Lubrication by meltwater may have enabled massive slide
Although the world’s ice and snow is melting rapidly on a geologic time scale, it still seems to be a gradual process, at least for casual observers. But last summer, July 16, to be exact, 70 million tons of ice broke off the Aru Glacier in western Tibet and crashed far down into the valley, killing nine nomadic yak herders. NASA scientists reported on the avalanche here.
A team of scientists who analyzed the giant avalanche now say there’s a good chance that global warming was a key factor in the unusual slide. The researchers, who published their findings this week in the Journal of Glaciology, said that that the avalanche lasted about four or five minutes, burying 3.7 square miles of the valley floor in that time. Something — likely meltwater at the base of the glacier — must have lubricated the ice to speed its flow down the mountain, they said.
“Given the rate at which the event occurred and the area covered, I think it could only happen in the presence of meltwater,” said Ohio State University scientist Lonnie Thompson. Other nearby glaciers may be vulnerable, he added, “but unfortunately as of today, we have no ability to predict such disasters.”
Researchers could not have predicted, for example, that a neighboring glacier in the same mountain range would give way just two months later, but it did in September 2016. That avalanche appears not to have resulted in any deaths, and the cause is still under investigation.
The researchers used satellite data and GPS to get precise measurements of how much ice fell in the first avalanche and the area it covered. They’ve since pieced together more answers by working with computer modelers who were able to replicate the avalanche virtually. In those simulations, the only condition that led to an avalanche was the presence of meltwater.
“We still don’t know exactly where the meltwater came from, but given that the average temperature at the nearest weather station has risen by about 1.5 degrees Celsius (2.7 degrees Fahrenheit) over the last 50 years, it makes sense that snow and ice are melting and the resulting water is seeping down beneath the glacier,” Thompson said.
Glacial collapse is unprecedented in western Tibet, which for decades has resisted the effects of climate change while glaciers in southern and eastern Tibet have melted at an accelerating rate. Increased snowfall has even led to the expansion of some glaciers in western Tibet–and the extra snowfall likely played some role in the avalanche by creating additional meltwater, said Lide Tian, a glaciologist at the Institute of Tibetan Plateau Research of the Chinese Academy of Sciences and lead author of the paper.