雲仙普賢岳噴火にともなう森林被害:1992年までの状況と変化

概要

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Forest damage which was caused by eruptions of Mt. Fugen, Unzen volcano, and the transition until 1992 was investigated with remote sensing and ground survey. Five images by SPOT satellite showed that the course of pyroclastic flow changed from Mizunashi river to Oshiga valley and to Akamatsu valley, and that the forest damage which was caused by pyroclastic flow and volcanic gas spread out gradually. Ground survey showed that most pine trees and many fir trees were dead and deciduous broad-leaved trees were declined in Nita mountain pass area where typical damage was observed. The area damaged by volcanic gas reached down to Mt. Nodaka and Mt. Iwatoko which were about 3 km south-east from the crater. Damaged Hinoki arificial forest especially stood out there. A forest damage transition map and a temporary forest damage map derived from a SPOT image were drawn based on the results described above. Causes of forest damage were classified as pyroclastic flow, volcanic gas and ash. The damage types and the mechanism were discussed. The damage caused by volcanic gas was characteristic of the wide area and the mechanism. It was estimated that forest damage by volcanic gas was generated by not only SO2, but sulfuric acid mist which SO2 and moisture of fog were compounded into. Chronic damage and decline of forest by volcanic ash on forest soil and leaves will spread on the continuous volcano activity.
社団法人砂防学会の論文