Journal of Natural Disaster Science
Journal of Natural Disaster Science Vol.20, No.1, 1998
The Landslide, Steam Explosions, and Debris Avalanche Sequence of May 1997 at Sumikawa Spa, Akita Prefecture, Japan
(Received 25 June, 1998 and In revised form 8 December, 1998)
Abstract
Hydrothermal activity, a common phenomenon in volcanic regions, may cause a very special type of landslide. Such a complex landslide, about 6 million cubic meters in volume, occurred at about 8:00 a.m. on 11 May 1997 at Sumikawa Spa, Akita Prefecture, northern Japan. The landslide's shear zone was approximately at the boundary between the underlying hydrothermally altered, impervious pyroclastic rocks and overlying pervious lava flows at depths of 60 to 70 meters. Many fumaroles were located near the toe of the landslide, and the landslide's foot closed their steam vents, resulting in later steam explosions. The steam explosions, in turn, converted the foot into a debris avalanche and debris flow. The landslide probably was triggered by groundwater recharged by snowmelt and heavy rain. Because of immediate evacuation there were no casualties, in spite of the large size and rapid movement of this landslide.
Key words
landslide, debris avalanche, debris flow, hydrothermal alteration, steam explosion