For many alpinists the 4506 metre high summit of the Weisshorn counts as the most beautiful in the Alps. Native author Ernesto Perren from Zermatt dedicated his book "On the road to the shining pyramid" (Am Wege zur leuchtenden Pyramide) (1) published in 2000, to the Weisshorn. An excerpt from the book says: "Randa, the picturesque village at the foot of the shining pyramid, which the glaciers come down to greet, is a calm refuge for true friends of the mountains." But do glaciers merely greet? One of them, the Bis Glacier, also seems to menace. A part of it on the north-east flank of the Weisshorn will soon break off, and the consequences are unforeseeable.

The hazard potential of the Bis Glacier, which builds two hanging glaciers on Weisshorn, has been known for a long time. Around twenty ice falls have been documented, some of which also took human lives. Despite comprehensive expertise of these ice giants in Switzerland, Martin Funk, Professor of Glaciology at ETH Zurich and co-author of "Inventory of dangerous glaciers in Switzerland", published in 2003, considers the constellation at the Bis Glacier unique (2)(3). The great difference in altitude of around 3000 metres and the possible danger to human settlements and infrastructure were really very special.

Researchers from ETH have installed various tracking and measuring apparatus on the north-east slope of Weisshorn. Two opening cracks are clearly discernable. large

Camera installed right next to the opening crack

Within the framework of a surveillance concept in the Canton of Valais last September experts installed a camera at the summit of Bishorn in order to better survey the slope of the Weisshorn on the opposite side of the divide. As coincidence had it, first signs of a small crack appeared in October. In the meantime this has grown to a width of ten metres and a second crack has appeared. It soon became clear that it is only a question of time until it breaks off. The situation led the Canton of Valais and scientists from ETH to install measuring probes on the glacier about a month ago.

Seismic activities in glaciers: useful for prognosis?

The measurements, which are still on-going, rely on three systems. Movement of the glacier is measured both with distance measures, using a laser system, as well as with GPS devices. While the latter, from the Siders company Geosat, are expensive they do have the advantage of being able to function whatever the weather conditions, in contrast to the laser system. This is more delicate because, from a distance of six kilometres, high levels of humidity suffice to affect a laser system. In addition to these a Geophon, which was made available to Martin Funk by the Swiss Seismological Service and the Institute of Geophysics, is also being used to record the seismic activities in the glacier. It was a known fact, explains Funk, that glaciers make quite a lot of noise before they come crashing down, rumbles which stem from agitations deep within the glacier. What scientists now wanted to examine was whether this phenomenon could also be used to predict a break off from the glacier.

The Weisshorn in Mattertal taken from the Bishorn on 9th March. On the left edge of the picture one can see the hanging glacier where an ice avalanche will take place. (Picture: ETH Glaciology) large

Waiting for acceleration

So what is the current situation? The ETH glaciologist, although surprised by the rapidly opening crevice in the ice in the winter, doesn't think the acceleration measured over the past few days is dramatic. Just as for rock slides it is not the speed with which a crevice opens up that is decisive–at the moment between 15 and 20 centimetres a day–but rather the acceleration that determines the actual time that it will break off. At a rough estimate, Funk thinks it likely that the ice could break off in about a month but it wasn't possible at the moment to predict the exact time.

So what will happen then? First of all, the team will carry out a new estimate of the volume of ice expected to break off, explains Funk. Together with specialists from the Swiss Institute for Snow and Avalanche Research and the authority responsible for natural hazards in the Canton of Valais they can then make an a more accurate assessment of the danger of an ice-snow avalanche.. Randa was only threatened if the ice fall led to an avalanche of snow. This was hardly a threat at present because of the low levels of snow on the flank of the Weisshorn.

Funk is however also aware that a certain amount of uncertainty exists. This had to be communicated. However, he and the people of Canton Valais have no problems here. Evidence of this is that he will take the (slight) risk of retrieving some of the expensive technological devices from the glacier shortly before the forecasted breaking off of the ice. If successful, he and the population of Randa will not have to wait much longer before they know for sure how far down into the valley the glacier will send its icy greetings.

Interior view of a glacier crevice. large