2016 Volume 15 Issue 1-2 Pages 49-57
2013 Typhoon Wipha has brought serious landslide and debris-flow hazard on the northwestern hillside of Mt. Mihara which caused 36 deaths in Motomachi District in Izu-Oshima Island. This debris flow was accompanied by copious amount of driftwood that accelerated the debris flow damage. This study has reconstructed recent change in tree height around the landslide area by using aerial photogrammetry and airborne LiDAR data to clarify background of the hazard. A digital surface model (DSM) was produced from three air photos taken in 1976 by Geological Survey Institute (GSI). The 2013 DSM and digital elevation model (DEM) were surveyed by the airborne LiDAR on the second day after the landslide. Vegetation height was calculated from the difference between 1976 DSM and 2013 DEM derived from the airborne LiDAR by Tokyo Metropolitan Government. Comparison between 1976 and 2013 DSM clarified that tree height around the landslide area has increased 50 – 100% over the past 37 years. This tree growth would be mostly induced by tree growth and decrease of charcoal production due to the fuel revolution since 1960’s.