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2nd massive ice avalanche in Tibet

“Even one of these gigantic glacier avalanches is very unusual. Two within close geographical and temporal vicinity is, to our best knowledge, unprecedented.”

Acquired June 24 -September 24, 2016. Image via NASA.

Satellites images of the twin avalanches, acquired June 24 -September 24, 2016. The June 24 image shows the area before either avalanche occurred; the July 21 image shows the first avalanche; the September 24 image shows the area after both avalanches. (Notice that the older avalanche appears significantly darker than the newer one in the later image. The brightness of a radar image varies based on the “roughness” of the surface and how much moisture it contains. Rougher surfaces and those with low water content appear brighter. The first avalanche either had a smoother and/or wetter surface than the newer avalanche, most likely because ice on the surface of the older avalanche has been exposed longer and had time to partially melt. Distinguishing between wetness and surface roughness based on this satellite imagery is not possible.) Image via NASA.

In July 2016, a massive and mysterious avalanche sent glacial ice and rock spilling down a valley in the Aru Range of Tibet, killing nine people. In September, a second massive avalanche occurred just a few kilometers to the south of the first.

Glaciologists don’t know what caused the avalanche in July. Both temperature and rainfall amounts had been normal in the the months before the avalanche. And, most surprisingly, the part of the glacier that collapsed sat on fairly flat terrain. The second avalanche makes the story even stranger. Andreas Kääb is a glaciologist at the University of Oslo. In a statement from NASA’s Earth Observatory, Kääb said:

Even one of these gigantic glacier avalanches is very unusual. Two of them within close geographical and temporal vicinity is, to our best knowledge, unprecedented.

Despite their close proximity, Kääb said there is no evidence of a direct physical connection between the glaciers or their collapse. The similarities between the two events, though, imply that shared factors — such as short-term weather conditions, longer term climate change, and the underlying geological or topographic environment — might have played a role.

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Image via NASA.

This image from NASA’s Terra satellite shows both avalanches in false color. This image was acquired on October 4, 2016. Image via NASA.

Ever since the first avalanche, scientists affiliated with the International Association of Cryospheric Sciences and the International Permafrost Association have been trying to figure out what caused it. According to a statement from the NASA Earth Observatory:

While analyzing optical and radar data from satellites for the months prior to the collapse, they noticed a distinctive pattern of crevasses on the glacier surface, as well as changes in the height. Both suggested that it was in the process of surging—a term glaciologists use to describe the unusually rapid flow of ice from the upper part of a glacier to the lower part.

Though ice in a surging glacier can flow 10 to 100 times faster than usual, there have been no documented cases of surging glaciers causing abrupt and violent collapses. However, in the case of the Tibet glaciers, satellite observations suggest that the surging process may have primed the glaciers for collapse.

Avalanches are difficult to predict. But when the scientists detected the same telltale crevasses and changes in elevation that preceded the first collapse, they suspeced that a second avalanche was poised to happen. On September 21, 2016, the team warned Chinese scientists and government officials that a second avalanche appeared to be imminent to the south. The warning turned out to be just a little too late. Just a few hours before the warning arrived, the second glacier had already collapsed.

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Bottom line: In September 2016, a massive and mysterious avalanche spilled down a valley in the Aru Range of Tibet.

Read more from NASA’s Earth Observatory

Eleanor Imster