Temporal and spatial variation of infilling processes in a landslide scar in a steep mountainous region, Japan

Abstract

The duration of the soil-depth recovery needed for reoccurrence of shallow colluvial landslides at a given site in humid regions is much longer than the return period of rainfall needed to generate sufficient pore water pressure to initiate a landslide. Knowledge of the rate of change in soil depth in landslide scars is therefore necessary to evaluate return intervals of landslides. Spatial variation in sediment transport at the Kumanodaira landslide scar in central Japan was investigated by field observations. Spatial distribution of the rate of change in soil depth was estimated using sediment transport data and geographic information system (GIS) analysis. Observations revealed that the timing of sediment transport differed for shallow and deep soil layers. Near-surface sediment transport (mostly dry ravel and some shallow soil creep at depths ≤0·05 m) measured in sediment traps was active in winter and early spring and was affected by freezing-thawing; soil creep of subsoil (i.e. >0·05 m), monitored by strain probes, was active in summer and autumn when precipitation was abundant. Near-surface sediment flux was estimated by a power law function of slope gradient. Deeper soil creep was more affected by relative location to the landslide scar, which influences soil depth, than by slope gradient. Our study indicated that the rate of soil-depth recovery is high just below the head scarp of the landslide. Abrupt changes in the longitudinal slope topography immediately above, within and just below the head scarp became smoother with time due to degradation proximate to the landslide head scarp and flanks, as well as aggradation just below the head scarp.

Parallel retreat of rock slopes underlain by alternation of strata

“…Relationships between sediment transport rate and topographic factors (e.g., slope gradient, contributing area) differ among transport process types (Matsuoka, 2001;Imaizumi et al, 2014). Spatial nonuniformity in the contribution of each sediment transport process could increase spatial variability in the erosion rate within each layer, and likely interrupt fulfillment of the simple parallel retreat model.…”

“…Multiple types of sediment transport processes usually contribute to the development of topography in other areas (Roberts and Church, 1986;Imaizumi et al, 2014). Relationships between sediment transport rate and topographic factors (e.g., slope gradient, contributing area) differ among transport process types (Matsuoka, 2001;Imaizumi et al, 2014).…”

Forest harvesting impacts on micrometeorological conditions and sediment transport activities in a humid periglacial environment

“…10). These are likely to be affected by episodic sediment supply, such as small slope failure and the release of sediment from woody debris (e.g., Kirchner et al, 2001;Imaizumi et al, 2015). In addition, some 15 sediment transport processes (e.g., dry ravel and rockfall) are triggered not only by the rainfall, but also by other mechanisms (e.g., decrease in cohesion by evaporation of soil moisture, wind, and disturbance by animals) (Verity and Anderson, 1990;Gabet, 2003), also obscuring the relationship between rainfall factors and sediment transport activities.…”

“…Therefore, forest harvesting changed the type of sediment transport from seasonal frost creep, which is common in seasonal freeze-thaw areas with a thick freezing depth, to needle ice creep, which is observed in areas with shallow diurnal freeze-thaw activity (Fig. 13) (Boelhouwers, 1998;Matsuoka, 2001;Imaizumi et al, 2015). Thickness of soil creep layers, which are affected by the thickness of the freezing layer (Matsuoka, 2001;Harris et al, 2008a), were larger in site NC than in site CC.…”

GIS-Based Random Forest Weight for Rainfall-Induced Landslide Susceptibility Assessment at a Humid Region in Southern China

“…The occurrence probability can be expected if such correlations are properly revealed and estimated. Landslide susceptibility assessment, one of most important measures analyzing the correlations, becomes a vital parameter for landslide early warning systems and is a necessary component of natural and urban planning for government policies worldwide [20][21][22][23][24][25][26]. Benefitting from development of computer technique, the convenience in application and compatibility of geographical information systems (GIS), numerous assessment methods have been applied to evaluate the landslide susceptibility.…”