Global Volcanism Program - Volcanic Activity Reports - ...al Volcanism Network - Volume 21, Number 4 (April 1996) http://www.volcano.si.edu/gvp/archive/1996/2104bull.htm
Global Volcanism Program Volcanic Activity Reports Bulletin of the Global Volcanism Network Volume 21, Number 4 (April 1996)
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VOLCANOES
Soufriere Hills (Montserrat) Significant explosions and pyroclastic flows; vigorous dome growth Colima (México) Minor rockfalls; measurements of SO2 flux and fumarole temperatures Popocatépetl (México) Explosion on 30 April kills five climbers near the crater rim Telica (Nicaragua) Low-level degassing and sulfur deposits observed in crater Cerro Negro (Nicaragua) Gentle degassing and lava-flow fumaroles; 1995 cone partially collapsed Momotombo (Nicaragua) High seismicity and a black plume, but no crater changes Masaya (Nicaragua) Incandescent vent in Santiago crater emitting large amounts of gas Galeras (Colombia) Small earthquake swarm and some tornillo events Deception Island (Antarctica) Seismicity at a level similar to that recorded in the 1994-95 survey Stromboli (Italy) Increased seismicity and Crater 1 activity after mid-April Vulcano (Italy) Decrease in fumarole temperatures Ol Doinyo Lengai (Tanzania) Carbonititic lava flows from a hornito active since July 1995 Soputan (Indonesia) Small eruption on 15 March seen on satellite imagery Manam (Papua New Guinea) Small ejection of incandescent particles; minor inflation Langila (Papua New Guinea) Occasional ash-and-vapor clouds and night glows Rabaul (Papua New Guinea) Low-level eruptive activity from Tavurvur White Island (New Zealand) Uplift of the main crater floor and changes in the hydrothermal system Ruapehu (New Zealand) Landslides and lahars in the aftermath of the 23 September eruption Fukutoku-okanoba (Japan) Yellowish-brown discolored seawater seen again Kuchinoerabu-jima (Japan) Number of volcanic earthquakes continues to increase Kuju (Japan) Seismicity and steam plume without ash Adatara (Japan) Volcanic tremor detected on four days in April Akutan (Aleutian Islands) Seismicity decreases and remains low Long Valley (USA) Summary of 1995 activity; March-April 1996 earthquake swarm
EARTHQUAKES
South Fiji Basin (M 6.8) 16 April; Solomon Islands (M 7.5) 29 April
Editors: Rick Wunderman and Ed Venzke Editorial Assistants: Giuseppina Kysar and Genyong Peng
All information contained in these reports is preliminary and subject to change.
Soufriere Hills Montserrat, West Indies 16.72°N, 62.18°W; summit elev. 915 m All times are local (= UTC - 4 hours)
Volcanic activity in the summit crater was very high during early April, but explosions decreased in the second half of the month. Dome growth, most conspicuously in the form of spines, remained vigorous. Activity late in the month was dominated by small to moderate-sized rockfalls with associated ash clouds. Steam production was almost continuous, along with SO2 emission, throughout the month. Episodes of low-amplitude broadband tremor, usually <1 hour duration, were also recorded, but there were few long-period or shallow volcano-tectonic earthquakes. No major deformation events were recorded. Eruptive activity on 3 April began at 0652 with a small explosion (Bulletin v. 21, no. 3). Near-continuous seismic activity afterwards was a result of more small explosions and ash emission from the dome. After a reassessment of the situation by the Montserrat Volcano Observatory at 1300, the civil authorities began an evacuation of the S part of the island. At 1518, an eruption generated a significant pyroclastic flow in the Tar River valley area and an ash plume that rose to ~6 km altitude. Further pyroclastic flows in the same area were generated at 1808 and 1818. These pyroclastic flows slightly overtopped the N embankment of the Tar River valley but caused no destruction to property in Long Ground, ~2 km NE of the dome. Fires started by the pyroclastic flows continued for several days in the Tar River area. Several smaller explosions and rockfalls during 4-5 April generated clouds that deposited ash in Plymouth and environs. The most significant of these was a moderately strong explosive eruption at about 1253 on 5 April that produced a column to ~1,500 m altitude and a small pyroclastic flow into the Tar River valley. A series of eruptions starting at 0839 on 6 April generated ash plumes up to ~3 km high and sent at least six small pyroclastic flows into the Tar River area. After 1337 the activity level increased again, with continuous ash emission and several ash plumes. At 1445, a significant explosive eruption began and continued for about an hour. It consisted of two main pulses that sent ash to ~9 km altitude and generated a relatively large pyroclastic flow. Several small-to-moderate eruptions produced ash columns and possibly small pyroclastic flows in the Tar River valley again that afternoon. A new spine observed close to the center of the dome on the morning of 4 April was ~828 m above sea level at mid-morning the next day. By 6 April it had grown to ~906 m elevation and was visible from many points around the island; by 7 April the spine was taller than Chance's Peak (the highest topographic feature on Montserrat at 915 m). A moderate explosion at 0659 on 7 April was heard at the Bramble Airport ~6 km NE of English's Crater and fed an eruptive column that deposited ash to the NW. During the night of 7 April the top half of the spine broke off but the remnant continued to grow from the base throughout 8 April so that once again it became higher than Chance's Peak; this spine was the largest seen so far. On 8 April there was another series of eruptions, including two large explosions at 1354 and 1357. During this period, near-continuous pyroclastic flows moved into the Tar River valley, and several large ash clouds drifted out to sea. The pyroclastic flows did not reach as far as those on 3 April, but some trees in the Tar River valley were set on fire. Activity in the crater area during 11-17 April was dominated by rockfalls and explosions creating small ash clouds. The spine that began rising on 5 April collapsed on 12 April towards the SW. A pyroclastic flow from this event was observed at 1559 on 12 April, but remained confined to the upper part of the Tar River valley away from inhabited areas. A twenty-five minute period of explosions and rockfalls began at 2037 on 13 April. On 15 April a new spine was growing
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photographs taken from the ground with a 35 mm single-lens reflex camera. The most striking morphological changes are probably in Crater 1, which saw the construction of a series of cones and their subsequent destruction, which led to the present configuration near vents 1/3 and 1/4. The zone around vent 1/2 in the foreground now appeared more open towards the Sciara del Fuoco, thus allowing better visibility of the crater from Punta Labronzo. Changes were also observed at vent 3/1, now better separated from Crater 2 on the rear and more connected to the rest of Crater 3 due to slumping of blocks between vents 3/1 and 3/3. Information Contacts: Jürg Alean, Kantonsschule Zürcher Unterland, CH-8180 Bülach, Switzerland (Email: [email protected]); Roberto Carniel, Dipartimento di Georisorse e Territorio, via Cotonificio 114, I-33100 Udine (Email: [email protected], URL: http://www.ezinfo.ethz.ch/volcano/strombolihomee.html).
Vulcano Aeolian Islands, Italy 38.404°N, 14.962°E; summit elev. 500 m
The "La Fossa" crater was visited during 9-11 May by a group from the Federal Institute of Technology in Zurich. Fumarolic emissions were observed on the SW inner crater wall, on the outer N slope ~100 m below the crater rim, and on the NE outside flank about half way down from the rim towards the sea. During the night of 9-10 May, several new fissures, 2-3 m long and 2-5 cm wide, opened on the inner crater slopes. They formed as an extension of a major fissure reaching W from fumarole FF, concentric to the crater rim. Temperatures of gases emitted from these fissures ranged from 160 to 220°C. During the same night, pre-existing fissures widened by a few centimeters (<5 cm). New fissures just below the rim towards the crater were a few millimeters in width. The inner crater slope showed widening of both radial and tangential fractures. Fumarole temperatures were measured on the NE crater rim and on the inner crater flanks, but those from radial fractures in the inner crater were not measured. Maximum temperature observed was 507°C on an extension fissure of fumarole FF on the inner crater slopes (table 3). This compares to the maximum temperature of 552°C in the same period last year at the same location. Temperatures on the crater rim peaked at 326°C at fumarole F5 compared to 512°C last year. Temperatures of outlets situated at the edge of the slope from the inner crater to its floor reach a maximum of 435°C. Fumarole temperatures therefore showed decreasing trends, but maximum temperatures remained high. The decrease was strongest at the rim fumaroles.
Table 3. Measured temperatures at La Fossa Crater, Vulcano, in May 1995 and 1996. Fumaroles F0/F1 and F5 are located at the crater rim; FF, FA and the extension fissure occur in the inner crater. Courtesy of C. Wahrenberger.
Peak Temperature (°C) Fumarole 1-5 May 1995 9-11 May 1996
F0 369 320 F1 302 320 F5 512 326 FF 484 435 FA 474 445 Extension 552 507 fissure FF
Temperature measurements were done using a Cr-Al Type K thermocouple at ~5 cm below the surface. All 1996 measurements were taken at the same locations as those made in 1995. Temperatures at each point were also taken on three successive days; deviations in 1996 were <5°C from day to day. Gas and condensate samples were also taken because the research focus of the group is trace-element transport in volcanic gases. Vulcano last erupted in 1888-90 when numerous meter-sized bombs and blocks fell in the area now occupied by the village of Vulcano Porto, which hosts thousands of tourists daily during the summer season. Vulcanello, the youngest part of Vulcano Island, began to form only ~2,100 years ago as an isolated island that later became connected with the main island. The latest activity at Vulcanello occurred in the 16th century when lava flows, now covered by large hotel complexes, were extruded. Information Contacts: Christoph Wahrenberger, Terry M. Seward, and Volker Dietrich, Institute for Mineralogy and Petrography, Federal Institute of Technology, Sonneggstrasse 5, 8092 Zurich, Switzerland (Email: [email protected]).
Ol Doinyo Lengai northern Tanzania 2.751°S, 35.902°E; summit elev. 2,890 m All times are local (= UTC + 3 hours)
A French team spent three days at the summit during 4-6 April 1996. Abundant gas was emitted from three radial fractures oriented E-W and less gas came from three other fractures oriented NE-SW. Numerous fumaroles were present on the N crater rim. Hornito T34 (as numbered in Bulletin v. 20, no. 11/12) released large amounts of gas. Significant changes in the crater morphology were noted since the December 1995 description. Three hornitos in the N part of the crater (T8, T14, T15) had disappeared under lava flows from T37. Only the top 50 cm of T8 was exposed, but a chimney 30 m deep was observed below. In the S part of the crater, hornitos T27 and T30 were notably modified. Magmatic activity was observed from three hornitos. The spatter cone T37 was hooded but open to the WSW. Inside, a 10-m-diameter lava pond exploded every 2 seconds, throwing lava 2-5 m high. As the group arrived at 1200 on 4 April the T37 lava pond overflowed, producing a lava flow that had a pahoehoe surface near the pond, and changed to an aa texture at a distance. Numerous such lava flows occurred until 0730 on 5 April; they traveled ~150 m SSW towards T23 and T30. The lava pond level then dropped, leaving solid lava "stalactites" on the walls. Explosions continued, but no further lava emission was observed through 1300 on 6 April. Because of sloshing lava sounds, another lava pond was thought to exist inside another hornito (between T5/T9 and T37), but it remained invisible. Hornito T36D became active early on 6 April, ejecting small lava fountains to an average height of 2 m. During one 2-minute episode there were 20-30 ejections. Episodes (up to 5 minutes long) were separated by repose periods of 15-20 minutes. Noisy gas emissions followed each episode. Activity increased near 1300 with continuous lava emission during each episode. This symmetrical stratovolcano in the African Rift Valley rises abruptly above the plain S of Lake Natron. It is the only volcano known to have erupted carbonatite tephra and lavas in historical time. The cone-building stage of Ol Doinyo Lengai ended about 15,000 years ago and was followed by periodic Holocene ejections. Historical eruptions have consisted of smaller tephra ejections and emission of numerous natrocarbonatite lava flows on the floor of the summit crater. Information Contacts: Jacques-Marie Bardintzeff, Lab. Petrographie-Volcanologie, bat 504, Universite Paris-Sud, 91405 Orsay, France (Email: [email protected]).
Soputan Sulawesi, Indonesia 1.11°N, 124.73°E; summit elev. 1,784 m
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