Climate change could be to blame for Tibetan tragedy. One of the world's largest documented ice avalanches is flummoxing researchers.
But they suspect that glacier fluctuations caused by a changing climate may be to blame.
About 100 million cubic metres of ice and rocks gushed down a narrow valley in Rutog county in Central Tibet (Ch: Rutog County, the west of the Tibet Autonomous Region) on 17 July, killing nine herders and hundreds of sheep and yaks.
The debris covered nearly 10 square kilometres at a thickness of up to 30 metres, says Zong Jibiao, a glaciologist at the Chinese Academy of Sciencesâ Institute of Tibetan Plateau Research (ITPR) in Beijing, who completed a field investigation of the site last week.
The only other known incident comparable in scale is the 2002 ice avalanche from the Kolka Glacier1, 2 in the Caucasus Mountains in Russia, says Andreas KÃ¤Ã¤b, a glaciologist at the University of Oslo in Norway. That catastrophic event killed 140 people.
Preliminary analyses show that the Rutog avalanche was unusual because it started from a flat point at 5,200â6,200 metres above sea level rather than in steep terrain. The ice crashed down nearly one kilometre along the narrow gully and ran into the Aru Co lake, 6 kilometres away.
âThe site of collapse is baffling â¦ the Rutog avalanche initiated at quite a flat spot. It doesnât make sense,â says Tian Lide, a glaciologist also at the ITPR, who runs a research station in Rutog.
Zong adds: âIt went with such a force that the gully was widened out by the process."
This force is likely to have been caused by lubrication of the ice from rain or glacial melt, and researchers think that increasing precipitation in recent years may be partly to blame.
Temperatures in Tibet have soared by 0.4 Â°C per decade since 1960 â twice the global average. Warming can generate melt-water that carves out a glacier from within, making it vulnerable to collapse, says Tian.
KÃ¤Ã¤b thinks that both the Kolka and Rutog avalanches could have been triggered by a rare glacier surge, in which a glacier periodically advances 10â100 times faster than its normal speed. The phenomenon affects about 1% of glaciers globally.
Western Tibet has many surge-type glaciers, and some researchers suspect that climate change at high elevations could affect the frequency of surges3.
Regardless of what triggered the Rutog avalanche, âclimate change is causing more glacial hazards through mechanisms we donât fully understandâ, says Tian. âThere is an urgent need for more monitoring and research efforts, especially in populated areas in high mountains.â