Cosmogenic age constraints on post-LGM catastrophic rock slope failures in the Tatra Mountains (Western Carpathians)

摘要

Although deglaciation is one of the crucial factors controlling the stability of slopes in high mountains, the chronological response of rock slope failure (RSF) to glacier retreat still remains poorly known. Here we provide the first cosmogenic (Be-10) age constraints on prominent rock avalanches and rockfalls (collectively termed 'rock slope failures' - RSFs) from the Tatra Mountains, the highest mountain range with the most pronounced glacier morphology within the Carpathians. Six representative RSF5 were selected for surface exposure dating in the mountain range. Two sites are situated in the western part with less pronounced local relief and gentler slope gradient, and four come from the highest eastern part with oversteepened rock slopes. Our dataset also contains the largest known RSF in the Tatra Mountains; the Koprova rock avalanche with a volume of similar to 5.4 x 10(6) m(3). Based on 26 1 Be dated boulders, the weighted mean ages of individual RSF accumulations range between 20.2 +/- 1.2 and 10.1 +/- 0.3 ka. Our results suggest that smaller, structurally predisposed failures (mainly rockfalls) in the steepest parts of the mountains reacted immediately (i.e. a few hundred years) to deglaciation, whereas more complex slope deformations in terrain with lower local relief, involving the largest rock avalanche in the Tatra Mountains, experienced a substantial time lag (i.e. several millennia) in respect to ice retreat. In the case of delayed RSF5, their origin can be well correlated with warmer and more humid periods in the Lateglacial/early Holocene such as the Bolling-Allerod chronozone and after the onset of the Holocene. (C) 2015 Elsevier B.V. All rights reserved.