Suffosion Landslides as a Specific Type of Slope Deformations in the European Part of Russia

Abstract

AbstractLandslide classification systems are based on the analysis of mechanisms of slope deformation and consideration of landslide-forming earth materials. The main types of landslide movement are fall, topple, slide, spread and flow. Within the European part of Russia, a specific type of slope deformation is often observed, where suffosion (the process of washout and mechanical removal of fine particles from saturated soils under the influence of infiltrating groundwater flow) plays an essential role. Suffosion landslides are defined as a type of complex landslide formed in regions characterized by alternating horizons of unsaturated and saturated sands, loams and clays. Such hydrogeological conditions occur in the European part of Russia, most of which is occupied by the East European Plain. In the East European Plain, suffosion landslides are confined to the valleys of large rivers and their tributaries (Volga, Oka, Don, etc.), where their volumes can reach several million m3. In the Volgograd and Moscow regions, suffosion can result in soil decompaction at the base of slopes, or the formation of underground cavities in massifs, niches and grottoes on slopes, ultimately leading to the formation of suffosion landslides. Suffosion landslides are complex displacements of waterlogged soil masses formed as a result of suffosion and the subsequent associated collapse of the sides of suffosion cavities and niches. Indicators of suffosion landslides are: (1) the presence of a prograding fan of finely dispersed material at the base of slope and adjacent terrain, whose boundaries often exceed the landslide limits; and (2) a large number of ledges of different sizes on the surface of the landslide body created by uneven settling of blocks into the roof of suffosion cavities, and on the sides of suffosion niches. Suffosion landslides are often elongated, horseshoe-shaped, or ∞-shaped with a narrowing in the central part formed in saturated soils breaching from an underground suffosion cavity. Suffosion landslides do not have a marked sliding surface. Rather, soil displacement occurs over layers with strongly dispersed groundwater. The displacement rate of such landslides depends on the scale and speed of development of mechanical suffosion at the base of the slope.