Abstract
The 1990-1995 eruption of Unzen volcano in southwestern Japan cause pyroclastic flows and deposited a vast quantity of blocks and ash in Mizunashi watershed. Purpose of this study is to know yearly DEM change in a gully bottom in the watershed after the eruption. In advance, 1/8,000 scale aerial photos that were annually taken between 1995 and 1999 were prepared. First, annual photos were precisely oriented by photogrammetry and an operator measured DEM at each grid by analytical plotter. Finally 2 m grid DEM of 1995, 1996, 1997, 1998 and 1999 were obtained at the precision of 0.3 m in standard deviation. Next, DEM difference of successive two years e.g., 1996 DEM -1995 DEM, were calculated at each grid. As a result, it was found that DEM changes were not so remarkable, especially after 1997.
