title: Early Holocene (8.6 ka) rock avalanche deposits, Obernberg valley (Eastern Alps): Landform interpretation and kinematics of rapid mass movement.
abstract: In the Obernberg valley, the Eastern Alps, landforms recently interpreted as moraines are re-interpreted as rock avalanche deposits. The catastrophic slope failure involved an initial rock volume of about 45 million m³, with a runout of 7.2 km over a total vertical distance of 1330 m (fahrböschung 10°).36Cl surface-exposure dating of boulders of the avalanche mass indicates an event age of 8.6 ± 0.6 ka. A14C age of 7785 ± 190 cal yr BP of a palaeosoil within an alluvial fan downlapping the rock avalanche is consistent with the event age. The distal 2 km of the rock-avalanche deposit is characterized by a highly regular array of transverse ridges that were previously interpreted as terminal moraines of Late-Glacial. 'Jigsaw-puzzle structure' of gravel to boulder-size clasts in the ridges and a matrix of cataclastic gouge indicate a rock avalanche origin. For a wide altitude range the avalanche deposit is preserved, and the event age of mass-wasting precludes both runout over glacial ice and subsequent glacial overprint. The regularly arrayed transverse ridges thus were formed during freezing of the rock avalanche deposits.
authors: Institute for Geology and Palaeontology, University of Innsbruck, A-6020 Innsbruck, Austria.
authors: Marc
authors: M
authors: Ostermann
authors: Institute for Geology and Palaeontology, University of Innsbruck, A-6020 Innsbruck, Austria.
authors: Diethard
authors: D
authors: Sanders
authors: Department of Geography, University of Zurich, CH-8057 Zurich, Switzerland ; Laboratory of Ion Beam Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors: Susan
authors: S
authors: Ivy-Ochs
authors: Laboratory of Ion Beam Physics, ETH Zurich, CH-8093 Zurich, Switzerland.
authors: Vasily
authors: V
authors: Alfimov
authors: Geological Survey of Austria, A-1030 Vienna, Austria.
authors: Manfred
authors: M
authors: Rockenschaub
authors: Geological Survey of Austria, A-1030 Vienna, Austria.
authors: Alexander
authors: A
authors: Römer
keywords: Alps; Cosmic ray exposure dating; Electrical tomography; LIDAR interpretation; Rock avalanche; Rock avalanche kinematics