Abstract
A land slide and a debris flow occurred in the vicinity of Sumikawa-Onsen in Akita Prefecture on May, 11 th, 1997. This land slide and debris flow destroyed Sumikawa-Onsen and Akagawa-Onsen Spa resorts, and reached the confluence of Kumazawagawa River passing through Route 341 located at 1.7 km downstream.
In order to study the status of displacement of the moving mass occurred by this abrupt landslide, a quantitative analysis was implemented using aerial photographs taken before and after the landslide. In this analysis, only natural forests were selected as tracking points of the displacement focused on the distribution status of canopy gaps of climax beech forest within the ground in a landsliding area.
Coordinate values of 55 points within the area of landslide were designated using Digital Photogrammetry System and displacement vectors were found out.
The moved mass from this landslide were divided into 4 blocks and the status of the displacement of each block was made clear analyzing the results of photo interpretations and displacement vectors.
Next, 2 circularity slip surfaces and a slip surface showing a form of vertical direction which connects each circularity slip by a straight line were presumed from the status of these displacements.
A part of this presumed slip surface was 12 m deeper than the position of a slip surface presumed from the materials of boring survey.
