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[MIS10-P04] The environmental conditions of glacier-derived rock glacier in the Tien Shan, Central Asia
Keywords:rock glacier, mountain permafrost, glacier, Tien Shan
1. Introduction
Rock glaciers are known as indicator landforms of mountain permafrost (Barsch, 1996), and are classified into “talus origin type" and "glacier origin type" based on the difference in the source of debris and internal ice (Matsuoka, 1998). The “talus origin type" is a type that develops on a talus formed by gravels supplied from the bedrock , with snow and groundwater as a source of permafrost. The “glacier origin type" is a type of glacier upstream of a rock glacier, which is fed by debris deposited during glacier shrinkage, glacial ice, and melting ice water from the glacier. Although there have been many studies on “talus origin type" rock glaciers, the formation environment of “glacier origin type" rock glaciers, which are limited in their distribution area, is not clear. The northern Tianshan Mountains region is unique in that glacier-derived rock glaciers account for 60% of all rock glaciers in this study area, and there are glaciers with rock glaciers and glaciers with moraines at their termini. Since mountain permafrost plays an important role as a water resource in arid regions, it is important to understand the formation environment and distribution of rock glaciers. In this study, we investigated the spatial distribution and formation environment of “glacier origin type" rock glaciers in the Teskay Range of the northern Tien Shan Mountains using satellite image analysis and GIS.
2. Research Methodology
To investigate the spatial distribution of rock glaciers in the Teskei Mountains, we extracted rock glaciers from aerial photographs, Corona satellite images, PlanetScope satellite images, and Google Earth Pro satellite images based on morphological characteristics.
Rock glaciers with surface changes were selected using differential interferometric SAR (DInSAR) analysis using ALOS-2/PALSAR-2, and were classified as “glacier origin" rock glaciers of the “active/intact" type, including buried ice. In order to extract debris-supplying rock walls of rock glaciers, polygon data were generated in GIS using PlanetScope satellite images and Google Earth Pro satellite images. The rock walls were extracted from the top of the glacier to the end of the rock glacier, based on Nagai et al (2013).
3. RESULTS
There were 107 “glacier origin" rock glaciers identified in the Teskey Range, and about 70% of them were distributed on the north, northeast, and northwest slopes on the north side of the range.
The correlation between rock glaciers and rock face area showed a positive correlation (correlation coefficient r = 0.755), indicating that the larger the rock glacier area, the larger the rock face area. However, rock-wall area is not a sufficient condition for the formation of rock glaciers, although it is related to the development of rock glaciers, because even glaciers with moraines have sufficient rock-wall area.
Next, we focused on the ratio of glacier ice to debris supply and calculated the ratio of glacier area to the area of rock wall in contact with glaciers, and found that “glacier origin" rock glaciers formed in environments where the ratio of rock wall area was large in the northern part of the mountain range. On the east side of the mountain range, where precipitation is higher, the percentage of rock glaciers was higher than on the dry west side.
4. rock glacier formation environment
The formation of rock glaciers requires a topographic environment that is relatively surrounded by rock walls with a high proportion of rock walls, as well as a climatic environment that preserves dead ice. These environments are considered to be the reasons for the existence of many “glacier origin" rock glaciers in the northern Tianshan Mountains.
Rock glaciers are known as indicator landforms of mountain permafrost (Barsch, 1996), and are classified into “talus origin type" and "glacier origin type" based on the difference in the source of debris and internal ice (Matsuoka, 1998). The “talus origin type" is a type that develops on a talus formed by gravels supplied from the bedrock , with snow and groundwater as a source of permafrost. The “glacier origin type" is a type of glacier upstream of a rock glacier, which is fed by debris deposited during glacier shrinkage, glacial ice, and melting ice water from the glacier. Although there have been many studies on “talus origin type" rock glaciers, the formation environment of “glacier origin type" rock glaciers, which are limited in their distribution area, is not clear. The northern Tianshan Mountains region is unique in that glacier-derived rock glaciers account for 60% of all rock glaciers in this study area, and there are glaciers with rock glaciers and glaciers with moraines at their termini. Since mountain permafrost plays an important role as a water resource in arid regions, it is important to understand the formation environment and distribution of rock glaciers. In this study, we investigated the spatial distribution and formation environment of “glacier origin type" rock glaciers in the Teskay Range of the northern Tien Shan Mountains using satellite image analysis and GIS.
2. Research Methodology
To investigate the spatial distribution of rock glaciers in the Teskei Mountains, we extracted rock glaciers from aerial photographs, Corona satellite images, PlanetScope satellite images, and Google Earth Pro satellite images based on morphological characteristics.
Rock glaciers with surface changes were selected using differential interferometric SAR (DInSAR) analysis using ALOS-2/PALSAR-2, and were classified as “glacier origin" rock glaciers of the “active/intact" type, including buried ice. In order to extract debris-supplying rock walls of rock glaciers, polygon data were generated in GIS using PlanetScope satellite images and Google Earth Pro satellite images. The rock walls were extracted from the top of the glacier to the end of the rock glacier, based on Nagai et al (2013).
3. RESULTS
There were 107 “glacier origin" rock glaciers identified in the Teskey Range, and about 70% of them were distributed on the north, northeast, and northwest slopes on the north side of the range.
The correlation between rock glaciers and rock face area showed a positive correlation (correlation coefficient r = 0.755), indicating that the larger the rock glacier area, the larger the rock face area. However, rock-wall area is not a sufficient condition for the formation of rock glaciers, although it is related to the development of rock glaciers, because even glaciers with moraines have sufficient rock-wall area.
Next, we focused on the ratio of glacier ice to debris supply and calculated the ratio of glacier area to the area of rock wall in contact with glaciers, and found that “glacier origin" rock glaciers formed in environments where the ratio of rock wall area was large in the northern part of the mountain range. On the east side of the mountain range, where precipitation is higher, the percentage of rock glaciers was higher than on the dry west side.
4. rock glacier formation environment
The formation of rock glaciers requires a topographic environment that is relatively surrounded by rock walls with a high proportion of rock walls, as well as a climatic environment that preserves dead ice. These environments are considered to be the reasons for the existence of many “glacier origin" rock glaciers in the northern Tianshan Mountains.