Collapse at the eastern Eiger flank in the Swiss Alps

Landslides are a significant natural hazard in mountainous regions(1) and are often triggered by external factors, such as earthquakes, rainfall, permafrost melting or retreat of glaciers(2). A large landslide occurred in the Swiss Alps on 13 July 2006, when portions of an immense rock spur on the eastern flank of the Eiger peak(3) collapsed. Here we use field observations and terrestrial laser scanning data to record and quantify the relative motion along the various blocks of rock that form this spur. The data show that during the year of observation the blocks moved relative to one another by up to tens of metres along fractures that can be related to pre-existing planes of weakness. Rates of motion and deformation were high throughout July 2006, particularly in the northern part of the spur that partially collapsed on 13 July. The rates decreased considerably during the subsequent months, although a slight increase was noted in June and July 2007. These observations are consistent with instability of the spur initiated by subsidence of a single block at the rear, which acted as a wedge and disintegrated over time owing to loss of lateral confinement.