9:45 AM - 10:00 AM
[MIS15-04] Investigation of the collapse volume due to the occurrence of Jinba debris avalanche, Haruna Volcano from a geomorphological interpretation of the distribution of hummocks
Keywords:Jinba debris avalanche, hummocky landform, collapse volume, Haruna Volcano, artificial landform transformation of hummocks
At Mt. Haruna, a Quaternary volcano in Gunma Prefecture, a large amount of debris was supplied to the southeastern foot of Mt. Haruna due to the sector collapse of the mountain that occurred in the late Pleistocene. This sector collapse is called Jinba debris avalanche, and an alluvial fan (Somagahara alluvial fan) was formed at the southeastern foot of Mt. Haruna by the Jinba debris avalanche deposit and the subsequent debris flow. Many hummocky landforms are formed on the sedimentary surface of the Jinba debris avalanche deposits. However, the detailed distribution of the hummocky landforms formed by the Jinba debris avalanche and the amount of sediment supply by the Jinba debris avalanche have not been clarified.
In this study, aerial photographs taken by the U.S. military in the late 1940s were used, and GIS data (polygons) of the hummocky landforms were created after taking into account the results of field survey. The evolution of distribution of hummocky landforms due to artificial topographical changes since the 1960s were investigated by aerial photographs interpretation taken by the Geospatial Information Authority of Japan. After that, on GIS, topographical measurements such as the area, major axis, and minor axis of each hummocks were performed, and the distance from the source (collapse source) to the hummock was measured, and the amount of debris supply due to the Jinba debris avalanche was estimated by using Yoshida's series of studies (Yoshida et al. 2010, 2012) by using the empirical formula showing the relationship between the distribution characteristics of the hummocks and the amount of debris supply due to the debris avalanche.
The hummocks due to the Jinba debris avalanche are widely distributed at the southeastern foot of Mt. Haruna, and a total of 299 hummocks have been identified. The distribution is recognized within a range of about 13 km from the source area, and reaches on the right bank along the river channel of the Tone River at the southeastern end of Yoshioka Town. The distribution pattern of the hummocks suggested that it branched into multiple flow units at the end of the Jinba debris avalanche. Similar to existing studies, field survey shows that debris avalanche deposits are covered by a loam layer sandwiching the As-YP (1.5-1.6 ka) outcrops in multiple river basins, and the same thing was also confirmed at one outcrop of the cross section of the hummock.
The size (bottom area) of the hummock due to the debris avalanche varies in size from 165 to 19,600 m2, but the size tends to decrease as the running distance increases from source area. As a result of estimating the amount of collapse due to debris avalanche using the empirical formula showing the relationship between the distribution characteristics of hummocks and the amount of sector collapse presented in a series of studies by Yoshida, 87 × 107 m3 was estimated.
As a result of aerial photographs interpretation, it was found that a part of the hummocks shown in this study disappeared due to the improvement of fields and development of residential land and large-scale commercial facilities.
In this study, aerial photographs taken by the U.S. military in the late 1940s were used, and GIS data (polygons) of the hummocky landforms were created after taking into account the results of field survey. The evolution of distribution of hummocky landforms due to artificial topographical changes since the 1960s were investigated by aerial photographs interpretation taken by the Geospatial Information Authority of Japan. After that, on GIS, topographical measurements such as the area, major axis, and minor axis of each hummocks were performed, and the distance from the source (collapse source) to the hummock was measured, and the amount of debris supply due to the Jinba debris avalanche was estimated by using Yoshida's series of studies (Yoshida et al. 2010, 2012) by using the empirical formula showing the relationship between the distribution characteristics of the hummocks and the amount of debris supply due to the debris avalanche.
The hummocks due to the Jinba debris avalanche are widely distributed at the southeastern foot of Mt. Haruna, and a total of 299 hummocks have been identified. The distribution is recognized within a range of about 13 km from the source area, and reaches on the right bank along the river channel of the Tone River at the southeastern end of Yoshioka Town. The distribution pattern of the hummocks suggested that it branched into multiple flow units at the end of the Jinba debris avalanche. Similar to existing studies, field survey shows that debris avalanche deposits are covered by a loam layer sandwiching the As-YP (1.5-1.6 ka) outcrops in multiple river basins, and the same thing was also confirmed at one outcrop of the cross section of the hummock.
The size (bottom area) of the hummock due to the debris avalanche varies in size from 165 to 19,600 m2, but the size tends to decrease as the running distance increases from source area. As a result of estimating the amount of collapse due to debris avalanche using the empirical formula showing the relationship between the distribution characteristics of hummocks and the amount of sector collapse presented in a series of studies by Yoshida, 87 × 107 m3 was estimated.
As a result of aerial photographs interpretation, it was found that a part of the hummocks shown in this study disappeared due to the improvement of fields and development of residential land and large-scale commercial facilities.