[HDS14-P12] Study on topographic features and landslide development process in slope failure by Typhoon Talas
Keywords:slope failure, development of landslide process, microtopography
1. Introduction
We have not established a prediction of landslide. The cause of this landslide is complicatedly related to the predisposition.In order to clarify the process leading to the slope failure, accumulation and analysis of cases and long-term observation and evaluation are necessary.The microtopography before disaster occurrence can clarify the process of collapse occurrence.Therefore, we tried to examine the topographic features and the landslide development process of the place where the collapse occurred, by micro-topography interpretation on the location of the slope failure occurrence site.
2. Location
Typhoon Talus crossing western Japan from 2 September to 5 September 2011 brought rain close to 2000 mm to the Kii mountain range, causing more than 50 deep-seated landslides. The scope covered by this research is the upper Totsu-gawa. In this basin, the LiDAR-data before and after the disaster is being carried out by the Kinki Regional Development Bureau, Ministry of Land, Infrastructure and Transport. Particularly in areas where many collapses occurred, the accumulated rainfall exceeded 600 mm. In addition, it corresponds to the distribution area of the Shimanto belt in the upper reaches of the Totsu-gawa, and the north to northwest slope is the dip slope.
3. Method
The verification, 38 places with a collapse area of 1,000 m2 or more that collapsed due to the Talus. We tried micro topography interpretation of the aerial laser topographic map before the collapse. The authors chose main scarp, flank, and knickpoint, which are topographies showing the gravitational deformation of the mountain body as the topography of micro topography interpretation. In addition, as the characteristic topography recognized in the deep layer collapse in the Kii mountain range, the terminal cliff and the gravitationaldeformation appeared surface in which the back slope and the moving rock body are not completely separated are targeted. In addition, the gully was the topography showing the influence of surface water and groundwater. These micro topographies were classified into three types of "nothing", "unclear" and "clear". Next, as an index showing the developmental state of the collapsed terrain, we consider it in relation with the landslide topography development process.
4. Result
As a result of micro-topography interpretation in Table 1, seven places with the topographical features total as 1 to 3 were observed as the first group. For these, the clear of main scarp, flank is not recognized, and the gravitationaldeformation at the top of the slope is the subject. Comparing the collapsed range, the moving body is unclear. This can be classified as the earliest gravity deformation in the landslide topography development process shown in Table 2, which is very close to the initial stage. I concluded that this is also the stage of the earlier stage in the transitional stage. The topographical features of the second group are total number 3 to 7, including main scarp,flank or include clear topographical features. Since the gravitationaldeformation, knickpoint,terminal cliff is remarkable, it can be considered that gravity deformation is being clarified. The whole contour is partially clear. Although they are transitional stage, they are thought to be close to the main moving stage. It was separated from the late stage of the transitional stage. The third group has a total number of topographical features of 4 to 12, and it is a group including main scarp. Terminal cliff and accompanying knickpoint are also often clear. Gravitationaldeformation and knickpoint are clear in the slope. This is thought to be due to weight deformation progressing, juvenile landslide sliding surface connected and "main moving stage" equivalent.
5. Discussion
According to this study, the appearance of main scarp, gully, flank is uncertain though topographic features in the early and late stages of the transitional stage, but the appearance of gravitationaldeformation and terminal cliff was high probability. In addition, if it is a landslide slide in a narrow sense, it is thought that it undergoes a stepwise development process from the early stage to the late stage of the transitional stage, but in Talus in 2011 it has collapsed even at the earlier stage. The gravitational deformation which is frequently observed at this stage is thought to have appeared on the surface because it corresponds to gravitational rock creep and the structure of the basement rock is sound. Focusing on such gravitationaldeformation, we think that there is a possibility of predicting collapse by understanding the features.
We have not established a prediction of landslide. The cause of this landslide is complicatedly related to the predisposition.In order to clarify the process leading to the slope failure, accumulation and analysis of cases and long-term observation and evaluation are necessary.The microtopography before disaster occurrence can clarify the process of collapse occurrence.Therefore, we tried to examine the topographic features and the landslide development process of the place where the collapse occurred, by micro-topography interpretation on the location of the slope failure occurrence site.
2. Location
Typhoon Talus crossing western Japan from 2 September to 5 September 2011 brought rain close to 2000 mm to the Kii mountain range, causing more than 50 deep-seated landslides. The scope covered by this research is the upper Totsu-gawa. In this basin, the LiDAR-data before and after the disaster is being carried out by the Kinki Regional Development Bureau, Ministry of Land, Infrastructure and Transport. Particularly in areas where many collapses occurred, the accumulated rainfall exceeded 600 mm. In addition, it corresponds to the distribution area of the Shimanto belt in the upper reaches of the Totsu-gawa, and the north to northwest slope is the dip slope.
3. Method
The verification, 38 places with a collapse area of 1,000 m2 or more that collapsed due to the Talus. We tried micro topography interpretation of the aerial laser topographic map before the collapse. The authors chose main scarp, flank, and knickpoint, which are topographies showing the gravitational deformation of the mountain body as the topography of micro topography interpretation. In addition, as the characteristic topography recognized in the deep layer collapse in the Kii mountain range, the terminal cliff and the gravitationaldeformation appeared surface in which the back slope and the moving rock body are not completely separated are targeted. In addition, the gully was the topography showing the influence of surface water and groundwater. These micro topographies were classified into three types of "nothing", "unclear" and "clear". Next, as an index showing the developmental state of the collapsed terrain, we consider it in relation with the landslide topography development process.
4. Result
As a result of micro-topography interpretation in Table 1, seven places with the topographical features total as 1 to 3 were observed as the first group. For these, the clear of main scarp, flank is not recognized, and the gravitationaldeformation at the top of the slope is the subject. Comparing the collapsed range, the moving body is unclear. This can be classified as the earliest gravity deformation in the landslide topography development process shown in Table 2, which is very close to the initial stage. I concluded that this is also the stage of the earlier stage in the transitional stage. The topographical features of the second group are total number 3 to 7, including main scarp,flank or include clear topographical features. Since the gravitationaldeformation, knickpoint,terminal cliff is remarkable, it can be considered that gravity deformation is being clarified. The whole contour is partially clear. Although they are transitional stage, they are thought to be close to the main moving stage. It was separated from the late stage of the transitional stage. The third group has a total number of topographical features of 4 to 12, and it is a group including main scarp. Terminal cliff and accompanying knickpoint are also often clear. Gravitationaldeformation and knickpoint are clear in the slope. This is thought to be due to weight deformation progressing, juvenile landslide sliding surface connected and "main moving stage" equivalent.
5. Discussion
According to this study, the appearance of main scarp, gully, flank is uncertain though topographic features in the early and late stages of the transitional stage, but the appearance of gravitationaldeformation and terminal cliff was high probability. In addition, if it is a landslide slide in a narrow sense, it is thought that it undergoes a stepwise development process from the early stage to the late stage of the transitional stage, but in Talus in 2011 it has collapsed even at the earlier stage. The gravitational deformation which is frequently observed at this stage is thought to have appeared on the surface because it corresponds to gravitational rock creep and the structure of the basement rock is sound. Focusing on such gravitationaldeformation, we think that there is a possibility of predicting collapse by understanding the features.