北アルプス北部における高山湖沼の成因と分布に対する地すべりの影響

<p>In the northern Japanese Alps, more than 100 perennial snow patches exist (Higuchi and Iozawa, 1971)．Recently, several groups measured the ice thickness and horizontal flow velocity of seven perennial snow patches in the region, finding them to be active glaciers (e.g., Arie et al., 2019). As they are less than 0.5 km<sup>2</sup> in area, they are classified as very small glaciers (VSGs). According to Arie et al. (2021), who observed the mass balance using geodetic methods from 2015 to 2019, 1) the fluctuation of the annual mass balance of Japanese VSGs was highly dependent on yearly fluctuation in accumulation depth, 2) the mass balance amplitude was the largest of all glaciers in the world recorded by WGMS, 3) VSGs can be formed only in terrains where avalanches and snowdrifts can acquire more than double the snowfall. However, for avalanches and snowdrifts in 3), the specific topographic conditions that indicate the magnitude of these contributions are not clear. Hughes (2009) found that the contribution of avalanches to the glacier is large where the "avalanche ratio," which is the ratio of total avalanche discharge area to total glacier area, is high.<br> <br>In this study, we compared the avalanche ratio, distribution altitude, and slope direction of the seven confirmed VSGs, seven large perennial snow patches (over 10,000 m²), and three small perennial snow patches (under 1000 m²) to show the topographic conditions for the formation of glaciers and perennial snow patches in the northern Japanese Alps. As a result, there was a positive correlation between the average snow depth of VSGs calculated by the geodetic method from 2015 to 2021 and the avalanche ratio. A negative correlation was seen between the avalanche ratio and distribution altitude in the VSGs, and the lower the altitude, the higher the avalanche ratio. In addition, the relationship between avalanche ratio and distribution altitude showed that the avalanche ratio of VSGs and large perennial snow patches were larger than that of small perennial snow patches at the same altitude. The avalanche ratio of Ikenotan Glacier, which is the only glacier on the windward slope with no snowdrift, was more than twice as large as that of VSGs at the same altitude. These results suggest that the magnitude of the contribution of avalanche and snowdrift deposition and the distribution altitude determine the size of glaciers and perennial snow patches.<br> <br>Arie, K., Narama, C., Fukui, K., Iida, H. and Takahashi, K.: Ice thickness and flow of the Karamatsuzawa perennial snow patch in the northern Japanese Alps, Journal of the Japanese Society of Snow and Ice, 81(6), 283–295, doi:10.5331/seppyo.81.6_283, 2019.<br>Arie, K., Narama, C., Yamamoto, R., Fukui, K. and Iida, H.: Characteristics of mountain glaciers in the northern Japanese Alps, cryosphere, 1–28, doi:10.5194/tc-2021-182, 2021.<br>Higuchi, K. and Iozawa, T.: Atlas of perennial snow patches in central Japan, Water Research Laboratory. Faculty of Science, Nagoya University., 1971.<br>Hughes, P. D.: Twenty-first Century Glaciers and Climate in the Prokletije Mountains, Albania, Arct. Antarct. Alp. Res., 41(4), 455–459, 2009.</p>

Landslide-induced terminal moraine-like landforms on the east side of Mount Shiroumadake, Northern Japanese Alps

Long-term geo-environmental changes on a post-fire alpine slope of Mt. Shirouma-dake in the northern Japanese Alps are examined. The fire event occurred on May 9, 2009 on an alpine slope of Mt. Shirouma-dake and spread to Pinus pumila communities and grasslands. The fire resulted in significant damage to P. pumila communities, while that to grassland was minimal. The burning of needles of P. pumila communities exposed the forest floor to atmospheric conditions such as rain, wind, and snow. A map of micro-landforms based on geomorphological field observations was prepared. These micro-landforms were observed for a period of seven years after the fire event. The results do not indicate significant changes to the micro-landforms; however, litter from the forest-floor of burned P. pumila communities was flushed out to surrounding areas. The average thickness of the litter layer of the forest-floor of burned P. pumila communities was 3.5 cm in September 2011, which had decreased to less than 0.5 cm by September 2015. The P. pumila communities on the slope were established on angular and sub-angular gravel having an openwork texture covered with a thin soil layer. It is necessary to pay attention to soil erosion following the outflow of litter because the soil layer can be easily eroded. In addition, ground temperatures of burned and unburned P. pumila communities were measured from 2009 to determine the influence of fire. Ground temperature sensors were installed in the soil at depths of 1 cm, 10 cm, and 40 cm. Diurnal freeze-thaw cycles occurred at a soil depth of 1 cm on the post-fire slope in October and November from 2011 to 2016. However, these cycles did not occur in 2009 and 2010. In addition, the periods of seasonal frost at depths of 10 cm and 40 cm on the post-fire slope were extended by a period of two weeks in comparison to the unburned P. pumilla community. These thermal changes were triggered by a decrease in the thickness of the litter layer in the burned P. pumila community.

The dynamics of a seasonal snow cover in the temperate cryosphere are critical for discussing climate change and understanding Earth systems. The most basic information is the previously unknown surface energy balance of snow and ice that can describe the snow dynamics in Japanese Alps. We show the surface energy balance properties of seasonal snow cover in the Northern Japanese Alps: one is the net radiation controlling the surface energy balance variation, and the negative latent heat flux (sublimation). We found that the surface energy balance property in this region is similar to that in the continental climate region due to the specific climate of Japan (winter monsoon) and topographic conditions (steep elevation gradient) of the Japanese Alps. This is a novel finding because Japanese seasonal snow cover is thought to accumulate and ablate under a maritime climate. It has been reported that the sensitivity of snow ablation to global warming depends on current atmospheric conditions. The results offer vital context for discussing environmental changes in the temperate cryosphere and environment of the Japanese Alpine region.

Mountain glaciation in Japan and Taiwan at the global Last Glacial Maximum

A number of collapses, landslides, and debris flows occurred in the Himekawa river basin, in the northeastern part of the Japanese Alps, caused by an intense rainstorm (814 mm/2 days) on 11 and 12 July 1995 after the long periods of rainfall. A debris flow induced by failures of late glacial moraines at thresholds of two cirques traveled down into the Shirouma-daisekkei valley, a tributary of the Himekawa river in the midst of the rainstorm. The debris flow deposits (2, 200 m in length, 80 m100 m in width, 2.5×104 m3 in volume), covered the large snowpatch remaining on the valley bottom, and a longitudinal trench was formed at the center of the snow patch by debris flow. The moraines had been saturated with a large quantity of precipitation during the rainy season and snow meltwater in early summer, followed by the large volume of water of the rainstorm. Consequently, a voluminous discharge concentrated on the cirque floors, and rushed out to the moraines of the cirques, causing their collpse. The frequency of such an intense rainstorm in the area is considered to be once in two hundred years, therefore, the volume of moraine failures induced by intense rainstorms can be estimated to be more than 1×106 m3 during the Post Glacial period. This kind of moraine failure plays an important role in the degrading processes of Pleistocene glacial landforms located in the upstream of the glaciated valleys in Japan, because of its rainy and snowy climatic characteristics.

Mass balance characteristics of the active glaciers in the northern Japanese Alps

口絵3：北アルプスの景観と地すべり

飛騨山脈北部における“なだれ涵養型”氷河・雪渓の質量収支

Transient and permanent deformation of central Japan estimated by GPS

99 Extensive glacial-deposits and their ages on Tateyama, Northern Japanese Alps

Revisiting the origin of pseudo moraines on Goshikigahara plateau, Tateyama Volcano, Northern Japanese Alps

Ice thickness and flow of Karamatsusawa perennial snow patch in the northern Japanese Alps

The Quaternary Kurobegawa Granite and the neotectonics in the Northern Japanese Alps

The relationships between the formation of accumulation terraces and climatic changes, especially changes in the mountain permafrost environment, were investigated in the upper reaches of the Gamata River on the western side of the Yari-Hotaka Mountains, northern Japanese Alps. Optically stimulated luminescence (OSL) dating of these river terrace deposits is now in progress. The present distributions of mountain permafrost and permafrost-related landforms (e.g. rock glaciers) were investigated around Mt. Shirouma, located in the northern part of the northern Japanese Alps, and Mt. Suisyo, located in the central part of the northern Japanese Alps. The low bottom temperature of the winter snow cover (BTS <- 3 °C) and the negative mean annual ground surface temperature (MAST) on the blocky landform (protalus lobe) in the Suisyo C cirque indicate the presence of permafrost.