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Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 This information is from a worldwide network of correspondents, who receive a Bulletin that includes illustrations and tables not available in this electronic version. The issue date is the closing date for regular monthly reports, not the publication date; more recent information about ongoing activity is often included. * The Bulletin is available by subscription from the American Geophysical Union, 2000 Florida Ave. NW, Washington, DC 20009 USA, at $18/year for US addresses, $28/year outside the US. * The information in our reports is necessarily preliminary, and subject to change as the reported events are studied in more detail. Please contact the original sources for updates and corrections before using Bulletin information. * The network depends on prompt communication from observers around the world. Please help by sending news of current activity via Bitnet (mnhms017@sivm.bitnet), Internet (mnhms017@sivm.si.edu), telephone (202:357-1511), fax (202:357-2476), or airletter (NHB MRC 129, Smithsonian Institution, Washington, DC 20560 USA). TABLE OF CONTENTS Volcanic Activity in Russia Sheveluch (Kamchatka) Activity increasing; steam and ash explosions Volcanic Activity in Japan Aso (Kyushu) Activity decreases; crater lake forms Sakura-jima (Kyushu) 40-hour long earthquake swarm Unzen (Kyushu) Dome 11 extruded; endogenous dome growth deforms old crater rim Suwanose-jima (Ryukyu) Sporadic weak ash eruptions Nii-jima and Kozu-shima (Izu Islands) Two earthquake swarms; no surface anomalies Volcanic Activity in the Mariana Islands Pagan (N. Mariana Islands) Banded tremor; increased ash eruptions Volcanic Activity in the Philippines Mayon Strombolian eruption; activity wanes Volcanic Activity in Papua New Guinea Manam Activity continues at very low level Langila Explosions send incandescent material 80 m above summit Rabaul Seismic activity increases; no significant surface deformation Ulawan Activity continues at low level Volcanic Activity in New Zealand Raoul Island Tectonic earthquake swarm; strongest swarm since 1964 Volcanic Activity in Italy Etna 1991-93 eruption ends Volcanic Activity in Antarctica Deception Island Activity declines from last year's levels Volcanic Activity in Colombia Galeras Three small explosions; ashfall to 65 km Volcanic Activity in Costa Rica Irazu Fumarolic activity declines Poas Gas columns to 500 m; gradual deflation Arenal Strombolian activity increases; new lava flow Rincon de la Vieja Hour-long earthquake swarm Volcanic Activity in Nicaragua Concepcion Detailed description of crater Masaya Crater walls stabilizing Momotombo Small gas plume El Hoyo (Las Pilas) Complex Weak fumarolic activity Cerro Negro No fumarolic activity; vegetation recovers from 1992 eruption Telica No observed activity `San Cristobal Gas plume; little evidence of acid rain Volcanic Activity in the United States Kilauea (Hawaii) Lava continues to flow into ocean; phreatic explosion kills 1 Atmospheric Effects Tropical-zone aerosols return to pre-Pinatubo levels EARTHQUAKES Santa Cruz Is. (M 7.1) 6 March; Fiji (M 6.7) 6 March, (M 6.5) 12 March; Solomon Is. (M 6.5) 6 March; SW Atlantic (M 6.5) 10 March; China (M 6.0) 20 March; Greece (M 5.1) 26 March Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Russia Sheveluch Kamchatka Peninsula, Russia (56.78N, 161.58E) All times are local (= GMT + 13 hours) Explosive activity at Sheveluch's active dome and increased seismicity prompted the Kamchatkan Volcanic Eruptions Response Team at the Institute of Volcanic Geology and Geochemistry to raise the Level of Concern Color Code from yellow to orange on 7 April, stating that an explosive eruption was possible within several hours or days with little warning. A major eruption occurred on 21 April that produced a column to an estimated altitude of 18 km. Details will be provided in the next Bulletin. Explosive bursts began on 18 March. A gas and ash explosion at 0900 on 20 March sent an eruption cloud about 1 km above the summit. Another eruption cloud rose about 4 km at 2400 on 21 March, and spread to a diameter of 20 km in the absence of any wind. Explosions occurred every day 22-28 March and 3-4 April, with 2/day on 25, 27, and 28 March. Observers in early April saw no unusual activity in the crater, but the normal fumarolic emissions on the SE part of the active dome were continuing. Shallow earthquake swarms were detected in early April by the seismic network of 4 stations that monitor Sheveluch. The nearest station is about 8 km from the summit on the slope of Sheveluch. Other stations are in Kliuchi, about 50 km SW of the summit, and on the Sredinny Ridge to the W, with the farthest station about 100 km from the summit. Earthquake counts increased above background (5 earthquakes/day) to 14 on 4 April, 30 in 4 hours on 5 April, and 42 in 20 hours on 6 April. The earthquakes had amplitudes >5 microns and durations of 2-2.5 minutes. There was a continuous swarm with 90 distinct earthquakes registered over constant weak background seismicity on 7 April. Seismicity beneath the active dome continued at similar levels 8-11 April. A 400-m-high fumarolic plume was visible during clear weather on 11 April. At 1300 the next day, steam and gas explosions with a small amount of ash occurred at 5-minute intervals and produced columns that rose 1 km above the dome and extended 15 km SE. Small mudflows also traveled 1.5 km from the dome. Shallow seismicity beneath the dome decreased following the explosive activity. The number of earthquakes remained high, however, and their magnitudes increased during the period 12-15 April, with a maximum of 124 earthquakes 14 April. Sheveluch volcano is thought to be about 65,000 years old and contains a large 10-km-wide caldera open to the S that formed before 23-24 Ka. In recent eruptive history, dome growth has alternated with collapse to produce debris avalanche calderas. The largest historical eruptions occurred in 1854 and 1964. The 1854 eruption destroyed a cone that had grown within the older caldera, formed another caldera, and caused a large debris avalanche. A violent explosive eruption in 1964 in turn destroyed a younger dome complex, creating a new caldera 1.5 x 3 km (Gorshkov and Dubik, 1970). A lava dome grew in the new caldera in 1980-81, and phreatic explosions began in 1984 (see Bulletin v. 9, no. 5). A funnel- shaped crater was formed in 1987 by the coalescence of several smaller vents following an increase in explosive activity (see Bulletin v. 13, no. 4). An explosive eruption in April 1991 ejected an ash cloud 6-8 km high that extended 50 km SE (see Bulletin v. 16, no. 3). Reference: Gorshkov, G. S., and Dubik, Y. M., 1970, Gigantic directed blast at Shiveluch Volcano (Kamchatka): Bulletin Volcanologique, v. 34, p. 261-288. Information Contact: Vladimir Kirianov, Piip Ave. 9, Institute of Volcanic Geology and Geochemistry, Petropavlosk-Kamchatsky, 683006, Russia. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Japan Aso Kyushu (32.88N, 131.10E) Activity in March and early April was lower than in previous months. Rain created a small lake in part of Nakadake cone's crater 1. On roughly half of the March visits, mud and blocks were seen being ejected a few meters above the lake. A white steam plume continually rose 200-500 m; it contained a minor amount of ash on 7 March. Seismic activity was low. Information Contact: Volcanological Affairs Office, Seismological and Volcanological Department, Japan Meteorological Agency, 1-3-4 Ote-machi, Chiyoda-ku, Tokyo 100 Japan. Sakura-jima Kyushu (31.58N, 130.67E) Explosions continued at Minami-dake cone in March (19 total) at a similar rate as in February (15 total). A 40-hour-long swarm of B- type earthquakes occurred on 8-10 March. The highest ash plume of the month, 4000 m above the crater, resulted from an explosion at 1004 on 5 March. Information Contact: same as for Aso. Unzen Kyushu (32.75N, 130.30E) Dome 10 continued exogenous growth on the top of the dome complex until mid-March when its NE half began collapsing, generating relatively large pyroclastic flows that traveled 4 km E into Kitakamikoba, an evacuated area, (9 March) and 3.5 km E (12 and 16 March) (see last month's Bulletin). A 17 March overflight revealed a new lava dome, number 11, growing on the resulting collapse-cliff on the E slope of dome 10. From late March through early April, endogenous growth of the dome complex and exogenous growth of dome 11 occurred simultaneously. Despite frequent collapses, dome 11 was 200 m long, 150 m wide, and 70 m thick by mid-April, and dome 10 reached 1440-m elevation, 80 m above Mt. Fugen, Unzen's previous summit peak. The endogenous growth resulted in cracks radiating out from the epicentral location of the magma supply vent on dome 10. The estimated magma supply rate increased from 1-2 x 10E5 m3/day in February (see last month's Bulletin) to 1-3 x 10E5 m3/day during mid-March to mid-April. A portion of the NW crater wall was moved out from the dome complex as a result of the endogenous growth. EDM measurements by the Geological Survey of Japan and GPS measurements by the Shimabara Earthquake and Volcano Observatory, Kyushu University, showed up to 2 m of NW movement at a point roughly 150 m NW of the dome complex. The affected area of the crater wall had many small, steaming cracks trending towards dome 10, and small-scale pressure ridges had formed on its surface near the dome complex. The frequency of pyroclastic flows generated by partial dome collapses gradually increased from 1/day to 10/day in the first half of March. The frequency of flows had been low since mid- November, the longest lull of the current eruption. The total of seismically recorded flows in March was 171, 4x that recorded in February. Collapses from domes 10 and 11 in late March to mid-April resulted in pyroclastic flows that typically traveled 1-3 km E and NE. The rate of pyroclastic flows remained at about 10/day. The low seismicity of the dome complex since early February continued until an earthquake swarm slowly developed on 9 March. After reaching a peak of 492 events on 14 March, activity declined to background by 17 March. The number of recorded earthquakes rose from 542 in February to 2985 in March. As in previous months, a steam plume, occasionally containing ash, continued to rise a few hundred meters above the dome complex. Information Contact: same as for Aso; and Setsuya Nakada, Department of Earth and Planetary Sciences, Faculty of Science 33, Kyushu University, Fukuoka 812 Japan. Suwanose-jima Ryukyu Islands (29.63N, 129.72E) Sporadic, weak ash eruptions resulted in slight ashfall on inhabited areas of this small volcanic island. Frequent eruptions have occurred since 1956, and explosions were reported throughout 1992 (see Bulletin v. 17, nos. 5 and 10). The island has about 60 inhabitants. Information Contact: same as for Aso. Nii-jima and Kozu-shima Izu Islands (34.29N, 139.27E and 34.22N, 139.15E) A weak earthquake swarm occurred 23 March in the N part of Nii-jima island. The earthquakes, M 1.9 maximum, were located both onshore and offshore. On 25 March, a swarm occurred at Kozu-shima island, approximately 20 km SW of Nii-jima. The largest event was M 3.9. No surface anomalies, onshore or offshore, were observed at either island. Earthquake swarms around the islands have been frequent since January 1992 (see Bulletins vol. 17, nos. 1, 3-5, 8, and 10). Kozu-shima last erupted in 838-840 AD, Nii-jima in 886. Information Contact: same as for Aso. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in the Mariana Islands Pagan Northern Mariana Islands (18.13N, 145.80E) The number of reports of ash columns above North Pagan, the larger of the two strato-volcanoes on Pagan island, has increased since the beginning of the year. A 168-km deep Benioff-zone earthquake (Mb 5.7) occurred at 0118 GMT on 18 January with an epicentral location (18.38N, 145.71E) approximately 40 km N of Pagan. In January 1982, 3 earthquakes, 500-600 km deep, in the vicinity of Pagan preceded eruptive activity (see Bulletin v. 8, no. 2), and it is speculated that the January 1993 event affected the behavior of the volcano. Columns rising to 2000 m above the summit were observed in mid- January and on 17 March. It is thought that other, unobserved eruptive events have also occurred. A distinct change in seismic activity took place on about 13 February. Before then, the seismicity consisted of 12-24 long-period events/day, each lasting 30-60 seconds. The dominant frequency of the events was 2-5 Hz and their amplitude was 2-3x background. Occasional small ash columns to 30 m were observed. Since mid-February, there have been frequent reports of intermittent ash eruptions, and banded tremor has been recorded at 10x background levels. The tremor episodes last 30 minutes to an hour, and are separated by 1-2 hour intervals of relative quiet. Though battery problems at the solar-powered seismic station prevent recording of activity when there is insufficient sunlight, the banded tremor has been consistently recorded when the station was functioning. It is speculated that the frequent ash emissions are associated with the tremor episodes. A large plinian eruption in May 1981 sent ash >13 km above North Pagan (see Bulletin v. 6, no. 5). Occasional small ash eruptions have occurred since then (see Bulletin v. 17, no. 6). Information Contacts: Bob Koyanagi, USGS Hawaiian Volcano Observatory, Hawaii Volcanoes National Park, HI 96718 USA; Ray Chong, Disaster Control Office, Capitol Hill, Saipan, MP 96950 USA; Dick Moore, U.S. Geological Survey, MS 903, Box 25046, Denver Federal Center, Denver, CO 80225 USA. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in the Philippines Mayon Luzon (13.26N,123.68E) All times are local (= GMT + 8 hours) Lava fountaining began on 21 March after almost 2 months of intermittent precursors, including a small, but deadly, phreatomagmatic eruption on 2 February (see Bulletin v. 18, no. 1). Following the 2 February eruption, sluggish and intermittent production of lava (see last month's Bulletin) continued until 19 March when its extrusion rate increased. Several tens of small collapse-type pyroclastic flows on both 19 and 20 March resulted from portions of the flow front detaching and rolling down the steep upper slopes of the volcano. On the night of 21 March, lava fountaining to heights of several hundred meters began, forming a small cone at the head of Bonga Gully where it descends from the summit crater. Most of the lava fell back into the crater and around the vent, but eventually flowed SSE down Bonga Gully. By 26 March the flow front was 4.5 km from the summit, and the estimated volume of lava extruded was 60 x 10E6 m3, more than half the volume of the 1984 flow. Ash-bearing steam clouds from the fountains rose 2-3.5 km above the crater and deposited a few millimeters of ash on nearby towns. This was less ash than resulted from the pyroclastic flows, which stopped when fountaining began. The fountaining episodes typically lasted 20 minutes; the longest lasted 50 minutes. They were separated by repose periods lasting 30 minutes to 1 hour. Some episodes were followed by 10-20 minutes of intermittent 2-Hz tremor, the amplitude of which varied greatly suggesting that each tremor episode consisted of a series of tremor events. The tremor did not correlate with any visible steaming. Continuous, strong gas jets, glowing "like a blowtorch" and emitting a continuous "jet plane sound," were visible from Legazpi city, 14 km SE of the summit. They appeared to be in the summit crater, 100-200 m upslope from the vent. COSPEC measurements of SO2 flux increased from 4000 metric tons/day (t/d) on 1 March, to 5000 t/d on 24 March. On 26 March, the SO2 flux measured in the morning was 3920 t/d rising to 7600 and 8800 t/d in the afternoon (two sets of measurements). By 2 April, lava fountaining had ceased, and little or no new material was feeding the flow. Seismicity was low to moderate and dominated by small explosion-type earthquakes. Ash puffs were rare and weak. A single small pyroclastic flow occurred on 1 April, originating in the crater. The glow from the crater persisted, but was considerably dimmer and the gas jets burning in the crater had disappeared. However, SO2 emission remained high and variable, 3000-8000 t/d, and the volcano was not deflating. The lava flow front, still about 5.4 km from the vent, was not expected to advance much farther, having moved only a few meters on 1 April. The flow was confined to Matanag Gully except for a small finger that reached the lower Bonga Channel (see Bulletin v. 18, no. 1, for map). Lateral levees and pressure ridges were well defined. On 9 April a dirty-white steam plume rose only 50 m above the crater rim. At night, a faint glow from the crater was visible. Small "explosion-type" earthquakes, continued; 57 were detected in the 24-hour period beginning at 1700 on 8 April. Most, however, were associated with incandescent materials detaching from the lava deposits in the Bonga Gully. The rate of SO2 emission was 2272 t/d. More than 45,000 people fled their homes during the early stages of the eruption, from 2 February to 19 March, filling 43 evacuation centers. An additional 12,000 evacuated their homes as the eruption entered its Strombolian phase on 19-21 March. Since the 2 February event, which killed 75 people, no deaths directly attributable to the eruption have been reported. Information Contacts: Philippine Institute of Volcanology and Seismology, 6th Floor Hizon Bldg., 29 Quezon Ave., Quezon City, Philippines; Chris Newhall, U.S. Geological Survey, 12201 Sunrise Valley Drive, Reston, VA 22092 USA; Reuters News Service. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Papua New Guinea The following is from the Rabaul Volcano Observatory. Manam off the N coast of New Guinea (4.10S, 145.06E) "Activity at Manam's two summit craters continued at a very low level throughout March. During the month's first and last weeks, when the summit area was clear, emissions from both craters consisted of thin white vapours being released at a weak-to-moderate rate. No night glow was reported. There was a report of acid rainfall 12 March on the upper slopes SE of the summit. Seismicity throughout March consisted of discontinuous low-amplitude tremor and small low-frequency events. Tilt measurements showed no trends." Information Contacts: Herman Patia, Rod Stewart, and Chris Mckee, Rabaul Volcano Observatory, P.O. Box 386, Rabaul, Papua New Guinea. Rabaul New Britain Island (4.27S, 152.20E) "There was a marked increase in seismic activity in March; 1685 earthquakes were recorded, compared to 256 in February and 352 in January (see last 2 Bulletins). This is the highest monthly total since April 1986 (1769 earthquakes), and the second highest since the 1983-1985 crisis period. The earthquakes occurred both individually and in swarms. Large swarms, with over 100 events, occurred 9, 15, 18, and 30 March. Only a few of the earthquakes were felt, the largest on the 15th, M 3.0-3.5. All of the 35 accurately located earthquakes were on the ring-fault system, and the majority were clustered near the recent eruptive centres of Vulcan (9) and Tavurvur/Rabalanakaia (16). Most of the events were located at depths <2 km. Nearly all of the Vulcan earthquakes occurred before 4 March, though the Tavurvur/Rabalanakaia events occurred throughout the month. Routine monthly leveling on the 23rd showed no significant changes from previous months. Wet and dry tilt measurements also showed no trends." Information Contacts: same as for Manam. Langila New Britain Island (5.53S, 148.42E) "Eruptive activity at Langila remained at a moderate-to-strong level during March. Crater 2 continued to release white-grey ash-laden vapour at a moderate-to-strong rate and occasional thick dark grey-to-brown ash clouds. These emissions were accompanied by weak-to-loud explosion noises. From the 23rd until the end of the month, continuous dark grey ash clouds rose several hundred meters above the summit. Fine ashfall was reported downwind (SE). These emissions were accompanied by weak explosions and rumbling noises. The summit area was cloud-covered on most nights during the first half of the month. However, incandescent Strombolian projections were visible on the 4th and 5th. On 15, 19-20, and after 23 March until the end of the month, steady weak to occasional bright fluctuating glow was visible. Incandescent Strombolian projections up to 80 m above the summit were seen on the 27th and 29th. "Activity at Crater 3 was mild during the month, with weak-to-moderate emissions of white and blue vapour accompanied by the occasional forceful ejection of moderate-to-thick dark grey ash clouds rising several hundred meters above the summit. During the last 3 weeks of the month the emissions were accompanied by occasional weak explosion noises. Night glow and incandescent projections were seen on 15, 16, and 19 March. "A slight increase in seismicity during the month was recorded by the seismograph 9 km N of the volcano. About 200 Vulcanian explosion earthquakes were recorded during the month with the highest daily total of 24 events on both the 23rd and 24th." Information Contacts: same as for Manam. Ulawun New Britain Island (5.04S, 151.34E) "Activity at Ulawun continued at the low levels reported for February (see last month's Bulletin). White vapour emissions usually varied from weak to moderate but were more forceful 26-27 March. Weak glow was reported on the 8th. "Seismic activity was at a low level throughout the month; no distinct B-type earthquakes were recorded. Both Real-time Seismic Amplitude Measurement (RSAM) and routine manual amplitude readings indicate a gradual decline in tremor levels since mid-February. However, the level of tremor is still higher than before January's brief flurry of activity (see Bulletin v. 18, no. 1)." Information Contacts: same as for Manam. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in New Zealand Raoul Island Kermadec Islands (29.27S,177.93W) The strongest earthquake swarm since the 1964 eruption began at 0150 on 9 March. About 1 earthquake/minute was felt at the island's meteorological station, approximately 2 km N of Raoul Caldera and 3 km NW of Denham Bay. The larger events shook trees and caused small rockfalls. There were no apparent changes to the lakes in the caldera or to Denham Bay. On the afternoon of 9 March an overflight revealed no indications of volcanic activity. Though mechanical problems prevented the island's one seismograph from recording any earthquakes until that evening, 7 earthquakes were detected in Wellington, about 1600 km S. The strongest, M 4.3, occurred at 0734. Because the swarm may have been precursory to an eruption, the meteorological station staff of 4 men and 1 dog was evacuated by ship to a location 10 km from the island. They returned the following day and saw that the number of earthquakes had diminished considerably. Earthquakes continued to decline in number and intensity, and on 13 March, the ship departed the island, leaving the staff behind. Analysis of the seismicity indicated the swarm was of tectonic rather than volcanic origin. The 1964 eruption was primarily phreatic and formed 12 small craters in Raoul Caldera. A submarine eruption in Denham Bay is believed to have occurred at about the same time. No volcanic earthquakes or tremor, such as recorded in the 11 days prior to the 1964 eruption, were detected in this swarm, and the recent earthquakes were fewer and smaller than in 1964. There was no evidence of the increased heat flow to the surface that preceded the 1964 eruption. Though the level of one of the caldera lakes rose 38 cm on 12-25 March, this was minor compared to the rise of 600 cm in 11 days prior to the 1964 eruption. Information contacts: Ian Nairn and Bradley J. Scott, Institute of Geological & Nuclear Sciences, Wairakei Research Centre, Private Bag 2000, Taupo, New Zealand; J.H. Latter, Institute of Geological & Nuclear Sciences, P.O. Box 1320, Wellington, New Zealand. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Italy Etna Sicily, Italy (37.73N, 15.00E) All times are local (= GMT + 1 hour) The following, based on the report of the Istituto Internazionale di Vulcanologia, describes activity in March. The 1991-93 eruption ended on March 30 after 473 days of continuous lava flows. Lava stopped flowing to the S side of the flow field in mid-February, but continued to flow from several vents at 1700-1650 m elevation on the N side of the field, covering previous flows from the current eruption. Shortly after 8 March, an overflight revealed a thin flow that had traveled 0.5 km from an ephemeral vent at 2020-m elevation. On 11 March a large lava flow moved toward the Valle del Bove over an area not yet covered during this eruption. Flowing 1.5 km from a large ephemeral vent at the end of a tube at 1550-m elevation, lava spread down some gullies, stopping after 3 days at 1390-m elevation, 5 km from the eruptive fissure. Lava flows declined in the second half of March. On 21 March a vigorous flow emerged from a vent at 1850-m elevation and traveled several hundred meters NE in a few hours before slowing and finally stopping within 2 days. The remaining ephemeral vents gradually disappeared and the last small lava flow was observed on the morning of 30 March. In the following days, fieldwork at the eruptive fissure and along the upper lava tube revealed that no molten lava remained in the tube and that the delivery system was cooling. Steady degassing continued through March at the summit craters. The floor of the NE crater dropped another several meters. Seismicity remained low, especially from 1-10 March. For the month, 65 long- period events and 8 volcano-tectonic events (maximum M 2.4) were recorded. The only notable swarm occurred on 28 March when 10 events were recorded in 2 minutes. There were no significant variations in the volcanic tremor amplitude. Four of the 9 bore- hole tiltmeters recorded a sharp deformation event of moderate amplitude at the beginning of March. The 1991-93 eruption began on 15 December 1991 and lasted 473 days. It was probably the largest eruption at Etna in the last 300 years, covering approximately 7 km2 with >250 million m3 of lava. The following information compiled by volcanologists at the Istituto Internazionale di Vulcanologia, Universita di Catania, and Osservatorio Vesuviano, complements the official IIV report above. The lava flow that had reached 1400-m elevation on 14 March (see last month's Bulletin) stopped on 17 March. At about 1700 on 21 March a modest lava flow escaped through a skylight on the main lava tube just below 2000-m elevation. It was accompanied by intense degassing from the upper part of the eruptive fissure. Through 25 March lava was observed flowing inside the main vent at 2205-m and small, short-lived flows issued from ephemeral vents in the N part of the lava field at about 1900-m elevation. Poor weather prevented detailed observation of the last days of the eruption. Degassing (vapor and gas) from the upper part of the eruptive fissure declined. By 20 March it was difficult to observe from a distance. Degassing increased at the summit craters (especially from the central crater) during the final phase of the eruption. Through 9 April, the NE crater, where recent rockfalls had occurred, continued to be obstructed and weak fumarolic activity was present along the walls. COSPEC measurements of SO2 flux revealed a sharp increase during the last half of March (>16 x 10E3 tons/day on 23 March). Measurements in April indicated the flux was returning to a normal level of 6-8 x 10E3 tons/day. From 16 March to 19 April, 337 seismic events were recorded. They ranged from M 1.0-3.0 and showed characteristic frequencies of 1-6 Hz. All were located in the summit crater region except a M 2.7 at 0649 on 14 April that was located low on the E flank. Volcanic tremor was totally absent. During the 1991-93 eruption an estimated 300 million m3 of lava flowed from the fissure on the W wall of Valle del Bove at an average rate of 7.3 m3/sec. Information Contact: The first section is from the official report of the Istituto Internazionale di Vulcanologia, CNR-Istituto Internazionale di Vulcanologia (L. Villari, Director), Piazza Roma 2, 95123 Catania, Italy. The second section is from Romolo Romano, Tommaso Caltabiano, Maria Felicia Grasso, and M. Porto, Istituto Internazionale di Vulcanologia, CNR, Piazza Roma 2, 95123 Catania, Italy; Pietro Carveni and C. Monaco, Istituto di Geologia and Geofisica, Universita di Catania, Italy; and Giuseppe Luongo, Director, Osservatorio Vesuviano, via Manzoni 239, 80100 Napoli Italy. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Antarctica Deception Island South Shetland Islands (62.93S, 60.57W) Activity has declined from the more vigorous behavior seen during the 1991-92 survey to levels recorded during earlier surveys (see Bulletin v. 17, no. 4). Only 135 seismic events (M 0.3-0.9) were recorded compared to the 766 events detected during the 1991-92 survey. Episodes of tremor in the NW sector of the island were recorded on 1 January, 2 February, and 16 February 1993. Five deep (55-85 km) earthquakes, M 1.6-2.4, were detected. Fumaroles emitted mainly CO2 (87-98%) and H2S (1.8-13%); no SO2 was detected. Dry-tilt measurements of 600 microradians uplift at Fumarole Bay (see Bulletin v. 16, no. 5 for sketch map of island) indicated a slight elevation of the entire fumarolic area. Temperature measurements made by the Spanish Oceanographic Ship "Hesperides" showed a decrease in the intensity of the submarine emissions in Port Foster Bay since the 1990-91 survey. Deception Island's 7-km-wide caldera forms a natural harbor and numerous vents located along ring fractures have been historically active. The last known eruptive period was 1967-72, which included several events of VEI 3. The volcano has been monitored every austral summer since 1986. Information Contacts: Ramon Ortiz, Museo Nacional de Ciencias Naturales, CSIC, Jose Gutierrez Abascal 2, 28006 Madrid, Spain; Corina Risso, Instituto Antartico Argentino, Cerrito 1248, Buenos Aires, Argentina. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Colombia Galeras S Colombia (1.22N, 77.37W) All times are local (= GMT - 5 hours) Small eruptions occurred on 23 March, 4 April, and 13 April. The seismic signal associated with the pyroclastic eruption at 2239 on 23 March (VEI 1) lasted 12 minutes, saturating the seismic network for 90 seconds. The eruption produced a column calculated to have been 8 km high, and ejected >8.35 x 10E5 m3 of material. About 6.35 x 10E5 m3 of ejecta went W and ashfall was noted 65 km from the volcano. Approximately 2 x 10E5 m3 of projectiles, some as large as 90 cm in diameter, fell within a 2 km radius of the vent and destroyed the communications station on the caldera rim, approximately 700 m from the active crater. Two policemen in the station at the time of the event were not injured. Incandescent ballistics and lightning were seen from Pasto and a loud roar was heard, but no shock wave was felt. During the 10 hours following the eruption, 445 seismic events, both long-period and tremor, were recorded. The mechanical characteristics of the eruption appeared to be the same as those for the July 1992 eruption; obstruction of the conduit at depth and subsequent explosion because of overpressurization. Overflights of the crater after the eruption revealed a reactivation of circular and radial fractures associated with collapses on the border of the active crater. New craters and associated fumarolic activity were also noted. In the weeks prior to the eruption, SO2 flux was low, 37-81 t/d. Following the eruption, the SO2 flux rose to 800 t/d on 24 March, but then declined to 581 t/d on 26 March and to 132 t/d by 29 March. Forty-two screw-type (see Bulletin v. 17, no. 12) seismic events were recorded in March. They were located slightly W of the active crater at depths between 0.2 and 1.0 km. The dominant frequency for individual events ranged from 2.35 to 4.00 Hz, and the durations were between 22 and 185 seconds. The event lasting 185 seconds occurred on 12 March and had a dominant frequency of a 2.9 Hz. An eruption at 1603 on 4 April produced a 5-km high ash column. The eruption was smaller than others this year and no ballistics fell outside the active crater. The seismic network recorded the eruption as a long-period event lasting 123 seconds, saturating the network for only 17 seconds. There were no precursors. After the eruption, SO2 flux was approximately 200 t/d, but fell to 100 t/d by the next day. Through 7 April, SO2 flux remained low and the amplitude and duration of long-period events declined. An ash eruption at 0321 on 13 April lasted 140 seconds and saturated the seismic network for 33 seconds. An increase in gas emissions was noted later that morning during an overflight. Recorded in the preceding week were two small episodes of tremor, occasional screw-type events and a swarm of small, strongly impulsive seismic events. Information Contacts: Marta Calvache, INGEOMINAS, Observatorio Vulcanologico de Pasto, Apartado Aereo 1795, Pasto Colombia; Tobias Fischer and Dave Lescinsky, Department of Geology, Arizona State University, Tempe, AZ 85287-1404 USA; John Ewert and Andy Lockhart, Cascades Volcano Observatory, 5400 MacArthur Blvd., Vancouver, WA 98661 USA. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Costa Rica All times are local (= GMT - 6 hours) Irazu (9.98N, 83.85W) Fumarolic activity in the N and NW portions of the crater decreased and the lake remained green. Lake temperature varied depending on the sampling site. ICE volcanologists measured 14 degrees C at the surface, 17 degrees C near the bottom, and 24 degrees C near subaqueous fumaroles. UNA volcanologists measured 40 degrees C near fumaroles and 24 degrees C near the center of the lake. Lake level fluctuated 10-15 cm depending on rainfall, with smaller daily variations. Collapses continued from the E and SE crater walls. Major fumaroles in the NW portion of the crater had temperatures of 91-92 degrees C. No change was evident in the acidity or temperature of springs around the volcano. Dry-tilt measurements at the summit continued to indicate deflation through March. Areal dilatation has continued to decline, with decreases similar to those since September. Irazu last erupted in 1963-65. That eruption was characterized by Strombolian and Vulcanian explosions, which killed 2 tourists on the summit. In December 1963, a torrential rain remobilized ash deposits on the SW flank, triggering lahars in the Reventado River that caused much damage and about 20 deaths in Taras de Cartago, 15 km SW from Irazu. Information Contacts: Gerardo Soto and Rafael Barquero, Oficina de Sismologia y Vulcanologia, Departamento de Geologia, Instituto Costarricense de Electricidad (ICE), Apartado 10032-1000, San Jose, Costa Rica; Erick Fernandez, Jorge Barquero, Vilma Barboza, Tomas Marino, Rodolfo Van Der Laat, Franklin de Obaldia, and Rodrigo Saenz, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica. Poas (10.19N, 84.23W) Fumarolic activity in the N part of the crater lake continued as gas columns rose 500 m, one of them producing a jet-like noise that could be heard at the observation site, 1 km S of the active crater. The turquoise-green lake had a temperature of 67 degrees C and contained floating patches of sulfur. Plumes to 1 m rose from sporadic phreatic eruptions in the central and SE portions of the lake. During March, the seismic station 2.5 km SW of the main crater recorded 4825 low-frequency events, an average of 156 events/day. An earthquake of M 2.3, located 6 km SW of the main crater at 9 km depth, occurred on 25 March at 0813 GMT. A precise level line running 1.8 km S down the main edifice from the observation site showed possible deflation since June 1992. Measurements at a dry-tilt site also indicated deflation. EDM measurements to the inner cone have not significantly changed since January 1991. Information Contacts: Erick Fernandez, Jorge Barquero, Vilma Barboza, Tomas Marino, Rodolfo Van Der Laat, Franklin de Obaldia, and Rodrigo Saenz, Observatorio Vulcanologico y Sismologico de Costa Rica, Universidad Nacional, OVSICORI-UNA, Apartado 86-3000, Heredia, Costa Rica. Arenal (10.46N, 84.71W) Gas emission and lava flows continued from Crater C. Both the number and magnitude of Strombolian eruptions increased from January and February levels. Some eruptions caused vibration of windows at the Macadamia Biological Observatory (2.7 km S) and ballistic bombs reached the 1000-m elevation on the flanks. The more-SW lava flow that was active last month advanced over a grassy field and stopped at 760-m elevation (see last month's Bulletin). A new flow descended SW, following the same route as the December 1992 flow (see last 3 Bulletins). At 1350-m elevation it divided; one lobe went W, reaching 1100-m elevation, while the other traveled SW to 1200-m elevation. Another lava flow moved down the SSW flank to 1450-m elevation. At 0920 on 31 March, gravitational failure of this flow produced numerous small avalanches falling to 750-850 m elevation. On 23 March at 1930 a pyroclastic flow descended SE to 1100-m elevation. Seismic activity remained normal. An average of 40 earthquakes/day were recorded by ICE, a slight increase from last month. A seismometer operated by UNA, 2.7 km NE of the main crater, registered a total of 465 explosions and 226.5 hours of tremor during 13-31 March. The dominant frequencies of these events were 1.5-2.3 Hz. During 28-30 March the tremor increased, becoming continuous for a 24-hour period. The highest daily total of explosions for the month occurred on 16 March, the fewest on 30 March. Fumaroles near the summit continued to emit sulfur gases and water vapor. Explosions were accompanied by decreased gas emission. The slight inflationary trend seen at most of the dry-tilt stations stopped. Occasional slight deflation occurred at dry-tilt sites Ferreto (3 km SW of summit) and Cedeno (4 km NW of summit). EDM lines on the S and W contracted in March. Information Contacts: same as for Irazu. Rincon de la Vieja (10.83N, 85.32W) The seismic station 5 km SW of the main crater recorded an hour- long swarm of 10 volcano-tectonic earthquakes (M <1.9) on 26 March. Fumarolic activity continued inside the crater and in the crater lake. Information Contacts: same as for Irazu. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in Nicaragua Concepcion (11.53N, 85.62W) "On 10 January geologists climbed Concepcion in unusually clear conditions, allowing a survey of the summit crater. The crater is almost circular, 300 m in diameter and about 250 m deep. The upper part has a funnel shape, which descends into a pit crater. The N and E sides have a break in slope half way down; the SW side is a vertical cliff. This cliff is the head scarp of a landslide that fell into the crater in December 1992, forming a 100 m-wide scree slope infilling part of the pit crater. A 30 m-wide elliptical area plastered with yellow sulphur and containing two small sulphur mounds is at the lowest point. "The summit morphology and crater shape have changed considerably since the pre-1957 eruption topographic map, which shows a broad 600 m-wide summit plateau with a 200 m-diameter crater. Now the summit is marked by a steep cone with a slope of 30-40 degrees, and a knife-edged crater rim. Altered red lava below 1957 pyroclastics in the deep gullies to the W probably represent the pre-1957 surface and indicate that the present summit is 50-100 m higher than the spot height of 1610 m surveyed before the 1957 eruption. If this interpretation is correct, Concepcion could be the highest volcano in Nicaragua. "Lava flows exposed in the crater walls and on the W flank are associated with copious semi-welded and welded pyroclastics and breccia. A prominent thick dyke on the NE side of the crater has the same strike as one of the historical lava flows, which it appears to have fed. Fractures running at 20N cut the crater bottom near the sulphur mounds and on the N and SW walls. The strike is similar to fractures observed on the SW flank of the volcano, which are responsible for the formation of the deep SW gully. Other fractures in the crater are N-oriented, some extending as far as the N flank of the cone, where they have fumarolic activity. These fumaroles are visible from the base of the volcano and have been periodically observed since 1986 (see Bulletin v. 11, no. 5). Fumarolic areas with yellow-grey sulphur are also found around the crater walls. The most active fumaroles, however, are at the base of the pit crater, either on the sulphur mounds or along the 20N- oriented fissures. Two moderate fumarolic areas with yellow-grey sulphur are on the S and W walls. No glow was observed from the crater rim, suggesting that no large high-temperature fumaroles were present. "A local fireman reported ashfall on Alta Gracia (about 5.5 km NE of the summit) in December 1992, and a plume was reported during the same month. These phenomena were probably caused by the crater landslide. Vegetation, almost exclusively 'Sombrilla del Pobre' (Nostoc Gunnera) has begun to re-colonize the upper 200 m of the cone, which was bare in 1990, thus gas and ash emissions have been considerably lower than in the 1980's. However, analyses by Warren Spring Laboratory, UK, of SO2 diffusion tubes placed in the garden of a house in Esquipulas, 8 km E of the volcano, recorded an average SO2 concentration of 60 g/m3, indicating that gas emissions from the crater were sufficient to cause mild fumigation of populated areas downwind. "Lahars continue to form during rainstorms, with the main loci of activity being the SW gully and the N flank. The road N of the volcano was cut by a lahar in late 1992. Erosion remains rapid on higher slopes, where some gullies had widened by 2-5 m since 1990. The 1957/74 pyroclastic deposits are especially vulnerable to erosion and gully headwalls have almost intersected the crater rim to the N, W, and SW in the last two years. Rapid erosion of these deposits probably constitutes much of the source for the laharic material to the N and W of the cone. The towns of San Jose del Sur (6.2 km SSW), San Marcos (5.6 km NNW), and La Flor (5.3 km NW) are in a particularly dangerous situation because they are in the paths of lahars descending these gullies. The fracture system in the crater walls could be a potential conduit for a future lava eruption that would flow toward the town of San Jose del Sur." There have been 24 eruptions reported from Concepcion since 1883. A tephra eruption in December 1984 ejected blocks and ash that damaged crops (see Bulletin v. 10, nos. 5 and 11). Ash emissions were reported between late 1985 and April 1986 (see Bulletin v. 11, no. 5). Information Contacts: Andrea Borgia, Instituto Nazionale di Geofisica, via di Vigna Murata 605, 00143 Roma, Italy; Benjamin van Wyk de Vries, The Open University, Walton Hall, Milton Keynes MK7 6AA, England; and Peter J. Baxter, Department of Community Medicine, Fenner's, Gresham Road, Cambridge, England. Masaya (11.98N, 86.16W) "Masaya's Santiago crater, visited on 7 and 13-14 January, contains a few weak fumaroles on the rim of the 1989 vents and on the wall adjoining the Nindiri crater. The crater walls have stabilized since the 1989/90 collapses, and there is now little rockfall activity. Vegetation is beginning to colonize the crater walls." Masaya has frequently been active since the 16th century, with intermittent lava lakes and minor explosive eruptions. A part of Santiago crater's S wall collapsed in November 1989 (see Bulletin v. 16, no. 2), dropping 50,000 m3 of rock into the crater. An inner crater that began growing in 1982 in the cooling lava lake was 300 m in diameter in April 1992 (see Bulletin v. 17, no. 4). Information Contacts: same as for Concepcion. Momotombo (12.42N, 86.53W) A small gas plume was present on 6-7 January, with no apparent change from previous years (see Bulletin v. 14, no. 4; v. 15, no. 4; and v. 16, no. 2). Momotombo is a strato-volcano on the N shore of Lake Managua and 20 km ESE of Cerro Negro. It has had 14 reported eruptions since the 16th century, but activity since 1905 has been largely fumarolic. Geothermal power production began in 1982. Information Contacts: same as for Concepcion. El Hoyo (Las Pilas) Complex (12.49N, 86.69W) El Hoyo's main fumarole was emitting vapor at usual levels on 6-7 January. Weak fumarolic activity has been reported since 1980 (see Bulletin v. 5, nos. 7 and 12; v. 13, no. 1; v. 15, no. 4; v. 16, no. 2; and v. 17, no. 4). The last eruption of El Hoyo lasted for 3 days in 1954, formed a 1-km-long fissure, and deposited ash on Leon, 20 km WSW. Information Contacts: same as for Concepcion. Cerro Negro (12.51N, 86.70W) "No sign of fumarolic activity was seen when the base of Cerro Negro was visited on 6 January. Predictions that the farming area between Cerro Negro and the city of Leon (18 km WSW), would be devastated by the ashfall of April 1992 (about 4 cm of ashfall: see Bulletin v. 17, nos. 3 and 4) had fortunately not been fulfilled. Fields >2 km from the volcano were cultivated again after the April 1992 event and farmers were expecting good harvests. Wild vegetation appeared healthy and had regrown to original levels. A few large trees close to the volcano appeared to have died after the eruption." Created with an eruption in April 1850, Cerro Negro is one of 4 young cinder cones NW of Las Pilas volcano. Strong explosive eruptions in 1968 were accompanied by a lava flow that travelled 1.5 km from a S-flank spatter cone. Brief explosive eruptions also occurred in December 1969 and February 1971. Violent Strombolian activity 9-12 April 1992 produced an ash plume 7-7.5 km high that extended 300 km WSW and caused heavy ashfall that forced evacuations from nearby towns (see Bulletin v. 17, nos. 3 and 4). Information Contacts: same as for Concepcion. Telica (12.60N, 86.85W) There have been no reports of activity in the past year, and none was observed 6-7 January. Telica last erupted in November 1987, when an incandescent column deposited fresh bombs nearby (see Bulletin v. 13, no. 1). Vigorous fumarolic activity observed in June 1989 (see Bulletin v. 14, nos. 2 and 6) had decreased by February 1990 (see Bulletin v. 16, no. 2). Information Contacts: same as for Concepcion. San Cristobal (12.70N, 87.00W) "San Cristobal was producing a gas plume in January 1993 at levels comparable to recent years. On 6 and 7 January a plume extended over Chinandega (about 15 km SW) at about 1000 m above sea level. No gas was smelled at farms at the base of the volcano. There was patchy evidence of acid rain on the leaves of a few coffee bushes and other plant species, but effects were mild and the coffee crops were not reported to be affected. Analyses of rainwater collected for drinking purposes at one farm revealed cation and anion concentrations expected of normal rainwater, as did a sample from the spring of a neighbouring farm. The analyses were undertaken by the British Geological Survey." Summit fumarolic activity has been strong since 1971 (see frequent Bulletin reports since 1989 in v. 14, no. 2; v. 16, no. 2; and v. 17, no. 4). San Cristobal's most recent known eruption was a 45- minute ash emission in October 1977 (see Bulletin v. 2, no. 10), although a small ash emission may have occurred in November 1987 (see Bulletin v. 13, no. 1). Information Contacts: same as for Concepcion. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Volcanic Activity in the United States Kilauea Hawaii (19.42N, 155.27W) All times are local (= GMT - 10 hours) The East rift zone eruption continued as lava from episodes 51 and 53 vents fed several channelized flows that descended from Pulama Pali (see last month's Bulletin). Flows on the Kamoamoa delta entered the ocean on 2 March while a flow near Laeapuki (approximately 750 m W of the Kamoamoa delta) stagnated within 30 m of the Chain of Craters Road. Breakouts on 5 March began covering new land E of the delta, including nearly 200 m of the Chain of Craters Road. By 15 March, much of the Kamoamoa delta had been resurfaced by new flows and lava was entering the ocean on the E and W sides of the delta. More flows cascaded over Paliuli on 13 March and advanced towards Chain of Craters Road N of Laeapuki. On 28 March, the Laeapuki flow cascaded over Paliuli W of the Kamoamoa flkM1 crossed Chain of Craters Road and entered the ocean. The Laeapuki flow inflated rapidly creating a hummocky, tumuli-covered surface. Lava continued to enter the ocean at Laeapuki and on the E and W sides of the Kamoamoa delta through 12 April. Small blocks of Laeapuki bench collapsed into the ocean on 11 April. A new collapse pit, containing lava, formed in late February halfway up Pu'u 'O'o cone from the episode-51 vent. In the first half of March the spatter cone at the episode-53 vent collapsed to half its original height. On 18 March, a vigorous flow broke out of the episode-51 lava tube between the 51 and 53 vents, filling most of the 52 collapse area before it stopped. On 26 February the crater floor of Pu'u 'O'o was 59 m below the crater rim. In late March, the floor was 4 m lower and the lava pond fluctuated 1-14 m below that. During early April the lava pond fluctuated from 73-77 m below the rim. The summit of Kilauea continued to deflate until 5 March, when it reached the low recorded during last February's earthquake swarm in the upper East rift zone (see last month's Bulletin). From 5 to 15 March, the summit water-tube tiltmeter recorded approximately 7 microradians WNW inflation. This trend continued until about 20 March. During 20-27 March, the tiltmeter recorded almost 20 microradians deflation, surpassing the low of 5 March. After some reinflation, no significant changes occurred 30 March-12 April. Tremor amplitudes recorded by a station near Pu'u 'O'o were 2-3x background. Microearthquake activity continued at low rates beneath the summit and at low-to-average rates along the East rift. At approximately 2100 on 19 April, a group of as many as 20 people ventured into a restricted area near Laeapuki to observe lava flowing into the ocean. A lava bench on which they were standing collapsed, causing the group to flee. The collapse was followed by 3 distinct earthquake-like events and the sudden explosion of a lava tube that had filled with ocean water. The explosion threw 35- cm-diameter rocks as far as 170 m inland. One man did not attempt to leave the initial collapse area and was last seen falling into the ocean. This is the first known death attributable to explosive volcanic activity at Kilauea since 1924. Others in the group sustained 3rd-degree burns and serious abrasions caused by falling incandescent rock and hot ocean water. No one was seriously hurt by the large bombs. Information Contact: Tari Mattox and Dave Clague, USGS Hawaiian Volcano Observatory, Hawaiian Volcanoes National Park, HI 96718 USA; Hawaii Volcanoes National Park, P.O. Box 52, Hawaii Volcanoes, HI 96718 USA. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 Atmospheric Effects Lidar data. March lidar data from Mauna Loa, Hawaii, were very similar to February observations (table 1). The biggest changes are still occurring above 20 km. However, these changes are minor compared to those that took place between November 1992 and February 1993. The sudden decline in Pinatubo aerosols in November 1992 is very similar to the decline observed 8-9 months after the El Chichon stratospheric aerosol injection. Both occurred at the same time of the year, just after the easterly peak in the 50 mbar zonal winds above Singapore. Weather-satellite observations. Aerosol Optical Thickness (AOT) measured by weather satellite showed a continued gradual decline over the world's oceans, except in the high N latitudes. Aerosol particles have apparently been transported from the tropics into the high N latitudes during the winter, resulting in AOT values almost identical to those observed 5 months earlier. The continued presence of aerosols at N latitudes may explain the below-normal winter and spring temperatures in the N hemisphere. The tropical zone (20S-30N) AOT has dropped below pre-Pinatubo levels, suggesting that the stratosphere in that zone has been cleared of aerosol particles to below an AOT of <0.02, the Advanced Very High Resolution Radiometer (AVHRR) detection limit for stratospheric aerosols. AOT values in the 40-60S zone continued to decline at a rate similar to the previous 4 months. Calculations indicate that stratospheric AOT values in the high S latitudes will be near zero (undetectable using the AVHRR) by late summer of 1993. Information Contacts: Thomas DeFoor, Mauna Loa Observatory, P.O. Box 275, Hilo, Hawaii 96720 USA; Juan Carlos Antuna, Centro Meteorologico de Camaguey, Apartado 134, Camaguey 70100, Cuba; Horst Jager, Fraunhofer-Institut fur Atmospharische Umweltforschung, Kreuzeckbahnstrasse 19, D-8100 Garmisch- Partenkirchen, Germany; Sergey Khmelevtsov, Institute of Experimental Meteorology, Lenin Str. 82, Obninsk, Kaluga Region, Russia; Larry Stowe, NOAA/NESDIS, World Weather Bldg., 5200 Auth Road, Camp Springs, MD 20746 USA. LOCATION DATE LAYER ALT (KM) BACKSCATTERING (peak) COEFF RATIO INTEGRATED Mauna Loa, HI 19 Mar 15-26 (19.2) 1.3x10E-7 3.6 0.56x10E-3 (19.5N, 155.6W) 26 Mar 15-26 (20.1) 1.2x10E-7 3.9 0.61x10E-3 31 Mar 14-23 (20.1) 1.2x10E-7 3.8 0.60x10E-3 8 Apr 15-23.5 (19.2) 1.3x10E-7 3.7 0.57x10E-3 14 Apr 16-23 (20.1) 1.1x10E-7 3.6 0.41x10E-3 Camaguey, Cuba 1 Dec 16.0 (21.7) 5.00 2.32x10E-3 (21.2N, 77.5W) 10 Dec 16.3 (21.4) 4.77 1.97x10E-3 16 Dec 16.6 (21.7) 4.21 1.68x10E-3 23 Dec 14.5 (19.6) 3.62 1.74x10E-3 (22.3) 4.09 30 Dec 14.8 (19.9) 3.73 2.13x10E-3 (21.7) 4.57 9 Jan 16.0 (19.9) 3.46 1.55x10E-3 13 Jan 16.6 (19.9) 3.61 1.50x10E-3 20 Jan 16.3 (21.7) 3.63 1.58x10E-3 28 Jan 16.0 (20.8) 3.46 1.55x10E-3 4 Feb 16.0 (19.0) 3.17 1.37x10E-3 (30.4) 1.62 11 Feb 16.0 (19.3) 2.99 1.26x10E-3 (22.9) 2.58 (30.7) 1.49 16 Feb 16.6 (20.8) 3.31 1.11x10E-3 26 Feb 16.0 (20.8) 3.00 1.33x10E-3 3 Mar 16.0 (19.9) 3.05 1.35x10E-3 12 Mar 15.4 (20.2) 2.89 1.06x10E-3 19 Mar 14.8 (20.5) 3.16 1.32x10E-3 (30.1) 1.36 27 Mar 16.0 (19.0) 2.66 1.05x10E-3 31 Mar 15.7 (19.0) 2.61 0.80x10E-3 Garmisch- 13 Jan 12-27 (18.1) 3.1(6.2) Partenkirchen 21 Jan 12.5-27 (20.5) 3.4(6.8) Germany 2 Feb 12-28 (18.1) 3.4(7.0) (47.5N, 11.0E) 11 Feb 12-28 (18.3) 3.3(6.6) Obninsk, Russia 6 Jan 15.0-23.3 (17.0) 2.36 0.96x10E-3 (55N, 38E) 9 Jan 15.0-23.3 (18.2) 2.75 1.43x10E-3 23.3-26.0 (23.7) 1.76 18 Jan 15.0-26.1 (19.7) 3.70 2.06x10E-3 2 Feb 15.0-20.1 (18.3) 2.60 0.97x10E-3 20.1-21.6 (20.6) 2.22 9 Feb 15.0-17.4 (16.5) 2.76 1.21x10E-3 17.4-24.6 (17.6) 2.61 11 Feb 15.0-22.5 (16.4) 3.11 1.10x10E-3 15 Feb 15.6-25.5 (18.0) 2.94 1.53x10E-3 24 Feb 15.0-21.0 (15.2) 1.98 0.39x10E-3 Table 1: Lidar data from various locations, showing altitudes of aerosol layers. Note that some layers have multiple peaks. Backscattering ratios from Hawaii are for the ruby wavelength of 0.69 microns; those from Cuba, Germany, and Russia are for the Nd-YAG wavelength of 0.53 microns, with equivalent ruby values in parentheses for data from Germany. The integrated value shows total backscatter, expressed in steradiansE-1, integrated over 300-m intervals from 15.8 to 33 km at Mauna Loa, 16 to 33 km at Camaguey, from the tropopause to 30 km at Garmisch-Partenkirchen, and over 150-m intervals from 15 to 30 km at Obninsk. Global Volcanism Network Bulletin v. 18, no. 3, March 31, 1993 EARTHQUAKES The Santa Cruz Islands earthquake, the first M r7.0 event this year, was centered about 175 km SW of Tinakula volcano. The earthquake 13 hours later (Solomon Islands) was its largest aftershock (table a). The 6 March Fiji earthquake was centered about 330 km N of Raoul Island. The SW Atlantic Ocean earthquake on 10 March was centered approximately 200 km NE of Montagu volcano. The epicenter of the 12 March Fiji earthquake was approximately 400 km NW of Taveuni volcano. No casualties or damage were reported for any of the above earthquakes. One person was killed and 1,000 houses damaged during the China earthquake, centered 250 km NE of Kathmandu. One person was killed, 16 were injured, and 600 buildings damaged during the earthquake in Greece, centered about 200 km SW of Athens. Information Contacts: National Earthquake Information Center, MS 967, Denver Federal Center, Box 25046, Denver, CO 80225 USA; Associated Press. DATE TIME(GMT) MAG LAT LONG FOCAL DEPTH REGION 6 Mar 0305 7.1 Ms 10.90S 164.20E shallow Santa Cruz Is. 6 Mar 1002 6.7 Ms 26.30S 177.60N shallow Fiji 6 Mar 1626 6.5 Ms 11.00S 163.42E shallow Solomon Is. 10 Mar 1239 6.5 Ms 58.30S 21.60W shallow SW Atlantic Ocean 12 Mar 1401 6.5 Ms 13.90S 178.30W shallow Fiji 20 Mar 1452 6.0 Ms 29.05N 87.35E shallow China 26 Mar 1158 5.1 Ms 37.22N 21.57E shallow S. Greece Table 2: Summary of large earthquakes, January 1993. Courtesy of the National Earthquake Information Center.