The Tamins rock avalanche (eastern Switzerland): timing and emplacement processes

The Tamins rock avalanche lies adjacent to the Flims rock avalanche, the largest in the Alps. Its deposit forms a ridge across the Rhine Valley just downstream of the confluence of the Vorderrhein and Hinterrhein rivers. The deposit is dominated by a 1.6-km-long longitudinal ridge, Ils Aults, and two roughly 600-m-long transverse ridges. Several extensional scarps bear witness to spreading of the deposit. A breach through the deposit, where the Rhine River presently flows, reveals a carapace and intense fragmentation. Exposure dating using cosmogenic Cl-36 yields an age of 9420 +/- 880 years. This suggests that the Tamins event occurred in a time frame similar to the Flims event but was slightly earlier than the Flims rock avalanche, as also required by stratigraphic relationships. 3D volume modeling reveals bulking of only 14%. The motion of the rock avalanche seems to have occurred first as a flexible block, which underwent fragmentation and simple shearing where the top moved faster than the bottom. The ensuing spreading led to the formation of extensional scarps. There is no identified weak layer along the sliding surface; nevertheless, modeling suggests a friction angle of 10 degrees.

Automated summary

The Tamins rock avalanche is located next to the Flims rock avalanche, the largest in the Alps. Its deposit forms a ridge across the Rhine Valley downstream of the confluence of the Vorderrhein and Hinterrhein rivers. The deposit shows signs of spreading and has an estimated age of 9420 +/- 880 years. The motion of the rock avalanche involved fragmentation and simple shearing, leading to the formation of extensional scarps. The friction angle along the sliding surface is estimated to be 10 degrees.