Preprints
https://doi.org/10.5194/esurf-2022-20
https://doi.org/10.5194/esurf-2022-20
 
03 Jun 2022
03 Jun 2022
Status: this preprint is currently under review for the journal ESurf.

Geophysical evidence of consecutive evolution of Tamins rockslide and lake formation, Flims rockslide, and Bonaduz push wave gravels with embedded Toma hills

Sibylle Knapp1, Michael Schwenk2, and Michael Krautblatter1 Sibylle Knapp et al.
  • 1Landslides Research Group, Technical University of Munich, Munich, Germany
  • 2Institute of Geological Sciences, University of Bern, Bern, Switzerland

Abstract. Rockslides and rock avalanches are amongst the most destructive natural hazards in the alpine environment. The Flims rockslide is the largest known rock-slope failure in the Alps, which provides excellent outcrops and has fascinated researchers since the early 20th century. The postulated impact of the Flims rockslide on (Paleo-) Lake Bonaduz caused intensely fluidized rock material, which formed the so-called Bonaduz Gravel and Toma hills, probably accompanied by a catastrophic impact wave. So far, this hypothesized sequence of events is based only on sedimentological and geomorphic analyses. We present electrical resistivity tomography (ERT) profiles which we correlated with the sedimentological information obtained from dill logs. Our study provides new insights into the distribution, thickness, and internal structure of the Bonaduz Gravel, the Toma and Cresta hills, as well as other flood deposits around the Ils Aults where we studied the sediment to a depth of up to 160 m. There is new field evidence that the Bonaduz Gravel formed an onlap onto the Ils Aults and is thus the stratigraphically younger unit. The Toma/Cresta hills consist of blocky cores with an agglomeration of smaller mixed sediments, which drift and override the Toma/Cresta core, causing their smoothly shaped top. We consider simultaneous transport of the Cresta within the Bonaduz Gravel, yet a slightly slower movement at the front due to a bulldozing effect. This study contributes to an improved understanding of i) the complex stratigraphical context of the Tamins and Flims deposits, ii) water-rich entrainment in rock avalanches, and iii) the genesis and transport of outburst-flood deposits, in particular of Toma hills.

Sibylle Knapp et al.

Status: open (until 15 Jul 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2022-20', Anonymous Referee #1, 07 Jun 2022 reply
  • RC2: 'Comment on esurf-2022-20', O. Adrian Pfiffner, 10 Jun 2022 reply

Sibylle Knapp et al.

Sibylle Knapp et al.

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Short summary
The Flims area in the Swiss Alps has fascinated the researchers with its complex geological history ever since. Especially the order of events related to the Tamins and Flims rockslides has long been debated. This paper presents novel results based on up to 160 m deep geophysical profiles, which show onlaps of the Bonaduz Gravel onto the Tamins deposits (Ils Aults) and thus indicate that the Tamins rockslide occurred first. The consecutive evolution of this landscape is shown in four phases.