[Put this together with Simon Gascoin (CNRS – Toulouse) after a request from Brian Kahn, at Climate Central, @blkahn]
Recent posts by NASA and Nature describe a mysterious glacier collapse on the Tibetan Plateau:
Figure 1: Sentinel-2 imagery acquired 24 July 2016, after the event (NASA; S. Gascoin)
This event really has no precedent, and no apparent trigger. Possible mechanisms for the collapse could be earthquake, rockfall on the glacier, or excessive melt or precipitation leading to extremely high water pressures at the glacier bed. There are no reported earthquakes in the region around the timing of the event (17 July; earthquake.usgs.gov). A small mass movement on the southeast slopes above the glacier appear as a dark streak in the post-event imagery, but it doesn’t appear to be big enough to trigger the ice avalanche, and may have occurred because of the avalanche.
Is there a climate signal in this event? Right now the answer appears to be no. Excessive melt does not appear to be likely, as surface temperatures based on NCEP/NCAR reanalysis are only slightly above normal (+1 to +2C) in the region from June 2016 – July 2016 (Figure 2). Much higher temperature anomalies occurred in the Pamirs and Karakoram region (but no glacier collapses were reported there). The Global Precipitation Mission satellites show decent precipitation in the region in the 24-48 hours prior to the event (Figure 2), but not at the site. Local measurements would help confirm if the event was triggered by precipitation.
Figure 2: Surface air temperature anomalies [C] for May-June-July 2016. Departures from 1981-2010 climatology (NCEP/NCAR)
Figure 3: Mean precipitation rate [mm/hour], 16-17 July 2016, from GPM (source: giovanni.gsfc.nasa.gov)
The glacier is heavily crevassed, or broken up, above the detachment point (Figure 4), and it appeared to be in a similar shape before the event. Beyond this basic information there are no clues. But low-angle glaciers generally don’t just slide off mountains, so the field investigations and local data will be really important for determining the cause of this disaster.
The risk of natural hazards is amplified in the mountains and by the mountains. And climate change generally acts to enhance these risks even further. In the Himalayas, glacier changes are leading to the formation of lakes that can pose downstream flood risks (e.g. Dig Tsho, Nepal); the loss of glaciers can reduce the stability of mountain slopes and lead to landslides; and extreme precipitation events can cause severe, rapid, and widespread flooding (Pakistan 2010 and Uttarakhand 2013). And as we saw in Nepal in 2015, and now here on the Tibetan Plateau, glaciers can release deadly snow and ice avalanches.
If this event is climate related, its another ominous sign for the future.
Figure 4: Sentinel-2 imagery of the Aru Co slide, acquired 21 July 2016, and enhanced for better contrast in glacierized areas (S. Gascoin)