Bulletin of the Global Volcanism Network

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

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

 Bulletin of the Global Volcanism Network - Volume 18, Number 02 (February 1993)


Managing Editor: Edward Venzke

Aira (Japan)

Explosions continue; three earthquake swarms

Arenal (Costa Rica)

Gas emission, explosions, lava flows continue; tremor activity increases

Asosan (Japan)

Scoria eruption; seismicity declines

Chichon, El (Mexico)

Fumarolic activity continues; lake chemistry unchanged

Etna (Italy)

Lava flows continue; volume estimates reported

Galeras (Colombia)

Low seismicity and SO2 levels; episodes of long-period tremor

Guagua Pichincha (Ecuador)

Phreatic explosion kills two scientists

Hudson, Cerro (Chile)

Increased gas emission and mudflows

Irazu (Costa Rica)

Decreased fumarolic activity continues

Kilauea (United States)

Episode 53 begins; lava flows from tube breakout reach Kamoamoa delta

Langila (Papua New Guinea)

Small Vulcanian eruptions

Manam (Papua New Guinea)

Weak emissions; discontinuous low-amplitude tremor

Mayon (Philippines)

Eruption continues; pyroclastic flows; lava extrusion

Pinatubo (Philippines)

Seismic activity continues

Poas (Costa Rica)

Fumarolic activity continues

Popocatepetl (Mexico)

Increased fumarolic activity; seismicity remains low

Rabaul (Papua New Guinea)

Seismicity remains low; no significant deformation

Rincon de la Vieja (Costa Rica)

Gas plumes rise to 500 m; lake level drops

Ruapehu (New Zealand)

Little change in crater lake; episodes of tremor

Spurr (United States)

Low seismic activity; level of concern reduced from Yellow to Green

Stromboli (Italy)

Seismicity and tremor resume after 10 February explosions

Ulawun (Papua New Guinea)

Activity continues to decline; glow observed in crater

Unzendake (Japan)

Dome complex continues to grow; large pyroclastic flow



Aira (Japan) — February 1993 Citation iconCite this Report

Aira

Japan

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

All times are local (unless otherwise noted)


Explosions continue; three earthquake swarms

Explosions . . . continued at a rate similar to that recorded in January. Two of the 15 explosions recorded in February produced observable incandescent columns rising 100 m above the crater. An explosion at 1822 on 3 February produced the highest ash plume of the month, 2,000 m. Seismicity remained normal. Three swarms of B-type earthquakes were recorded: on 9 February (duration 5 hours), 10 February (5 hours), and 25 February (10 hours).

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: JMA.


Arenal (Costa Rica) — February 1993 Citation iconCite this Report

Arenal

Costa Rica

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

All times are local (unless otherwise noted)


Gas emission, explosions, lava flows continue; tremor activity increases

Gas emission, explosions, and lava flows continued from Crater C. Strombolian activity was similar to last month, with relatively quiet explosions of moderate size that produced columns, with minor ash content, to 500-1,000 m above Crater C. Ash fell 1.8 km W of the active crater down to 735 m elevation. Sudden small-moderate degassing events, separated by a few to tens of minutes, were accompanied by frequent loud sounds. A pyroclastic flow in mid-February moved down the S flank to 850 m elevation.

The lava flow that began to descend in December 1992 remained active after dividing into two lobes at 1,100 m elevation. The W lobe, with an approximate thickness of 18 m, descended to 800 m elevation in February. During the same period, the SE lobe descended from a flat area just above 800 m down to 700 m elevation.

Tremor activity recorded at Fortuna station, 3.5 km E of the active crater, has increased since the end of January. The increase is thought to be associated with the rise of new magma to the surface. The number of seismic events (average of 36/day; figure 52), was similar to last month and in the normal range. However, there was an increase in the number of seismic events after each tremor episode.

Figure (see Caption) Figure 52. Number of seismic events/day at Arenal (Fortuna station), February 1993. Courtesy of G. Soto and R. Barquero.

Sulfur and chlorine gas emissions from fumaroles on the rim of Crater C continued to produce acid rain that has damaged vegetation on the NE, E, and SE flanks. Fumarolic activity continued from Crater D.

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

Information Contacts: G. Soto and R. Barquero, ICE; E. Fernández and J. Barquero, OVSICORI.


Asosan (Japan) — February 1993 Citation iconCite this Report

Asosan

Japan

32.884°N, 131.104°E; summit elev. 1592 m

All times are local (unless otherwise noted)


Scoria eruption; seismicity declines

The eruptive phase . . . continued through February at Crater 1. At noon on 20 February, vent 922 ejected scoriae to 100 m above the vent, the first eruption observed during daily visits to the crater rim since 22 January. The ejecta, consisting of blocks up to 50 cm across, fell within the 400-m-wide, 150-m-deep crater. Incandescent fountaining, also to a height of 100 m, was observed that night. Inclement weather prevented visual observations in the following days and the ending date for the eruption is not known.

The amplitude of the continuous tremor, which increased in late December, persisted at an elevated level until 10 February, when it rapidly declined (figure 23). The decline was not accompanied by any observed change in surface phenomena. At 0600 on 20 February, the tremor amplitude increased. Tremor amplitude remained high during and after the eruption, abruptly returning to background level at 1215 on 25 February after a small block ejection. An area within 1 km of the crater has been closed since 18 January.

Figure (see Caption) Figure 23. Daily mean amplitude of volcanic tremor (top) and height of steam plume (bottom) at Aso from 1 January 1992 to 8 March 1993. Arrows at the top indicate eruptions. Courtesy of JMA.

Ash was observed in the steam plume on 1-5, 12-13, 18-20, and 23-25 February. The plume rose to heights of 500 m, increasing briefly to 1,000 m n 19-20 February (figure 23).

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: JMA.


El Chichon (Mexico) — February 1993 Citation iconCite this Report

El Chichon

Mexico

17.36°N, 93.228°W; summit elev. 1150 m

All times are local (unless otherwise noted)


Fumarolic activity continues; lake chemistry unchanged

Fieldwork on 11-18 January revealed continued fumarolic activity around the crater lake and crater walls as observed in June 1992 (17:06). The boiling mud and water ponds remained active. Geyser-like fumaroles emitted a gas phase only, and extensive mud cracks indicated an 85 cm drop in the level of the crater lake. The changes were probably due to the decrease in rainfall during December and January.

The drop in lake level prevented temperature and pH measurements at the same sites sampled last June. Two new sites were chosen. Site 1, which better reflected the ambient conditions of the lake because of the absence of nearby fumaroles or boiling zones, had a temperature of 30.7°C and a pH of 2.3. The temperature at site 2 was 66.6°C and its pH was 1.7. Analysis of a water sample taken at site 1 indicated that the lake has remained chemically stable since 1992 except for minor boron variations.

On 13 January, two apparent phreatic explosions similar to one reported last year were heard and felt on the crater rim. A small rockfall avalanche on the SE inner wall of the crater followed the first explosion.

Geologic Background. El Chichón is a small, but powerful trachyandesitic tuff cone and lava dome complex that occupies an isolated part of the Chiapas region in SE México far from other Holocene volcanoes. Prior to 1982, this relatively unknown volcano was heavily forested and of no greater height than adjacent nonvolcanic peaks. The largest dome, the former summit of the volcano, was constructed within a 1.6 x 2 km summit crater created about 220,000 years ago. Two other large craters are located on the SW and SE flanks; a lava dome fills the SW crater, and an older dome is located on the NW flank. More than ten large explosive eruptions have occurred since the mid-Holocene. The powerful 1982 explosive eruptions of high-sulfur, anhydrite-bearing magma destroyed the summit lava dome and were accompanied by pyroclastic flows and surges that devastated an area extending about 8 km around the volcano. The eruptions created a new 1-km-wide, 300-m-deep crater that now contains an acidic crater lake.

Information Contacts: José Luis Macías, Michael F. Sheridan, and Carmelo Ferlito, SUNY, Buffalo, NY; Juan Manuel Espíndola, Servando De la Cruz-Reyna, and M. Aurora Armienta, Instituto de Geofísica, UNAM.


Etna (Italy) — February 1993 Citation iconCite this Report

Etna

Italy

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

All times are local (unless otherwise noted)


Lava flows continue; volume estimates reported

The following information, based on the report of the IIV, covers the period December 1992 through February 1993.

The eruption ... continued as lava gently flowed from the vent on the W wall of Valle del Bove, significantly expanding the flow field formed after the flow diversion of May 1992 (17:05). Lava moved to Piano del Trifoglietto through a forked lava tube, emptying through several ephemeral vents located mainly on the N and S sides of the flow field (figure 58). In the first half of December, lava escaped mainly through the S vents. Many small flows gradually covered Poggio Canfareddi Hill, previously isolated by flows moving E toward Mt. Zoccolaro. In the second half of December, activity shifted to the N vents, expanding the flow field over a flat area that had not been covered by lava from the current eruption. Using data from a GPS survey done in January, the total volume of lava erupted through 1992 was estimated to be 198 ± 40 x 106 m3. The lava covers an estimated 6.7 x 106 m2 and the mean rate of lava production is 6m3/s.

Figure (see Caption) Figure 58. Topographic sketch map of the active portion of the 1991-93 lava flow field; 1. Flow field formed from 27 May 1992 through February 1993; 2. Flow field before 27 May 1992; 3. Limit of active lava flows by November 1991; 4. Directions of the main active flows December 1992-February 1993; 5. Lava tubes. Courtesy of IIV.

By January 1993, lava flows from the S vents advanced to the Poggio Canfareddi area and a complex network of minor flows reached the foot of Mt. Zoccolaro at 1,530-m elevation. Lava continued to flow from the N vents, expanding the field 400 m to the N. On 27-29 January, a fast-moving lobe of lava flowed to the NE, reaching 1,500 m elevation, 4 km distant from the eruptive fissure.

Effusive activity declined in February, ceased at the S vents by 8 February. Flow from the N vents was less than in previous months and shifted to vents on the northern-most side of the flow field. The new flows did not expand the flow field.

The seismic network recorded five swarms of long-period events. Fourteen events with M >1 occurred on 1 December, 14 events on 23 December, five events on 25 December, 51 events on 30 December-2 January, and 26 events on 3 February. No event exceeded M 3. The swarms were located in a small focal volume between the summit craters and Pizzi Deneri (~2 km NE) at depths asl. Volcano-tectonic seismicity during the period remained low (only three events) comparable to that observed throughout 1992.

The 9-station bore-hole tiltmeter network recorded no significant deformation except for a sharp event 18-19 December. Steady degassing from the Etna summit craters was observed and a weak ash emission occurred on the morning of 3 December from the Bocca Nuovo vent. Minor landslides repeatedly affected the E inner wall of the NE crater until January. The crater floor had sunk by early morning on 3 February.

The following report from geologists at the IIV and the Univ di Catania with seismic information from G. Luongo, updates and complements the official IIV report above.

A lava flow, at least a few hundred meters wide, has formed on the NE side of the lava field that has been building since 27 May 1992 (figure 58). The flow, in the vicinity of Monti Centenari (2 km NE of the active fissure), is completely independent from the old field and is moving E in the middle of Valle del Bove. The lava of this flow is visible from between 2,205 and 1,700 m through a series of skylights on the main tube. Lava is surfacing through 4-5 ephemeral vents at ~1,500 m elevation; the vents active in the past on the N, S, and central parts of the old lava field have closed. On the morning of 12 March, the most advanced flows had reached 1,425 m elevation and were moving over lava of previous eruptions. By 1300 on 14 March, the lava front was at 1,400 m elevation, ~ 5 m wide, 1 m high, and moving at an estimated 1 m/h.

The estimated volume of lava produced after 458 days of activity is 295 x 106 m3. This estimate was calculated using the same method as previous estimates reported in the Bulletin, but is ~ 50% higher than the GPS value reported above. No significant changes in degassing of the summit craters were noticed. Northeast crater is still obstructed, with very active fumaroles along the inside walls. COSPEC measurements of SO2 flux remained normal (5-6 x 103 t/d), except in early March when measured values were 12.5 x 103 t/d.

Between 12 February and 15 March, 169 events of M 1.2-2.9 were recorded, mainly in the summit crater area. The majority of events appeared to be related to active degassing at the surface, with characteristic frequencies of 1-6 Hz. Volcanic tremor was completely absent.

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: IIV. The last three paragraphs are fromR. Romano, T. Caltabiano, M. Grasso, and M. Porto, IIV; P. Carveni and C. Monaco, Univ di Catania; G. Luongo, OV.


Galeras (Colombia) — February 1993 Citation iconCite this Report

Galeras

Colombia

1.22°N, 77.37°W; summit elev. 4276 m

All times are local (unless otherwise noted)


Low seismicity and SO2 levels; episodes of long-period tremor

Seismic activity at Galeras continued in February at the low levels that followed the 14 January eruption. The majority of earthquakes were located slightly to the W of the caldera at depths <1.5 km. COSPEC measurements of SO2 remained low and the [Crater Station] electronic tiltmeter showed no significant changes. Continuous gas emissions came from the main crater and fumaroles located to the W and SW. No seismicity could be correlated with periodic reports of roaring noises or explosions from the active crater.

Beginning on 13 February, long-period, "screw-type" seismic events referred to as tornillos were detected, their occurrence increasing towards the end of the month. As of 12 March, twenty-six of these events had been recorded. During the last days of February the tornillos changed character. Though still remaining low-frequency and long-duration, the signature varied or the dominant frequency increased. Some of the tornillos were located near the surface towards the W flank of the volcano.

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: M. Calvache, INGEOMINAS, Pasto.


Guagua Pichincha (Ecuador) — February 1993 Citation iconCite this Report

Guagua Pichincha

Ecuador

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

All times are local (unless otherwise noted)


Phreatic explosion kills two scientists

A phreatic explosion at 1146 on 12 March in the young crater of Guagua Pichincha's central dome killed two young volcanologists from the Instituto Geofísico. Ing. Victor Hugo Pérez, 31, and Egdo. Alvaro Sánchez, 25, had gone onto the dome, . . . (figure 3), to document recent activity when the strong blast hurled rocks and ash upon them, killing them instantly. Based on seismicity, a warning of possible activity had been transmitted to them by radio at 1030, but for unknown reasons they were still on the dome when the eruption occurred. Search and rescue operations were initiated late that afternoon and at about 0730 the following morning their bodies were discovered by M. Hall near the dome's crater rim.

Guagua Pichincha had been quiet since phreatic activity April-June 1990. The main fumarolic vents on the S side of the dome and the major steam vents at the foot of the S caldera wall exhibited normal fumarolic behavior. Fumarolic activity in the active crater on the NE flank of the dome has been variable but low.

Evidence of recent phreatic activity that had blasted ash and rocks NE against the inner wall of the caldera was noted during routine fieldwork on 11 March. A guard stationed near the caldera rim confirmed that an explosion had occurred on 9 March, depositing up to 10 cm of non-juvenile ash. The Instituto officially advised Civil Defense early on 12 March that Pichincha had resumed dangerous activity and that tourists and mountaineers should be advised of the danger in entering the caldera.

As in past explosive cycles, phreatic activity seems to be related to the rainy season, which normally begins in March. Activity may have begun earlier this year because of the abnormally high rainfall in February.

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

Information Contacts: M. Hall, Instituto Geofísico de la Escuela Politécnica Nacional.


Cerro Hudson (Chile) — February 1993 Citation iconCite this Report

Cerro Hudson

Chile

45.9°S, 72.97°W; summit elev. 1905 m

All times are local (unless otherwise noted)


Increased gas emission and mudflows

The following, from Peter Ippach and Rolf Kilian, describes observations during a caldera crossing and overflight between 11 February and 5 March. These are the first reported caldera observations since January 1992 (16:12). One of the largest eruptions of the 20th century began on 8 August 1991 from a fissure cutting the caldera rim (16:7-12, and 17:3). The paroxysmal phase began on 12 August, producing eruption columns up to 16-18 km for 3 days, resulting in ashfall in the Falkland Islands, 1,000 km away. Pyroclastic flows were mostly restricted to the caldera floor, and a lava flow traveled 4 km down the WNW flank.

The basaltic eruption phase of 8-9 August 1991 (16:8) took place on the W caldera rim under 20-30 m of ice, forming an elliptical N 25°W-trending fissure vent about 2.5 km long, 300 m wide, and 200 m deep. A lava flow from the eruption extended 3.5 km WNW along the Huemules glacier from the N flank of the fissure vent (see map in 16:7); it had a maximum thickness of 8 m. Lava debris flows and aa-like flows were observed on the N flank extending up to 2.5 km from the source. Lava- and spatter-flows traveled down the slope of the inner W caldera rim, one traveling 800-1,000 m before going into a 300 m-deep depression on the ice-covered caldera surface. The proximal fallout layer is about 1-5 m thick with individual pumice clasts up to 40 cm in diameter. Constant fumarolic activity was observed, and there was an intense sulfur smell.

Since the andesitic Plinian eruption of 12-15 August 1991 (16:7), gas emission has apparently increased in a 10 km2 area surrounding the vents. Gas columns from different locations were rising to 500 m altitude. A young phreatic eruption had produced a fan of reworked pyroclastic material 10 km to the E. Mudflow production has intensified as a result of strong geothermal activity increasing glacial melting. Volcaniclastic material was flowing in erosional channels SE of the caldera and following the Huemules glacier WNW. The increased mud- and mass-flow production in the Huemules valley is similar to the April 1973 volcaniclastic flow that followed the 1971 eruption. This implies a continuing risk for the valley, which is inhabited during the summer.

Crater-like depressions in a 5 km2 area in the SW part of the caldera probably indicated two eruption centers from the August 1991 eruption. The depressions contained lakes 650 m and 800 m in diameter, surrounded by an intensively cracked glacier. Pyroclastic material was reworked and redeposited in the lower NW part of the caldera during the austral summer of 1991/92, leaving deposits up to 50 m thick. These deposits were then covered by snow during the winter of 1992. Geothermal activity was not present in the NE part of the caldera.

Pyroclastic material on the SE-directed fan from the August 1991 eruption, between the Ibáñez and Murta rivers, was also extensively reworked during the 1991/92 summer. After a rainy summer, reworking and deposition had stopped by March 1993, with a great reduction in ash transport by the rivers. However, on the W side of the volcano, irregular meltwater flows from the Huemules glacier carried a large amount of pyroclastic material down the Huemules river.

Geologic Background. The ice-filled, 10-km-wide caldera of the remote Cerro Hudson volcano was not recognized until its first 20th-century eruption in 1971. It is the southernmost volcano in the Chilean Andes related to subduction of the Nazca plate beneath the South American plate. The massive volcano covers an area of 300 km2. The compound caldera is drained through a breach on its NW rim, which has been the source of mudflows down the Río de Los Huemeles. Two cinder cones occur N of the volcano and others occupy the SW and SE flanks. This volcano has been the source of several major Holocene explosive eruptions. An eruption about 6700 years ago was one of the largest known in the southern Andes during the Holocene; another eruption about 3600 years ago also produced more than 10 km3 of tephra. An eruption in 1991 was Chile's second largest of the 20th century and formed a new 800-m-wide crater in the SW portion of the caldera.

Information Contacts: P. Ippach, GEOMAR; R. Kilian, Universität Tübingen, Germany.


Irazu (Costa Rica) — February 1993 Citation iconCite this Report

Irazu

Costa Rica

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

All times are local (unless otherwise noted)


Decreased fumarolic activity continues

Fumarolic activity in the main crater continued at a decreased level. The surface of the yellow-green crater lake rose about 12 cm from 1 December to January, but then dropped 40 cm by 15 February. Lake temperature ranged from 17.4 to 24.5°C. Areas along the edge of the lake with bubbles and gas emissions decreased in number and intensity, and had temperatures <92°C. The pH of the water has continued to rise since the low measurement of 5.7 on 15 February. The "steaming ground" on the debris fan N of the lake had fewer active fumaroles, and a maximum temperature of 87.9°C. There were no changes in the temperature or pH of the hot springs around the volcano.

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: G. Soto and R. Barquero, ICE.


Kilauea (United States) — February 1993 Citation iconCite this Report

Kilauea

United States

19.421°N, 155.287°W; summit elev. 1222 m

All times are local (unless otherwise noted)


Episode 53 begins; lava flows from tube breakout reach Kamoamoa delta

"An upper east rift intrusive swarm began at 2325 on 7 February. More than 5,000 microshocks were counted in the first 48 hours of the swarm; these continued, in smaller numbers, until 18 February, when counts gradually decreased to normal. Several hundred events were processed, most located near Makaopuhi Crater, ~15 km SE of the summit and 6.4 km SW of Pu'u ' O'o. High-amplitude tremor beneath the summit accompanied the swarm. The count of shallow, short-period events beneath the summit was low, while that of shallow, long-period events was slightly above average until 22 February, peaking at >100 events on 19 February. The Uwekahuna water-tube tiltmeter at the summit of Kilauea recorded ~15 µrad of deflation during the swarm. The tilt then reversed, recovering all of the deflation associated with the swarm by 23 February. The summit then slowly deflated again, with an E tilt of ~4 µrad recorded 23 February-1 March.

"On 8 February the magma supply to the E-51 vent was interrupted. Eruption tremor amplitudes, which had been ~2x background, rapidly diminished to background by 0400. As the E-51 tube system drained at the coast, sea water entered the tube, resulting in increased explosive activity starting at 0430 that continued intermittently for 3 hours. All flows stagnated by 9 February, but skylights remained incandescent for several days.

"The floor of Pu`u `O`o crater (35 m below the rim) collapsed on 8 February. After the collapse, the bottom of the crater consisted of talus slopes, with the lowest point >85 m below the crater rim. The lava pond reappeared on 10 February, and flows began to resurface the crater floor.

Episode 53 (E-53). "Eruption tremor remained at background levels until a gradual increase in amplitude on 16 February. On the same day, the lava pond in Pu`u `O`o rose dramatically and slow-moving lava was visible through the upper skylights of the E-51 tube. Two days later, sluggish pahoehoe flows broke out of the tube at 640 m elevation. More flows broke out at lower elevations, and by 20 February, channelized flows reached the top of Pulama pali. At 1450, lava fountains up to 4 m high were observed on the S flank of Pu`u `O`o, marking the beginning of E-53. The following day, the E-53 vent was ejecting spatter 15 m into the air and had formed a 30 m wide cone, with walls as high as 14 m. Flows from the vent area fanned out, filling the old E-52 collapsed pond and heading S towards the E-51 tube system.

"On 22 February, E-53 flows entered the E-51 tube through a skylight at 715 m elevation. The increase in magma in the tube led to an increase in activity. From 0000 to 0500, the eruption tremor amplitude increased noticeably to ~3-4x background. Amplitudes were sustained at 2-3x background for the remainder of the week. Large channelized flows advanced down the pali, fed by both the E-51 and E-53 vents. These flows merged with breakouts between 150 and 120 m elevation, reaching 60 m on 26 February. By 1 March, lava flows from the two vents were within 200 m of the ocean on the Kamoamoa delta, and within 40 m of Chain of Craters Road (figure 88).

Figure (see Caption) Figure 88. Map of recent lava flows from the East rift zone of Kilauea, April 1993. Courtesy of HVO.

"On 26 February, the crater floor in Pu`u `O`o was 59 m below the spillway rim. The last 2 weeks in February, lava in the pond fluctuated between this level and ~77 m below the rim."

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: T. Mattox and P. Okubo, HVO.


Langila (Papua New Guinea) — February 1993 Citation iconCite this Report

Langila

Papua New Guinea

5.525°S, 148.42°E; summit elev. 1330 m

All times are local (unless otherwise noted)


Small Vulcanian eruptions

"Langila was more active in February than it had been since February-March 1992, with strong, sub-continuous Vulcanian activity from Crater 2, and a few days of eruptive activity at Crater 3.

"Although the volcano was covered in atmospheric clouds for the first week of the month, strong explosion and rumbling sounds from 5 February onward suggested renewed activity. When visible (after the 8th), Crater 2 displayed a dark column of ash-laden vapour that was forcefully released, convoluting and rising ~1 km above the crater. At night on 12 February, incandescent ejecta were visible in the Vulcanian eruption cloud, with ballistic trajectories rising up to 500 m above the crater. The strength of the eruption seemed to decrease after the 12th, with only night glow or mild incandescent projections 15-18 February. During the remainder of the month, Crater 2 released a steady white-gray plume of ash-laden vapour.

"Activity at Crater 3 was mild for the first half of the month, with moderate or weak emission of thin white vapour. Discrete Vulcanian explosions resumed on 12 February. By the 15th, the plume was forcefully rising several hundred meters above the crater. The plume was accompanied by strong explosion sounds and incandescent projections of increasing strength 15-18 February (maximum 400 m above crater). This activity decreased by the next day, with mainly weak white or blue vapour, and only occasional ash-laden emissions on 21-22 and 28 February.

"The seasonal NW wind carried fine ash over villages 8-18 km to the SE. Field inspection showed ~1 mm of ash accumulation in that area."

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: R. Stewart, P. de Saint-Ours, and C. McKee, RVO.


Manam (Papua New Guinea) — February 1993 Citation iconCite this Report

Manam

Papua New Guinea

4.08°S, 145.037°E; summit elev. 1807 m

All times are local (unless otherwise noted)


Weak emissions; discontinuous low-amplitude tremor

"Low-level activity continued at Manam's S crater. Emissions consisted of weak white vapour, with occasional light ash content. A weak, fluctuating glow was seen above the crater whenever atmospheric conditions allowed. The main crater released only whisps of white vapour. Seismicity throughout the month consisted of discontinuous low-amplitude tremor and low-frequency events of small amplitude. Tiltmeter measurements showed no trends."

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: R. Stewart, P. de Saint-Ours, and C. McKee, RVO.


Mayon (Philippines) — February 1993 Citation iconCite this Report

Mayon

Philippines

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

All times are local (unless otherwise noted)


Eruption continues; pyroclastic flows; lava extrusion

Eruptive activity ... continued following the 2 February eruption that killed at least 70 people (18:1). The pyroclastic flow associated with that event traveled 6 km SSE down the Bonga Gully and covered approximately 4 km2 (figure 5). The total volume of the flow, roughly 1-2 x 106 m3, is much less than that of the 1984 pyroclastic flows (30 x 106 m3). As much as half of the volume of the 2 February flow may have been pre-1993 rock that was scoured from the gully as the flow descended. Calculations based on eyewitness accounts suggest an early speed for the flow of >120 km/hour. Up to 5 mm of ash fell 9 km SW of the volcano.

Figure (see Caption) Figure 5. Sketch map showing the extent of the 2 February 1993 pyroclastic deposits. Courtesy of PHIVOLCS.

Between 2 February and 19 March, activity consisted principally of slow lava extrusion, occasional ash puffs (100-500 m high), explosions (figure 6), and small pyroclastic flows generated by the collapse of lava deposits on the steep-sloped summit (table 2). Triggered by explosions or gravity, the collapses resulted in incandescent blocks rolling down the Bonga Gully. When a larger block (103-105 m3) spalled or slumped from the front of the slowly advancing lava flow, it formed a small collapse-type pyroclastic flow that traveled as far as 4 km. Ash columns from the pyroclastic flows rose as high as 1 km above the crater unless strong winds sheared them off at a lower elevation. Such flows occurred on 12-13 February, 28 February-3 March, 10 March, and 15-17 March. On 15 March the number of explosion-type seismic signals increased and a new lava flow was observed at the summit.

Figure (see Caption) Figure 6. Explosion-type earthquake count recorded at Mayon, 1 February to 18 March 1993. Courtesy of PHIVOLCS.

Table 2. Significant events at Mayon, 6 February-19 March 1993. Courtesy of PHIVOLCS.

[Skip text table]
    Date            Time  Event
    06 February     0425  Collapse-type pyroclastic flow travels 3 km.
    10-11 February   --   Intermittent lava extrusion and formation of
                          200-m-long lava deposit.
    12 February     1126  Explosion generates a 1.5-km-high ash column.
                          Collapse-type pyroclastic flow travels 3 km.
                    1230  Explosion generates 3-km-high ash column.
                          Collapse-type pyroclastic flow travels 3 km.
                    1509  Ash ejection to 1 km.
                    1512  Ash ejection 1.5 km high; cauliflower-shaped cloud.
                    2100  Intermittent lava extrusion.
    13 February     0445  Explosion generates a cauliflower-shaped cloud 1 km
                          high. Collapse-type pyroclastic flow travels 3.5
                          km.
    17-21 to 28 February  Intermittent, slow lava extrusion; formation of
                          200-m-long lava flow.
    01 March        0659  Collapse-type pyroclastic flow travels 2.5 km.
    03 March        1530  Explosion-generated 1-km-high ash column.
                          Collapse-type pyroclastic flow travels 4 km.
    10 March        0344  Collapse-type pyroclastic flow travels 1.5 km.
    15 March        0140  Start of lava extrusion.
    15 March        2130  Collapse-type pyroclastic flow travels 1.5 km.
    15 March        2258  Collapse-type pyroclastic flow travels 1.5 km.
                    2332  Collapse-type pyroclastic flow travels 2 km.
    16 March        2303  Collapse-type pyroclastic flow travels 4 km.
    17-19 March      --   Significant increase in the rate of lava extrusion
                          at the summit. Collapse of lava becomes more
                          frequent and produces numerous small collapse-type
                          pyroclastic flows that travel 2-3 km.

COSPEC measurements of SO2 began on 3 February (figure 7). Temporary decreases to 200-400 t/d on 12-13 February and 28 February were followed by small collapse-type pyroclastic flows. Most measurements after 7 March were ground-based instead of air-based. The ground-based measurements may not record all the SO2 that air-based measurements record because no available roads allow complete, rapid circumnavigation of Mayon. On 10 March, however, the two techniques were cross-checked and their values agreed.

Figure (see Caption) Figure 7. COSPEC measurements of SO2 emission at Mayon, 31 January-18 March, 1993. Courtesy of PHIVOLCS

During the last half of February, moderate to heavy rains on the SE flank remobilized the new pyroclastic deposits and generated small lahars. All lahars remained essentially confined to the channels.

There were numerous reports of a 2-3 m drop of the water table in the vicinity of Mayon in late 1992 and January 1993 as evidenced by water wells drying or decreasing production. Local observers also stated that similar drops occurred before the 1968, 1978, and 1984 eruptions, but that those drops were not as pronounced as the current one. A climber observed an increase in rockfalls and deepening of the Bonga Gully 6 days before the 2 February eruption but did not report his observations until after the eruption. Just prior to the 1984 eruption of Mayon he had reported a bulging of the normally concave crater floor into a convex dome. A PHIVOLCS observer reported that the temperature of a crater fumarole increased from 97°C in May 1991 to 150°C in July 1992.

Stephen O'Meara observed Mayon from 27 February to 7 March and reported the following.

Three N-S-trending vents or fissures in the summit crater were visible from the ruins near the village of Cagsaua (10 km SE of the summit) on 27 and 28 February. The N vent (also the highest) was the most active. At times the vents were clearly visible; at other times the entire throat of the summit crater was filled with a large, white, cauliflower-shaped cloud that did not rise above the crater. The steam cloud appeared to contain ash on 28 February.

Winds on the morning of 1 March blew the steam plume to Legazpi City, 14 km SE of the summit. It contained a dark gray tinge and smelled of sulfur. At 0700 a slow, silent pyroclastic flow traveled down the Bonga Gully. Simultaneously, a smaller flow moved S down the Miisi Gully. The gray cloud from the Bonga flow appeared to be composed of many segments produced by frequent bursts, but this may have been an illusion caused by strong winds. Ash fell on the S flank of the volcano.

At Arimbay (approximately 2.5 km N of Legazpi City), the smell of sulfur was noticed about 5 minutes prior to the arrival of a lahar at 1530 on 3 March. The knee-deep lahar was warm but not boiling. Approximately 1.5 m of mud, stones, and boulders deposited by previous lahars blocked traffic on the Legazpi-Tabaco road in Arimbay. Also on 3 March, a pyroclastic flow, larger and darker than the one seen on 1 March, "casually" rolled down the Bonga Gully.

On 4 March a reddish brown ash cloud traveled down the Bonga Gully, but did not develop into a strong pyroclastic flow. The cloud remained confined to the upper half of the gully. At 0100 on 5 March a faint crater glow was noticed with just a "spark" coming from the N vent. One small gray ash puff occurred between 0530 and 0730 and was confined to the crater. A reddish-brown ash puff seen in the afternoon also remained in the crater. Crater glow was observed before sunrise on 6 March and a reddish-brown ash puff similar to that observed on 5 March occurred in the early morning. At approximately 0800 on 7 March a larger, darker, gray ash eruption lasted 5 minutes. Nothing traveled down the Bonga, but a tiny pyroclastic flow may have traveled S down the Miisi Gully.

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

Information Contacts: PHIVOLCS; S. O'Meara, Sky & Telescope, Belmont, MA; Chris Newhall, USGS.


Pinatubo (Philippines) — February 1993 Citation iconCite this Report

Pinatubo

Philippines

15.13°N, 120.35°E; summit elev. 1486 m

All times are local (unless otherwise noted)


Seismic activity continues

Volcanic activity continues at Pinatubo. The following summarizes activity recorded in two 24-hour periods.

For the 24-hour period starting at 0600 on 02 March, a seismometer located 9 km SE of the crater recorded 17 high-frequency volcanic earthquakes. During the same period, a seismometer on the N rim recorded 18 high-frequency and 1 low-frequency volcanic earthquakes. The seismometer on the rim continued to record the small-amplitude low-frequency harmonic tremor that began 23 February. The tremor is similar to the tremor episodes associated with the volcano's dome building activity in July 1992, and indicates vertical movement of magma. During a 24-hour period beginning at 0600 on 19 March, 16 high-frequency and 2 low-frequency events were detected by the seismometer 9 km distant, while 12 high-frequency events and no low-frequency harmonic tremor were recorded. Weak to moderate emissions of white steam reaching heights 200-500 m above the caldera rim were observed from Clark Air Base on the morning of 19 March.

Steve O'Meara observed the caldera during an overflight on 8 March (figure 29). "The SW caldera floor was covered with a kidney-bean-shaped green lake, of which a portion is stained grayish black. The discoloration might have been from recent ash deposits or from runoff entering the lake from the caldera walls (though there does not appear to be any rivulets associated with that particular section of the lake). A striking black river with golden edges cuts through the talus SE of the dome. The N caldera floor was covered with what appeared to be a fresh layer of gray ash covering the talus, which was dappled with explosion pits. A steaming, black dome complex with at least three major lobes rose above the central floor. The dome's active portion had a tall spine. Several steaming cinder cones and remnant explosion pits were visible, and one of the pits contained a green pond. The smell of sulfur gases was intense above the cinder cones."

Figure (see Caption) Figure 29. Photograph of the crater of Mount Pinatubo looking SE, 8 March 1993. Courtesy of Stephen O'Meara.

Pinatubo erupted violently in June 1991, killing more than 700 people. The Philippine Institute of Volcanology and Seismology is maintaining Alert Level 3 at Pinatubo, warning that an explosive eruption is possible. Recommendations to avoid the 10-km radius "danger zone" around the volcano remain in effect.

Geologic Background. Prior to 1991 Pinatubo volcano was a relatively unknown, heavily forested lava dome complex located 100 km NW of Manila with no records of historical eruptions. The 1991 eruption, one of the world's largest of the 20th century, ejected massive amounts of tephra and produced voluminous pyroclastic flows, forming a small, 2.5-km-wide summit caldera whose floor is now covered by a lake. Caldera formation lowered the height of the summit by more than 300 m. Although the eruption caused hundreds of fatalities and major damage with severe social and economic impact, successful monitoring efforts greatly reduced the number of fatalities. Widespread lahars that redistributed products of the 1991 eruption have continued to cause severe disruption. Previous major eruptive periods, interrupted by lengthy quiescent periods, have produced pyroclastic flows and lahars that were even more extensive than in 1991.

Information Contacts: PHIVOLCS; Stephen O'Meara, Sky & Telescope, MA.


Poas (Costa Rica) — February 1993 Citation iconCite this Report

Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


Fumarolic activity continues

Fumarolic activity continued in the N part of the crater lake with gas columns that rose 500 m. The most active fumaroles inside the crater were generally located on terraces near the N side of the lake and produced sounds like an airplane. There were six fewer hot mud and sulfur springs in the thermal area on the SE side of the lake. Phreatic eruptions from areas SE and N of the lake ejected material to 1 m height. Dome fumarole temperatures in February were 80-89°C. A fumarole on the N side of the lake had a temperature of 90°C, and the gas condensate had a pH of 1.7. The turquoise-green lake was more yellow near the shore because of sulfur deposition. Lake temperature was 70-75°C, and the pH ranged from near zero to 1.1 in February. The lake surface has decreased 50 cm since January.

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: G. Soto and R. Barquero, ICE; E. Fernández and J. Barquero, OVSICORI.


Popocatepetl (Mexico) — February 1993 Citation iconCite this Report

Popocatepetl

Mexico

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

All times are local (unless otherwise noted)


Increased fumarolic activity; seismicity remains low

Increased fumarolic activity was observed from 4,500 m elevation during routine deformation studies on 25 February. A dilute white column, roughly the diameter of the summit crater, could be seen gently rising from the crater. The column was deflected by the wind immediately above the crater, even at low wind levels, and occasionally descended the flanks of the volcano, mainly to the NE. Snow on the NE crater rim was somewhat darkened, probably due to a wetting effect of the plume. The plume appeared to be mostly water vapor, with an occasional smell of sulfur. Tourists that have climbed to the summit reported that the crater is filled with a fog-like cloud, and there is a very strong smell of sulfur. The telemetered seismic station located at Tlamacas (4,000 m elevation on the NW flank) has recorded only normal background levels of seismicity, similar to those observed during the past three years. Based on current information, geologists believe that the increased fumarolic activity may be related to increased rainfall feeding the hydrothermal system. Installation of a third telemetered seismic station will be completed in the next few months. No change in fumarole activity was observed during fieldwork on 11 March, and seismic activity was low and within background levels.

Geologic Background. Volcán Popocatépetl, whose name is the Aztec word for smoking mountain, rises 70 km SE of Mexico City to form North America's 2nd-highest volcano. The glacier-clad stratovolcano contains a steep-walled, 400 x 600 m wide crater. The generally symmetrical volcano is modified by the sharp-peaked Ventorrillo on the NW, a remnant of an earlier volcano. At least three previous major cones were destroyed by gravitational failure during the Pleistocene, producing massive debris-avalanche deposits covering broad areas to the south. The modern volcano was constructed south of the late-Pleistocene to Holocene El Fraile cone. Three major Plinian eruptions, the most recent of which took place about 800 CE, have occurred since the mid-Holocene, accompanied by pyroclastic flows and voluminous lahars that swept basins below the volcano. Frequent historical eruptions, first recorded in Aztec codices, have occurred since Pre-Columbian time.

Information Contacts: S. De la Cruz-Reyna and H. Nolasco, Instituto de Geofísica, UNAM, Ciudad Universitaria, Delegación de Coyoacán; E. Ramos, CENAPRED.


Rabaul (Papua New Guinea) — February 1993 Citation iconCite this Report

Rabaul

Papua New Guinea

4.271°S, 152.203°E; summit elev. 688 m

All times are local (unless otherwise noted)


Seismicity remains low; no significant deformation

"Seismic activity remained low in February; 256 caldera earthquakes were recorded . . . . Only four of February's earthquakes were located. They occurred in the W (2), SW, and SE parts of the caldera seismic zone. Routine monthly leveling in the caldera showed no significant changes compared to January."

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: R. Stewart, P. de Saint-Ours, and C. McKee, RVO.


Rincon de la Vieja (Costa Rica) — February 1993 Citation iconCite this Report

Rincon de la Vieja

Costa Rica

10.83°N, 85.324°W; summit elev. 1916 m

All times are local (unless otherwise noted)


Gas plumes rise to 500 m; lake level drops

Fumarolic activity continued from the E wall of the active crater, with gas plumes rising 500 m. A strong smell of sulfur near the crater caused eye and skin irritation. Gas vents in the SE and SW parts of the crater had disappeared. Small collapses had occurred along the E and NE crater walls.

The level of the crater lake has dropped 1 m since last year. The light-gray colored lake had a temperature of 35°C in February and a pH of 1.6. The number of floating sulfur patches has decreased, and only one small bubbling area remains, producing very small intermittent bubbles.

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. Fernández and J. Barquero, OVSICORI.


Ruapehu (New Zealand) — February 1993 Citation iconCite this Report

Ruapehu

New Zealand

39.28°S, 175.57°E; summit elev. 2797 m

All times are local (unless otherwise noted)


Little change in crater lake; episodes of tremor

Fieldwork on 17 February revealed little change compared to previous visits. The lake was pale gray-green with a large area of brownish discoloration over the N vent area, where several convection cells were apparent. Blue-green meltwater around the N and W margins increased in area during the day. There was no shoreline evidence of recent surging. Following a decline in January, the lake temperature had increased from 21°C (measured on 12 January) to 24°C. Over the same period the lake outflow decreased from 100 l/s to 90 l/s. The Mg/Cl ratio in the lake water has remained essentially constant since December (table 3), after reaching a low of 0.042 in September.

Table 3. Temperature, outflow measurements, and water analyses from the crater lake of Ruapehu, 21 December 1992 to 10 December 1993. Discharge is in liters/second (l/s). Discharge of "0" indicates a lake level below overflow stage. A dash (--) signifies no measurement. (The low Mg and Cl values on 11 January were due to excessive meltwater dilution. Analyses done by M.E. Crump). Courtesy of IGNS.

[Skip text table]
    Date       Outlet  Logger Point  Discharge   Mg     Cl    Mg/Cl
                (°C)       (°C)        (l/s)    (ppm)  (ppm)

    21 Dec 92    --         --          --       311   6731   0.046
    11 Jan 93    --         --          --       273   5947   0.046
    17 Feb 93    --         --          --       299   6674   0.045
    03 Jun 93   14.0       16.5         <1       282   6403   0.044
    18 Jun 93   10.9       13.0         30       273   6194   0.044
    03 Jul 93   11.2       12.5         --       277   6267   0.044
    06 Aug 93   19.6        --          85       277   6404   0.043
    21 Sep 93   35.5        --          25       283   6753   0.042
    29 Sep 93   38.2        --           0       282   6883   0.041
    09 Oct 93   35.5        --           0       294   7016   0.042
    04 Nov 93   37.2       39.0          0       296   7233   0.041
    10 Dec 93   26.0        --           0       293   7175   0.041

EDM measurements revealed no long-term movements of volcanic significance. A key benchmark, buried by snow since July, was exhumed. Its burial prevented detection of any short-term inflationary changes.

The crater was revisited 28 February-2 March to install telemetry equipment. The lake initially appeared unchanged from 17 February, but by 2 March it was a uniform gray. Outflow was estimated to be 140 l/s. Lake temperatures of 28-29°C measured near the telemetry equipment were similar to the 29.2°C telemetered via ARGOS on 4 March.

Seismicity was generally low with some volcanic earthquakes recorded. Strong tremor was recorded 9-10 January and moderate tremor on 25-28 February.

Geologic Background. Ruapehu, one of New Zealand's most active volcanoes, is a complex stratovolcano constructed during at least four cone-building episodes dating back to about 200,000 years ago. The 110 km3 dominantly andesitic volcanic massif is elongated in a NNE-SSW direction and surrounded by another 100 km3 ring plain of volcaniclastic debris, including the Murimoto debris-avalanche deposit on the NW flank. A series of subplinian eruptions took place between about 22,600 and 10,000 years ago, but pyroclastic flows have been infrequent. A single historically active vent, Crater Lake, is located in the broad summit region, but at least five other vents on the summit and flank have been active during the Holocene. Frequent mild-to-moderate explosive eruptions have occurred in historical time from the Crater Lake vent, and tephra characteristics suggest that the crater lake may have formed as early as 3000 years ago. Lahars produced by phreatic eruptions from the summit crater lake are a hazard to a ski area on the upper flanks and to lower river valleys.

Information Contacts: P. Otway, IGNS Wairakei.


Spurr (United States) — February 1993 Citation iconCite this Report

Spurr

United States

61.299°N, 152.251°W; summit elev. 3374 m

All times are local (unless otherwise noted)


Low seismic activity; level of concern reduced from Yellow to Green

Because of continued low seismicity, on 5 March 1993 the Alaska Volcano Observatory downgraded its Level of Concern Color Code for Spurr from Yellow to Green. Seismicity has remained low since December 1992, longer than the quiet period between the 27 June and 18 August 1992 eruptions. Between 12 February and 12 March 1993 two or fewer events/day were recorded. Measurements on 18 February of CO2 (400 tons/day) and SO2 (none detected) were similar to those made in early January. Visual inspection of Crater Peak between 12 and 19 February showed no significant morphological changes to the crater area, although one large slab of glacial ice is detaching from the outer NE flank. It may produce a significant seismic signal if it fails suddenly.

Spurr was last at color code green from 8 July to 18 August 1992. Green indicates that the "volcano is in its normal 'dormant' state." The observatory did warn that "the possibility for steam and ash explosions still exists. Should such explosions occur, they are unlikely to pose a hazard to high-flying aircraft or to communities downwind."

Geologic Background. The summit of Mount Spurr, the highest volcano of the Aleutain arc, is a large lava dome constructed at the center of a roughly 5-km-wide horseshoe-shaped caldera open to the south. The volcano lies 130 km W of Anchorage and NE of Chakachamna Lake. The caldera was formed by a late-Pleistocene or early Holocene debris avalanche and associated pyroclastic flows that destroyed an ancestral edifice. The debris avalanche traveled more than 25 km SE, and the resulting deposit contains blocks as large as 100 m in diameter. Several ice-carved post-caldera cones or lava domes lie in the center of the caldera. The youngest vent, Crater Peak, formed at the breached southern end of the caldera and has been the source of about 40 identified Holocene tephra layers. Spurr's two historical eruptions, from Crater Peak in 1953 and 1992, deposited ash on the city of Anchorage.

Information Contacts: AVO.


Stromboli (Italy) — February 1993 Citation iconCite this Report

Stromboli

Italy

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

All times are local (unless otherwise noted)


Seismicity and tremor resume after 10 February explosions

Seismicity between 1 November 1992 and 28 February 1993 was stable except for two episodes of heightened activity (figure 28). High tremor energy and >25 explosion-earthquakes/hour were recorded on 6 December. On 10 February, three strong explosions occurred followed by a sudden decrease of tremor to about one-sixth the energy and one-third the number of events. In the week preceding the 10 February explosions, a large number of strong shocks occurred, with a maximum of 76 on 7 February. After a few days of low seismicity following the explosions, tremor amplitude and the number of events gradually increased, reaching an isolated maximum on 22 February.

Figure (see Caption) Figure 28. Seismicity recorded at Stromboli, November 1992-February 1993. Open bars show the number of recorded events/day, the solid bars those with ground velocities >100 mm/s. The lines show daily tremor energy computed by averaging daily 60-second samples. Courtesy of M. Riuscetti.

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 from about 13,000 to 5000 years ago was followed by formation of the modern edifice. The active summit vents are located at the head of the Sciara del Fuoco, a prominent horseshoe-shaped scarp formed about 5000 years ago as a result of the most recent of 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: M. Riuscetti, Univ di Udine.


Ulawun (Papua New Guinea) — February 1993 Citation iconCite this Report

Ulawun

Papua New Guinea

5.05°S, 151.33°E; summit elev. 2334 m

All times are local (unless otherwise noted)


Activity continues to decline; glow observed in crater

"Activity . . . continued to decline following the brief phreatic or phreatomagmatic activity in mid-January (BGVN 18:01). However, activity is still above normal levels. Emissions throughout the month consisted of white vapour, in weak to moderate volumes. Blue vapour was seen occasionally. A steady weak night glow was seen 14-18 February. There were also unconfirmed reports of glow at other times during February.

"Seismic activity consisted of low-level, sub-continuous tremor with almost no discrete B-type events. The CVO's RSAM (Real-time Seismic Amplitude Measurement) system was deployed at the end of January to monitor tremor levels. From 29 January until 6 February the tremor level declined markedly. The system was inoperative until 17 February, when the tremor level was about the same as on the 6th. Helicorder readings indicated that tremor level was fairly constant from the 6th until the end of the month. This level of tremor is lower, by a factor of 2-3, than that seen during the peak of activity in mid-January and is comparable to the levels seen in early January.

"An aerial inspection on 18 February gave a reasonably clear view of the base of the crater. The source of the glow, on the E side of the crater, could not be seen directly. Only the glow's reflection on the walls of a vent at the crater base was seen. It was not possible to say whether this has changed since the last observation in January, but no other features in the crater have changed.

"EDM and dry-tilt surveys were carried out from 16-19 February. The EDM surveys showed little change since the last survey in September 1992, although there was some evidence of inflation at two stations high on the flanks. Dry-tilt results from two stations (S. Ridge and NW Valley, respectively 3 and 6.2 km from the summit) showed radial inflation of 25 and 17 µrads since September. Changes at three other stations were not conclusive."

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 north coast of the island of New Britain across a low saddle NE of Bamus volcano, the South Son. The upper 1000 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: R. Stewart, P. de Saint-Ours, and C. McKee, RVO.


Unzendake (Japan) — February 1993 Citation iconCite this Report

Unzendake

Japan

32.761°N, 130.299°E; summit elev. 1483 m

All times are local (unless otherwise noted)


Dome complex continues to grow; large pyroclastic flow

Dome 10 . . . grew at a faster rate (1-2 x 105 m3/day) than the dome complex grew during November-January. This rate, nearly equal to the magma supply rate, is less than half of the maximum value recorded at Unzen of ~ 5 x 105 m3/day. The dome is significantly less silicic, 63.5 wt.% SiO2, than the earlier domes, which had 65 wt.% SiO2. It eventually covered the gas-emitting sites and most of the remaining surfaces of domes 1 and 3 in the topographically lower area to the N. Because dome 10 grew on the nearly flat surface of the older domes (figure 49), collapses seldom occurred, and the observed frequency of pyroclastic flows and the monthly total of seismically recorded pyroclastic flows remained low (figure 50). Relatively large collapses, though still less than 5 x 105 m3 in volume, started just after the dome began overflowing the top. During February, pyroclastic flows traveled ~ 2 km to the E, NE, and SE.

Figure (see Caption) Figure 49. NE-looking view of the lava dome complex at Unzen based on theodolite measurements October 1992-March 1993. Courtesy of Setsuya Nakada.
Figure (see Caption) Figure 50. Daily count of earthquakes (top) and pyroclastic flows (bottom) at Unzen, 1 January 1991 to 8 March 1993. The 10 longer arrows at the top mark the onset of each of the domes; the short arrow indicates a phreatic eruption. Courtesy of JMA.

A pyroclastic flow at 1642 on 9 March descended between two wings of dome 4 (figure 48). Part of the flow traveled 3.5 km E into the Mizunashi Valley. The other part traveled NE through the Oshiga Valley with an overflow out of the valley to the N. The remainder moved to the SE, eventually rejoining the Mizunashi Valley flow. It was the longest flow since 20 December and the first flow to pass through the Oshiga Valley since 15 September 1991, that flow being the largest of the current eruption. The seismic duration of the 9 March flow, 190 seconds, was the longest since 15 January. The flow remained in the evacuated area and caused no damage although a section of highway, 6 km E of the volcano, was temporarily closed. The ash cloud from the flow rose 1.5 km above the summit, the highest since April 1992. Ash fell heavily on the E foot of the volcano in Shimbara and Fukae. Kumamoto, 40 km E, received a small ashfall. Additional pyroclastic flows occurred 12 March.

The steam plume, occasionally mixed with ash, continued to rise a few hundred meters above the dome complex. The height has gradually declined since the summer of 1991 (figure 51). Mid-February work by the Tokyo Institute of Technology indicated that the SO2 flux from the dome complex remained at the low level measured at the end of 1992 (during endogenous growth) and the temperature of gases in the crater was as high as 800°C.

Figure (see Caption) Figure 51. Monthly mean height of the continuous steam plume from Jigokuato crater, Unzen, January 1991 to February 1993. The arrow indicates the onset of dome growth. Courtesy of JMA.

The number of small earthquakes beneath the dome complex declined rapidly in early February and has remained low (figure 50). The monthly total of recorded earthquakes dropped from more than 3,000 to 542. Seismicity around the volcano remained low.

Geologic Background. The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

Information Contacts: JMA; S. Nakada, Kyushu Univ.

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 Atmospheric Effects


The enormous aerosol cloud from the March-April 1982 eruption of Mexico's El Chichón persisted for years in the stratosphere, and led to the Atmospheric Effects section becoming a regular feature of the Bulletin. Descriptions of the initial dispersal of major eruption clouds remain with the individual eruption reports, but observations of long-term stratospheric aerosol loading will be found in this section.

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 Special Announcements


Special announcements of various kinds and obituaries.

View Special Announcements Reports

 Additional Reports


Reports are sometimes published that are not related to a Holocene volcano. These might include observations of a Pleistocene volcano, earthquake swarms, or floating pumice. Reports are also sometimes published in which the source of the activity is unknown or the report is determined to be false. All of these types of additional reports are listed below by subregion and subject.

Kermadec Islands


Floating Pumice (Kermadec Islands)

1986 Submarine Explosion


Tonga Islands


Floating Pumice (Tonga)


Fiji Islands


Floating Pumice (Fiji)


Andaman Islands


False Report of Andaman Islands Eruptions


Sangihe Islands


1968 Northern Celebes Earthquake


Southeast Asia


Pumice Raft (South China Sea)

Land Subsidence near Ham Rong


Ryukyu Islands and Kyushu


Pumice Rafts (Ryukyu Islands)


Izu, Volcano, and Mariana Islands


Acoustic Signals in 1996 from Unknown Source

Acoustic Signals in 1999-2000 from Unknown Source


Kuril Islands


Possible 1988 Eruption Plume


Aleutian Islands


Possible 1986 Eruption Plume


Mexico


False Report of New Volcano


Nicaragua


Apoyo


Colombia


La Lorenza Mud Volcano


Pacific Ocean (Chilean Islands)


False Report of Submarine Volcanism


Central Chile and Argentina


Estero de Parraguirre


West Indies


Mid-Cayman Spreading Center


Atlantic Ocean (northern)


Northern Reykjanes Ridge


Azores


Azores-Gibraltar Fracture Zone


Antarctica and South Sandwich Islands


Jun Jaegyu

East Scotia Ridge


 Additional Reports (database)


08/1997 (BGVN 22:08) False Report of Mount Pinokis Eruption

False report of volcanism intended to exclude would-be gold miners

12/1997 (BGVN 22:12) False Report of Somalia Eruption

Press reports of Somalia's first historical eruption were likely in error

11/1999 (BGVN 24:11) False Report of Sea of Marmara Eruption

UFO adherent claims new volcano in Sea of Marmara

05/2003 (BGVN 28:05) Har-Togoo

Fumaroles and minor seismicity since October 2002

12/2005 (BGVN 30:12) Elgon

False report of activity; confusion caused by burning dung in a lava tube



False Report of Mount Pinokis Eruption (Philippines) — August 1997

False Report of Mount Pinokis Eruption

Philippines

7.975°N, 123.23°E; summit elev. 1510 m

All times are local (unless otherwise noted)


False report of volcanism intended to exclude would-be gold miners

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

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

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

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

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

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

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

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

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


False Report of Somalia Eruption (Somalia) — December 1997

False Report of Somalia Eruption

Somalia

3.25°N, 41.667°E; summit elev. 500 m

All times are local (unless otherwise noted)


Press reports of Somalia's first historical eruption were likely in error

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

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

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

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


False Report of Sea of Marmara Eruption (Turkey) — November 1999

False Report of Sea of Marmara Eruption

Turkey

40.683°N, 29.1°E; summit elev. 0 m

All times are local (unless otherwise noted)


UFO adherent claims new volcano in Sea of Marmara

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Information Contacts: Erol Erkmen, Tuvpo Project Alp.


Har-Togoo (Mongolia) — May 2003

Har-Togoo

Mongolia

48.831°N, 101.626°E; summit elev. 1675 m

All times are local (unless otherwise noted)


Fumaroles and minor seismicity since October 2002

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


Elgon (Uganda) — December 2005

Elgon

Uganda

1.136°N, 34.559°E; summit elev. 3885 m

All times are local (unless otherwise noted)


False report of activity; confusion caused by burning dung in a lava tube

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

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

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

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

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

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

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