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Hokkaido-Komagakate

koma2.gif Hokkaido-Komagatake
42.06N, 140.68E
1133m

Southeast view of Hokkaido-Komagatake
Photo by T.Soya







Komagatake in summer is here.

Outline

Hokkaido-Komagatake is located 30 km north of Hakodate City in the southern Hokkaido island. It is a pyroxene andesite stratovolcano. At the summit, there is a 2km wide horseshoe shaped caldera opening to the east. The edifice extends 17km in diameter at the foot, and is mostly covered by historic or prehistoric pyroclastic falls, flows and surges. There are also debris avalanche deposits around the volcano. They have many hummocks and, in the southern foot of the volcano, form dammed lake, O-numa, Ko-numa and so on.

The main stratovolcano edifice that consists of andesite lava and pyroclastics were formed several ten thousand (40-30 ka) years ago (Stage I).

After that stage, the activities of the volcano were becoming more explosive. Stage II activity started with the collapse of the summit and formed Komagatake Debris Avalanche Deposit (30-23ka). Subsequently, Plinian eruptions accompanying with pyroclastic flows occurred twice until 17ka. At 6ka and 3ka, Stage III activities were Plinian Eruptions with pyroclastic flows.

In Stage IV, historical records of the large eruptions are recorded in 1640, 1694, 1856, 1929 (see Table). These eruptions were Plinian eruptions with pyroclastic flows. It is characteristic that the precursors of eruption were recognized just before the eruptions (one day or several hours before) and the eruptions were become quiet in several days.

Historical Records of the Hokkaido-Komagatake

1640 Large EruptionD
Collapse of the edifice, Kurumi-sawa Debris avalanche, Tsunami killed over 700 people. Ko-d pumice fall and pyroclastic flow.
1694 Large Eruption? Ko-c2 pumice fall and pyroclastic flow.
1765 Small eruption?
1784 Small eruption.
1856 Large eruption. Ko-c1 pumice fall and pyroclastic flow. Ansei crater and lava dome were formed. Two people were killed by pumice fall and 20+ by pyroclastic flow.
1888 Small eruption.
1905 Small eruption.
1919-1924 Small eruption.
1929 Large eruption. Ko-a pumice fall and pyroclastic flow. Syowa-4 crater were formed. Two people were killed.
1935-1938 Small eruption.
1942 Middle eruption. Ash fall. Syowa-17 crater and 1.6km long fissure were formed.
1996 Small eruption. Ash fall.
Large > 1*10^8m^3 > Middle > 1*10^6m^3 > Small
Modified after Geological Map of Hokkaido- Komagatake Volcano (Geological Maps of Volcanoes; Katsui et.al.,1989)

Link to the Other Sites about Hokkaido-Komagatake Volcano

Earthquake Research Institute, Univ. of Tokyo: Volcano Research Center (VRC)
Tatsuro Chiba's Page (Nihon Univ.) Air Photo of 1996 Komagatake Eruption
Prof. Hayakawa Page, Gunma Univ.(mainly in Japanese) Details of the Historical and Geologiclal Records of Eruptions of Hokkaido-Komagatake Volcano etc..
Hakodate Home Page (Hakodate Information Network Co. Ltd.jFHOKKAIDO KOMAGATAKE ERUPTION. Informations from Hakodate City.
Last modified 97.4.6 D mail to Yoshihisa Kawanabe(yagi@gsj.go.jp)

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