セント・ヘレンズ火山の噴火に伴う災害現象と対応

Abstract

On Sunday, May 18, 1980, Mount Saint Helens in the Cascade Range, Washington State tremen-dously exploded. This eruption not only interested the volcanologists due to its uncommon explosiontype in the United States, but also offered many problems to all scientists who are concerned with volca-nic hazard. The blast leveled over 400 km2 of the forest on the north side of the mountain. One ortwo km3 of the debris avalanche flowed down about 30 km. Mud flood of over 3, 000 m3/s flowed as faras the distance of 110 km to the Cowlitz River and the Columbia River. The debris flows occurred inother rivers. The ash and gas circulated around the earth and some scientists are anxious about theeffect on the climate of the world.This paper tries the fluid mechanical explanation of these phenomena on the basis of the data ofthe field survey, and further tries to learn some lessons from the response of the governments andpeople to the hazard.