Distribution and Development Processes of Wetlands on Landslides in the Hachimantai Volcanic Group, NE Japan

Abstract

This study examines geomorphological controls on the distribution and development of wetlands in the Hachimantai Volcanic Group, northeastern Japan. The study area is dissected by various sizes of landslides and has many wetlands of varied origin. Among 526 wetlands in the study area, 195 are on landslides and account for 63.9% of the total area of wetlands. Wetlands outside of landslides tend to be found in clusters on undissected volcanic surfaces. Many of these are small wetlands in nivation hollows that are supplied by meteoric water from snow, and some of them are ponds in the craters of Hachimantai volcano and large peat bogs on lava flows. Wetlands inside landslides are widely scattered in large or deep depressions along landslide scarps and in small depressions among pressure ridges. Many of these are ponds supplied mainly by groundwater. Large landslides tend to have ponds. On the larger landslides, depressions created by landslide processes provide favorable conditions for the development of wetlands, and their size is constrained by the microtopography of the landslide surface. When drainage channels that dissect landslide bodies breach these closed depressions, the wetlands there progress rapidly from ponds to peat bogs. Landslide activities can create wetlands of various ages, and the dissection of landslide bodies controls the developmental stages of these wetlands. Therefore, a large landslide may contain coexisting wetlands of various ages and types.