Genesis, types and evolution of crevice-type caves in the flysch belt of the Western Carpathians (Czech Republic)

Crevice-type caves are among the least investigated natural phenomena connected with the development of slope failures. These caves present complex and peculiar underground systems with their own development and resulting landforms. We investigated eight caves in the Czech part of the Outer Western Carpathians to determine their genesis, types and evolution. Crevice formation is predisposed according to the lithological, tectonic and morphological characteristics of the landslide body, including the position and location of bedding planes, joints and faults. We performed several analyses, including speleological mapping, evaluation of high-resolution topography above the caves, geophysical (ERT) measurements and structural investigations within cave passages. In accordance with these analyses, various mechanisms responsible for cave development were revealed. An intra-bed translation is responsible for the creation of regularly shaped passages with flat ceilings. Toppling as well as back and horizontal rotation of rock blocks determine the specific morphology and shapes of passages. A relatively novel aspect of the current study is the identification of the subsidence of massive rock wedges due to the widening of cracks. All of these mechanisms control the specific morphological characteristics within crevices, e.g., typical shapes of passages, cave level ordering and ceiling types. Some of these processes also influence topography above the caves. Finally, the different phases of evolution of these caves were determined.