IN 2016, two glaciers in Tibet fell apart triggering huge avalanches that caused widespread devastation. Such a collapse had only been seen once before, so the events suggested that glaciers collapse more frequently than anybody realised. But we don鈥檛 yet know which other ones are at risk.
Andreas K盲盲b of the University of Oslo, Norway, and his colleagues have combined eyewitness reports with remote-sensing images and other data to better understand how the glaciers came to disintegrate. They have also spotted the telltale signs of impending collapse, knowledge that could be used to warn people nearby.
The first glacier to give way was in the Aru Range on the western Tibetan plateau. The researchers dubbed it Aru-1. On 17 July 2016, almost half of the glacier broke off in one huge chunk and went sliding and crashing down the valley. The ensuing avalanche covered more than 8 kilometres and killed nine people, all animal herders. K盲盲b鈥檚 team estimates that the collapse of Aru-1 released 68 million cubic metres of ice.
Advertisement
Two months later, on 21 September, a second glacier called Aru-2 also fell apart just 2.6 km away. This time its bottom half sheared off in two distinct chunks, totalling 83 million cubic metres. Each event was terrifyingly fast, taking just 2 or 3 minutes. The ice moved at an average speed of 20 metres per second.
K盲盲b鈥檚 team analysed satellite photos of the glaciers taken in the months leading up to the collapses. They spotted telltale crevasses in the middle of the glacier, which had formed over that time period and were roughly where it split in two. They also looked at seismometer data in the area to check that no earthquakes might have set off the collapse (Nature Geoscience, ).
So are glaciers breaking up more often? The world is warming as a result of our greenhouse gas emissions, and this has caused glaciers around the world to retreat. Intuitively, then, it would make sense if some disintegrated as a result, but K盲盲b says it is too early to tell.
鈥淪ome of the factors that we鈥檙e pretty sure were involved in the collapses鈥� are changing through climate change,鈥� he says. However, some factors like the type of bedrock are not, and they are just as influential in the potential break-up of a glacier. It is also impossible to tell which areas are more at risk. 鈥淭hey could happen in places it didn鈥檛 happen before and nobody was thinking it could happen,鈥� says K盲盲b. He hopes local people will come forward with stories of collapses, which will help scientists.
The good news is that warning signs seem to be visible in satellite imagery. 鈥淲e know now, if we see specifically a special type of crevasse, in our heads alarm bells go,鈥� says K盲盲b.
This article appeared in print under the headline 鈥淲hat caused freak glacier collapse?鈥�
