1. Introduction

Glacial erosion results in U-shaped valleys with oversteepened rock walls. These are prone to rockfalls triggered by physical weathering by roots and frost wedging. However, it is not yet clear how frozen waterfalls contribute to rockfall activity and how large the erosion rate is in such a setting.

 

Lauterbrunnen Valley in the Bernese Oberland is a textbook example for an U-shaped valley with subvertical walls rising up to 1000 m from the ground. It is about 6 km long with numerous waterfalls of varying sizes. The exposed rock is made of Jurassic limestones. Talus slopes along both sides of the valley indicate that rockfall events in this valley occur and are a source of valley wall erosion.

 

LiDAR (Light Detection And Ranging) is a promising technique that has gained popularity over the last couple of years for monitoring mass changes on the Earth’s surface. It is capable of measuring changes down to a sub-m³ scale, discontinuities in the rock wall surface, or precursory deformations of mass wasting events [Abellán et al., 2009, Jaboyedoff et al., 2012, Sturzenegger and Stead, 2009a,b]. The detailed monitoring ability is an advantage if frequency-magnitude relationships of rockfalls or erosion rates should be determined [Abellán et al., 2011, Lim et al., 2005]. Furthermore, it is also possible to calculate larger volume changes, e.g. volumes and spatial extent of frozen waterfalls. However, to our knowledge there are no studies that relate temporary ice occurrences like frozen waterfalls to erosional events by rockfall.


The aims of this study are: (1) to calculate the volumes and locations of rockfall and ice cover, (2) to identify any controls (e.g. ice, vegetation) on mass wasting events, (3) to quantify the capabilities and limitations of this technique and (4) to build a basis for future rockfall monitoring work in the valley. This study provides a baseline data set for the next decade of studies in this valley, and for the calculation of a frequency-magnitude relationship and an erosion rate.

Fig. 1: Topography of Lauterbrunnen Valley and its location in Switzerland (top right corner). Aster GDEM overlain on a hillshade model. (Aster GDEM is a product of METI and NASA.)