Structural control and types of movements of rock mass in anisotropic rocks: Case studies in the Polish Flysch Carpathians

Abstract

Types of gravitational movements in the Flysch Carpathians are related to tectonic and lithologic anisotropy of rock massifs. This article presents the main types of mass movements in the highly anisotropic flysch massifs: lateral spreading and rock flow, topple, translational, rotational and compound sliding and complex type of mass movements, which are illustrated by chosen forms described using structural analysis (joints, faults and other structural planes orientation). Topple is the typical mass movement for double ridges and top trenches (e.g. Gaworzyna in the Beskid Sądecki Mts.). Translational landslides with flat, structural sliding surfaces typical for shallow forms can develop along bedding planes (e.g. Duszatyn, Western Bieszczady Mts.) as well as along joints (Łopuszna, Gorce Mts.) and fault planes (Rzeki, Gorce Mts.). Currently used classification of the “structural landslides” is applied only to translational landslides. Shearing zones of deep-seated landslides are composed of structural sections (of joints, faults, bedding planes) and shearing elements. Consequently, most of the Carpathian landslides have developed as compound type (with non-circular sliding zones) representing complex movements, combined with various types of displacement: rotation, translation and/or topple. Purely rotational movements with circular failure (typical for isotropic material) have developed in the flysch where thick-bedded, hard sandstones are underlain by plastic shales (e.g. Mt. Kostrza in the Beskid Wyspowy Mts.). The influence of anisotropy of these rocks on sliding surface is significantly reduced, and plastic-type rocks stimulate rock flow development, which is usually later transformed into complex landslides with predominant rotational movement (e.g. rotational landslide with topple and flow elements on Mt. Muronka in the Beskid Śląski Mts.). Compound landsliding on Mt. Luboń Wielki (Beskid Wyspowy Mts.) represents an antithetic rotational slide with topple- and rotational-type movements.