above the crater. View is to the N from the Inogishi webcam. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).
Figure (see Caption) Figure 41. An explosion on 5 April 2018 from the Shinmoedake crater at Kirishimayama sent incandescent ejecta several hundred meters above the crater. Courtesy of Kyodo News via Reuters.
Figure (see Caption) Figure 42. Significant lightning was reported in the large ash plume from the 5 April 2018 explosion at the Shinmoedake summit crater at Kirishimayama. Courtesy of Kyodo News via Reuters.
Figure (see Caption) Figure 43. The OMPS instrument on the Suomi NPP satellite recorded an SO2 plume drifting SE after the 5 April 2018 explosion at the Shinmoedake crater of Kirishimayama. Courtesy of NASA Goddard Space Flight Center.

A large amount of ashfall was reported in parts of Kobayashi city and Takaharu (15 km E) (figures 44 and 45) on 5 April 2018. Ashfall reports also indicated that a wide area to the N of Shinmoedake including Hitoyoshi City (30 km N), to the NE including Kadogawa Town (95 km NE), and to the E including Miyazaki City (50 km E) were also affected. Another eruption took place the following day, on 6 April, but weather clouds obscured views of the summit. No eruptions were recorded after 6 April for the remainder of the month.

Figure (see Caption) Figure 44. Ashfall was measured and sampled on 5 April 2018 in Kobayashi City (25 km NE) after an explosion with a large ash plume rose from the Shinmoedake crater at Kirishimayama. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).
Figure (see Caption) Figure 45. Ashfall covered major roadways and buildings in Takaharu, 15 km E of Kirishimayama, after an explosion from the Shinmoedake crater on 5 April 2018. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).

In multiple flyovers, on 19, 20, and 21 April 2018, authorities observed lava continuing to flow down the NW flank (figure 46), along with residual high temperatures in the central part of the lava flow (figure 47). Additionally, fumarolic areas around the fractures on the W slope persisted. By the end of April, the flow on the NW flank of the crater was 150 m long. Seismicity had declined at the end of March, but increased again during the explosive period in early April. Occasional tremors were recorded during 5-14 April. Intermittent spikes of around 100 small earthquakes were also recorded on 14 and 21 April.

Figure (see Caption) Figure 46. The lava flow down the NW flank of Shinmoedake crater at Kirishimayama was nearly stagnant by 21 April 2018, as seen in this view to the SW taken that same day by the Miyazaki Prefecture Disaster Preparedness Emergency Air Corps. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).
Figure (see Caption) Figure 47. Residual high heat flow was still visible near the center of the Shinmoedake crater of Kirishimayama on 21 April 2018 but the lava flow had cooled significantly since March (compare with figure 36). Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).

Another spike in earthquakes with epicenters within 2 km of Shinmoedake occurred on 2 May 2018 with over 700 events recorded. A substantial explosion on 14 May generated an ash plume that rose 4.5 km above the crater according JMA (figure 48). The Tokyo VAAC reported the ash plume initially at 4.9 km altitude drifting SE based on webcam reports; when the plume appeared in satellite data a short time later it was drifting SE at 7.3 km altitude and was continuously visible in satellite imagery for about 24 hours before dissipating. Ashfall was confirmed in numerous areas of the Miyazaki prefecture to the E, and the Kagoshima prefecture to the S and W. Seismicity increased briefly after the explosion. Enough ash fell in Miyakonojo City (30 km S) that it covered the white lines on the roadways (figure 49). A thermal image taken on 15 May showed a new high-heat flow area on the E side of the new lava flow inside the crater that JMA concluded was likely the result of the explosive event of the previous day (figure 50).

Figure (see Caption) Figure 48. A large explosion at the Shinmoedake crater of Kirishimayama on 14 May 2018 sent an ash plume to 4,500 m above the crater as seen in this view to the NE from the Inogishi webcam. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, May, Heisei 30 (2018)).
Figure (see Caption) Figure 49. Enough ash fell in Miyakonojo City (30 km S) after an explosion at Shinmoedake crater of Kirishimayama on 14 May 2018, that it covered the white lines on the roadways. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, May, Heisei 30 (2018)).
Figure (see Caption) Figure 50. The thermal signature at Shinmoedake crater at Kirishimayama on 15 May 2018 revealed a high-heat flow area that JMA concluded likely resulted from the explosion the previous day. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, May, Heisei 30 (2018)).

Activity at Iwo-yama during 2014-2017. An increase in seismicity around Iwo-yama, on the NW flank of the Karakunidake stratovolcano (figure 22) beginning in December 2013 was noted by JMA. The epicenters were distributed from 1-6 km below Iwo-yama. Satellite measurements suggested minor inflation in the area around Karakunidake beginning in December 2013, which lasted until January 2015. A 7-minute-long tremor event occurred near Iwo-yama on 20 August 2014. Although inspections of the area by JMA revealed no thermal or fumarolic activity, they listed the Iwo-yama area with an unofficial Alert Level of "Danger around the crater" on 24 October 2014, equivalent to the official Alert Level 2. They modified the warning during May 2015 to "Normal, keep in mind, it is an active volcano," the same as the official Alert Level 1. During the second half of 2015 there were occasional earthquakes and tremors reported in the area, but no surface or thermal activity was recorded (figure 51) until December. Thermal anomalies appeared in the area for the first time during the first week of December 2015; weak fumarolic activity accompanied by H2S odors were first reported during 15-17 December 2015 on the SW side of the Iwo-yama crater (figure 52).

Figure (see Caption) Figure 51. No surface activity, and very little thermal activity was present at the Iwo-yama (Ebino Kogen) area of Kirishimayama on 2 November 2015. View is to the N, taken from the N flank of Karakunidake. Courtesy of JMA (JMA Kirishimayama annual report, Heisei 27 (2015)).
Figure (see Caption) Figure 52. Steam plumes and a thermal anomaly at the Iwo-yama area of Kirishimayama first appeared during December 2015 (images from 28 December 2015, view to the S). Courtesy of JMA (JMA Kirishimayama annual report, Heisei 27 (2015)).

Periods of intermittent microtremor activity occurred once in January, four times in February, and twice in December during 2016, with durations ranging from 40 seconds to 5 minutes. A seismic swarm on 28 February led JMA to raise the unofficial Alert Level to "danger around the crater" for the month of March (equivalent to the official Alert Level 2). A new thermal area with fumarolic activity appeared on 24 March 2016 on the SE side of the crater. Intermittent steam plumes were observed throughout 2016; the highest rose 200 m on 11 October. Thermal anomalies also persisted throughout the year on the S and SW areas of the crater. Alert Level 1 (Note that it is an active volcano) was formally assigned to Iwo-yama on 6 December 2016. The Alert Level was raised to 2 on 12 December after a seismic swarm, tremor, and the observation of inflation in the inclination data in the previous days.

Fumarolic activity decreased in January 2017 after a brief increase at the end of December 2016; JMA lowered the Alert Level back to 1 on 13 January and steam plumes generally rose only 30 m high during the month. The thermal anomalies persisted in the same areas of the SW and W portions of the crater as before, though new fumarolic activity appeared in those areas during February 2017. During March field surveys, observers identified hot water emerging from the fumaroles in the SW and S areas of the crater. The inclinometer detected inflation beginning on 25 April 2017, but it leveled off during August. An increase in the number of fumaroles in the area of the thermal anomaly at the SW side of the crater was confirmed by a JMA field inspection in late April. When the University of Tokyo Earthquake Research Institute visited the site on 8 May 2017, they observed sediment-laden water deposits that had been dispersed on the SW side within the crater, and ejecta around the SW edge. This led JMA to increase the Alert Level to 2.

Fumarolic activity increased during mid-to-late July 2017 and steam plumes were reported at 300 m above the crater for a brief period. On 27 July visitors confirmed dead and discolored plants on the NE side of the crater, and audible fumarolic activity. A new thermal anomaly zone with fumaroles was visible on the SW flank outside the crater during a site visit on 31 August. Low levels of seismicity were intermittent throughout 2017, but no tremor events were recorded. A large amplitude earthquake with its epicenter under Iwo-yama occurred on 5 September 2017; no sudden changes were observed at the site a few days later, although thermal images taken on 9 September revealed an increase in temperature from two years prior (figure 53, compared with figure 52). JMA lowered the warning level to 1 at the end of October. During November and December 2017, steam plumes generally rose 100-200 m above the crater.

Figure (see Caption) Figure 53. Steam plumes and a thermal anomaly persisted into September 2017 at the Iwo-yama crater of Kirishimayama. Emissions of the plume on the left were audible during the July visit. Compare with the lower temperatures measured in December 2015, figure 52. Image taken on 9 September 2017 from the Iwomayama South webcam on the S side of the area. Courtesy of JMA (JMA Kirishimayama annual report, Heisei 29 (2017)).

Activity at Iwo-yama during January-May 2018. An analysis of nearby hot-spring waters indicated a significant jump in Cl/SO4 ratios characteristic of high-temperature volcanic gas beginning in November 2017. The first tremor since 12 December 2016 was recorded on 19 January 2018 and coincided with a brief period of inflation in the vicinity of Iwo-yama. Regional inflation of the area had begun again in July 2017 and continued into 2018. Low-frequency, small-amplitude earthquakes were intermittent during January 2018 and steam plumes rose 100-200 m. Increases in seismicity, fumarolic activity, and the temperatures of the thermal anomalies during mid-February 2018 prompted JMA to raise the Alert Level on 20 February 2018 at Iwo-yama to 2. Steam plume heights increased to 200-300 m after 20 February. Seismicity decreased during March 2018, however observations from the webcam revealed an increase in fumarolic and thermal activity (figure 54).

Figure (see Caption) Figure 54. Fumarolic activity and heatflow increased at the Iwo-yama crater of Kirishimayama during March 2018, with steam plumes at the central vent rising several hundred meters. Images taken on 23 March 2018. View is to the N from the Iwo-yama south webcam. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, March, Heisei 30 (2018)).

The infrared imaging webcam recorded a burst of heat from a vent on the SW side of the crater on 7 April; the amplitude of seismic vibrations also increased. A field visit on 9 April revealed a hot water pool several meters in diameter on the SW side of the crater with sediment-laden water flowing from it and a 10-m-high steam plume. Local inflation recorded at Iwo-yama turned to deflation on 19 April; large-amplitude earthquakes were also reported. A tremor that day was followed by an explosion a few minutes later from a new vent on the S side of Iwo-yama. The plume rose 500 m and ejecta was scattered 200-300 m from the vent to the SE. During an overflight on 19 April JMA noted ash deposits around the vent; ash emission from the vent continued until the following morning (figure 55). The Tokyo VAAC reported a small ash emission on 19 April from Kirishimayama that rose to 1.8 km altitude and drifted E, but it was not visible in satellite imagery. On the evening of 20 April, another new vent with a vigorous steam plume appeared 500 m W of Iwo-yama (figure 56). Sediment-laden water was observed around the vent the following day. Increased seismicity at Iwo-yama lasted for about 20 days; additional tremor activity was reported on 20 and 24 April.

Figure (see Caption) Figure 55. An explosion sent steam and ash 500 m high, and ejecta 200-300 m SE from a new vent on the S side of Iwo-yama on 19 April 2018 at Kirishimayama. Ash emission continued until the following morning. N is to the left, fresh ash deposits cover the area SE of the new vent (upper right). Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).
Figure (see Caption) Figure 56. A new fumarole with a vigorous steam plume appeared about 500 m W of Iwo-yama during the evening of 20 April 2018. N is to the left. Miyazaki Prefecture Disaster Preparedness Emergency Air Corps Photograph taken from a helicopter on 21 April 2018. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).

A brief explosion that lasted about ten minutes occurred from this new vent around 1815 on 26 April 2018 sending a plume of ash about 200 m above the vent (figure 57). A small ash emission from Kirishimayama was reported by the Tokyo VAAC on 26 April that rose to 1.5 km altitude. In a site visit on 30 April, JMA noted active fumaroles and small explosions around both vent areas (figure 58). After the explosion of 19 April, steam plumes rose as high as 700 m from the vent on the S side of the crater, and intermittent spouts a few meters high of sediment-laden water were also observed. Steam plumes rose as high as 500 m from the vent located 500 m to the W.

Figure (see Caption) Figure 57. An explosion from the new vent located 500 m W of Iwo-yama at Kirishimayama on 26 April 2018 sent ash 200 m above the vent. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).
Figure (see Caption) Figure 58. Vigorous steam plumes rose from both the S side vent at Iwo-yama (background) and the new vent 500 m W (foreground) on 30 April 2018 at the Kirishimayama complex. North is to the left. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).

Fumarolic activity continued at Iwo-yama during May 2018, but no new explosions nor ash emissions were reported. Shallow seismic events were intermittent, but significantly decreased from April. No tremors were recorded. JMA lowered the Alert Level on 1 May 2018 from 3 to 2. Steam plumes rose 300-500 m from the vents, and thermal anomalies persisted at the crater and the adjacent new vent to the W throughout the month. Jets of sediment-laden hot water rising several meters continued from the vent on the S side of Iwo-yama (figure 59).

Figure (see Caption) Figure 59. Jets of sediment-laden hot water (gray spout at center) rose several meters from the S vent at Iwo-Yama at Kirishimayama during May 2018. Image taken on 15 May 2018. Courtesy of JMA (Volcanic activity commentary on Kirishimayama, April, Heisei 30 (2018)).

Geologic Background. Kirishimayama is a large group of more than 20 Quaternary volcanoes located north of Kagoshima Bay. The late-Pleistocene to Holocene dominantly andesitic group consists of stratovolcanoes, pyroclastic cones, maars, and underlying shield volcanoes located over an area of 20 x 30 km. The larger stratovolcanoes are scattered throughout the field, with the centrally located, 1700-m-high Karakunidake being the highest. Onamiike and Miike, the two largest maars, are located SW of Karakunidake and at its far eastern end, respectively. Holocene eruptions have been concentrated along an E-W line of vents from Miike to Ohachi, and at Shinmoedake to the NE. Frequent small-to-moderate explosive eruptions have been recorded since the 8th century.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); 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/); 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/); Geographical Survey Institute, Geospatial Information Authority of Japan, Ministry of Land, Infrastructure, Transport and Tourism, No. 1 North Town, Tsukuba city, Ibaraki Prefecture 305-0811 Japan Tel: 029-864-1111 (Representative) Fax: 029-864-1807 (URL: http://www.gsi.go.jp/index.html); Kyodo News (URL: https://www.kyodonews.jp/english/); Associated Press (URL: http://www.ap.org/ ); Reuters (http://www.reuters.com/).


Sabancaya (Peru) — June 2018 Citation iconCite this Report

Sabancaya

Peru

15.787°S, 71.857°W; summit elev. 5960 m

All times are local (unless otherwise noted)


Strong, sporadic explosions with ash plumes throughout December 2017-May 2018

Although tephrochronology has dated activity at Sabancaya back several thousand years, renewed activity that began in 1986 was the first recorded in over 200 years. Intermittent activity since then has produced significant ashfall deposits, seismic unrest, and fumarolic emissions. A renewed period of explosive activity began in early November 2016 and continued through 2017. It was characterized by continuing pulses of ash emissions with plume heights exceeding 10 km altitude, thermal anomalies, and numerous significant SO2 plumes (BGVN 42:12). Details of the continuing eruptive activity from December 2017 to May 2018 in this report come from the two Peruvian observatories that monitor the volcano: Instituto Geofisico del Peru - Observatoria Vulcanologico del Sur (IGP-OVS), and Observatorio Volcanologico del INGEMMET (Instituto Geológical Minero y Metalúrgico) (OVI-INGEMMET). Aviation notices come from the Buenos Aires Volcanic Ash Advisory Center (VAAC), and satellite data is reported from several sources.

Sabancaya continued with its explosive eruption that began on 6 November 2016 during December 2017-May 2018. Around 100 aviation notices were issued each month by the Buenos Aires VAAC; tens of daily explosions were reported, fluctuating from highs in the 60s per day in December 2017 to lows in the teens per day during February-April 2018. Ash plumes heights varied at 3-5 km above the summit; altitudes mentioned in the VAAC reports were between 7.3 and 8.5 km altitude most days, although plume heights over 9.1 km were observed a number of times. MIROVA thermal anomalies were recorded every week; MODVOLC thermal alerts occurred every month. A significant number of SO2 anomalies greater than two Dobson Units were measured by NASA's Goddard Space Flight Center each month (table 2).

Table 2. Eruptive Activity at Sabancaya, December 2017-May 2018. Compiled using data from IGP-OVS, OVI-INGEMMET, Buenos Aires VAAC, HIGP - MODVOLC Thermal Alerts System, and NASA Goddard Space Flight Center.

Month VAAC Reports Avg Daily Explosions by week Max Plume Heights (m above crater) Plume Drift MODVOLC Alerts Min Days with SO2 over 2 DU
Dec 2017 120 69, 63, 55, 67, 42 2,500-3,300 40-50 km, SW, NE, NW, W, N 2 7
Jan 2018 101 41, 57, 57, 33 2,500-3,300 50 km, SW, W, NW, N 2 13
Feb 2018 94 22, 18, 19, 17 2,500-4,500 30-50 km, SE, S, SW, NW 1 12
Mar 2018 115 12, 10, 17, 17, 18 2,000-5,350 30-50 km, S, SW, W, NW, N 3 13
Apr 2018 114 15, 15, 19, 22 2,000-3,200 30-40 km, All 3 12
May 2018 132 25, 27, 30, 35, 28 1,900-4,300 30-40 km, NW, N, NE, E, SE, S 4 7

Activity during December 2017-February 2018. The Buenos Aires VAAC issued 120 aviation alerts during December 2017; webcam and satellite imagery revealed continuous emissions of water vapor and gas, accompanied by sporadic puffs of ash, throughout the month. When visible in satellite imagery, plumes rose to 7.3-8.2 km altitude (figure 46); a few plumes were reported to 9.1 km altitude. According to OVI-INGEMMET, about 1,800 explosions took place in December. During the third week, ashfall was reported in Huambo (28 km WNW). There were two MODVOLC thermal alerts issued, on 3 and 10 December.

Figure (see Caption) Figure 46. Webcam photo of an ash plume at Sabancaya on 16 December 2017. The Buenos Aires VAAC reported a plume that day to 8.2 km altitude. Courtesy of OVI-INGEMMET (RSSAB-51-2017/OVI-INGEMMET & IGP Semana del 11 al 17 de diciembre de 2017).

The number of explosions reported by OVI-INGEMMET dropped slightly to about 1,400 during January 2018. The number of VAAC reports was similar to December; when weather clouds prevented observations of emissions, seismic activity showed intermittent peaks that suggested puffs of ash. Plume descriptions by the Buenos Aires VAAC ranged from intermittent plumes that rose to 7.0-7.6 km altitude early in the month to persistent puffs of ash that rose to 7.9-8.2 km altitude during the last two weeks of January. The prevailing winds were directed SW and NW, and ash plumes often drifted as far as 50 km. NASA Goddard Space Flight Center recorded at least 13 days with SO2 emissions greater than two Dobson Units (DU) (figure 47). HIGP issued two MODVOLC thermal alerts on 4 and 20 January.

Figure (see Caption) Figure 47. SO2 emissions at Sabancaya were significant throughout the report period. Most months, NASA-GSFC measured 10 or more days where the Dobson Unit (DU) values exceeded two. Dobson Units are a measure of the molecular density of SO2 in the atmosphere. The larger plumes shown here are from 6 January 2018 (top left), 23 February 2018 (top right), 18 March 2018 (bottom left), and 28 April 2018 (bottom right). Courtesy of NASA Goddard Space Flight Center.

OVI-INGEMMET reported ash plume heights during February 2018 at 2,500-4,500 m above the summit. They also noted that deflation was measured during the middle two weeks of the month. The number of daily explosions decreased significantly from the previous few months, with about 500 total explosions recorded in February. The Buenos Aires VAAC noted that the webcam showed continuous emissions of gases with sporadic puffs of ash every day that the summit was visible. Ash plumes were only visible in satellite imagery a few times during the month; during 8-10 February, intermittent emissions were seen moving SE between 7.9 and 8.5 km altitude. During 17-24 February, weak, thin ash plumes drifted several different directions at 7.3-7.9 km altitude (figure 48), and on 28 February a plume was visible drifting NW at 7.6 km altitude. Only a single MODVOLC thermal alert was issued on 18 February.

Figure (see Caption) Figure 48. A strong pulse of ash rose from the summit of Sabancaya early in the morning of 21 February 2018. Courtesy of OVI-INGEMMET (RSSAB-08-2018/OVI-INGEMMET & IGP Semana del 19 al 25 de febrero de 2018).

Activity during March-May 2018. Three MODVOLC thermal alerts were issued in March 2018, two on 14 March and one on 27 March. Sporadic ash explosions continued, but with the lowest number per day of the reporting period. About 450 explosions were recorded during March. In spite of the smaller number of explosions, some of the tallest ash plumes of the period occurred this month. The Buenos Aires VAAC reported a diffuse ash plume drifting NW in satellite imagery on 2 March at 8.8 km altitude. The following week, several ash plumes were spotted in satellite imagery at altitudes of 7.3-8.2 km drifting either SW or NW. On 11 March, cloudy weather prevented visual satellite imagery observations, but multispectral imagery and the webcam revealed intermittent pulses of ash moving SW at 7.6 km altitude. The following day sporadic strong pulses of ash were observed in the webcam, and there was a pilot report of an ash plume at 9.1 km altitude. During the second half of March, ash plumes were noted in satellite imagery most days at altitudes of 6.4-8.2 km; a few pulses produced short-lived ash plumes that rose over 9.1 km, including on 14, 22, 24, and during 27-30 March (figure 49). The highest plume was observed in visible imagery drifting E on 28 March at 10.1 km altitude. A lahar was also reported on 28 March descending the SE flank, towards the Sallalli River; no damage was reported.

Figure (see Caption) Figure 49. An ash plume at Sabancaya on 30 March 2018 can be seen rising from the summit and above the meteorological cloud in this webcam image. The Buenos Aires VAAC reported ash plumes on 30 March that rose to 9.1 and 9.5 km and drifted NE. Courtesy of OVI-INGEMMET (RSSAB-13-2018/OVI-INGEMMET & IGP Semana del 26 de marzo al 01 de abril de 2018).

The number of explosions during April 2018 increased slightly from March to about 540. The maximum plume heights ranged from 2,000 to 3,200 m above the summit according to OVI-INGEMMET. The webcam showed continuous emissions of water vapor and gas and sporadic pulses of ash throughout the month. Ashfall was reported during the first week in Achoma (23 km NE), Chivay (33 km NE), and Huanca. During the second week, the prevailing winds brought ashfall to the W and NW to Huambo (28 km W) and Cabanaconde (22 km NW). The Buenos Aires VAAC reported faint ash plumes visible in satellite imagery nearly every day; plume heights consistently ranged from 7.0 to 8.2 km altitude. Three MODVOLC thermal alerts were issued during the month, one on 13 April and two on 17 April.

Activity increased in many ways during May 2018. The Buenos Aires VAAC issued 132 aviation alerts, the most of any month during the period. The numbers of daily explosions increased compared to April, resulting in a monthly total of around 900. OVI-INGEMMET reported plume heights up to 4,300 m above the summit. MODVOLC thermal alerts were issued on 8, 19, 24, and 26 May. In addition to ash plumes visible in satellite imagery every day at altitudes of 7.3-8.2 km altitude (figure 50), a significant number of ash plumes were reported to altitudes greater than 9.1 km during the month, resulting in more VONA's (Volcanic Observatory Notice to Aviation) issued than in previous months. Sporadic strong puffs of ash were observed in the webcam on the days that satellite imagery measurements of ash plume heights exceeded 9.1 km including on 4, 5, 10, 14, 19, 21, 22, 25, 28, and 31 May. The highest plumes reached 10.4 km altitude on 19 May and 10.1 km altitude on 25 May. Hotspots were also reported on 20, 24, and 27 May. As in previous months, the webcam showed constant emissions of steam and gas, with intermittent pulses of volcanic ash throughout the month.

Figure (see Caption) Figure 50. An IGP webcam at Sabancaya recorded the plume height above the summit at 2,800 m on 27 May 2018. Courtesy of OVI-INGEMMET (RSSAB-22-2018/OVI-INGEMMET & IGP Semana del 28 de mayo al 3 de junio del 2018).

Geologic Background. Sabancaya, located in the saddle NE of Ampato and SE of Hualca Hualca volcanoes, is the youngest of these volcanic centers and the only one to have erupted in historical time. The oldest of the three, Nevado Hualca Hualca, is of probable late-Pliocene to early Pleistocene age. The name Sabancaya (meaning "tongue of fire" in the Quechua language) first appeared in records in 1595 CE, suggesting activity prior to that date. Holocene activity has consisted of Plinian eruptions followed by emission of voluminous andesitic and dacitic lava flows, which form an extensive apron around the volcano on all sides but the south. Records of historical eruptions date back to 1750.

Information Contacts: Observatorio Volcanologico del INGEMMET, (Instituto Geológical Minero y Metalúrgico), Barrio Magisterial Nro. 2 B-16 Umacollo - Yanahuara Arequipa, Peru (URL: http://ovi.ingemmet.gob.pe); Instituto Geofisico del Peru, Observatoria Vulcanologico del Sur (IGP-OVS), Arequipa Regional Office, Urb La Marina B-19, Cayma, Arequipa, Peru (URL: http://ovs.igp.gob.pe/); 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); 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/).


Masaya (Nicaragua) — June 2018 Citation iconCite this Report

Masaya

Nicaragua

11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)


Lava lake persists during July 2017-April 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 Chillan (Chile) — June 2018 Citation iconCite this Report

Nevados de Chillan

Chile

36.868°S, 71.378°W; summit elev. 3180 m

All times are local (unless otherwise noted)


Hundreds of ash-bearing explosions; dome appears in crater in mid-December 2017

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).


Marapi (Indonesia) — June 2018 Citation iconCite this Report

Marapi

Indonesia

0.38°S, 100.474°E; summit elev. 2885 m

All times are local (unless otherwise noted)


Two explosions during April-May 2018 cause ashfall to the southeast

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


Nyiragongo (DR Congo) — June 2018 Citation iconCite this Report

Nyiragongo

DR Congo

1.52°S, 29.25°E; summit elev. 3470 m

All times are local (unless otherwise noted)


Thermal anomalies show that lava lake remains active through May 2018

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


Ebeko (Russia) — June 2018 Citation iconCite this Report

Ebeko

Russia

50.686°N, 156.014°E; summit elev. 1103 m

All times are local (unless otherwise noted)


Ash explosions remained frequent through May 2018, with plumes typically rising more than 1 km

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

Date Plume Altitude Plume Distance Plume Direction Other observations
1-4 and 7 Dec 2017 2 km -- -- ACC at Orange. Ashfall reported in Severo-Kurilisk. Explosions on 2-4 and 7 Dec.
8, 9, 11 Dec 2017 2.3 km -- -- Explosions.
16, 18-19, and 21-22 Dec 2017 3.5 km 16 km SSW Explosions. Ash plume and weak thermal anomaly on 16 Dec.
25 Dec 2017 1.5 km -- -- Explosion.
01-05 Jan 2018 -- -- -- No activity noted.
08-10 Jan 2018 2.5 km -- -- Explosions.
11-12, 14-16, and 18 Jan 2018 3.1 km -- -- Explosion. Minor ashfall reported in Severo-Kurilsk on 15,16, and 18 Jan.
22-23 Jan 2018 2 km -- -- Explosions.
26-27 and 29-31 Jan 2018 2.5 km -- -- Explosions. Ashfall reported in Severo-Kurilsk on 29 Jan.
05-08 Feb 2018 2.4 km -- -- Explosions. Ashfall reported in Severo-Kurilisk on 8 Feb.
09-10 and 14 Feb 2018 2.2 km -- -- Explosions.
17-18 and 20-21 Feb 2018 2.4 km -- -- Explosions. Ashfall reported in Severo-Kurilisk on 17-18 Feb.
23-25 and 27-28 Feb 2018 3.3 km -- -- Explosions.
06 Mar 2018 1.7 km -- -- Explosions.
12-13 Mar 2018 2.7 km -- -- Explosions.
18 and 21-22 Mar 2018 1.8 km -- -- Explosions. Ashfall reported in Severo-Kurilisk on 17 and 21 Mar.
23-25 and 28-29 Mar 2018 2.3 km -- -- Explosions.
31 Mar-06 Apr 2018 2.7 km -- -- Explosions.
07 and 11-12 Apr 2018 1.8 km -- -- Explosions. Ashfall reported in Severo-Kurilisk on 6 Apr.
15 and 17-19 Apr 2018 2.6 km -- -- Explosions.
21 and 25 Apr 2018 2.5 km -- -- Explosions.
01-03 May 2018 2.8 km -- -- Explosions.
04 and 06-10 May 2018 2.4 km -- -- Explosions.
12-14 May 2018 2.8 km 21 km SW Explosions. Ash plume drifted SW on 13 May.

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 (see Caption) 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 (Papua New Guinea) — June 2018 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Gradual decline in activity after July 2017, but continuing through May 2018

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 (see Caption) 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.

Dates Ash Plume Altitude (km) Ash Plume Drift Other Observations
07 Aug 2017 2.1 55 km NW --
09 Aug 2017 1.8 N --
16 Aug 2017 2.1 NW --
01-02 Sep 2017 1.8 N, NW --
07-08, 10-12 Sep 2017 1.8-2.4 NNW, NW, SW --
22-23 Sep 2017 2.1 NNW --
04 Oct 2017 1.8 N Minor ash emission
11, 15-16 Oct 2017 1.8-2.1 NE, NNW, NW --
17-18, 20 Oct 2017 1.5-1.8 NE, NNW, NW --
05 Nov 2017 3.7 SE, ESE --
15-16 Nov 2017 1.8-2.7 S, SW --
15 Apr 2018 3.7 S --
24 Apr 2018 4 SW Ash dissipated in 6 hours
13 May 2018 5.5 W At 0709; ash dissipated in 6 hours
17-18, 21-22 May 2018 2.1-2.4 WSW, W, WNW --
23, 26-28 May 2018 2.4-3 WSW, W, NW --

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 (see Caption) 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 (see Caption) 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.


Pacaya (Guatemala) — May 2018 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Pyroclastic cone fills MacKenney crater; lava flows emerge from fissures around the crater rim

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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/).


Reventador (Ecuador) — May 2018 Citation iconCite this Report

Reventador

Ecuador

0.077°S, 77.656°W; summit elev. 3562 m

All times are local (unless otherwise noted)


Near-daily explosions produce 1-km-high ash plumes and incandescent blocks on all flanks, October 2017-March 2018.

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Santa Maria (Guatemala) — May 2018 Citation iconCite this Report

Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)


Daily explosions with minor ash and block avalanches at Caliente, November 2017-April 2018

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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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 (see Caption) 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).


Sheveluch (Russia) — May 2018 Citation iconCite this Report

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)


Intermittent thermal anomalies along with gas and steam emissions continue through April 2018

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 (see Caption) 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/).

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Bulletin of the Global Volcanism Network - Volume 22, Number 03 (March 1997)

Managing Editor: Richard Wunderman

Arenal (Costa Rica)

Explosions diminished in January but continued through March

Callaqui (Chile)

Continuous fumarolic activity at main vent and upper S flank

Copahue (Chile-Argentina)

Crater lake lies several meters below drainage notch

Jan Mayen (Norway)

Weak fumaroles on the inner NE crater wall

Karymsky (Russia)

Ash plumes reported by aircraft pilot

Kilauea (United States)

Lava flows outside of Pu`u `O`o for the first time since 31 January

Klyuchevskoy (Russia)

Continuous presence of gas-and-steam plume up to 4 km above crater

Llaima (Chile)

Fumarolic activity at summit vent

Lonquimay (Chile)

1988-89 lava flows continue emitting steam

Manam (Papua New Guinea)

Activity low with increase near the end of the month

Masaya (Nicaragua)

Strombolian explosion; incandescent vent in Santiago crater; seismicity increases

Okmok (United States)

Emission of steam, ash, and lava continues

Pacaya (Guatemala)

Graduate students study gas emission and lava flow

Platanar (Costa Rica)

Dormancy continues but S-flank residents felt six earthquakes on 30 March

Poas (Costa Rica)

Relatively stable but seismically active

Popocatepetl (Mexico)

Summaries for March and parts of February and April

Rabaul (Papua New Guinea)

Lava flow issues from Tavurvur crater during 14 March eruption

Santa Maria (Guatemala)

Reports of 6 February dome collapse proven false

Sheveluch (Russia)

Steam and ash plume rises 1.5 km above the crater

Soufriere Hills (United Kingdom)

Pyroclastic flows advance over Galway's Wall on 29 March

Stromboli (Italy)

Summary of seismic and volcanic activity during May 1996-January 1997

Telica (Nicaragua)

Seismicity increases and fumarolic activity continues



Arenal (Costa Rica) — March 1997 Citation iconCite this Report

Arenal

Costa Rica

10.463°N, 84.703°W; summit elev. 1670 m

All times are local (unless otherwise noted)


Explosions diminished in January but continued through March

During January explosive activity diminished with respect to December 1996 in terms of both the number of eruptions and the quantity of ejected tephra. A S-flank avalanche on 1 January descended to ~1,000 m elevation. On the night of 14 January, a NE-flank pyroclastic flow traveled down to 800 m elevation, scalding vegetation. During February eruptive activity dropped yet lower, and in March, lower still. Despite these decreases, an incandescent avalanche was noted on 27 February at 1600. In addition, during the last week of that month the number of eruptions increased. March ash columns rose <1 km above Crater C. Crater D remained fumarolically active.

During January and February the lava flow on the N flank became active at 950 m elevation. During March, the N-flank flow maintained activity down to 800 m elevation and a new flow began, its path following the previous flow's channel and its front reaching 1,300 m elevation. Cold rock avalanches took place down local drainages (eg. Calle de Arenas, Gillermina, and Rio Caliente).

Tremor duration peaked in April and June 1996 at around 400 hours/month; thereafter tremor typically remained at ~200-300 hours/month (figure 81). The number of earthquakes peaked in middle to late 1996 (figure 81). Surveys of the distance array revealed that between November 1996 and January 1997 the relative positions of survey stations contracted by an average of 4-5 ppm/month. In March it was reported that the average contraction seen in recent years (~27 ppm) continued along the radial lines on the volcano's W, SW, and S flanks. A dry-tilt station at the base of the volcano typically has small measured tilts amounting to 7-10 µrad/year.

Figure (see Caption) Figure 81. Arenal seismicity and tremor recorded during March 1996 through March 1997 (registered at station "VACR," 2.7 km NE of the main crater). Courtesy of OVSICORI-UNA.

The vegetation that had begun to regrow on the NE, E, and SE flanks continued to be affected by acid rain. Some species displayed burns on the edges and tops of leaves, while others showed signs of discolored leaves.

Geologic Background. Conical Volcán Arenal is the youngest stratovolcano in Costa Rica and one of its most active. The 1670-m-high andesitic volcano towers above the eastern shores of Lake Arenal, which has been enlarged by a hydroelectric project. Arenal lies along a volcanic chain that has migrated to the NW from the late-Pleistocene Los Perdidos lava domes through the Pleistocene-to-Holocene Chato volcano, which contains a 500-m-wide, lake-filled summit crater. The earliest known eruptions of Arenal took place about 7000 years ago, and it was active concurrently with Cerro Chato until the activity of Chato ended about 3500 years ago. Growth of Arenal has been characterized by periodic major explosive eruptions at several-hundred-year intervals and periods of lava effusion that armor the cone. An eruptive period that began with a major explosive eruption in 1968 ended in December 2010; continuous explosive activity accompanied by slow lava effusion and the occasional emission of pyroclastic flows characterized the eruption from vents at the summit and on the upper western flank.

Information Contacts: E. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86, 3000 Heredia, Costa Rica.


Callaqui (Chile) — March 1997 Citation iconCite this Report

Callaqui

Chile

37.92°S, 71.45°W; summit elev. 3164 m

All times are local (unless otherwise noted)


Continuous fumarolic activity at main vent and upper S flank

A late-March overflight made after a prolonged dry season enabled views of Callaqui with relatively low snow levels. At the time of the overflight, the main vent at the summit showed vigorous steam emissions and sulfur deposits were noted around the two main fumarolic vents. Similar levels of fumarolic activity were noted over the preceding three weeks. Both the south side of the summit and the uppermost southern flank, at the head of the glaciers feeding the Río Malla, had continuous fumarolic activity. Rocks in these areas were highly altered. Emissions from the southern flank were more diffuse.

Geologic Background. The late-Pleistocene to Holocene Callaqui stratovolcano has a profile of an overturned canoe, due to its construction along an 11-km-long, SW-NE fissure above a 1.2-0.3 million year old Pleistocene edifice. The ice-capped, basaltic-andesite volcano contains well-preserved cones and lava flows, which have traveled up to 14 km. Small craters 100-500 m in diameter are primarily found along a fissure extending down the SW flank. Intense solfataric activity occurs at the southern portion of the summit; in 1966 and 1978, red glow was observed in fumarolic areas (Moreno 1985, pers. comm.). Periods of intense fumarolic activity have dominated; few historical eruptions are known. An explosive eruption was reported in 1751, there were uncertain accounts of eruptions in 1864 and 1937, and a small phreatic ash emission was noted in 1980.

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


Copahue (Chile-Argentina) — March 1997 Citation iconCite this Report

Copahue

Chile-Argentina

37.856°S, 71.183°W; summit elev. 2953 m

All times are local (unless otherwise noted)


Crater lake lies several meters below drainage notch

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

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

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

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

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


Jan Mayen (Norway) — March 1997 Citation iconCite this Report

Jan Mayen

Norway

71.087°N, 8.146°W; summit elev. 2085 m

All times are local (unless otherwise noted)


Weak fumaroles on the inner NE crater wall

On 6 April, members of an SVE excursion visited the volcano and reported only weak fumarolic activity. White steam rose a few meters above the inner low part of the NE crater wall.

Beerenberg is a large glacier-covered stratovolcano at the N end of Jan Mayen Island. Numerous cinder cones have erupted along flank fissures, the latest in 1985.

Geologic Background. Remote Jan Mayen Island, located in the Norwegian Sea along the Jan Mayen Ridge about 650 km NE of Iceland, consists of two volcanic complexes separated by a narrow isthmus. The large Beerenberg basaltic stratovolcano (Nord-Jan) forms the NE end of the 40-km-long island, which is ringed by high cliffs. The glacier-covered Beerenberg has a 1-km-wide summit crater and numerous cinder cones that were erupted along flank fissures. It is composed primarily of basaltic lava flows with minor amounts of tephra. Historical eruptions at Beerenberg date back to the 18th century. The Sor-Jan group of pyroclastic cones and lava domes occupies the SW tip of Jan Mayen. The Holocene Sor-Jan cinder cones, tephra rings, and trachytic lava domes were erupted from short fissures with a NE-SW trend.

Information Contacts: Henry Gaudru, Michel Caplain, Alain Hirsh, and Yves Chetcuti, Société Volcanologique Européenne, C.P. 1, 1211 Genève 17, Switzerland (URL: http://www.sveurop.org/); Michel Halbwachs, Laboratoire d'Instrumentation Geophysique, University of Savoie, BP 1104, 73011 Chambery, France.


Karymsky (Russia) — March 1997 Citation iconCite this Report

Karymsky

Russia

54.049°N, 159.443°E; summit elev. 1513 m

All times are local (unless otherwise noted)


Ash plumes reported by aircraft pilot

No direct visual observations were made during 25 March-25 April, however the above-background seismicity suggested ongoing low-level Strombolian eruptions. On 14 April an airline pilot reported an ash plume at 6.1 km, but no plume was detected on GMS-5 satellite imagery.

Geologic Background. Karymsky, the most active volcano of Kamchatka's eastern volcanic zone, is a symmetrical stratovolcano constructed within a 5-km-wide caldera that formed during the early Holocene. The caldera cuts the south side of the Pleistocene Dvor volcano and is located outside the north margin of the large mid-Pleistocene Polovinka caldera, which contains the smaller Akademia Nauk and Odnoboky calderas. Most seismicity preceding Karymsky eruptions originated beneath Akademia Nauk caldera, located immediately south. The caldera enclosing Karymsky formed about 7600-7700 radiocarbon years ago; construction of the stratovolcano began about 2000 years later. The latest eruptive period began about 500 years ago, following a 2300-year quiescence. Much of the cone is mantled by lava flows less than 200 years old. Historical eruptions have been vulcanian or vulcanian-strombolian with moderate explosive activity and occasional lava flows from the summit crater.

Information Contacts: Tom Miller, Alaska Volcano Observatory; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry.


Kilauea (United States) — March 1997 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Lava flows outside of Pu`u `O`o for the first time since 31 January

Between 11 and 27 March, activity at the Pu`u `O`o vent along Kilauea's E rift zone was confined to the lava pond within the crater. Pond activity remained sluggish, with periodic resurfacing and localized overturning of the crust. On 21 March, the pond's surface rose to within 84 m of the NE rim of the crater, as indicated by a crusted-solidified shelf on the W floor of the crater, then subsided 14 m to 98 m below the crater rim. Reports of the crater glowing at night were thought to correspond with periods when the level of the pond's surface rose. Fumes emanating from the eruption site remained at low levels.

During these two weeks, the summit of Kilauea showed 8 µrad of inflationary tilt. In total, the summit recovered 29 µrad of the roughly 30 µrad of summit deflation that occurred on 30 January (BGVN 22:01).

On 28 March, lava was observed outside of the Pu`u `O`o crater for the first time since 31 January. Lava emanated from a collapse pit on the episode 51 shield that flanks the W side of Pu`u `O`o. This lava flowed into a depression to the S before it entered the old tube system, abandoned 30 January, through collapse pits and skylights. The following day, lava was seen flowing through the old tube system at the 2,400-ft (770 m) skylight. Also, the level of the pond in Pu`u `O`o rose to within 52 m of the NE rim, a level comparable to before the 30 January drain-back.

Three substantial lava flows escaped from the lava tube on 3 April. The lowest of the three breakouts fed a surface flow at the 721-m level. This flow progressed to the edge of the flow field and ignited vegetation along its edges as it advanced to elevations as low as 640 m. The next day, geophysical measurements showed that there was no lava flowing through tubes below the 705-m level. Through 7 April, flows repeatedly inflated, advanced, and stagnated.

Shallow, long-period summit earthquakes and earthquakes along the E rift zone remained at high to very high levels.

This latest resumption of activity, designated episode 55 by the Hawaiian Volcano Observatory, was considered likely to spread flows S over Pulama pali to the coast.

Kilauea is one of five coalescing volcanoes that comprise the island of Hawaii. Historically its eruptions originate primarily from the summit caldera or along one of the lengthy E and SW rift zones that extend from the summit caldera to the sea. This latest Kilauea eruption began in January 1983 along the E rift zone. The eruption's early phases, or episodes, occurred along a portion of the rift zone that extends from Napau Crater on the uprift (towards the summit) end to ~8 km E on the downrift (towards the sea) end. Activity eventually centered on what was later named Pu`u `O`o. Between January 1983 and December 1996, erupted lava totaled ~1.45 km3.

Geologic Background. Kilauea, which overlaps the E flank of the massive Mauna Loa shield volcano, has been Hawaii's most active volcano during historical time. Eruptions are prominent in Polynesian legends; written documentation extending back to only 1820 records frequent summit and flank lava flow eruptions that were interspersed with periods of long-term lava lake activity that lasted until 1924 at Halemaumau crater, within the summit caldera. The 3 x 5 km caldera was formed in several stages about 1500 years ago and during the 18th century; eruptions have also originated from the lengthy East and SW rift zones, which extend to the sea on both sides of the volcano. About 90% of the surface of the basaltic shield volcano is formed of lava flows less than about 1100 years old; 70% of the volcano's surface is younger than 600 years. A long-term eruption from the East rift zone that began in 1983 has produced lava flows covering more than 100 km2, destroying nearly 200 houses and adding new coastline to the island.

Information Contacts: Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, PO Box 51, Hawaii National Park, HI 96718, USA (URL: https://volcanoes.usgs.gov/observatories/hvo/).


Klyuchevskoy (Russia) — March 1997 Citation iconCite this Report

Klyuchevskoy

Russia

56.056°N, 160.642°E; summit elev. 4754 m

All times are local (unless otherwise noted)


Continuous presence of gas-and-steam plume up to 4 km above crater

Seismicity remained above background during 24 March-25 April. The presence of a gas-and-steam plume was reported from 25 March to 13 April at a height variable between 50 and 500 m above the crater and drifting NE to SE with the prevailing winds. On 27 March the plume rose to 1,500-4,000 m and spread 70 km to the E, and on 2 April to 1,500-3,000 m, moving 50 km to the E.

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

Information Contacts: Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia.


Llaima (Chile) — March 1997 Citation iconCite this Report

Llaima

Chile

38.692°S, 71.729°W; summit elev. 3125 m

All times are local (unless otherwise noted)


Fumarolic activity at summit vent

A late-March overflight made after a prolonged dry season enabled scientists to see Llaima with relatively low snow levels. The main vent, in the SE part of the summit crater, emitted a bluish gas in poorly defined pulses at intervals of ~45 seconds. Similar pulses observed in mid-March took place at intervals of ~100 seconds.

The upper part of the main crater wall in the NW sector and small areas within the Pichillaima scar E of the main crater gave off diffuse steam emissions. A grayish plume at summit height was traceable for a few tens of kilometers to the ESE.

Geologic Background. Llaima, one of Chile's largest and most active volcanoes, contains two main historically active craters, one at the summit and the other, Pichillaima, to the SE. The massive, dominantly basaltic-to-andesitic, stratovolcano has a volume of 400 km3. A Holocene edifice built primarily of accumulated lava flows was constructed over an 8-km-wide caldera that formed about 13,200 years ago, following the eruption of the 24 km3 Curacautín Ignimbrite. More than 40 scoria cones dot the volcano's flanks. Following the end of an explosive stage about 7200 years ago, construction of the present edifice began, characterized by Strombolian, Hawaiian, and infrequent subplinian eruptions. Frequent moderate explosive eruptions with occasional lava flows have been recorded since the 17th century.

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


Lonquimay (Chile) — March 1997 Citation iconCite this Report

Lonquimay

Chile

38.379°S, 71.586°W; summit elev. 2832 m

All times are local (unless otherwise noted)


1988-89 lava flows continue emitting steam

A late-March overflight made after a prolonged dry season enabled observations with relatively low snow levels. The volcano lacked signs of fumarolic or other activity. However, during fieldwork S of La Holandesa crater, the 1988-89 lava flows to the NE of the main cone within the Las Paramelas valley continued to emit steam.

Geologic Background. Lonquimay is a small, flat-topped, symmetrical stratovolcano of late-Pleistocene to dominantly Holocene age immediately SE of Tolguaca volcano. A glacier fills its summit crater and spills down the S flank. It is dominantly andesitic, but basalt and dacite are also found. There is an E-W fissure, although the prominent NE-SW Cordón Fissural Oriental fissure zone cuts across the entire volcano, that produced a series of NE-flank vents and cinder cones, some of which have been the source of voluminous lava flows, including those during 1887-90 and 1988-90 that traveled up to 10 km.

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


Manam (Papua New Guinea) — March 1997 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Activity low with increase near the end of the month

During March, Manam was only mildly active and visibility was poor. When visible, the crater was gently emitting a white plume and on two nights there were reports of crater glow. Activity increased slightly during the last week of March. Main Crater had white-to-gray emissions accompanied by occasional weak roaring. Aviation reports noted that at around 1600 on 22 March an eruption plume rose to 3,000 m and drifted SSE. The Tabele water-tube tiltmeter recorded a slight but steady radial inflation.

There was a slow and steady rise in seismicity throughout the month. The number of low-frequency earthquakes increased from ~1,400-1,600 events/day. The amplitude of the events also increased with time.

Geologic Background. The 10-km-wide island of Manam, lying 13 km off the northern coast of mainland Papua New Guinea, is one of the country's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical 1807-m-high basaltic-andesitic stratovolcano to its lower flanks. These "avalanche valleys" channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five small satellitic centers are located near the island's shoreline on the northern, southern, and western sides. Two summit craters are present; both are active, although most historical eruptions have originated from the southern crater, concentrating eruptive products during much of the past century into the SE valley. Frequent historical eruptions, typically of mild-to-moderate scale, have been recorded since 1616. Occasional larger eruptions have produced pyroclastic flows and lava flows that reached flat-lying coastal areas and entered the sea, sometimes impacting populated areas.

Information Contacts: B. Talai, H. Patia, D. Lolok, P. de Saint Ours, and C. McKee, RVO; Bureau of Meteorology, Northern Territory Regional Office, P.O. Box 735, Darwin, NT 0801 Australia.


Masaya (Nicaragua) — March 1997 Citation iconCite this Report

Masaya

Nicaragua

11.984°N, 86.161°W; summit elev. 635 m

All times are local (unless otherwise noted)


Strombolian explosion; incandescent vent in Santiago crater; seismicity increases

A small Strombolian explosion on 5 December 1996 ejected blocks (<10 cm in diameter), ash, and some Pelee's hair. Some of the inner crater walls collapsed, partly closing the incandescent vent. Prior to this eruption the vent's gas temperature was 1,084°C; afterwards, it dropped to 360°C.

During three consecutive days in 1997, COSPEC SO2 fluxes varied as follows: on 12 February, 159 ± 73 metric tons/day (t/d) (1 sigma, n = 5); on 13 February, 363 ± 182 t/d (1 sigma, n = 6); on 14 February, 290 ± 65 t/d (1 sigma, n = 4). The 363 t/d figure is a minimum estimate since on the first 3 traverses the instrument went off the chosen recording scale indicating still larger values than reported.

A visit in March 1997 yielded COSPEC values of 300-400 t/d; these values were lower than those obtained during March 1996 (BGVN 21:04). Nightime observations of the active Santiago crater revealed that large amounts of incandescent gas were being released frequently through a conduit that had partially collapsed on 5 December 1996. As a result of the collapse, it was not possible to see incandescent magma during the night.

Seismicity increased since September 1996; in January 1997, 41 events (4 high- and 47 low-frequency) were recorded along with constant tremor. During 22 February-20 March, 18 events occurred, 15 of which were low-frequency and three high-frequency. Since November 1994 background levels of RSAM have varied between 12 and 16 RSAM units. Since mid-January, however, RSAM increased, fluctuating between 22 and 32 units.

In the crater area, gravity decreased steadily during 1993-95; it remained stable in 1996 and possibly increased a little in 1997.

A NE-trending fracture at the base of Comalito cone emitted gases reaching 68°C. In this same vicinity soil gas concentrations contained up to 25% CO2.

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: Hazel Rymer and Mark Davies, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; John Stix, Dora Knez, Glyn Williams-Jones, and Alexandre Beaulieu, Departement de Geologie, Universite de Montreal, Montreal, Quebec H3C 3J7, Canada; Nicki Stevens, Department of Geography, University of Reading, Reading RG2 2AB, United Kingdom; Martha Navarro and Pedro Perez, INETER, Apartado Postal 2110, Managua, Nicaragua.


Okmok (United States) — March 1997 Citation iconCite this Report

Okmok

United States

53.43°N, 168.13°W; summit elev. 1073 m

All times are local (unless otherwise noted)


Emission of steam, ash, and lava continues

Reports on 27 March, and 4, 11, 18, and 25 April, confirmed that the eruption which began on 13 February was continuing at relatively low levels. Satellite images examined by AVO indicated the presence of hot lava flows in the caldera, and occasional thin, low-level plumes drifting downwind from the volcano. NOAA/NESDIS also reported that on 4 April an aircraft pilot saw lava flows and [observed] an ash column at ~3,500 m, drifting slowly SE. On 12 April another ash plume was reported by a pilot at 2.4 km; this same plume was detected in visible and infrared satellite imagery.

Okmok volcano is not monitored seismically and is not assigned a color code. Based on past eruptive history, lava flows and low--level ash emission could continue for weeks to months. Eruptive activity could intensify at any time.

Geologic Background. The broad, basaltic Okmok shield volcano, which forms the NE end of Umnak Island, has a dramatically different profile than most other Aleutian volcanoes. The summit of the low, 35-km-wide volcano is cut by two overlapping 10-km-wide calderas formed during eruptions about 12,000 and 2050 years ago that produced dacitic pyroclastic flows that reached the coast. More than 60 tephra layers from Okmok have been found overlying the 12,000-year-old caldera-forming tephra layer. Numerous satellitic cones and lava domes dot the flanks of the volcano down to the coast, including 1253-m Mount Tulik on the SE flank, which is almost 200 m higher than the caldera rim. Some of the post-caldera cones show evidence of wave-cut lake terraces; the more recent cones, some of which have been active historically, were formed after the caldera lake, once 150 m deep, disappeared. Hot springs and fumaroles are found within the caldera. Historical eruptions have occurred since 1805 from cinder cones within the caldera.

Information Contacts: Alaska Volcano Observatory (AVO); NOAA/NESDIS Satellite Analysis Branch (SAB).


Pacaya (Guatemala) — March 1997 Citation iconCite this Report

Pacaya

Guatemala

14.382°N, 90.601°W; summit elev. 2569 m

All times are local (unless otherwise noted)


Graduate students study gas emission and lava flow

Between 5 and 13 February graduate students from Northern Illinois University in collaboration with INSIVUMEH scientists conducted studies at Pacaya volcano. Focused fumarolic activity was observed at the summit, whereas diffuse gas emissions occurred around the SW flanks. Numerous micro-seismic earthquakes were recorded daily during this period.

Lava samples were collected from the 11 November 1996 flow. Analysis showed that the lava was a highly- vesicular, plagioclase-phyric basalt that resembles basaltic flows from previous eruptions.

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: Otoniel Matías, Seccion Vulcanología, INSIVUMEH (Instituto Nacional de Sismología, Vulcanología, Meteorología e Hydrología of the Ministerío de Communicacíones, Transporte y Obras Publicas), 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala; Barry Cameron and Shane Rundle, Department of Geology, Northern Illinois University, USA.


Platanar (Costa Rica) — March 1997 Citation iconCite this Report

Platanar

Costa Rica

10.3°N, 84.366°W; summit elev. 2267 m

All times are local (unless otherwise noted)


Dormancy continues but S-flank residents felt six earthquakes on 30 March

On 30 March 1997 residents in the S-flank settlement of San Vicente felt about six earthquakes between 0900 and 2100. One of these earthquakes took place at 1429; it was M 2.7 and its epicenter was 5 km SE of the volcano. No residents in other nearby settlements (Porvenir, Sucre, and Quesada) reported feeling these earthquakes.

About 10 days after the earthquakes, two dry-tiltmeters, measured every 2-3 years, showed differing results. One showed great changes but had been disturbed; the other, which was considered more reliable, had changed little. An April 1980 seismic swarm near Platanar, attributed to a local fault, continued for 2-3 weeks.

Geologic Background. The Platanar volcanic center is the NW-most volcano in the Cordillera Central of Costa Rica. The massive complex covers about 900 km2 and is dominated by two largely Pleistocene stratovolcanoes, Platanar and Porvenir. These volcanoes were constructed within the Pleistocene Chocosuela caldera, which may have formed during a major slope failure. The Cerro Platanar volcano (known locally as Volcán Congo) on the N side of the complex has prehistorical lava flows on its W flanks and is the youngest volcanic center. The highest peak is Porvenir, whose summit crater lies 3 km S of Platanar. A thin layer of phreatic ash suggested that an eruption from Platanar occurred within the past few thousand years (Stine and Banks, 1991). The Aguas Zarcas group of nine basaltic cinder cones, located on the N flank of the Platanar-Porvenir complex to as low as 160 m altitude is, in part, Holocene in age.

Information Contacts: E. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86, 3000 Heredia, Costa Rica.


Poas (Costa Rica) — March 1997 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Relatively stable but seismically active

Periodic visits revealed that the crater lake level changed as follows compared to December 1996: January, a 31 cm decrease; February, a 55 cm decrease; and March, an 88 cm decrease. Lake-water temperatures during January, February, and March measured 32, 30, and 29°C, respectively. A pH of 1.7 was measured in March. During January-March constant bubbling took place on the lake's S and SW shores. During January and February one fumarole remained noisy; as late as March those on the SE, S, and SW remained at 91- 93°C. The migration of fumaroles was noted in March. Fumarolic gases emitted from the accessible parts of the pyroclastic cone had temperatures of 92°C (January) and 92-93°C (February). Temperatures were not reported for March. During January-March, steam clouds rose 400 m above the crater floor.

Scientists collected acid rain at Cerro Pelón on five days during 7 January-10 March. The respective SO4 and Cl ion concentrations ranged between ~5 and 12 mg/liter, and 1 and 6 mg/liter; pH ranged between 3.5 and 4.5.

A seismic swarm on 31 January consisted of 47 primarily low-frequency earthquakes; some occurred <5 km from the main crater at 1-5 km depths; they were M 3. According to park guards, five of these events were felt. Low-frequency earthquakes for March 1996-March 1997 peaked during September (figure 64). This peak was at 2,351 events; however, a previous peak, during the month of January 1996, represented 4,045 events. During the March 1996-March 1997 interval other earthquakes had these monthly event-counts: mid-frequency earthquakes (2.1-3.0 Hz), 13-237; and high-frequency (>3.0 Hz), 0-99. During the same interval, monthly tremor prevailed for 0-28 hours, peaking in October 1996.

Figure (see Caption) Figure 64. Poás seismicity (at frequencies below 2 Hz) recorded 2.7 km SW of the active crater (station POA2), March 1996 to March 1997. Courtesy of OVSICORI-UNA.

During January, both the distance network and dry-tilt readings at the summit remained stable. As of March, the three deformation lines across the crater and one external radial line had shown no significant changes during 1997. Another line, from the S side of the overlook (mirador) to the crater bottom, detected a cumulative contraction of 119 ppm/year. This contraction may have come from adjustments due to shallow phreatic venting and an increase in the crater lake's height. Changes in the inclinometer network were not considered significant.

Geologic Background. The broad, well-vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.

Information Contacts: E. Fernández, E. Duarte, V. Barboza, R. Van der Laat, E. Hernandez, M. Martinez, and R. Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA).


Popocatepetl (Mexico) — March 1997 Citation iconCite this Report

Popocatepetl

Mexico

19.023°N, 98.622°W; summit elev. 5393 m

All times are local (unless otherwise noted)


Summaries for March and parts of February and April

A series of non-technical reports covering the volcano's behavior during the interval 17 February to 4 April are summarized in table 4. During this interval the hazard alert remained at yellow on a scale that encompasses the categories green (low), yellow, and red (high). The summaries document a pattern of isolated exhalations (some bearing ash) and occasional type-A seismic events. Noteworthy exhalations occurred on many days in the last three weeks of March. For example, on 20 March a relatively large exhalation lasted 7 minutes and spawned an ash column that rose to 4 km above the vent.

Table 4. Summary of non-technical reports describing activity at Popocatépetl, 17 February-4 April 1997. The alert status remained moderate (yellow) during this entire interval. Courtesy of Roberto Quaas, CENAPRED-UNAM.

Report Date Comment
17 Feb 1997 During 15-16 February activity was low and stable. Seismicity was also low but there were indications of isolated exhalations.
19 Feb 1997 Activity remained similar to that described in on the 17 February report; a type-A event of very small magnitude occurred at 0727.
25 Feb 1997 During the interval 1017-1130, tremor occurred accompanied by two intense exhalations (at 1029 and 1031). The exhalations produced a column of gas and ash that reached up to 3 km in altitude drifting to the SE. At 1239 a less-intense exhalation occurred but gas and ash were still emitted over a prolonged interval.
26 Feb 1997 After a short period of relative tranquility, during the previous night there was a moderate increase in the level of exhalations. At 0620 on 26 February a major exhalation occurred followed by prolonged tremor. A second large exhalation at 0915 accompanied increased tremor. Starting on 25 February, the volcano produced a plume of variable intensity that occasionally contained ash.
27 Feb 1997 Overall activity fell considerably compared to yesterday. Seismicity was limited to some weak exhalations and three type-A events of very low magnitude. Plume diminished in size and density.
28 Feb 1997 Stable activity such that in the last 24 hours there were only occasional exhalations and two type-A events of very low magnitude.
10 Mar 1997 During 8-9 March, activity remained stable without important changes. A few type-A events with low level magnitudes were registered. The plume was very small.
12 Mar 1997 At 0430 a moderate ash-bearing exhalation occurred associated with light tremor, which continued until the time of the report. High-velocity winds led to light ash rains on towns near the volcano. Local authorities were informed. Up until the time of the report, activity remained moderate without the threat of danger.
14 Mar 1997 General activity has decreased compared to that of 12 March. There persisted a white plume of small volume and on average, six small exhalations per day. Seismicity remained moderate except for type-A events: one, this day at 1130 (M 3.3) and the other, the previous day at 2130 (M 2.3).
17 Mar 1997 During 15-16 March there was a significant increase in exhalations both in terms of number and size, with an average of 50 per day. Between exhalations, type-A events occurred, many of low magnitude (only three reached near M 3). The larger earthquakes took place on 14, 15, and 17 March. The volcano produced a grayish-white plume. This level of activity was similar to that of April and May of 1996.
18 Mar 1997 The general level of activity stabilized, tending towards low values with respect to those seen yesterday. Although in minor proportion, the exhalations and type-A events persisted. The plume lacked significant changes.
19 Mar 1997 During the night, and today, the number and size of exhalations increased and at 0750 tremor occurred. It accompanied a plume that probably carried a moderate amount of ash.

The Satellite Analysis Branch of NOAA (SAB) conveyed several messages about ash plumes during February-March 1997. In one case, aviators near México City on American Airlines flight 1211 reported ash at 1500 on 5 February reaching 9.1 km. At 1715, GOES-8 satellite imagery indicated a detached plume ~90 km to the volcano's E; the plume was 45 km wide and at 7.6-9.1 km altitude. After that, Air Traffic Control in México City received no further pilot reports, and according to SAB, the plume dissipated in GOES-8 imagery around 2015.

A message from a United Airlines flight on 8 February around 0945 noted ash above México City at ~9.1 km altitude. Another pilot report noted that at 1715 there were narrow bands of ash at unspecified distances from the volcano at 5.5-6.1 km altitude, and farther S between 7.3 and 7.9 km altitude. A SIGMET issued in México City (valid during 1210-1800) warned of ash 28 km NE of the volcano between 5.2 and 6.4 km altitude. In addition, at 0945 a GOES-8 satellite image showed a plume near the summit extending S. By 1600 the eruption had stopped and radiosonde data established the plume at an altitude of ~9.4 km. At that time, the plume had become barely visible and rapidly fading on infrared imagery; it had moved 37 km SSE.

The third message, from a United Airlines flight at 0815 on 12 March, noted an eruption then. GOES-8 satellite imagery indicated a plume oriented ESE (on a bearing of 110 degrees). The plume extended for 70 km by 0945; at that time it was very narrow, linear, and at ~7.9 km altitude. Later, at 1115, a faint fan-shaped plume reached 55 km wide at 135 km SE of the volcano. The plume became covered by high-altitude weather clouds by 1315.

In addition, one available CENAPRED weekly seismic report (Number 59) covered the interval 7-13 April 1997; it showed a) the seismic and tiltmeter network (figure 16), b) computed epicenters during that time (figure 17), and c) cumulative seismicity for the interval 5 February 1996-15 April 1997 (figure 18). Figure 17 illustrates that many of the epicenters plot ~10 km SE of the crater. The epicenters SE of the crater caused investigators to ask if these earthquakes arose from volcanic or fault-related sources. To address this question, the investigators planned to deploy a network of portable broad-band seismometers to better cover this area.

Figure (see Caption) Figure 16. Popocatépetl seismic and tilt stations, February 1997. Courtesy of Roberto Quaas, CENAPRED-UNAM.
Figure (see Caption) Figure 17. Epicenters for Popocatépetl earthquakes registered on the monitoring network, 7-13 April 1997. The contour interval is 100 meters. Courtesy of Roberto Quaas, CENAPRED-UNAM.
Figure (see Caption) Figure 18. Number of weekly Popocatépetl earthquakes counted by visual inspection and using Xdetect software, 5 February-15 April 1997. The number of times alarms were triggered is also shown. Courtesy of Roberto Quaas, CENAPRED-UNAM.

Figure 18 shows monthly totals both for earthquakes counted by eye directly from the seismograms (higher bars) and by using software called Xdetect (lower bars). Although this latter technique detects events automatically, the totals (which depend on the trigger thresholds) are much smaller than counts made by eye.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: Roberto Meli, Roberto Quaas Weppen, Servando De la Cruz- Reyna1, Alejandro Mirano, Bertha López Najera, and Alicia Martinez Bringas, Centro Nacional de Prevencion de Desastres (CENAPRED), Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacan, 04360, México D.F., Mexico. 1Instituto de Geofisica, 1UNAM, Circuito Cientifico C.U.,04510 México D.F., México; NOAA/NESDIS Satellite Analysis Branch (SAB), Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA.


Rabaul (Papua New Guinea) — March 1997 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Lava flow issues from Tavurvur crater during 14 March eruption

On 14 March, a strong Strombolian and lava-producing eruption occurred at Tavurvur, the small active cone on the E side of the Rabaul Caldera (figure 29). This was the third eruption of this type since October 1996 (BGVN 21:12 and 22:01). Two photos of Tavurvur and vicinity from November 1996 show the effects of eruptions since 1994 (figures 30 and 31).

Figure (see Caption) Figure 29. Map of Rabaul Caldera showing locations of volcanic vents, selected towns, and features (modified from Almond and McKee, 1982).
Figure (see Caption) Figure 30. Photograph of a weakly steaming Tavurvur cone taken from the peninsula leading to Matupit Island, November 1996. Turanguna cone sits in the background. The abundant ash in the foreground was deposited during the 1994 eruption. Courtesy of Nancy Roper.
Figure (see Caption) Figure 31. Photograph of Tavurvur's extreme N flank (upper right edge), Turanguna (right background), and devastated groves and structures, November 1996. Courtesy of Nancy Roper.

Emissions from Tavurvur in early March consisted of pale gray vapor clouds that commonly rose ~600 m above the crater. Vulcanian explosions occurred occasionally and were commonly followed by ash emission lasting from 20 minutes to 2 hours. On 6 March, a Vulcanian explosion ejected lithic blocks that fell over the entire cone, the farthest reaching Greet Harbor (1 km from the vent). During the explosion, a small landslide on the NW flank of the volcano left a scar several hundred meters long.

At 0736 on 14 March a large and loud explosion was accompanied by a gray ash-rich eruption plume. Within an hour, Strombolian explosions ejected fragments that showered Tavurvur cone. By 0930, sub-continuous Strombolian eruptions occurred; these commonly produced loud detonations; in addition, flashing arcs were noted in the eruption plume. Some of the explosions sent "large lumps of lava" up to 1 km above the crater at intervals of <5 seconds. A short time later, the lava inside the crater almost reached the rim. Gas bubbles broke the surface and splashed spatter over the entire cone. By 1000, lava was flowing over the S lip of Tavurvur's crater. Though clinkery, the lava seemed relatively fluid and was 4-5 m thick. The flow progressed as two lobes. The lobes surrounded a bulge left by slumping of the S crater rim in January (BGVN 22:01) and partially overrode the October 1996 and January 1997 lava flows. The strength of the eruption did not begin to decrease until about 1530. By 2200 the eruption had declined to discontinuous explosions. Lava reached the sea near Sulphur Point sometime during the night (figure 29).

Due to a strong wind, the eruption plume was dispersed to the SW and remained below 2 km in height. Approximately 2 km SW, the town of Talway accumulated a 13-cm-thick pumiceous deposit. The detonations were very loud in the Kokopo area, 14 km SW. The Tokua airport ~20 km SW was closed for most of the day due to the threat of ashfall.

On 15 March, strong eruptions continued at intervals of minutes to hours and eruption plumes rose 400-600 m. Occasionally a peculiar pulsating roaring sound was heard that generally correlated with periods of harmonic tremor.

The level of activity continued to decrease between 16 and 19 March. There were progressively less frequent, but still loud, explosions with occasional roaring sounds. For the remainder of March, the level of activity was low, with weak white plumes rising to ~500 m above the crater. Occasionally, large explosions sent plumes as high as 3,000 m above the crater.

Seismicity began to increase on 7 March and reached 300 events/day with real-time seismic amplitude measurement (RSAM) levels rising to ~60-120. Levels decreased during 11-12 March but increased again on the 13th. During the eruption on 14 March, RSAM levels reached a plateau of ~ 850, similar to October 1996 and January 1997 eruption levels. By 2200 on 14 March, RSAM levels had dropped to ~100. A few intervals of harmonic tremor were recorded on 18-20, 22, 24-25, and 28 March.

Correlation spectrometer (COSPEC) measurements early in the month revealed SO2 fluxes of <250 tons/day. Between 14 and 17 March, SO2 fluxes increased to 400-700 tons/day before returning to background levels on 18 March. By the end of March, SO2 fluxes began to rise again.

In response to the eruption, the SCK water-tube tiltmeter 3.3 km NW of Tavurvur showed a radial deflation of 11 µrad (compared to 16 µrad and 11 µrad during the October and January eruptions, respectively). By the end of the month, radial inflation began to increase again.

Reference. Almond, R.A., and McKee, C.O., 1982, Location of volcano-tectonic earthquakes within the Rabaul Caldera: Geological Survey of Papua New Guinea report 82/19.

Geologic Background. The low-lying Rabaul caldera on the tip of the Gazelle Peninsula at the NE end of New Britain forms a broad sheltered harbor utilized by what was the island's largest city prior to a major eruption in 1994. The outer flanks of the 688-m-high asymmetrical pyroclastic shield volcano are formed by thick pyroclastic-flow deposits. The 8 x 14 km caldera is widely breached on the east, where its floor is flooded by Blanche Bay and was formed about 1400 years ago. An earlier caldera-forming eruption about 7100 years ago is now considered to have originated from Tavui caldera, offshore to the north. Three small stratovolcanoes lie outside the northern and NE caldera rims. Post-caldera eruptions built basaltic-to-dacitic pyroclastic cones on the caldera floor near the NE and western caldera walls. Several of these, including Vulcan cone, which was formed during a large eruption in 1878, have produced major explosive activity during historical time. A powerful explosive eruption in 1994 occurred simultaneously from Vulcan and Tavurvur volcanoes and forced the temporary abandonment of Rabaul city.

Information Contacts: B. Talai, H. Patia, D. Lolok, P. de Saint Ours, and C. McKee, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea; Bureau of Meteorology, Northern Territory Regional Office, P.O. Box 735, Darwin, NT 0801 Australia.


Santa Maria (Guatemala) — March 1997 Citation iconCite this Report

Santa Maria

Guatemala

14.757°N, 91.552°W; summit elev. 3745 m

All times are local (unless otherwise noted)


Reports of 6 February dome collapse proven false

Reports of a significant dome collapse at Santiaguito on 6 February were proven false during investigations conducted by geologists from the Instituto Nacional de Sismología, Vulcanología, Meteorología e Hydrología (INSIVUMEH). It is likely that minor downslope movement of loose debris near the summit caused the report.

At 1900 and 2100 on 11 February, local residents from farms S of the dome saw a significant dacitic lava flow.

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: Otoniel Matías, INSIVUMEH, Guatemala; Barry Cameron and Shane Rundle, Northern Illinois University, USA.


Sheveluch (Russia) — March 1997 Citation iconCite this Report

Sheveluch

Russia

56.653°N, 161.36°E; summit elev. 3283 m

All times are local (unless otherwise noted)


Steam and ash plume rises 1.5 km above the crater

On 25 March, a steam-and-ash plume rose ~1,500 m above the volcano and extended 30 km to the NW. During 26-31 March the usual fumarolic activity was observed above the crater. A steam-and-ash plume at 100- 200 m above the crater was also reported during 1-4 April.

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: Tom Miller, Alaska Volcano Observatory (AVO), a cooperative program of a) U.S. Geological Survey, 4200 University Drive, Anchorage, AK 99508-4667, USA (URL: http://www.avo.alaska.edu/), b) Geophysical Institute, University of Alaska, PO Box 757320, Fairbanks, AK 99775-7320, USA, and c) Alaska Division of Geological & Geophysical Surveys, 794 University Ave., Suite 200, Fairbanks, AK 99709, USA; Vladimir Kirianov, Kamchatka Volcanic Eruptions Response Team (KVERT), Institute of Volcanic Geology and Geochemistry, Piip Ave. 9, Petropavlovsk-Kamchatsky, 683006, Russia.


Soufriere Hills (United Kingdom) — March 1997 Citation iconCite this Report

Soufriere Hills

United Kingdom

16.72°N, 62.18°W; summit elev. 915 m

All times are local (unless otherwise noted)


Pyroclastic flows advance over Galway's Wall on 29 March

The following summarizes the weekly Scientific Reports of the Montserrat Volcano Observatory for the period 9 March-5 April 1997.

Visual observations. During the first 20 days of March several ash clouds drifted W on the prevailing wind, small pyroclastic flows issued from the E and S areas of the dome, and small-scale rockfalls were confined to the area SE to NE of the dome complex.

Small, relatively cool, pyroclastic flows with a maximum run-out distance of ~1 km were almost continuous from the pre-17 September dome to the N of Galway's Wall (see map in BGVN 22:02). An erosional chute was formed in the pyroclastic-flow deposit leading out from the crater wall. Small landslides occurred from areas E and W of the point on the wall over which the flows traveled. On 18 March fresh deposits with well-developed levee structures reached beyond 1 km from the crater wall to the SW. On 20 March new fractures 100-150 m long and trending SSE were observed running through the S buttress of Galway's Wall, in the area adjacent to Perches Mountain.

Growth continued in the uppermost areas of the 20 January dome: during 13-21 March new spines appeared on the summit area and afterwards moved up toward the E side of the dome. Eventually extrusion in the summit region overgrew the original January scar and overall the shape of the dome changed from flat topped to a more conical geometry.

During the week of 22-29 March a large block tilting to the SSW appeared in the SW region of the dome complex. Two distinct peaks began to develop in the summit area of the dome, the highest being on the S side of the dome overlooking the Galway's Wall. A cleft formed between the two peaks, with material being extruded upwards and to the SW. The dome grew so much above Galway's Wall that there was no barrier left between the new material and the wall itself. Fresh cracks were observed running through the E shoulder of the Galway's Wall on 25 March. Fresh landslide scars and cracks were observed in the Gages Wall on 26 and 28 March, but no fresh activity was noted in the dome behind and above it.

At 1630 on 29 March a large pyroclastic flow occurred over the Galway's Wall into the White River valley. The flow traveled ~400 m farther than previous flows in this region and produced a dark ash cloud that rapidly convected to ~1,500 m. Activity increased at around 1330 on 30 March when another pyroclastic flow occurred over Galway's Wall from the SE summit. Observations from the helicopter of the Galway's Soufriere region revealed that the pyroclastic material was cascading over the Galway's Wall almost contiguously, with the higher velocity flows surging through the smaller, slower-moving flows. Vigorously convecting, co-ignimbrite-type ash clouds rose to heights of 3.5 km. Pyroclastic-flow activity waned at around 1630 after flows traveled 3.6 km down the White River and caused some burning of vegetation. Trees in the distal portion of the flows remained standing, suggesting sluggish movement of flows in the lower part of the valley.

The intense pyroclastic flow activity on 31 March sent material only ~50 m farther down the White River than the previous day. Pyroclastic flows observed from a helicopter on 31 March were valley-confined; on the W side of Galway's Soufriere there were fine-grained deposits and tree flattening associated with pyroclastic surges. Considerable ponding of pyroclastic-flow deposits had occurred, and the Great Alps Falls in the White river were reduced to only ~10 m high from the original 50 m. Finally it was observed that the pyroclastic flows had cut a gully 80 m deep and 50 m wide into Galway's Wall.

The "Easter scar"— the collapse scar formed in the dome complex — was composed of two scallops, one in the 20 January dome with a near vertical head wall, and the second cut into the pre-September dome. Growth of the dome since collapse, and rockfall debris, have rapidly begun to fill the scar.

At around 1500 and 1515 on 31 March two major pyroclastic flows from the NE summit of the dome occurred in the Tar River to the E. The first flow reached ~200 m past the first break in slope, the second flow reached to within ~50 m of the fan. Temperature patches positioned down the track leading into the Tar River valley were engulfed by the surge clouds of the latter flow, and indicated temperatures of 99-149°C for lateral distances of 60 m inside the pyroclastic surge.

Several relatively large pyroclastic flows occurred over the Galway's Wall starting from 1230 on 1 April, but none of them reached as far as those on the 30 and 31 March although considerably more tree flattening occurred in the area directly W of the Galway's Soufriere. This indicated that these flows had a large surge component, probably due to the earlier valley filling.

Large ash clouds associated with the flows rose to 4.3 km and drifted NW producing ash fall over large part of the island as far N as St Peters and St Johns. On 2 April more pyroclastic flows over Galway's Wall generated ash clouds to ~3.3 km of altitude.

Dome growth since the collapse was confined to the Easter scar with upward and southward growth of the steep head wall. The actively growing area had a smooth, scabby, arcuate upper surface with local fractures and N-S running striations indicative of extrusion. Vigorous brown gas jets were seen emerging from cracks in the upper surface. Rockfall debris began to fill the chute carved by the pyroclastic flows into the Galway's wall toward the end of the reporting period. Mudflows during the nights of 3 and 4 April in Fort Ghaut and Aymer's Ghaut left debris on roads and close to houses.

Seismicity. During 8-21 March there were swarms of mainly hybrid events interspersed with periods of relative quiescence. The foci were located at 1-3 km depth below the crater area. Rockfall activity was mainly concentrated in periods between the earthquake swarms, although some of the larger events during a swarm were followed by rockfall and pyroclastic signals from material cascading over the Galway's Wall.

After 22 March the seismicity decreased. The swarms became shorter and less intense, whereas there was a slight increase in the level of rockfall activity and in the number of long-period earthquakes. Occasionally long- period events were present for a few days to weeks, with a maximum of 40 events/day, mostly very small. About 50% of the long-period earthquakes were immediately followed by rockfall signals, as in October and December 1996. It is possible that the long-period events are caused by some dome process, such as gas venting or a sudden growth spurt that leads to partial collapse.

During 30 March-2 April, the dominant seismicity was related to dome collapse, with many rockfall and pyroclastic-flow signals. The level of rockfall and long-period activity decreased abruptly on 3 April, when a swarm of volcano-tectonic events followed by hybrid earth a very slow trend of shortening, respectively. EDM measurements on the N triangle (Windy Hill-Farrells-St. George's Hill) showed an overall stable trend. On 29 March a very slow shortening trend was recorded for the line Windy Hill-St. George's Hill: the total shortening over the past 15 months was ~15 mm.

GPS occupations on 10-11 March with a base station at Harris showed that Hermitage station had moved by 2.5 cm to the NNE since 18 January and had risen by ~9 cm. A GPS occupation of the Eastnet on 15 March recorded a total movement of 2.5 cm to the NNE for Farrells station, ~700 m from the N edge of the dome, since 13 June 1996. During 22-29 March GPS occupations with a base at Harris showed that Station FT3 (Farrells Crater Wall) , had moved 17.6 cm to the NW since 18 January (2.7 mm/day), Hermitage had no significant movement since 17 March, and Perches recorded a 1.6 cm movement to the N since 18 January.

A new crack on the shoulder of Galway's Mountain was measured for the first time on 25 March, with nails hammered into trees on either side of the crack. One array of nails was placed on the steep flank of the mountain at ~ 50 m from the crater wall; the second array was 90 m to the S in a flatter area. All the lines measured on 28 March showed no significant changes in length.

The GPS occupation of Eastnet on 30-31 March and 4 April revealed that the Farrells site had moved ~4 cm to the N since June 1996 at an increasing rate of movement.

Both the GPS and EDM techniques showed the ongoing slow deformation of the N crater wall in the Farrells area; deformation rate drops rapidly with distance from the dome. Neither technique was able to detect any significant deformation around the volcano.

Dome volume measurements. A survey completed on 14 March using the fixed location photographic method showed 1.34 x 106 m3 added to the dome since 1 March, at an average extrusion rate of 1.08 m3/s.

A GPS survey of the talus at the base of the dome combined with the fixed-location photographic method and the GPS/range-finding binocular method resulted in an estimate of 0.8 x 106 m3 material added to the dome from 14 to 19 March. From the photographic profiles it became apparent that the summit dome had grown by 15 m during the same period.

Evidence was found that the pre-September scar material, surrounding the dome on the NW, W, and SW sides, was pushed outward by the growing dome. The amount of movement was 3.9 m during 23 November to 8 January (80 mm/day), and 9.1 m during 8 January-19 March 1997 (13 mm/day).

A GPS bathymetry survey around the pyroclastic fan at the foot of the Tar River Valley on 21 March, combined with a survey of the fan surface on 12 February resulted in a total fan volume estimate of 15.5 x 106 m3.

The results of a 27 March GPS survey indicated that since 19 March the dome volume had increased by 0.98 x 106 m3, at a rate of 1.26 m3/s. This gave a total dome volume of 49.7 x 106 m3 (44.7 x 106 m3 DRE). Digital elevation models created from this survey indicated that growth was focused on the S peak of the dome and the rest of the dome remained relatively unchanged. A GPS dome survey on 2-3 April indicated that the last collapse removed ~1.6 x 106 m3 of material, of which roughly 40% was preSeptember 1996 scar material and 60% new dome material.

Environmental monitoring. Measurements of sulfur dioxide flux were made using the MiniCOSPEC on 10, 14, 15, 17, 24, 28 March, and 4 April and results were as follows: 700, 213, 341, 317, 198, 160, and 573 t/d respectively. The high values on 10 March and 4 April were associated with the recurrence of earthquake swarms and an increase in activity, respectively.

Results for SO2 diffusion tubes collected during the period 9-23 February showed values similar to those measured over the last few months and are presented in table 15.

Table 15. Sulfur dioxide diffusion tube results at Soufriere Hills for the period between 9 February and 23 February 1997. Courtesy of MVO.

Location SO2 (ppb)
Upper Amersham 47.70
Lower Amersham 17.30
Airport 0.80
Police HQ, Plymouth 9.00
Weekes 9.00
Control 0.00

Results from rain water samples collected at 4 locations around the volcano on 9, 16, 23, and 31 March, showed that the rainwater directly W of the volcano was still highly acidic and had high concentrations of certain anions (table 16). One sample collected from the overflow of Trials reservoir in Fairfield was within World Health Organization levels for all measured components.

Table 16. Rain and surface water geochemistry at Montserrat. Courtesy of MVO.

Date Location pH Conductivity (mS/cm) Total Dissolved Solids (g/l) Sulfates (mg/l) Chlorides (mg/l) Fluorides (mg/l)
09 Mar 1997 Upper Amersham 2.39 2.120 1.050 25 250 1.5
09 Mar 1997 Lower Amersham 2.55 1.162 0.582 16 115 1.5
09 Mar 1997 Police HQ, Plymouth 2.57 0.926 0.464 -- 97 1.5
09 Mar 1997 Weekes 6.49 0.172 0.086 -- 27 0.3
16 Mar 1997 Upper Amersham 2.39 1.883 0.942 34 232 1.35
16 Mar 1997 Lower Amersham 2.70 0.731 0.366 8 100 1.5
16 Mar 1997 Police HQ, Plymouth 2.81 0.571 0.285 3 68 1.4
16 Mar 1997 Weekes 6.11 0.070 0.035 -- 14.4 0.1
16 Mar 1997 Trials Reservoir 7.55 0.659 0.330 40 83 0.55
23 Mar 1997 Upper Amersham 2.28 2.41 1.20 36 211 1.45
23 Mar 1997 Trials Reservoir 7.63 0.675 0.388 39 76 0.40

The maximum thickness of ash collected on 31 March in Plymouth was 16 mm, at the American University of the Caribbean, and the total erupted airborne ash volume on 30-31 March was calculated to be 0.1 x 106 m3, dense rock equivalent (DRE).

Geologic Background. The complex, dominantly andesitic Soufrière Hills volcano occupies the southern half of the island of Montserrat. The summit area consists primarily of a series of lava domes emplaced along an ESE-trending zone. The volcano is flanked by Pleistocene complexes to the north and south. English's Crater, a 1-km-wide crater breached widely to the east by edifice collapse, was formed about 2000 years ago as a result of the youngest of several collapse events producing submarine debris-avalanche deposits. Block-and-ash flow and surge deposits associated with dome growth predominate in flank deposits, including those from an eruption that likely preceded the 1632 CE settlement of the island, allowing cultivation on recently devegetated land to near the summit. Non-eruptive seismic swarms occurred at 30-year intervals in the 20th century, but no historical eruptions were recorded until 1995. Long-term small-to-moderate ash eruptions beginning in that year were later accompanied by lava-dome growth and pyroclastic flows that forced evacuation of the southern half of the island and ultimately destroyed the capital city of Plymouth, causing major social and economic disruption.

Information Contacts: Montserrat Volcano Observatory (MVO), c/o Chief Minister's Office, PO Box 292, Plymouth, Montserrat (URL: http://www.mvo.ms/).


Stromboli (Italy) — March 1997 Citation iconCite this Report

Stromboli

Italy

38.789°N, 15.213°E; summit elev. 924 m

All times are local (unless otherwise noted)


Summary of seismic and volcanic activity during May 1996-January 1997

The following summarizes the interval from 15 May 1996 to 31 January 1997. Eruptive activity increased in mid-April 1996 (BGVN 21:04) and continued through mid-June with significant explosions (BGVN 21:05). A flight on 16 July 1996 documented a plume rising from Stromboli using a Wide Angle Optoelectronic Stereo Scanner (figure 50). This image of the entire island also shows older lava flows, the Sciara del Fuoco, and the Pizzo Sopra La Fossa (120 m above and 250 m SE of the vent), where people often make observations from.

Figure (see Caption) Figure 50. Wide Angle Optoelectronic Stereo Scanner (WAOSS) image of Stromboli taken on 16 July 1996. Courtesy of Martin Scheele, DLR.

Figure 51 illustrates the change in crater morphology between April 1996 and September 1996. Unfortunately the morphological changes in Crater 1 (typically a site of ongoing changes) were obscured on the September stereo photographs; however, the other two craters underwent noteworthy changes. In Crater 3, the front vent (3/3), which was essentially a pit in April, had become a small cone by September as a tephra apron enclosed the vent. In the westernmost part of Crater 3, vents 3/1 and 3/2 merged into a single chasm distinct from the rest of the crater.

Figure (see Caption) Figure 51. Sketches made from terrestrial stereo photographs shot on 25 April 1996 and 19 September 1996. View is towards the NW. The sketches allow comparison of morphological changes in the crater area between these two dates; vents and craters labeled 3/2? and 3/3? were inferred indirectly from ejecta trajectories; areas labeled "?" were obscured by particulate and gases. Courtesy of Jürg Alean (original photos by Alean and Carniel).

During the first half of August the activity increased at Crater 3, in particular at vent 3/1, where the magma rose to increasingly shallow levels. During 16--17 August 1996, amid vigorous seismicity (figure 52), local volcano guide Nino Zerilli saw a small lava flow discharged from vent 3/1. The lava flow proceeded for only a few meters inside the crater and stopped by the evening of 18 August. Around this same time interval magma also reached high levels in Crater 1.

On 22 August 1996 at 0230 a tourist was hit by volcanic ejecta while in a sleeping bag ~80 m from the crater. He had to be transported by helicopter to Messina for head surgery. Zerilli reported that during the previous days ejecta from Crater 3 had been thrown as far as observation sites between the Pizzo and Crater 3. Thus, this injury appeared to have been more a case of camping too close to the crater rather than an especially violent outburst that particular night.

By 26 August, vent 3/1 was completely inactive, whereas vents 3/2 and 3/3 had almost joined, and their activity consisted of very powerful Strombolian explosions sending small fragments onto the Pizzo. At Crater 1, vent 1/4 only rarely exploded but did so with strong gas jets. In contrast, vent 1/3 ceased the continuous activity that it had begun on 16 April 1996, a change interpreted as either another pause there or the end of an unusually long period of continuous spattering.

On 4 September 1996 at 1545 a blast threw incandescent pyroclastic material onto slope vegetation. This started several fires and the explosion was clearly heard and watched from the village of Stromboli. According to the local newspaper "Il Piccolo" some tourists were caught by the explosion in the crater area and six of them were slightly injured. After this, the Mayor of Lipari ordered the closure of the path to the craters. After the blast, however, Strombolian activity continued to decrease. In terms of seismicity, both the number of major events and the total number of events decreased to very low values, a situation which prevailed through the end of January 1997 (figure 52).

Figure (see Caption) Figure 52. Seismicity recorded at Stromboli 15 May 1996-31 January 1997. Open bars show the number of recorded events/day, and the solid bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is 300 m from the craters at 800 m elevation. Arrows highlight the two powerful explosions of 1 June and 4 September 1996. Courtesy of R. Carniel.

A visit by Carniel at the end of September revealed extremely low activity as judged by the few audible eruptions seen or heard; however, smoke often covered most of the crater area. Remarkable were some very long rumbles, which could be heard even from the village of Stromboli. These rumbles were probably associated with strong degassing from Crater 2, although this interpretation remained unconfirmed by direct observation.

Matthias Hort and Ralf Seyfried visited and photographed portions of the volcano during 30 September-2 October (figures 53 and 51). They witnessed small eruptions from vent 2 at Crater 3. These eruptions took place while Craters 1 and 2 were inactive. Rumbling noises heard on 30 September from Crater 1 disappeared within the next two days. Overall, activity gradually declined from 30 September to 2 October. According to Hort, the most spectacular event during the observation period was an ash emission that produced a plume to 100 m above the craters. Periods of up to 2 hours passed without eruption.

Figure (see Caption) Figure 53. Ash and bomb emission from Crater 3 seen from Pizzo on 30 September 1996. Courtesy of Matthias Hort, GEOMAR.
Figure (see Caption) Figure 54. View of vent 1 in Crater 3, 30 September 1996. Bright incandescence is seen during daylight, indicating active magma at shallow depth. Courtesy of Matthias Hort, GEOMAR.

On the evening of 10 October Boris Behncke saw two lava fountains shooting up from Crater 3 during a 5- minute interval, reaching 80-100 m above the vent (to the height of Pizzo sopra la Fossa). Each fountain lasted ~20 seconds. About 10 minutes after the second fountain, an eruption apparently occurred at Crater 1.

Unusually low seismic activity appeared on 10 November, when the seismic station recorded only 17 events within 24 hours (none of them saturating the acquisition system). Exceptionally long intervals without a single event occurred on several other days: 7 hours on 25 October, 8 hours on 10 November, 10 hours during the night between 12 and 13 November. Although the tremor intensity slowly increased from September 1996 (1-2 V.s) to January 1997 (3-5 V.s), there was no significant increase in the number of recorded events or saturating events. Thus, activity at the end of January was still considered "low to moderate."

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period from about 13,000 to 5000 years ago was followed by formation of the modern edifice. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5000 years ago as a result of the most recent of a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Roberto Carniel, Dipartimento di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine; Jürg Alean, Kantonsschule Zürcher Unterland, CH-8180 Bülach, Switzerland; Matthias Hort, Ralf Seyfried, and Boris Behncke, Geomar Research Center for Marine Geosciences, Wischhofstrasse 1-3, 24148 Kiel, Germany; Martin Scheele, Institut für Weltraumsensorik (Institute for Space Sensor Technology), Deutsche Forschungsanstalt für Luft- und Raumfahrt (German Aerospace Research Establishment), Forschungszentrum Berlin-Adlershof, Rudower Chaussee 5, 12489 Berlin (URL: http://www.dlr.de/).


Telica (Nicaragua) — March 1997 Citation iconCite this Report

Telica

Nicaragua

12.606°N, 86.84°W; summit elev. 1036 m

All times are local (unless otherwise noted)


Seismicity increases and fumarolic activity continues

On 27 February, during a visit to the summit crater, scientists noted continuing minor fumarolic activity with maximum temperatures of 300-350°C and an active collapse zone on the E crater rim (figure 10). At this time a portable seismic station recorded microearthquakes at 30-40 minute intervals. Night observations of the crater confirmed the absence of any incandescence.

Figure (see Caption) Figure 10. Sketch of the active crater at Telica indicating areas of fumarolic activity. Temperature is degrees C. Courtesy of Alain Creusot.

During March 1997, seismicity was high with about 150 seismic signals/day recorded. Seismicity levels increased from December 1996, when there were less than 100 signals/day. Most March events had frequencies of 1.5-4.6 Hz and durations of 9-40 seconds. Visits to the summit crater showed the presence of fresh ashfall, numerous small landslides inside the crater, and moderate fumarolic activity in the walls and floor of the crater. Scientists also measured Telica's gas emissions, thermal infrared signals, and microgravity. Small amounts of gas were emitted from fumaroles on the E and W crater walls; however, COSPEC measurements failed to detect any SO2, although local farmers smelled sulfur in the afternoon when the wind shifted to the W. Thus, the amount of released gas appeared to be less than in March 1996.

Fumaroles located along a NE-SW trending fracture near the seismic station outside the active crater had maximum temperatures of 85°C. Soil gas measurements made along the fracture on 11 March 1997 showed maximum CO2 concentrations of 3.2%. This fracture first appeared in September 1996.

Infrared camera measurements on 20 March 1997 detected a zone of high temperatures near the base of the W crater wall. This zone had temperatures up to 190°C. Since this was a remote measurement, it should be considered as a minimum estimate. The crater fumaroles were at a lower temperature than those at the base of the W crater wall. Minimum temperatures measured with the infrared camera were 58°C for fumaroles on the W side, 47°C for fumaroles on the N wall, and 107°C for fumaroles on the E wall.

On 20 March, gravity measurements with a Lacoste and Roberg meter near the crater measured a repetitive signal with a periodicity of about 18 seconds. Also, on 23 March, a large gas emission from the crater was visible at the seismic station.

An eruption on 31 July 1994 produced a gas-and-ash column to ~ 800 m above the summit; detectable ash fell as far as 17 km from the summit (BGVN 19:07). Phreatic explosions continued until 12 August 1994 when seismicity began decreasing (BGVN 19:09).

Geologic Background. Telica, one of Nicaragua's most active volcanoes, has erupted frequently since the beginning of the Spanish era. This volcano group consists of several interlocking cones and vents with a general NW alignment. Sixteenth-century eruptions were reported at symmetrical Santa Clara volcano at the SW end of the group. However, its eroded and breached crater has been covered by forests throughout historical time, and these eruptions may have originated from Telica, whose upper slopes in contrast are unvegetated. The steep-sided cone of Telica is truncated by a 700-m-wide double crater; the southern crater, the source of recent eruptions, is 120 m deep. El Liston, immediately E, has several nested craters. The fumaroles and boiling mudpots of Hervideros de San Jacinto, SE of Telica, form a prominent geothermal area frequented by tourists, and geothermal exploration has occurred nearby.

Information Contacts: Hazel Rymer and Mark Davies, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; John Stix, Dora Knez, Glyn Williams-Jones, and Alexandre Beaulieu, Departement de Geologie, Universite de Montreal, Montreal, Quebec H3C 3J7, Canada; Nicki Stevens, Department of Geography, University of Reading, Reading RG2 2AB, United Kingdom; Martha Navarro and Pedro Perez, INETER, Apartado Postal 2110, Managua, Nicaragua; Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua

Atmospheric Effects

The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

View Atmospheric Effects Reports

Special Announcements

Special announcements of various kinds and obituaries.

View Special Announcements Reports

Additional Reports

Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


Additional Reports (database)

08/1997 (BGVN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (BGVN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

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.


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

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.


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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 (see Caption) 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 (see Caption) 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 (see Caption) 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.


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

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/).