This region of Tibet’s Aru Range has been the site of two enormous ice avalanches in recent months. Image: NASA Earth Observatory

When the first deadly avalanche struck the Aru Range in Tibet on July 17th, scientists were puzzled. But when a second enormous ice slide occurred just a few kilometers south and two months later, they were shocked.

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Two of the largest glacial avalanches on record have sent rock and ice spilling down a valley in Tibet and left scientists scrambling for answers. Climactic conditions have been average this summer, and the terrain itself is relatively flat. But something is causing a stir beneath the ice.

October 4th, 2016. Image: NASA Earth Observatory

“Even one of these gigantic glacier avalanches is very unusual,” glaciologist Andreas Kääb of the University of Oslo told NASA’s Earth Observatory. “Two of them within close geographical and temporal vicinity is, to our best knowledge, unprecedented.”

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As researchers pore over satellite images to try and understand the events, a working theory is starting to emerge. NASA explains that crevices in the ice hint at a process called “surging”, wherein ice flows rapidly from the top to the bottom of the glacier, causing it to advance at 10 to 100 times its usual speed.

Computer simulations indicate that this surge process, which appeared to be happening last fall before it stalled out, could have led to a buildup of water inside the glacier, lubricating its foundation, and priming it for collapse. Long-term warming in Tibet, as well as a recent uptick in precipitation, may be accelerating the buildup of meltwater.

Of course, if the two events have the same underlying cause, it raises an unsettling question—when will it happen again?

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[NASA Earth Observatory]