火山活動終了後の雲仙普賢岳・溶岩ドーム周辺の地形変化

概要

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The 1990-1995 eruption of Unzen volcano in southwestern Japan caused pyroclastic flows and deposited vast quantities of rock and ash in a neighboring valley. Previous studies have reported quantitative landform changes during volcanic activity, but after ceasing activities, few studies have reported changes quantitatively. Multi-temporal 5 m-grid digital elevation model (DEM) on and around the lava dome was prepared in this study to detect those changes. Before examination, DEMs in 1994, 1995, 1997, and 1999 were generated photogrammetrically; the DEM in 2001 was measured by airborne laser scanning. Accuracy of DEM measurement was estimated to be 0.6 m in elevation. Next, DEM differences were calculated for successive two-year periods. Consideration of DEM differences with aerial photo interpretation and other studies revealed that: 1) the lava dome was uplifted between 1994 and 1995 at the volume of 736,000 ± 39,000 m^3; 2) in the Akamatsudani River watershed, 41,000 ± 7,000 m^3 of sediment from gully erosion was estimated between 1995 and 1997. The edge of the lava dome collapsed into the watershed in January 1996. A volume of 65,000 ± 2,000 m^3 was lost and crushed debris of 56,000 ± 6,000 m^3 accumulated at the foot of the lava dome; 3) in the Mizunashi River watershed, the slope was classified into three kinds of landforms, no change was measured in any of those landforms.
日本地形学連合の論文
2004-01-25