The summer of 2015 brought an “exceptionally large” number of rockslides in the Swiss Alps because of warmer temperatures, according to a report from the Institute for Snow and Avalanche Research.
The Davos-based organisation found that most of those rockslides occurred in areas higher than 2,500 metres above sea level. They were caused by above-average air temperatures, with the freezing altitude located above 4,000 metres for a period of about six weeks.
The largest such rockslide occurred on September 2 in the Valais region, where 80,000 cubic metres of rock were dislodged. According to the institute, a volume of 5,000 cubic metres is about equal to five houses.
The video below shows an example of a significant rockslide event in Switzerland in October.
Switzerland experienced a lengthy heat wave in the summer of 2015, which has been compared to the scorching summer of 2003 that broke multiple heat records. However, scientists from the institute found that unlike in 2003, when many rockslides also occurred, the 2015 rockslides were triggered in part by significant precipitation at high altitudes.
Whereas the summer of 2003 was very dry, 2015 saw more thunderstorms at high elevations. Scientists believe the melting permafrost ice combined with other precipitation contributed to the dislodging of rocks from mountainsides.
It is not yet known how the summer of 2015 affected the Alpine permafrost in Switzerland. Those results are expected from the avalanche institute early next year.
swissinfo.ch and agencies