Photograph courtesy of and copyrighted by Paul
The 24-km-wide Aso caldera was formed during four major explosive eruptions
to 80,000 years ago. These produced voluminous pyroclastic flows that
covered much of Kyushu.
A group of 17 central cones was constructed in the middle of the caldera,
one of which,
Naka-dake, is one of Japan's most active volcanoes. It was the location
of Japan's first
documented historical eruption in 553 AD. The Naka-dake complex has
throughout the Holocene. Several other cones have been active during
including the Kometsuka scoria cone as recently as about 210 AD.
Historical eruptions have largely consisted of basaltic to basaltic-andesite
ash emission with
periodic strombolian and phreatomagmatic activity. The summit crater
of Naka-dake is accessible
by toll road and cable car, and is one of Kyushu's most popular tourist
As of the 29th of July, the Global Volcanism Network (GVN) and the Japanese
Agency (JMA) has reported that Aso Volcano on the afternoon of 28 July
2003 had a continuous
volcanic tremor event started around 2 p.m. 27 July. The same event
had not been observed afte
r November 1995. Though the daily number of volcanic quakes ranges around
10, that of isolated
tremor around 100 since 23 July. This day, water of crater lake in the
Crater 1 was gray in colour,
and the temperature was 76 C. Boiling was observed in the centre. JMA
had observed seismic
signals implying small phreatic eruptions 5 times during 12-14 July.
Geologists surveyed the deposit of the 10 July eruption on the following
day, and estimated
the total mass of eject as about 130 t. Ash was deposited as distant
as 14 km EWE of the
crater. They confirmed small amount of fresh vesicular glass particles
in the ejecta under the
microscope. They posed a possibility that the juvenile material may
be related to the eruption.
crater. Believe the signs means something like 'STAY AWAY!'
of the Aso-crater. One of the many cones may be seen in the foreground.
courtesy of and copyrighted by Paul
there is rich