2:15 PM - 2:30 PM
[ACC28-02] Evaluation of permafrost distribution at north cirque of Mt. Shakushi, in the northern Japanese Alps
Keywords:Mountain permafrost, Rock glacier, DInSAR analysis, GPR, Electrical resistivity
A rock glacier, which is a sedimentary landform where ice and rock debris are mixed, is an indicator landform of mountain permafrost because permafrost exists inside the glacier. When permafrost exists in the thick debris of rock glaciers, it flows due to plastic deformation, and the possibility of mountain permafrost can be indicated by confirming the flow. The possibility of mountain permafrost distribution has been pointed out in the alpine zone of the northern Japanese Alps because there are mountain areas that satisfy the condition of "ground temperature below 0°C for more than two years," which is a condition for the existence of permafrost. The rock glaciers around Mt. Hakubadake and in the Yarihotaka mountain range are representative examples (Matsuoka and Ikeda, 1998; Aoyama, 2002; Ishikawa et al.) However, the current mountain permafrost in the northern Japanese Alps has been found only in the Kuranosuke cirque in Tateyama (Fukui and Iwata, 2000), and the entire distribution of mountain permafrost in the Chubu Mountains and its formation and maintenance environment are still unclear. In this study, we examined the possibility of mountain permafrost distribution in the rock glaciers of the north cirque of Mt.Shakushi in the northern Japanese Alps, where the possibility of mountain permafrost distribution has been pointed out.
Differential interferometric SAR analysis using SAR data from two-month, one-year, and two-year observation periods showed that rock glacier surface changes were observed in all periods. The amount of movement was several centimeters in one year and more than ten centimeters in two years, indicating continuous flow. These results suggest that there is a high possibility that permafrost exists in the rock glacier.
Next, we conducted a ground-penetrating radar survey at a location 100 m upstream from the terminus of the rock glacier, which was considered to have the highest flow rate by differential interferometric SAR analysis. As a result, the base was found at a depth of 10 to 12 meters, and the interior was composed of three layers. The depth of the rock glacier is about 12 m. The surface layer is composed of angular gravel of siliciclastics, and the upper and lower layers are composed of different materials mixed with gravel.
To confirm the composition of the three layers inside the rock glacier observed by the ground-penetrating radar survey, a two-dimensional electrical resistivity survey was carried out in the same survey line. As a result, a part with a resistivity value of 10^4 to 10^5 Ωm, which is an indicator of permafrost, was detected in the area around 10 m from the ground surface. The resistivity values of 10^4 to 10^5 Ωm, which are indicators of permafrost, were detected from the surface to a depth of 10 m. The resistivity value of the rock glacier was lower than 8×10^3Ωm below 12m depth. This result suggests that there is a high possibility that mountain permafrost exists inside the rock glacier.
Differential interferometric SAR analysis using SAR data from two-month, one-year, and two-year observation periods showed that rock glacier surface changes were observed in all periods. The amount of movement was several centimeters in one year and more than ten centimeters in two years, indicating continuous flow. These results suggest that there is a high possibility that permafrost exists in the rock glacier.
Next, we conducted a ground-penetrating radar survey at a location 100 m upstream from the terminus of the rock glacier, which was considered to have the highest flow rate by differential interferometric SAR analysis. As a result, the base was found at a depth of 10 to 12 meters, and the interior was composed of three layers. The depth of the rock glacier is about 12 m. The surface layer is composed of angular gravel of siliciclastics, and the upper and lower layers are composed of different materials mixed with gravel.
To confirm the composition of the three layers inside the rock glacier observed by the ground-penetrating radar survey, a two-dimensional electrical resistivity survey was carried out in the same survey line. As a result, a part with a resistivity value of 10^4 to 10^5 Ωm, which is an indicator of permafrost, was detected in the area around 10 m from the ground surface. The resistivity values of 10^4 to 10^5 Ωm, which are indicators of permafrost, were detected from the surface to a depth of 10 m. The resistivity value of the rock glacier was lower than 8×10^3Ωm below 12m depth. This result suggests that there is a high possibility that mountain permafrost exists inside the rock glacier.