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).

Suwanosejima is an active volcanic island south of Japan in the Ryuku islands with recent activity centered at Otake crater. The current eruption began in October 2004 and activity has mostly consisted of small ash plumes, ballistic ejecta, and visible incandescence at night. This report summarizes activity during January through June 2019 and is based on reports by the Japan Meteorological Agency (JMA), and various satellite data.

Thermal activity recorded by the MIROVA system was low through January and February after a decline in November (figure 36), shown in Sentined-2 thermal infrared imagery as originating at a vent in the Otake crater (figure 37). During January an explosive event was observed at 1727 on the 3rd, producing a gray plume that rose 600 m above the crater. A white gas-and-steam plume rose to 1.5 km above the crater and nighttime incandescence was observed throughout the month. Reduced activity continued through February with no reported explosive eruptions and light gray plumes up to 900 m above the crater. Incandescence continued to be recorded at night using a sensitive surveillance camera.

Figure 36. MIROVA log radiative power plot of MODIS thermal infrared data at Suwanosejima during September 2018 through June 2019. There was reduced activity in 2019 with periods of more frequent anomalies during March and June. Courtesy of MIROVA.

Figure 37. A Sentinel-2 thermal satellite image shows Suwanosejima with the active Otake crater in the center with elevated temperatures shown as bright orange/yellow. There is a light area next to the vent that may be a gas plume. False color (urban) satellite image (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

There was an increase in thermal energy detected by the MIROVA system in mid-March and there was a MODVOLC thermal alert on the 15th. Occasional small explosions occurred but no larger explosive events were recorded. A white plume was noted on the 27th rising to 900 m above the crater and an event at 1048 on the 30th produced a light-gray plume that rose to 800 m. Incandescence was only observed using a sensitive camera at night (figure 38).

Figure 38. Incandescence from the Suwanosejima Otake crater reflecting in clouds above the volcano. Courtesy of JMA (Volcanic activity of Suwanosejima March 2019).

No explosive events were observed through April. A white gas-and-steam plume rose to 1,200 m above the crater on the 19th and incandescence continued intermittently. Minor explosions were recorded on 5, 30, and 31 May, but no larger explosive events were observed during the month. The event on the 30th produced ash plume that reached 1.1 km above the crater. Similar activity continued through June with one explosive event occurring on the 2nd. Overall, there was a reduction in the number of ash plumes erupted during this period compared to previous months (figure 39).

Figure 39. Observed activity at Suwanosejima for the year ending in July 2019. The black vertical bars represent steam, gas, or ash plume heights (scale in meters on the left axis), yellow diamonds represent incandescence observed in webcams, gray volcano symbols along the top are explosions accompanied by ash plumes, red volcano symbols represent large explosions with ash plumes. Courtesy of JMA (Volcanic activity of Suwanosejima June 2019).

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: Japan Meteorological Agency (JMA), Otemachi, 1-3-4, Chiyoda-ku Tokyo 100-8122, Japan (URL: http://www.jma.go.jp/jma/indexe.html); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground).

The Great Sitkin volcano is located about 40 km NE of Adak Island in the Aleutian Islands and has had a few short-lived eruptions over the past 100 years. Prior to the latest activity in early June 2019 described below, small phreatic explosions occurred in June and August 2018 (BGVN 43:09). An eruption in 1974 produced a lava dome in the center of the crater. The Alaska Volcano Observatory (AVO) is the primary source of information for this September 2018-June 2019 reporting period.

Low-level unrest occurred from September 2018 through February 2019 with slightly elevated seismic activity (figure 6). Small explosions were seismically detected by AVO on 30 October, 5 and 16 November, and 11 December 2018, but they were not seen in regional infrasound data and satellite data did not show an ash cloud.

On 1, 7, and 9 June 2019, AVO reported small steam explosions as well as slightly elevated seismic activity. Steam plumes and surficial evidence of an explosion were not observed during these events. On 18 June 2019 weakly elevated surface temperatures were recorded, field crews working on Adak observed some steam emissions, and a gas flight was conducted. Elevated concentrations of carbon dioxide detected above the lava dome were likely associated with the steam explosions earlier in the month (figures 7 and 8). From 23 June through the end of the month seismicity began to decline back to background levels.

Figure 6. A steam plume was seen at the summit of Great Sitkin on 7 December 2018. Photo by Andy Lewis and Bob Boyd; courtesy of AVO/USGS.

Figure 7. Some degassing was observed on the southern flank of the Great Sitkin during an overflight on 18 June 2019. Photo by Laura Clor; image courtesy of AVO/USGS.

Figure 8. View of Great Sitkin with white plumes rising from the summit on 20 June 2019. Photo by Laura Clor, courtesy of AVO/USGS.

Geologic Background. The Great Sitkin volcano forms much of the northern side of Great Sitkin Island. A younger parasitic volcano capped by a small, 0.8 x 1.2 km ice-filled summit caldera was constructed within a large late-Pleistocene or early Holocene scarp formed by massive edifice failure that truncated an ancestral volcano and produced a submarine debris avalanche. Deposits from this and an older debris avalanche from a source to the south cover a broad area of the ocean floor north of the volcano. The summit lies along the eastern rim of the younger collapse scarp. Deposits from an earlier caldera-forming eruption of unknown age cover the flanks of the island to a depth up to 6 m. The small younger caldera was partially filled by lava domes emplaced in 1945 and 1974, and five small older flank lava domes, two of which lie on the coastline, were constructed along northwest- and NNW-trending lines. Hot springs, mud pots, and fumaroles occur near the head of Big Fox Creek, south of the volcano. Historical eruptions have been recorded since the late-19th century.

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

Ibu volcano on Halmahera island in Indonesia began the current eruption episode on 5 April 2008. Since then, activity has largely consisted of small ash plumes with less frequent lava flows, lava dome growth, avalanches, and larger ash plumes up to 5.5 km above the crater. This report summarizes activity during December 2018 through June 2019 and is based on Volcano Observatory Notice for Aviation (VONA) reports by MAGMA Indonesia, reports by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG) and Badan Nasional Penanggulangan Bencana (BNPB), and various satellite data.

During December PVMBG reported ash plumes ranging from 200 to 800 m above the crater. There were 11 MODVOLC thermal alerts that registered during 1-12 December. An explosion on 12 January 2019 produced an ash plume that reached 800 m above the crater and dispersed to the S (figure 15). A report released for this event by Sutopo at BNPB said that Ibu had erupted almost every day over the past three months; an example given was of activity on 10 January consisting of 80 explosions. There were four MODVOLC thermal alerts through the month.

Figure 15. An eruption at Ibu at 1712 on 21 January 2019 produced an ash plume that rose to 800 m above the crater. Courtesy of BNPB (color adjusted).

Throughout February explosions frequently produced ash plumes as high as 800 m above the crater, and nine MODVOLC thermal alerts were issued. Daily reports showed variable plume heights of 200-800 m most days throughout the month. Wind directions varied and dispersed the plumes in all directions. A VONA released at 1850 on 6 February reported an ash plume that rose to 1,925 m altitude (around 600 m above the summit) and dispersed S. Activity continued through March with the Darwin VAAC and PVMBG reporting explosions producing ash plumes to heights of 200-800 m above the crater and dispersing in various directions. There were ten MODVOLC alerts through the month.

Similar activity continued through April, May, and June, with ash plumes reaching 200-800 m above the crater. There were 12, 6, and 15 MODVOLC Alerts in April, May, and June, respectively.

Planet Scope satellite images show activity at a two vents near the center of the crater that were producing small lava flows from February through June (figure 16). Thermal anomalies were frequent during December 2018 through June 2019 across MODVOLC, MIROVA, and Sentinel-2 infrared data (figures 17 and 18). Sentinel-2 data showed minor variation in the location of thermal anomalies within the crater, possibly indicating lava flow activity, and MIROVA data showed relatively constant activity with a few reductions in thermal activity during January and February.

Figure 16. Planet Scope natural color satellite images showing activity in the Ibu crater during January through June 2019, with white arrows indicating sites of activity. One vent is visible in the 21 February image, and a 330-m-long (from the far side of the vent) lava flow with flow ridges had developed by 24 March. A second vent was active by 12 May with a new lava flow reaching a maximum length of 520 m. Activity was centered back at the previous vent by 23-27 June. Natural color Planet Scope Imagery, copyright 2019 Planet Labs, Inc.

Figure 17. Examples of thermal activity in the Ibu crater during January through May 2019. These Sentinel-2 satellite images show variations in hot areas in the crater due to a vent producing a small lava flow. Sentinel-2 false color (urban) images (bands 12, 11, 4) courtesy of Sentinel Hub Playground.

Figure 18. MIROVA log radiative power plot of MODIS thermal infrared at Ibu from September 2018 through June 2019. The registered energy was relatively stable through December, with breaks in January and February. Regular thermal anomalies continued with slight variation through to the end of June. Courtesy of MIROVA.

Geologic Background. The truncated summit of Gunung Ibu stratovolcano along the NW coast of Halmahera Island has large nested summit craters. The inner crater, 1 km wide and 400 m deep, contained several small crater lakes through much of historical time. The outer crater, 1.2 km wide, is breached on the north side, creating a steep-walled valley. A large parasitic cone is located ENE of the summit. A smaller one to the WSW has fed a lava flow down the W flank. A group of maars is located below the N and W flanks. Only a few eruptions have been recorded in historical time, the first a small explosive eruption from the summit crater in 1911. An eruption producing a lava dome that eventually covered much of the floor of the inner summit crater began in December 1998.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); Badan Nasional Penanggulangan Bencana (BNPB), National Disaster Management Agency, Graha BNPB - Jl. Scout Kav.38, East Jakarta 13120, Indonesia (URL: http://www.bnpb.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.vsi.esdm.go.id/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Planet Labs, Inc. (URL: https://www.planet.com/).

The Ebeko volcano, located on the northern end of the Paramushir Island in the Kuril Islands, consists of many craters, lakes, and thermal features and has been frequently erupting since late February 2017. Typical activity includes ash plumes, explosive eruptions, and gas-and-steam activity. The previous report through November 2018 (BGVN 43:12) described frequent ash explosions that sometimes caused ashfall in Severo-Kurilsk (7 km E). The primary source of information is the Kamchatka Volcanic Eruptions Response Team (KVERT). This report updates the volcanic activity at Ebeko for December 2018 through May 2019.

Frequent moderate explosive activity continued after November 2018. Volcanologists in Severo-Kurilsk observed explosions sending up ash, which drifted N, NE, and E, resulting in ash falls on Severo-Kurilsk on 28 different days between December 2018 and March 2019. On 25 December 2018 an explosion sent ash up to a maximum altitude of 4.5 km and then drifted N for about 5 km. Explosions occurring on 8-10 March 2019 sent ash up to an altitude of 4 km, resulting in ashfall on Severo-Kurilsk on 9-10 March 2019. An ash plume from these explosions rose to a height of 2.5 km and drifted to a maximum distance of 30 km ENE.

Satellite data analyzed by KVERT registered 12 thermal anomalies from December 2018 through May 2019. According to satellite data analyzed by MIROVA (Middle InfraRed Observation of Volcanic Activity), only one thermal anomaly was recorded from December 2018-May 2019, and no hotspot pixels were recognized using satellite thermal data from the MODVOLC algorithm.

Geologic Background. The flat-topped summit of the central cone of Ebeko volcano, one of the most active in the Kuril Islands, occupies the northern end of Paramushir Island. Three summit craters located along a SSW-NNE line form Ebeko volcano proper, at the northern end of a complex of five volcanic cones. Blocky lava flows extend west from Ebeko and SE from the neighboring Nezametnyi cone. The eastern part of the southern crater contains strong solfataras and a large boiling spring. The central crater is filled by a lake about 20 m deep whose shores are lined with steaming solfataras; the northern crater lies across a narrow, low barrier from the central crater and contains a small, cold crescentic lake. Historical activity, recorded since the late-18th century, has been restricted to small-to-moderate explosive eruptions from the summit craters. Intense fumarolic activity occurs in the summit craters, on the outer flanks of the cone, and in lateral explosion craters.

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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/).

Klyuchevskoy has had alternating eruptive and less active periods since August 2015. Activity has included lava flows, a growing cinder cone, thermal anomalies, gas-and-steam plumes, and ash explosions. Though some eruptions occur near the summit crater, major explosive and effusive eruptions have also occurred from flank craters (BGVN 42:04 and 43:05). Intermittent moderate gas-and-steam and ash emissions were previously reported from mid-February to mid-August 2018. The Kamchatka Volcanic Eruptions Response Team (KVERT) is the primary source of information for this September 2018-June 2019 reporting period.

KVERT reported that moderate gas-and-steam activity, some of which contained a small amount of ash, and weak thermal anomalies occurred intermittently from the beginning of September 2018 through mid-April 2019. On 21-22 April 2019 webcam data showed a gas-and-steam plume extending about 160 km SE (figure 31). Moderate Strombolian-type volcanism began late April 2019 and continued intermittently through June 2019. On 11-12 June webcam data showed explosions that sent ash up to a maximum altitude of 6 km, with the resulting ash plume extending about 200 km WNW.

Figure 31. Gas-and-steam plume containing some amount of ash rising from the summit of Klyuchevskoy on 22 April 2019. Photo by A. Klimova, courtesy of Institute of Volcanology and Seismology (IVS FEB RAS).

Thermal anomalies were noted by KVERT during two days in September 2018, six days in April 2019, eleven days in May 2019, and six days in June 2019. MIROVA (Middle InfraRed Observation of Volcanic Activity) analysis of MODIS satellite data showed infrequent weak thermal anomalies December 2018 through early May 2019.

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

Information Contacts: Kamchatka Volcanic Eruptions Response Team (KVERT), Far Eastern Branch, Russian Academy of Sciences, 9 Piip Blvd., Petropavlovsk-Kamchatsky, 683006, Russia (URL: http://www.kscnet.ru/ivs/kvert/); 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/).

Yasur volcano on Tanna Island has been characterized by Strombolian activity with large incandescent bombs, frequent explosions, lava fountaining, and ash emissions for much of its known eruptive history. Melanesians from nearby islands are believed to have settled Tanna in about 400 BCE; it is now part of the nation of Vanuatu, independent since 1980. The Kwamera language (or Tannese) spoken on the SE coast of the island is thought to be the source of the name of the island. No known oral history describes volcanic activity; the first written English-language documentation of activity dates to 5 August 1774, when Captain James Cook saw "a great fire" on Tanna Island. Cook realized that it "was a Volcano which threw up vast quantities of fire and smoak and made a rumbling noise which was heard at a good distance" (The Captain Cook Society) (figure 51).

Figure 51. Incandescence, steam, and dark ash from Yasur fill the sky in this sketch representing Captain James Cook's landing in the 'Resolution' at Tanna Island on 5 August 1774. The form of the volcano is behind the ship, the incandescence is in the upper right next to the ship's masts. "Landing at Tanna" by William Hodges, 1775-1776, National Maritime Museum, Greenwich, London. The Maritime Museum noted that this is one of a group of panel paintings produced by Hodges of encounters with islanders during the voyage, in which the European perception of each society at the time is portrayed. Image taken from Wikimedia Commons.

Based on numerous accounts from ships logs and other sources, volcanic activity has been continuous since that time. During periods of higher activity, multiple vents within the summit crater send ejecta 100 m or more above the crater rim, with large bombs occasionally landing hundreds of meters away. Continued activity during February-May 2019 is covered in this report with information provided by the Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD) which monitors the volcano and satellite data; photographs from tourists also provide valuable information about this remote location.

VMGD has maintained Alert Level 2 at Yasur since October 2016, indicating that it is in a major state of unrest. There is a permanent exclusion zone within 395 m of the eruptive vents where access is prohibited due to multiple hazards, primarily from large incandescent bombs up to 4 m in diameter which have been ejected from the vents onto the crater rim in the past, resulting in fatalities (BGVN 20:08).

Satellite and ground based information all support high levels of thermal activity during February -May 2019. MODVOLC thermal alerts were issued 11 times in February, 27 times in March, and 20 times each in April and May. The MIROVA graph also indicated the ongoing consistently high levels of thermal energy throughout the period (figure 52). Plumes of SO₂ emissions are common from Vanuatu's volcanoes; newer higher resolution data available beginning in 2019 reveal a persistent stream of SO₂ from Yasur on a near-daily basis (figure 53).

Figure 52. The MIROVA graph of thermal energy at Yasur from 3 September 2018 through May 2019 indicates the ongoing activity at the volcano. Courtesy of MIROVA.

Figure 53. The SO2 plumes from Yasur were persistent during January-May 2019 when they were visible many days of each week throughout the period. Top left: On 12 January plumes were visible drifting E from both Ambrym (top) and Yasur (bottom). Top right: Plumes drifted W from three Vanuatu volcanoes on 7 February, Gaua (top), Ambrym (middle) and Yasur (bottom). Bottom left: On 12 March N drifting plumes could be seen from Ambae (top) and Yasur (bottom). On 27 April, only Yasur had an SO2 plume drifting W. Courtesy of Goddard Space Flight Center.

Satellite imagery confirmed that the heat sources from Yasur were vents within the summit crater of the pyroclastic cone. Both northern and southern vent areas were active. On 7 March 2019 the N vent area had a strong thermal signal. Ten days later, on 17 March, similar intensity thermal anomalies were present in both the N and S vent areas (figure 54). On 6 April the S vent area had a stronger signal, and gas emissions from both vents were drifting N (figure 55). Satellite imagery from 21 May 2019 indicated a strong thermal signal inside the crater in the area of the vents, and included a weaker signal clearly visible on the inside E crater rim. Strong Strombolian activity or spatter sending large incandescent bombs as far as the crater rim are a likely explanation for the signal (figure 56), underscoring the hazardous nature of approaching the crater rim.

Figure 54. Strong thermal anomalies from the crater of Yasur's pyroclastic cone seen in satellite images confirmed the ongoing high level of activity. Left: 7 March 2019, a strong thermal anomaly from the N vent area, shown with "Geology" rendering (bands 12, 4, 2). Right: 17 March 2019, thermal anomalies at both the N and S vent areas, shown with "Atmospheric Penetration" rendering (bands 12, 11, 8A). The crater is about 500 m in diameter. Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.

Figure 55. Strong thermal anomalies (left) and gas emissions (right) at Yasur were captured with different bands in the same Sentinel-2 satellite image on 6 April 2019. Left: The thermal anomaly in the S vent area was stronger than in the N vent area, "Atmospheric Penetration" rendering (bands 12, 11, 8A). Right: Gas plumes drifted N from both vent areas, "Natural color" rendering (bands 4, 3, 2). The crater is about 500 m in diameter. Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.

Figure 56. Thermal activity from the crater of Yasur on 21 May 2019 produced a strong thermal signal from the center of the crater and a weaker signal on the inside E crater rim, likely the result of hazardous incandescent bombs and ejecta, frequent products of the activity at Yasur. Left: "Atmospheric Penetration" rendering (bands 12, 11, 8A). Right: "Geology" rendering (bands 12, 4, 2). The crater is about 0.5 km in diameter. Sentinel-2 satellite imagery courtesy of Sentinel Hub Playground.

Tourists visit Yasur on a regular basis. A former lake on the N side of Yasur has left ripples in the sand deposits over older volcanic rocks on the N side of the volcano (figure 57) since it drained in 2000 (BGVN 28:01). Visitors are allowed to approach the S rim of the crater where incandescence from both the N and S vents is usually visible (figure 58). Incandescent spatter from the convecting lava in the vents is highly dangerous and unpredictable and often covers the inner slopes of the rim as well as sending bombs outside the crater (figure 59).

Figure 57. The pyroclastic cone of Yasur viewed from the north on 6 May 2019. Ripples in volcaniclastic sand in the foreground are remnants of a lake that was present on the N side of the volcano until a natural dam breached in 2000. Copyrighted photo by Nick Page, used with permission.

Figure 58. Two glowing vents were visible from the south rim of Yasur on 6 May 2019. The S vent area is in the foreground, the N vent area is in the upper left. Copyrighted by Nick Page, used with permission.

Figure 59. Incandescent spatter at Yasur on 6 May 2019 sent fragments of lava against the inside crater wall and onto the rim. The convecting lava in the vent can be seen in the lower foreground. Copyrighted photo by Nick Page, used with permission.

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

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); 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/); The Captain Cook Society (URL: https://www.captaincooksociety.com/home/detail/225-years-ago-july-september-1774); Royal Museums Greenwich (URL: https://collections.rmg.co.uk/collections/objects/13383.html); Wikimedia Commons, (URL: https://commons.wikimedia.org/wiki/File:The_Landing_at_Tana_one_of_the_New_Hebrides,_by_William_Hodges.jpg); Nick Page, Australia,Flickr: (URL: https://www.flickr.com/photos/152585166@N08/).

With historical eruptions reported back to 1842, Papua New Guinea's Bagana volcano on the island of Bougainville has been characterized by viscous andesitic lava flows down the steep flanks of its cone, along with intermittent ash plumes and pyroclastic flows. Ongoing thermal anomalies and frequent ash plumes have been typical of activity during the current eruption since it began in early 2000. Activity declined significantly in December 2018 and remained low through May 2019, the period covered in this report (figure 33). Information for this report comes primarily from satellite images and thermal data.

Figure 33. The MIROVA plot of radiative power at Bagana from 1 September 2018 through May 2019 shows a marked decline in thermal activity during December 2018 after ash explosions and satellite observations of flows during the previous months. Courtesy of MIROVA.

The last ash emission at Bagana was reported on 1 December 2018 by the Darwin Volcanic Ash Advisory Center (VAAC). A Sentinel-2 satellite image showed a linear thermal anomaly trending NW from the summit on 14 December (BGVN 50:01). On 8 January 2019, an image contained a dense steam plume drifting E and a very faint thermal anomaly on the N flank a few hundred meters from the summit. A more distinct thermal anomaly at the summit appeared on 22 February 2019 (figure 34). A visitor to the region photographed incandescence on the flank, likely from the volcano, at dawn around 19 February 2019 (figure 35).

Figure 34. Sentinel-2 satellite imagery revealed thermal anomalies at Bagana in January and February 2019. Left: a very faint thermal anomaly was N of the summit at the edge of the E-drifting steam plume on 8 January 2019. Right: A thermal anomaly was located at the summit, at the base of the NE-drifting steam plume on 22 February 2019. Sentinel-2 satellite images with "Atmospheric Penetration" rendering (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 35. A visitor near Bagana spotted incandescence on the flank at dawn, possibly from a lava flow. Posted online 19 February 2019. Courtesy of Emily Stanford.

Two faint thermal anomalies were visible at the summit in satellite imagery on 19 March; a single one appeared on 29 March 2019 (figure 36). No thermal anomalies were recorded in Sentinel-2 images during April or May, but steam plumes and gas emissions were visible through cloud cover on multiple occasions (figure 37).

Figure 36. Faint thermal anomalies at Bagana were recorded in satellite imagery twice during March 2019. Left: 19 March, two anomalies appear right of the date label. Right: 29 March, a small anomaly appears right of the date label. Sentinel-2 image rendered with "Atmospheric Penetration" (bands 12, 11, 8A). Courtesy of Sentinel Hub Playground.

Figure 37. Steam and gas emissions at Bagana were recorded in satellite imagery during April and May 2019. Left: A steam plume drifted NW from the summit on 23 April, visible through dense cloud cover. Right: A gas plume drifted SW from the summit on 18 May. Sentinel-2 image with "Geology" rendering (bands 12, 4, 2). Courtesy of Sentinel Hub Playground.

Geologic Background. Bagana volcano, occupying a remote portion of central Bougainville Island, is one of Melanesia's youngest and most active volcanoes. This massive symmetrical cone was largely constructed by an accumulation of viscous andesitic lava flows. The entire edifice could have been constructed in about 300 years at its present rate of lava production. Eruptive activity is frequent and characterized by non-explosive effusion of viscous lava that maintains a small lava dome in the summit crater, although explosive activity occasionally producing pyroclastic flows also occurs. Lava flows form dramatic, freshly preserved tongue-shaped lobes up to 50 m thick with prominent levees that descend the flanks on all sides.

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/); Darwin Volcanic Ash Advisory Centre (VAAC), Bureau of Meteorology, Northern Territory Regional Office, PO Box 40050, Casuarina, NT 0811, Australia (URL: http://www.bom.gov.au/info/vaac/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Emily Stanford (Twitter: https://twitter.com/NerdyBatLady, image posted at https://twitter.com/NerdyBatLady/status/1098052063009792001/photo/1).

Ambae (Aoba) is a large basaltic shield volcano in the New Hebrides arc, part of the multi-island country of Vanuatu. Its periodic phreatic and pyroclastic explosions originating in the summit crater lakes have been recorded since the 16th century. A pyroclastic cone appeared in Lake Voui during November 2005-February 2006 (BGVN 31:12, figure 30); an explosive eruption from a new pyroclastic cone in the lake began in mid-September 2017 (BGVN 43:02). Activity included high-altitude ash emissions (9.1 km), lava flows, and Strombolian activity. Intermittent pulses of ash emissions during the following months resulted in extensive ashfall and evacuations; multiple communities were affected by lahars. The most recent episode of the eruption from July to September 2018 (BGVN 44:02) resulted in 11-km-altitude ash plumes and the evacuation of the entire island due to heavy ashfall and lahars. This report covers activity from February to May 2019, with information provided by the Vanuatu Geohazards Observatory of the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and satellite data from multiple sources.

Activity diminished after the extensive eruptive phase of July-September 2018 when substantial ash plumes and ashfall resulted in evacuations. An explosion with an ash plume on 30 October 2018 was the last activity reported for 2018. Thermal alerts were reported by the Hawai'i Institute of Geophysics and Planetology (HIGP) MODVOLC thermal alerts system through January 2019, and the Log Radiative Power graph prepared by the MIROVA project showed decreasing thermal anomalies into June 2019 (figure 92). Satellite images recorded in April and May 2019 (figure 93) showed the configuration of the summit lakes to be little changed from the previous November except for the color (BGVN 44:02, figure 89). No ash emissions or SO₂ plumes were reported during the period. VMGD noted that the volcano remained at Alert Level 2 through May 2019 with a 2-km-radius exclusion zone around the summit.

Figure 92. The MIROVA log radiative power plot for Ambae showed ongoing intermittent thermal anomalies from early September 2018 through May 2019. Courtesy of MIROVA.

Figure 93. Satellite imagery in April and May 2019 showed little change in the configuration of lakes at the summit of Ambae since November 2018 (see BGVN 44:02, figure 89). Left: 24 April 2019. Right: 29 May 2019. Sentinel-2 satellite imagery with "Natural Color" rendering (bands 4, 3, 2); courtesy of Sentinel Hub Playground.

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

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

Sangay is the southernmost active volcano in Ecuador, with confirmed historical eruptions going back to 1628. The previous eruption occurred during August and December and was characterized by ash plumes reaching 2,500 m above the crater. Lava flows and pyroclastic flows descended the eastern and southern flanks. This report summarizes activity during January through July 2019 and is based on reports by Instituto Geofísico (IG-EPN), Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

After the December 2018 eruption there was a larger reduction in seismicity, down to one event per day. During January, February, and most of March there was no recorded activity and low seismicity until the Washington VAAC reported an ash plume at 0615 on 26 March. The ash plume rose to a height of around 1 km and dispersed to the SW as seen in GOES 16 satellite imagery as a dark plume within white meteorological clouds. There was no seismic data available due to technical problems with the station.

More persistent eruptive activity began on 10 May with thermal alerts (figure 30) and an ash plume at 0700 that dispersed to the W. An explosion was recorded at 1938 on 11 May, producing an ash plume and incandescent material down the flank (figure 31). Two M 2 earthquakes were detected between 3.5 and 9 km below the crater on 10 May, possibly corresponding to explosive activity. By 17 May there were two active eruptive centers, the central crater and the Ñuñurcu dome (figure 32).

Figure 30. MIROVA log radiative power plot of MODIS thermal infrared at Sangay for the year ending June 2019. The plot shows the August to December 2018 eruption, a break in activity, and resumed activity in May 2019. Courtesy of MIROVA.

Figure 31. An explosion at Sangay on 10 May 2019 sent ballistic projectiles up to 650 m above the crater at a velocity of over 400 km/hour, an ash plume that rose to over 600 m, and incandescent blocks that traveled over 1.5 km from the crater at velocities of around 150 km/hour. Screenshots are from video by IG-EPN.

Figure 32. A photograph of the southern flank of Sangay on 17 May 2019 with the corresponding thermal infrared image in the top right corner. The letters correspond to: a) a fissure to the W of the lava flow; b) an active lava flow from the Ñuñurcu dome; c) the central crater producing a volcanic gas plume; d) a pyroclastic flow deposit produced by collapsing material from the front of the lava flow. Prepared by M. Almeida; courtesy of IG-EPN (special report No. 3 – 2019).

Activity at the central crater by 21 May was characterized by sporadic explosive eruptions that ejected hot ballistic ejecta (blocks) with velocities over 400 km/hour; after landing on the flanks the blocks travelled out to 2.5 km from the crater. Ash plumes reached heights between 0.9-2.3 km above the crater and dispersed mainly to the W and NW; gas plumes also dispersed to the W. The Ñuñurcu dome is located around 190 m SSE of the central crater and by 21 May had produced a lava flow over 470 m long with a maximum width of 175 m and an estimated minimum volume of 300,000 to 600,000 m³. Small pyroclastic flows and rockfalls resulted from collapse of the lava flow front, depositing material over a broad area on the E-SE flanks (figure 33). One pyroclastic flow reached 340 m and covered an area of 14,300 m2. During the 17 May observation flight the lava flow surface reached 277°C.

Figure 33. A view of the ESE flanks of Sangay on 17 May 2019. The area within the black dotted line is the main area of pyroclastic flow deposition from the Ñuñurco Dome. Photo by M. Almeida; courtesy of IG-EPN (special report No. 4 – 2019).

At the end of June activity was continuing at the central crater and Ñuñurco Dome. At least three lava flows had been generated from the dome down the SE flank and pyroclastic flows continued to form from the flow fronts (figure 34). Pyroclastic material had been washed into the Upano river and steam was observed in the Volcán River possibly due to the presence of hot rocks. Ash plumes continued through June reaching heights of 800 m above the crater (figure 35), but no ashfall had been reported in nearby communities.

Figure 34. Sentinel-2 natural color (left) and thermal (center) images (bands 12, 11, 4), and 1:50 000 scale maps (right) of Sangay with interpretation on the background of a 30 m numerical terrain model (WGS84; Zone 17S) (Prepared by B. Bernard). The dates from top to bottom are 17 May, 22 May, 27 May, 16 June, and 26 June 2019. Prepared by B. Bernard; courtesy IG-EPN (special report No. 4 – 2019).

Figure 35. Plots giving the heights and dispersal direction of ash plumes at Sangay during May and June 2019. Top: Ash plume heights measures in meters above the crater. Bottom: A plot showing that the dominant dispersal direction of ash plumes is to the W during this time. Courtesy of IG-EPN (special report No. 4 – 2019).

Geologic Background. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within horseshoe-shaped calderas of two previous edifices, which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been sculpted by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of a historical eruption was in 1628. More or less continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

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

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/).