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For thousands of years the ice-capped Aru mountain range in western Tibet has been a steady presence, but this year, two vast ice avalanches changed the shape of the region in an instant.
The first, which occurred without warning on 17 July, sent 60m cubic metres (24,000 olympic swimming pools) of ice and rock tearing down a narrow valley in Rutog county, killing nine herders and hundreds of sheep and yaks. By the time it stopped the debris covered 10sq km and was up to 30 metres deep.
Dramatic glacier collapses like this are exceedingly rare - the only known ice avalanche of comparable size was the 2002 Kolka glacier event in the Caucasus mountains - and yet, just two months later on 21 September, a neighbouring Tibetan glacier also imploded, generating a similarly large avalanche deposit, but thankfully no casualties this time.
That "one such event should occur is remarkable; two is unprecedented", writes the geoscientist Dave Petley in his landslide blog.
The trigger for these massive avalanches, which occurred on relatively gentle slopes, has left scientists baffled. One explanation for the sudden movement may be global warming. Temperatures in Tibet have risen by 0.4°C per decade - double the global average. Glacier melt plus increased rainfall may have rapidly lubricated the base of these glaciers.
"The most likely explanation for the Tibet avalanches ... is climate change," Petley concludes in his blog. If he is right then we can expect to see more of these events, and scientists are now keeping a careful eye on satellite images, to spot the next glacier failure before it occurs.
