8 July 2008
In 2006 Hans Rudolf Keusen of Geotest raised concerns that a large pillar on the Eiger mountain in Switzerland had become unstable. Over the next few weeks the pillar did indeed progressively fail, providing some amazing images of a large rockfall in action (Fig 1):
Yesterday, Hans Rudolf Keusen again warned of the dangers of summer rockfalls on the Eiger. Once again, rockfalls have been occurring on the northwest side of the mountain, associated with the melting of the Lower Grindelwald glacier, which has left the flank of the mountain unsupported. The concern this time is that a rockfall could fall into a small lake at the toe of the slope, displacing “up to 900,000 cubic metres of water…in the space of several hours” (see here). Fortunately, monitoring systems are in place to detect any sudden rises in lake level, so a warning should be available.
The Swiss Glacier Monitoring Network has a rather nice image of the glacier in question (Fig. 2):
The magnitude of the problem is well-illustrated by annual monitoring data that they have collected on the length of the glacier (Fig. 3). This shows the dramatic retreat of the glacier over a century, in which more than a kilometre has been lost. Unfortunately the data only extends to 1983, but the current average retreat rate is about 20 m per year.