River-damming, late-Quaternary rockslides in the Otz Valley region (Tyrol, Austria)

摘要

The Otz Valley and adjacent regions in Tyrol (Austria) have been repeatedly affected by large rockslope failures following deglaciation. Six rockslides, each over 10(7) m(3) in volume, were emplaced into the Otz and Inn valleys, five of which formed persistent rockslide dams. Even though catastrophic rockslope failures are short-lived events (commonly minutes) they can have long-lasting impacts on the landscape. For example, large fans have built in the Otz Valley and knickpoints persist at the former darn sites even though the Otz River has eroded through the deposits during the past thousands of years; exact age-constraints of rockslide darn failure, however, are still scarce. Empirical, geomorphic stability indices from the literature successfully identified the least and the most stable darns of this group, whereas the rest remain inconclusive with some indices variably placing the dams in the stable, unstable, and uncertain categories. This shows (a) that further index calibrations and (b) better age constraints on darn formation and failure are needed, and (c) that the exact processes of darn failure are not always trivial to pinpoint for ancient (partially) breached darns. This study is a contribution towards better constraining the nature and landscape impact of dam formation following large rockslope failures. (C) 2013 Elsevier B.V. All rights reserved.