EXPERIMENTAL STUDIES ON THE DENSIFICATION RATE OF WATER-SATURATED FIRN IN THE ACCUMULATION AREA OF TEMPERATE GLACIERS

• Main Authors: カワシマ カツヒサ, ヤマダ トモミ, ワカハマ ゴロウ, Katsuhisa KAWASHIMA, Tomomi YAMADA, Gorow WAKAHAMA
• Format: Report
• Language: English
• Published: ABSTRACT 1992
• Subjects: Polar meteorology and glaciology; Proceedings of the NIPR Symposium on Polar Meteorology and Glaciology
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3762; http://id.nii.ac.jp/1291/00003762/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3762&item_no=1&attribute_id=18&file_no=1

To clarify the densification rate of the water-saturated firn layer (firn aquifer), which is formed just above the firn-ice transition in temperate glaciers during the ablation period, compression tests under constant load of water-saturated firn were carried out. The overburden pressures were changed from 0.01 MPa to 0.2 MPa. The experimental results were compared with existing field data measured on temperate glaciers. At each experiment, the following relationship was obtained : ln ρ=k-0.8ln t, where ρ is the densification rate of firn (kg/m^3/s) at a dry density ρ (kg/m^3), t is the time (s) and k is the constant. Using this empirical equation, the time required for firn with dry density of 500kg/m^3 to transform into ice (ρ=830) was calculated. Consequently, it is suggested that water-saturated firn can transform into ice within the ablation period (2-4 months) at a pressure above 0.1MPa. The pressure of 0.1MPa equals 20m depth of firn with density of 500kg/m^3. This result is considered to correspond with the fact that depths of firn-ice transition in the accumulation area of temperate glaciers are concentrated between 17m and 32m. Furthermore, a linear relation was found between the logarithm of strain rate of densification and the logarithm of pressure, and the slope of proportionality changed at a pressure around 0.1MPa, showing that the densification rate of water-saturated firn increased markedly above 0.1MPa. This may be one of the most important phenomena determining the depth of the firn-ice transition in temperate glaciers.