[H-GM03] Geomorphology

[HGM03-01] High-resulution mapping of patterned grounds in Daisetsu Mountains, Hokkaido, northern Japan

*Ishikawa Mamoru¹, Go Iwahana² (1.Hokkaido University, 2.University of Alaska)

Keywords:patterned ground, freeze-thaw cycle, Daisetsu Mountains, high-resolution mapping, snow redistribution

Patterned ground is the microtopography, commonly seen on the ground materials that experience frequent freeze-thaw cycles. We evaluated spatial characteristics of and meteorological controls on the patterned grounds in the summit areas of Daisetsu Mountain, Hokkaido. To end this we applied orthophoto images and digital elevation models generated from unmanned aerial vehicle observations and structure from motion technologies, in order to create high-resolution maps of the location and morphology of sorted polygons, stripes, lobate patterns, and turf banked terraces. Furthermore we conducted meteorological observation to collect air temperature, wind speed and direction, and ground temperature profiles. The sorted polygons are relatively large equiform on the flat terrain and elliptical and small ones on the gentle slope. The sorted strips and lobate patterns are dominant on the slopes steeper than 3.5–4.5°. The form transition of patterned grounds is explained by the activities of gelifluction and frost creep processes, and spatiality of soil wetness. In the steeper slopes the ground materials easily move downslope forming lobate patterns and sorted stripes. On the leeward flat summit and eastern sides, relatively thick snow accumulation prevents ground materials from cooling and deepens active layers thickness that allow sorting in greater depths and enlarging diameter of the polygons. The snow redistribution and subsequent snowmelt infiltration produce local moist soils on leeward (i.e., eastern) sides of microtopography, which is favorable environments for plant growth. Soils covered with rich plants prevent ground materials from further downslope movements, damming the movement of less vegetated soils. This locally different soil movements contribute significantly to the formation of turf banked terraces that mostly develop slightly facing eastward from the principal azimuth of slope directions.