Deep-seated gravitational slope deformations in the highest parts of the Czech Flysch Carpathians: Evolutionary model based on kinematic analysis, electrical imaging and trenching

Abstract

Deep-seated gravitational slope deformations (DSGSDs) played an important role during the Quaternary evolution of mountain ridges formed by anisotropic flysch rocks of the Outer Western Carpathians (OWC). Four DSGSD-affected ridges in the highest part of the Czech sector of the OWC have been subjected to multidisciplinary investigation involving mapping, structural and kinematic analysis, geoelectrical imaging, trenching and dating. All the studied DSGSDs are strongly predisposed by regional structural fabric given by the intersection of bedding planes, joint sets and faults. Performed research suggests high diversity of mechanisms leading to the origin of individual DSGSDs. The area of a single DSGSD can be affected by various types of movements such as sackung, lateral spreading, toppling or incipient sliding. Electrical imaging and trenching revealed that besides these mechanisms, anisotropic flysch massifs formed by thick-bedded sandstones are strongly exposed to subsurface opening of air-filled voids related to widened crevices. Such a process is driven by deep-seated creep and translational sliding of sandstone beds upon plastic claystones whose strength has been reduced to residual values of the angle of internal friction. Performed radiocarbon and OSL dating revealed that some of the studied DSGSDs originated in the Holocene period, particularly in the Atlantic and Subboreal chronozones.