Origin and geographical characteristics of ponds in a high mountain region of central Japan

This study examines the role of landforms in pond formation in alpine and subalpine regions of central Japan. Mountain ponds larger than ca. 50 m(2) were detected by interpretation of stereo-paired aerial photographs, and mapped in areas over 2000 m (above sea level). The mapped ponds totaled 304 in the 1347 km(2) study area. Mass movement landforms are the major sites of pond basins, comprising 66.5 % of the total number; 65 ponds occur in depressions in displaced masses downslope of ridges, and 137 occur in linear depressions along main ridges. These ponds occur frequently in the snowiest parts of the study area, although geological setting also affects pond formation. The second and third major types of landforms with ponds are of volcanic and glacial origins, accounting for 16.8 and 15.8 % of all ponds, respectively. Nearly 90 % of these mapped ponds have an area smaller than 1000 m(2). The size distribution of ponds varies with origin type. Mass movement landforms have a greater range of pond sizes, including both small (< 1000 m(2)) and medium (1000-6000 m(2)), than do glacial and periglacial landforms. Volcanic landforms have the largest ponds, which exceed 10,000 m(2) in some cases. Ponds on glacial landforms are at higher elevations and may be of uniform age post-glaciation, while other landform types can occur at any elevation and may span a wide range of ages. Landslide ponds may provide better habitats for aquatic species than those originating from other landforms, because they are not subject to the strong acid conditions of volcanic ponds or the longer snow-covered period of ponds on glacial landforms.