Update on the Attabad landslide

According to the latest report on Dave's Landslide Blog, there is less than 2 meters freeboard before the lake behind the landslide dam reaches the engineered spillway. Monitoring has been difficult because no one is allowed on the dam due to the hazard. I recommend his most recent report in which he addresses the difficulty of predicting exactly when the overtopping will occur, discusses some likely scenarios, and criticizes the shape of the spillway (too narrow, too shallow, and too steep). (Remember that there's not a lot of time for engineering solutions to be implemented--in this case, less than 4 months.)


Before and after photos of the erosion of a landslide dam. Photos from Dave's Landslide Blog, but not sure where he first got them.

He compares the current situation at Attabad with a similar situation that he monitored at Tangjiashan, China, two years ago. (Here's a direct link to his posting on that at a comparable time before breaching. Read forward and backward to see the whole history.) For those who want material for teaching, this is a great example of what the failure of a landslide dam looks like. The dam was formed in 2008 by the Sichuan earthquake. In this case, the spillway was engineered to start eroding when the lake overtopped and started flowing through it. It was not as steep as the Attabad spillway (this is good), but was also too narrow. Five hours after flow started, the dam failed, but the engineering solution had worked fairly well, and Dave is hopeful that the outcome at Attabad will be like this, rather than more catastrophic. Unfortunately, the dam at Attabad is narrower, and so it will be more prone to fail entirely instead of just along the spillway axis. It is also composed of smaller particles than the Tangjiashan dam and will therefore be more erodible.

I have not been able to find out details of evacuations and preparations downstream. Some information is contained on Dave's WWW site in earlier postings.