Note the people on the road for scale.
Compare it with yesterday's image:
The waterfall has now smoothed out, probably because the water is now eroding the landslide mass rather than the excavated material from the spillway, to create a set of rapids that are clearly eroding back up the channel. The head of the rapids are close to the saddle. The key point is probably the location where the channel become notably steeper - this is where scour accelerates. One this point is reaches and passes the saddle, the rate of flow will start to increase and we might well see the breach developing. Unless the top of the rapids is being impeded by a large boulder or similar, this will probably develop quite quickly.
It remains hard to know how quickly this will develop once the saddle is reached, but downstream communities need to be prepared for a rapid breach.
Great to see your dedicated work on this event.
ReplyDeleteDuring my years of travel in Himalayas and Karakorams I have come across several similar incidents where a huge landslide blocked the flow of a large stream or a river. This is a natural continuing process owing to the relatively rapid growth of these ranges.
However in most cases there is no rapid breach of the dam oweing to the mixed composition of large boulders, scree and sand. In some cases lakes formed by such landslides still exists after over a hundred years. A good examples is Saif-ul-Muloke lake in Kaghan valley.
I forsee very little errosion after the initial errossion of sand and soil which has mostly taken place already.
I see a long process of lake drainage over years perhaps.
Please refer to an earlier landslide (or mudslide to be precise) at Shishkot village which had similarly blocked the upper Hunza valley and formed a large lake that stretched all the way to Batura bridge.
Similarly there was another blockage during 80s near Sust which was smaller but still blocked the valley for over a year.
The only recorded breach was during late 1800 which wiped out a British cantonement close to Attock. This happened due to a large snow and ice avalanche from Nanga Parbat near Tato. As ice erodes much quicker, is lighter and melts the dam became unstable as the waters rose upstram of the block and the resulting wave which was estimated to be over 100 ft high travelled at very high speeds hundreds of kilometers down to the plaines of Punjab where it finally spread out over a vast flat river delta. There is no record of the casualities due to the remoteness and inaccessibility of Kohistan and most of this region at that period. But one can imagine that due to lack of any advance warning system there must have been high casualities in low lying communities.
I hope that in this case there will be no rapid breach and there fore no destruction down stream.
However I forsee more rapid flow as the river start flowing over the block and there fore more rapid errosion of the dam from that point onwards until the river erodes all the way down to its previous lavel, draining the lake gradually during this process.
Malik (Canada)
I am not a Geologist but certainly a mountaineer and trekker with an eye on Geology. My questions1:
ReplyDelete1. Would it be practical to carryout some limited demolitions near the boulder and hard rocks of the right bank that prevent erosion, otherwise a complete civilization may suffer permanent submersion like Saif Ul Maluk Lake?
2. In case the inflows continue to beat the outflow, the lake could quickly extend to moraines and mouths of glaciers. That will be a bombshell?