4 March 2015
Chitral and Humla – two new valley-blocking landslides in the high mountains of South Asia?
Posted by Dave Petley
The last few days have seen unusually heavy rainfall across parts of the Himalayas and associated mountain ranges, resulting in reports of two valley-blocking landslides. The first occurred in the Reshun Valley of Chitral in northern Pakistan, and is very well reported in the Pamir Times, who have included the following images (amongst others):-
But this is a really odd one as the lake is quite large already, and the dam appears to have water flow over the top. I wonder therefore when this happened. Nonetheless, the volume of water trapped behind the blockage is substantial, so at least on the face of it there appears to be a substantial risk here. This shows the approximate location of the Reshun Valley, although the position of the landslide itself is not clear:
Meanwhile in Nepal there are reports of another valley-blocking landslide, this time in Humla in the west of the country. There is much less clarity as to the situation here. Republica carried the story yesterday, including some river gauging station data. Note though that as this station is a long way downstream it is not likely that the gauging station would show a signal of the landslide. But other reports suggest that the potential landslide is as yet unidentified, and that the main concern is a dramatic fall in the river level, which could be due to a variety of reasons:
Thousands of people living in the downstream villages of Karnali River Basin were put on high alert on Tuesday morning after the water volume in one of the two tributaries of the country’s longest river dropped significantly, raising fears of possible damming upstream.
Locals along with authorities in Humla district rang alarm bells after Limi Khola, which flows into the Karnali, recorded a dramatic 80 percent drop in water levels since Tuesday morning. Limi and Muchu rivers feed the Karnali.
“We have suspected damming of the river in the high altitude region along the Nepal-China border after the water level dropped significantly in the rivers flowing in Humla. However, we are yet to ascertain whether the river is blocked due to an avalanche or has frozen,” said Keshab Adhikari, deputy inspector general of police in the mid-western region, who is updating the situation in Humla.
The authorities are of course right to be very cautious as the water is being stopped by something, and will inevitably be released sooner or later. There clearly is an urgent need to find out what is going on upstream as soon as possible. I believe that this is the Limi Khola, the valley affected by the landslide:-
There is a nice description of the valley on this trekking website. The good news is that the catchment of the river looks to be very small, suggesting that the rate of inflow behind the blockage should be slow.
Of course the valley-blocking landslide in Zanskar in northern India is also unresolved so we may now be in a situation of having two or three serious landslide dams simultaneously.