Logo link to homepage

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

Masaya (Nicaragua) Lava lake persists with decreased thermal output, November 2018-February 2019

Santa Maria (Guatemala) Daily explosions cause steam-and-ash plumes and block avalanches, November 2018-February 2019

Reventador (Ecuador) Multiple daily explosions with ash plumes and incandescent blocks rolling down the flanks, October 2018-January 2019

Kuchinoerabujima (Japan) Weak explosions and ash plumes beginning 21 October 2018

Kerinci (Indonesia) A persistent gas-and-steam plume and intermittent ash plumes occurred from July 2018 through January 2019

Yasur (Vanuatu) Eruption continues with ongoing explosions and multiple active crater vents, August 2018-January 2019

Ambae (Vanuatu) Ash plumes and lahars in July 2018 cause evacuation of the island; intermittent gas-and-steam and ash plumes through January 2019

Agung (Indonesia) Ongoing intermittent ash plumes and frequent gas-and-steam plumes during August 2018-January 2019

Erebus (Antarctica) Lava lakes persist through 2017 and 2018

Villarrica (Chile) Intermittent Strombolian activity ejects incandescent bombs around crater rim, September 2018-February 2019

Popocatepetl (Mexico) Explosions with ash plumes and incandescent ejecta continue during September 2018-February 2019

Pacaya (Guatemala) Continuous activity from the cone in Mackenney crater; daily lava flows on the NW flank during October 2018-January 2019



Masaya (Nicaragua) — March 2019 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 with decreased thermal output, November 2018-February 2019

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 an actively circulating 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. 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 which has varied in strength but continued at a moderate level into early 2019. Information for this report, which covers the period from November 2018 through February 2019, is provided by the Instituto Nicareguense de Estudios Territoriales (INETER) and satellite -based imagery and thermal data.

The lava lake in Santiago Crater remained visible and active throughout November 2018 to February 2019 with little change from the previous few months (figure 70). Seismic amplitude RSAM values remained steady, oscillating between 10 and 40 RSAM units during the period.

Figure (see Caption) Figure 70. A small area of the lava lake inside Santiago Crater at Masaya was visible from the rim on 25 November 2018 (left) and 17 January 2019 (right). Left image courtesy of INETER webcam; right image courtesy of Alun Ebenezer.

Every few months INETER carries out SO2 measurements by making a transect using a mobile DOAS spectrometer that samples for gases downwind of the volcano. Transects were done on 9-10 October 2018, 21-24 January 2019, and 18-21 February 2019 (figure 71). Average values during the October transect were 1,454 tons per day, in January they were 1,007 tons per day, and in February they averaged 1,318 tons per day, all within a typical range of values for the last several months.

Figure (see Caption) Figure 71. INETER carries out periodic transects to measure SO2 from Masaya with a mobile DOAS spectrometer. Transects taken along the Ticuantepe-La Concepcion highway on 9-10 October 2018 (left) and 21-24 January 2019 (right) showed modest levels of SO2 emissions downwind of the summit. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua. Octubre 2018 and Enero 2019).

During a visit by INETER technicians in early November 2018, the lens of the Mirador 1 webcam, that had water inside it and had been damaged by gases, was cleaned and repaired. During 21-24 January 2019 INETER made a site visit with scientists from the University of Johannes Gutenberg in Mainz, Germany, to measure halogen species in gas plumes, and to test different sampling techniques for volcanic gases, including through spectroscopic observations with DOAS equipment, in-situ gas sampling (MultiGAS, denuders, alkaline traps), and using a Quadcopter UAV (drone) sampling system.

Periodic measurements of CO2 from the El Comalito crater have been taken by INETER for many years. The most recent observations on 19 February 2019 indicated an emission rate of 46 +/- 3 tons per day of CO2, only slightly higher than the average value over 16 measurements between 2008 and 2019 (figure 72).

Figure (see Caption) Figure 72. CO2 measurements taken at Masaya on 19 February 2019 were very close to the average value measured during 2008-2019. Courtesy of INETER (Boletín Sismos y Volcanes de Nicaragua, Febrero 2019).

Satellite imagery (figure 73) and in-situ thermal measurements during November 2018-February 2019 indicated constant activity at the lava lake and no significant changes during the period. On 14 January 2019 temperatures were measured with the FLIR SC620 thermal camera, along with visual observations of the crater; abundant gas was noted, and no explosions from the lake were heard. The temperature at the lava lake was measured at 107°C, much cooler than the 340°C measured in September 2018 (figure 74).

Figure (see Caption) Figure 73. Sentinel-2 satellite imagery (geology, bands 12, 4, and 2) clearly indicated the presence of the active lava lake inside Santiago crater at Masaya during November 2018-February 2019. North is to the top, and the Santigo crater is just under 1 km in diameter for scale. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 74. Thermal measurements were made at Masaya on 14 January 2019 with a FLIR SC620 thermal camera that indicated temperatures over 200°C cooler than similar measurements made in September 2018.

Thermal anomaly data from satellite instruments also confirmed moderate levels of ongoing thermal activity. The MIROVA project plot indicated activity throughout the period (figure 75), and a plot of the number of MODVOLC thermal alerts by month since the lava lake first appeared in December 2015 suggests constant activity at a reduced thermal output level from the higher values in early 2017 (figure 76).

Figure (see Caption) Figure 75. Thermal anomalies remained constant at Masaya during November 2018-February 2019 as recorded by the MIROVA project. Courtesy of MIROVA.
Figure (see Caption) Figure 76. The number of MODVOLC thermal alerts each month at Masaya since the lava lake first reappeared in late 2015 reached its peak in early 2017 and declined to low but persistent levels by early 2018 where they have remained for a year. Data courtesy of MODVOLC.

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

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


Santa Maria (Guatemala) — March 2019 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 cause steam-and-ash plumes and block avalanches, November 2018-February 2019

The dacitic Santiaguito lava-dome complex on the W flank of Guatemala's Santa María volcano has been growing and actively erupting since 1922. The youngest of the four vents in the complex, Caliente, has been erupting with ash explosions, pyroclastic, and lava flows for more than 40 years. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Daily explosions of steam and ash also continued during November 2018-February 2019, the period covered in this report, with information primarily from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and the Washington VAAC (Volcanic Ash Advisory Center).

Activity at Santa Maria continued with little variation from previous months during November 2018-February 2019. Plumes of steam with minor magmatic gases rose continuously from the Caliente crater 100-500 m above the summit, generally drifting SW or SE before dissipating. In addition, daily explosions with varying amounts of ash rose to altitudes of around 2.8-3.5 km and usually extended 20-30 km before dissipating. Most of the plumes drifted SW or SE; minor ashfall occurred in the adjacent hills almost daily and was reported at the fincas located within 15 km in those directions several times each month. Continued growth of the Caliente lava dome resulted in daily block avalanches descending its flanks. The MIROVA plot of thermal energy during this time shows a consistent level of heat flow with minor variations throughout the period (figure 89).

Figure (see Caption) Figure 89. Persistent thermal activity was recorded at Santa Maria from 6 June 2018 through February 2019 as seen in the MIROVA plot of thermal energy derived from satellite thermal data. Daily explosions produced ash plumes and block avalanches that were responsible for the continued heat flow at the volcano. Courtesy of MIROVA.

During November 2018 steam plumes rose to altitudes of 2.8-3.2 km from Caliente summit, usually drifting SW, sometimes SE. Several ash-bearing explosions were reported daily, rising to 3-3.2 km altitude and also drifting SW or SE. The highest plume reported by INSIVUMEH rose to 3.4 km on 25 November and drifted SW. The Washington VAAC reported an ash emission on 9 November that rose to 4.3 km altitude and drifted W; it dissipated within a few hours about 35 km from the summit. On 11 November another plume rose to 4.9 km altitude and drifted NW. INSIVUMEH issued a special report on 2 November noting an increase in block avalanches on the S and SE flanks, many of which traveled from the crater dome to the base of the volcano. Nearly constant avalanche blocks descended the SE flank of the dome and occasionally traveled down the other flanks as well throughout the month. They reached the bottom of the cone again on 29 November. Ashfall was reported around the flanks more than once every week and at Finca Florida on 12 November. Finca San Jose reported ashfall on 11, 13, and 23 November, and Parcelamiento Monte Claro reported ashfall on 15, 24, 25, and 27 November.

Constant degassing from the Caliente dome during December 2018 formed white plumes of mostly steam that rose to 2.6-3.0 km altitude during the month. Weak explosions averaging 9-13 per day produced gray ash plumes that rose to 2.8-3.4 km altitude. The Washington VAAC reported an ash emission on 4 December that extended 25 km SW of the summit at 3.0 km altitude and dissipated quickly. Small ash plumes were visible in satellite imagery a few kilometers WNW on 8, 12, 30, and 31 December at 4.3 km altitude; they each dissipated within a few hours. Ashfall was reported in Finca Monte Claro on 1 and 4 December, and in San Marcos Palajunoj on 26 and 30 December along with Loma Linda. On 28 December ashfall on the E flank affected the communities of Las Marías, Calahuache, and El Nuevo Palmar. Block avalanches occurred daily, sending large blocks to the base of the volcano that often stirred up small plumes of ash in the vicinity (figure 90).

Figure (see Caption) Figure 90. Activity during December 2018 at Santa Maria included constant degassing of steam plumes, weak explosions with ash plumes, and block avalanches rolling down the flanks to the base of the cone. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Diciembre 2018).

Multiple explosions daily during January 2019 produced steam-and-ash plumes (figure 91). Constant degassing rising 10-500 m emerged from the SSE part of the Caliente dome, and ashfall, mainly on the W and SW rim of the cone, was a daily feature. Seismic station STG-3 detected 10-18 explosions per day that produced ash plumes, which rose to between 2.7 and 3.5 km altitude. The Washington VAAC noted a faint ash emission in satellite imagery on 1 January that was about 25 km W of the summit at 4.3 km altitude. A new emission appeared at the same altitude on 4 January about 15 km NW of the summit. A low-density emission around midday on 5 January produced an ash plume that drifted NNE at 4.6 km altitude. Ash plumes drifted W at 4.3 km altitude on 11 and 14 January for short periods of time before dissipating.

Figure (see Caption) Figure 91. Explosions during January produced numerous steam-and-ash plumes at the Santiaguito complex of Santa Maria. A moderate explosion on 31 January 2019 produced an ash plume that rose to about 3.1 km altitude (top). A thermal image and seismograph show another moderate explosion on 18 January 2019 that also rose nearly vertically from the summit of Caliente. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Ash drifted mainly towards the W, SW, and S, causing ashfall in the villages of San Marcos Palajunoj, Loma Linda, Monte Bello, El Patrocinio, La Florida, El Faro, Patzulín and a few others several times during the month. The main places where daily ashfall was reported were near the complex, in the hilly crop areas of the El Faro and San José Patzulín farms (figure 92). Blocks up to 3 m in diameter reached the base of the complex, stirring up ash plumes that settled on the immediate flanks. Juvenile material continued to appear at the summit of the dome during January; the dome had risen above the edge of the crater created by the explosions of 2016. Changes in the size and shape of the dome between 23 November 2018 and 13 January 2019 showed the addition of material on the E and SE side of the dome, as well as a new effusive flow that travelled 200-300 m down the E flank (figure 93).

Figure (see Caption) Figure 92. Near-daily ashfall affected the coffee plants at the El Faro and San José Patzulín farms (left) at Santiaguito during January 2019. Large avalanche blocks descending the flanks, seen here on 23 January 2018, often stirred up smaller ash plumes that settled out next to the cone. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).
Figure (see Caption) Figure 93. A comparison of the growth at the Caliente dome of the Santiaguito complex at Santa Maria between 23 November 2018 (top) and 13 January 2019 (bottom) shows the emergence of juvenile material and a 200-300 m long effusive flow that has moved slowly down the E flank. Courtesy of INSIVUMEH (Informe mensual de actividad Volcanica enero 2019, Volcan Santiaguito).

Persistent steam rising 50-150 m above the crater was typical during February 2019 and accompanied weak and moderate explosions that averaged 12 per day throughout the month. White and gray ash plumes from the explosions rose to 2.8-3.3 km altitude; daily block avalanches usually reached the base of the dome (figure 94). Ashfall occurred around the complex, mainly on the W, SW, and NE flanks on a daily basis, but communities farther away were affected as well. The Washington VAAC reported an ash plume on 7 February in visible satellite imagery moving SW from the summit at 4.9 km altitude. The next day a new ash plume was located about 20 km W of the summit, dissipating rapidly, at 4.3 km altitude. Ashfall drifting SW affected Palajuno Monte Claro on 5, 9, 15, and 16 February. Ash drifting E and SE affected Calaguache, Las Marías and surrounding farms on 14 and 17 February, and fine-grained ash drifting SE was reported at finca San José on 21 February.

Figure (see Caption) Figure 94. Activity at the Caliente dome of the Santiaguito complex at Santa Maria included daily ash-and-steam explosions and block avalanches descending the sides of the dome in February 2019. A typical explosion on 2 February 2019 produced an ash plume that rose to about 3 km altitude and drifted SW (left). A block avalanche on 14 February descended the SE flank and stirred up small plumes of ash in the vicinity (right, top); the avalanche lasted for 88 seconds and registered with seismic frequencies between 3.46 and 7.64 Hz (right bottom). Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Santiaguito (1402-03), Semana del 01 al 08 de febrero de 2019).

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 stratovolcano has a sharp-topped, conical profile that is cut on the SW flank by a 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/); 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); 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/).


Reventador (Ecuador) — March 2019 Citation iconCite this Report

Reventador

Ecuador

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

All times are local (unless otherwise noted)


Multiple daily explosions with ash plumes and incandescent blocks rolling down the flanks, October 2018-January 2019

The andesitic Volcán El Reventador lies well east of the main volcanic axis of the Cordillera Real in Ecuador and has historical eruptions with numerous lava flows and explosive events going back to the 16th century. The eruption in November 2002 generated a 17-km-high eruption cloud, pyroclastic flows that traveled 8 km, and several lava flows. Eruptive activity has been continuous since 2008. Daily explosions with ash emissions and ejecta of incandescent blocks rolling hundreds of meters down the flanks have been typical for many years. Activity continued during October 2018-January 2019, the period covered in this report, with information provided by Ecuador's Instituto Geofisico (IG-EPN), the Washington Volcano Ash Advisory Center (VAAC), and infrared satellite data.

Multiple daily reports were issued from the Washington VAAC throughout the entire October 2018-January 2019 period. Plumes of ash and gas usually rose to altitudes of 4.3-6.1 km and drifted about 20 km in prevailing wind directions before either dissipating or being obscured by meteoric clouds. The average number of daily explosions reported by IG-EPN for the second half of 2018 was more than 20 per day (figure 104). The many explosions during the period originated from multiple vents within a large scarp that formed on the W flank in mid-April (BGVN 43:11, figure 95) (figure 105). Incandescent blocks were observed often in the IG webcams; they traveled 400-1,000 m down the flanks.

Figure (see Caption) Figure 104. The number of daily seismic events at El Reventador for 2018 indicated high activity during the first and last thirds of the year; more than 20 explosions per day were recorded many times during October-December 2018, the period covered in this report. LP seismic events are shown in orange, seismic tremor in pink, and seismic explosions with ash are shown in green. Courtesy of IG-EPN (Informe Anual del Volcán El Reventador – 2018, Quito, 29 de marzo del 2019).
Figure (see Caption) Figure 105. Images from IG's REBECA thermal camera showed the thermal activity from multiple different vents at different times during the year (see BGVN 43:11, figure 95 for vent locations). Courtesy if IG (Informe Anual del Volcán El Reventador – 2018, Quito, 29 de marzo del 2019).

Activity during October 2018-January 2019. During most days of October 2018 plumes of gas, steam, and ash rose over 1,000 m above the summit of Reventador, and most commonly drifted W or NW. Incandescence was observed on all nights that were not cloudy; incandescent blocks rolled 400-800 m down the flanks during half of the nights. During episodes of increased activity, ash plumes rose over 1,200 m (8, 10-11, 18-19 October) and incandescent blocks rolled down multiple flanks (figure 106).

Figure (see Caption) Figure 106. Ash emissions rose over 1,000 m above the summit of Reventador numerous times during October 2018, and large incandescent blocks traveled hundreds of meters down multiple flanks. The IG-EPN COPETE webcam that captured these images is located on the S caldera rim. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-282, 292, 295, 297).

Similar activity continued during November. IG reported 17 days of the month with steam, gas, and ash emissions rising more than 1,000 m above the summit. The other days were either cloudy or had emissions rising between 500 and 1,000 m. Incandescent blocks were usually observed on the S or SE flanks, generally travelling 400-600 m down the flanks. The Washington VAAC reported a discrete ash plume at 6.1 km altitude drifting WNW about 35 km from the summit on 15 November. The next day, intermittent puffs were noted moving W, and a bright hotspot at the summit was visible in satellite imagery. During the most intense activity of the month, incandescent blocks traveled 800 m down all the flanks (17-19 November) and ash plumes rose over 1,200 m (23 November) (figure 107).

Figure (see Caption) Figure 107. Ash plumes rose over 1,000 m above the summit on 17 days during November 2018 at Reventador, and incandescent blocks traveled 400-800 m down the flanks on many nights. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-306, 314, 318, 324).

Steam, gas, and ash plumes rose over 1,200 m above the summit on 1 December. The next day, there were reports of ashfall in San Rafael and Hosteria El Hotelito, where they reported an ash layer about 1 mm thick was deposited on vehicles during the night. Ash emissions exceeded 1,200 m above the summit on 5 and 6 December as well. Incandescent blocks traveled 800 m down all the flanks on 11, 22, 24, and 26 December, and reached 900 m on 21 December. Ash emissions rising 500 to over 1,000 m above the summit were a daily occurrence, and incandescent blocks descended 500 m or more down the flanks most days during the second half of the month (figure 108).

Figure (see Caption) Figure 108. Ash plumes that rose 500 to over 1,000 m were a daily occurrence at Reventador during December 2018. Incandescent blocks traveled as far as 900 m down the flanks as well. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, numbers 2018-340, 351, 353, 354, 358, 359).

During the first few days of January 2019 the ash and steam plumes did not rise over 800 m, and incandescent blocks were noted 300-500 m down the S flank. An increase in activity on 6 January sent ash-and-gas plumes over 1,000 m, drifting W, and incandescent blocks 1,000 m down many flanks. For multiple days in the middle of the month the volcano was completely obscured by clouds; only occasional observations of plumes of ash and steam were made, incandescence seen at night through the clouds confirmed ongoing activity. The Washington VAAC reported continuous ash emissions moving SE extending more than 100 km on 12 January. A significant explosion late on 20 January sent incandescent blocks 800 m down the S flank; although it was mostly cloudy for much of the second half of January, brief glimpses of ash plumes rising over 1,000 m and incandescent blocks traveling up to 800 m down numerous flanks were made almost daily (figure 109).

Figure (see Caption) Figure 109. Even during the numerous cloudy days of January 2019, evidence of ash emissions and significant explosions at Reventador was captured in the Copete webcam located on the S rim of the caldera. Courtesy of IG Daily Reports (Informe diario del estado del Volcan Reventador, number 2019-6, 21, 26, 27).

Visual evidence from the webcams supports significant thermal activity at Reventador. Atmospheric conditions are often cloudy and thus the thermal signature recorded by satellite instruments is frequently diminished. In spite of this, the MODVOLC thermal alert system recorded seven thermal alerts on three days in October, four alerts on two days in November, six alerts on two days in December and three alerts on three days in January 2019. In addition, the MIROVA system measured moderate levels of radiative power intermittently throughout the period; the most intense anomalies of 2018 were recorded on 15 October and 6 December (figure 110).

Figure (see Caption) Figure 110. Persistent thermal activity at Reventador was recorded by satellite instruments for the MIROVA system from 5 April 2018 through January 2019 in spite of frequent cloud cover over the volcano. The most intense anomalies of 2018 were recorded on 15 October and 6 December. Courtesy of MIROVA.

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

Information Contacts: Instituto Geofísico (IG-EPN), Escuela Politécnica Nacional, Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).


Kuchinoerabujima (Japan) — March 2019 Citation iconCite this Report

Kuchinoerabujima

Japan

30.443°N, 130.217°E; summit elev. 657 m

All times are local (unless otherwise noted)


Weak explosions and ash plumes beginning 21 October 2018

Activity at Kuchinoerabujima is exemplified by interim explosions and periods of high seismicity. A weak explosion occurred on 3 August 2014, the first since 1980, and was followed by several others during 29 May-19 June 2015 (BGVN 42:03). This report describes events through February 2019. Information is based on monthly and annual reports from the Japan Meteorological Agency (JMA) and advisories from the Tokyo Volcanic Ash Advisory Center (VAAC). Activity has been limited to Kuchinoerabujima's Shindake Crater.

Activity during 2016-2018. According to JMA, between July 2016 and August 2018, the volcano was relatively quiet. Deflation had occurred since January 2016. On 18 April 2018 the Alert Level was lowered from 3 to 2 (on a scale of 1-5). A low-temperature thermal anomaly persisted near the W fracture in Shindake crater. During January-March 2018, both the number of volcanic earthquakes (generally numerous and typically shallow) and sulfur dioxide flux remained slightly above baselines levels in August 2014 (60-500 tons/day compared tp generally less than 100 tons/day in August 2014).

JMA reported that on 15 August 2018 a swarm of deep volcanic earthquakes was recorded, prompting an increase in the Alert Level to 4. The earthquake hypocenters were about 5 km deep, below the SW flanks of Shindake, and the maximum magnitude was 1.9. They occurred at about the same place as the swarm that occurred just before the May 2015 eruption. Sulfur dioxide emissions had increased since the beginning of August; they were 1,600, 1,000, and 1,200 tons/day on 11, 13, and 17 August, respectively. No surficial changes in gas emissions or thermal areas were observed during 16-20 August. On 29 August, JMA downgraded the Alert Level to 3, after no further SO2 flux increase had occurred in recent days and GNSS measurements had not changed.

A very weak explosion was recorded at 1831 on 21 October, with additional activity between 2110 on 21 October and 1350 on 22 October; plumes rose 200 m above the crater rim. During an overflight on 22 October, observers noted ash in the emissions, though no morphological changes to the crater nor ash deposits were seen. Based on satellite images and information from JMA, the Tokyo VAAC reported that during 24-28 October ash plumes rose to altitudes of 0.9-1.5 km and drifted in multiple directions. During a field observation on 28 October, JMA scientists did not observe any changes in the thermal anomalies at the crater.

JMA reported that during 31 October-5 November 2018, very small events released plumes that rose 500-1,200 m above the crater rim. On 6 November, crater incandescence began to be periodically visible. During 12-19 November, ash plumes rose as high as 1.2 km above the crater rim and, according to the Tokyo VAAC, drifted in multiple directions. Observers doing fieldwork on 14 and 15 November noted that thermal measurements in the crater had not changed. Intermittent explosions during 22-26 November generated plumes that rose as high as 2.1 km above the crater rim. During 28 November-3 December the plumes rose as high as 1.5 km above the rim.

JMA reported that at 1637 on 18 December an explosion produced an ash plume that rose 2 km and then disappeared into a weather cloud. The event ejected material that fell in the crater area, and generated a pyroclastic flow that traveled 1 km W and 500 m E of the crater. Another weak explosion occurred on 28 December, scattering large cinders up to 500 m from the crater.

The Tokyo VAAC did not issue any ash advisories for aviation until 21 October 2018, when it issued at least one report every day through 13 December. It also issued advisories on 18-20 and 28 December.

Activity during January-early February 2019. JMA reported that at 0919 local time on 17 January 2019 an explosion generated a pyroclastic flow that reached about 1.9 km NW and 1 km E of the crater. It was the strongest explosion since October 2018. In addition, "large cinders" fell about 1-1.8 km from the crater.

Tokyo VAAC ash advisories were issued on 1, 17, 20, and 29 January 2018. An explosion at 1713-1915 on 29 January produced an ash plume that rose 4 km above the crater rim and drifted E, along with a pyroclastic flow. Ash fell in parts of Yakushima. During 30 January-1 February and 3-5 February, white plumes rose as high as 600 m. On 2 February, an explosion at 1141-1300 generated a plume that rose 600 m. No additional activity during February was reported by JMA. The Alert Level remained at 3.

Geologic Background. A group of young stratovolcanoes forms the eastern end of the irregularly shaped island of Kuchinoerabujima in the northern Ryukyu Islands, 15 km west of Yakushima. The Furudake, Shindake, and Noikeyama cones were erupted from south to north, respectively, forming a composite cone with multiple craters. The youngest cone, centrally-located Shintake, formed after the NW side of Furutake was breached by an explosion. All historical eruptions have occurred from Shintake, although a lava flow from the S flank of Furutake that reached the coast has a very fresh morphology. Frequent explosive eruptions have taken place from Shintake since 1840; the largest of these was in December 1933. Several villages on the 4 x 12 km island are located within a few kilometers of the active crater and have suffered damage from eruptions.

Information Contacts: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/); Tokyo Volcanic Ash Advisory Center (VAAC), 1-3-4 Otemachi, Chiyoda-ku, Tokyo, Japan (URL: http://ds.data.jma.go.jp/svd/vaac/data/).


Kerinci (Indonesia) — February 2019 Citation iconCite this Report

Kerinci

Indonesia

1.697°S, 101.264°E; summit elev. 3800 m

All times are local (unless otherwise noted)


A persistent gas-and-steam plume and intermittent ash plumes occurred from July 2018 through January 2019

Kerinci is a frequently active volcano in Sumatra, Indonesia. Recent activity has consisted of intermittent explosions, ash, and gas-and-steam plumes. The volcano alert has been at Level II since 9 September 2007. This report summarizes activity during July 2018-January 2019 based on reports by The Indonesia volcano monitoring agency, Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), MAGMA Indonesia, notices from the Darwin Volcano Ash Advisory Center (Darwin VAAC), and satellite data.

Throughout this period dilute gas-and-steam plumes rising about 300 m above the summit were frequently observed and seismicity continued (figure 6). During July through January ash plumes were observed by the Darwin VAAC up to 4.3 km altitude and dispersed in multiple directions (table 7 and figure 7).

Figure (see Caption) Figure 6. Graph showing seismic activity at Kerinci from November 2018 through February 2019. Courtesy of MAGMA Indonesia.

Table 7. Summary of ash plumes (altitude and drift direction) for Kerinci during July 2018 through January 2019. The summit is at 3.5 km altitude. Data courtesy of the Darwin Volcanic Ash Advisory Center (VAAC) and MAGMA Indonesia.

Date Ash plume altitude (km) Ash plume drift direction
22 Jul 2018 4.3 SW
28-30 Sep 2018 4.3 SW, W
02 Oct 2018 4.3 SW, W
18-22 Oct 2018 4.3 N, W, WSW, SW
19 Jan 2019 4 E to SE
Figure (see Caption) Figure 7. Dilute ash plumes at Kerinci during July 2018-January 2019. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub Playground.

Based on satellite data, a Darwin VAAC advisory reported an ash plume to 4.3 km altitude on 22 July that drifted to the SW and S. Only one day with elevated thermal emission was noted in Sentinel-2 satellite data for the entire reporting period, on 13 September 2018 (figure 8). No thermal signatures were detected by MODVOLC. On 28-29 September there was an ash plume observed to 500-600 m above the peak that dispersed to the W. Several VAAC reports on 2 and 18-22 October detected ash plumes that rose to 4.3 km altitude and drifted in different directions. On 19 January from 0734 to 1000 an ash plume rose to 200 m above the crater and dispersed to the E and SE (figure 9).

Figure (see Caption) Figure 8. Small thermal anomaly at Kerinci volcano on 13 September 2018. False color (urban) image (band 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 9. Small ash plume at Kerinci on 19 January 2018 that reached 200 m above the crater and traveled west. Courtesy of MAGMA Indonesia.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Yasur (Vanuatu) — February 2019 Citation iconCite this Report

Yasur

Vanuatu

19.532°S, 169.447°E; summit elev. 361 m

All times are local (unless otherwise noted)


Eruption continues with ongoing explosions and multiple active crater vents, August 2018-January 2019

According to the Vanuatu Meteorology and Geo-Hazards Department (VMGD), which monitors Yasur, the volcano has been in essentially continuous Strombolian activity since Captain Cook observed ash eruptions in 1774, and undoubtedly before that time. VMGD reported that, based on visual observations and seismic data, activity continued through January 2019, with ongoing, sometimes strong, explosions. The Alert Level remained at 2 (on a scale of 0-4). VMGD reminded residents and tourists to remain outside the 395-m-radius permanent exclusion zone and warned that volcanic ash and gas could reach areas influenced by trade winds.

Thermal anomalies, based on MODIS satellite instruments analyzed using the MODVOLC algorithm, were recorded 6-15 days per month during the reporting period, sometimes with multiple pixels. The MIROVA (Middle InfraRed Observation of Volcanic Activity) volcano hotspot detection system, also based on analysis of MODIS data, detected numerous hotspots every month. Active crater vents were also frequently visible in Sentinel-2 satellite imagery (figure 50).

Figure (see Caption) Figure 50. Sentinel-2 satellite color infrared image (bands 8, 4, 3) of Yasur on 17 November 2018 showing at least three distinct heat sources in the crater. Courtesy of Sentinel Hub Playground.

Geologic Background. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island, this mostly unvegetated pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide, horseshoe-shaped caldera associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department, Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Ambae (Vanuatu) — February 2019 Citation iconCite this Report

Ambae

Vanuatu

15.389°S, 167.835°E; summit elev. 1496 m

All times are local (unless otherwise noted)


Ash plumes and lahars in July 2018 cause evacuation of the island; intermittent gas-and-steam and ash plumes through January 2019

Ambae is one of the active volcanoes of Vanuatu in the New Hebrides archipelago. Recent eruptions have resulted in multiple evacuations of the local population due to ashfall. The current eruption began in September 2017, with the initial episode ending in November that year. The second episode was from late December 2017 to early February 2018, and the third was during February-April 2018. The Alert Level was raised to 3 in March, then lowered to Level 2 again on 2 June 2018. Eruptive activity began again on 1 July and produced thick ash deposits that significantly impacted the population, resulting in the full evacuation of the Island of Ambae. This report summarizes activity from July 2018 through January 2019 and is based on reports by the Vanuatu Meteorology and Geo-hazards Department (VMGD), The Vanuatu Red Cross, posts on social media, and various satellite data.

On 1 July Ambae entered a new eruption phase, marked by an ash plume that resulted in ashfall on communities in the W to NW parts of Ambae Island and the NE part of Santo Island (figure 78). On 9-10 July VMGD reported that a small eruption continued with activity consisting of ongoing gas-and-steam emissions. An observation flight on 13 July confirmed that the eruption was centered at Lake Voui and consisted of explosions that ejected hot blocks with ongoing gas-and-steam and ash emissions. Populations on Ambae and a neighboring island could hear the eruption, smell the volcanic gases, and see incandescence at night.

Figure (see Caption) Figure 78. Ash plume at Ambae on 1 July 2018 that resulted in ashfall on the W to NW parts of the island, and on the NE part of Santo Island. Courtesy of VMGD.

On 16 July the Darwin VAAC reported an ash plume to 9.1 km that drifted to the NE. During 16-24 July daily ash plumes from the Lake Voui vent rose to altitudes of 2.3-9.1 km and drifted N, NE, E, and SE (figure 79 and 80). Radio New Zealand reported that on the 16th significant ash emission blocked out sunlight, making the underlying area dark at around 1600 local time. Much of E and N Ambae Island experienced heavy ashfall and the eruption could be heard over 30 km away. The Vanuatu Red Cross Society reported worsening conditions in the south on 24 July with ashfall resulting in trees falling and very poor visibility of less than 2 m (figures 81, 82, and 83). The Daily Post reported that by 19 July lahars had washed away two roads and other roads were blocked to western Ambae. Volcanologists who made their way to the area reported widespread damage (figure 84). The Alert Level was raised from level 2 to 3 (on a scale of 0-5) on 21 July due to an increase in ash emission and more sustained plumes, similar to March 2018 activity.

Figure (see Caption) Figure 79. Ash plumes produced by the Ambae eruption in July 2018 as seen in Terra/MODIS visible satellite images. Images courtesy of NASA Worldview.
Figure (see Caption) Figure 80. Sentinel-2 satellite image of an ash plume from Ambae in Vanuatu on 23 July 2018 with the inset showing the ash plume at the vent. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 81. Ashfall at Ambae, posted on 25 July 2018. Courtesy of the Vanuatu Red Cross Society.
Figure (see Caption) Figure 82. An ash plume at Ambae in July during a day and a half of constant ashfall, looking towards the volcano. Courtesy of Michael Rowe.
Figure (see Caption) Figure 83. Ashfall from the eruption at Ambae blocked out the sun near the volcano on 24 July 2018. Courtesy of the Vanuatu Red Cross Society.
Figure (see Caption) Figure 84. Impacts of ashfall near Ambae in July 2018. Photos by Nicholson Naki, courtesy of the Vanuatu Red Cross (posted on 22 July 2018).

At 2100 on 26 July the ongoing explosions produced an ash plume that rose to 12 km and spread NE, E, SE. A state of emergency was announced by the Government of Vanuatu with a call for mandatory evacuations of the island. Ash emissions continued through the next day (figure 85 and 86) with two episodes producing volcanic lightning at 1100-1237 and 1522-2029 on 27 July (figure 87). The Darwin VAAC reported ash plumes up to 2.4-6.4 km, drifting SE and NW, and pilots reported heavy ashfall in Fiji. Large SO2 plumes were detected accompanying the eruptions and moving towards the E (figure 88).

Figure (see Caption) Figure 85. Ash plumes at Ambae at 0830 and 1129 local time on 27 July 2018. The ash plume is significantly larger in the later image. Webcam images from Saratamata courtesy of VMGD.
Figure (see Caption) Figure 86. Two ash plumes from Ambae at 1200 on 27 July 2018 as seen in a Himawari-8 satellite image. Courtesy of Himawari-8 Real-time Web.
Figure (see Caption) Figure 87. Lightning strokes detected at Ambae on 27 July 2018. There were two eruption pulses, 1100-1237 (blue) and 1522-2029 local time (red) that produced 185 and 87 lightning strokes, respectively. Courtesy of William A. Brook, Ronald L. Holle, and Chris Vagasky, Vaisala Inc.
Figure (see Caption) Figure 88. Aura/OMI data showing the large SO2 plumes produced by Ambae in Vanuatu during 22-31 July 2018. Courtesy of NASA Goddard Space Flight Center.

Video footage showed a lahar blocking a road around 2 August. The government of Vanuatu told reporters that the island had been completely evacuated by 14 August. A VMGD bulletin on 22 August reported that activity continued with ongoing gas-and-steam and sometimes ash emissions; residents on neighboring islands could hear the eruption, smell volcanic gases, and see the plumes.

On 1 September at 2015 an explosion sent an ash plume to 4-11 km altitude, drifting E. Later observations in September showed a decrease in activity with no further explosions and plumes limited to white gas-and-steam plumes. On 21 September VMGD reported that the Lake Voui eruption had ceased and the Alert Level was lowered to 2.

Observed activity through October and November dominantly consisted of white gas-and-steam plumes. An explosion on 30 October at 1832 produced an ash plume that rose to 4-5 km and drifted E and SE. Satellite images acquired during July-November show the changing crater area and crater lake water color (figure 89). VMGD volcano alert bulletins on 6, 7, and 21 January 2019 reported that activity continued with gas-and-steam emissions (figure 90). Thermal energy continued to be detected by the MIROVA system through January (figure 91).

Figure (see Caption) Figure 89. The changing lakes of Ambae during volcanic activity in 2018. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 90. A steam plume at Ambae on 21 January 2019. Courtesy of VMGD.
Figure (see Caption) Figure 91. Log radiative power MIROVA plot of MODIS infrared data at Ambae for April 2018 through January 2019 showing the increased thermal energy during the July 2018 eruption and continued activity. Courtesy of MIROVA.

Geologic Background. The island of Ambae, also known as Aoba, is a massive 2500 km3 basaltic shield that is the most voluminous volcano of the New Hebrides archipelago. A pronounced NE-SW-trending rift zone dotted with scoria cones gives the 16 x 38 km island an elongated form. A broad pyroclastic cone containing three crater lakes (Manaro Ngoru, Voui, and Manaro Lakua) is located at the summit within the youngest of at least two nested calderas, the largest of which is 6 km in diameter. That large central edifice is also called Manaro Voui or Lombenben volcano. Post-caldera explosive eruptions formed the summit craters about 360 years ago. A tuff cone was constructed within Lake Voui (or Vui) about 60 years later. The latest known flank eruption, about 300 years ago, destroyed the population of the Nduindui area near the western coast.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, http://www.ssd.noaa.gov/VAAC/OTH/NZ/messages.html); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); NASA Worldview (URL: https://worldview.earthdata.nasa.gov/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); Himawari-8 Real-time Web, developed by the NICT Science Cloud project in NICT (National Institute of Information and Communications Technology), Japan, in collaboration with JMA (Japan Meteorological Agency) and CEReS (Center of Environmental Remote Sensing, Chiba University) (URL: https://himawari8.nict.go.jp/); Vanuatu Red Cross Society (URL: https://www.facebook.com/VanuatuRedCross); William A. Brooks and Ronald L. Holle, Vaisala Inc., Tucson, Arizona, and Chris Vagasky, Vaisala Inc., Louisville, Colorado (URL: https://www.vaisala.com/); Michael Rowe, The University of Auckland, 23 Symonds Street, Auckland, 1010, New Zealand (URL: https://unidirectory.auckland.ac.nz/profile/michael-rowe); Radio New Zealand, 155 The Terrace, Wellington 6011, New Zealand (URL: https://www.radionz.co.nz/international/pacific-news/359231/vanuatu-provincial-capital-moves-due-to-volcano); Vanuatu Daily Post (URL: http://dailypost.vu/).


Agung (Indonesia) — February 2019 Citation iconCite this Report

Agung

Indonesia

8.343°S, 115.508°E; summit elev. 2997 m

All times are local (unless otherwise noted)


Ongoing intermittent ash plumes and frequent gas-and-steam plumes during August 2018-January 2019

Agung is an active volcano in Bali, Indonesia, that began its current eruptive episode in September 2017. During this time activity has included ash plumes, gas-and-steam plumes, explosions ejecting ballistic blocks onto the flanks, and lava extrusion within the crater.

This report summarizes activity from August 2018 through January 2019 based on information from Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG), also known as the Indonesian Center for Volcanology and Geological Hazard Mitigation (CVGHM), MAGMA Indonesia, the National Board for Disaster Management - Badan Nasional Penanggulangan Bencana (BNPB), the Darwin Volcanic Ash Advisory Center (VAAC), and satellite data.

During August 2018 through January 2019 observed activity was largely gas-and steam plumes up to 700 m above the crater (figures 39 and 40). In late December and January there were several explosions that produced ash plumes up to 5.5 km altitude, and ejected ballistic blocks.

Figure (see Caption) Figure 39. Graph showing the observed white gas-and-steam plumes and gray ash plumes at Agung during August 2018 through January 2019. The dates showing no data points coincided with cloudy days where the summit was not visible. Data courtesy of PVMBG.
Figure (see Caption) Figure 40. A white gas-and-steam plume at Agung on 21 December 2018. Courtesy of MAGMA Indonesia.

The Darwin VAAC reported an ash plume on 8-9 August based on satellite data, webcam footage, and ground report information. The ash plume rose to 4.3 km and drifted to the W. They also reported a diffuse ash plume to 3.3 km altitude on 16-17 August based on satellite and webcam data. During September through November there were no ash plumes observed at Agung; activity consisted of white gas-and-steam plumes ranging from 10-500 m above the crater.

Throughout December, when observations could be made, activity mostly consisted of white gas-and-steam plumes up to 400 m above the crater. An explosion occurred at 0409 on 30 December that lasted 3 minutes 8 seconds produced an ash plume rose to an altitude of 5.5 km and moved to the SE and associated incandescence was observed at the crater. Light Ashfall was reported in the Karangasem regency to the NE, including Amlapura City and several villages such as in Seraya Barat Village, Seraya Tengah Village, and Tenggalinggah Village (figure 41).

Figure (see Caption) Figure 41. A webcam image of an explosion at Agung that began at 0409 on 30 December 2018. Light Ashfall was reported in the Karangasem regency. Courtesy of PVMBG.

White gas-and-steam plumes continued through January 2019 rising as much as 600 m above the crater. Several Volcano Observatory Notices for Aviation (VONAs) were issued during 18-22 January. An explosion was recorded at 0245 on 19 January that produced an ash plume to 700 m above the crater and ejected incandescent blocks out to 1 km from the crater. On 21 January another ash plume rose to an estimated plume altitude of 5.1 km. The next morning, at 0342 on the 22nd, an ash plume to an altitude of 2 km that dispersed to the E and SE.

Satellite data shows continued low-level thermal activity in the crater throughout this period. MIROVA thermal data showed activity declining after a peak in July, and a further decline in energy in September (figure 42). Low-level thermal activity continued through December. Sentinel-2 thermal data showed elevated temperatures within the ponded lava in the crater (figure 43).

Figure (see Caption) Figure 42. Log radiative power MIROVA plot of MODIS infrared data for May 2018 through January 2019 showing thermal anomalies at Agung. The black data lines indicate anomalies more than 10 km from the crater, which are likely due to fires. Courtesy of MIROVA.
Figure (see Caption) Figure 43. Sentinel-2 thermal satellite images showing areas of elevated temperatures within the lava ponded in the Agung crater during August 2018 through January 2019. Courtesy of Sentinel Hub Playground.

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

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Erebus (Antarctica) — January 2019 Citation iconCite this Report

Erebus

Antarctica

77.53°S, 167.17°E; summit elev. 3794 m

All times are local (unless otherwise noted)


Lava lakes persist through 2017 and 2018

Between the early 1980's through 2016, activity at Erebus was monitored by the Mount Erebus Volcano Observatory (MEVO), using seismometers, infrasonic recordings to measure eruption frequency, and annual scientific site visits. MEVO recorded occasional explosions propelling ash up to 2 km above the summit of this Antarctic volcano and the presence of two, sometimes three, lava lakes (figure 26). However, MEVO closed in 2016 (BGVN 42:06).

Activity at the lava lakes in the summit crater can be detected using MODIS infrared detectors aboard the Aqua and Terra satellites and analyzed using the MODVOLC algorithm. A compilation of thermal alert pixels during 2017-2018 (table 4, a continuation of data in the previous report) shows a wide range of detected activity, with a high of 182 alert pixels in April 2018. Although no MODVOLC anomalies were recorded in January 2017, detectors on the Sentinel-2 satellite imaged two active lava lakes on 25 January.

Table 4. Number of MODVOLC thermal alert pixels recorded per month from 1 January 2017 to 31 December 2018 for Erebus by the University of Hawaii's thermal alert system. Table compiled by GVP from data provided by MODVOLC.

Year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec SUM
2017 0 21 9 0 0 1 11 61 76 52 0 3 234
2018 0 21 58 182 55 17 137 172 103 29 0 0 774
SUM 0 42 67 182 55 18 148 233 179 81 0 3 1008
Figure (see Caption) Figure 26. Sentinel-2 images of the summit crater area of Erebus on 25 January 2017. Top: Natural color filter (bands 4, 3, 2). Bottom: Atmospheric penetration filter (bands 12, 11, 8A) in which two distinct lava lakes can be observed. The main crater is 500 x 600 m wide. Courtesy of Sentinel Hub Playground.

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

Information Contacts: Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).


Villarrica (Chile) — March 2019 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Intermittent Strombolian activity ejects incandescent bombs around crater rim, September 2018-February 2019

Historical eruptions at Chile's Villarrica, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. An intermittently active lava lake at the summit has been the source of explosive activity, incandescence, and thermal anomalies for several decades. Sporadic Strombolian activity at the lava lake and small ash emissions have continued since the last large explosion on 3 March 2015. Similar continuing activity during September 2018-February 2019 is covered in this report, with information provided primarily by the Southern Andes Volcano Observatory (Observatorio Volcanológico de Los Andes del Sur, OVDAS), part of Chile's National Service of Geology and Mining (Servicio Nacional de Geología y Minería, SERNAGEOMIN), and Projecto Observación Villarrica Internet (POVI), part of the Fundacion Volcanes de Chile, a research group that studies volcanoes across Chile.

After ash emissions during July 2018 and an increase in of thermal activity from late July through early September 2018 (BGVN 43:10), Villarrica was much quieter through February 2019. Steam plumes rose no more than a few hundred meters above the summit and the number of thermal alerts decreased steadily. Intermittent Strombolian activity sent ejecta a few tens of meters above the summit crater, with larger bombs landing outside the crater rim. A small pyroclastic cone appeared at the surface of the lava lake, about 70 m below the rim, in November. The largest lava fountain rose 35 m above the crater rim in late January 2019.

Steam plumes rose no more than 300 m above the crater during September 2018 and were less than 150 m high in October; incandescence at the summit was visible during clear nights, although a gradual decrease in activity suggested a lowering of the lake level to SERNAGEOMIN. SERNAGEOMIN attributed an increase in LP seismic events from 1,503 in September to 5,279 in October to dynamics of the lava lake inside the summit crater; counts decreased gradually in the following months.

POVI reported webcam evidence of Strombolian activity with ejecta around the crater several times during November 2018. On 5 November the webcam captured an image of an incandescent bomb, more than a meter in diameter, that landed on the NW flank. The next day, explosions sent ejecta 50 m above the edge of the crater, and pyroclastic debris landed around the perimeter. Significant Strombolian explosions on 16 November sent incandescent bombs toward the W rim of the crater (figure 71). The POVI webcam in Pucón captured incandescent ejecta landing on the crater rim on 23 November. POVI scientists observed a small pyroclastic cone, about 10-12 m in diameter, at the bottom of the summit crater on 19 November (figure 72); it was still visible on 25 November.

Figure (see Caption) Figure 71. Strombolian activity at the summit of Villarrica was captured several times in the POVI webcam located in Pucón. An explosion on 5 November 2018 ejected a meter-sized bomb onto the NW flank (left). On 16 November, incandescent bombs were thrown outside the W rim of the crater (right). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).
Figure (see Caption) Figure 72. A small pyroclastic cone was visible at the bottom of the summit crater at Villarrica (about 70 m deep) on 19 November 2018 (left); it was still visible on 25 November (right). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

During December 2018 webcam images showed steam plumes rising less than 350 m above the crater. Infrasound instruments identified two small explosions related to lava lake surface activity. SERNAGEOMIN noted a minor variation in the baseline of the inclinometers; continued monitoring indicated the variation was seasonal. A compilation by POVI of images of the summit crater during 2018 showed the evolution of the lava lake level during the year. It had dropped out of sight early in the year, rose to its highest level in July, and then lowered slightly, remaining stable for the last several months of the year (figure 73).

Figure (see Caption) Figure 73. Evolution of the lava pit at Villarrica during 2018. During July the lava lake level increased and for November and December no significant changes were observed. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Between 25 December 2018 and 15 January 2019, financed with funds contributed by the Fundación Volcanes de Chile, POVI was able to install new HD webcams with continuous daily image recording, greatly improving the level of detail data available of the activity at the summit. POVI reported that after a five-week break, Strombolian explosions resumed on 3 January 2019; the lava fountains rose 20 m above the crater rim, and pyroclastic ejecta fell to the E. On 24 January the Strombolian explosions ejected ash, lapilli, and bombs up to 15 cm in diameter; the lava fountain was about 35 m high.

An explosion on 7 February reached about 29 m above the crater's edge; on 9 February a lava fountain three meters in diameter rose 17 m above the crater rim. Sporadic explosions were imaged on 12 February as well (figure 74). During a reconnaissance overflight on 24 February 2019, POVI scientists observed part of the lava pit at the bottom of the crater (figure 75). As of 28 February they noted a slight but sustained increase in the energy of the explosions. SERNAGEOMIN noted that steam plumes rose 400 m in January and 150 m during February, and incandescence was visible on clear nights during both months.

Figure (see Caption) Figure 74. Strombolian activity at Villarrica in January and February 2019 was imaged with a new HD webcam on several occasions. On 24 January 2019 explosions ejected ash, lapilli, and bombs up to 15 cm in diameter; the lava fountain was about 35 m high (left); on 12 February 2019 explosions rose about 19 m above the crater rim (right). Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).
Figure (see Caption) Figure 75. During a reconnaissance overflight on 24 February 2019, POVI scientists observed part of the lava pit at the bottom of the crater at Villarrica; gas and steam emissions and incandescence from small explosions were noted. Courtesy of POVI (Volcán Villarrica, Resumen Gráfico del Comportamiento, November 2017 a Febrero 2019).

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

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/); Proyecto Observación Villarrica Internet (POVI) (URL: http://www.povi.cl/).


Popocatepetl (Mexico) — March 2019 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Explosions with ash plumes and incandescent ejecta continue during September 2018-February 2019

Frequent historical eruptions have been reported from Mexico's Popocatépetl going back to the 14th century. Activity increased in the mid-1990s after about 50 years of quiescence, and the current eruption, ongoing since January 2005, has included numerous episodes of lava-dome growth and destruction within the 500-m-wide summit caldera. Multiple emissions of steam and gas occur daily, rising generally 1-3 km above the 5.4-km-elevation summit; many contain small amounts of ash. Larger, more explosive events with ash plumes and incandescent ejecta landing on the flanks usually occur several times every week.

Activity through August 2018 was typical of the ongoing eruption with near-constant emissions of water vapor, gas, and minor ash, as well as multiple explosions every week with ash-plumes and incandescent blocks scattered on the flanks (BGVN 43:11). This report covers similar activity from September 2018 through February 2019. Information about Popocatépetl comes from daily reports provided by México's Centro Nacional de Prevención de Desastres (CENAPRED); ash emissions are also reported by the Washington Volcanic Ash Advisory Center (VAAC). Satellite visible and thermal imagery and SO2 data also provide helpful observations of activity.

Near-constant emissions of steam and gas, often with minor ash content, were typical activity throughout September 2018-February 2019. Intermittent larger explosions with plumes of moderate ash content that generated ashfall in nearby communities were reported each month except November. Periods with increased explosive activity that consisted of multiple daily explosions included all of September into early October, early December 2018, and the second half of February 2019 (figure 116). Increased observations of incandescence at the summit generally coincided with increases in explosive activity. Increases in thermal anomalies measured by the MIROVA project during this time also correlated with times of increased explosive activity as reported by CENAPRED (figure 117).

Figure (see Caption) Figure 116. The numbers of low intensity emissions of steam and gas, often with minor amounts of ash ranged from a few tens to several hundred per day throughout September 2018-February 2019 (blue, left axis). Increases in the daily numbers of larger ash-bearing explosions occurred during September-early October 2018, early December, and the second half of February 2019 (orange, right axis). Data courtesy of CENEPRED.
Figure (see Caption) Figure 117. Thermal anomalies registered by the MIROVA project from 5 April 2018 through February 2019 had periods of increased frequency and intensity during September-early October, early December 2018, and in the second half of February 2019. Courtesy of MIROVA.

Activity during September 2018. Multiple explosions with ash plumes were reported nearly every day in September (figure 118). The Washington VAAC reported an ash plume visible in satellite imagery 15 km NW of the summit at 7.6 km altitude on 4 September. Most plumes reported by the VAAC during the month rose to 6.1-7.6 km and drifted up to 40 km in multiple directions. Two small episodes of ash emissions with tremor on 16 September were followed the next day by a series of emissions, explosions, and tremor that lasted for over six hours; incandescent blocks were visible on the flanks in the early morning. An increase in activity late on 18 September produced Strombolian eruptions that lasted for nearly eight hours along with ash emissions and incandescent blocks on the flanks. A plume on 19 September still had detectable ash 150 km NE of the summit; a smaller plume drifting E was responsible for ashfall reported in Tlaxcala.

Figure (see Caption) Figure 118. Multiple explosions with ash plumes were reported nearly every day in September at Popocatépetl, generating ash plumes that rose from 1.5-3 km above the crater and drifted in multiple directions. The CENAPRED webcams captured images of ash plumes on 8, 11, and 19 September, and the Sentinel-2 satellite (rendering is Atmospheric penetration, based on bands 12, 11 and 8A) imaged ash plumes from two of seven reported explosions on 24 September 2018. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 9, 11, y 20 de septiembre de 2018) and Sentinel Hub Playground (lower image).

Discrete puffs of ash were observed by the Washington VAAC on 20 September moving WSW extending around 200 km from the summit. Three explosions on 21 September ejected incandescent blocks onto the NE flank. During an overflight on 21 September, CENAPRED observed dome number 80, partly destroyed by the recent explosions (figure 119). The Washington VAAC reported an ash plume at 8.8 km altitude on 21 September 30 km WSW from the summit. Ashfall was reported by CENACOM (Mexican National Communications Center) on 29 September in Atlautla, Tehuixtitlan, and Cuecuecuautitla in the State of Mexico, and in the Tláhuac Delegation, Iztapalapa, and Xochimilco in Mexico City.

Figure (see Caption) Figure 119. During an overflight on 21 September 2018, CENAPRED observed dome number 80 at Popocatépetl, partly destroyed by the recent explosions. Courtesy of CENAPRED (Sobrevuelo al volcán Popocatépetl hoy 21 de septiembre de 2018).

Activity during October and November 2018. The Washington VAAC reported an ash plume at 7 km altitude on 2 October, 35 km W of the summit. Numerous smaller plumes were reported by the VAAC during both months at about 6 km altitude drifting in multiple directions. Two larger explosions on 8 October produced ash plumes that rose to 3.5 and 2.4 km, respectively, above the summit, and drifted NE (figure 120). As a result, ashfall was reported at the Puebla airport. On 10 and 12 October, extended periods of LP tremor were accompanied by gas emissions, but otherwise lower levels of activity were noted for much of the month. An ash plume extended over 80 km NE at 7.6 km altitude on 10 November. An explosion on 13 November produced incandescent fragments on the flanks. During 19-21 November episodes of LP seismicity and tremors produced gas and ash emissions; some of the episodes lasted for as long as 13 hours; incandescent fragments were observed on the upper slopes during the more intense periods. On 22 November scientists on an overflight by CENAPRED observed dome 81 with a diameter of 175 m and an estimated depth of 30 m (figure 121).

Figure (see Caption) Figure 120. A large explosion early on 8 October 2018 at Popocatépetl sent an ash plume to 3.5 km above the summit crater that drifted NE. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 9 de Octubre de 2018).
Figure (see Caption) Figure 121. On 22 November 2018 scientists on an overflight by CENAPRED observed dome 81 at Popocatépetl with a diameter of 175 m and an estimated depth of 30 m. Courtesy of CENAPRED (Sobrevuelos, herramienta útil para el monitoreo volcánico del Popocatépetl, jueves, 22 de noviembre de 2018).

Activity during December 2018. Increased ash emissions were reported in early December 2018, producing ash plumes that rose at least 1 km above the crater and drifted mostly E; incandescent blocks ejected on 5 December fell mostly back into the crater. Multiple explosions on 6 and 7 December produced ash plumes that rose as high as 2.5 km above the crater and resulted in ashfall in Amecameca and Tlalmanalco; they also produced incandescent blocks that traveled as far at 2.5 km from the crater, according to CENAPRED. An explosion on 9 December produced a 2-km-high ash plume that drifted NE (figure 122). Satellite images captured during clear skies on 18 December showed incandescence at the dome inside the summit crater, and dark ash and ejecta covering much of the upper flanks (figure 123). An ash plume was centered about 100 km NE of the summit on 24 December at 7.6 km altitude, and dissipating rapidly, according to the Washington VAAC. Incandescent blocks were ejected onto the flanks on 26 December during an evening explosion.

Figure (see Caption) Figure 122. An explosion on 9 December 2018 produced a 2-km-high ash plume at Popocatépetl that drifted NE. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 9 de diciembre de 2018).
Figure (see Caption) Figure 123. Clear skies on 18 December 2018 resulted in a Sentinel-2 satellite image of Popocatépetl that showed incandescence on the dome inside the summit crater, and dark tephra surrounding all the upper flanks. Rendering is Atmospheric penetration, based on bands 12, 11 and 8A. Courtesy of Sentinel Hub Playground.

Activity during January 2019. An explosion in the early morning of 16 January 2019 produced incandescent blocks that traveled 1.5 km down the slopes. It also produced an ash emission that lasted for 25 minutes; the seismic signal associated with the event was a mixture of harmonic tremor and high-frequency low-amplitude earthquakes. In the first minutes the height of the column reached 1,000 m above the crater, later it decreased to 500 m; ash was dispersed ENE. Late on 22 January a large explosion produced an ash plume that rose 3.5 km above the crater and numerous incandescent blocks that were observed as far as 2 km from the summit (figure 124); ashfall was reported in Santa Isabel Cholula, Santa Ana Xalmimilulco, Domingo Arenas, San Martin Texmelucan, Tlalancaleca, San Salvador el Verde, San Andres Calpan, San Nicolás de los Ranchos, and Huejotzingo, all in the state of Puebla. A large discrete ash plume was observed in satellite imagery by the Washington VAAC on 24 January at 6.7 km altitude moving NE to about 35 km distance before dissipating. In an overflight on 27 January CENAPRED noted that the internal crater remained about 300 m wide and 150 m deep, and no dome was visible (figure 125).

Figure (see Caption) Figure 124. Late on 22 January 2019 a large explosion at Popocatépetl produced an ash plume that rose 3.5 km above the crater and produced numerous incandescent blocks that were observed as far as 2 km from the summit. Courtesy of CENAPRED (Actualización de Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 22 de enero de 2019).
Figure (see Caption) Figure 125. During an overflight of Popocatépetl on 27 January 2019 observers from CENAPRED noted that the internal crater remained about 300 m wide and 150 m deep, and no dome was visible. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl hoy 27 de enero de 2019).

Activity during February 2019. Several days of increased activity of harmonic tremor and explosions were reported during 14-19 February 2019 (figure 126). Incandescent blocks from Strombolian activity appeared on the flanks late on 14 February traveling as far as 1.5 km, along with a continuous stream of ash and gas that drifted SW for seven hours. The initial ash plume rose 800 m, but by early the next day had risen to 2 km. Ashfall was reported in the communities of Hueyapan, Tetela del Volcán, Zacualpan, Temoac, Jantetelco, Cuautla, Ocuituco, and Yecapixtla, in the state of Morelos, and in Tochimilco, Puebla, on 15 February.

Figure (see Caption) Figure 126. Several days of increased activity at Popocatépetl, including harmonic tremor and explosions, were reported during 14-19 February 2019. Incandescent blocks from Strombolian activity appeared on the flanks late on 14 February traveling as far as 1.5 km, along with a continuous stream of ash and gas that drifted SW for seven hours (left). Steam and gas streamed continuously from the summit for many hours on 17 February (right); the plume drifted NNE at 1-1.5 km altitude. Courtesy of CENAPRED (Reporte del monitoreo de CENAPRED al volcán Popocatépetl 14 y 18 de febrero de 2019).

A new episode of Strombolian activity early on 16 February lasted for six hours and produced 2-km-high ash plumes that drifted SE. Later that afternoon, a new harmonic tremor episode, again lasting about six hours, was accompanied by water vapor and gas emissions that drifted NE and incandescent blocks ejected 400 m down the flanks. A Sentinel-2 satellite image that day recorded a significant thermal signature from the summit dome (figure 127).

Figure (see Caption) Figure 127. A Sentinel-2 satellite image on a clear 16 February 2019 recorded a significant thermal signature from the summit dome of Popocatépetl. Rendering is Atmospheric penetration (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Satellite instruments recorded a strong SO2 signature from the volcano during 15-18 February (figure 128). Multi-hour periods of harmonic tremor were recorded during 17-19 February, accompanied by gas-and-ash emissions. Ash plume heights were between 1 and 2 km above the crater, and minor ashfall was reported in Tlaxco and Xalostoc in Nativitas, and Hueyotlipan, Amaxac de Guerrero, Tepetitla de Lardizábal, and Texoloc in Tlaxcala, on 18 February. Two overflights on 18 and 19 February confirmed the formation of dome 82 inside the summit crater, estimated to be 200 m in diameter (figure 129).

Figure (see Caption) Figure 128. Significant SO2 plumes were measured by the TROPOMI instrument on the Sentinel-5P satellite during 15-18 February 2019 at Popocatépetl. The plume initially drifted SW (top left, 15 February); changes in the wind direction carried the plume to the N (top right, 16 February), then to the NE (bottom left, 17 February), and back to the N on 18 February (bottom right). Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 129. An overflight on 19 February by CENAPRED confirmed the formation of dome 82 inside the summit crater at Popocatépetl, estimated to be 200 m in diameter. Courtesy of CENAPRED (Actualización del reporte del monitoreo de CENAPRED al volcán Popocatépetl, 19 de febrero de 2019).

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: Centro Nacional de Prevención de Desastres (CENAPRED), Av. Delfín Madrigal No.665. Coyoacan, México D.F. 04360, México (URL: http://www.cenapred.unam.mx/); 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); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard, Maryland, USA (URL: https://so2.gsfc.nasa.gov/).


Pacaya (Guatemala) — March 2019 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Continuous activity from the cone in Mackenney crater; daily lava flows on the NW flank during October 2018-January 2019

Extensive lava flows, bomb-laden Strombolian explosions, and ash plumes emerging from MacKenney crater have characterized the 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. The pyroclastic cone has continued to grow, rising above the crater rim in late 2017 and sending numerous flows down the flanks of the crater throughout 2018 (BGVN 43:11). Similar activity continued during October 2018-January 2019, covered in this report, with information provided primarily by Guatemala's Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH).

There were few variations in the eruptive activity at Pacaya during October 2018-January 2019. Virtually constant Strombolian activity from the summit of the pyroclastic cone within Mackenney crater produced ejecta that rose 5-30 m daily. Periods of increased activity occasionally increased the height of the ejecta to 50 m. Lava flows descended the NW flank of Mackenney cone towards Cerro Chino crater, usually one or two a day, sometimes three or four. They travelled 50-300 m down the flank; the longest reached 600 m in mid-October and 500 m at the end of January. Steam and gas plumes persisted from the summit; a single VAAC report mentioned dilute ash in mid-October. Plumes generally rose a few hundred meters above the summit, occasionally reaching 700-800 m. Incandescent avalanche blocks at the heads of the flows were sometimes as large as a meter in diameter and traveled far down the flanks.

Constant Strombolian activity during October 2018 from the pyroclastic cone within Mackenney crater was ejected up to 30 m above the summit of the cone throughout the month, with occasional more intense episodes rising 50 m. Lava flows were reported daily by INSIVUMEH on the NW flank from 50 to 300 m long. White and blue gas-and-steam emissions generally rose a few hundred meters from the summit of the pyroclastic cone and usually drifted S or N. The highest rose 800 m on 26 and 27 October. In a special report issued late on 12 October INSIVUMEH noted that seismicity had increased during the day; Strombolian explosions also increased and ejected material 25-50 m above the summit, producing block avalanches in the vicinity of the flows (figure 103). The cone within Mackenney crater continued to grow, reaching 75 m above the rim and nearly filling the crater at its base. According to the Washington VAAC, on 14 October a pilot reported minor ash emissions moving W at an estimated 650 m above the summit. Multi-spectral imagery showed a faint ash plume moving W at 3.4 km altitude, and a well-defined hotspot was seen in short-wave infrared imagery.

Figure (see Caption) Figure 103. Strombolian activity sent ejecta 25-50 m above the summit of Pacaya on 12 October 2018, and lava flows traveled 600 m down the NW flank towards Cerro Chino, as seen from the community of Escuintla located about 20 km W. Courtesy of Carlos Barrios and INSIVUMEH.

Similar activity persisted throughout November 2018 (figures 104 and 105). The Strombolian activity usually rose 5-30 m high; on 24 November INSIVUMEH reported ejecta 75 m high and the presence of four lava flows on the NW flank that traveled distances ranging from 50 to 200 m. Steam-and-gas emissions rose no more than 500 m above the summit. On 24 and 28 November incandescent avalanche blocks were observed at the fronts of the lava flows.

Figure (see Caption) Figure 104. Constant Strombolian activity rising 25-50 m above the summit of Pacaya was reported on 12 November 2018. In addition, a lava flow 150 m long traveled down the NW flank towards Cerro Chino, as seen in this image with incandescent blocks below the flow. A diffuse plume of mostly gas and steam rose 350 m above the crater. Courtesy of CONRED.
Figure (see Caption) Figure 105. Continuous lava flows up to 300 m long were observed during the last week of November 2018 at Pacaya. They traveled down the NW flank and often had large incandescent blocks that descended the flank beneath the flow. Courtesy of INSIVUMEH (Reporte Semanal de Monitoreo: Volcán Pacaya (1402-11), Semana del 24 al 30 de noviembre de 2018).

During December 2018, continuous Strombolian activity was observed 25 m high. Incandescent avalanche blocks were noted at the fronts of the lava flows more frequently than in previous months. One to three lava flows extending 50-300 m down the NW flank towards Cerro Chino were reported every day that the flanks were visible (figure 106). Late on 13 December INSIVUMEH released a special bulletin noting that explosions were heard as far as 8 km from Mackenney crater, and Strombolian activity rose 25-50 m. Constant tremor activity had been produced from the ongoing lava flows descending the flank; the incandescent avalanche blocks up to 1 m in diameter were falling from the front of the flows. By the end of December, the growing pyroclastic cone had filled the inside of Mackenney crater, reaching 75-100 m above the crater rim. In a special information report on 28 December, INSIVUMEH noted that changes in the eruptive patterns included an increase in seismic tremor along with more persistent and higher energy Strombolian activity from the active cone, which frequently sent material outside of the crater onto the flanks.

Figure (see Caption) Figure 106. Lava flows traveled down the NW flank of Pacaya on 7 December 2018. Courtesy of INSIVUMEH (Informe mensual de la actividad volcanica, diciembre 2018, Volcan de Pacaya).

There were no significant changes in activity during January 2019. Constant Strombolian activity rose 5-30 m above the summit; INSIVUMEH reported the height at 50 m on 7 January. Large incandescent avalanche blocks were noted at the front of the lava flows several times; one or two flows daily reached lengths of 100-300 m. The flow reported on 29 January reached 500 m, traveling down the NW flank towards Cerro Chino. Steam plumes, sometimes with bluish gas, rose generally to around 100 m above the summit, occasionally higher. Growth and destruction of the pyroclastic cone inside Mackenney crater continued as it had for the previous several months. The persistent Strombolian and lava flow activity was responsible for a strong thermal signature recorded in satellite data and plotted by the MIROVA project during the period (figure 107).

Figure (see Caption) Figure 107. A MIROVA graph of thermal radiative power at Pacaya from 5 April 2018 through January 2019 showed little change during the period from October 2018-January 2019 covered in this report. Courtesy of MIROVA.

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

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hydrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié 21-72, Zona 13, Guatemala City, Guatemala (URL: http://conred.gob.gt/www/index.php); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Carlos Barrios (Twitter: @shekano, URL: https://twitter.com/shekano).

Search Bulletin Archive by Publication Date

Select a month and year from the drop-downs and click "Show Issue" to have that issue displayed in this tab.

   

The default month and year is the latest issue available.

Bulletin of the Global Volcanism Network - Volume 19, Number 12 (December 1994)

Managing Editor: Richard Wunderman

Aira (Japan)

Explosive ash eruptions continue

Arenal (Costa Rica)

Continued lava flows and mild Strombolian eruptions

Asosan (Japan)

Intermittent mud ejection and large-amplitude tremor

Bezymianny (Russia)

Small white steam plume; normal seismicity

Bulusan (Philippines)

Phreatic eruptions continue, but at a slower rate

Dukono (Indonesia)

Small eruptions prompt aviation notices

Galeras (Colombia)

Low seismicity characterized by "screw-type" events

Irazu (Costa Rica)

Phreatic explosion on 8 December

Kilauea (United States)

Lava-flow breakouts cover new land and reach the ocean

Klyuchevskoy (Russia)

Small eruption in mid-January

Krakatau (Indonesia)

Ash eruptions in October-December seen by pilots

Langila (Papua New Guinea)

Weak to moderate vapor emissions continue from Crater 2

Manam (Papua New Guinea)

Eruptive activity at South Crater ends in mid-December

Merapi (Indonesia)

Pyroclastic flows continue through 7 December

Pinatubo (Philippines)

Alert status raised following increased seismicity in early January

Poas (Costa Rica)

Seismicity low; bubbling fumaroles disappear

Popocatepetl (Mexico)

Gas and visual observations following the small 21 December eruption

Rabaul (Papua New Guinea)

Explosive activity at Tavurvur declines and finally stops

Rincon de la Vieja (Costa Rica)

Minor seismicity

Ruapehu (New Zealand)

New heating episode in crater lake begins after a burst of acoustic noise

Sheveluch (Russia)

Low-level fumarolic and seismic activity

Suwanosejima (Japan)

Intermittent weak eruptions throughout 1994 cause ashfall on the island

Ulawun (Papua New Guinea)

White vapor emissions and low-level seismicity

Unzendake (Japan)

Endogenous dome growth increases summit to 1,500 m

Villarrica (Chile)

Gas discharges and one thin ashfall in late December

White Island (New Zealand)

Lake persists in Wade Crater; rockslides; inflation continues



Aira (Japan) — December 1994 Citation iconCite this Report

Aira

Japan

31.593°N, 130.657°E; summit elev. 1117 m

All times are local (unless otherwise noted)


Explosive ash eruptions continue

Explosive volcanism . . . continued during December with 64 eruptions, including 54 explosions; no damage occurred. The highest ash plume of the month rose > 2.5 km on 30 December. Volcanic swarms registered at a seismic station 2.3 km NW of Minamidake on 18-19 and 23 December. A total of 743 earthquakes were registered during the month. The ashfall measured at [KLMO] was 16 g/m3.

Volcanism at Sakura-jima in 1994 was generally moderate, with explosive activity during January-February and June-December. Explosions on 2 February broke windshields of two cars. The total number of eruptions in 1994 was 277, including 148 explosive ones.

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

Information Contacts: JMA.


Arenal (Costa Rica) — December 1994 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Continued lava flows and mild Strombolian eruptions

Strombolian eruptions and lava output from Crater C continued in December with columns reaching as high as 1 km above the crater. Both the magnitude and number of explosions increased in December compared to those seen in November. OVSICORI reported that lava flows discharged from Crater C divided at ~1,200 m elev forming three arms: one reaching 950 m (NW arm), and the other two, 1,100 m (W and SW arms).

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: OVSICORI.


Asosan (Japan) — December 1994 Citation iconCite this Report

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Intermittent mud ejection and large-amplitude tremor

Intermittent mud ejection from the pool of water on the floor of Crater 1 continued in December. Ejections on 18 and 23 December rose 150 m, almost to the level of the crater rim. Large-amplitude tremor was often registered, and 12 seismic events were felt at the AWS.

Geologic Background. The 24-km-wide Asosan caldera was formed during four major explosive eruptions from 300,000 to 90,000 years ago. These produced voluminous pyroclastic flows that covered much of Kyushu. The last of these, the Aso-4 eruption, produced more than 600 km3 of airfall tephra and pyroclastic-flow deposits. A group of 17 central cones was constructed in the middle of the caldera, one of which, Nakadake, is one of Japan's most active volcanoes. It was the location of Japan's first documented historical eruption in 553 CE. The Nakadake complex has remained active throughout the Holocene. Several other cones have been active during the Holocene, including the Kometsuka scoria cone as recently as about 210 CE. Historical eruptions have largely consisted of basaltic to basaltic-andesite ash emission with periodic strombolian and phreatomagmatic activity. The summit crater of Nakadake is accessible by toll road and cable car, and is one of Kyushu's most popular tourist destinations.

Information Contacts: JMA.


Bezymianny (Russia) — December 1994 Citation iconCite this Report

Bezymianny

Russia

55.972°N, 160.595°E; summit elev. 2882 m

All times are local (unless otherwise noted)


Small white steam plume; normal seismicity

During breaks in the cloudy weather during late October and November, observers in Kozirevsk (~50 km WNW) reported a white steam cloud reaching 50 m above crater on 27 October and 150 m on 18 November that was directed SE. On 24-28 November, observers in Kozirevsk noted weak fumarolic activity above the summit dome. Seismicity remained normal throughout November and early December. No information was available for the second half of December because of the suspension of communications from KVERT.

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

Information Contacts: V. Kirianov, IVGG; AVO.


Bulusan (Philippines) — December 1994 Citation iconCite this Report

Bulusan

Philippines

12.769°N, 124.056°E; summit elev. 1535 m

All times are local (unless otherwise noted)


Phreatic eruptions continue, but at a slower rate

The phreatic eruptions that started in late November seem to have slowed down, as evident from an apparent increase in intervals between ash explosions. There has been no great change in seismic character, with only a few daily earthquakes plus a few episodes of low-frequency tremor, some of which were probably related to steam jetting. An explosion at 2213 on 31 December ejected ash and was accompanied by rumbling and lightning flashes observed at Salvacion Monitoring Station (South). Areas affected were Cogon, Tinampo, Monbon, Bagsanga. Another ash explosion at 0008 on 7 January caused light ashfall at Barangay Cogon, Irosin (5-6 km from summit). At 1344 on 10 January, an ash explosion sent a plume 1 km above summit (1.5 km elevation) that drifted SSW. Very light ashfall was reported in villages up to 7 km SW.

Geologic Background. Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter dacitic-to-rhyolitic Irosin caldera, which was formed about 36,000 years ago. It lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic complex. Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit is unvegetated and contains a 300-m-wide, 50-m-deep crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded since the mid-19th century.

Information Contacts: R. Punongbayan and E. Corpuz, PHIVOLCS.


Dukono (Indonesia) — December 1994 Citation iconCite this Report

Dukono

Indonesia

1.693°N, 127.894°E; summit elev. 1229 m

All times are local (unless otherwise noted)


Small eruptions prompt aviation notices

NOTAMs issued from the Ujung Pandang aviation control center on 22 November and 1 December 1994 indicated that Dukono was active, but the height of the ash cloud and its direction of drift were unknown. Satellite imagery on 22 November showed cumulus clouds but no evidence of ash. A pilot report from Qantas Airlines on 7 January 1995 described an ash cloud extending to ~6 km altitude and drifting NW, consistent with upper-level wind data; satellite imagery showed no evidence of ash.

Eruptive activity during he first half of 1993 consisted of dark ash clouds, sometimes associated with incandescent fragments (VSI, 1993a). The height of the ash cloud generally varied from 300-600 m above Malupang Magiwe crater . . . .

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

Information Contacts: BOM Darwin, Australia.


Galeras (Colombia) — December 1994 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Low seismicity characterized by "screw-type" events

Seismicity remained low in December, characterized principally by "screw-type" events (monochromatic signals with a slow declining coda) associated with pressurization phases within the volcanic system. At the beginning of the month activity was associated with rock fractures in the W sector of the active cone at depths of <3.5 km. The largest earthquake of the month, on 7 December in the W sector of the crater, was M 2.7. "Screw-type" events have been registered periodically since 20 October; 43 of these events were detected during December. The durations of these signals, taken from the analog register at the Crater-2 station, were within a range of 12-330 seconds. The latter value, from 7 December, is the longest duration recorded. Dominant frequencies were within the range of 2.19-3.48 Hz. Frequencies decreased in December to 2.24 Hz until a sharp change on 13 December to 3.13 Hz before stabilizing around this value.

Electronic tiltmeters increased their noise level because of climatic conditions; however clear stability and a minor change at the Peladitos tiltmeter started on 17 December. The ground stability was corroborated by measurements of the short leveling-line network. COSPEC measurements of SO2 showed low values of 22-50 t/d, consistent with the low degasification observed during overflights.

Geologic Background. Galeras, a stratovolcano with a large breached caldera located immediately west of the city of Pasto, is one of Colombia's most frequently active volcanoes. The dominantly andesitic complex has been active for more than 1 million years, and two major caldera collapse eruptions took place during the late Pleistocene. Long-term extensive hydrothermal alteration has contributed to large-scale edifice collapse on at least three occasions, producing debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed. Major explosive eruptions since the mid-Holocene have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.

Information Contacts: INGEOMINAS, Pasto.


Irazu (Costa Rica) — December 1994 Citation iconCite this Report

Irazu

Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)


Phreatic explosion on 8 December

On 8 December 1994 a small phreatic explosion vented from a well-established fumarole on the upper NW-flank (figure 7). Eighteen shallow October earthquakes (M <=2) and a 255-event November seismic swarm were both discussed in previous reports (19:10-11). ICE workers have suggested that based on the response in San José (station RSN of the national network), the explosion's released energy was similar to a M 4.4 earthquake. In addition, ICE workers noted that people living near Irazú felt the event with an intensity of IV on the modified Mercalli scale. Some residents also heard a jet-like sound and more than one explosion.

Figure (see Caption) Figure 7. Sketch map illustrating the material associated with the phreatic explosion at Irazú, 8 December 1994. Courtesy of ICE.

Prior to the 8 December explosion, but in the same area where it later took place, residents living nearby on the N-flank heard the sound of landslides beginning in November 1994. The sounds came from the N and NW sides of the volcano, an area underlain by deeply incised, altered rocks. The same area has hosted intense fumarolic activity, first observed in 1886. The fumaroles have remained active since then and in the last few years reached temperatures up to 95.4°C.

ICE reported that air surveys and field work completed a few days after the 8 December explosion revealed that the event left an irregularly shaped crater 60-80 m in diameter. Deposits related to landslides, lahars, and a small "lateral blast" were chiefly confined to one drainage radiating from the summit (figure 7). The blast apparently produced no juvenile material, but it deposited blocks, ash, sand, and mud. OVSICORI workers pointed out that after the explosion ash was carried SW and there were other tenuous reports of ashfall in an area 22 km W of the volcano and about 3 km from the capital.

Seismicity was erratic from the end of October through the end of December (figure 8). Although the 8 December event was followed neither by significant explosions nor earthquakes of comparable magnitude, on 9 December nearly 70 smaller earthquakes were registered on a newly installed portable system. That system, which began operation on 9 December, was placed very near the new explosion crater (station PHE, figure 7). Earthquakes declined in number after that (figures 8 and 9), and 5-7 days after the explosion even the system nearest the active crater detected only a few low-frequency events (figure 9).

Figure (see Caption) Figure 8. Number of earthquakes at Irazú during the interval 27 October through December 1994. Collected at seismic station IRZ2, 5 km SW of the main crater. Courtesy of OVSICORI.
Figure (see Caption) Figure 9. Number of earthquakes at Irazú during the interval 9 December to the middle of 17 December 1994. Collected using a portable system situated at the W end of Playa Hermosa ~800 m from the new explosion crater (station PHE, figure 1). Courtesy of ICE.

ICE workers interpreted the explosion as small, phreatic, and they associated it with the November seismic swarm, decompression of a shallow hydrothermal system, and heavy rains destabilizing the NW flank. They also advocated increased seismic monitoring at the volcano.

Geologic Background. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: G. Soto, Guillermo E. Alvarado, and Francisco (Chico) Arias, ICE; E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI.


Kilauea (United States) — December 1994 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-flow breakouts cover new land and reach the ocean

Following a short pause . . ., lava flows broke out on 26 October and entered the ocean on 4 November in the same location as the previous Laeapuki entries. These flows quickly formed a tube system with many skylights and fluid pahoehoe breakouts active from the top of Pulama pali to the ocean. Lava flows extended to the W margin of the flow field, covering new land and burning more of Chain of Craters road. Flows were soon at the same level as the former sea cliff W of the eruption site. Lava entered the ocean across a broad front, but by 15 November the flow began to consolidate. On 23 November, flows active along the W side of the flow field were entering the ocean in the Laeapuki area. On the 25th, lava entry into the ocean slowed, eventually stopping altogether, coincident with a breakout on Pulama pali. Many flows were active on and above Paliuli during 25-28 November, but not on the coastal plain. On the 29th, a flow cascaded over Paliuli and advanced almost 300 m towards the ocean. The eruption paused the same day; this was the 6th pause since the beginning of 1994. By 30 November there were no active flows on the coastal plain, and only minor surface breakouts above Paliuli. The skylights were noticeably cooler and the flow in the tubes was low and sluggish. Pasty breakouts continued from the W side of the flow field as the system drained. At the end of November, a collapse pit on the W flank of Pu`u `O`o, immediately upslope of the E-51 vent, grew to ~80 m in diameter (4-5 times its former size).

On the morning of 1 December, no active surface flows were visible from the coastal area. By early afternoon, large channelized surface flows broke out between 630 and 180 m elevation. In the days that followed, much of the surface of the flow field above Paliuli was covered by new flows. By 5 December the flows had begun to consolidate. Two flows, on the W and the central part of the flow field, had come together and were close to Paliuli W of the Laeapuki area. One large flow had advanced down the E side of the flow field on Pulama pali, and on 6 December cascaded over Paliuli inland of the former Kamoamoa village site. Fingers from this flow headed for the ocean but stagnated within 200 m of the coast on 16 December. The E flow continued to break out at the base of Paliuli, and by 19 December the distal end was close to the ocean in the Kamoamoa area. Lava on the W side of the flow field cascaded over Paliuli on 7 December. This W flow appeared to be less voluminous than the E flow, and by 19 December breakouts from this flow had only advanced 500 m from the base of Paliuli. Both the E and W flows had breakouts active along much of their length above and below Paliuli. Lava flows were active on Pulama pali for most of this interval. On 20 December, the E flow entered the ocean in the Kamoamoa area. By 2 January 1995 the new entry had not yet consolidated, and several small streams were entering the ocean across a 300-m-wide area. Breakouts were active on this flow for much of this period, particularly near Paliuli. The W flow remained active and fed multiple active breakouts below Paliuli. By the end of this interval, the terminus of this flow was within 500 m of the ocean. Flows continued to break out above Paliuli and on Pulama pali, but none advanced to the coastal plain.

The collapse pit on the W flank of Pu`u `O`o grew during this interval, eroding more tephra on the uphill (E) side of the pit. If this growth continues, the summit of Pu`u `O`o may soon be engulfed. The pond in Pu`u `O`o was active throughout December, at 80-88 m below the crater rim.

Eruption tremor . . . persisted in banded patterns near background levels, alternating with amplitudes of 2-3x background. The number of microearthquakes was low beneath the summit and rift zones. Banded tremor continued up to about 1 January, when the STC (Steam Crack) seismic station, located near Pu`u `O`o, began to register an over-all low-level tremor with minimal banding. Intermediate-depth long-period events were marginally high in number during 22-25 December. Only a few of these events were large enough to be located. The number of short-period microearthquakes was low beneath the summit and rift zones.

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: T. Mattox, HVO.


Klyuchevskoy (Russia) — December 1994 Citation iconCite this Report

Klyuchevskoy

Russia

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

All times are local (unless otherwise noted)


Small eruption in mid-January

During the week of 8-14 December, 3-14 shallow earthquakes/day and 1.5-8.0 hours/day of volcanic tremor were recorded, down from the previous week. No visual observations were made because of a snow storm in the area. No information was available for the second half of December because of the suspension of communications from KVERT.

While in Petropavlovsk in mid-January 1995, Tom Miller (AVO) reported a small eruption that occurred sometime between 0630 and 1830 on 14 January. Weather in the area was poor, but an ash cloud was observed at ~9 km altitude. Seismic data indicated a single eruptive burst and not a continuous eruption. Satellite imagery showed weather clouds cover the area. However, at 0857 on 14 January a short, narrow plume, ~35 km long, was very evident on satellite imagery blowing NE. The apex of this plume appeared to start at the SE flank of the volcano, but at 1 km resolution this is uncertain. A band 4 minus band 5 image showed a distinct plume.

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: V. Kirianov, IVGG; AVO.


Krakatau (Indonesia) — December 1994 Citation iconCite this Report

Krakatau

Indonesia

6.102°S, 105.423°E; summit elev. 813 m

All times are local (unless otherwise noted)


Ash eruptions in October-December seen by pilots

A pilot on a 16 October Qantas Airlines flight enroute from Perth to Singapore reported a light-gray, moderately dense, mushroom-shaped ash cloud rising to ~2 km altitude and drifting ~55 km W from the summit. Another pilot report on 28 November noted ash from the volcano rising to ~3 km altitude. A similar report on 18 December stated that an ash cloud was as high as 3 km and drifting E.

On 26 July 1994, J. Sesiano made observations from the sea, from the summit of the 1930 peak, and from the slopes of the active cone. Activity consisted of violent explosions (averaging one every 15 minutes) with ejecta (small tephra and bombs) erupted vertically to heights of 100-200 m that fell back into the crater. Finer particles were blown NW by winds. Longer intervals between eruptions (30-45 minutes) were followed by a single or series of very strong explosions that generated a dark plume 1,000-1,500 m above the crater. Ejecta from these stronger explosions, including some bombs >1 m3 in size, fell over the entire cone. Boulders were seen rolling down the slopes, reaching and slowly burying the November 1992-Apr 1993 lava flow (18:07), which had a surface temperature of ~30°C and was still degassing.

A rough examination was done on two thin sections made from fresh lava samples (collected while still hot). Phenocrysts were mostly zoned plagioclase, some augite, and rare olivine with reaction rims. The groundmass consisted of fine-grained opaque grains and scattered plagioclase, but no glass. Plagioclase composition, determined from very few properly oriented crystals, was An$45-55. Based on these observations, the samples were identified as andesite to basaltic andesite.

Geologic Background. The renowned volcano Krakatau (frequently misstated as Krakatoa) lies in the Sunda Strait between Java and Sumatra. Collapse of the ancestral Krakatau edifice, perhaps in 416 or 535 CE, formed a 7-km-wide caldera. Remnants of this ancestral volcano are preserved in Verlaten and Lang Islands; subsequently Rakata, Danan, and Perbuwatan volcanoes were formed, coalescing to create the pre-1883 Krakatau Island. Caldera collapse during the catastrophic 1883 eruption destroyed Danan and Perbuwatan, and left only a remnant of Rakata. This eruption, the 2nd largest in Indonesia during historical time, caused more than 36,000 fatalities, most as a result of devastating tsunamis that swept the adjacent coastlines of Sumatra and Java. Pyroclastic surges traveled 40 km across the Sunda Strait and reached the Sumatra coast. After a quiescence of less than a half century, the post-collapse cone of Anak Krakatau (Child of Krakatau) was constructed within the 1883 caldera at a point between the former cones of Danan and Perbuwatan. Anak Krakatau has been the site of frequent eruptions since 1927.

Information Contacts: J. Sesiano and J. Bertrand, Univ de Genéve; BOM Darwin, Australia; T. Fox, ICAO.


Langila (Papua New Guinea) — December 1994 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)


Weak to moderate vapor emissions continue from Crater 2

"The eruptive activity . . . declined in the first half of December. There were a few Vulcanian explosions from Crater 2 in the first half of the month, and virtually no activity during the second half of the month. Crater 3 continued to release only fumarolic emissions, with occasional wisps of blue vapour. Seismicity remained low throughout the month.

"Activity at Crater 2 in the first two weeks consisted mainly of weak-moderate emissions of white-grey vapour. Roaring and rumbling sounds were heard on 2 and 3 December; fluctuating glow was observed at night. A deep explosion heard on 7 December generated an ash column several hundreds of metres above the crater rim; there was fine ashfall to the SE. During 10-13 December there were occasional rumbling, roaring, and explosion noises, and steady weak glow was seen on 10 and 13 December. From 14 December until the end of the month, no sounds were heard and weak to moderate emissions again consisted of white-grey vapour. Steady weak night glow was seen on 23, 28, 29, and 31 December."

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: D. Lolok, R. Stewart, and B. Talai, RVO.


Manam (Papua New Guinea) — December 1994 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)


Eruptive activity at South Crater ends in mid-December

"The intermittent eruptive activity . . . continued until mid-December. There was no eruptive activity during the second half of the month. Main Crater continued to release weak to moderate volumes of white vapour throughout December. The water-tube tiltmeter at Tabele Observatory showed no significant changes during December. No seismograph was operational.

"On 1 December, emissions from South Crater were initially of ash-laden vapour, but changed to dark grey ash after 1250. The ash columns rose 500 m above the crater and produced fine ashfall to the ESE. The emissions were accompanied by weak roaring and rumbling noises at intervals of 5-10 minutes. Lava fragments were heard cascading down the SE and SW valleys and were seen at night as incandescent ejecta. There were further weak rumbling noises on 2 December and weak steady glow until the 4th. On 6 and 7 December there were occasional roaring noises and a small ash column was seen on December 6 with fine ashfall on the ESE side of the volcano. From 11 to 13 December, weak roaring and rumbling noises were again heard at 5-10 minute intervals with occasional booming and explosion noises. Dark grey ash emissions again accompanied this activity, the strongest of these (12 December) rising 600 m above the crater. On the night of 11 December, weak incandescent projections accompanied the explosions, rising 100 m above the crater. There was no eruptive activity from 15 December until the end of the month and emissions were mainly of weak white vapour. Weak glow was seen on all nights when the summit was visible. Occasional weak roaring sounds were heard on 30 and 31 December."

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: D. Lolok, R. Stewart, and B. Talai, RVO.


Merapi (Indonesia) — December 1994 Citation iconCite this Report

Merapi

Indonesia

7.54°S, 110.446°E; summit elev. 2910 m

All times are local (unless otherwise noted)


Pyroclastic flows continue through 7 December

Collapse of the active summit dome on 22 November sent pyroclastic flows down the SW flank (19:10), overrunning several villages. Although no eruption column was described by VSI observers, aviation warnings on the 22nd stated that ash rose to 10 km; satellite analysis the next day indicated that the plume was a low-level feature well below 6 km. As of 7 December, the UNDHA had confirmed 58 deaths; an Antara news report on 19 December placed the number at 60. Indonesian and Japanese medical teams conducted life-saving plastic surgery on 22 critically injured burn victims.

Continuing small eruptions through 7 December sent pyroclastic flows up to 1.5 km down the Boyong River. An estimated 1 x 106 m3 of pyroclastic sediment has been deposited along the Boyong River, while another 12 x 106 m3 remains on the slopes near the crater. Geochemical analysis in late November indicated increased SO2 emissions of up to 44 t/d.

Most of the >6,000 evacuees were allowed to return home in early December. However, local authorities decided that 2,700 evacuees from five villages within 5 km of the summit in Sleman District (Turgo, Kinahredjo, Kaliadem, Tritis, and Ngandong) would be resettled locally. Although pyroclastic flows had damaged the spring-water source that supplies clean water to the Kaliurang Hill Resort, part of it was reopened on 19 December; the W part was not reopened because it was still considered dangerous.

Residents along the Code River (15,000 people in 11 villages) in Yogyakarta were alerted to the possibility of evacuation, because heavy rainfall in the Boyong River drainage could trigger cold lahars. Existing lahar control works and sabo dams have been constructed on the W side of the volcano in the Magelang District. The Boyong River has only two sabo dams with a capacity of 400,000 m3. The Indonesian government plans to construct three sabo dams of 350,000 m3 capacity each, downstream from the Boyong River.

Geologic Background. Merapi, one of Indonesia's most active volcanoes, lies in one of the world's most densely populated areas and dominates the landscape immediately north of the major city of Yogyakarta. It is the youngest and southernmost of a volcanic chain extending NNW to Ungaran volcano. Growth of Old Merapi during the Pleistocene ended with major edifice collapse perhaps about 2000 years ago, leaving a large arcuate scarp cutting the eroded older Batulawang volcano. Subsequently growth of the steep-sided Young Merapi edifice, its upper part unvegetated due to frequent eruptive activity, began SW of the earlier collapse scarp. Pyroclastic flows and lahars accompanying growth and collapse of the steep-sided active summit lava dome have devastated cultivated lands on the western-to-southern flanks and caused many fatalities during historical time.

Information Contacts: UNDHA; Reuters; ANS; BOM Darwin, Australia.


Pinatubo (Philippines) — December 1994 Citation iconCite this Report

Pinatubo

Philippines

15.13°N, 120.35°E; summit elev. 1486 m

All times are local (unless otherwise noted)


Alert status raised following increased seismicity in early January

On 7 January an explosion-type earthquake with a duration of 6 minutes and 40 seconds was recorded, beginning around 0506. This event was followed about 30 minutes later by low-frequency harmonic tremor that continued through 16 January. Seven high-frequency volcanic earthquakes were also recorded. A total of 16 explosion-type events and nine episodes of low-frequency harmonic tremor indicates shallow magma activity beneath the crater. Three high-frequency volcanic earthquakes were recorded on 9 January. Because of this seismicity, the alert status was raised to Alert Level 2 (magma intrusion). Although a heightened alert status was declared, PHIVOLCS believed that explosions would likely be confined to the caldera and no enlargement of the danger zone was made at this time.

Again on 10 January two high-frequency volcanic earthquakes were recorded, followed by one the next day. During an overflight on 11 January a barely recognizable explosion pit was observed at the N side of the 1992 lava dome; it is probably the site of the small phreatic explosions on 7 January 1994. Only weak emission of white steam was observed along pre-existing vents formed after the 1991 eruption. The number of daily explosion-type earthquakes increased during the next few days (events in parentheses): on 12 (11), 13 (7), 14 (15), 15 (30), and 16 January (15). Low-frequency harmonic tremor persisted throughout this period.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: R. Punongbayan and E. Corpuz, PHIVOLCS.


Poas (Costa Rica) — December 1994 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Seismicity low; bubbling fumaroles disappear

OVSICORI reported that during December the re-established lake in the active crater remained turquoise-green in color, had a temperature of 40°C, and had risen 2 m with respect to its level in October.

In December, the bubbling gases previously emitted from the NW part of the lake ceased. Evaporating gases rose about 50 m above the lake surface; in addition, some gases emanated from the dome.

During December, the Poás seismometer (2.7 km SW of the active crater) registered the following number of events: low frequency (< 2 Hz), 2,539; medium frequency (2.1-3.0 Hz), 14; and high frequency (> 3 Hz), 2. Low-frequency seismicity for December appears in figure 56. With respect to the previous two months, December seismicity dropped in the low- to mid-ranges, but it remained about the same for the high-frequency events. With respect to all months during the year (1994), December seismicity in all three frequency ranges was near the minimum (see table 6).

Figure (see Caption) Figure 56. Poás low-frequency seismicity for December 1994 (from station POA2). Courtesy of OVSICORI-UNA.

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, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI.


Popocatepetl (Mexico) — December 1994 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Gas and visual observations following the small 21 December eruption

Popocatépetl erupted for the first time in decades on 21 December 1994. In the wake of the eruption, Claus Siebe contributed the following report.

"Visual observations at Popocatépetl since 21 January reveal that the emission of ash has decreased in general and become more irregular. Longer time intervals between single series of ash outbursts are observed. Outbursts of ash still occur in single pulses, normally several pulses in a row spaced at intervals of 2-5 minutes. During longer periods of low ash-emissions fumarolic gases are still emitted, preventing direct observation of the crater bottom. Despite this restricted visibility, it is certain that the ash emissions originate in the same area where previously a milky-green lake was located. This lake occupied the depression of the small interior crater that formed during the 1920-27 eruption, when a lava dome was emplaced. During that eruption the lava dome was destroyed by a Vulcanian explosion that created the depression. This interior crater is not located in the center of the main crater but has an eccentric position close to the eastern crater wall.

"In this respect, it is noteworthy that only one of the eight springs monitored by me during the past months has shown a conspicuous anomaly. This spring is located at Axocopan, near Atlixco, 25 km SE of the volcano. Measurements of pH on 11 July, 18 August, and 17 November fluctuated between 5.8 and 6.1. The last measurement taken prior to the 21 December eruption was on 10 December and yielded a pH of 2.5. This anomaly can be regarded as another premonitory sign. The last measurement was taken 14 January 1995 and yielded a value of 5.5, which is almost back to normal. Maybe, during the last weeks prior to the eruption enough pressure built up in the system to allow "magmatic juices" to be expelled laterally and affect the pH of the Axocopan spring."

Following the 21 December eruption a new series of ultraviolet absorption correlation spectrometry (COSPEC) measurements were made by scientists of the Univ of Colima (I. Galindo, A. González, R. Ayala, and L. S. Ivlev). The measurements were requested by the scientific committee organized through the auspices of the Centro Nacional de Prevención de Desastres (CENAPRED). The post-eruption measurements began 48 hours after the eruption, and were also made on 5 other days, with the latest reported being 14 January (figure 8 and table 3).

Figure (see Caption) Figure 8. Graphical reproduction of Popocatépetl SO2 gas flux shown with an arbitrary horizontal scale. ASU refers to data collected by Stan Williams. Courtesy of Ignacio Galindo.

Table 3. Popocatépetl SO2 gas flux for 5 November 1994 through 14 January 1995. Courtesy of Ignacio Galindo.

Day Average Maximum Minimum Std. Dev. n
05 Nov 1994 1,261 ± 538 1,877 485 285 12
23 Dec 1994 2,169 ± 435 2,488 1,617 244 8
24 Dec 1994 3,961 ± 577 4,555 3,402 444 5
27 Dec 1994 1,167 ± 263 1,513 987 140 13
29 Dec 1994 1,237 ± 340 1,616 935 194 11
06 Jan 1995 836 ± 169 1,054 716 123 12
14 Jan 1995 533 ± 95 652 462 117 7

The COSPEC instrument was deployed from rented airplanes (flown by R. González and C. De la Cruz) in a variety of weather and atmospheric conditions including air with fine suspended ash (23 December), high overcast clouds (27 December), and clear sky. The plume top was situated at 4,300-5,740 m altitude and traverses beneath the plume were made at altitudes between 3,000 and 4,545 m. The plume was identified and two navigational bench marks were placed using the aircraft's global positioning system (GPS) to assure that the traverses were perpendicular to the plume's axis. The speed and direction for both the plane and the wind were computed at two points inside of the plume. In addition, at the end of some sessions a parallel flight above the plume used the GPS to resample the wind speed.

Figure 8 and table 3 suggest the SO2 flux baseline for 1994 was about 1,000 tons/day, rising to about 4,000 tons/day during the eruption on 24 December. The airborne observations also indicated that the plume did not reach more than ~500 m above the summit, meaning that the thermal output of the volcano was low. The plume mainly consisted of water vapor with a minor ash component. Its color was dark gray to light brown.

Two tiltmeters have now been installed within several kilometers of the summit, and during their first 10 days of operation in mid-January they remained stable ( ± 0.5 µrad). Reflectors for survey lines have been replaced on the mountain's accessible N side; and they have been recently surveyed at 5-7 day intervals. Reportedly, in mid-January the surveyed line-lengths have also remained stable. In addition to four or more seismometers on the mountain, a TV video camera with a telephoto lens was aimed at the summit crater, affording a view of the summit monitored from CENAPRED data center. John Ewert reported that in the first week of January banded tremor prevailed, accompanied by nearly constant ash emission. The seismicity has quieted since then. In mid-January scientists saw several small earthquakes that were followed about 90 seconds later by distinct visible "puffs" seen coming from the summit on the TV video monitor. This, and other behavior, were taken to suggest the magmatic system was open and under comparatively little pressure. A terse summary is available on both activity as late as the end of December, and recommendations for future monitoring (S. McNutt, 1994).

Reference. McNutt, Stephen R., 1994, Report to CENAPRED on activity of Popocatépetl volcano and some recommendations for improved monitoring and response: unpublished manuscript, 7 p.

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: Claus Siebe, Instituto de Geofísica, UNAM, Coyoacán,; I. Galindo, A. González, R. Ayala, and L. S. Ivlev, CUICT-Univ de Colima; John Ewert, Cascades Volcano Observatory, U.S.G.S., USA; Steve McNutt, Alaska Volcano Obs., Univ of Alaska Fairbanks Geophysical Institute, USA.


Rabaul (Papua New Guinea) — December 1994 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)


Explosive activity at Tavurvur declines and finally stops

"The 1994 eruption . . . stopped in December. Explosive activity at Tavurvur varied in strength during the month and stopped completely on 23 December. Vulcan remained quiet, with the last explosive activity on 2 October. Vulcan exhibited only very weak fumarolic activity during December from both the 1937 and 1994 craters. A landslide took place on the NW portion of the inner wall of its 1994 crater some time between 2 and 5 December, leaving a near-vertical face.

"Following the decline in explosive activity during November, there was very little activity at Tavurvur on 1-2 December. A new phase of explosive activity began at about 2300 on 3 December; this peaked in intensity on the 5th and then declined slowly until 19 December. The decline was evident in the ash content of the clouds and their height (up to 2 km altitude at the peak of activity) but not in the interval between explosions (1-40 minutes). Ash emissions usually lasted for about a minute. The ash clouds were blown mainly NNW over Rabaul Town, where there was light-moderate ashfall, and occasionally to the SE. A series of explosions would sometimes create a discontinuous ash plume. There were no audible sounds associated with the explosions. During an aerial inspection on 9 December, a small lava mound was seen on the floor of the crater and incandescence was seen in cracks between the rocks.

"At night on 19 and 20 December, weak roaring and rumbling sounds were heard; incandescent projections were noted on 20 December. At 0137 on 21 December there was a large explosion that was heard and felt over a wide area. For the next two days, there were many of these explosions as well as some long (up to 6 hours) periods of quiescence. The ash content of the explosion clouds was higher than during the first two-thirds of the month and the ash emissions lasted up to 3 minutes. Due to changes in the prevailing wind direction, a 20-km-long horizontal plume spreading both NW and SE was generated at a height of 1-2 km. On 23 December, there were only a few short periods of weaker explosive activity. The last explosion noted occurred at 1500. From then until the end of the month, the only visible activity was emission of white vapour, low-moderate in volume, from the crater. The vapour rose several hundreds of metres above sea level, rarely to a kilometer.

"Seismicity in December consisted mainly of explosive and low-frequency earthquakes associated with the activity at Tavurvur - the level of seismic activity followed the visual activity. Between 13 and 19 December, a new type of event came to dominate the records. These events were of longer duration and lower amplitude than the low-frequency events that had been recorded since the start of the eruption. More normal events returned with the explosive activity on 20 December and continued until the 26th. Seismic activity was very low from then until the end of the month. There were again very few high-frequency earthquakes: 30 in December, compared to 37 in November and 58 in October. Ground deformation from electronic tiltmeters and dry-tilt measurements showed a further reduction in the rate of deflation. There were reports of a rainbow linking Tavurvur and Vulcan on 25 December."

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: D. Lolok, R.Stewart, and B. Talai, RVO.


Rincon de la Vieja (Costa Rica) — December 1994 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Minor seismicity

During December 1994, Rincón de la Vieja was seismically active. The local station (5 km SW of the active crater) registered three small-amplitude events on 19 December and, at 2121, a fourth of Richter magnitude 3.0. The last event had a focal depth of 23 km and an epicenter 4.5 km NE of the active crater. One event took place each day on 23, 24, and 25 December; these events each had an S -P delay in the range of 1.9 to 2.5 seconds.

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

Information Contacts: OVSICORI.


Ruapehu (New Zealand) — December 1994 Citation iconCite this Report

Ruapehu

New Zealand

39.28°S, 175.57°E; summit elev. 2797 m

All times are local (unless otherwise noted)


New heating episode in crater lake begins after a burst of acoustic noise

Crater Lake appears to have commenced a new heating episode following a burst of acoustic noise on 25 November, and has been accompanied by a significant increase in volcanic tremor. The last heating episode, in June 1994, was short-lived and apparently not accompanied by eruptions. The crater lake on 7 December was generally pale gray with a blue-green tinge in some places. An area of dark gray water, signifying upwelling, was located over the central vent and streaming NE towards the shore. At least five upwelling cells in the N vents area, one of which was moderately vigorous, were associated with local discoloration and yellow slicks. There was no evidence of surging around the shoreline. Snow around the S half of the lake was discolored by sulfur sublimate stains and newly exposed ash due to recent snow recession.

Lake temperature had increased ~4°C since 27 October: to 21.3°C at Logger Point and 22.0°C at Outlet. Outflow was measured at ~80 l/s in the early afternoon of 7 December, but had increased noticeably since late morning, presumably due to increased snow-melt during daylight. A replacement solar cell was installed at the ARGOS station on Logger Point. The increased voltage on subsequent days was accompanied by a 2-2.5°C increase in recorded temperature, confirming the suspicion that recent temperatures have been in error by this amount. Previously recorded trends, however, are believed by IGNS to be reliable. ARGOS temperatures since 27 October remained low at ~15°C (~17-18°C true) until around 25 November, when a steady temperature rise coincided with a burst of 2-Hz acoustic noise. By 7 December, the temperature had risen 5°C and had reached 25°C (true) by 12 December (0.4°C/day). The manually recorded temperature at Logger Point also rose from 18°C on 27 October to 21.3°C on 7 December.

Volcanic tremor remained at low levels (~200 watts) through October to mid-November. Tremor levels began rising on 17 November, with a peak of 12,600 watts on the 25th. This high level closely followed the peak of 2-Hz acoustic noise. Tremor decreased again in early December.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: P. Otway, IGNS Wairakei.


Sheveluch (Russia) — December 1994 Citation iconCite this Report

Sheveluch

Russia

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

All times are local (unless otherwise noted)


Low-level fumarolic and seismic activity

Although frequently obscured by weather clouds, low-level fumarolic activity was noticed on 10 November. Seismicity at or near the active dome was above normal in early November (9-16 events/day), with weak tremor (18-36 minutes/day). Seismicity remained above normal on 11 November, with 8 events at the active dome between 10 November and noon the next day; continuous tremor for 2.6 hours was recorded before 1230. Weak fumarolic activity continued on the 12th with a gas-and-steam plume to 1 km above volcano being blown SE. During 12-18 November, 10 shallow earthquakes were recorded near the active dome; weak tremor (0.1 µm) lasted for ~54 minutes on 18th. Seismicity on the 23rd consisted of two shallow earthquakes beneath the active dome. On 24 November, ground observers noted fumarolic activity at the summit dome with a gas-and-steam plume rising 800 m. Weak volcanic tremor on 23 and 24 November had a duration of ~18 minutes each day with a maximum amplitude of 0.1 µm. Other earthquake activity remained slightly above normal. Slight fumarolic activity on 28 November from the summit dome was seen from Kliuchi; weak tremor and six shallow earthquakes were detected. The seismic station closed indefinitely as of December 7. The volcano was obscured by clouds 8-14 December, and no information was available for late December because of the suspension of communications from KVERT.

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: V. Kirianov, IVGG; AVO.


Suwanosejima (Japan) — December 1994 Citation iconCite this Report

Suwanosejima

Japan

29.638°N, 129.714°E; summit elev. 796 m

All times are local (unless otherwise noted)


Intermittent weak eruptions throughout 1994 cause ashfall on the island

Weak ash eruptions were observed and explosion sounds were heard by local residents throughout 1994. Heavy ash sometimes fell in a village on the island. Occasional ash emissions occurred in mid-February, with ashfall reported on the 11th. Emissions began again in mid-March, with ash falls on the island on 19 and 27 March. The next month, ash eruptions took place on 3-4 and 30 April. Frequent ash ejections during 8-12 May also caused ashfall on the island; detonations were heard on the 8th. Ash ejections were again observed on 14-21 and 29-30 July, with ashfall on the 15th and 20th. Detonations and ashfall were again reported on 12 August. Ashfall was frequent in September and the second half of October, with larger volumes on 13-14 and 31 October. Ash emission in December was observed at the beginning and end of the month, with ashfall on 1-4 and 31 December; rumbling was heard the night of the 3rd.

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

Information Contacts: JMA; Y. Sawada, JMA; D. Shackleford, Fullerton, CA.


Ulawun (Papua New Guinea) — December 1994 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


White vapor emissions and low-level seismicity

Activity remained low from September through December 1994. Similar to previous months, white vapor emissions varied from profuse to moderately weak. Low-level seismicity continued.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the north coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: D. Lolok, R. Stewart, and B. Talai, RVO.


Unzendake (Japan) — December 1994 Citation iconCite this Report

Unzendake

Japan

32.761°N, 130.299°E; summit elev. 1483 m

All times are local (unless otherwise noted)


Endogenous dome growth increases summit to 1,500 m

Theodolite crest-line measurements from the UWS revealed continued steady endogenous growth of the center of the dome up towards the W at a rate of ~0.7 m/day. The elongated lava-block spine reached 1,500 m elevation in early January 1995 (figure 77). [This is ~140 m higher than the summit of Fugen-dake, previously the highest peak of the Unzen volcanic complex.] Thickness of the dome above the original crater floor increased to 250 m. Three periods of vertical growth have taken place during this endogenous event that started in the end of 1993: January-March 1994, June-July, and November-January 1995. After each uplift event, a new part of the dome increased in height while the old peak subsided.

Figure (see Caption) Figure 77. Profile of the Unzen lava dome, 30 December 1993 and 9 January 1995, determined by theodolite measurements from ~2 km SSW. Courtesy of JMA.

Microearthquakes beneath the lava dome totaled 329 in December (less than 35/day) at a seismic station ~3.6 km SW of the dome (table 15). The number of daily events beneath the dome varied, but generally decreased in early 1995. For the first time since 5 January 1994, an earthquake beneath the dome on 28 December was felt at the UWS. Collapse of the lava dome caused 12 pyroclastic flows in December that went NE and SE; the longest traveled 2 km SE.

Table 15. Monthly number of seismic events at Unzen, 1994. Monthly totals for 1991-92 can be found in 17:12, and for 1993 in 19:6. Courtesy of JMA.

Year/Month Earthquakes Pyroclastic Flows
1990 4,018 --
1991 19,101 2,756
1992 53,400 3,918
1993 54,987 1,951
1994 34,566 782
 
Jan 1994 1,863 75
Feb 1994 1,725 80
Mar 1994 5,110 10
Apr 1994 4,606 16
May 1994 3,171 33
Jun 1994 3,279 105
Jul 1994 2,488 44
Aug 1994 7,306 264
Sep 1994 3,260 128
Oct 1994 993 7
Nov 1994 436 8
Dec 1994 329 12

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: S. Nakada, Univ of Tokyo; JMA.


Villarrica (Chile) — December 1994 Citation iconCite this Report

Villarrica

Chile

39.42°S, 71.93°W; summit elev. 2847 m

All times are local (unless otherwise noted)


Gas discharges and one thin ashfall in late December

Between 25 and 30 December the volcano discharged continuously. At 1000 on 25 December 1994 personnel of Villarrica National Park saw "a small scroll of dark vapor." The plume was estimated as <250 m tall and prevailing winds carried it toward the SE.

The next day at 0815 park rangers noticed a second plume, dark brown to black in color ultimately rising to about 600 m above the summit. Winds again carried this plume SE.

Informants reported that on 29 December they could detect a thin layer of gray ash discoloring all of the snow-covered SE sector of the volcano. They also saw a dark gray stain trending N 120° E reaching at least 6 km (to the Portezuelo Chinay area). That same day, Villarrica discharged gas at 20-30 second intervals that looked grayish to sky blue, apparently rich in SO2. Occasionally light gray to brown drab discharges were also noticed and tentatively interpreted as minor gaseous explosions with a fine-grained ash component.

On 30 December at 0800 and 1100, the volcano produced dense plumes of dark gray to dark brown color. These reached up to 250 m above the crater where they were carried to the SE. After noon a weather front crossed the region and the escaping gases condensed as a great mass and slid down the SE flank. No discharges were specifically reported after this event.

Seismic monitoring began at 1807 on 26 December using a portable MEQ-800 seismograph installed 13.5 km from the principal crater.

During the next few days, tremor was seen; it typically had an amplitude of 2 mm and fundamental frequencies 0.8 Hz. During the first 4 hours of operation, 20-30 second intervals of tremor occurred ~60 times/hour. The next day (27 December) tremor increased to 120 times/hour. Starting at 1700 on 28 December tremor increased still further and it reached higher frequency, up to 1.1 Hz. On 29 and 30 December tremor remained essentially constant in terms of amplitude and duration, but after 0100 on 31 December, intervals of tremor took place more often, an average of 200 times/hour (i.e. 200 distinct intervals of tremor an hour). The number of tremor intervals an hour remained constant until 2100 (31 December) when tremor dropped to the levels seen on 29 and 30 December.

The tremor on 26 and 30 December was similar to that seen routinely during times of repose. Nevertheless, some lower frequency events (~2 Hz) took place coincident with weak ash eruptions. As of 31 December 1994 no new activity was reported.

Geologic Background. Glacier-clad Villarrica, one of Chile's most active volcanoes, rises above the lake and town of the same name. It is the westernmost of three large stratovolcanoes that trend perpendicular to the Andean chain. A 6-km-wide caldera formed during the late Pleistocene. A 2-km-wide caldera that formed about 3500 years ago is located at the base of the presently active, dominantly basaltic to basaltic-andesitic cone at the NW margin of the Pleistocene caldera. More than 30 scoria cones and fissure vents dot the flanks. Plinian eruptions and pyroclastic flows that have extended up to 20 km from the volcano were produced during the Holocene. Lava flows up to 18 km long have issued from summit and flank vents. Historical eruptions, documented since 1558, have consisted largely of mild-to-moderate explosive activity with occasional lava effusion. Glaciers cover 40 km2 of the volcano, and lahars have damaged towns on its flanks.

Information Contacts: H. Moreno, G. Fuentealba, M. Petit-Breuilh, and P. Peña, SERNAGEOMIN, Temuco.


White Island (New Zealand) — December 1994 Citation iconCite this Report

White Island

New Zealand

37.52°S, 177.18°E; summit elev. 321 m

All times are local (unless otherwise noted)


Lake persists in Wade Crater; rockslides; inflation continues

No evidence of eruptive activity was observed on 5 October, although clear conditions allowed for good views into the 1978/90 crater complex (figure 22). The floor of Wade Crater remained occupied by a lake that appeared light-gray with several dark-gray slicks; no convection or geysering was seen. On the rear wall below the May 91 embayment, there was a large audible fumarole. All traces of Royce Crater had been removed by landslide debris, and the floor of Princess Crater contained a small pond. The Wade Crater lake was still light-gray on 11 November with a bright green zone in the NW part. The ridge between TV1 Crater and Wade/Princess continued to fail. During a visit on 21 November the large lake in Wade Crater was covered by plates of gray scum in constant motion. Strong ebullition was occurring in the lake center to a height of 1-2 m. There was no sign of recent eruptions; a number of recent rockfalls had occurred from the steep walls of Wade, Princess, TV1, and Donald Duck craters. A small green lake was present in TV1 Crater.

Figure (see Caption) Figure 22. Sketch map of Main Crater at White Island showing craters and peg locations as of 21 November 1994. Contour elevations are in meters. Courtesy of the IGNS.

A complete deformation survey on 21 November showed a continuation of the crater-wide uplift noted during the June and August surveys. The Donald Duck-TV1 area, previously rising much less rapidly than the area to the S, has recently been rising at a comparable rate. This uplift is interpreted by the IGNS as minor crater-wide inflation that began in early 1993, although the strong deflation that characterized the Donald Mound area persisted until mid-1994. Magnetic changes since 28 June 1994 showed a pattern similar to the three previous periods, with a positive anomaly NW of Donald Duck, a negative anomaly N of Donald Mound, and a positive anomaly S of Donald Mound. The magnitude of the changes is slightly less than for the 12 February 1993 to 28 June 1994 period, but the rate of change had increased slightly. These magnetic changes are again interpreted as resulting from a shallow heating under Donald Mound (~50 m deep) and shallow cooling under TV1.

Geologic Background. Uninhabited 2 x 2.4 km White Island, one of New Zealand's most active volcanoes, is the emergent summit of a 16 x 18 km submarine volcano in the Bay of Plenty about 50 km offshore of North Island. The island consists of two overlapping andesitic-to-dacitic stratovolcanoes; the summit crater appears to be breached to the SE, because the shoreline corresponds to the level of several notches in the SE crater wall. Volckner Rocks, four sea stacks that are remnants of a lava dome, lie 5 km NNE. Intermittent moderate phreatomagmatic and strombolian eruptions have occurred throughout the short historical period beginning in 1826, but its activity also forms a prominent part of Maori legends. Formation of many new vents during the 19th and 20th centuries has produced rapid changes in crater floor topography. Collapse of the crater wall in 1914 produced a debris avalanche that buried buildings and workers at a sulfur-mining project.

Information Contacts: B. Scott and P. Otway, IGNS, Wairakei.

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/).