[A-CC25] Glaciology

[ACC25-03] Maintenance Mechanisms of very small glaciers in northern Japanese Alps

*Kenshiro Arie¹, Chiyuki Narama² (1.Graduate School of Science and Technology, Niigata University, 2.Department of Environmental Science, Niigata University.)

Keywords:Glacier, Perennial snow patch, Northern Japanese Alps, Mass balance

Since 2012, seven "avalanche-deposited" perennial snowpacks in the Northern Alps have been identified as very small glaciers (VSGs) (Fukui and Iida, 2012; Fukui et al., 2018; Arie et al., 2019), but their maintenance mechanisms have not been understood. Arie et al. (2022a) calculated the geodetic mass balance of five VSGs in Japan and showed that the accumulation and ablation depths of VSGs in the northern Japanese Alps exceed 20 m, and their mass balance amplitude is the largest among the glaciers observed in the world (WGMS glaciers). However, the annual mass balance observation results cannot define a glacier equilibrium line that separates the accumulation area upstream and the ablation area downstream, and the maintenance mechanism of these has not been cleared yet. In typical glaciers, ice bodies upstream of the glacier move to downstream by flow due to gravity. Therefore, for a glacier to maintain its morphology, an accumulation area with a positive surface mass balance upstream and an ablation area with a negative surface mass balance downstream are required.
In this study, we calculated the altitude profile of the annual surface mass balance of the Shakushizawa snow patches, which is considered to be a VSG (Arie et al., 2022b), under steady-state conditions based on measured ice thickness and flow velocity, horizontal movement on the debris deposit area, and glacier flow continuum equations.
The results show that the Shakushizawa snow patch (glacier) has a steady-state annual surface mass balance altitude profile (long-term average) with the accumulation area upstream and the ablation area downstream. These results suggest that VSGs in the northern Japanese Alps are formed and maintained, under the condition below the climatic snow line altitude, by creating localized accumulation area in the long-term mean surface mass balance due to avalanche topography effects.

Reference
1: Arie K, Narama C, Yamamoto R, Fukui K and Iida H (2022a) Characteristics of mountain glaciers in the northern Japanese Alps. The cryosphere 16(3), 1091–1106.
2: Arie K, Narama C, Yamamoto R, Fukui K and Iida H(2022b) Ice thickness of three perennial snow patches in the Hakuba Mountain Range, In: Japan Geoscience Union Meeting 2022 MIS15-12.
3: Arie K, Narama C, Fukui K, Iida H and Takahashi K (2019) 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.
4: Fukui K and Iida H (2012) Identifying active glaciers in Mt. Tateyama and Mt. Tsurugi in the northern Japanese Alps, central Japan, Journal of the Japanese Society of Snow and Ice, 74, 213–222,
5: Fukui K, Iida H and Kosaka T (2018) Newly Identifying Active Glaciers in the Northern Japanese Alps and Their Characteristics, Geographical Review of Japan Series A., 91(1), 43–61.