Subject: Komaga-take Eruption, 5 March 1996
From: Global Volcanism Network mnhms017@sivm.si.edu
Date: Wed, 6 Mar 1996 08:54:19 MST
The following information obtained by the Global Volcanism Network is preliminary and subject to change.
In addition to the reports below, Jon Dehn (at the Geological Survey of Japan in Hokkaido) informed us that there were many helicopter flights to observe the activity on the morning of 6 March, and that the activity appears to be primarily phreatic.
The following report is from the Volcano Research Center (Univ of Tokyo) Web
site.
For the most recent updates and a photographs of the volcano
Five minutes-long volcanic tremor occurred in 18:10 JST on 5 March 1996, according to the Usu Volcano Obsevatory (UVO), Hokkaido University. More than 10 small volcanic earthquakes occurred this day, more frequent than usual days at this volcano. Ash falling was observed on the southern flank of the volcano, more than 10 km from the summit. Local people recognized white-colored eruption plume rising from a fissure of the 1929 eruption in the night. Japan Meteorological Agency (JMA) also reported around 150-m-high white plume rising above the summit in the 6 March morning. This volcano has been monitored by both UVO and JMA. No obvious precursor phenomena of this small eruption had been detected. Volcanic tremor has not been observed since the 5 March evening (as of 6 March noon).
Hokkaido-Komagatake, or Komagatake (Hokkaido), Volcano is located 30 km north of Hakodate City, with a population of 320,000. This is an andesite stratovolcano (1,133 m high) whose summit has a 2 km-wide horseshoe-shaped caldera open to the E, resulted from large collapse 30-40 ka. Large-scale pumice-flow eruptions had occurred several times from craters within the caldera, including three historical major eruptions; 1640, 1856, and 1929.
In the 1640 eruption, the summit part collapsed and the avalanche entered into sea, resulting in the generation of tsunami, killing 700 people. In 1929, a one-day eruption issued 0.38 km^3 of ash falls and 0.14 km^3 of pumice flows; 2 killed and 4 injured. The eruption column height was 14 km. The pumice flows descended in all directions, reached about 8 km from the summit. Major eruptions at this volcano are characterized by very short activity duration (less than several days). The latest eruption took place in moderate-scale, such that eruption column reached 8 km above, in 1942.
An aviation notice (NOTAM) was posted from Tokyo (see below).
RJTD A1365/1996 NOTAMN : INVALID
AFTN MESSAGE HEADING
BNA0323 052223
GG YBBBYNYX
052221 RJAAYNYX
AFTN MESSAGE TEXT
A1365/96 NOTAMN
Q)RJCG/QWWXX/IV/NB/EW/038/043/4204N14041E001
A)RJTD B)9603052050 C)9603060250
E)
TOKYO FIR
VOLCANIC ACTIVITY INFO MT.HOKKAIDOKOMAGATAKE(AIP RAC9-10 NR12)
MT.HOKKAIDOKOMAGATAKE 420339N1404051E ERUPTED AT 9603052050
VOLCANIC ASH CLOUD TOP :4209FT
DRIFT DIRECTION :UNKNOWN
F)3717FT G)4209FT