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Tuesday, May 23, 2017
- Melting glaciers are the most visible effect of global warming in the Swiss Alps. Meanwhile, permafrost is invisible and melting too, often causing rockfall and massive debris flows, ultimately threatening mountain villages.
Guttannen, home to 310 residents, is a tiny village in the Bernese Alps, the last one that travellers drive through on the way up to Grimsel Pass. It’s spring and the snow is retreating from the steep slopes of the valley. As the pass is still closed, calm reigns in the picturesque village centre. Only cowbells and the rushing of the nearby Aar river break the silence.
For some residents though, living in Guttannen has become rather uneasy and, on the long term, even dangerous. The root cause of the peril lies further uphill, in the northeastern flank of the 3,282 metres high Ritzlihorn. In July 2009, a huge rockfall had occurred and since then, massive debris flows have roared downhill each summer.
“These mudslides as well as the volume of transported rubble have grown from year to year,” says Nils Hählen, hydraulic engineer at the cantonal public works service. “The debris partly ends up in the Aar, lifting and widening its channel.” Within three years, 630,000 cubic metres were transported into the river, increasingly endangering civil infrastructure.
In summer, after heavy rainfall, the only road leading through the narrow valley often has to be temporarily closed. A house near the river already had to be taken down, the local sewage treatment plant may be next. Since 2010, the debris flows reach as far as the hamlet Boden, threatening ten houses and 30 inhabitants.
“The next few mudslides won’t be a big problem,” says Guttannen council leader Hans Abplanalp. However, some houses would effectively be threatened in two to five, others in five to seven years, he adds.
One of these homes belongs to Martin Leuthold. “I’ve lived here for 60 years and my father was already a farmer here,” he says. Leuthold claims he has no fear, as he’s grown up with the moods of nature. Nevertheless, the farmer doesn’t ignore the peril: “Perhaps nothing will happen for the next 10 years, but maybe this summer it could all rumble down on us. Nobody knows.”
Nearby, Hans von Weissenfluh lives less than 20 metres away from the river. “The threat is real, we can see it,” he says. Von Weissenfluh remembers well how impressive amounts of water and debris came down the Aar last summer. “Only five years ago, the river channel was much more narrow,” he notices.
Engineers, geologists and glaciologists assume permafrost melt to be the underlying problem. Permafrost is underground material such as rock or rubble that permanently remains at or below zero degrees centigrade. Ice is a possible, but not a necessary ingredient. “The issue is, that permafrost occurrence is generally not known,” says Nils Hählen. There are maps designed on calculated probabilities, but as the hydraulic engineer explains, in any case things have to be evaluated locally.
In northeastern mountain slopes, permafrost may occur roughly above 2,600 meters altitude. Scientists estimate that about 5 percent of Switzerland’s area contains permafrost. It stabilises steep rocky or scree slopes in the high mountains and protects them from erosion by serving as a kind of natural putty. When permafrost melts, the result may be rockfalls and debris flows. “The lower permafrost zones are the most vulnerable,” explains Hählen.
He locates the cause of permafrost melt in rising air temperatures which have been measured over the past years in the European Alps. Jeannette Nötzli, glaciologist at the University of Zurich, mentions that atmosphere and underground permafrost are often not directly coupled. Ice content and changes in surface coverage can mask atmospheric signals. Nötzli heads the Coordination Office of the Swiss Permafrost Monitoring Network PERMOS.
“As PERMOS’ systematic monitoring commenced in 2000, most of our data cover around a decade, whereas for robust statements about trends in climate science typically a 30-year period is considered,” Nötzli points out. “However,” the researcher adds, “much of our data points to permafrost degradation. For example, in the past three years active layer depths in summer have increased with new record values at many of the observed sites.”
Reliable forecasting of permafrost changes isn’t possible. In the case of Guttannen, experts limit their predictions to the next year. Hählen expects that in the long term, debris flows from the Ritzlihorn will stop, as ultimately the catchment area in the flank is limited.
Removing the rubble from the valley floor and the Aar is no option. It’s too risky, but also too costly. Additionally, dumping places in the region are limited. Only to remove the current rubble from the river would cost more than 18 million Swiss Francs and accumulate to at least 50,000 lorry loads.
There’s not much hope for the residents of Boden. Ultimately, they’ll have to leave their homes and resettle somewhere else. Hans Abplanalp, the council president, has talked to all persons concerned. “Nearly all of them want to stay in Guttannen,” he says. “We can offer them land and homes to buy.”
Boden resident Hans von Weissenfluh plans to move up to Guttannen as soon as possible. Others such as Martin Leuthold are more hesitant. He wouldn’t mind living somewhere else in the village, but is reluctant to tear down his house and move all the belongings.
“That’s a lot of work,” he says. Leuthold fears he will not be fully compensated. He’d only be compensated for his stable if he built a new one in another place. “I wouldn’t know what to build a new stable for, as I’ll soon be retired.”