In steep mountainous regions, deep catastrophic landslides that involve weathered bedrock as well as soils can cause serious damage. However, there is currently no widely used method for estimating spatial patterns of susceptibility to deep catastrophic landslides. We propose a new method to estimate landslide susceptibilities for many small catchments (~1 km 2) over relatively large areas (hundreds of square kilometers). Our method identifies catchments prone to deep catastrophic landslides according to three criteria: (1) catchments with ancient deep catastrophic landslide scars, (2) catchments with faults and landforms caused by long-lasting mass movements, and (3) catchments with many steep slopes that have large upslope contributing areas. We demonstrated the applicability of this method using data from Mount Wanitsuka, Miyazaki Prefecture, Japan, where deep catastrophic landslides occurred during a typhoon in 2005.
Deep catastrophic landslides (DCLs) sometimes lead to large-scale debris flows with serious impacts on human life and infrastructure. However, no adequate information about DCL-triggered debris flows, such as the topography of eroded and deposited areas or the grain size distribution, exist. We compiled published data and obtained additional new data for the topographic characteristics and grain size distributions of 10 recent DCL-triggered debris flows in Japan. We compared these data with previously published data of small-scale debris flows, steep-slope failures, and large-scale debris flows. We examined the effects of topography and DCL volume on erosion and deposition due to debris flow as well as on grain size distribution. The longitudinal gradient of the lower end of the deposited area decreased with increasing landslide volume, and about half of DCL-triggered debris flows deposited material where the longitudinal gradient of the lower end of the deposited area was less than 2°. However, the minimum longitudinal gradient of the eroded section due to debris flow was not affected by the landslide or the debris flow volume. We found that the travel distance of debris flow, including DCL-triggered debris flow, might also be a function of landslide and/or debris flow volume and that the grain size of debris flows triggered by DCLs spanned more than eight orders of magnitude.
In steep mountainous regions, landslides may include both soil and underlying weathered bedrock (hereafter, "deep catastrophic landslides"). The method for assessing susceptibility to deep catastrophic landslides, originally developed for landslides caused by heavy rain, was tested in this study against historical landslides caused by the Iwate and Miyagi inland earthquake of 2008. The method proved to be capable of independently identifying catchments in which deep catastrophic landslides occurred with fair accuracy.
Owing to the large quantities of volcanic ash that falls continuously on basins, it is generally known that debris flows can be easily triggered by even a small rainfall in such circumstances. The process of occurrence of debris flow is explained that the infiltration capacities of slopes are reduced because of the accumulation of ash, and therefore, rainfall events induce large quantities of surface runoff and subsequent increase in erosion. The authors established the observation slope at Sakurajima Volcano, one of the most active volcanos in Japan. Surface runoff was observed on the bare slope on which volcanic ash accumulates continuously by eruptions. The purpose of observation is better understanding the relationship between the amount of ash fall and the rainfall threshold for debris flow occurrence. The rainfall conditions necessary for the occurrence of surface runoff were investigated over an observation period that included periods of relatively high ash fall rates and periods with relatively low ash fall rates. Results reveal that there is no evident difference in rainfall intensity that causes surface runoff or in the apparent infiltration capacity of the slope in the case of short-term temporal changes in volcanic ash fall. It was also revealed that if a no-rain period lasts for a long time, the amount of rainfall loss from the onset of rains to the occurrence of surface runoff will increase to some extent.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.