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31
July 2000
TWO VOLCANOLOGISTS KILLED ON INDONESIA'S SEMERU
A minor explosive
eruption at the summit crater of Semeru
volcano on the Indonesian island of Java killed two Indonesian volcanologists
and injured three American and one Israeli volcanologists on 27 July.
Press sources did not give the names of the two Indonesiand who died,
but the names of the injured were released. Among the Americans is Lee
Siebert of the Smithsonian Institution in Washington, D.C., specialized
on volcanic debris avalanches and co-author of world-famed books like
"Volcanoes of the World". The other two Americans are Paul Kimberly
and Mike Ramsey, of which the earlier received somewhat heavier injuries
and had to be brought to a hospital in Singapore. Bad weather prevented
rescue teams from reaching the dead and injured for one day, and the corpses
of the two dead Indonesians could be retrieved only on 31 July.
Semeru is one of the most persistently active volcanoes of the world.
Minor explosive eruptions occur frequently at its summit crater, some
being accompanied by pyroclastic flows. However, it appears that the scientists
at the were hit by flying rock fragments. In recent years, almost all
fatalities related to volcanic activity have occurred in similar manner
- simply because people came too close to active craters. In all cases
the lethal eruptive events were very small on a geological scale. The
most recent case of volcanologists killed by an eruption was in March
1993, when two Ecuadorian volcanologists were killed by a small phreatic
explosion at Guagua Pichincha volcano in their home country.
In Japan, geophysical unrest has continued at the volcanic island of Miyakejima.
Two strong earthquakes (measuring 5.4 and 6.2 on the Richter scale) shook
the island on 30 July, causing landslides and minor damage, and injuring
one person. The volcano on the island remained quiet. In the first half
of July, the summit crater of Oyama volcano, the central peak of the island,
had collapsed to form a small caldera more than 400 m deep. This was accompanied
by spectacular emissions of gray ash, whose volume was estimated at about
10 million cubic meters. Japanese volcanologists observed several episodes
of deflation alternating with inflating during that period; however no
magma appears to have come close to the surface. Tens of thousands of
minor and about a dozen larger earthquakes have shaken Miyakejima and
neighboring islands since late June, and a possible submarine eruption
occurred off the W side of Miyakejima on 27 June. Many residents of the
island have left their homes. Scientists are expecting further earthquakes
in the area.
In Chile, two volcanoes erupted in early and mid July: Copahue
volcano, in the central area of the country, and Làscar,
which lies much further to the north. Both eruptions were quite spectacular
and caused ash falls to the east, in neighboring Argentina. While the
Làscar eruption was apparently one single explosive event, the
eruptions at Copahue were more prolonged, and Chilean volcanologists described
them as the most intense ever observed at that volcano.
On the island of Réunion in the Indian Ocean, Piton
de la Fournaise volcano was in eruption from 23 June to 30
July. Lava flowed to the east from a new crater, around which a large
cone was built by mild lava fountaining and Strombolian activity. This
cone was named Piton P�rv�di. This is the longest eruption at this volcano
since the long-lived Piton Kapor eruption in March-September 1998. Three
shorter eruptions had occurred in July and September 1999, and February-March
2000.
15
July 2000
MORE ERUPTIONS ON MIYAKEJIMA
The summit
crater of Oyama volcano on the Japanese island of Miyakejima
has been the site of further explosive (probably phreatic) eruptions on
14 and 15 July, which appear to have been associated with ongoing episodic
subsidence in the summit area of the volcano. The most recent ash emissions
were much stronger than that of 8 July, when collapse occurred for the
first time, triggering the venting of lithic ash. Japanese television
showed footage of billowing dark gray ash plumes which are strikingly
similar to those emitted at Usu volcano (on the Japanese island of Hokkaido)
earlier this year. The ash was blown over the northern sector of the island
where it left a deposit which appears quite voluminous on press photos;
some Japanese web sites dedicated to the Miyakejima crisis show photos
of lithic blocks up to 20 cm in diameter, which created impact craters.
Some residents of the affected area were evacuated.
The Oyama subsidence with the associated ash emissions occurred within
a framework of much more widespread geophysical unrest, affecting the
northern part of the Izu island chain within which Miyakejima is located.
Intense seismic activity has affected that area since the beginning of
volcanic unrest on Miyakejima in late June, including several earthquakes
with magnitudes above 6 on the Richter scale. The latest strong shock
with its epicenter near the small islands of Kozushima and Niijima (located
to the NNW of Miyakejima) occurred on 15 July and triggered numerous rockfalls
on these islands already affected by similar events in the past three
weeks. Press sources reported that 8 people were injured.
On the Chile-Argentina border, eruptive activity is continuing since late
June at Copahue volcano. Thirteen
explosive ash emissions were observed since 14 July in the latest spasm
of activity, which followed several days of minor activity. The eruption
column reportedly rose up to 5 km high, and ash fell up to 60 km away
to the E in Argentina. Chilean volcanologists remarked that the eruption
is the most vigorous known of Copahue which last erupted in 1992.
Explosive volcanism has also been reported in the past few days from Guagua
Pichincha volcano, Ecuador, where a portion of a lava dome
formed several months ago failed, and at Popocatépetl
volcano in Mexico.
9
July 2000
OYAMA ON MIYAKEJIMA ERUPTS; NUMEROUS EARTHQUAKES
On the Japanese
island of Miyakejima, a short-lived,
small eruption occurred on the late afternoon of 8 July at the summit
crater of Oyama volcano. This event consisted of a single pulse of gas
and ash emission, and all ejecta appear to be old lithic material. This
indicates that no fresh magma has been involved in the event. Aerial photographs
taken the morning after show that the entire area of the summit crater
- which actually consists of a miniature caldera with a small central
cone formed in 1940 - has subsided notably. The ash emission may have
been caused by the subsidence, which in turn may be a result of magma
withdrawing at depth. Magma evidently intruded into the volcano on 26-27
June but did not reach the surface on the island; an area of bubbling
and steaming water was discovered on 27 June off the W coast of the island.
So far it is not clear whether this was the effect of a small eruption
on the submarine slope of the volcano, or if it was only caused by submarine
gas emissions from a fracture caused by magmatic intrusion.
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Crater
of Oyama, Miyakejima island, Japan - 9 July 2000
Two aerial
views of the summit crater of Oyama volcano on Miyakejima island,
Japan, taken on the morning of 9 July 2000. That crater was the
site of a small and short-lived ash emission on the previous afternoon.
The upper photo shows a streak of ash extending over the upper NE
flank of the volcano and covering vegetation (foreground). Black
lava from the 1983 SW flank eruption can be seen in the upper left
part of the photo. The photo below shows more detail of the crater,
which evidently subsided notably sometime during or after the 8
July ash emission. Subsidence has occurred two concentric areas,
of which the inner one includes the small central cone formed during
the 1940 eruption
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The ash emission
at Oyama was followed a few hours later by a magnitude 6 earthquake, whose
epicenter lay near the volcanic island of Kozushima, NW of Miyakejima.
On that island numerous landslides occurred. During the past 10 days,
the area between Kozushima and Miyakejima has been shaken by more than
30,000 earthquakes, some of which were quite powerful. The strongest earthquake,
with a magnitude of 6.4, occurred on 1 July, causing numerous landslides
on Kozushima. One man was buried in his car and killed by one of the landslides.
About half of the population of the island was evacuated because more
earthquakes were expected. The situation at the Izu islands became even
more difficult in the past few days due to the passage of a typhoon, which
had caused damage in the Philippines before and swept over Japan and Taiwan,
causing deaths and destruction.
On Miyakejima, about 2000 residents had been evacuated in late June because
of the fear of an impending eruption; they were later allowed to return
home. The single ash emission from Oyama on 8 July is not interpreted
as related to new magma movement towards the surface, and residents were
only advised to keep an eye on the volcano, since it could not be totally
excluded that it will still erupt.
27
June 2000
MIYAKEJIMA ERUPTS BELOW SEA LEVEL; EVACUATIONS
Following
a dramatic increase in seismic activity on late 26 June, residents of
the southwestern part of the small volcanic island of Miyakejima,
located in the Pacific about 200 km SSW of Tokyo in Japan, were ordered
to evacuate because it was feared that an eruption was imminent on the
island. Furthermore ground cracking, an increase of the ground temperature,
and a small landslide (possibly triggered by the seismic activity) were
detected. Volcanologists supposed that the eruption could occur on the
W flank of Oyama, the central cone of the volcano that forms the island.
Through the night of 26-27 June, about 2500 residents were evacuated from
areas believed to be at risk, some to the N part of the island, and others
were brought by ships to the mainland of Honshu, the largest of the four
main islands of Japan.
On the morning of 27 June, the volcano apparently became active. However,
rather than erupting somewhere on the island, it did so on the submarine
W flank, about 1.8 km from the W coast. Discolored sea water and steaming
was observed at that site, both from a ship passing nearby and from airplanes
flying over the area. Scientists voiced concern that more eruptive vents
might open closer to the island or at the coast and produce violent phreatomagmatic
explosions, caused by the contact of magma with sea water.
Miyakejima is the second largest of the Izu islands that extend from the
Bay of Tokyo to the S (the largest of these islands is Izu-Oshima, with
its famous volcano Mihara) and has a long record of historical eruptions.
During the 20th century there were three eruptions, in 1940, 1962 (both
in the same area on the NE flank) and 1983 (on the SW flank). All three
caused extensive damage, and in the case of the 1940 eruption 11 people
were killed. Lava flows of the 1983 eruption destroyed one village almost
entirely, while many other buildings were damaged by heavy tephra falls.
Miyakejima is the second volcano in Japan to force evacuations this year.
In late March and early April, Usu on the northern island of Hokkaido
began a new phase of phreatic and phreatomagmatic eruptions accompanied
by significant ground uplift. Small phreatic eruptions are continuing
to the present day. Several buildings have been damaged by the fall of
lithic blocks and by fracturing of the ground.
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Discolored,
steaming sea water off the W coast of Miyakejima island is shown in
this press photo taken on 27 June 2000 from a helicopter. The coast
of the island is seen in the background. Eruptive activity may have
taken place on the submarine flank of the volcano, which had its last
eruption in 1983. |
During
the past few weeks several other volcanoes had significant eruptions.
On 30 May an eruption started in the summit area of Mount
Cameroon, following a series of earth tremors. A lava flow
advanced several kilometers, approaching to the village of Bokwango, but
by mid June the speed of the lava flow slowed significantly, and a few
days later it seems that the activity ended. Mount Cameroon had last erupted
in April-May 1999 when a voluminous lava flow stopped only a few hundred
meters from the Atlantic coast.
On 23 June a new effusive eruption began on the SE flank of Piton
de la Fournaise on the island of Réunion in the Indian
Ocean, emitting lava flows to the E; one flow rapidly reached a length
of 5 km. This eruption, which came only three months after the latest
eruption of that volcano, was preceded by vigorous seismicity, and scientists
had warned of an imminent eruption. So far the eruption does not present
any hazard to inhabited areas on the island.
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