LiDAR measurements of rock fall and snow cover in a deglaciated valley, Lauterbrunnen, Switzerland

Daniel Brehm

daniel-brehm(at)web(dot)de

Abstract

Determination of erosion rates requires quantification of the erosional processes active within a landscape. LiDAR provides a fast and precise monitoring technique that enables the acquisition of detailed data sets of mass wasting events such as rockfalls. Furthermore, LiDAR allows quantification of variations in ice cover from frozen waterfalls, which are expected to contribute to rockfall activity by frost wedging. In this thesis I present results from multiple LiDAR scans of an Alpine valley to quantify variations in rock fall and ice volume changes. Data was collected from the 6 km long glacial valley of Lauterbrunnen, which has up to 1000 m high subvertical walls. Over a monitoring period of three months 24 rockfalls and 10 frozen waterfalls were detected. The rockfalls appeared between March/April 2012 and May 2012, with volumes ranging from 0.06 to 6.24 m³. Their occurrence is distributed over the whole wall and is not focused to waterfall affected areas. Rather, nearly 50 % of the rockfalls observed are associated with vegetation on the valley wall. The observed rockfalls show an anticipated relationship of frequency with increasing magnitude. However, the time interval between repeat scans is too short to establish if a power law relationship is present. Frozen waterfalls scanned in February 2012 show volumes between 13.94 and 13397.93 m³, but suffer from a high uncertainty. Features affecting these values are data holes in the scans and ice-free space between the ice surface and the rock wall at overhanging parts. These volumes are of qualitative value to estimate the influence of frozen waterfalls on rockfall patterns. This study is considered as a basis for further investigations in Lauterbrunnen Valley. The applicability of LiDAR for rockfall and ice monitoring in that region is assessed and first data sets are acquired and evaluated. Future work will complement the collected data and aim to determine an erosion rate for the valley.

View into Lauterbrunnen Valley (800-900 m a.s.l.) and to Jungfrau mountain (4158 m a.s.l.).