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Bulletin of the Global Volcanism Network

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

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


Recently Published Bulletin Reports

Tengger Caldera (Indonesia) Ash emissions on 19 and 28 July 2019; lahar on the SW flank of Bromo

Unnamed (Tonga) Submarine eruption in early August creates pumice rafts that drifted west to Fiji

Popocatepetl (Mexico) Frequent explosions continue during March-August 2019

Semeru (Indonesia) Intermittent activity continues during March-August 2019; ash plumes and thermal anomalies

Saunders (United Kingdom) Intermittent activity most months, October 2018-June 2019; photographs during February and May 2019

Pacaya (Guatemala) Lava flows and Strombolian explosions continued during February-July 2019

Colima (Mexico) Renewed volcanism after two years of quiet; explosion on 11 May 2019

Masaya (Nicaragua) Lava lake activity declined during March-July 2019

Rincon de la Vieja (Costa Rica) Occasional weak phreatic explosions during March-July 2019

Aira (Japan) Explosions with ejecta and ash plumes continue weekly during January-June 2019

Agung (Indonesia) Continued explosions with ash plumes and incandescent ejecta, February-May 2019

Kerinci (Indonesia) Intermittent explosions with ash plumes, February-May 2019



Tengger Caldera (Indonesia) — August 2019 Citation iconCite this Report

Tengger Caldera

Indonesia

7.942°S, 112.95°E; summit elev. 2329 m

All times are local (unless otherwise noted)


Ash emissions on 19 and 28 July 2019; lahar on the SW flank of Bromo

The Mount Bromo pyroclastic cone within the Tengger Caldera erupts frequently, typically producing gas-and-steam plumes, ash plumes, and explosions (BGVN 44:05). Information compiled for the reporting period of May-July 2019 is from the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC).

The eruptive activity at Tengger Caldera that began in mid-February continued through late July 2019, including white-and-brown ash plumes, ash emissions, and tremors. During the months of May through June 2019, white plumes rose between 50 to 600 m above the summit. Satellite imagery captured a small gas-and-steam plume from Bromo on 5 June (figure 18). Low-frequency tremors were recorded by a seismograph from May through July 2019.

Figure (see Caption) Figure 18. Sentinel-2 satellite image showing a small gas-and-steam plume rising from the Bromo cone (center) in the Tengger Caldera on 5 June 2019. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

According to PVMBG and a Volcano Observatory Notice for Aviation (VONA), an ash eruption occurred on 19 July 2019; however, no ash column was observed due to weather conditions. A seismograph recorded five earthquakes and three shallow volcanic tremors the same day. In addition, rainfall triggered a lahar on the SW flank of Bromo.

On 28 July the Darwin VAAC reported that ash plumes originating from Bromo rose to a maximum altitude of about 3.9 km and drifted NW from the summit, based on webcam images and pilot reports. PVMBG reported that lower altitude ash plumes (2.4 km) on the same day were also recorded by webcam images, satellite imagery (Himawari-8), and weather models.

Geologic Background. The 16-km-wide Tengger caldera is located at the northern end of a volcanic massif extending from Semeru volcano. The massive volcanic complex dates back to about 820,000 years ago and consists of five overlapping stratovolcanoes, each truncated by a caldera. Lava domes, pyroclastic cones, and a maar occupy the flanks of the massif. The Ngadisari caldera at the NE end of the complex formed about 150,000 years ago and is now drained through the Sapikerep valley. The most recent of the calderas is the 9 x 10 km wide Sandsea caldera at the SW end of the complex, which formed incrementally during the late Pleistocene and early Holocene. An overlapping cluster of post-caldera cones was constructed on the floor of the Sandsea caldera within the past several thousand years. The youngest of these is Bromo, one of Java's most active and most frequently visited volcanoes.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/).


Unnamed (Tonga) — November 2019 Citation iconCite this Report

Unnamed

Tonga

18.325°S, 174.365°W; summit elev. -40 m

All times are local (unless otherwise noted)


Submarine eruption in early August creates pumice rafts that drifted west to Fiji

Large areas of floating pumice, termed rafts, were encountered by sailors in the northern Tonga region approximately 80 km NW of Vava'u starting around 9 August 2019; the pumice reached the western islands of Fiji by 9 October (figure 7). Pumice rafts are floating masses of individual clasts ranging from millimeters to meters in diameter. The pumice clasts form when silicic magma is degassing, forming bubbles as it rises to the surface, which then rapidly cools to form solid rock. The isolated vesicles formed by the bubbles provide buoyancy to the rock and in turn, the entire pumice raft. These rafts are spread and carried by currents across the ocean; rafts originating in the Tonga area can eventually reach Australia. This report summarizes the pumice raft eruption from early August 2019 using witness accounts and satellite images (acquisition dates are given in UTC). Pending further research, the presumed source is the unnamed Tongan seamount (volcano number 243091) about 45 km NW of Vava'u, the origin of an earlier pumice raft produced during an eruption in 2001.

Figure (see Caption) Figure 7. The path of the pumice from the unnamed Tongan seamount from 9 August to 9 October 2019 based on eye-witness accounts and satellite data discussed below, as well as additional Aqua/MODIS satellite images from NASA Worldview. Blue Marble MODIS/NASA Earth Observatory base map courtesy of NASA Worldview.

The first sighting of pumice was around 1430 on 9 August NW of Vava'u in Tonga (18° 22.068' S, 174° 50.800' W), when Shannon Lenz and Tom Whitehead on board SV Finely Finished initially encountered isolated rocks and smaller streaks of pumice clasts. The area covered by rock increasing to a raft with an estimated thickness of at least 15 cm that extended to the horizon in different directions, and which took 6-8 hours to cross (figure 8). There was no sulfur smell and the sound was described as a "cement mixer, especially below deck." There was also no plume or incandescence observed. Their video, posted to YouTube on 17 August, showed a thin surface layer of cohesive interconnected irregular streaks of pumice with the ocean surface still visible between them. Later footage showed a continuous, undulating mass of pumice entirely covering the ocean surface. Larger clasts are visible scattered throughout the raft. The pumice raft was visible in satellite imagery on this day NW of Late Island (figure 9). By 11 August the raft had evolved into a largely linear feature with smaller rafts to the SW (figure 10). Approximately four hours later, about 15 km to the WSW, Rachel Mackie encountered the pumice. Initially the pumice was "ribbons several hundred meters long and up to 20m wide. It was quite fine and like a slick across the surface of the water." By 2130 they were surrounded by the pumice, and around 25 km away the smell of sulfur was noted.

Figure (see Caption) Figure 8. The pumice raft from the unnamed Tongan seamount on 9 August 2019 taken by Shannon Lenz and Tom Whitehead on board SV Finely Finished. The photos show the pumice raft extending to the horizon in different directions. Scattered larger clasts protrude from the relatively smooth surface that entirely obscures the ocean surface. Courtesy of Shannon Lenz and Tom Whitehead via noonsite.
Figure (see Caption) Figure 9. The pumice raft from the unnamed Tongan seamount on 9 August 2019 (UTC) can be seen NW of Late Island of Tonga in this Aqua/MODIS satellite image. The dashed white line encompasses the visible pumice. The location of the pumice in this image is shown in figure 7. Courtesy of NASA WorldView.
Figure (see Caption) Figure 10. The Sentinel-2 satellite first imaged the pumice from the unnamed Tongan seamount on 11 August 2019 (UTC). This image indicates the pumice distribution with the main raft towards the W and the easternmost area of pumice approximately 45 km away. The eastern tip of the pumice area is located approximately 30 km WNW of Lake islands in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

Michael and Larissa Hoult aboard the catamaran ROAM encountered the raft on 15 August (figure 11). They initially saw isolated clasts ranging from marble to tennis ball size (15-70 mm) at 18° 46′S, 174° 55'W. At around 0700 UTC (1900 local time) they noted the smell of sulfur at 18° 55′S, 175° 21′W, and by 0800 UTC they were immersed in the raft with visible clasts ranging from marble to basketball (25 cm) sizes. At this point the raft was entirely obscuring the ocean surface. On 16 and 21 August the pumice continued to disperse and drift NW (figures 12 and 13). On 20 August Scott Bryan calculated an average drift rate of around 13 km/day, with the pumice on this date about 164 km W of the unnamed seamount.

Figure (see Caption) Figure 11. Images of pumice from the unnamed Tongan seamount encountered by Michael and Larissa Hoult aboard the catamaran Roam on 15 August. Left: Larissa takes photographs with scale of pumice clasts; top right: a closeup of a pumice clast showing the vesicle network preserving the degassing structures of the magma; bottom left: Michael holding several larger pumice clasts. The location of their encounter with the pumice is shown in figure 7. Courtesy of SailSurfROAM.
Figure (see Caption) Figure 12. The pumice from the unnamed Tongan seamount (volcano number 243091) on 16 August 2019 UTC. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 13. On 21 August 2019 (UTC) the pumice from the unnamed Tongan seamount (volcano number 243091) had drifted at least 120 km WNW of Late Island in Tonga. The location of the pumice in this image is shown in figure 7. Natural color (bands 4, 3, 2) Sentinel-2 satellite image courtesy of Sentinel Hub Playground.

An online article published by Brad Scott at GeoNet on 9 September reported the preliminary size of the raft to be 60 km2, significantly smaller than the 2012 Havre seamount pumice raft that was 400 km2. Satellite identification of pumice-covered areas by GNS scientists showed the material moving SSW through 14 August (figure 14).

Figure (see Caption) Figure 14. A compilation of mapped pumice raft extents from 9 August (red line) through to 14 August (dark blue) from Suomi NPP, Terra, Aqua, and Sentinel-2 satellite images. The progression of the pumice raft is towards the SW. Courtesy of Salman Ashraf, GNS Science.

On 5 September the Maritime Safety Authority of Fiji (MSAF) issued a notice to mariners stating that the pumice was sighted in the vicinity of Lakeba, Oneata, and Aiwa Islands and was moving to the W. On 6 September a Planet Labs satellite image shows pumice encompassing the Fijian island of Lakeba over 450 km W of the Tongan islands (figure 15). The pumice entered the lagoon within the barrier reef and drifted around the island to continue towards the W. The pumice was imaged by the Landsat 8 satellite on 26 September as it moved through the Fijian islands, approximately 760 km away from its source (figure 16). The pumice is segmented into numerous smaller rafts of varying sizes that stretch over at least 140 km. On 12 September the Fiji Sun reported that the pumice had reached some of the Lau islands and was thick enough near the shore for people to stand on it.

Figure (see Caption) Figure 15. Planet Labs satellite images show Lakeba Island to the E of the larger Viti Levu Island in the Fiji archipelago. The top image shows the island on 7 July 2019 prior to the pumice raft from the unnamed Tongan seamount. The bottom image shows pumice on the sea surface almost entirely encompassing the island on 6 September. The location of the pumice in this image is shown in figure 7. Courtesy of Planet Labs.
Figure (see Caption) Figure 16. Landsat 8 satellite images show the visible extent of the unnamed seamount pumice on 26 September 2019 (UTC), up to approximately 760 km from the Tongan islands. The pumice seen here extends over a distance of 140 km. The top image shows the locations of the other three images in the white boxes, with a, b, and c indicating the locations. White arrows point to examples of the light brown pumice rafts in these images, seen through light cloud cover. The island in the lower right is Koro Island, the island to the lower left is Viti Levu, and the island to the top right is Vanua Levu. The location of the pumice in this image is shown in figure 7. Landsat 8 true color-pansharpened satellite images courtesy of Sentinel Hub.

Pumice had reached the Yasawa islands in western Fiji by 29 September and was beginning to fill the eastern bays (figure 17). By 9 October bays had been filled out to 500-600 m from the shore, and pumice had also passed through the islands to continue towards the W (figure 18). At this point the pumice beyond the islands had broken up into linear segments that continued towards the NW.

Figure (see Caption) Figure 17. These Sentinel-2 satellite images show the pumice from the unnamed Tongan seamount drifting towards the Yasawa islands of Fiji. The 24 September 2019 (UTC) image shows the beaches without the pumice, the 29 September image shows pumice drifting westward towards the islands, and the 9 October image shows the bays partly filled with pumice out to a maximum of 500-600 m from the shore. These islands are approximately 850 km from the Tongan islands. The Yasawa islands coastline impacted by the pumice shown in these images stretches approximately 48 km. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.
Figure (see Caption) Figure 18. This Sentinel-2 satellite image acquired on 9 October 2019 (UTC) shows expanses of pumice from the unnamed Tongan seamount that passed through the Yasawa islands of Fiji and was continuing NWW, seen in the center of the image. The location of the pumice in this image is shown in figure 7. Sentinel-2 natural color (bands 4, 3, 2) satellite images courtesy of Sentinel Hub.

Geologic Background. A submarine volcano along the Tofua volcanic arc was first observed in September 2001. The newly discovered volcano lies NW of the island of Vava'u about 35 km S of Fonualei and 60 km NE of Late volcano. The site of the eruption is along a NNE-SSW-trending submarine plateau with an approximate bathymetric depth of 300 m. T-phase waves were recorded on 27-28 September 2001, and on the 27th local fishermen observed an ash-rich eruption column that rose above the sea surface. No eruptive activity was reported after the 28th, but water discoloration was documented during the following month. In early November rafts and strandings of dacitic pumice were reported along the coast of Kadavu and Viti Levu in the Fiji Islands. The depth of the summit of the submarine cone following the eruption determined to be 40 m during a 2007 survey; the crater of the 2001 eruption was breached to the E.

Information Contacts: GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/); Salman Ashraf, GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.gns.cri.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Brad Scott, New Zealand GeoNet Project, a collaboration between the Earthquake Commission and GNS Science, Wairakei Research Centre, Private Bag 2000, Taupo 3352, New Zealand (URL: http://www.geonet.org.nz/, https://www.geonet.org.nz/news/8RnSKdhaWOEABBIh0bHDj); Scott Bryan, School of Earth, Environmental & Biological Sciences, Science and Engineering Faculty, Queensland University of Technology, R Block Level 2, 204, Gardens Point (URL: https://staff.qut.edu.au/staff/scott.bryan); Shannon Lenz and Tom Whitehead, SV Finely Finished (URL: https://www.noonsite.com/news/south-pacific-tonga-to-fiji-navigation-alert-dangerous-slick-of-volcanic-rubble/, YouTube: https://www.youtube.com/watch?v=PEsHLSFFQhQ); Michael and Larissa Hoult, Sail Surf ROAM (URL: https://www.facebook.com/sailsurfroam/); Rachel Mackie, OLIVE (URL: http://www.oliveocean.com/, https://www.facebook.com/rachel.mackie.718); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/); Fiji Sun (URL: https://fijisun.com.fj/2019/09/12/pumice-menace-hits-parts-of-lau-group/).


Popocatepetl (Mexico) — September 2019 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Frequent explosions continue during March-August 2019

The current eruptive period of Popocatépetl began on 9 January 2005 and it has since been producing frequent explosions accompanied by ash plumes, gas emissions, and ballistic ejecta that can impact several kilometers away from the crater, as well as dome growth and destruction. This activity continued through March-August 2019 with an increase in volcano alert level during 28 March-6 May. This report summarizes activity during this period and is based on information from Centro Nacional de Prevención de Desastres (CENAPRED), Universidad Nacional Autónoma de México (UNAM), and various webcam and remote sensing data.

An overflight on 28 February confirmed that dome 82, which was first observed on 14 February, was still present and was 200 m in diameter. During March there were 3,291 observed low-intensity emissions, and 33 larger explosions that produced ash plumes to a maximum height of 5 km, accompanied by near-continuous emission of water vapor and volcanic gases. Explosions ejected blocks that fell on the flanks out to 1.2-2 km on 1, 10, 13, 17, 26, 27, and 29 March. The events on the 17th and 27th resulted in vegetation fires. Frequent sulfur dioxide (SO2) plumes were detected by TropOMI (figure 130). An overflight on 7 March showed intense degassing and an ash plume at 1142, preventing visibility into the crater (figure 131). On 13 March Strombolian activity was observed for approximately 15 minutes at 0500, accompanied by incandescent ejecta that deposited mainly on the ESE flank.

An overflight on 15 March was taken by CENAPRED and UNAM personnel to observe changes to the crater after explosions on the 13th and 14th. They reported that dome 82 had been destroyed and the crater maintained its previous dimensions of 300 m in diameter and 130 m deep. An explosion on the 27th ejected incandescent rocks out to 2 km from the crater and produced a 3-km-high ash plume that dispersed to the NE. Ashfall was reported in Santa Cruz, Atlixco, San Pedro, San Andrés, Santa Isabel Cholula, San Pedro Benito Juárez, and in the municipalities of Puebla, Hueyapan, Tetela del Volcán, and Morelos.

On 28 March an explosion at 0650 generated a 2.5-km-high ash plume and ejecta out to 1 km from the crater, and a 130-minute-long event produced gas and ah plumes (figure 132). On this day the volcano alert level was increased from Yellow Phase 2 to Yellow Phase 3. On the 29th an ash plume rose to 3 km and was accompanied by ejecta that reached 2 km away from the crater. Later that day a 20-minute-long event produced ash and gas. During a surveillance flight on 30 March a view into the crater showed no dome present, and the crater size had increased to 350 m in width and 250-300 m in depth after recent explosions (figure 131). On this day Strombolian activity was also observed lasting for 14 minutes, producing an ash plume to 800 m and ejecta out to 300 m from the crater. Incandescence at the crater was often seen during nighttime throughout the month.

Figure (see Caption) Figure 130. Significant SO2 plumes at Popocatépetl detected by the TROPOMI instrument on the Sentinel-5P satellite during 3-11 March 2019. SO2 plumes are frequently observed and these images show examples of plume drift directions on 3 March 2019 (top left), 6 March 2019 (top right), 7 March 2019 (bottom left), and 11 March 2019 (bottom right). Date, time, and measurements are provided at the top of each image. Courtesy of NASA Goddard Flight Center.
Figure (see Caption) Figure 131. Activity at Popocatépetl and views of the crater during surveillance flights in March 2019. The top images show an ash plume (left) and a gas-and-steam plume (right) on 7 March. On 30 March (bottom left and right) no lava dome was observed in the crater, which was measured to be 350 m in diameter and 250-300 m deep. Courtesy of CENAPRED and Geophysics Institute of UNAM.
Figure (see Caption) Figure 132. Explosive activity at Popocatépetl on 28 March 2019 producing ash plumes (top and bottom left) and ejecting incandescent ejecta out to 2 km from the crater at 1948. Courtesy of Carlos Sanchez/AFP (top), CENAPRED (bottom left and right), and Webcams de Mexico (bottom left).

There was a decrease in events during the next two months with 1,119 recorded low-intensity emissions and no larger ash explosions throughout April, followed by 1,210 low-intensity emissions and seven larger ash explosions through May (figure 133). Water vapor and volcanic gas emissions were frequently observed through this time and incandescence was observed some nights. A surveillance overflight on 26 April noted no new dome within the crater. On 6 May the alert level was lowered back to Yellow Phase 2. Another overflight on 9 May showed no change in the crater. An explosion at 1910 on 22 May produced an ash plume to 3.5 km above the crater with ashfall reported in Ozumba, Temamatla, Atlautla, Cocotitlán, Ayapango, Ecatzingo, Tenango del Aire and Tepetlixpa.

Figure (see Caption) Figure 133. Graph showing the number of daily ash explosions and low-intensity emissions at Popocatépetl during March-August 2019. There was a decrease in the number of events during April and March, with an increase from March onwards. Data courtesy of CENAPRED.

Through the month of June there were 2,820 low-intensity emissions and 21 larger ash explosions recorded. Gas emissions were observed throughout the month. Two explosions on 3 June produced ash plumes up to 3.5 and 2.8 km, with ejecta out to 2 km S during the first explosion. On 11 June an explosion produced an ash plume to 1 km above the crater and ballistic ejecta out to 1 km E. Observers on a surveillance overflight on the 12th reported no changes within the crater

Explosions with estimated plume heights of 5 km occurred on the 14th and 15th, with the latter producing ashfall in the municipalities of San Pablo del Monte, Tenancingo, Papantla, San Cosme Mazatencocho, San Luis Teolocholco, Acuamanala, Nativitas, Tepetitla, Santa Apolonia Teacalco, Santa Isabel Tetlatlahuaca, and Huamantla, in the state of Tlaxcala, as well as in Nealtican, San Nicolás de los Ranchos, Calpan, San Pedro Cholula, Juan C. Bonilla, Coronango, Atoyatempan, and Coatzingo, in the state of Puebla.

On 17 June an explosion produced an ash plume that reached 8 km above the crater and dispersed towards the SW. An ash plume rising 2.5 km high was accompanied by incandescent ejecta impacting a short distance from the crater on the 21st, and another ash plume reached 2.5 km on the 22nd. Explosions on 26, 29, and 30 June resulted in ash plumes reaching 1.5 km above the crater and ballistic ejecta impacting on the flanks out to 1 km.

For the month of July there was an increased total of 5,637 recorded low-intensity emissions, and 173 larger ash explosions (figure 134). On 8 July an explosion produced ballistic ejecta out to 1.5 km and an ash plume up to 1 km above the crater. An ash plume up to 2.6 km was produced on the 12th. On 19 July a surveillance overflight observed a new dome (dome 83) with a diameter of 70 m and a thickness of 15 m (figure 135). Explosions on 20 July produced ashfall, and minor explosions that ejected incandescent ballistics onto the slopes. An event on the 24th produced an ash plume that reached 1.2 km, and ash plumes the following day reached 1 km. An overflight on 27 July confirmed that these explosions destroyed dome 83, and the crater dimensions remained the same (figure 136). The following day, ash plumes reached up to 1.6 km above the crater, and up to 2 km on the 29th. Minor ashfall was reported in the municipality of Ozumba on 30 June.

Figure (see Caption) Figure 134. Examples of ash plumes at Popocatépetl on 1 July (top left), 18 July (top right and bottom left), and 30 July (bottom right) 2019. In the night time image taken on 18 July hot rocks are visible on the flank. Webcam images courtesy of CENAPRED and Webcams de Mexico.
Figure (see Caption) Figure 135. A surveillance overflight at Popocatépetl on 19 July 2019 confirmed a new dome, dome number 83, with a width of 70 m and a thickness of 15 m. Courtesy of CENAPRED and Geophysics Institute of UNAM.
Figure (see Caption) Figure 136. Photos of the summit crater of Popocatépetl taken during a surveillance flight on 27 July 2019 confirmed that the 83rd lava dome was destroyed by recent explosions and the crater maintained the same dimensions as previously measured. Courtesy of CENAPRED and Geophysics Institute of UNAM.

Throughout August the number of recorded events was higher than previous months, with 5,091 low-intensity emissions and 204 larger ash explosions (figure 137). Two explosions generated ash plumes and incandescent ejecta on 2 August, the first with a plume up to 1.5 km with ejecta impacting the slopes, and the second with an 800 m plume and ejecta landing back in the crater. Ashfall from the events was reported in in the municipalities of Tenango del Aire, Ayapango and Amecameca. On the 14th ashfall was reported in Juchitepec, Ayapango, and Ozumba. Explosions on 16 August produced ash plumes up to 2 km that dispersed to the WSW. Over the following two days ash plumes reached 1.2 km and resulted in ashfall in Cuernavaca, Tepoztlán, Tlalnepantla, Morelos, Ozumba, and Ecatzingo. Over 30-31 August ash plumes reached between 1-2 km above the crater and ashfall was reported in Amecameca, Atlautla, Ozumba, and Tlalmanalco. Incandescence was sometimes observed at the crater through the month.

Figure (see Caption) Figure 137. Ash plumes at Popocatépetl on 7 August (top) and 26 August 2019 (bottom). Courtesy of CENAPRED and Webcams de Mexico.

The MODVOLC algorithm for MODIS thermal anomalies registered thermal alerts through this period, with 22 in March, three in May, five in July, and one in August. The MIROVA system showed that the frequency of thermal anomalies at Popocatépetl was higher in March, sporadic in April and May, low in June, and had increased again in July and August (figure 138). Elevated temperatures were frequently visible in Sentinel-2 thermal satellite data when clouds and plumes were not covering the crater (figure 139).

Figure (see Caption) Figure 138. Thermal activity at Popocatépetl detected by the MIROVA system showed frequent anomalies in March, intermittent anomalies through April-May, low activity in June, and an increase in July-August 2019. Courtesy of MIROVA.
Figure (see Caption) Figure 139. Sentinel-2 thermal satellite images frequently showed elevated temperatures in the crater of Popocatépetl during March-August 2019, as seen in this representative image from 7 May 2019. Sentinel2- atmospheric penetration (bands 12, 11, 8A) scene courtesy of Sentinel Hub Playground.

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/); Universidad Nacional Autónoma de México (UNAM), University City, 04510 Mexico City, Mexico (URL: https://www.unam.mx/); 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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Webcams de Mexico (URL: http://www.webcamsdemexico.com/); Agence France-Presse (URL: http://www.afp.com/).


Semeru (Indonesia) — September 2019 Citation iconCite this Report

Semeru

Indonesia

8.108°S, 112.922°E; summit elev. 3657 m

All times are local (unless otherwise noted)


Intermittent activity continues during March-August 2019; ash plumes and thermal anomalies

The ongoing eruption at Semeru weakened in intensity during 2018, with occasional ash plumes and thermal anomalies (BGVN 44:04); this reduced but ongoing level of activity continued through August 2019. The volcano is monitored by the Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM) and the Darwin Volcanic Ash Advisory Centre (VAAC). The current report summarizes activity from 1 March to 31 August 2019. The Alert Level remained at 2 (on a scale from 1-4); the public was warned to stay 1 km away from the active crater and 4 km away on the SSE flank.

Based on analysis of satellite images, the Darwin VAAC reported that ash plumes rose to an altitude of 4-4.3 km on 19 April, 20 June, 10 July, and 13 July, drifting in various directions. In addition, PVMBG reported that at 0830 on 26 June an explosion produced an ash plume that rose around 600 m above the summit and drifted SW. A news article (Tempo.com) dated 12 August cited PVMBG as stating that the volcano had erupted 17 times since 8 August.

During March-August 2019 thermal anomalies were detected with the MODIS satellite instruments analyzed using the MODVOLC algorithm only on 5 July and 22 August. No explosions were recorded on those two days. Scattered thermal anomalies within 5 km of the volcano were detected by the MIROVA (Middle InfraRed Observation of Volcanic Activity) system, also based on analysis of MODIS data: one at the end of March and 3-6 hotspots over the following months, almost all of low radiative power. Satellite imagery intermittently showed thermal activity in the Jonggring-Seloko crater (figure 37), sometimes with material moving down the SE-flank ravine.

Figure (see Caption) Figure 37. Sentinel-2 satellite images showing the persistent elevated thermal anomaly in the Jonggring-Seloko crater of Semeru were common through August 2019, as seen in this view on 20 July. Hot material could sometimes be identified in the SE-flank ravine. Atmospheric penetration rendering (bands 12, 11, 8A) courtesy of Sentinel Hub Playground.

Geologic Background. Semeru, the highest volcano on Java, and one of its most active, lies at the southern end of a volcanic massif extending north to the Tengger caldera. The steep-sided volcano, also referred to as Mahameru (Great Mountain), rises above coastal plains to the south. Gunung Semeru was constructed south of the overlapping Ajek-ajek and Jambangan calderas. A line of lake-filled maars was constructed along a N-S trend cutting through the summit, and cinder cones and lava domes occupy the eastern and NE flanks. Summit topography is complicated by the shifting of craters from NW to SE. Frequent 19th and 20th century eruptions were dominated by small-to-moderate explosions from the summit crater, with occasional lava flows and larger explosive eruptions accompanied by pyroclastic flows that have reached the lower flanks of the volcano.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); 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); Tempo.com (URL: https://www.tempo.com/).


Saunders (United Kingdom) — August 2019 Citation iconCite this Report

Saunders

United Kingdom

57.8°S, 26.483°W; summit elev. 843 m

All times are local (unless otherwise noted)


Intermittent activity most months, October 2018-June 2019; photographs during February and May 2019

Historical observations of eruptive activity from the glacier-covered Mount Michael stratovolcano on Saunders Island in the South Sandwich Islands were not recorded until the early 19th century at this remote site in the southernmost Atlantic Ocean, and remain extremely rare. With the advent of satellite observation technology, indications of more frequent eruptive activity have become apparent. Vapor emission is frequently reported from the summit crater, and AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater (Lachlan-Cope and others, 2001). Limited thermal anomaly data and satellite imagery indicated at least intermittent activity during May 2000-November 2013, and from November 2014 through April 2018 (Gray and others, 2019). Ongoing observations, including photographs from two site visits in February and May 2019 suggest continued activity at the summit during most months through May 2019, the period covered in this report. Information, in addition to on-site photographs, comes from MIROVA thermal anomaly data, NASA SO2 instruments, and Sentinel-2 and Landsat satellite imagery.

Near-constant cloud coverage for much of the year makes satellite data intermittent and creates difficulty in interpreting the ongoing nature of the activity. Gray and others (2019) concluded recently after a detailed study of shortwave and infrared satellite images that there was continued evidence for the previously identified lava lake on Mount Michael since January 1989. MIROVA thermal anomaly data suggest intermittent pulses of thermal energy in September, November, and December 2018, and April 2019 (figure 17). Satellite imagery confirmed some type of activity, either a dense steam plume, evidence of ash, or a thermal anomaly, each month during December 2018-March 2019. Sulfur dioxide anomalies were recorded in January, February, and March 2019. Photographic evidence of fresh ash was captured in February 2019, and images from May 2019 showed dense steam rising from the summit crater.

Figure (see Caption) Figure 17. MIROVA thermal anomaly data from 19 September 2018 through June 2019 showed sporadic, low-level pulses of thermal energy in late September, November, and December 2018, and April 2019. Courtesy of MIROVA.

After satellite imagery and thermal anomaly data in late September 2018 showed evidence for eruptive activity (BGVN 43:10, figure 16), a single thermal anomaly in MIROVA data was recorded in mid-November 2018 (figure 17). A rare, clear Sentinel-2 image on 2 December revealed a dense steam plume over the active summit crater; the steam obscured the presence of any possible thermal anomalies beneath (figure 18).

Figure (see Caption) Figure 18. Sentinel-2 images of Mount Michael on Saunders Island on 2 December 2018 revealed a dense steam plume over the summit crater that was difficult to distinguish from the surrounding snow in Natural Color rendering (bands 4,3,2) (left), but was clearly visible in Atmospheric Penetration rendering (bands 12,11, 8a) (right). Courtesy of Sentinel Hub Playground.

Clear evidence of recent activity appeared on 1 January 2019 with both a thermal anomaly at the summit crater and a streak of ash on the snow (figure 19). Steam was also present within the summit crater. A distinct SO2 anomaly appeared in data from the TROPOMI instrument on 14 January (figure 20).

Figure (see Caption) Figure 19. A thermal anomaly and dense steam were recorded at the summit of Mount Michael on Saunders Island on 1 January 2019 in Sentinel-2 Satellite imagery with Atmospheric Penetration rendering (bands 12, 11, 8a) (left). The same image shown with Natural Color rendering (bands 4,3,2) (right) shows a recent streak of brown particulates drifting SE from the summit crater. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 20. A distinct SO2 plume was recorded drifting NW from Saunders Island by the TROPOMI instrument on the Sentinel 5-P satellite on 14 January 2019. Courtesy of NASA Goddard Space Flight Center.

Multiple sources of satellite data and sea-based visual observation confirmed activity during February 2019. SO2 emissions were recorded with the TROPOMI instrument on 10, 11, 15, and 16 February (figure 21). A Landsat image from 10 February showed a dense steam plume drifting NW from the summit crater, with the dark rim of the summit crater well exposed (figure 22). Sentinel-2 images in natural color and atmospheric penetration renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February (figure 23). An expedition to the South Sandwich Islands between 15 February and 8 March 2019 sponsored by the UK government sailed by Saunders in late February and observed a stream of ash on the NNE flank beneath the cloud cover (figure 24).

Figure (see Caption) Figure 21. Faint but distinct SO2 plumes were recorded drifting away from Saunders Island in various directions on 10, 11, 15, and 16 February 2019. Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 22. The dark summit crater of Mount Michael on Saunders Island was visible in Landsat imagery on 10 February 2019. A dense steam plume drifted NW and cast a dark shadow on the underlying cloud cover. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 23. At the summit of Mount Michael on Saunders Island, Sentinel-2 images in Natural Color (bands 4,3,2) (left) and Atmospheric Penetration (bands 12, 11, 8a) (right) renderings identified a dense steam plume drifting S and a thermal anomaly within the summit crater on 15 February 2019. Courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 24. Recent ash covered the NNE flank of Mount Michael on Saunders Island in late February 2019 when observed by an expedition to the South Sandwich Islands sponsored by the UK government. Courtesy of Chris Darby.

Faint SO2 emissions were recorded twice during March 2019 (figure 25), and a dense steam plume near the summit crater was visible in Landsat imagery on 23 March (figure 26). Two thermal anomalies were captured in the MIROVA data during April 2019 (figure 17).

Figure (see Caption) Figure 25. Faint SO2 plumes were recorded on 1 and 11 March 2019 emerging from Saunders Island. Courtesy of NASA Goddard Space Flight Center.
Figure (see Caption) Figure 26. A dense steam plume drifted E from the summit crater of Mount Michael at Saunders Island on 25 March 2019. Landsat-8 image courtesy of Sentinel Hub Playground.

A volcano-related research project "SSIVOLC" explored the South Sandwich Islands volcanoes during 15 April-31 May 2019. A major aim of SSIVOLC was to collect photogrammetric data of the glacier-covered Mount Michael (Derrien and others, 2019). A number of still images were acquired on 17 and 22 May 2019 showing various features of the island (figures 27-30). The researchers visually observed brief, recurrent, and very weak glow at the summit of Mount Michael after dark on 17 May, which they interpreted as reflecting light from an active lava lake within the summit crater.

Figure (see Caption) Figure 27. The steep slopes of an older eroded crater on the E end of Saunders island in the 'Ashen Hills' shows layers of volcanic deposits dipping away from the open half crater. In the background, steam and gas flow out of the summit crater of Mount Michael and drift down the far slope. Drone image PA-IS-03 taken during 17-22 May 2019, courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.
Figure (see Caption) Figure 28. A dense steam plume drifts away from the summit of Mount Michael on Saunders Island in this drone image taken during 17-22 May 2019. The older summit crater is to the left of the dark patch in the middle of the summit. North is to the right. Image SU-3 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.
Figure (see Caption) Figure 29. This close-up image of the summit of Mount Michael on Saunders Island shows steam plumes billowing from the summit crater, and large crevasses in the glacier covered flank, taken during 17-22 May 2019. The old crater is to the left. Image TL-SU-1 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.
Figure (see Caption) Figure 30. A dense plume of steam rises from the summit crater of Mount Michael on Saunders Island and drifts over mounds of frozen material during 17-22 May 2019. The older crater is to the left, and part of the Ashen Hills is in the foreground. Image TL-SU-2 courtesy of Derrien and others (2019) used under Creative Commons Attribution 4.0 International (CC-BY 4.0) License.

References: Lachlan-Cope T, Smellie J L, Ladkin R, 2001. Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery. J. Volcanol. Geotherm. Res., 112: 105-116.

Gray D M, Burton-Johnson A, Fretwell P T, 2019. Evidence for a lava lake on Mt. Michael volcano, Saunders Island (South Sandwich Islands) from Landsat, Sentinel-2 and ASTER satellite imagery. J. Volcanol. Geotherm. Res., 379:60-71. https://doi.org/10.1016/j.volgeores.2019.05.002.

Derrien A, Richter N, Meschede M, Walter T, 2019. Optical DSLR camera- and UAV footage of the remote Mount Michael Volcano, Saunders Island (South Sandwich Islands), acquired in May 2019. GFZ Data Services. http://doi.org/10.5880/GFZ.2.1..2019.003

Geologic Background. Saunders Island is a volcanic structure consisting of a large central edifice intersected by two seamount chains, as shown by bathymetric mapping (Leat et al., 2013). The young constructional Mount Michael stratovolcano dominates the glacier-covered island, while two submarine plateaus, Harpers Bank and Saunders Bank, extend north. The symmetrical Michael has a 500-m-wide summit crater and a remnant of a somma rim to the SE. Tephra layers visible in ice cliffs surrounding the island are evidence of recent eruptions. Ash clouds were reported from the summit crater in 1819, and an effusive eruption was inferred to have occurred from a N-flank fissure around the end of the 19th century and beginning of the 20th century. A low ice-free lava platform, Blackstone Plain, is located on the north coast, surrounding a group of former sea stacks. A cluster of parasitic cones on the SE flank, the Ashen Hills, appear to have been modified since 1820 (LeMasurier and Thomson, 1990). Analysis of satellite imagery available since 1989 (Gray et al., 2019; MODVOLC) suggests frequent eruptive activity (when weatehr conditions allow), volcanic clouds, steam plumes, and thermal anomalies indicative of a persistent, or at least frequently active, lava lake in the summit crater. Due to this observational bias, there has been a presumption when defining eruptive periods that activity has been ongoing unless there is no evidence for at least 10 months.

Information Contacts: 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/); 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Chris Darby (URL: https://twitter.com/ChrisDDarby, image at https://twitter.com/ChrisDDarby/status/1100686838568812544).


Pacaya (Guatemala) — August 2019 Citation iconCite this Report

Pacaya

Guatemala

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

All times are local (unless otherwise noted)


Lava flows and Strombolian explosions continued during February-July 2019

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

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

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

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

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

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

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

Figure (see Caption) Figure 110. An active lava flow on Pacaya on 9 June 2019 with incandescent blocks rolling down the flank from the flow front. Courtesy of Paul Wallace, University of Liverpool.
Figure (see Caption) Figure 111. Activity at Pacaya on 22 June 2019 with a degassing plume dispersed to the W and a 300-m-long lava flow. Photos by Miguel Morales, courtesy of CONRED.
Figure (see Caption) Figure 112. Two lava flows were active to the N and NW at Pacaya on 20 July 2019. Photos courtesy of CONRED.

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

Figure (see Caption) Figure 113. Sentinel-2 thermal satellite images of Pacaya show lava flows to the N and NW during February through April 2019. There was a reduction in visible activity in early March. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 114. Sentinel-2 thermal satellite images of Pacaya showing lava flow and hot avalanche activity during June and July 2019. False color (urban) satellite images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 115. MIROVA log radiative power plot of MODIS thermal infrared at Pacaya during October 2018 through July 2019. Detected thermal energy is relatively stable with a decrease through June and subsequent increase during July. Courtesy of MIROVA.

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

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


Colima (Mexico) — August 2019 Citation iconCite this Report

Colima

Mexico

19.514°N, 103.62°W; summit elev. 3850 m

All times are local (unless otherwise noted)


Renewed volcanism after two years of quiet; explosion on 11 May 2019

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

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

Figure (see Caption) Figure 131. Gas emissions from Colima during the 11 May 2019 eruption as seen from the Naranjal station. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 17 mayo 2019 no 121).
Figure (see Caption) Figure 132. A drone photo showing fumarolic activity occurring within the NE wall of the crater at Colima on 22 May 2019. Courtesy of CUEIV-UdC (Boletin Seminal de la Actividad del Volcan de Colima 24 mayo 2019 no 122).

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

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

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

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


Masaya (Nicaragua) — August 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 activity declined during March-July 2019

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

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

Figure (see Caption) Figure 77. Active lava lake visible in the Santiago Crater at Masaya on 27 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).
Figure (see Caption) Figure 78. Gas emissions coming from the Santiago Crater at Masaya on 29 June 2019. Photo by Sheila DeForest (Creative Commons BY-SA license).

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

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

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

Figure (see Caption) Figure 80. Thermal anomalies were relatively constant at Masaya from early September 2018 through early May 2019 and then abruptly decreased until mid-June 2019 as recorded by MIROVA. Courtesy of MIROVA.
Figure (see Caption) Figure 81. Sentinel-2 thermal satellite image showing a detected heat signature from the active lava lake at Masaya on 10 March 2019. The lava lake is visible (bright yellow-orange). Approximate diameter of the crater containing the lava lake is 500 m. Thermal (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

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

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


Rincon de la Vieja (Costa Rica) — August 2019 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)


Occasional weak phreatic explosions during March-July 2019

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

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

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

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

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

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

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


Aira (Japan) — July 2019 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Explosions with ejecta and ash plumes continue weekly during January-June 2019

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

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

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

Month Ash emissions (explosive) Max. plume height above crater Max. ejecta distance from crater
Jan 2019 8 (6) 2.1 km 1.1 km
Feb 2019 15 (11) 2.3 km 1.7 km
Mar 2019 29 (12) 3.5 km 1.3 km
Apr 2019 10 (5) 2.2 km 1.7 km
May 2019 15 (9) 2.9 km 1.3 km
Jun 2019 5 (2) 2.2 km 1.3 km

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

Figure (see Caption) Figure 76. Incandescent ejecta and ash emissions characterized activity from Sakurajima volcano at Aira during January 2019. Left: A webcam image showed incandescent ejecta on the flanks on 9 January 2019, courtesy of JMA (Explanation of volcanic activity in Sakurajima, January 2019). Right: An ash plume rose hundreds of meters above the summit, likely also on 9 January, posted on 10 January 2019, courtesy of Mike Day.
Figure (see Caption) Figure 77. The summit of Sakurajima consists of the larger Minamidake crater and the smaller Showa crater on the E flank. Left: The Minamidake crater at the summit of Sakurajima volcano at Aira on 18 January 2019 seen in an overflight courtesy of JMA (Explanation of volcanic activity in Sakurajima, March 2019). Right: Two areas of thermal anomaly were visible in Sentinel-2 satellite imagery on 27 January 2019. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

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

Figure (see Caption) Figure 78. An explosion from Sakurajima at Aira on 7 February 2019 sent ejecta up to 1,700 m from the Minamidake summit crater. Courtesy of JMA (Explanation of volcanic activity in Sakurajima, February 2019).
Figure (see Caption) Figure 79. Thermal anomalies and ash emissions were captured in Sentinel-2 satellite imagery on 6, 21, and 26 February 2019 originating from Sakurajima volcano at Aira. Top: Thermal anomalies within the summit crater were visible underneath steam and ash plumes on 6 and 26 February (closeup of bottom right photo). Bottom: Ash emissions on 21 and 26 February drifted SE from the volcano. "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

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

Figure (see Caption) Figure 80. A large ash emission from Sakurajima volcano at Aira was photographed by a tourist on the W flank and posted on 1 March 2019. Courtesy of Kratü.
Figure (see Caption) Figure 81. An ash plume from Sakurajima volcano at Aira on 18 March 2019 produced enough ashfall to disrupt the trains in the nearby city of Kagoshima according to the photographer. Image taken from about 20 km away. Courtesy of Tim Board.
Figure (see Caption) Figure 82. An ash plume drifted SE from the summit of Sakurajima volcano at Aira on 13 March (left) and a thermal anomaly was visible inside the Minamidake crater on 18 March 2019 (right). "Geology" rendering (bands 12, 4, and 2) courtesy of Sentinel Hub Playground.

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

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

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

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

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

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

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

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


Agung (Indonesia) — June 2019 Citation iconCite this Report

Agung

Indonesia

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

All times are local (unless otherwise noted)


Continued explosions with ash plumes and incandescent ejecta, February-May 2019

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

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

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

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

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

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

Figure (see Caption) Figure 46. Ash plumes from Agung on 15 (left) and 17 (right) March 2019 resulted in ashfall in communities 10-20 km from the volcano. Courtesy of PVMBG and MAGMA Indonesia (Information on G. Agung Eruption, 15 March 2019 and Gunung Agung Eruption Press Release March 17, 2019).
Figure (see Caption) Figure 47. A thermal anomaly was visible through thick cloud cover at the summit of Agung on 29 March 2019 less than 24 hours after a gray ash plume was reported 2,000 m above the summit. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

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

Figure (see Caption) Figure 48. Incandescent ejecta appeared on the flanks of Agung after an eruption on 4 April 2019 (local time) as viewed from the observation post in Rendang (8 km SW). Courtesy of Jamie Sincioco.
Figure (see Caption) Figure 49. Ashfall in a nearby town dusted mustard plants on 4 April 2019 from an explosion at Agung the previous day. Courtesy of Pantau.com (Photo: Antara / Nyoman Hendra).

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

Figure (see Caption) Figure 50. An explosion at Agung on 21 April 2019 sent incandescent eject 3,000 m from the summit. Courtesy of MAGMA Indonesia (Gunung Agung Eruption Press Release April 21, 2019).
Figure (see Caption) Figure 51. Multiple thermal anomalies were still present within the summit crater of Agung on 23 April 2019 after two substantial explosions produced ash and incandescent ejecta around the summit two days earlier. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

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

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

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

Figure (see Caption) Figure 53. The 18 May 2019 explosion at Agung produced an ash plume that rose to over 7 km altitude and large bombs of incandescent material that traveled hundreds of meters down the NE flank within the first 20 seconds of the explosion. Images taken from a private webcam located 12 km NE. Courtesy of Volcanoverse, used with permission.
Figure (see Caption) Figure 54. Satellite images from 3, 8, 13, and 18 May 2019 at Agung showed persistent and increasing thermal anomalies within the summit crater. All images were captured within 24 hours of explosions reported by PVMBG. "Atmospheric Penetration" rendering (bands 12, 11, and 8A) courtesy of Sentinel Hub Playground.

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

Figure (see Caption) Figure 55. A large explosion at Agung on 24 May 2019 produced incandescent ejecta that covered all the flanks and dispersed ash to many communities to the SW. Courtesy of PVMBG (Gunung Agung Eruption Press Release 24 May 2019 20:38 WIB, Kasbani, Ir., M.Sc.).
Figure (see Caption) Figure 56. An explosion at Agung on 31 May 2019 sent an ash plume to 8.2 km altitude, the highest for the report period. Courtesy of Sutopo Purwo Nugroho, BNPB.

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

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


Kerinci (Indonesia) — June 2019 Citation iconCite this Report

Kerinci

Indonesia

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

All times are local (unless otherwise noted)


Intermittent explosions with ash plumes, February-May 2019

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

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

Figure (see Caption) Figure 10. Sentinel-2 satellite imagery of Kerinci from 15 (left) and 25 (right) March 2019 showed evidence of ash plumes rising from the summit. Kerinci's summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 11. Dense ash plumes from Kerinci were reported by local news media on 18 and 19 March 2019. Courtesy of Nusana Jambi.

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

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

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

Figure (see Caption) Figure 13. Ashfall was reported from five villages on the flanks of Kerinci on 2 May 2019. Courtesy of Uzone.
Figure (see Caption) Figure 14. An ash plume at Kerinci rose hundreds of meters on 2 May 2019; ashfall was reported in several nearby villages. Courtesy of Kerinci Time.
Figure (see Caption) Figure 15. Ash emissions from Kerinci were captured in Sentinel-2 satellite imagery on 14 (left) and 24 (right) May 2019. The summit crater is about 500 m wide. "Geology" rendering (bands 12, 4, 2), courtesy of Sentinel Hub Playground.
Figure (see Caption) Figure 16. Weak SO2 anomalies from Kerinci emissions were captured by the TROPOMI instrument on the Sentinel-5P satellite multiple times each month from February to May 2019. Courtesy of NASA Goddard Space Flight Center.

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

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

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Bulletin of the Global Volcanism Network - Volume 24, Number 06 (June 1999)

Managing Editor: Richard Wunderman

Arenal (Costa Rica)

Comparatively weak explosive activity during past 1.5 years

Batur (Indonesia)

New eruption beginning in March; frequent explosions

Colima (Mexico)

Diminished activity during much of June; a large explosion on 17 July

Etna (Italy)

Lava-flow temperature measurements

Guagua Pichincha (Ecuador)

Continued frequent steam-and-ash explosions

Irazu (Costa Rica)

Occasional earthquakes and 5-70 microseisms a month during last 1.5 years

Langila (Papua New Guinea)

Mild emissions with rare ash-bearing outbursts

Lengai, Ol Doinyo (Tanzania)

Ongoing intracrater activity; fresh extra-crater lava flows; wet vs. dry carbonatites

Long Valley (United States)

Continued dome inflation and persistent earthquake swarms through 1998

Manam (Papua New Guinea)

Ashfalls and infrequent explosions

Mayon (Philippines)

Explosion on 22 June sends a plume to ~10-12 km altitude

Momotombo (Nicaragua)

Fumarole temperatures remain high in April 1999

Monowai (New Zealand)

Strong acoustic crisis recorded during 5-10 June

Negro, Cerro (Nicaragua)

New map of changes to crater after 1992 and 1995 eruptions

Poas (Costa Rica)

Strong drop in tremor duration and mid-frequency earthquakes in early 1998

Popocatepetl (Mexico)

Small exhalations, minor fumarolic activity, and variable seismicity

Rabaul (Papua New Guinea)

The active intracaldera cone (Tavurvur) continues mild emissions through June

Rincon de la Vieja (Costa Rica)

1.5-year record of seismicity and eruptions through May 1999

Stromboli (Italy)

Vents in summit craters still active; variable seismicity

Turrialba (Costa Rica)

A 4-fold increase in microseisms during December-April 1999

White Island (New Zealand)

Visit on 30 June reveals decreased activity



Arenal (Costa Rica) — June 1999 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Comparatively weak explosive activity during past 1.5 years

In November 1998-May 1999, Arenal's explosive activity continued, although at a reduced pace compared with past years. Crater C continued to emit gases, lava flows, and sporadic Strombolian eruptions. Fumarolic activity persisted at Crater D.

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

Information Contacts: E. Fernandez, V. Barboza, E. Duarte, R. Saenz, E. Malavassi, M. Martinez, and R. Van der Laat, T. Marino, and E. Hernandez, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Wendy Perez Fernandez, Seccion de Seismologia, Vulcanologia y Exploracion Geofisica, Escuela Centroamericana de Geologia, Universidad de Costa Rica, POB 35-2060, San José, Costa Rica.


Batur (Indonesia) — June 1999 Citation iconCite this Report

Batur

Indonesia

8.242°S, 115.375°E; summit elev. 1717 m

All times are local (unless otherwise noted)


New eruption beginning in March; frequent explosions

During the week of 9-15 March, white ash plumes rose 10-100 m above the crater. Booming noises were heard six times, and volcanic earthquakes increased drastically compared to the previous week (table 1). It was later determined that an ash eruption had begun on 15 March, sending bluish-white plumes 10-50 m high. On 17 March, two relatively recent craters merged when a connecting ridge collapsed as a result of earthquakes and small eruptions.

Table 1. Weekly seismicity recorded at Batur, March-July 1999. Types of events include volcanic A-type, volcanic B-type, tectonic, explosion earthquakes, and ash emissions (small explosion earthquakes). No data were available for the period 30 March-19 April. Maximum explosion amplitudes were reported as 2-26 mm during May; more typical, smaller amplitudes were 1.5-24 mm during May-July. Courtesy of VSI.

Date A-type B-type Tectonic Explosion Emission
02-08 Mar 1999 2 0 1 0 2
09-15 Mar 1999 106 241 1 0 26
16-22 Mar 1999 0 14 1 270 5
23-29 Mar 1999 -- -- 1 299 --
30 Mar-05 Apr 1999 -- -- -- -- --
06-12 Apr 1999 -- -- -- -- --
13-19 Apr 1999 -- -- -- -- --
20-26 Apr 1999 1 2 2 79 35
27 Apr-03 May 1999 0 0 0 42 21
04-10 May 1999 0 0 0 26 39
11-17 May 1999 8 3 6 68 21
18-24 May 1999 0 0 3 337 47
25-31 May 1999 1 6 0 112 31
01-07 Jun 1999 3 4 1 6 19
08-14 Jun 1999 12 5 4 0 52
15-21 Jun 1999 4 6 4 85 48
22-28 Jun 1999 5 13 1 141 31
29 Jun-05 Jul 1999 10 10 2 171 50
06-12 Jul 1999 1 6 1 122 32
13-19 Jul 1999 0 0 1 206 14

Volcanic activity was dominated by emission events (small explosions) during the week of 23-29 March; the eruption plume was white-blue in color, rising 10-100 m above crater rim. Booming noises were heard three times on 22 March, but no glow was observed. Reports are not available for most of April, but during late April through the middle of May the seismic record was dominated by explosion events. Ash plumes, described as "white" or "white-bluish" were observed rising 50-100 m above the crater. Neither explosion sounds nor glow was observed.

Six explosions on 17 May ejected materials that fell around the crater. Another explosion on 25 May was accompanied by incandescent ejections that fell around the crater. Explosion sounds were heard on 17 occasions during the week of 25-31 May. "White ash emissions" rose only to 25 m during 1-14 June, but varied between 10 and 100 m the rest of the month. Similar activity continued through mid-July, and a variable rumbling noise was heard the week of 13-19 July.

Geologic Background. The historically active Batur is located at the center of two concentric calderas NW of Agung volcano. The outer 10 x 13.5 km wide caldera was formed during eruption of the Bali (or Ubud) Ignimbrite about 29,300 years ago and now contains a caldera lake on its SE side, opposite the satellitic Gunung Abang cone, the topographic high of the complex. The inner 6.4 x 9.4 km wide caldera was formed about 20,150 years ago during eruption of the Gunungkawi Ignimbrite. The SE wall of the inner caldera lies beneath Lake Batur; Batur cone has been constructed within the inner caldera to a height above the outer caldera rim. The Batur stratovolcano has produced vents over much of the inner caldera, but a NE-SW fissure system has localized the Batur I, II, and III craters along the summit ridge. Historical eruptions have been characterized by mild-to-moderate explosive activity sometimes accompanied by lava emission. Basaltic lava flows from both summit and flank vents have reached the caldera floor and the shores of Lake Batur in historical time.

Information Contacts: Volcanological Survey of Indonesia (VSI), Jalan Diponegoro No. 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/).


Colima (Mexico) — June 1999 Citation iconCite this Report

Colima

Mexico

19.514°N, 103.62°W; summit elev. 3850 m

All times are local (unless otherwise noted)


Diminished activity during much of June; a large explosion on 17 July

Details about another large explosion on 17 July that sent a plume to over 10 km altitude will be reported in a future issue. Prior to that, during the month of June, degassing and explosions continued. The highest level of activity in 13 days was recorded on 1 June, but by 4 June activity had dropped to the lowest level in a month and it remained low through the end of June. Accordingly, during June explosions and degassing events became less frequent, shorter in duration, and of lower intensity. On 5 July one of two explosions sent an ash column to ~2,500 m and produced ashfall 10-20 km W of the summit.

A 3 June aerial inspection verified that no new summit crater has been formed, but did record a recent increase in the size of the crater formed during the 10 February and 10 May explosions. The crater diameter is now 180-200 m, with the deepest sector measuring 70 m.

Early in June authorities continued the evacuation of La Yerbabuena, in the state of Colima, and Juan Barragán, Los Machos, El Borbollón, and Durazno, in the state of Jalisco. The Observatory recommended controlled access to areas within 8.5 km of the summit and alert to persons within 11.5 km. People in other high-risk areas were told to be prepared to evacuate. By 10 June, however, reduced activity enabled authorities to relax restrictions. They trimmed the evacuated zone to within 6.5 km of the summit and maintained immediate response capacity to 8.5 km (including the villages of La Yerbabuena, Juan Barragán, El Agostadero, Los Machos, Borbollón, and El Durazno). Radio alert was maintained to a 11.5 km radius of the summit (encompassing the settlements of Causentla, Cofradía de Tonila, Atenguillo, Saucillo, El Fresnal, El Embudo). Authorities allowed residents to return to evacuated communities in both Colima and Jalisco. On 2 July, due to recent rain and the potential for lahars, authorities recommended avoiding the bed of the Cordobán river.

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

Information Contacts: Colima Volcano Observatory, University of Colima, Ave. 25 de Julio 965, Colima 28045 México (URL: https://portal.ucol.mx/cueiv/).


Etna (Italy) — June 1999 Citation iconCite this Report

Etna

Italy

37.748°N, 14.999°E; summit elev. 3295 m

All times are local (unless otherwise noted)


Lava-flow temperature measurements

During the winter of 1998-99, Southeast Crater underwent a series of short eruptions. On 4 February 1999 a similar outbreak led to fracturing of the SE cone with subsequent lava flows to the NNE and SSE (observation by Giuseppe Scarpinati). The SE flow developed a lava field between 2,900 and 2,800 m elevation on the rim of the Valle del Bove (BGVN 24:05), with numerous branches that nearly reached its bottom at about 2,000 m elevation. This mild effusive activity was characterized by very small and slow degassed lava flows coming from ephemeral vents through the superficially congealed crust of the field.

Temperature measurements were carried out on lavas from several of these effusive vents during the first days of April. Special thanks are due to Antonio and Orazio Nicoloso and the Etnean Guides for assistance in the field. Consumable "Temtip" Pt / Pt-10%Rh thermocouples were used following a procedure described in Archambault and Tanguy (1976). The maximum lava temperature recorded at depths of 40-60 cm within the fluid lava was 1,085 ± 5°C (figure 78), slightly higher than that measured during the last two major flank eruptions of 1983 and 1991-93 (1,070-1,080°C). As already shown in Archambault and Tanguy (1976), such small lava flows showed a strong thermal gradients, so that measurements made at 5-15 cm depth give results 10-15°C lower than the true internal temperature (figure 79). This means that devices reaching only the superficial parts of the flows are unsuitable for such temperature measurements.

Figure (see Caption) Figure 78. Histogram showing the number of Etna lava measurements at each temperature; the 16 measurements were taken at depth on fluid lava.
Figure (see Caption) Figure 79. Lava flow temperatures measured at Etna during early April plotted versus depth. Different symbols (circles, squares, and triangles) represent different sets of measurements.

Although relatively low for a trachybasalt (or basaltic hawaiite) lava, the temperature of 1,085°C is consistent with their high crystal content of ~40% phenocrysts. As usual in recent Etna lavas, these phenocrysts consist of plagioclase, clinopyroxene, olivine and titanomagnetite lying in a glassy alkaline groundmass.

Reference. Archambault, C., and Tanguy, J.C., 1976, Comparative temperature measurements on Mount Etna lavas: Journal of Volcanology and Geothermal Research, 1, 113-125.

Geologic Background. Mount Etna, towering above Catania, Sicily's second largest city, has one of the world's longest documented records of historical volcanism, dating back to 1500 BCE. Historical lava flows of basaltic composition cover much of the surface of this massive volcano, whose edifice is the highest and most voluminous in Italy. The Mongibello stratovolcano, truncated by several small calderas, was constructed during the late Pleistocene and Holocene over an older shield volcano. The most prominent morphological feature of Etna is the Valle del Bove, a 5 x 10 km horseshoe-shaped caldera open to the east. Two styles of eruptive activity typically occur, sometimes simultaneously. Persistent explosive eruptions, sometimes with minor lava emissions, take place from one or more summit craters. Flank vents, typically with higher effusion rates, are less frequently active and originate from fissures that open progressively downward from near the summit (usually accompanied by Strombolian eruptions at the upper end). Cinder cones are commonly constructed over the vents of lower-flank lava flows. Lava flows extend to the foot of the volcano on all sides and have reached the sea over a broad area on the SE flank.

Information Contacts: Roberto Clocchiatti, Lab. Pierre Sue, CEA Saclay, France; Charles Rivière, CGE, France; Santo La Delfa, Giuseppe Patanè, and Jean-Claude Tanguy, University of Catania, Italy.


Guagua Pichincha (Ecuador) — June 1999 Citation iconCite this Report

Guagua Pichincha

Ecuador

0.171°S, 78.598°W; summit elev. 4784 m

All times are local (unless otherwise noted)


Continued frequent steam-and-ash explosions

The "yellow alert" status was uninterrupted as Guagua Pichincha expelled steam and ash throughout June. Explosions occurred on 31 May and on 1, 5, 6, 7, 8, 10, 11, 12, 13, 17, 24, 28, and 30 June. Explosions were more frequent in early-to mid-June, but the 28 June explosion was the largest in three months. A large explosion on 11 June sent a steam-and-ash column to ~5 km that lasted for about 5 minutes before dispersing to the south. Explosions were usually accompanied by long periods of tremor. A sulfur smell persisted throughout June and loud noises were also common. Steam frequently escaped to heights between 15 and 1,200 m from vents known as Alineadas, 1981 Crater, and Locomotora, along with those in the NW area of the summit. Alineadas discharged the highest plumes. Phreatic explosions as well as volcano-tectonic (VT), long-period (LP), and hybrid earthquakes occurred almost daily throughout June at levels similar to the last few months (figures 14 and 15). In addition to activity on the volcano, the seismic swarm N of Quito has altered. This may reflect changes in the regional stress field.

Figure (see Caption) Figure 14. Monthly totals at Guagua Pichincha for phreatic explosions from August 1998 through June 1999. Courtesy of Instituto Geofisico.
Figure (see Caption) Figure 15. Monthly totals at Guagua Pichincha for seismic events (LP, VT, and hybrid) from August 1998 through June 1999. Courtesy of Instituto Geofisico.

Geologic Background. Guagua Pichincha and the older Pleistocene Rucu Pichincha stratovolcanoes form a broad volcanic massif that rises immediately to the W of Ecuador's capital city, Quito. A lava dome is located at the head of a 6-km-wide breached caldera that formed during a late-Pleistocene slope failure ~50,000 years ago. Subsequent late-Pleistocene and Holocene eruptions from the central vent in the breached caldera consisted of explosive activity with pyroclastic flows accompanied by periodic growth and destruction of the central lava dome. One of Ecuador's most active volcanoes, it is the site of many minor eruptions since the beginning of the Spanish era. The largest historical eruption took place in 1660, when ash fell over a 1000 km radius, accumulating to 30 cm depth in Quito. Pyroclastic flows and surges also occurred, primarily to then W, and affected agricultural activity, causing great economic losses.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional, Apartado 17-01-2759, Quito, Ecuador.


Irazu (Costa Rica) — June 1999 Citation iconCite this Report

Irazu

Costa Rica

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

All times are local (unless otherwise noted)


Occasional earthquakes and 5-70 microseisms a month during last 1.5 years

In late 1998 and early 1999, seismographic station IRZ2 continued to register a few microseisms and occasional earthquakes (figure 13). During February and March, the color of the lake was clear yellow; in May, green. As is typical, the lake contained zones of constant bubbling. Weak fumarolic activity continued on the NE flank.

Figure (see Caption) Figure 13. Monthly seismicity at Irazú, January 1998-April 1999. Courtesy of OVSICORI-UNA.

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: E. Fernandez, V. Barboza, E. Duarte, R. Saenz, E. Malavassi, M. Martinez, and R. Van der Laat, T. Marino, and E. Hernandez, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Wendy Perez Fernandez, Seccion de Seismologia, Vulcanologia y Exploracion Geofisica, Escuela Centroamericana de Geologia, Universidad de Costa Rica, POB 35-2060, San Jose, Costa Rica.


Langila (Papua New Guinea) — June 1999 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)


Mild emissions with rare ash-bearing outbursts

Crater 2 exhibited mild, continuous volcanic activity during May and very low activity during June. The May activity primarily consisted of the escape of moderately thick gray to brown ash clouds. Weak rumbling and roaring noises occasionally accompanied the emissions and fairly significant ash columns were forcefully ejected to 2 km height on 4, 9, 11, and 30 May. The ash clouds drifted NW, resulting in downwind ashfall. The June activity was summarized as the escape of mostly small to moderate amounts of vapor. Occasional ash-bearing (gray-brown) ash clouds were seen. In both months, there was no visible night glow, Crater 3 remained quiet and only occasionally released thin white vapor. The seismograph remained inoperative.

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: Ben Talai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.


Ol Doinyo Lengai (Tanzania) — June 1999 Citation iconCite this Report

Ol Doinyo Lengai

Tanzania

2.764°S, 35.914°E; summit elev. 2962 m

All times are local (unless otherwise noted)


Ongoing intracrater activity; fresh extra-crater lava flows; wet vs. dry carbonatites

Eruptions from the summit crater continued at a steady state. The activity level was low, but new observations during the rainy season conflicted with previous assumptions of color and age relationships among the natrocarbonatite flows. On 3 April two fresh flows, each having volumes of ~30 m3, had apparently issued from two separate hornitos in the summit crater. The pahoehoe flows were extruded over older lavas saturated with water from recent rainfall and earlier that day had generated a prominent steam plume many hundreds of meters high and visible from Engare Sero, 10 km N of the volcano. Large areas of the highest part of the N crater floor remained unusually hot (>150°C) throughout the day and sounds of sloshing magma suggest that substantial collapse of this region might be imminent. Small amounts of lapilli surrounding a hornito indicated a recent small scale (~10 m) lava fountain.

Cross-sections cut through the strongly porphyritic ~0.5 m flows (gregoryite and neyereite) revealed compact non-vesicular interiors and a near-glassy crystal-supported matrix. During a rain squall individual rain drops were observed whitening the flow surface (perhaps 50-150°C) in seconds. The margins of the recent flows also had turned white during cooling (figure 60). Clearly the timing between eruption and direct precipitation can change the age/color relationship previously established for Lengai, and is unreliable during the rainy season, an important consideration for photo-reconnaissance interpretations.

Figure (see Caption) Figure 60. View of lava flows at Ol Doinyo Lengai on 3 April 1999 showing alteration of the flow margins from dark gray to white due to hydration during cooling. Courtesy of Matthew Genge.

Intense fumarole activity from at least five of the larger hornitos, and from crater-rim fissures and cooling cracks on the lava flows, continued throughout 3-4 April (figure 61). Hornitos produced continuous steam and/or H2S gas, although one emanated blue and then black smoke. Another large hornito produced substantial heat haze but no visible gas. Fumaroles from cooling cracks in the fresh lava were associated with delicate salt deposits (figure 62).

Figure (see Caption) Figure 61. Fumarolic activity from hornitos in the crater of Ol Doinyo Lengai on 3 April 1999. Courtesy of Matthew Genge.
Figure (see Caption) Figure 62. Salt deposits lining cooling cracks on recent lava flows at Ol Doinyo Lengai, 3 April 1999. Courtesy of Matthew Genge.

At the time of the visit lava that flowed over the crater rim in the N and E (see BGVN 24:02) extended many hundreds of meters down the flanks of the volcano. The state of weathering of these flows suggested they were 1-2 weeks old, consistent with reports that glowing lava could be observed on the flanks of the volcano from Engare Sero at night during this period. Lava was also close to the NW rim of the crater. During this rainy season (as in the last one) vigorous flowing streams of water delivered both volcanic solutes (soda-rich) and volcanic detritus directly to Lake Natron, which was wet from shore to shore.

Geologic Background. The symmetrical Ol Doinyo Lengai is the only volcano known to have erupted carbonatite tephras and lavas in historical time. The prominent stratovolcano, known to the Maasai as "The Mountain of God," rises abruptly above the broad plain south of Lake Natron in the Gregory Rift Valley. The cone-building stage ended about 15,000 years ago and was followed by periodic ejection of natrocarbonatitic and nephelinite tephra during the Holocene. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatitic lava flows on the floor of the summit crater and occasionally down the upper flanks. The depth and morphology of the northern crater have changed dramatically during the course of historical eruptions, ranging from steep crater walls about 200 m deep in the mid-20th century to shallow platforms mostly filling the crater. Long-term lava effusion in the summit crater beginning in 1983 had by the turn of the century mostly filled the northern crater; by late 1998 lava had begun overflowing the crater rim.

Information Contacts: Matthew J. Genge, Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, United Kingdom; Matt Balme and Adrian P. Jones, Department of Geological Sciences, University College, London, United Kingdom.


Long Valley (United States) — June 1999 Citation iconCite this Report

Long Valley

United States

37.7°N, 118.87°W; summit elev. 3390 m

All times are local (unless otherwise noted)


Continued dome inflation and persistent earthquake swarms through 1998

The following summarizes activity at Long Valley during the second half of 1997 and all of 1998 (Hill, 1998). A summary of activity during 1996 and the first half of 1997 can be found in BGVN 22:11 and 22:12.

Summary of activity during July-December, 1997.After nearly a year of relative seismic quiescence within the caldera, earthquake swarm activity returned in early July. The deeper focus (>10 km) , long-period (LP) earthquakes centered beneath the SW flank of Mammoth Mountain and the Devil's Postpile area, which had increased in early 1997, continued at an elevated rate through the end of the year. Altogether over 200 of these events were detected during 1997, all M <2.0 (figure 21). This exceeded the total number of deep LP events detected from their onset in 1989 through 1996. Earthquake activity in the shallow crust beneath Mammoth Mountain (depths <10 km) at the SW margin of the caldera remained low throughout 1997.

Figure (see Caption) Figure 21. Earthquake epicenters in the Long Valley region during 1997. Courtesy of USGS.

The gradual increase in the inflation rate of the resurgent dome begun in late May 1997 marked the onset of an episode of unrest in the caldera that intensified at an accelerating rate through the summer and fall, culminating in a series of strong earthquake swarms from mid-November through early January 1998. The extension rate of an 8-km baseline spanning the resurgent dome peaked at over 20 cm/year during the second week of November. Following a strong earthquake swarm on 22 November that included three M >4.5 earthquakes, the deformation pattern briefly changed to one dominated by right-oblique slip along the WNW-striking "S-moat fault zone." In early December and through the rest of 1997, the deformation resumed the earlier pattern of dome inflation with a relatively steady 12-15 cm/year extension rate. By the end of 1997, the 8-km baseline was 7 cm longer than in late May.

The earthquake activity associated with the swarms begun in early July developed over a broad 15-km zone spanning the S-moat and southern margin of the resurgent dome. Typically, several areas within this zone were active simultaneously. This swarm activity, which included more than 12,000 M >1.2 and 120 M >3.0 earthquakes over a 7-month period through mid-January 1998, had a cumulative seismic moment of 3.3 x 1024 dyne-cm, equivalent to a single earthquake of M 5.4. The peak in seismicity from mid-November through early January included eight M >4.0 earthquakes. Focal mechanism data for the larger earthquakes indicated a dominantly right-lateral slip along a WNW-trending fault zone within the S-moat, although broadband seismograms admit the possibility of a dilatational component (volume increase) in the source mechanism for some of the M >4 earthquakes. The great majority of earthquakes had the broadband character of brittle, double-couple events (tectonic or volcano-tectonic earthquakes). A few shallow (<3 km) events beneath the southern half of the resurgent dome had energy concentrated in the 1-3 Hz band typical of shallow LP earthquakes. Whether the unusual appearance of the seismograms can be attributed to the earthquake source or wave propagation effects remains to be determined.

Monitoring of the gases around Mammoth Mountain showed two noteworthy changes in 1997, both more likely related to the increased deep LP earthquake activity beneath the SW flank of the mountain than to the much stronger activity within the caldera. The helium isotope ratio, 3He/4He, in samples collected in May and October from the MMF fumarole on the NE flank of Mammoth Mountain showed an increase with respect to the gradually declining values measured in late 1995 through early 1997. Continuous CO2 monitors in tree-kill areas on opposite sides of Mammoth Mountain detected an abrupt increase in CO2 soil-gas concentrations beginning in late September and ending in early December before significant snow accumulations.

The episode of persistent unrest during the second half of 1997 is the third most energetic activity in the caldera since the intense earthquake swarms of May 1980 (which included four M 6 earthquakes) and January 1983 (which included two M 5.3 earthquakes). The strongest seismic activity in the 1980 and 1983 episodes occurred within the first few days of the swarm sequences. The 1997 activity level accelerated gradually over a 4-month period prior to the strongest seismicity, which then spread out over nearly an additional 3 months. This activity provided the first test of the color-code notification system for ranking activity levels within the caldera. "Condition Green" (no immediate risk) remained throughout the year but the activity peaks on 22 and 30 November came close to meeting the guidelines for "Condition Yellow" (watch).

Summary of activity during 1998. Three events dominated activity during 1998. First, a decline in the acceleration of the resurgent dome uplift and the persistent earthquake swarm activity in the S-moat, which began in June-July 1997 and peaked in November-December 1998. Second and third, M 5.1 earthquakes on 8 June and 14 July 1998, centered W of the Hilton Creek fault and 2-4 km S of the caldera, together with their aftershock sequences.

In the S-moat of the caldera, the final phase of the strong earthquake swarms that dominated activity through the second half of 1997 extended into January 1998. An earthquake (M 4.8) on 31 December marked a shift in the center of the most intense activity from beneath the western part to the eastern-central section. A strong swarm burst occurred during 1-5 January in which >2,000 earthquakes were detected and located, including more than a dozen with M >3. On 6 January, a M 4.1 earthquake was the last of nine earthquakes with magnitudes of 4.0-4.9 in the S-moat since 13 November 1997.

Activity in the S-moat area declined to background levels by midsummer, interrupted by occasional M >3 earthquakes and brief swarms, particularly in February and March. The latter period included several days with 80-180 small swarm events. A M 3.2 earthquake occurred on 13 February, and swarm events on 2, 6-7, and 15-16 March included earthquakes of M >2.5. The last six months of 1998 included five M >3.0 caldera earthquakes. The two largest, on 14 July and 7 December, had magnitudes of 3.7 (the 14 July event occurred 2 hours after the M 5.1 earthquake).

Geodimeter measurements confirmed that the inflation rate of the resurgent dome gradually slowed from a peak of 30 cm/year in November 1997 to ~15 cm/year in early 1998 and by mid-May had dropped to 1-2 cm/year, a rate that persisted through the end of 1998.

Long-period earthquake activity 10-25 km beneath Devil's Postpile and the SW flank of Mammoth Mountain continued through 1998 (figure 22). Some 140 of the LP events were detected in 1998, just over half the 1997 number (250 events). That rate is still higher than any time since the mid-1989 onset of LP activity; during 1989-96 a total of only 165 LP events were detected. In 1998, many of the LP earthquakes were preceded by several tens of seconds of a tremor-like signal with a dominant frequency around 1 Hz. This was a change from the character of the LP activity in earlier years, when the tremor-like signals were generally of shorter duration and the dominant frequency was 2-3 Hz.

Figure (see Caption) Figure 22. Earthquake epicenters in the Long Valley region during 1998. Courtesy of USGS.

An event of M 1.8 at a depth of 12 km on 11 November was the largest LP event recorded since the initial activity in 1989; it was followed by a week of ~25 smaller events. Occasional LP earthquakes continued to occur through 1998 at depths between 15 and 30 km centered beneath an area roughly 7 km W of Mono Craters. One of the largest in this area, M ~2.4, occurred at a depth of 24 km on 26 September.

Over the summer months, field studies around the flanks of Mammoth Mountain suggested that the CO2 flux rate had been slowly decreasing over the past 3 years. Airborne measurements in September and November detected a CO2 plume downwind, consistent with the multiple sources around the flanks of the mountain.

The first of the two M 5.1 earthquakes occurred on 8 June just 1.5 km S of the caldera at a depth of 6.7 km. The second occurred on 14 July and was centered 3 km to the SSE at 6.2 km depth. Both earthquakes were located within the footwall of the E-dipping Hilton Creek fault; neither appeared to have involved slip on the fault itself. Both earthquakes were followed by rich aftershock sequences that tailed off though the end of the year and, together, included nine earthquakes with magnitudes between 4.0 and 4.5. The aftershock epicenters defined a nearly orthogonal pattern in map view. Those of the 8 June event were confined to a WNW lineation through the mainshock epicenter, whereas those of the 14 July event were confined to a more diffuse SSW lineation through the mainshock epicenter. Both lineations cut across the Hilton Creek fault and intersect just E of the 8 June epicenter.

Earthquake activity elsewhere in the region showed no significant variation from background activity over the past several years.

References. Hill, David P., 1997, Long Valley Caldera monitoring report (July-December 1997): U.S. Geological Survey, Volcano Hazards Program.

Hill, David P., 1998, Long Valley Caldera monitoring report (October- December 1998): U.S. Geological Survey, Volcano Hazards Program.

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

Information Contacts: David Hill, U.S. Geological Survey, MS 977, 345 Middlefield Rd., Menlo Park, CA 94025 USA (URL: https://volcanoes.usgs.gov/observatories/calvo/).


Manam (Papua New Guinea) — June 1999 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)


Ashfalls and infrequent explosions

Mild to weak eruptive activity from Main Crater continued in May and June. During May there were small to moderate pale gray ash emissions. Ash clouds then rose 500-600 m above the summit before being blown NW with resulting light ashfall on 1, 22, 26-27, and 31 May. A slight wind change on 15 and 25 May caused the ash clouds to drift SW and the ashfall to move downwind. There were no noises or night glow observed in May. A weak, steady glow was visible between 2 and 5 May.

Although Southern Crater was generally quiet with only thin white emissions, a small explosion took place on 10 June. A weak discharge of lava fragments accompanied loud noises that lasted only a short time. Later, on 26 June, Main Crater vented gray-brown ash clouds resulting in ash fall over some parts of the island.

During May-June, seismicity remained low. Evidence for deformation was absent at the water-tube tiltmeter located at Tabele Observatory, 4 km from the summit on the SW flank.

Inhabitants of the 10-km-wide island of Manam reside on one of Papua New Guinea's most active volcanoes. Four large radial valleys extend from the unvegetated summit of the conical stratovolcano to its lower flanks. These "avalanche valleys," regularly spaced 90 degrees apart, channel lava flows and pyroclastic avalanches that have sometimes reached the coast. Five satellitic centers are located near the island's shoreline. Two summit craters are present and both are active, although most historical eruptions have originated from the southern crater and drained into the SE avalanche valley. Frequent historical eruptions have been recorded since 1616.

More recent activity began in December 1956 and lasted through January 1966. Lava flows and a nuee ardente from the South Crater occurred in June and December 1974, and intermittent moderate explosive activity has continued into 1993, with peaks of activity in 1982 and 1984.

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: Ben Talai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.


Mayon (Philippines) — June 1999 Citation iconCite this Report

Mayon

Philippines

13.257°N, 123.685°E; summit elev. 2462 m

All times are local (unless otherwise noted)


Explosion on 22 June sends a plume to ~10-12 km altitude

At 1658 on 22 June Mayon emitted an ash column that rose 7-10 km above the vent (figure 8). The emission was recorded by the seismic network of the Philippines Institute of Volcanology and Seismology (PHIVOLCS) as an explosion that lasted for 10 minutes. No volcanic earthquakes nor other visible signs of abnormal activity were observed before the explosion. During May, however, low-frequency volcanic earthquakes had been recorded intermittently, accompanied by faint crater glow.

Figure (see Caption) Figure 8. A column of steam and ash rising from Mayon's crater and a pyroclastic flow descending its SE flank during its sudden isolated explosion on 22 June. Photograph courtesy of PHILVOCS.

The explosion represented an isolated event as activity immediately declined to typical incidents of weak steaming without measurable seismicity. Faint glow was seen the next day at the summit crater. An aerial survey noted a new explosion pit at the summit; the small diameter pit was later described as a deep hole lined with sulfur deposits (figure 9). The presence of sulfur suggested that lava had not yet ascended to the surface.

Figure (see Caption) Figure 9. The crater of Mayon as it appeared after the 22 June explosion. A new, circular explosion pit developed on the crater floor; the shadow formed along the rim of this pit can be seen in this NW-looking photo shot through the breech. Courtesy of PHILVOCS.

Beginning at 0700 on 25 June there was a slight increase in seismicity and SO2 emission. The COSPEC measured an SO2 flux of 4,800 tons/day, compared with 4,200 tons/day the previous day. SO2 fluxes normally average 500 tons/day. A short interval of high-frequency tremor was also recorded.

Tremor, light steaming, low-frequency volcanic earthquakes, and elevated SO2 fluxes continued for several days. Also, deformation surveys conducted with laser-ranging EDM equipment indicated sustained inflation on the SE slope.

PHIVOLCS maintained an alert status of "Level 1," advising the public not to venture within 6 km of the summit area (figure 10). In particular, residents were advised to avoid the Bonga pyroclastic fan, an area on the SE side of the volcano that contains a deep canyon and lies directly below the crater rim notch. This fan was the site of most of the fatalities in the 1993 eruption and is considered the area most vulnerable to future pyroclastic flows.

Figure (see Caption) Figure 10. Details on Mayon and vicinity taken from a volcanic hazards map (PHILVOCS, 1999). The legend describes some effects of the 1993 eruption. The solid black circle represents the 6-km-radius safety zone currently in effect. An additional 1-km-wide precautionary zone lies to the SE of the volcano below the Bonga Pyroclastic Fan. Some local cities and river drainage are also shown. Courtesy of PHILVOCS.

Reference. Philippine Institute of Volcanology and Seismology (PHIVOLCS), 1999, 1999 Mayon permanent danger & high susceptibility areas (map), URL: http://www.philonline.com/~seismo/Volcanoes/Mayon/MayonHazMaps.htm.

Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.

Information Contacts: Raymundo S. Punongbayan and Ronnie Torres, Philippine Institute of Volcanology and Seismology (PHIVOLCS), C.P. Garcia St. Diliman, Quezon City Philippines (URL: http://www.phivolcs.dost.gov.ph/).


Momotombo (Nicaragua) — June 1999 Citation iconCite this Report

Momotombo

Nicaragua

12.423°N, 86.539°W; summit elev. 1270 m

All times are local (unless otherwise noted)


Fumarole temperatures remain high in April 1999

Fumarole temperatures have been rising on Momotombo since 1996. An April 1996 summit visit reported that temperatures were unchanged over the past year (BGVN 21:04), but by November of that year the temperatures had begun to fluctuate (BGVN 21:11). Fumarole temperatures in November 1996 registered between 130 and 677°C, higher than those recorded in October but lower than those in April. The flux was attributed to seasonal change; an intense rainy season and associated erosion accounted for the October lows. Temperatures had increased again by July 1997 to 232-773°C (BGVN 22:07).

In October 1997 higher than normal fumarole temperatures were attributed to arid conditions. During a 1 September visit to the summit area, fumarole temperatures were measured at their usual points and found escalated. The maximum temperature was 740°C. Because the temperature increase coincided with a dry spell, the heightened fumarolic activity was not deemed alarming.

Elevated temperatures were also reported in March 1998 (BGVN 23:03). Measurements during a 28 February visit revealed higher-than-normal fumarolic temperatures in the summit area. The high temperatures were again associated with a recent period of aridity, during which time fumarolic activity increased. Temperatures ranged from 318 to 748°C.

On 24 April 1999 the summit area was visited and temperatures again found inflated in the five areas of fumarolic activity. The maximum temperatures were, in the south area of the crater, 725°C and, in the north, 550°C. Significant changes in the crater morphology were noted and attributed to the strong erosion induced by Hurricane Mitch in October 1998.

Geologic Background. Momotombo is a young stratovolcano that rises prominently above the NW shore of Lake Managua, forming one of Nicaragua's most familiar landmarks. Momotombo began growing about 4500 years ago at the SE end of the Marrabios Range and consists of a somma from an older edifice that is surmounted by a symmetrical younger cone with a 150 x 250 m wide summit crater. Young lava flows extend down the NW flank into the 4-km-wide Monte Galán caldera. The youthful cone of Momotombito forms an island offshore in Lake Managua. Momotombo has a long record of Strombolian eruptions, punctuated by occasional stronger explosive activity. The latest eruption, in 1905, produced a lava flow that traveled from the summit to the lower NE base. A small black plume was seen above the crater after a 10 April 1996 earthquake, but later observations noted no significant changes in the crater. A major geothermal field is located on the south flank.

Information Contacts: Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua.


Monowai (New Zealand) — June 1999 Citation iconCite this Report

Monowai

New Zealand

25.887°S, 177.188°W; summit elev. -132 m

All times are local (unless otherwise noted)


Strong acoustic crisis recorded during 5-10 June

The French Polynesian Seismic Network recorded a strong acoustic crisis originating from Kermadec, very near Monowai Seamount, during 5-10 June. The acoustic crisis started at 0300 on 6 June (1500 on 5 June GMT) and ended at 0100 on 11 June (1300 on 10 June GMT) with no precursory activity (figure 7). Two distinct episodes were separated by a 4-hour period of inactivity. The network recorded more than 394 strong acoustic T-waves; the strongest took place at 1115 on 6 June (2315 on 5 June GMT). The first signal received on 6 June began with an impulse and lasted more than 12 minutes. Many of them had explosive characteristics, short and strong. The activity stopped with a small explosive T-wave. No tremor was recorded.

Figure (see Caption) Figure 7. Acoustic wave amplitudes recorded by the French Polynesian Seismic Network during 5-10 June. The source of these waves was near the Monowai Seamount. Courtesy of Olivier Hyvernaud.

Monowai Seamount lies midway between the Kermadec and Tonga Islands, ~1,400 km NE of New Zealand. The adjacent trench is much shallower (~4 km) compared with the Tonga and Kermadec trenches (9-11 km deep). There was a T-wave swarm in November 1995 (BGVN 20:11/12). Other noteworthy recent activity at Monowai included a possible eruption in 1944, and about seven documented eruptions during 1977-90 (BGVN 16:03).

Geologic Background. Monowai, also known as Orion seamount, rises to within 100 m of the sea surface about halfway between the Kermadec and Tonga island groups. The volcano lies at the southern end of the Tonga Ridge and is slightly offset from the Kermadec volcanoes. Small parasitic cones occur on the N and W flanks of the basaltic submarine volcano, which rises from a depth of about 1500 m and was named for one of the New Zealand Navy bathymetric survey ships that documented its morphology. A large 8.5 x 11 km wide submarine caldera with a depth of more than 1500 m lies to the NNE. Numerous eruptions from Monowai have been detected from submarine acoustic signals since it was first recognized as a volcano in 1977. A shoal that had been reported in 1944 may have been a pumice raft or water disturbance due to degassing. Surface observations have included water discoloration, vigorous gas bubbling, and areas of upwelling water, sometimes accompanied by rumbling noises.

Information Contacts: Olivier Hyvernaud, Laboratoire de Géophysique, BP 640 Pamatai, Tahiti, French Polynesia.


Cerro Negro (Nicaragua) — June 1999 Citation iconCite this Report

Cerro Negro

Nicaragua

12.506°N, 86.702°W; summit elev. 728 m

All times are local (unless otherwise noted)


New map of changes to crater after 1992 and 1995 eruptions

A team from Southwest Research Institute and Arizona State University visited Cerro Negro during 24 February-2 March. Their objectives were to map geomorphologic changes to the cone resulting from the 1995 eruption, estimate the respirable fraction of ash suspended above the 1992 and 1995 tephra blankets, and perform stratigraphic studies of tephra deposits.

A topographic map was prepared from 8,700 GPS measurements collected on and around the cinder cone (figures 12 and 13). Precision of individual measurements was within 1 cm and the survey had gross precision within 0.5 m.

Figure (see Caption) Figure 12. Topographic map of Cerro Negro volcano, prepared during 24 February-2 March. The contour interval is 10 m. Shaded triangles indicate the 1995 eruption vents, arrows show the direction of 1995 lava flows from the crater, shaded circles show positions of active fumarole areas, and the shaded square indicates the position of the INETER seismic station. Courtesy of Chuck Conner.
Figure (see Caption) Figure 13. Color-shaded topographic map of Cerro Negro volcano, prepared during 24 February-2 March. The contour interval is 10 m. The black square indicates the position of the INETER seismic station. Courtesy of Chuck Conner.

The cinder cone's morphology was changed significantly by the 1992 and 1995 eruptions. During the 1992 eruption the crater widened and now has an average diameter of 340 m. It was widest, 418 m, along its NE-SW axis because of a broad shoulder of tephra deposited on the SW side of the cone (during the 1992 and 1995 eruptions prevailing wind directions were from the NE). The diameter of the base of the cone was 945 m, measured between Cerro La Mula Ridge to the N of the cone and the Cristo Rey vent on the S. Data derived from air photos taken in 1986 revealed that this basal diameter had not changed substantially since then despite the 1992 and 1995 eruptions. The high point on Cerro Negro was measured at 728 m elevation, giving the cone a height of 258 m when measured relative to a topographic break in slope at the cone base, just west of Cristo Rey vent.

A small pyroclastic cone within the 1992 crater was created during the 1995 eruption. This new cone had a rim diameter of 124-130 m. Its crater depth was 94 m from the W rim (corresponding to the high point on Cerro Negro) and 44 m from the low point on the E side. Lava flows, emitted from at least two boccas on the 1992 crater floor during the 1995 activity, breached the N side of the 1992 cone. Because of this breach the low point on the 1992 crater rim was 9 m below the average rim elevation of 625 m.

No substantial degassing or other signs of volcanic unrest were observed during the seven days that the team was on-site and the area seemed unchanged since the cessation of the 1995 eruption. No thermal activity was observed on the 1995 lava flows, even on flow levees thicker than 3 m. These lava flows appeared to have cooled substantially as a result of the more than 3 m rainfall the region received during Hurricane Mitch in the Fall of 1998. Two fumarole areas were active; one fumarole area on the E of the crater has likely persisted since before the 1992 eruption. These fumaroles were easily accessible due to the breaching of the N crater rim by the 1992 lava flows. A new fumarole area had been established high on the W rim of the 1995 pyroclastic cone, just below the high point on Cerro Negro. Sulfur, anhydrite, and halite were deposited in these areas. Low-temperature fumaroles (<100°C) were found along arcuate fractures that paralleled the 1992 cone rim. These fractures were most prominent on the S side of the cone where they were faulted with 0.1-1.0 m displacements, down toward the outer cone flank and up toward the crater, because of slumping on the outer flank. They were radial on the SW of the cone, where the outer cone slope was buttressed by 1992 and 1995 tephra accumulations. Similar fractures and small faults also occurred on the NW rim and around the 1995 pyroclastic cone. Low-temperature fumaroles were also found on the southernmost 1995 bocca and a small mound within the 1992 crater. Fumaroles and steaming ground persisted on Cerro La Mula Ridge.

Crater fumarole measurements. The temperature of crater fumaroles has been measured during visits by Alain Creusot since 1995 (BGVN 21:11, 21:12, and 23:03). From November 1995, when a significant eruption took place, to October 1996, fumarole temperatures were as high as 700°C. On 27 November 1996, a visit to the crater found that fumarole temperatures had generally decreased by 80-100°C and the maximum temperature was only 630°C. On 23 December 1996 the maximum fumarole temperature was only 606°C. An additional decrease of fumarole temperatures was noted on a 5 September 1997 visit; the maximum temperature measured was only 405°C (previously unreported). The highest temperature found on 14 February 1998 was 340°C.

References. Hill and others, 1998, Eruptions of Cerro Negro volcano, Nicaragua, and risk assessment for future eruptions, Geological Society of America, Bulletin, v. 110, p. 1231-1241.

Connor and others, 1996, Soil 222Rn pulse during the initial phase of the June-August 1995 eruption of Cerro Negro, Nicaragua, Journal of Volcanology and Geothermal Research, vol. 73, p.119-127.

Geologic Background. Nicaragua's youngest volcano, Cerro Negro, was created following an eruption that began in April 1850 about 2 km NW of the summit of Las Pilas volcano. It is the largest, southernmost, and most recent of a group of four youthful cinder cones constructed along a NNW-SSE-trending line in the central Marrabios Range. Strombolian-to-subplinian eruptions at intervals of a few years to several decades have constructed a roughly 250-m-high basaltic cone and an associated lava field constrained by topography to extend primarily NE and SW. Cone and crater morphology have varied significantly during its short eruptive history. Although it lies in a relatively unpopulated area, occasional heavy ashfalls have damaged crops and buildings.

Information Contacts: Chuck Connor, Peter La Femina, Brittain Hill, James Weldy, Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, 6220 Culebra Rd, San Antonio, TX, 78238-5166; Kurt Roggensack and Berry Cameron, Department of Geological Sciences, Arizona State University, Tempe, AZ; Alain Creusot, Instituto Nicaraguense de Energía, Managua, Nicaragua.


Poas (Costa Rica) — June 1999 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Strong drop in tremor duration and mid-frequency earthquakes in early 1998

Seismicity registered at station POA2, located 2.8 km SW of the active crater, has declined since early 1998 (figures 71 and 72). Since then, gas columns continued to reach altitudes between 500 and 600 m above the floor of the crater as they had during the interval of greater seismicity. The pyroclastic cone remained the focus of fumarolic activity. The crater's W, E, and SE walls continued to slip into the lake. The lake maintained a constant bubbling on its S and SE edges. The active lake's color varied considerably; for example, at various times during April 1999, the ~32°C lake water appeared green, turquoise, or light blue. In November 1998, the lake appeared greenish turquoise and had a temperature of 29°C.

Figure (see Caption) Figure 71. Low-frequency earthquakes at Poás each month during January 1998-May 1999. Courtesy of OVSICORI-UNA.
Figure (see Caption) Figure 72. Monthly earthquakes of medium- and high-frequency (number of events on y-axis scale) at Poás and the tremor duration (in hours on y-axis scale). The plot covers the interval January 1998-February 1999. 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. Fernandez, V. Barboza, E. Duarte, R. Saenz, E. Malavassi, M. Martinez, and R. Van der Laat, T. Marino, and E. Hernandez, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Wendy Perez Fernandez, Seccion de Seismologia, Vulcanologia y Exploracion Geofisica, Escuela Centroamericana de Geologia, Universidad de Costa Rica, POB 35-2060, San Jose, Costa Rica.


Popocatepetl (Mexico) — June 1999 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Small exhalations, minor fumarolic activity, and variable seismicity

The low level of activity displayed in May continued, with small exhalations and minor fumarolic emissions until 12 June. However, seismic activity increased on 12 June and continued for the next 10 or 11 days. At 1209 and 1600 on 12 June, two M 2.2 volcano-tectonic events occurred under the crater and SW of the volcano. At 1542 on 15 June, a large earthquake (M 6.7) centered between the states of Puebla and Oaxaca did not affect the volcano. Bad weather had obstructed visibility earlier, but that afternoon observers saw small fumarolic emissions of steam and gas.

Seismicity increased on 16 June as several volcano-tectonic events were recorded in the morning, most with magnitudes between 2.5 and 3 and two larger ones with M >3. These events were located 4-7 km below the summit crater. The last event occurred at 0206 on 17 June. This seismicity did not produce any important external manifestations except a small exhalation on the morning of 17 June accompanied by a light ash puff blown to the W.

On 21 June two earthquakes in Guerrero did not effect the volcano. No other events were reported for the month and by 30 June the radius of restricted access was reduced to 5 km from the 7 km previously recommended.

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: Servando De la Cruz-Reyna1,2, Roberto Quaas1,2; Carlos Valdés G.2, and Alicia Martinez Bringas1. 1-Centro Nacional de Prevencion de Desastres (CENAPRED), Delfin Madrigal 665, Col. Pedregal de Santo Domingo, Coyoacán, 04360, México D.F. (URL: https://www.gob.mx/cenapred/); 2-Instituto de Geofisica, UNAM, Coyoacán 04510, México D.F., México.


Rabaul (Papua New Guinea) — June 1999 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)


The active intracaldera cone (Tavurvur) continues mild emissions through June

The mild Vulcanian activity continuing since November 1998 continued through June 1999. With time, the eruption's from Rabaul's Tavurvur cone appeared to be progressively waning in intensity. Still, during May and June several moderate explosions occurred.

Some May and June explosions sent ash clouds 1 km above the summit. The ash clouds drifted NW, some resulted in light ashfall over Rabaul Town. The mild ash-bearing outbursts in June occurred with very long intervals (sometimes 24 hours) between them. Notable outbursts took place on 9 days during the month (3, 5, 6, 9, 13, 15, 16, 17, 19, 23 and 25 June); although many only lasted 2-10 minutes, the last one of the set prevailed for 25 minutes. Typical plumes rose to 500 m high; SE winds typically blew these plumes and fine ash fell, including some on Rabaul Town.

In accord with these visual observations, both deformation and caldera seismicity remained low. Although during May, April, and March there had been 150, 142, and 120 low-frequency earthquakes, respectively, during June there occurred only 38 such earthquakes. The two located earthquakes appeared to the NE of the main ring fault. Anomalously, during the past 2 years there has been an absence of recorded high-frequency earthquakes on the ring fault. Instead, located earthquakes have consistently struck NE of the ring-fault system.

On the 16th a regional earthquake directly E of Wide Bay triggered a 31-cm tsunami. Since then, more than 20 regional events have occurred within a 20 km radius of the initial quake.

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: Ben Talai, Rabaul Volcano Observatory (RVO), P.O. Box 386, Rabaul, Papua New Guinea.


Rincon de la Vieja (Costa Rica) — June 1999 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)


1.5-year record of seismicity and eruptions through May 1999

Seismicity during 17 months through April 1999 (figure 14) showed pronounced peaks at over 100 events/month in one parameter, microseisms, during September- October 1998. Otherwise, relative quiet prevailed; microseisms, high-frequency, and low-frequency events all generally took place fewer than 20 times/month. Tremor was nearly absent during roughly half the months of 1998 and in 1999 during January, February, and April. Months with 2-10 hours of tremor included February, August, September 1998 and March and May 1999.

Figure (see Caption) Figure 14. Selected seismic parameters at Rincón de la Vieja during January 1998-May 1999. The arrows indicate months with detected eruptions (mainly in February 1998, a month with ~10; the other indicated months with fewer than 2). Courtesy of OVSICORI-UNA.

In March, fumarolic activity continued on the NE, S, and SW walls of the main crater. The lake had a gray color and contained suspended particles of sulfur. The temperature of the lake was 35.5°C.

During May, the main crater's N-flank fumarolic activity fluctuated in temperature between 68°C and 92°C. The lake in the crater was light blue with particles of sulfur, and a temperature of 37°C. On the S and N walls, there were columns of gases that irritated eyes and skin.

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: E. Fernandez, V. Barboza, E. Duarte, R. Sáenz, E. Malavassi, M. Martinez, and R. Van der Laat, T. Marino, and E. Hernandez, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Wendy Perez Fernandez, Seccion de Seismologia, Vulcanologia y Exploracion Geofisica, Escuela Centroamericana de Geologia, Universidad de Costa Rica, POB 35-2060, San José, Costa Rica.


Stromboli (Italy) — June 1999 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Vents in summit craters still active; variable seismicity

After the strong summit explosions of 23 August and 8 September 1998 (BGVN 23:10), at least two others followed during 1998: the first at 1805 on 24 November, the second at 0245 on 28 December. Both were reported by Pierre Cottens from the village of Stromboli, with pyroclasts clearly seen from the village, reaching estimated heights of at least 700 m over the craters in November and 500 m in December, but with little ashfall over the village. Technical problems kept the seismic station maintained by the University of Udine out of service through the end of January 1999.

Seismicity during February-June 1999. The seismic station was restored on 1 February 1999, and in the first part of the month the daily number of events declined from 130 to 50-80/day (figure 58). Saturating events showed a similar trend. The second half of February was characterized by an increasing number of events, reaching a maximum of 275 events on 2 March. During this period the tremor intensity showed fluctuations around an average of 3.6 V s, with an isolated peak on 23 February.

Figure (see Caption) Figure 58. Seismicity detected at the summit of Stromboli from February through June 1999. The gray bars show the number of recorded events/day, and the black bars those saturating the instrument (ground velocity exceeding 100 µm/s). The line shows daily tremor intensity computed by averaging hourly 60-second samples. The seismic station is located 300 m from the craters at 800 m elevation. Courtesy of Roberto Carniel.

During 12-20 March there was a general decrease in activity, with a minimum number of 52 seismic events recorded on 16 March, and a minimum tremor intensity of 1.8 V s on 15 March. The gain in activity was observed first in the tremor intensity, with a local maximum of 4.7 V s on 29 March, then in the number of events, which reached a high of 208 events on 30 March.

A sharp decline was observed on 7 April both in the tremor intensity (from 3.0 to 1.2) and in the number of events (from 180 to 76). Saturating events also stopped, after an average of five saturated events during the three preceding days. Seismic activity increased slightly during the following two days, and on 9 April Cottens reported two strong blasts at about 0300, separated by a few minutes. Bad weather did not allow observation of the summit area, but the noise was similar to that produced by the strong eruptions of 1998. The seismic station recorded an event with greater than usual energy, which may have been from one of the explosions. Another decrease of activity was observed the day after the explosion, with the number of daily events falling to 83 and the tremor intensity to 1.9. The following days were characterized by a slow increase in seismicity, but activity remained low to moderate for the rest of the month.

After another gap in the seismic acquisition, the activity was still low after mid-May 1999, with <100 events/day between 20-24 May. The last week of May showed a rise in the number of events, with a maximum of 183 events on 26 May. A relatively high number of saturating events was also observed, starting on 23 May and peaking on 27 May (21 saturating events) and 30 May (23 saturating events). Another minimum in the number of events (66), number of saturating events (0) and tremor intensity (1.6) was recorded on 5-6 June 1999. During several days on the island in the second half of June, seismic activity remained at low to moderate levels, with a short duration increase in the tremor intensity on 21-22 June.

Observations during 17-20 June 1999. Observations during 17-20 June allowed mapping of the crater terrace (figure 59). Observations were made over two 3-4 hour periods: 2109-0100 (18-19 June), and 2030-2320 (19 June).

Figure (see Caption) Figure 59. Sketch map of Stromboli's Crater Terrace drawn on 18-19 June 1999 from Pizzo sopra la Fossa and fitted to the map produced from a September 1995 EDM survey of the Crater Terrace (BGVN 20:11/12). Courtesy of Andy Harris and Roberto Carniel

Crater 1 contained four active vents (figure 59). During the first observation period, the vicinity of Vent 1/2 was the source of persistent widespread glow; but no ejecta was observed. Vent 1/1, however, was the source of glow and near-persistent low-energy activity, characterized by repeated phases of ejecta emission separated by periods of little or no emissions. Each phase consisted of numerous pulses of ejecta. During each pulse a few (typically 1-10) bombs were ejected <10 m above the crater rim, with pulses every few seconds. Around 11 periods of this persistent, pulsing emission were observed. Each period lasted 2-29 minutes and was separated by intervals of 3-28 minutes with occasional bomb emissions. This pattern at Vent 1/1 was broken by 16 high-energy events during which explosions sent ejecta ~100 m high.

Vent 1/3 produced high-energy events only, with 18 observed during the first period. High energy events from vents 1/1, 1/3, and 1/4 were synchronized. It was difficult to distinguish eruptions from 1/4 and 1/1 from the viewing angle, so eruptions from these two vents may have been occasionally assigned to the wrong vent; the eruption counts for 1/1 and 1/4 together were therefore combined. Vents 1/3, 1/1, and/or 1/4 erupted together on 11 occasions. On these occasions ejection from each vent was either synchronous or closely linked. During such synchronized events there appeared to be no set order in terms of which of the three vents started erupting and which followed. Vents 1/1 (and/or 1/4) and 1/3 erupted on their own on 5 and 7 occasions, respectively.

As in the first observation period, glow persisted above Vent 1/2 throughout the second period. Unlike the previous evening, however, ejecta was observed from Vent 1/2, where activity followed the style observed at Vent 1/1 during the previous evening. Around eight periods of low-energy but persistent pulsing activity were observed. These lasted 3-33 minutes and were separated by 2-23-minute-long periods of apparently no emission. This pattern of activity from Vent 1/2 was interrupted by five high-energy events lasting 4-6 seconds.

Vent 1/1 issued regular gas puffs (typically one puff every 1-2 seconds), but the frequency of ejecta emission had declined, with the periods of persistent, pulsing activity observed the previous evening replaced by discrete emissions. Ejections were observed from 1/1 on nine occasions, where only one event was of the high-energy type, and the remainder were short (<40-second-long) periods during which 1-10 bombs were ejected <10 m above the rim in pulses. As in the previous period, Vent 1/3 was characterized by high-energy events only. Seven occurred during the second period, of which three were synchronous with high energy events from 1/2 or 1/1.

Although no activity or glow was observed from Crater 2, a hornito (figure 59) had grown in the vicinity of the low cone observed during May 1997 (BGVN 22:05). The area surrounding Crater 2 no longer seemed to be marked by a crater-like feature. The subsidence bowl observed SE of Crater 2 in May 1997 had developed into a deep, funnel-shaped pit, which was the source of faint glow. On a previous map (BGVN 22:05), the vent numbering indicated that this area was part of Crater 2; this interpretation is questionable and this feature could be considered a crater by itself now. On figure 59 we denote this vent as 3/3 (therefore part of Crater 3) in order to allow for easy comparison with older maps of the crater terrace (e.g., BGVN 22:03).

Crater 3 was the location of two additional active vents (figure 59). Glow was observed from vent 3/1 only after an eruption at 2317 on 18 June. Eruptions from Crater 3 were high-energy only, and typically larger (in terms of volume and height, attaining heights of 150 ± 50 m) and longer (lasting 8-23 seconds) than those from Crater 1. Nine and eleven eruptions, respectively, occurred from Crater 3 during the two observation periods.

During our descent in the early hours of 19 June there was a rock fall/slide at about 0200 lasting 1-2 minutes. Boulders from the cliffs on the N edge of the Rina Grande rolled and bounced down the Rina Grande. Owing to the steepness of this flank, once in motion the rocks probably did not stop until they reached the sea in the direction of Forgia Vecchia, crossing the route that descends the Rina Grande ash slope within seconds. Such events pose a very serious hazard to anyone using this route, especially at night.

Geologic Background. Spectacular incandescent nighttime explosions at this volcano have long attracted visitors to the "Lighthouse of the Mediterranean." Stromboli, the NE-most of the Aeolian Islands, has lent its name to the frequent mild explosive activity that has characterized its eruptions throughout much of historical time. The small island is the emergent summit of a volcano that grew in two main eruptive cycles, the last of which formed the western portion of the island. The Neostromboli eruptive period took place between about 13,000 and 5,000 years ago. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5,000 years ago due to a series of slope failures that extend to below sea level. The modern volcano has been constructed within this scarp, which funnels pyroclastic ejecta and lava flows to the NW. Essentially continuous mild Strombolian explosions, sometimes accompanied by lava flows, have been recorded for more than a millennium.

Information Contacts: Andy Harris and Dawn Pirie, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom; Sarah Sherman, 41-485D Kalanianaole Hwy., Waimanolo, HI 96795 USA; Roberto Carniel, Dipartimento di Georisorse e Territorio, Università di Udine, Via Cotonificio, 114, I-33100 Udine (URL: http://www.swisseduc.ch/stromboli/).


Turrialba (Costa Rica) — June 1999 Citation iconCite this Report

Turrialba

Costa Rica

10.025°N, 83.767°W; summit elev. 3340 m

All times are local (unless otherwise noted)


A 4-fold increase in microseisms during December-April 1999

During the 17 months ending in May 1999, microseisms varied from ~30 to ~180 a month (figure 5). A 4-fold progressive increase began after December 1998.

Figure (see Caption) Figure 5. A histogram showing Turrialba's monthly microseisms during January 1998- April 1998. Courtesy of OVSICORI-UNA.

In March 1999, the main crater's fumaroles were visible on the NE, N, NW, E and SW walls. Escaping gases appeared constant and had a temperature of 89°C. During March, the seismographic station VTU, located 0.5 km NE of the active crater registered a total of 252 earthquakes. Of those 81 had high frequency, with S-P duration of less than 1.5 seconds and frequencies greater than 3.0 Hz. The 166 microseisms registered had amplitudes under 10 mm, short durations, and frequencies between 2.1 and 3.0 Hz. An earthquake registered at 1846 on 7 March, with a Richter magnitude of 2.3, a depth of 7 km, and an epicenter 4 km NE of the main crater.

During April, the station VTU registered 287 earthquakes. Of those, 105 were of high frequency (with S-P of less than 1.5 seconds and frequencies above 3.0 Hz), and 4 were of low frequency. The 178 microseisms registered were of short duration; their dominant frequencies were between 2.1 and 3.0 Hz.

During May, a total of 309 events were recorded, of which 120 were type AB with S-P less than 1.5 seconds and frequencies less than 3.0 Hz. There were 3 low-frequency events. The 186 microseisms registered had amplitudes under 10 mm.

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

Information Contacts: E. Fernandez, V. Barboza, E. Duarte, R. Saenz, E. Malavassi, M. Martinez, and R. Van der Laat, T. Marino, and E. Hernandez, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Wendy Perez Fernandez, Seccion de Seismologia, Vulcanologia y Exploracion Geofisica, Escuela Centroamericana de Geologia, Universidad de Costa Rica, POB 35-2060, San Jose, Costa Rica.


White Island (New Zealand) — June 1999 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)


Visit on 30 June reveals decreased activity

White Island was visited on 30 June by IGNS scientists who reported that no significant eruptive activity had occurred since the explosive activity in April (BGVN 24:04). PeeJay vent was inactive and the only significant emissions of steam and gas came from the vent that formed in early May (at a spot E of PeeJay vent).

As the group arrived on 30 June a weak white steam-and-gas plume was rising 500-700 m above the volcano and moving ENE (figure 43). The plume was being fed by emissions from within the 1978/90 Crater Complex; the new vent E of PeeJay was the plume's strongest contributing source. Most of the gas and steam emitted (at high velocity) from this vent was from an inclined orifice near the S side of the vent. Other prominent sources included fumaroles near the lakeshore and in the valley wall W of the lake. PeeJay vent was inactive and had been filled by sediment that formed a flat floor about 3 m below the vent's rim. Activity had stopped in late May or early June.

Figure (see Caption) Figure 43. View of the 1978/90 Crater complex at White Island looking toward the NW on 30 June. Photograph courtesy of IGNS.

The light-green colored lake within Metra Crater had enlarged and flooded into the NNE embayments of this crater. There was no evidence of further explosive activity from Metra Crater. No strong ebullition or convection was observed in the lake.

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: Brad Scott, Wairakei Research Centre, Institute of Geological and Nuclear Sciences (IGNS) Limited, Private Bag 2000, Wairakei, New Zealand (URL: http://www.gns.cri.nz/).

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.

Atmospheric Effects (1980-1989)  Atmospheric Effects (1995-2001)

Special Announcements

Special announcements of various kinds and obituaries.

Special Announcements

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/).