[A-CC26] Ice cores and paleoenvironmental modeling

[ACC26-P04] The transformetion firn to ice process of the Shakushizawa perennial snow patch in the northern Japanese Alps

*Takeda Komei¹, Chiyuki Narama², Ryo Inoue³, Kenshiro Arie¹ (1.Graduate School of Science and Technology, Niigata University, Environmental Science and Technology, 2.Niigata University, Program of Field Research in the Environment Sciences, 3.The Graduate University for Advanced Studies)

Keywords:Transformation of firn to ice, Perennial snow patch, Northern Japanese Alps

Perennial snow patches in the Northern Japanese Alps can be classified into two types: "drifting snow patch recharge type," which is recharged by the re-deposition of snow by strong northwest monsoon near the ridges, and "avalanche-fed type," which is recharged by avalanches (Higuchi, 1968). All of the snow gorges that have been identified as glaciers so far belong to the Avalanche-fed type. In the "drifting snow recharge type," which is located at a relatively high elevation just below the ridge line, the aquifer formed during the consuming season becomes ice only one year after snow accumulation due to cold air intrusion in early winter, and ice bodies are formed (Kawashima, 1997). On the other hand, there have been few cases where ice bodies have been confirmed by excavation in the Avalanche-fed type, which is located at a lower elevation than the drifting snow type. In the transformation process of firn to ice in the "avalanche-fed" type, Kawashima (1997) reported that even in the Avalanche-fed type, the ice is formed by direct freezing of the aquifer. The transformation process of firn to ice is still unclear. In this study, ice cores were drilled in the Shakushizawa Snow Canyon in the northern part of the Hisha Mountains, which is an Avalanche-fed area, and the transformation process of firn to ice was discussed. Ice core drilling was conducted on October 14-15, 2022 in the Shakushizawa Snow Canyon in the northern part of the Hisha Mountains. A hand auger (Anowi Co., Ltd.) was used to drill at an elevation of 2140 m above sea level. The obtained core was observed in situ for layer structure, and wet density and water content were measured and dry density was calculated. The snow depth was estimated from the DSM, which was created using data obtained from Cessna aerial photography, and the overburden pressure was estimated. The time of firn icing in Shakushozawa Snow Canyon was then calculated based on Kawashima and Yamada (1997). The total length of the obtained core was 754 cm, and a continuous ice layer existed from a depth of 364 cm. The density of the filn layer increased and the water content decreased as it approached the continuous ice layer, and the time required for consolidation ice formation was estimated by estimating the mean snow depth and overburden pressure from the difference in DSM. The density of the dry firn increased as it approached the continuous ice layer, and the water content decreased, suggesting that the final icing was completed by consolidation rather than cold wave intrusion.