2013 Volume 122 Issue 4 Pages 694-708
A snowpatch hollow is a landform that may reflect the timing of snow disappearance associated with Holocene climate fluctuations. Thus, the development of a snowpatch hollow provides information on geomorphic processes and landscape evolution on alpine slopes in the Holocene. In this study, first, we investigate micro-landforms and slope forming materials of snowpatch hollows located at the valley head of Okunishikochi-sawa, where the slopes were glaciated during MIS 4, around Daishojidaira (2699 m a.s.l.; 35°28.64′N, 138°09.40′E), near Mount Akaishi-dake, in the Southern Japanese Alps. Second, we monitor ground temperature at 1 cm depth and 20 cm depth in the snowpatch bare ground, and measure slow mass movements with a paint line drawn on the bare ground. The snowpatch hollows are divided into three landscape units based on slope profile, vegetation, and soil stratigraphy. Surface I unit is comparable to the margin of the snowpatch hollow. Pinus pumila communities occupy large parts of these slopes. The humic loam layer is generally thick, and directly covers the solifluction deposit, which is the surface material of the snowpatch hollow. The humic loam layer intercalates Kikai Akahoya tephra (K-Ah; 7300 cal BP) in the lower part. Surface II unit is located within surface I. The humic loam layer is less than 20 cm thick, and contains many clasts transported from nearby snowpatch bare ground. This layer does not intercalate K-Ah. Snowpatch plant communities are established on surface II. Surface III unit is comparable to the present-day snowpatch bare ground. Periglacial processes such as frost creep, needle ice creep, and gelifluction act on the slope surface.
The presence of K-Ah below surface I indicates that the nivational process became less active by the early Holocene. These geomorphic changes would have been promoted by atmospheric warming after the Late Glacial age. Subsequently, surface II was formed mainly by solifluction and slope-wash erosion. A layer composed of granules and fine pebbles, which were transported from snow-free ground by niveo-fluvial processes, overlay most of surface II. Deposition of this layer started around 5600 cal BP, and continued until at least 1200 cal BP. Therefore, surface II is estimated to have formed from 5600 cal BP to 1200 cal BP. Frost creep, needle ice creep, and gelifluction have been partially active on the snowpatch bare ground of surface III, although the slope processes weakened in the Holocene.