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Landslides affecting narrow mountainous valleys might significantly determine sedimentation dynamics of floodplains. We present here a detailed study of the sedimentary archive within a landslide-controlled impounded floodplain (Smrdutá site, Czech Flysch Carpathians) using geochronological (14C and 137Cs), sedimentological and pollen evidence. A sedimentary sequence deposited above the landslide dam points to three highly discontinuous and instantaneous depositional events dated to 4.6 and 2.0 cal. ka BP, whereas the last cycle started approximately in the 17–18th centuries and has continued to recent times. Such sedimentary pulses characterized by the duration of several decades to a few centuries originated as a consequence of the blockage and/or reduction of the valley floor width by successive long-runout landslides from a slope formed by tectonically and lithologically anisotropic flysch bedrock. Stages of mass movement activity revealed by the Smrdutá landslide correlate well with major humid late-Holocene oscillations suggesting its high sensitivity to century-scale climatic deteriorations. The character of lithological units forming individual sedimentary pulses, erosional hiatuses and sedimentary traces caused by the July 1997 extreme flood indicate a decisive role of large flood events during accretion and erosion of the floodplain-impounded section. [ABSTRACT FROM AUTHOR]

Abstract: One of the largest long-runout landslides in the modern history of the Czech Republic originated on the southern slopes of the Girová Mountain (Outer Western Carpathians) at the end of extreme rainfalls in May 2010. The structurally predisposed Girová Mountain rockslide occurred very quickly within fault-weakened, deeply-weathered flysch bedrock. Its main phase, during which a wedge-like block collapsed in the upper part of slope, lasted for a few hours. The overloaded slope collapsed and its motion lasted for the following 3days. The May 2010 Girová Mountain rockslide is an excellent case of a recurrent long-runout landslide nested within a deep-seated gravitational slope deformation with a long history of Late Quaternary mass movements. The chronology of slope failures within the studied slope was reconstructed by means of radiocarbon dating and dendrogeomorphological analysis. At least one Holocene long-runout landslide (7.4calka BP) and several smaller failures (~1.5 and ~0.6calka BP) preceded this recent catastrophic failure. Dendrogeomorphological analysis showed that the failure had been preceded by at least 80-year-long creep movement that accelerated over the years due to extreme rainfall events. Despite the fact that extreme precipitation of May 2010 represented the last incremental change before catastrophic collapse of the slope, its main reason was gradual weakening of rock massif and concentrated creeping (with some accelerated phases) in the upper part of the slope deformation. [Copyright &y& Elsevier]