11:00 AM - 1:00 PM
[MIS15-P03] Spatial distribution and revisiting the origin of pseudo moraines on Goshikigahara plateau, Tateyama Volcano, Northern Japanese Alps
Keywords:Alpine landforms, Glacial landforms, Rock avalanche, Pyroclastic flow plateau
This study clarified spatial distribution of pseudo moraines (P) on Goshikigahara plateau, Tateyama Volcano, Northern Japanese Alps. And we reconsiderd the origin of the P.
The P can be classified into three: the LP, the MD, and the LP from geomorphic features. The LP show elongated shapes close to a straight line. The MD show mound-like terrains. The LP show circularly curved terrains. Moreover, depressions are often distributed in clusters of the P.
As a result of field reconnaissance, it was found that the P consists of an unselected debris layer containing andesite and agglutinate rock masses. Boulders are concentrated on the ground surface and are poor in fine-grained substances. No glacial striation or glacial gravels is found.
Based on these results, we reconsiderd the origin of the P and concluded as follows:
a) The P has been regarded as moraine, but it is denied in the following points. That is, no glacier erosion landform is found in the estimated flow path of the glacier, and no structure peculiar to glacier geology such as subglacial deformation structure is found.
b) The P is thought to have been formed by a rock avalanche. The source is considered to be a volcanic body that once existed to the west of Goshikigahara from the extension of the LV in the long axis direction.
c) The depressions in the P's clusters were caused by the rock-snow-ice avalanche. The melting of the snow and ice mass in the moving material caused the ground surface to sink and a depression was formed. This presupposes that the source of rock avalanche were filled with glaciers or large perennial snowpatches.
d) According to this premise, the age of rock avalanche is considered to be the late Pleistocene.
The P can be classified into three: the LP, the MD, and the LP from geomorphic features. The LP show elongated shapes close to a straight line. The MD show mound-like terrains. The LP show circularly curved terrains. Moreover, depressions are often distributed in clusters of the P.
As a result of field reconnaissance, it was found that the P consists of an unselected debris layer containing andesite and agglutinate rock masses. Boulders are concentrated on the ground surface and are poor in fine-grained substances. No glacial striation or glacial gravels is found.
Based on these results, we reconsiderd the origin of the P and concluded as follows:
a) The P has been regarded as moraine, but it is denied in the following points. That is, no glacier erosion landform is found in the estimated flow path of the glacier, and no structure peculiar to glacier geology such as subglacial deformation structure is found.
b) The P is thought to have been formed by a rock avalanche. The source is considered to be a volcanic body that once existed to the west of Goshikigahara from the extension of the LV in the long axis direction.
c) The depressions in the P's clusters were caused by the rock-snow-ice avalanche. The melting of the snow and ice mass in the moving material caused the ground surface to sink and a depression was formed. This presupposes that the source of rock avalanche were filled with glaciers or large perennial snowpatches.
d) According to this premise, the age of rock avalanche is considered to be the late Pleistocene.