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 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/).

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 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 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 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 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 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 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 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 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 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 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 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 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/).

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 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 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 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 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 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 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 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 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 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 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/).

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 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/).

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 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 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 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 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 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 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 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 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 25. Faint SO2 plumes were recorded on 1 and 11 March 2019 emerging from Saunders Island. Courtesy of NASA Goddard Space Flight Center.

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 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 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 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 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). Vapor emission is frequently reported from the summit crater. Recent AVHRR and MODIS satellite imagery has revealed evidence for lava lake activity in the summit crater.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Minami-dake crater was active throughout November-December 1995. Eruption totals for November and December were 19 and 42, respectively. Of these, explosive eruptions for the same months numbered 14 and 36, respectively. The local seismic station recorded 453 earthquakes and 446 tremors during November and 467 earthquakes and 83 tremors during December. The highest monthly ash plumes took place on 30 November (2,300 m above the crater), and on 9 December (1,700 m). Ashfall measured 10 km W of the crater was as follows: November, 5 g/m²; and December, 18 g/m².

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: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

On 1 November there were 46 earthquakes recorded, and small amplitude volcanic tremor continued for ~2 minutes. High seismicity continued through the 5th with 18-28 events/day. The November earthquakes totaled 643.

Geologic Background. Akan is a 13 x 24 km caldera located immediately SW of Kussharo caldera. The elongated, irregular outline of the caldera rim reflects its incremental formation during major explosive eruptions from the early to mid-Pleistocene. Growth of four post-caldera stratovolcanoes, three at the SW end of the caldera and the other at the NE side, has restricted the size of the caldera lake. Conical Oakandake was frequently active during the Holocene. The 1-km-wide Nakamachineshiri crater of Meakandake was formed during a major pumice-and-scoria eruption about 13,500 years ago. Within the Akan volcanic complex, only the Meakandake group, east of Lake Akan, has been historically active, producing mild phreatic eruptions since the beginning of the 19th century. Meakandake is composed of nine overlapping cones. The main cone of Meakandake proper has a triple crater at its summit. Historical eruptions at Meakandake have consisted of minor phreatic explosions, but four major magmatic eruptions including pyroclastic flows have occurred during the Holocene.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

October plumes rose as high as 1 km above Crater C. During the second week of November explosive activity increased, growing both in terms of the number of outbursts and the overall quantity of tephra emitted. Blocks and bombs landed above 1,000 m elevation. Ash columns rose over 1 km and blew over the NW, W, and SW flanks. Windows vibrated in buildings 6.5 km E (La Fortuna).

A lava flow first emitted in July remained mobile; one arm reached 860 m and another reached 900 m elevation. A new flow began at the end of the month, venting from a point S of the vent for the previous month's flow, and moving SW. Re-established vegetation in the zone of lava flows continued to degrade due to acid rain.

For the frequency range below 3.5 Hz, there were 765 events during October and 444 seismic events during November (figure 74). These events chiefly occurred associated with Strombolian eruptions; some were of sufficient amplitude to reach station JTS, 30 km from the active crater. The largest number recorded in a single day was 40 (on 5 November). During October and November, 2.1-3.5 Hz tremor took place for about 232 and 238 hours, respectively (figure 74). On 15 and 17 November tremor prevailed for 21 and 20 hours, respectively.

Figure 74. Arenal seismicity and tremor for 1995 (recorded at station "VACR," 2.7 km NE of the main crater). Courtesy of OVSICORI-UNA.

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, E. Duarte, R. Saenz, W. Jimenez, and V. Barboza, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.

During November and December 1995 the floor of Naka-dake Crater 1 remained covered with hot water, yet there were few if any mud-and-water ejections. During November the number of isolated tremors reached 5,488; during December, 4,896. In addition, continuous tremor prevailed with amplitudes confined to 0.1-0.8 µm.

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

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

Based on observations in late June 1995, the Indian Coast Guard reported on 1 July that explosive activity in the crater area had stopped, but gas emissions were still coming from the area near the coast. On 2 December an aviation Notice to Airmen (NOTAM) was issued from the United Kingdom for increased activity at Barren Island. However, no eruptive activity was seen on GMS satellite imagery over the area.

Landsat TM images from January 1995 (20:04) showed activity from a subsidiary vent on the S slope of the central crater. Subsequent images from 24 February, 13, 14, and 30 March, and 15 April 1995 also revealed activity from the central crater. Some of the images showed a lava or debris flow present in the WNW channel leading towards the sea. A thermal infrared image on 13 March showed a large hot central vent, and at least two subsidiary vents on the S slope; the image also revealed a lava passageway and the cooler plume.

Further Reference. Haldar, D., Chakraborty, S.C., and Chakraborty, P.P., 1996, The 1995 eruption of the Barren Island volcano in the Andaman Sea: Records, Geological Survey of India, v. 129(3), p. 59-62.

Geologic Background. Barren Island, a possession of India in the Andaman Sea about 135 km NE of Port Blair in the Andaman Islands, is the only historically active volcano along the N-S volcanic arc extending between Sumatra and Burma (Myanmar). It is the emergent summit of a volcano that rises from a depth of about 2250 m. The small, uninhabited 3-km-wide island contains a roughly 2-km-wide caldera with walls 250-350 m high. The caldera, which is open to the sea on the west, was created during a major explosive eruption in the late Pleistocene that produced pyroclastic-flow and -surge deposits. Historical eruptions have changed the morphology of the pyroclastic cone in the center of the caldera, and lava flows that fill much of the caldera floor have reached the sea along the western coast.

Information Contacts: D. Haldar, Director, GSI Eastern Region, Calcutta; J. Lynch, SAB.

Significant collapse of the Inner Crater was occurring in late 1995, although the lava lake remained fairly constant in size at ~20 m diameter and generally in the same location. No significant eruptions have occurred from the lava lake over the last 5 years and no bombs have been observed on the crater rim. Magma composition has shown no change over the last 20 years. A recent volume of 12 papers (Kyle, 1994) summarizes some aspects of the volcanic activity and environmental effects of Erebus through the 1980's and early 1990's.

Passive degassing from the lake contributes a small plume and the SO₂ content has usually been monitored in December by COSPEC (see Kyle and others, 1994 for COSPEC data up to 1991). Since 1991 the SO₂ emissions have ranged between 40 and 70 Mg/day (megagrams/day is the SI unit equivalent to metric tons/day); bad weather limited measurements in December 1995. FTIR (Fourier Transform Infrared) open-field spectrometry measurements in December confirmed the HCl/SO₂ ratio of the emitted gases to be in agreement with measurements made by impregnated filters over the last 8 years. However, high CO levels significantly exceeded those of both HCl and SO₂. Although CO₂ in the plume has not been measured it is assumed to be high due to the alkalic nature of the magma. The high CO may be a function of the presumed high CO₂ concentrations in the magma and its fairly low oxygen fugacity.

A network of eight seismic stations are operated as part of the Erebus Volcano Observatory by the New Mexico Institute of Mining and Technology. Seven stations have 1-Hz vertical single-component instruments, and the eighth is a 1-Hz three-component station. The stations have radio telemetry links to McMurdo Station where a digital event detection system and several analog helirecorders record the data, which are automatically transferred daily via the Internet to New Mexico for analysis and archiving. Details about the seismic network and associated seismicity can be accessed on the WWW Erebus page (see below).

Magmatic eruptive activity has been continuous since the discovery of a anorthoclase phonolite lava lake in 1972 (Giggenbach and others, 1973). Activity has been relatively uniform over the last 15 years with the exception of two significant events. In 1984 there was a 3-4 month period of larger and more frequent Strombolian eruptions which ejected bombs >2 km from the summit crater. On 19 October 1993 two moderate phreatic eruptions blasted a new crater ~80 m in diameter on the Main Crater floor and ejected debris over the northern Main Crater rim. These are the first known phreatic eruptions at Erebus, and probably resulted from steam build-up associated with melting snow in the crater.

References. Giggenbach, W.F., Kyle, P.R., and Lyons, G., 1973, Present volcanic activity on Erebus, Ross Island, Antarctica: Geology, v. 1, p. 135-136.

Kyle, P.R., Sybeldon, L.M., McIntosh, W.C., Meeker, K., and Symonds, R., 1994, Sulfur dioxide emissions rates from Mount Erebus, Antarctica, in Kyle (1994), p. 69-82.

Kyle, P.R., ed., 1994, Volcanological and Environmental Studies of Erebus, Antarctica: Antarctic Research Series, American Geophysical Union, v. 66.

Geologic Background. Mount Erebus, the world's southernmost historically active volcano, overlooks the McMurdo research station on Ross Island. It is the largest of three major volcanoes forming the crudely triangular Ross Island. The summit of the dominantly phonolitic volcano has been modified by one or two generations of caldera formation. A summit plateau at about 3,200 m elevation marks the rim of the youngest caldera, which formed during the late-Pleistocene and within which the modern cone was constructed. An elliptical 500 x 600 m wide, 110-m-deep crater truncates the summit and contains an active lava lake within a 250-m-wide, 100-m-deep inner crater; other lava lakes are sometimes present. The glacier-covered volcano was erupting when first sighted by Captain James Ross in 1841. Continuous lava-lake activity with minor explosions, punctuated by occasional larger Strombolian explosions that eject bombs onto the crater rim, has been documented since 1972, but has probably been occurring for much of the volcano's recent history.

Information Contacts: Philip R. Kyle, Dept. of Earth and Environmental Sciences, New Mexico Institute of Mining and Technology, Socorro, NM 87801 USA.

Lava lakes have been present since 1967, and possibly 1906, although the N lava lake became inactive between 1988 and 1992. Recent ground observations were reported in September and November 1992. Observations have also been made using satellite imagery. New observations were made during 6-11 December 1995 by a team from Spele-Film and the Societe de Volcanologie Geneve while working for a French television network.

Only fumarolic activity was observed from the large crater (~300 m diameter) in the N part of the caldera. Fumaroles were concentrated SW of the pit within the crater, with some emissions coming from the inside wall and the slope of talus covering the pit floor. Almost all of the visible fumes came from the main pit, and seemed more abundant than in November 1992. A secondary pit crater with a diameter of ~15 m was seen in the SE part of the main pit.

Within the central part of the caldera, the S lava lake is located at the top of a small lava shield. The N and E flanks of this shield are partially covered by abundant lava flows originating from the N crater. The S flank of the shield is dominated by a large inactive cone. No fumes were visible, but the air near the pit-crater rim was very hot, frequently making it difficult to breathe without a mask. The diameter of the S pit-crater was ~140 m (based on a measured circumference of 446 +- 2 m), and the lake was 90 m below the W rim. The lava lake was similar in size and location to one observed in 1992, covering an area of ~60 x 100 m in the WSW part of the pit (figure 6). However, the level of the lake was believed to have risen ~5-6 m. Two slope breaks on the generally flat pit floor, not present in 1992, suggest that the entire floor may have subsided.

Figure 6. Sketch showing a cross-sectional view of the central pit-crater (S lava lake) at Erta Ale, December 1995. Courtesy of P. Vetsch.

Lava lake activity was characterized by intermittent fountaining from as many as four locations at a time. No regular pattern was noted, but fountaining was more frequent near the SW border of the lake, and the more intense fountains (5-15 m high), started near the center of the lake and migrated to the border. During the stronger fountaining phases, a large raft of cooled surface lava moved towards the lake center. The lava lake was generally more active than in 1992. Pele's hair was frequently seen above the fountains, and some rose on the hot air out of the pit.

Geologic Background. Erta Ale is an isolated basaltic shield that is the most active volcano in Ethiopia. The broad, 50-km-wide edifice rises more than 600 m from below sea level in the barren Danakil depression. Erta Ale is the namesake and most prominent feature of the Erta Ale Range. The volcano contains a 0.7 x 1.6 km, elliptical summit crater housing steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Fresh-looking basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera is renowned for one, or sometimes two long-term lava lakes that have been active since at least 1967, or possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: P. Vetsch, Societe de Volcanologie Geneve, B.P. 298, CH-1225 Chene-bourg, Switzerland; L. Cantamessa, Geo-Decouverte, 65 rue de Lausanne, CH-1202 Geneva, Switzerland; G. Farve and C. Rufi, Spele-Film, Borex, Switzerland; C. Peter, 14 Haupstrasse, D-82547 Eurasburg, Germany.

On 2 August 1995 explosive activity resumed at Northeast Crater (NEC) (BGVN 20:08). In August and September the activity was sporadic and low in intensity (BGVN 20:09), but after 2 October a vigorous Strombolian phase was observed (BGVN 20:10). Explosive activity occurred again during 19-22 October.

On 1 November there was vigorous spattering and bubbling of magma in a 15-m-wide pit on the NEC floor. Magma degassing formed large bubbles that burst, throwing spatter to the crater rim. In the following days the activity was discontinuous and less intense.

Lava fountaining episodes, 9-14 November. At 0014 on 9 November there was a sudden increase in volcanic tremor, but bad weather prevented summit observations. Between 0105 (at Trecastagni) and 0110 (at Catania, 30 km SSE) ash and lapilli fallout covered the SE flank (figure 61), eventually reaching as far as Siracusa, 75 km from the vent. The episode lasted only a few minutes and the material on the lower slope amounted to a few tens of grams per square meter, although rare dense lapilli broke some skylights and car windows. Fieldwork the next morning revealed that the NEC eruption produced a lava fountain followed by a strong phreatomagmatic blast. Part of the S rim collapsed inside the NEC and was later ejected. A welded spatter deposit several meters thick mantled the upper slope of the NEC cone and was overlain by a few centimeters of ash and lapilli. The bombs varied from 2-3 m close to the vent, to 25 cm at 2.5 km downwind. Several large accidental lithics (up to 1 m) occurred in the very proximal deposit. A large amount of spatter fell into the crater, raising its floor by several tens of meters. The crater appeared completely sealed, with wide red cracks on the crust of the spatter pile. The total volume of tephra from the 9 November eruption was ~1.5 x 10⁶ m³.

Figure 61. Map of the Etna area showing areas affected by ashfall on 9, 14, and 27 November, and 23 December 1995. Courtesy of IIV.

On 10 November a new lava fountain episode at NEC was observed from Catania around 0400-0530. Pulsating magma jets climbed up to 300 m above the crater rim; some were expelled up to 500 m. An ash-and-lapilli column ascended ~5,000 m and was blown SE. The spatter deposit was limited to the upper part of the volcano and in a narrow strip extending ~3 km SE; little ash fell on the middle slopes. The estimated volume of the pyroclastics was a few tens of thousands of cubic meters.

A third episode took place around 0600 on 14 November, and lasted ~3 hours. Between 0800 and 0900 the paroxysmal phase sent dense black ash columns through a white cloud covering the summit until they reached 5,000 m altitude. During the entire episode a non-continuous sustained eruptive column was observed and each ash puff contributed to a plume bent downwind that reached its buoyancy level at 6-7 km altitude. Ash and lapilli rained on the NE flank down to the coast (figure 61), leaving only a few grams of material per square meter on the middle and lower slopes. The proximal spatter deposits, mapped two days later, partially covered the previous ones on the cone and extended ~2 km NE in a band a few hundred meters wide. Lithic blocks and ash were less abundant than in deposits from the 9 November episode. The crater bottom was sealed by back-fallen welded spatter and was ~50 m below the crater rim, 100 m higher than before 9 November. The total volume of tephra from the 14 November eruptions was ~350,000 m³.

The volcano remained quiet after the 3rd episode. Within NEC, only a few large cracks on the welded spatter crust emitted fumes. Bocca Nuova crater showed a normal continuous degassing; Southeast and Voragine craters continued their steam emission.

Lava fountaining episodes, 22-27 November. Late on 22 November continuous glows were observed at NEC and some bangs were heard on the lower slopes. Beginning around midnight, two hours of fire fountaining and intense red glow was visible from Catania. The lava jets remained fairly low (~100 m above the crater rim) so the proximal spatter deposit mantled only the upper part of the cone, whereas the fine material fell on the SE flank as far as the coast. However, the total volume of the erupted material was limited to a few tens of thousand cubic meters, close to that of the second episode.

After the 22 November episode the vent was closed again by material that fell back into the crater. Three days later some bangs were heard at NEC and glow was observed during the night of 26-27 November. That morning seismic tremor rose suddenly and at 0715 an ash-and-lapilli column rose from the volcano. Cloud cover prevented direct observations. Ash and lapilli were carried by strong winds and fell on a narrow band of the N flank down to its foot (figure 61). Lapilli fallout ended around 1000, but the explosive activity continued for several hours. The thickness of the scoria-fall deposit varied from decimeters close to the vent to ~1 mm at 12 km away. The total tephra volume from this 5th eruptive episode was estimated at 0.4-0.5 x 10⁶ m³.

Fieldwork two days later revealed that the proximal spatter deposits of the 22 and 26 November episodes were thinner than earlier ones. Lithic blocks were less abundant than in the 9 November deposits, but large ballistic scoriaceous bombs were found up to 500 m from the vent. The crater floor was completely sealed by fall-back spatter, but every 40-60 minutes a gas pocket broke the solid crust and a single lava bubble burst. These phenomena were observed for a few more days.

Activity during December. In the first half of December the summit craters were quiet, with continuous steam emissions, except for NEC, which had no open vent. A short explosive phase was reported on the night of 6 December. Poor weather conditions prevented observations until 16 December, when continuous Strombolian activity was seen at a small vent on the crater floor; a cone grew within a few days. The activity was characterized by the bursting of single magma bubbles alternating with degassing jets and spatter lasting from tens of seconds to a few minutes. This intense Strombolian activity continued for several days.

Around 1100 on 23 December strong bangs were heard from skiers on the upper slope. Very soon the bangs became frequent and black ash puffs were observed from NEC. Between 1215 and 1220 the first jet of magma rose above the crater rim, followed shortly by several pulses of magma jets and a large eruptive column. Between 1235 and 1305 the paroxysmal phase occurred, with jets of magma that rose 500-600 m (measured on the video record of the surveillance camera at La Montagnola, 2,700 m elevation on the S flank). Fragments from the top of the jets fed an eruptive column that reached 9.5 km altitude (6.2 km above the summit). Clear weather allowed observation of the column from many places on Sicily, as far as the city of Palermo 190 km away. Abundant ash and lapilli fell on a wide band of the NE flank down to the coast (figure 61). A brownish ash plume was emitted by Voragine during the entire paroxysmal phase of the eruption. Around 1330 the eruption quickly declined, but isolated explosions occurred until the evening. This episode was the most energetic among the six at NEC during November and December 1995.

The proximal deposit mantled the NEC cone with meters of welded spatter. In the W and E saddles between NEC and the Central Cone, spatter formed two thick lava flows a few hundred meters long. The E flow was still active during the night of 23-24 December; downslope movement of fluid material in the core produced continuous collapses of large incandescent blocks at the flow front. Crater modifications included the thick new scoria bank and widening and lowering of the S crater rim. Ballistic clasts had been thrown up to 600 m from the vent and landed as cow-pie bombs up to 2 m in diameter. The distal deposit from the eruptive column was made of scoriaceous bombs and lapilli up to 10-15 km from the vent, and from lapilli and a minor ash up to the shoreline, 22 km away. The bombs were very brittle, flat, and up to 30 cm in diameter at 6 km from the vent (observed while still in the air). The scoria-fall deposit formed a continuous band from the vent to the coast, damaging fruit plantations, vehicles, and buildings. The Messina-Catania freeway had to be cleared of a scoria deposit along a 4-km-long stretch. The deposit thickness along the dispersal axis was 6-7 cm at 6 km, 3-4 cm at 13 km, 3 cm at 16 km along the freeway, and 1-2 cm at 20 km near the coast. The estimated total volume of pyroclastics erupted on 23 December was ~3 x 10⁶ m³.

On the days after 23 December eruption only a few blasts were heard from NEC, but on the nights of 27 and 28 December discontinuous glow was again seen, sometimes similar to those produced by mild Strombolian explosions. No further activity was reported at NEC or the other craters through the end of the year.

Tephra characteristics. Bombs and lapilli erupted during the November-December 1995 episodes are highly vesiculated and show glassy and smooth surfaces. Only in the volcanics erupted on 9 November are both vesicles and surfaces filled by reddish, fine-grained non-juvenile material. Juvenile ash consists of: 1) poorly vesiculated tachylitic (glassy) grains; 2) highly vesiculated clasts with glassy, smooth surfaces, and many Pele's hair and shards in the finer fraction; and 3) loose crystals covered in some cases by a thin film of glass.

Generally rounded grains with variable alteration form the non-juvenile fraction. In the ash fraction of all deposits, juvenile material is always the most abundant (60-100%), and preliminary investigation indicates that it increased with time. The juvenile fraction is ~60% of the 9 November ash, ~80% of the 14 November ash, and ~100% of the ash erupted during the following episodes (23 and 27 November, 23 December). The proportions of different juvenile components also changed during the eruptive sequence.

Scoria erupted during the November-December explosive episodes are, like most of Etna's historical volcanics, porphyritic hawaiites with phenocrysts of plagioclase, clinopyroxene, and olivine, and microphenocrysts of Ti-magnetite in a hyalopilitic groundmass. The scoria are more vesiculated and slightly less porphyritic than those erupted in October 1995. The chemical composition of November-December scoria is rather homogeneous even if the 9 and 14 November material is slightly more differentiated than those erupted after 23 November. Overall, the composition of the November-December volcanics is comparable to those of the Strombolian activity at NEC during the first half of October, and to the products erupted in the first days of the 1991-93 eruption.

Seismicity. Seismicity recorded by the permanent seismic network (12 stations; figure 62), during November-December 1995 was characterized by remarkable phases of increased volcanic tremor amplitude. Earthquake activity stayed at very low levels. A few tens of shocks took place and the only significant episode occurred on 24 December when a minor swarm (6 events; Mmax=3.2) was located near Mt. Maletto (NW slope of the volcano) at a depth of ~15 km.

Figure 62. Map of Etna showing locations of seismic stations, tilt stations, and EDM networks maintained by the Istituto Internazionale di Vulcanologia as of December 1995. Courtesy of IIV.

Since the end of August 1995 volcanic tremor recorded at Pizzi Deneri (PDN: ~2 km from NEC, 2,820 m elevation) and Serra Pizzuta Calvarina (ESP: ~7 km from NEC, 1,590 m elevation) stations has shown an increasing trend. This pattern became more evident in late September, when some increases in tremor amplitude were recorded for durations ranging from tens of minutes to a few hours. The most relevant increases in tremor amplitude occurred on 22-23 September, 2, 3 and 21 October, 9, 10, 14, 22-23, and 27 November, and 23 December. This tremor amplitude pattern correlated with visually observed NEC eruptive activity.

The volcanic tremor spectral amplitude temporal pattern at PDN and ESP stations showed a clear amplitude increase. Spectral amplitude peaks were superimposed on the increased trend and corresponded to the episodes listed above. Dominant peaks in tremor spectra recorded at PDN and ESP stations showed a high-frequency (~3.5 Hz) trend coincident with the high tremor amplitude. Each amplitude increase showed similar characteristics.

Ground deformation. After the end of the 1991-93 eruption deformation was dominated by steady inflation, mostly affecting the W and NE slopes. Positive trends of areal dilatation, cumulating at ~14 ppm, were clearly apparent on the SW and NE flank EDM networks (figure 62) following the 1991-93 eruption, while the S network was characterized by a flat trend of areal dilatation for several years. Both the SW and NE networks followed comparable trends, only differing in the recent sharp positive gradient variation (10 ppm) shown by the latter between August and October.

The shallow bore-hole permanent tilt network (figure 62) indicated a progressive increase (starting by the second half of 1993) in the radial tilt component recorded at the stations on the W flank (MSC: 50 µrad) and on the N flank (MNR: 10 µrad), while the S slope showed no appreciable positive variation until July 1995. The eruptive activity resumed at the summit craters by late July-early August, and the renewed ejection of magma appeared to be strictly related in time to the positive variation of the radial tilt at SPC (~15 µrad) and the sharp increase of areal dilatation in the NE sector. Radial tilt at PDN was affected by a sharp negative variation (35 µrad) at almost the same time.

September EDM survey on the S flank. J. Moss noted that reoccupation of a different S-flank EDM network in September 1995 showed only minor line extension since eruptive activity resumed in August. Significant extensions of lines perpendicular to the Valle del Bove accompanied dike emplacement prior to the 1991-93 eruption. However, the July 1995 survey showed only minor changes since July 1994. Over 80% of the lines measured between those two surveys showed extension, suggesting a pattern of broad edifice inflation. The small strain rates suggest that no magma was intruded into this part of the S rift zone prior to September 1995.

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: M. Coltelli, M. Pompilio, E. Privitera, S. Spampinato, and S. Bonaccorso, CNR Istituto Internazionale di Vulcanologia (IIV), Piazza Roma 2, 95123 Catania, Italy (URL: http://www.ingv.it/en/); Jane L. Moss, Cheltenham and Gloucester College of Higher Education, Francis Close Hall, Swindon Road, Cheltenham GL50 4AZ, United Kingdom.

The eruption that began on 2 April (BGVN 20:04 and 20:05) ended on or about 28 May, according to V. Martins. New lava flows covered ~6.3 km² of land. The total volume of lava extruded was ~60-100 x 10⁶ m³, assuming lava flow thicknesses of ~9-15 m; the known range was from 1 to >20 m. Based on six major-element XRF analyses, the lava flow erupted during the first night (3 April) was determined to be a differentiated kaersutite-bearing phonotephrite (IUGS system), whereas later lava flows and spatter were more primitive tephrite basanite.

Fogo Island consists of a single massive volcano with an 8-km-wide caldera breached to the E. The central cone was apparently almost continuously active from the time of Portuguese settlement in 1500 A.D. until around 1760. The June-August 1951 eruption from caldera vents S and NW of the central cone began with ejection of pyroclastic material.

Geologic Background. The island of Fogo consists of a single massive stratovolcano that is the most prominent of the Cape Verde Islands. The roughly circular 25-km-wide island is truncated by a large 9-km-wide caldera that is breached to the east and has a headwall 1 km high. The caldera is located asymmetrically NE of the center of the island and was formed as a result of massive lateral collapse of the ancestral Monte Armarelo edifice. A very youthful steep-sided central cone, Pico, rises more than 1 km above the caldera floor to about 100 m above the caldera rim, forming the 2829 m high point of the island. Pico, which is capped by a 500-m-wide, 150-m-deep summit crater, was apparently in almost continuous activity from the time of Portuguese settlement in 1500 CE until around 1760. Later historical lava flows, some from vents on the caldera floor, reached the eastern coast below the breached caldera.

Information Contacts: Richard Moore, U.S. Geological Survey, Mail Stop 903, Federal Center Box 25046, Denver, CO 80225 USA; Frank Trusdell, U.S. Geological Survey, Hawaiian Volcano Observatory, Hawaii National Park, HI 96718, USA; Veronica Carvalho Martins, U.S. Embassy, Rua Hoji Ya Henda 81, C.P. 201, Praia, Cape Verde; Arrigo Querido, INGRH Servicos Estudos Hidrologicos, C.P. 367, Praia, Cape Verde.

An aviator flying over the waters of the southern Volcano Islands for Japan's Maritime Safety Agency reported seeing light-green seawater on 25, 27, and 28 November. Discolored seawater was last seen at this location in September 1993.

Geologic Background. Fukutoku-Oka-no-ba is a submarine volcano located 5 km NE of the pyramidal island of Minami-Ioto. Water discoloration is frequently observed from the volcano, and several ephemeral islands have formed in the 20th century. The first of these formed Shin-Ioto ("New Sulfur Island") in 1904, and the most recent island was formed in 1986. The volcano is part of an elongated edifice with two major topographic highs trending NNW-SSE, and is a trachyandesitic volcano geochemically similar to Ioto.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

Volcanic activity remained low during November and December. No significant surface changes were detected during this period, in agreement with electronic tiltmeter measurements on the E flank. Gas emission was concentrated in the W part of the crater, and the El Paisita, Las Chavas, La Joya, and Las Deformes fumaroles remained active. During 2-22 November there were temperature increases at Las Deformes and Las Chavas of 28 and 14°C, respectively. Correlation spectrometer measurements of the SO₂ flux remained low (<100 metric tons/day).

There were a few small seismic events associated with fluid movement in November, and sporadic seismicity associated with rock fracturing 2-4 km NNE of the active crater. During December, high-frequency seismicity consisted of small events (M <2.6) concentrated in the seismogenic region 6 km NE of the crater. Local residents felt events on 4 and 29 December that were M 2.5 and 2.6, respectively. The first of these events was centered in the NE region at 5 km depth, and the second at 7 km SW of the crater at 8 km depth. Only three small long-period events were recorded.

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

Information Contacts: Pablo Chamorro, INGEOMINAS - Observatorio Vulcanologico y Sismologico de Pasto, A.A. 1795, San Juan de Pasto, Narino, Colombia (URL: https://www2.sgc.gov.co/volcanes/index.html).

During October Irazú's seismic station (IRZ2), located 5 km SW of the active crater, registered 14 low-frequency events and an additional 19 microseisms that were only detected locally.

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, E. Duarte, R. Saenz, W. Jimenez, and V. Barboza, OVSICORI-UNA.

The East Rift Zone eruption continued in the last quarter of 1995 with lava erupting from the 780-m elevation flank vent next to the Pu`u `O`o cone (figure 98). The lava immediately entered subsurface tubes and traveled SE toward the coast, a distance of ~11 km.

Figure 98. Map of recent lava flows from Kilauea's east rift zone, October 1995. Contours are in meters and the contour interval is approximately 150 m. Courtesy of the USGS Hawaiian Volcano Observatory.

Activity during 10 October-6 November. Most surface flows broke out from the tubes on the steep slope of Pulama Pali and on the coastal plain. Some of these flows burned vegetation and extended the flow field at the base of Pulama Pali several hundred meters E. On the flats at the coast, surface flows occurred just upslope from the ocean entry at Kamokuna, and also 1 km farther W, near the old Kamoamoa campground. A major bench collapse at the Kamokuna entry on 16-17 October was accompanied by explosive activity that built two littoral cones.

A portion of the crater floor in the Pu`u `O`o cone collapsed, leaving a pit ~50 m in diameter that was partially filled by a large rockslide from the base of the W crater wall. The timing of the pit formation probably coincided with seismic events either on 19 and/or 29 October. The lava pond rose to ~75 m below the N spillway. On the upper slope above Pulama Pali, new skylights in the roof of the lava tubes continued to appear and crust over rapidly. Surface flows in this area and on the slope of Pulama Pali were small and infrequent. Most of the lava traveled via lava tubes to the coastal plain on the E side of the Kamoamoa flow field. Isolated breakouts occurred in the central part of the flow field, below Paliuli. The ocean entry at Kamokuna continued to produce a large acidic plume. Interaction between lava and seawater was occasionally explosive and formed two littoral cones on the bench.

Eruption tremor levels remained relatively low with amplitudes ~2x background. Long-period events from both shallow- and intermediate-depth sources continued at low-moderate rates. The number of short period microearthquakes was low beneath the summit and rift zones.

Activity during 7 November-4 December. A brief pause during the night of 10-11 November was immediately preceded by increased shallow seismic tremor and slight summit deflation. By the morning of 11 November lava was no longer entering the ocean at Kamokuna; however, activity at the eruption vent and the Pu`u `O`o cone had already resumed. During the afternoon, the lava pond was very active, its level fluctuating at least 10-15 m within 30 minutes, with spattering up to a height of 30 m. By the following day, lava was once again entering the ocean. Since this short pause, the lava pond has maintained a level ~75 m below the N rim. The floor of the large collapse pit was partially resurfaced by new lava flows after the pause.

Surface flows on the lower slope of Pulama pali and on the coastal plain continued to expand the Kamoamoa flow field E into forest and grasslands. At the shoreline, advancing pahoehoe flows filled the gap created by Kupaianaha eruptions in 1992, at the E edge of the current Kamoamoa flow field. These flows have produced a new ocean entry ~500 m E of the Kamokuna entry.

A large bench at the West Kamokuna entry collapsed on 23 November. Sustained explosive activity on 26 November built a new littoral cone (3-4 m high) on the bench. Lava was entering the ocean at 2-3 locations along a new East Kamokuna bench, located inside the W edge of the old Kupaianaha flow field. Breakouts from the relatively immature tube system were continuously active on the coastal plain near this entry. An older tube continued to feed isolated breakouts in the middle of the Kamoamoa flow field. The long-lived skylight at 735 m elevation finally crusted over in late November, leaving the tube system completely sealed off for the first 4 km from the vent. However, new skylights continued to appear and crust over near the top of Pulama Pali.

Eruption tremor was low and relatively steady, with a few isolated increases in amplitude in banded patterns. Shallow, long-period microearthquakes were slightly above average on 11, 12, and 16 November, with daily counts of nearly 100. Intermediate-depth, long-period counts were high on 2 and 3 December. Short-period summit and rift microearthquake counts were low.

Activity during 5 December-1 January. Small surface breakouts were observed high on Pulama Pali and on the coastal plain. The West Kamokuna entry occupied a large, mature bench; on 12 December, explosive activity at this entry built a new littoral cone. The East Kamokuna entry continued building a new bench. A pause in the eruption began at 1500 on 14 December and lasted until midnight on 15-16 December. The plume from the ocean entries stopped completely by 16 December. When the eruption resumed, lava again flowed through the existing tube system and reached the ocean at West Kamokuna bench on the afternoon of 17 December. The East Kamokuna entry was not reactivated after the pause.

Just prior to the 14-16 December pause, only a solid crust was visible where the Pu`u `O`o lava pond had been, at 80-90 m below the rim. By 19 December the lava pond had risen to ~68 m below the rim of the cone and was actively circulating. The pond level then subsided several meters and stabilized by 28 December. Surface flows occurred high on Pulama Pali, between 675 and 570 m elevation, and in the area from the 300-m elevation on Pulama Pali, down to the far eastern side of the flow field, to the coastal plain and ocean entry. Flows moved E into the grassland and brush near the base of Pulama Pali. A single ocean entry at West Kamokuna was active in late December, where a major collapse between 30 December and 1 January took out a section of the bench ~50-70 x 200-300 m in surface area, including several littoral cones. Explosive activity was observed at the ocean entry both before and after the collapse, but the most energetic and spectacular activity was reported on 1 January, immediately following the bench collapse. This activity included lava bubble burst and spatter and tephra ejections to heights estimated at 60 m. These explosions built a new littoral cone.

Eruption tremor levels remained low at ~2-3x the background. Shallow, long-period (LPC-A, 3-5 Hz) microearthquake counts were high on 5 December and again from 15-18 December. On the 15th and 16th, LPC-A counts were 200/day, gradually diminishing on the 17th and 18th. Shallow, long period (LPC-B, 1-3 Hz) microearthquakes were also high in number during 16-18 December, peaking on the 17th, with more than 150 events counted. Both types of LPC events are from a source 0-5 km in depth. They differ in frequency, suggesting a possible change in the condition of the source.

Shallow summit activity continued in the second half of December, with many hundreds of long-period (LPC-B, 0-3 Hz) events per day. The high counts peaked on 22 and 24 December with daily totals of 1,730 and 1,346, respectively. By 26 December, LPC-B counts appeared to be decreasing, while a slight increase of LPC-A was noted. The increase of shallow activity was coincident with the mid-December eruptive pause. Microearthquake counts were below average.

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

Information Contacts: Dave Clague, Hawaiian Volcano Observatory (HVO), U.S. Geological Survey, Hawaii Volcanoes National Park, HI 96718, USA.

An aseismic phreatic eruption vented from the N flank (not E as previously reported) of Hosho dome on the evening of 11 October (BGVN 20:10). The eruption came from a 400-m-long E-W fissure that includes multiple sub-fissures and craters.

The Volcano Research Center (VRC) at the University of Tokyo reported that the estimated volume of tephra from the 11 October eruption was 22,000 m³. Violent steaming from the vents and craters along en-echelon cracks has reportedly continued since then. An image taken by the French SPOT-2 satellite on the morning of 13 October shows an ash plume extending SW.

JMA reported that on 12 and 13 November field observers saw steam vigorously escaping from Vent D. The steam carried volcanic lapilli up to 5 cm in diameter.

Another JMA field party witnessed a loud explosion on 13 December, but ejecta were not found. VRC reported that another phreatic eruption on the morning of 18 December produced ~20% of the tephra of the 11 October eruption. Associated tremor, local deflation, and earthquakes were noted. Small ash emissions continued until at least as late as the night of 13 January 1996. In material erupted since 20 December, clear juvenile rhyolite glass shards were recognized in the ash and comprised roughly 1% of its volume.

The highest plumes during November and December rose ~300 and 600 m above the vent. On 23 November, earthquakes increased and the daily total was 13; the monthly total was 69. During the most active days in December, the 2nd and 18th, daily totals were 22 and 29, respectively; the total for the month was 134.

Further Reference. Hiroki, H., and Tatsuro, C., 1995, Eruption of Iozan at Kuju volcano in October 1995: Journal of the Geological Society of Japan, v. 101, no. 12, p. 43-56.

Geologic Background. Kujusan is a complex of stratovolcanoes and lava domes lying NE of Aso caldera in north-central Kyushu. The group consists of 16 andesitic lava domes, five andesitic stratovolcanoes, and one basaltic cone. Activity dates back about 150,000 years. Six major andesitic-to-dacitic tephra deposits, many associated with the growth of lava domes, have been recorded during the Holocene. Eruptive activity has migrated systematically eastward during the past 5000 years. The latest magmatic activity occurred about 1600 years ago, when Kurodake lava dome at the E end of the complex was formed. The first reports of historical eruptions were in the 17th and 18th centuries, when phreatic or hydrothermal activity occurred. There are also many hot springs and hydrothermal fields. A fumarole on Hosho lava dome was the site of a sulfur mine for at least 500 years. Two geothermal power plants are in operation at Kuju.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan; Volcano Research Center, Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113 Japan (URL: http://www.eri.u-tokyo.ac.jp/VRC/index_E.html); Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305 Japan (URL: http://www.aist.go.jp/ GSJ/dEG/sVOLC/kuju_E.html).

Throughout November-December, Crater 2 continued to emit white-to-gray ash and vapor, with plumes rising up to several hundred meters above the crater. During November, ashfalls reached 10-15 km on the N-NW flank; these eruptions were accompanied by audible explosions and rumbling. The eruptions threw incandescent projectiles during the first half of both November and December, and steady crater glow took place on most November nights and on 9-11 December. Crater 3 remained quiet. The greatest December activity, during the 23rd through the 26th, had emissions similar to those in November, but plumes rose somewhat higher (up to 1 km above the crater) and ash fell 10-15 km SE and SW.

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, H. Patia, D. Lolok, and C. McKee, RVO.

Summit visits by members of the Societe de Volcanologie Geneve during 15-19 December revealed low rates of intermittent effusive activity and some small explosions. Five episodes of lava emission were observed from hornito cluster T36 (BGVN20:10), each lasting

Figure 37. Sketch map of part of the Ol Doinyo Lengai crater showing new features and lava flows, 15-19 December 1995. Modified from the January 1994 map in BGVN 19:04.

Almost continuous ejection of lava fragments occurred from a cinder cone T37 (~15-25 m high), and with less intensity from a hornito in a small collapse depression just W of T5/T9 (figure 37). A small lava pond, observed for ~3 hours on 16 December, inside the depression at the foot of the hornito exhibited splashing and small bubbles. Two major flank collapses of T37 released large quantities of very fast-moving (5-8 m/second) aa lava flows that were ~50 cm thick. The first flank failure, on 16 December, was a progressive event on the W side. However, the E-flank collapse on the 18th came without warning, quickly sending a lava flow NE between T5/T9 and F35, almost to the crater rim.

Fumarole temperature measurements were taken on the N crater rim, inside new cracks on the crater floor, and at the tops of T8 and T15. All temperatures were 70-80 degrees C.

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: P. Vetsch, S. Haefli, and C. Peter, Societe de Volcanologie Geneve, B.P. 298, CH-1225 Chene-bourg, Switzerland.

Throughout November, Manam's activity remained low and night glow from its craters was absent. On 8 December, weak projections of incandescent lava were seen, and steady glow took place on the nights of 9 and 10 December. During November and December, both summit craters chiefly released steam, but on 8, 17, and 19 November South Crater released wisps of blue vapor, and on 25 and 28 November it released gray ash. South Crater also made weak, low-frequency roaring sounds on 1 November. Except for 6-11 December, activity was low during most of the month.

Earthquakes increased at the end of October, but during November they took place at the moderate rate of 600-1,400/day. They remained moderate in December. In the first half of November a tiltmeter 4 km SW of the summit continued to register slight deflation followed during the latter half of the month by a 2 µrad inflation.

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, H. Patia, D. Lolok, and C. McKee, RVO.

During November, Reseau Sismique Polynesien (RSP) stations on the islands of Tahiti, Rangiroa, Tubuai, and Rikitea registered acoustic T-waves. The waves were associated with a seismic swarm centered >2,500 km E of these islands. The swarm was located at 25.92 S, 177.15 W, essentially the coordinates of the Monowai seamount.

The T-wave swarm consisted of four episodes. The first, at 1751 on 27 November, lasted for 20 minutes and included seven separate explosions and other strong events. The second, 1403 on 28 November lasted 4 minutes and included small-amplitude events. The third, at 1842 on 30 November, prevailed for 7 minutes and included moderate-amplitude events. Ten minutes later, the fourth episode included 25 distinct explosions and other strong events.

The character of the T-wave signals was consistent with volcanism. T-waves are sound waves with paths that propagate through the sea; on reaching land the energy travels at the higher speed of ordinary seismic waves. Compared to earthquake-generated T-waves, volcanically generated ones are impulsive and of comparatively short duration.

Recent activity includes a possible eruption in 1944, and about seven documented eruptions during 1977-90 (BGVN 16:03). The seamount lies midway between the Kermadec and Tonga Islands, ~1,400 km NE of New Zealand. The adjacent trench is significantly shallower (~4 km) compared to the Tonga and Kermadec trenches (9-11 km deep).

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: Francois Schindele, Laboratoire de Geophysique, B.P. 640, Papeete, Tahiti.

A significant eruption in November-December followed almost six months of unrest and minor eruptive activity. During a crater visit on 13 November no precursors were observed, and on 18 November only background seismicity was recorded by the CNGN station (500 m E of the crater).

Early phase of activity, 19-22 November. Local residents first noticed explosions about the time of the onset of 30 minutes of mildly increasing seismicity detected by the CNGN station at 1145 on 19 November. Following a pause, seismicity continued to gain strength. Increasing activity was reported that afternoon by residents in Malpaisillo (~10 km N). Observations on the night of 19-20 November indicated mild Strombolian activity, with vertically directed ejecta, that was gradually increasing in strength. A Notice to Airmen (NOTAM) was issued the next day warning aviators of the volcanic activity.

Eruption tremor amplitude increased continuously and saturated the CNGN station (60 dB gain) at 0200 on the 21st. Tremor was detected on short-period seismic stations within a 30 km radius (at San Cristóbal and Momotombo volcanoes, and near the city of León). Energy release increased continuously and tremor could be felt over 1 km away, when sitting down, as a smooth rocking motion.

At 2000 on 21 November incandescent bombs were being thrown up to 300-400 m above the 1992 crater rim. Ash content was low compared with the 1992 and May-August 1995 activity, and bombs were often very large (meters across), which deformed and broke up in flight. Because of near-vertical trajectories, few bombs fell outside the crater. The new cone being built within the 1992 crater (figure 8) had a steep (>45 degrees) basal scarp, 2-5 m high, followed by a level bench and then a less steep slope (25 degrees) to its crater. Ejecta pulses maintained a frequency of 20/minute, but the size and duration of each pulse varied. From 0255 to 0310 on 22 November ejecta heights were <150 m but ash content and degassing were much higher, emitting dark clouds with each explosion. A thick, white lower plume appeared to be escaping from a new lava dome in the 1992 crater, 50 m W of the new cone (figure 8). By 0500 the eruption had regained previous intensity levels and exhibited near-constant fire-fountain-like activity, bombs were larger, and pulse frequency increased to 22/minute. The eruption continued at this level for over 4 hours.

Figure 8. Sketch of the crater at Cerro Negro, 0700 on 22 November 1995. Drawn from photographs taken by Pedro Perez; courtesy of INETER.

The new cone had almost reached the lip of the 1992 crater by 0700 on 22 November. At that time the lava dome emitted a small lava flow, 2-5 m wide and 50 m long, that followed the edge of the new cone towards the lowest part of the 1992 crater (figure 9). From 0930 to 1000 a series of explosions ejected material to the lower slopes of the new cone. Sand to gravel size ash fell W of the cone, but no large ejecta. Compared to the 1992 ejecta this material is highly vesicular with millimeter-size vesicles; olivine, pyroxene, and plagioclase are present, and some plagioclase crystals are 1 cm long. That evening the new cone overgrew the N rim of the 1992 crater and material began spilling towards Cerro La Mula. From 1900 to 2300 a tongue of lava spilled over the N rim of the 1992 crater. The front moved at less than 1 m/hour, but blocks constantly tumbled from the front down to the base of the main cone.

Figure 9. Sketch map of Cerro Negro showing active lava flows, 2000 on 23 November 1995. Drawn by B. Van Wyk de Vries; courtesy of INETER.

Lava flows beyond the crater, 23 November. After 1400 on 23 November dark gray pulses observed from 25 km away formed a plume that rose faster and higher than on previous days, attaining several kilometers altitude. Observations were made from the seismic station after 1500. During about 1515-1525 the plume became less ash-rich, ejecta became less frequent, and strong degassing pulses were heard. When regular pulses resumed, some bombs were ejected laterally onto the flanks of the main cone. Periodic heavy falls of 1-3 cm scoria were encountered by the scientists walking under the plume 1.5 km from the cone. Red glow was visible at 1730 over Cerro La Mula, and there was a smell of burning vegetation, suggesting an active lava flow. The lava tongue was observed at 1800 between Cerro La Mula and Cerro Negro (figure 9). Later named the La Mula flow, it was ~20 m wide and 5 m thick, and advancing at ~2 m/hour.

At 1830 a 20-m-wide lava stream moved down the N flank through a small breach at a rate of ~150 m/minute from the crater rim to the base of the cone. A lava field spreading out from the base of the cone had reached ~1 km from the crater by 2000, advancing 10-30 m/hour along two 300-m-wide fronts (figure 9). To the E of the flow the volcano flank appeared to be bulging and was irregular with large blocks jutting out that occasionally fell downslope, revealing incandescent lava. It appeared to the scientists that a slow-moving 20-m-thick blocky lava flow was moving to the crater rim and collapsing down the flank; however, the shape of the flank also suggested outward bulging. The blocky lava extended at least 200 m NE from the base of the cone.

Continuous and voluminous pulses at 2000 created a fountain that sent bombs at least 600 m above the crater. Ash clouds accompanied each pulse and occasional flames of burning gas reached 100-200 m above the crater. This activity had decreased by 2045, and by 2115 pulses of bombs appeared only every 30 seconds, although continual noise suggested smaller pulses.

Of the four GPS stations set up in the vicinity of the cone, by 23 November one had been destroyed by lava and another was too dangerous to approach. Measurements at the remaining stations were within the error of the equipment (2 cm at best). However, two fresh fault scarps radial to the cone were observed on the W side with 5 cm of displacement. Tremor energy increased continuously until 1200 on 23 November, after which it maintained a constant level.

Continuing activity, 25-26 November.The eruption plume was again clearly visible on 25 November from Managua as a diffuse gray column turning horizontal at ~2,000 m. At 0900 distinct pulses of dark gray ash rose from the crater and formed mushroom shapes before drifting W and being incorporated into the plume; ashfall was reported in León and Corinto. At times only massive bombs were thrown out, while at others strong explosions sent up dense ash clouds. Ash and highly vesicular scoria

At 1100 on 25 November most bombs were still ejected vertically, but a significant number were exiting at low angles and falling low on the flanks. The new cone had grown to ~40 m across, and its top was ~30-50 m below the 1992 crater summit. Bombs fell mostly on the cone and rolled down to the base. The small breach where the 23 November lava flow exited was partly covered by a new blocky flow, which appeared to come straight N from the new cone, though no exit vent was visible. It may have been produced by accumulated, still liquid ejecta beginning to flow outwards, as seen on 22 November. The flow had advanced half way down the flank, covering another blocky flow. The dome in the crater had grown to ~100 m wide and 40 m high. Blocks were continually spalling off the dome, which also sustained a continuous rain of bombs from the new cone. Multiple small lava tongues originated from the dome. The crater dome was less pronounced on 26 November, and was blocky rather than spiny. The new cone had grown ~10 m overnight.

The two flows moving N on the 23rd had reached ~1-1.5 km from the volcano. The larger W lobe was ~400 m wide and 3-5 m thick at the front with a small lobe extending down the gully below Cerro La Mula, and another extending E into a depression in the old N lava field. The E lobe had extended into forest at the E side of the old N lava field. Over a three-hour period the flows advanced ~12 m. A low ash-covered area with a small old cinder cone separated the lobes. The sides of each flow were slowly (~1 m/hour) encroaching on this and thickening. The thick lava lobes below the dome were advancing, and many areas of the dome were glowing. The ~30-m-wide La Mula lava flow had advanced W ~500 m down a small valley and was moving at ~1 m/hour on 25 November; by 0600 on the 26th it had stopped. By 0645 the other lava fronts had advanced 20-50 m since the previous evening. The main W lobe had spread E and a large block in the middle of the flow had moved ~100 m.

Seismic tremor levels remained high through 26 November. Tremor was continuous and distinctly felt up to 1.5 km from the cone.

Satellite observations of the ash plume. Visible satellite imagery on 25 November indicated a possible low-level ash cloud at 1245 (figure 10). The height of the plume was estimated at 4,500 m altitude and was moving SW at ~30 km/hour. Another small low-level plume was seen on imagery at 0815 the next day at an estimated 2,750 m altitude and moving WSW at ~35 km/hour. Explosive activity increased on 1 December, when visible imagery at 1230 revealed a plume 18 km wide extending ~320 km W; it was estimated to be between 3,000 and 6,000 m altitude. By 0900 on 2 December, the plume extended at least 640 km W and was below 4,000 m.

Figure 10. Map showing ash plumes from Cerro Negro detected on visible satellite imagery on 25-26 November, and 1-2 December 1995. Courtesy of the Synoptic Analysis Branch, NOAA/NESDIS.

End of the eruption, early December. Explosive and effusive activity ended on 6 December. However, a lava flow was still moving N on 8 December. Isopach maps of the ashfall through 2 December (figure 11) were constructed by Markus Kesseler based on 85 GPS control points (precision +- 30 m). The 0.1 cm isopach encloses an area of ~200 km². An estimated 12,000 people were affected by this eruption, about 6,000 of whom had been evacuated from 15 rural communities. Farmland was significantly damaged by ashfall and lava flows during the harvesting season; most of those affected were farmers and their families.

Figure 11. Isopach maps of ashfall from Cerro Negro, 19 November-2 December 1995. Isopachs within the 5.0 cm limit are at 10-cm intervals, up to 50 cm closest to the crater. The 2-5 June isopachs (BGVN 20:09) are shown for comparison. Courtesy of Markus Kesseler; base map courtesy of Brittain Hill.

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: Wilfried Strauch, Virginia Tenorio, Rolf Schick, Helman Taleno, Leonel Urbina, Cristian Lugo, and Pedro Perez, Instituto Nicaraguense de Estudios Territorales, Managua, Nicaragua; Benjamin van Wyk de Vries, The Open University, Milton Keynes, United Kingdom; Markus Kesseler, Dept. of Mineralogy, Universite de Geneve, 13 rue des Maraichers, 1211 Geneve 4, Switzerland; Michael Conway and Brittain E. Hill, Center for Nuclear Waste Regulatory Analyses, Southwest Research Institute, 6220 Culebra Rd., San Antonio, TX 78238 USA; Jim Lynch, NOAA/NESDIS Synoptic Analysis Branch (SAB) , Room 401, 5200 Auth Road, Camp Springs, MD 20746, USA; Department of Humanitarian Affairs, United Nations, Palais des Nations, 1211 Geneva 10, Switzerland.

On 4 December, many earthquakes occurred in and around the island, some of which were felt. The largest one was M 4.3.

Geologic Background. The elongated island of Niijima, SSW of Oshima, is 11 km long and only 2.5 km wide. It is comprised of eight low rhyolitic lava domes that are clustered in two groups at the northern and southern ends of the island, separated by a low, flat isthmus. The flat-topped domes give the island the appearance of two large plateaus bounded by steep cliffs. The Mukaiyama complex at the southern end of the island and Achiyama lava dome at the northern end were formed during Niijima's only historical eruptions in the 9th century CE. Shikineyama and Zinaito domes form small islands immediately to the SW and west, respectively, during earlier stages of volcanism. Earthquake swarms occurred during the 20th century.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

The surface of the sky-blue crater lake rose in November (20 cm higher than October); the lake's temperature was 26°C. A vigorous subaqueous fumarole appeared adjacent the lake's S shore. The W-terrace fumarole emitted yellow, sulfur-rich gases and particles; other fumaroles located on the NW-SW terrace emitted only low amounts of gases. Measured fumarole temperatures were in the range 94-96°C along the S and SE crater, an area that produced 100-m-tall gas columns. Gases escaping the pyroclastic cone had temperatures of 93°C.

During 1-22 November the local seismic station recorded 5,146 events (predominantly of low-frequency), significantly fewer than the number seen in the two previous months (figure 59).

Figure 59. Poás seismicity for January-November 1995 recorded at station POA2 (2.7 km SW of the active crater). 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, E. Duarte, R. Saenz, W. Jimenez, and V. Barboza, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA).

Throughout most of November 1995 the two recently active centers remained quiet, with Tavurvur emitting only steam and Vulcan not emitting any visible vapor (figure 24). Then on 28 November, Tavurvur suddenly began erupting, creating a parasitic crater. Vulcan continued to remain quiet throughout December.

Figure 24. Index map of Rabaul and detail of soil CO2 transect. Elevation contours given in meters; base map after Johnson (1995).

The volume of Tavurvur's faint blue vapor emissions seemed to increase in the weeks prior to 28 November. On the morning of the eruption an impressive white steam cloud stood several hundred meters above Tavurvur's summit. The new eruption, which was preceded by weak roaring sounds, started at about 1020, and initially consisted of forceful emissions of gas and dark ash at 2-6 minute intervals. Those emissions lacked explosion sounds; they rose 400-800 m above the crater rim and blew over a broad arc between the SE and SW, resulting in fine ashfall both onshore and over the sea. No ashfall reached Kokopo, 25 km SE. The next day, 29 November, two intervals of stronger emission took place (at 1200-1300 and 1415-1430), sending columns ~1 km above the summit.

An aerial inspection on 30 November revealed a new crater on the 1994-95 crater's SSE rim. Although the 1994-95 crater displayed no new activity, fumaroles were particularly active along its E walls. An old explosion crater along the base of Tavurvur's S flank, in which 6 people were killed in 1990 by inhalation of carbon dioxide, was releasing weak-to-moderate emissions of white vapor from its N to E walls. Directly downslope and immediately offshore of this explosion crater a spring had become considerably more active since the 1994 eruption; during the 30 November aerial inspection it was prominent, giving off a strong stream of rusty brown water. During November and December, ground deformation remained low.

Tavurvur discharged dark ash clouds in December, typically at 3-6 minute intervals, that rose 400-1,000 m above the summit. On 2 December two ash clouds rose to 1.5-2 km. The second brought intense lightning causing minor damage to home appliances in Rabaul Town (figure 24). On 5 December, a particularly loud explosion, heard 30-40 km away, accompanied the discharge of an ash cloud that rose to 1.2 km. Additional loud explosions accompanied dense ash clouds that rose to 1-1.2 km; these took place during December as follows: 11th (1 time), 13th (1), 14th (4), 18th (1), 23rd (1), 24th (1), and 29th (2). Moderate-sized clouds blew SE, and very fine ash occasionally fell both in Kokopo and, due to shifting winds, in Rabaul Town. On December nights, observers saw incandescent fragments and during the second half of the month they heard occasional deep roaring noises.

Seismicity. November seismicity generally remained low, but was punctuated by 11 high- and 42 low-frequency events. Eight of the high-frequency events were located. Five occurred within the caldera's seismically active elliptical fault zone, in the NE (1 event), W (1), and S (3) quadrants. Although one of the extra-caldera events was centered S of the caldera, two events were located immediately to the caldera's NE, an area where the bulk of the high-frequency earthquakes have occurred in the past few months. One of these two events, ML 3.0 on 24 November, produced a felt intensity of MM III at Rabaul Town.

Of the 42 low-frequency earthquakes during November, 17 came from around Tavurvur volcano. Two of these occurred in late October, and 9 others in November prior to the 28 November eruption. The last time such events appeared was during the eruptive activity in March 1995. The other 25 low-frequency earthquakes not centered around Tavurvur were more difficult to locate accurately due to emergent waveforms and fewer stations outside the caldera. Many may have originated immediately N of the caldera. On 10 November a low-frequency earthquake centered 7-8 km outside of the caldera was strong enough to trigger aftershocks.

During December, seismic instruments detected 30 high-frequency earthquakes, 684 low-frequency earthquakes, and 488 explosion events. Instruments also recorded occasional discontinuous non-harmonic tremors. About 70% of the high frequency earthquakes occurred during 4-6 December. The five located events had epicenters in either the S part of the caldera's seismically active zone (the largest one, M 2.7), NE of the caldera (two events), or within the caldera. All of the seismic explosions and most low-frequency earthquakes originated at Tavurvur; the 20 exceptions originated farther NW and took place at the end of the month.

Fumarole and soil sampling. During 21-27 November, rainwater, water from hot springs, and gases from subaerial and submarine fumaroles were sampled at 13 sites (table 3). Compared to Vulcan, fumaroles at Tavurur displayed relatively high temperature, low pH, and high conductivity. Hot springs sampled near the shore of Greet Harbor were slightly acidic and comparatively conductive. All samples were more acid than those assessed prior to the 1994 eruption episode.

Table 3. Summary of fumarole and hot spring sampling at Rabaul Caldera, 21-27 November 1995. Courtesy of RVO.

A soil CO₂ survey E of Simpson Harbor (figure 24) showed that CO₂ concentrations varied widely, 0.4-20% (figure 25). As reported by Mori and McKee in 1987, the CO₂ concentrations peaked along the seismically active fault zone (near the old airport), some distance from either Tavurvur or Vulcan. Other anomalously high concentrations were seen at the Matupit causeway and Sulphur Creek. Low concentrations were seen at other places, including Matupit Island.

Figure 25. Soil CO2 concentrations at Rabaul Caldera along transect A-A'. Courtesy of RVO.

Isotopic analysis of six selected samples along the profile found that ¹³C ranged from -29.8 to -18.4 per mil suggesting chiefly biogenic contributions. A mixing process with a minor contribution of volcanogenic CO₂ might also account for the wide range of ratios seen. High soil CO₂ levels could be related to the effects of a higher thermal gradient along active fractures and faults.

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, H. Patia, D. Lolok, and C. McKee, RVO; N. M. Perez and H. Wakita; University of Tokyo, Earth Chemistry, Bunkyo-ku, Tokyo 113 Japan.

An eruption on 6 November 1995 followed increases in fumarolic activity and a several-month long increase in local earthquakes and tremor (figures 11 and 12). Park rangers who visited the summit at the start of October noted increased fumarolic activity and witnessed landslides down the main crater's walls. Strong sulfur smells were noted W-SW of the volcano on multiple occasions in the days prior to 6 November (figure 13).

Figure 11. Rincón de la Vieja's monthly totals for tremor and low-frequency seismicity, January-September 1995. Courtesy of OVSICORI-UNA.

Figure 12. Rincón de la Vieja's seismicity, 1-13 November 1995. An eruption began on 6 November. Courtesy of OVSICORI-UNA.

Figure 13. Map of NW Costa Rica showing key features associated with Rincón de la Vieja's 6 November 1995 eruption. Courtesy of OVSICORI-UNA.

The seismic receiver (RIN3) sits 5 km SW of the active crater. Although the OVSCICORI-UNA seismic system failed on 29 October (and possibly other times during the month), it functioned reliably again after the 31st. Low-frequency events gradually increased during 1-6 November (figure 12), followed by a modest decline. High-frequency events were only registered after 3 November. Tremor was absent prior to the 6 November eruption.

OVSCICORI reported that the first phase of the eruption consisted of vapor with subordinate ash in a discharge lasting 2 minutes. Later, vigorous fumarolic activity led to many hours of constant tremor. Only two more clear eruptions followed in the initial 17 hours of venting, but others followed in subsequent days. The eruption climaxed on the morning of the 8th, when columns reached 3.5 km altitude. Fine ash blew W and NW; larger blocks and tephra were confined to within ~1 km and the area of heavy ashfall reached ~5 km away (figure 13).

During some phases of the eruption, lahars flowed down the Azul and Penjamo rivers and an interfluvial ravine called the Quebrada Azumicrorada (figure 13). Upper reaches of these drainages sustained up to 6 m of erosion. Lahars on the 7th were cooler and more water-rich than those on the 8th. In addition to previously reported damage, on 8 November lahars shut down some communications systems.

At 0900 and 1130 on 8 November OVSICORI scientists visited the summit area and saw impact craters as large as 2 m in diameter; the craters were produced by 0.5-1.0 m diameter blocks, some of which were still warm to the touch. The scientists also saw ongoing phreatic eruptions escaping from a vent adjacent to the crater lake.

At 0411 on the 9th a shock wave was felt 25 km SE in the city of Liberia; the related outburst was seen from the N flank, where residents witnessed incandescent block ejections.

Amplitudes on the seismic recorders regularly peaked at over 30 mm on 6-9 November. The highest amplitudes, on 7-9 November, reached nearly 60 mm. Amplitudes decreased the morning of 9 November; following the eruption (10-14 November) amplitudes generally remained under 10 mm with infrequent spikes to ~20 mm and a few rare spikes to 30 mm. Tremor decreased by an order of magnitude on 10 November and it dropped to <1 hour/day on 13 November.

During fieldwork in early December, G. Soto (ICE) and G. Boudon (IPG) inspected the near-source region. For a radial distance of ~1 km from the crater they saw a deposit consisting of muddy ash, lapilli, and blocks. These reached 40 cm thick on the crater's southern outer rim at a point 150 m from the inner rim. The deposit's thickness and grain size decreased rapidly with distance, such that at 600 m SW of the crater the deposit was only 7 cm thick. The deposit's basal zone was enriched in fine grained, muddy-looking material, but throughout the deposit there occurred lustrous black juvenile clasts. Over ~1 km² of the upper surface of the deposit, there lay a blanket consisting of (a) dense, quenched blocks, (b) breadcrust bombs with notably vesicular cores, and (c) some highly vesiculated fragments. On 8 December at points 5 and 8 km from the summit, the Penjama and Blanco rivers, respectively, still ran milky and were slightly acidic in taste. That same day, the scientists saw only fumarolic activity. Although scientists looked for a lake in the depths of the crater, they failed to gain a clear view there.

Reference. Boudon, G., Rancon J.-P., Kieffer, G., Soto, G.J., Traineau, H., and Rossignol, J.-C., 1995, Estilio eruptivo actual del Volcan Rincón de la Vieja: evidencias de las productos de las erupciones de 1966-70 y 1991-92: Rothschildia, 2 (2): 10-13, Area de conservacion de Guanacaste, Costa Rica.

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, E. Duarte, R. Sáenz, W. Jimenez, and V. Barboza, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica; Georges Boudon, Institut de Physique du Globe de Paris, 4, Place Jussieu, 75252, Paris Cedex 05, France.

Based on satellite imagery and pilot reports received by the U.S. Federal Aviation Administration, an eruption began at 1830 on 23 December. Between 1830 and 2000 on 23 December, pilots reported an ash plume as high as 10.5 km altitude (35,000 feet); prevailing winds carried the plume primarily N and NW. Analysis of a satellite image from 1912 showed a possible small ash plume extending ~50 km NW. Possible very light ashfall was reported at approximately 0130 on 24 December in Cold Bay, 90 km NE; this ash would have been carried by westerly low-altitude winds.

Geologic Background. The beautifully symmetrical volcano of Shishaldin is the highest and one of the most active volcanoes of the Aleutian Islands. The 2857-m-high, glacier-covered volcano is the westernmost of three large stratovolcanoes along an E-W line in the eastern half of Unimak Island. The Aleuts named the volcano Sisquk, meaning "mountain which points the way when I am lost." A steady steam plume rises from its small summit crater. Constructed atop an older glacially dissected volcano, it is Holocene in age and largely basaltic in composition. Remnants of an older ancestral volcano are exposed on the west and NE sides at 1500-1800 m elevation. There are over two dozen pyroclastic cones on its NW flank, which is blanketed by massive aa lava flows. Frequent explosive activity, primarily consisting of strombolian ash eruptions from the small summit crater, but sometimes producing lava flows, has been recorded since the 18th century.

Information Contacts: Alaska Volcano Observatory.

Although there was relative quiet during October (20:10), during the first 10 days of November three large phreatic eruptions occurred. Each of these eruptions blanketed Plymouth, 4.5 km W of the active vent, with ~2 mm of ash (table 2). Dome growth within the crater started on 16 November, the estimated date when juvenile material first reached the surface, and continued through at least December. Estimates of the dome's rate of growth from 16 November to 6 December were on the order of 0.5 m³/sec.

Table 2. Summary of the daily behavior of Soufriere Hills, 1 November through 11 December 1995. The table omits most geophysical and geodedic observations, however, "eruption signal" refers to seismically determined eruptions, and "mudflow signal" refers to seismically determined mudflows. Courtesy of MVO.

Small rockfalls from the flanks of the new, locally incandescent dome were witnessed on several occasions. During early December, debris from a larger rock avalanche was seen in the moat of English's Crater. As of early January, neither local avalanches nor material liberated during the failure of spines escaped the crater area. The limited mobility of the rock avalanches suggested they were not propelled by gas explosions with great overpressures. Although floods and dilute mudflows were distinguished seismically, no significant debris avalanches or pyroclastic flows occurred.

Heavy rainfall after 11 December may have triggered several small ash emissions, depositing red-brown ash on the upper W-flanks. The ash presumably consisted of non-juvenile material, from rock avalanches sloughing off the new dome, and some hot juvenile ejecta from small explosions vented in or around the new dome.

Although quantitative SO₂ flux measurements were lacking, as of early December related damage to vegetation extended ~3 km downwind and 1.5 km laterally. Tree damage was severe on the upper W flank. Gases sampled at three of the established fumaroles (soufrieres) around the volcano showed no change in composition. Although gas and acid aerosol production had been at enhanced levels from mid-November to early December, air sampled in Plymouth during early December contained very little SO₂.

Dome growth.Beginning on 30 November, good visibility allowed observers to watch a single dome develop from two smaller bodies (figure 6). One body was NW of the September cryptodome (an intrusion that produces a surficial bulging), and the other at Vent 1. The evolving dome had a rough blocky carapace that initially had some small (

Figure 6. Topographic map of the crater area at Soufriere Hills showing pre-eruption morphology (thin lines) and new features (bold lines) as of 10 December 1995. Contour interval is 50 feet, values shown are feet x 100 (3.28 feet = 1 m); coordinates shown are UTM. CH indicates Chances Peak; CA indicates Castle Peak. Courtesy of MVO.

A prominent spine on the new dome's E side grew in height until 7 December when it began to collapse. The spine's maximum vertical growth rate was estimated to be 5-8 m/day. Further dome growth at a slower rate occurred until 9-10 December, and slower growth, or a possible halt, continued as late as 13 December. On 13 December a small, radial crack on the N side of the new dome emitted steam and ash for most of the day. At least two columns reached in excess of 500 m above the crater rim.

A new batch of extruded material reached the surface on 15 December. On the 17th, in addition to widespread incandescence radiating from the new dome, observers saw a new ~ 40-m-tall spine. Between the 17th and 20th the spine grew vertically at 7 m/day, and the adjacent dome also rose, but at a slightly slower rate. The spine's growth rate during some undisclosed intervals reached up to 20 m/day. On 17 December observers also saw a narrow crack in the dome within Vent 1 that emitted glowing ejecta. Many small ash releases sent columns up to ~1.1 km above the summit.

During the week ending 27 December, several spines grew 5-10 m/day then subsequently collapsed. One spine had grown to ~15 m higher than Castle Peak (summit elevation ~910 m) prior to failing late on 25 December.

Explosions on 21 December produced a mildly convecting ash cloud that rose ~1.5 km above the volcano. Ash fell to the N, reaching the N portion of the island. Although apparently phreatic events took place in early- to mid-November, this was the most vigorous explosion since then and it may have been driven magmatically. Steam production remained constant during 21-27 December, feeding a plume that sometimes carried small amounts of ash. From 28 December to 3 January there was relative quiet and slow dome growth. Only 3 m of dome growth took place during the week, and for a least a few days after about 1 January, the dome may have ceased growing.

Deformation. Data from two electronic tiltmeters showed no significant changes during the crisis. Despite their stability, around 10 November deformation in the upper part of the volcanic edifice was recorded by EDM and GPS measurements at Castle Peak Dome and Chances Peak. Four days of significant deformation were followed on 15 November by intense seismic activity (see below). These were followed on 17 and 18 November by an upward extension of the dome that formed in September. The dome also appeared to have extended slightly towards Chance's Peak. Although visibility was poor for the next 10 days, glimpses through steam and cloud cover suggested further doming and rock avalanching. These processes influenced a wide area on the NW side of Castle Peak Dome, including the edge of Vent 1.

From mid-November until about mid-December, the rate of deformation remained very low, with daily shortening on the order of a few millimeters along most lines, even those aimed at the presumably less stable upper flanks.

The EDM data for 10-12 December showed lengthening of the lines to Castle Peak—a deflation of the edifice. Around this time, a longer interval of GPS data also showed their lines had lengthened by >1 cm overall (with some shorter-term variability). This rate was equal to or greater than the average rate during the month of October. Late December deformation measurements using GPS and EDM techniques suggested either a return to slight inflation (14-20 December) or stability (21-27 December).

Seismicity. Montserrat seismic activity falls into four categories: 1) tremor, 2) long-period events, 3) volcano-tectonic earthquakes, and 4) regional earthquakes.

After 15 November, elevated seismicity prevailed with relatively few quiet periods. The pattern appeared very similar to that seen in late September associated with the formation of a cryptodome and possibly associated with the later extrusion of a spine. The elevated seismicity was inferred to be due to a high-level magmatic intrusion.

After 27 November there was a loss of discreet, locatable events. Low-amplitude tremor became intermixed with intervals of intense, low-amplitude, long-period events; these arrived at rates of up to 5/minute but were recorded only on the closest seismic station (MGAT, Upper Gages, figure 7). In early December tremor increased somewhat at other stations farther from the crater (MLGT, Long Ground, and MBCT, Bethel); at this time amplitudes of events at Gages also increased and the RSAM seismic index rose as high as it has been since 15 November.

Figure 7. Montserrat seismic stations and epicenters shown in map and cross-section views, 10 December 1995. The intersection of the two cross sections is indicated by an asterisk. Epicenters are shown with two symbols, indicating variations in data quality (square, A and B quality; cross, C and D quality). Stations MSAT and MPVF were off line; MVPZ and MSSZ were 3-component stations. Courtesy of MVO.

Until 9 December there were also small, frequent, long-period earthquakes. These were accompanied by low-to-variable amplitude tremor at the Gages station, but tremor disappeared from all other stations by 8 December. The number of locatable earthquakes dropped to 1-2/day, the lowest observed during this crisis. Located earthquakes were mostly volcano-tectonic and at slightly greater depths (0-5 km) than the long-period and hybrid-type earthquakes that had dominated since 24 November. High-amplitude, high-frequency tremor was recorded at station MGAT for several hours during 10-11 December; this was probably due to an increase in steam venting from several areas on Castle Peak.

The dome grew during the week ending on 13 December, with few accompanying earthquakes early on 6 December. In contrast, during 14-20 September there were 2-20 locatable earthquakes/day, many with epicenters along the N flanks at depths of 0-6 km. During the week ending on 20 December all stations registered earthquakes with emergent onsets and a dominant frequency of 2.2 Hz; these took place 5-15 times/day. Some of the earthquakes corresponded to small explosions. Heavy rains on 16-19 December triggered floods and dilute mudflows who's acoustic signals were detected by the seismic network.

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

Information Contacts: MVO, Plymouth; Seismic Research Unit, UWI.

During October-December there were no explosions or gas-and-ash emissions from the lava dome, and no explosion-like seismicity was detected. Surveys of the lava dome indicated that deformation rates have remained at background levels. No increase in deformation of the dome occurred as a consequence of the recent earthquake activity, but the NW side of the dome continued to move downward very slowly as it has since a series of small explosions between 1989 and 1991. Periods of intense rainfall in November generated several lahars from the crater. All of the lahars were detected by the USGS real-time acoustic-flow network and probably flowed into Spirit Lake. Such lahars are common during intense rainfall following the dry summer months.

The number of small-magnitude (M <1) earthquakes beneath the crater decreased slowly from nearly 100/month in September (BGVN 20:09) to ~25/month in December. Seismicity at the end of December was similar to the first 6 months of 1995. The gradual decrease in seismicity, combined with the lack of small explosions related to the September increase, has lowered the concern of scientists monitoring the volcano. Small dome explosions are still possible, but their likelihood is no greater early in 1995.

Geologic Background. Prior to 1980, Mount St. Helens formed a conical, youthful volcano sometimes known as the Fuji-san of America. During the 1980 eruption the upper 400 m of the summit was removed by slope failure, leaving a 2 x 3.5 km horseshoe-shaped crater now partially filled by a lava dome. Mount St. Helens was formed during nine eruptive periods beginning about 40-50,000 years ago and has been the most active volcano in the Cascade Range during the Holocene. Prior to 2200 years ago, tephra, lava domes, and pyroclastic flows were erupted, forming the older St. Helens edifice, but few lava flows extended beyond the base of the volcano. The modern edifice was constructed during the last 2200 years, when the volcano produced basaltic as well as andesitic and dacitic products from summit and flank vents. Historical eruptions in the 19th century originated from the Goat Rocks area on the north flank, and were witnessed by early settlers.

Information Contacts: Dan Dzurisin, Cascades Volcano Observatory, U.S. Geological Survey, 5400 MacArthur Blvd., Vancouver, WA 98661 USA (URL: http://volcanoes.usgs.gov/); Steve Malone, Geophysics Program, University of Washington, Seattle, WA 98195 USA (URL: https://volcanoes.usgs.gov/observatories/cvo/ home.html).

In contrast to very intense activity seen in summer-autumn 1994, Boris Behncke noted that activity remained low from early 1995 through October. The low level of activity, also shown by seismic data acquired by the University of Udine (see recent Bulletins), was interpreted by some researchers as a possible precursor of a more powerful eruption in the near future, resulting in a warning and access restrictions in April-May.

Eruptions during August-October produced low lava fountains and ash plumes. Activity from vent 3/1 (figure 46) consisted of night glow and spatter ejections, at times throwing bombs outside the crater. Vent 1/1 had periods of vigorous lava fountaining, often dropping incandescent bombs on the Sciara del Fuoco, particularly in early September. During dry weather, a dense gas plume often formed a hazy layer at 850-900 m altitude that extended for tens of kilometers.

Figure 46. Map of the crater terrace at Stromboli, 19-20 September 1995, showing active vents. The map was produced using EDM and triangulation measurements. Vent numbering is consistent with sketch maps from April 1995 (BGVN 20:04). Courtesy of Andy Harris and Nicki Stevens.

During a 19-20 September visit by Andy Harris and Nicki Stevens, activity was observed from five vents (figure 47). A 4-m-diameter vent in the side of a hornito (1/4), had incandescent walls and an internal temperature of 940°C, as measured with a Minolta/Land Cyclops 152 infrared (0.8-1.1 µm) thermometer. Gas-jet eruptions from this vent sent incandescent gas and minor ejecta ~50 m high. Regular explosions from vents 1/2 and 3/2 ejected bombs and brown ash clouds up to ~100 m. Seven eruptions during a 90-minute period from vent 2/1 sent bombs to a height of ~50 m. No explosions were seen from vent 3/1, but it exhibited continuous night glow and apparently quietly ejected a few bombs to no more than 10 m above the crater rim.

Observations by Behncke on 28-29 September showed that craters 2 and 3 had not changed significantly since a visit on 20 April (BGVN 20:04). Vent 3/1 showed fluctuating glow at night but had no ejections. Vent 3/2 had very weak emissions of reddish ash every 5-20 minutes. Crater 1 had been largely filled with small spatter cones during the summer of 1994, but their destruction began with a powerful phreatic explosion on 5 March 1995 (BGVN 20:04). However, the twin cones (1/4 & 5) in vent area 1/3 remained. Neither of them had erupted after September/October 1994, but an incandescent vent (~10 m wide) at the SE base of the SW cone (1/4) had brief noisy gas explosions that emitted a diffuse incandescent gas cloud.

Vigorous eruptions observed by Behncke from vent 1/1 ejected black ash plumes that occasionally rose >100 m. After dark, incandescent ejections were seen, and loud roaring noises were audible. Reports by other observers in early October disclosed continuing low-level eruptions from vents 1/1 and 3/2 and incandescence from vents 1/3 and 3/1. In addition to the vents active in September, a vent behind the twin cones in Crater 1 and a vent in the NW part of Crater 3 were active when observed by Open University geologists on 15 and 30 October.

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: Boris Behncke and Giada Giuntoli, Department of Volcanology and Petrology, GEOMAR, Wischhofstr. 1-3, 24148 Kiel, Germany; Andy Harris, Department of Earth Sciences, The Open University, Milton Keynes MK7 6AA, United Kingdom; Nicki Stevens, ESSC, University of Reading, P.O. Box 227, Reading RG2 2AB, United Kingdom.

Eruptive activity took place from March to June and from August to December 1995. Some ashfalls were observed at a village 4 km SSW of the crater. The two historically active summit craters and typically have Strombolian eruptions.

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

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

During the second half of December, the number of earthquakes gradually increased, totalling 103 for the month. Consisting of a NE-SW aligned group of stratovolcanoes, Tokachi has a record that includes a partial cone collapse in 1925 that led to ~144 deaths and 5,000 homes destroyed.

Geologic Background. Tokachidake volcano consists of a group of dominantly andesitic stratovolcanoes and lava domes arranged on a NE-SW line above a plateau of welded Pleistocene tuffs in central Hokkaido. Numerous explosion craters and cinder cones are located on the upper flanks of the small stratovolcanoes, with the youngest Holocene centers located at the NW end of the chain. Frequent historical eruptions, consisting mostly of mild-to-moderate phreatic explosions, have been recorded since the mid-19th century. Two larger eruptions occurred in 1926 and 1962. Partial cone collapse of the western flank during the 1926 eruption produced a disastrous debris avalanche and mudflow.

Information Contacts: Volcanological Division, Seismological and Volcanological Department, Japan Meteorological Agency (JMA), 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan.

During October-December emissions generally consisted of moderate-to-high amounts of white vapor. Gray emissions were also reportedly observed on three days in October and a number of days in November. Seismic activity was very low in October-November and unreported for December.

Geologic Background. The symmetrical basaltic-to-andesitic Ulawun stratovolcano is the highest volcano of the Bismarck arc, and one of Papua New Guinea's most frequently active. The volcano, also known as the Father, rises above the N coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1,000 m is unvegetated. A prominent E-W escarpment on the south may be the result of large-scale slumping. Satellitic cones occupy the NW and E flanks. A steep-walled valley cuts the NW side, and a flank lava-flow complex lies to the south of this valley. Historical eruptions date back to the beginning of the 18th century. Twentieth-century eruptions were mildly explosive until 1967, but after 1970 several larger eruptions produced lava flows and basaltic pyroclastic flows, greatly modifying the summit crater.

Information Contacts: Ben Talai, H. Patia, D. Lolok, and C. McKee, RVO.

On 15 November, residents of Perryville, ~30 km S, heard rumblings and booms through the early evening. They also observed minor ash emission, as well as increased steaming. Minor steam and ash emission was again observed on 30 November. Veniaminof was obscured by clouds on satellite imagery of 15 November, and no hot spot was visible during the last week of the month. Low-level eruptive activity has been intermittent since July 1993 (BGVN 18:07).

Geologic Background. Veniaminof, on the Alaska Peninsula, is truncated by a steep-walled, 8 x 11 km, glacier-filled caldera that formed around 3,700 years ago. The caldera rim is up to 520 m high on the north, is deeply notched on the west by Cone Glacier, and is covered by an ice sheet on the south. Post-caldera vents are located along a NW-SE zone bisecting the caldera that extends 55 km from near the Bering Sea coast, across the caldera, and down the Pacific flank. Historical eruptions probably all originated from the westernmost and most prominent of two intra-caldera cones, which rises about 300 m above the surrounding icefield. The other cone is larger, and has a summit crater or caldera that may reach 2.5 km in diameter, but is more subdued and barely rises above the glacier surface.

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

The following summarizes observations between August and December 1995 made by pilot R. Fleming and IGNS scientists. No significant eruptive activity has occurred since minor ash emissions on 28-29 June (BGVN 20:07).

A new 30-m-diameter crater was noted on 12 August in the area of the May '91 embayment. It had destroyed a large fumarole and was ejecting mud at intervals of 2-5 seconds. By 3 October, Wade, TV1, and Princess craters were joined in a single lake, following the failure of their divides. On 13 November the rising lake level was encroaching on the area of fumaroles and hot ground. Several new fumarolic vents were noted 20-30 m above the lake level. No more crater changes were observed through 12 December. Very little seismicity was recorded: low-frequency tremor accompanied the formation of the 12 August vent. Seismicity revealed no evidence of eruptive activity since 28-29 June.

Ground deformation and magnetic surveys continued to record trends indicative of future eruptive activity. Inflation was localized in the Donald Mound area, in contrast with the earlier pattern of crater-wide inflation between November 1994 and July 1995. Inflation is occurring at a much greater rate than that observed before the 1976 eruption. Magnetic decreases under Donald Mound and on the NE side of the 1978/90 Crater Complex indicate shallow heating. Other indicators like heatflow and gas chemistry do not suggest an incipient eruption. Fumarole temperatures remain relatively low, and gas samples from fumaroles were richer in water than in the past, consistent with the rise of the water table. However, the influence of the rising water level and its possible masking effects remain uncertain.

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

Information Contacts: B.J. Scott, Institute of Geological & Nuclear Sciences (IGNS), Private Bag 2000, Wairakei, New Zealand.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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