Impact of an 0.2 km³ Rock Avalanche on Lake Eibsee (Bavarian Alps, Germany) – Part I: Reconstruction of the paleolake and Effects of the Impact

Abstract

Rock avalanches destroy and reshape landscapes in only a few minutes and are among the most hazardous processes on Earth. The surface morphology of rock avalanche deposits and the interaction with the underlying material are crucial for runout properties and reach. Water within the travel path is displaced, producing large impact waves and reducing friction, leading to long runouts. We hypothesize that the 0.2 km3 Holocene Eibsee rock avalanche from Mount Zugspitze in the Bavarian Alps overran and destroyed Paleolake Eibsee and left a unique sedimentological legacy of processes active during the landslide. We captured 9.5 km of electrical resistivity tomography (ERT) profiles across the rock avalanche deposits, with up to 120 m penetration depth and more than 34 000 datum points. The ERT profiles reveal up to ~50 m thick landslide debris, locally covering up to ~30 m of rock debris with entrained fine‐grained sediments on top of isolated remnants of decametre‐wide paleolake sediments. The ERT profiles allow us to infer processes involved in the interaction of the rock avalanche with bedrock, lake sediments, and morainal sediments, including shearing, bulging, and bulldozing. Complementary data from drilling, a gravel pit exposure, laboratory tests, and geomorphic features were used for ERT calibration. Sediments overrun by the rock avalanche show water‐escape structures. Based on all of these datasets, we reconstructed both position and size of the paleolake prior to the catastrophic event. Our reconstruction of the event contributes to process an understanding of the rock avalanche and future modelling and hazard assessment. Here we show how integrated geomorphic, geophysical, and sedimentological approaches can provide detailed insights into the impact of a rock avalanche on a lake. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Impact of an 0.2 km3 Rock Avalanche on Lake Eibsee (Bavarian Alps, Germany) – Part II: Catchment Response to Consecutive Debris Avalanche and Debris Flow

“…and then ~1017 m a.s.l. We interpret these plains to be the result of water runoff towards the northeast during and after Event 2, which infilled the lower basin of the paleolake north of Zirmerskopf (see Figures 3b and c in Part I, Knapp et al ., 2020).…”

“…Here, the paleolake basin was not filled with rock avalanche deposits, and the ground surface is relatively low (~980 m a.s.l., Figure 7b). Swamps and wetlands in this area are interpreted to be remnants of Paleolake Eibsee prior to the Eibsee rock avalanche (see Figure 7 in Part I, Knapp et al ., 2020).…”

“…A hillshade 3D digital elevation model (DEM; Bavarian Surveying and Mapping Authority, 2006) of the main depositional area north of Lake Eibsee was used for geomorphic interpretation (see also Part I, Knapp et al, 2020). Field investigation and a geological map (Hornung and Haas, 2017) provided further information.…”

“…Plattenkalk Limestone and Hauptdolomite bedrock are exposed north of the lake. A Paleolake Eibsee, larger than the modern one, existed at this site until the Eibsee rock avalanche impacted and destroyed it (see Part I, the companion to this article, Knapp et al ., 2020 ).…”

Special issue: German Society for Geomorphology

“…Knapp et al ( 2021a , b ) analysed the massive impact of a multistage 0.2 km 3 rock slope which detached from Zugspitze, Germany's highest peak, into a paleolake. This event provides unprecedented insights into rock avalanche fragmentation, entrainment, effects of lubrication and fluidization due to a lake impact and the effects on rock avalanche dynamics and runout.…”