8 June 2008

Updated@ Tangjiashan images deepen the mystery

Posted by Dave Petley

NB – I have now updated this with an image at the end that shows this more clearly.

A quick image search today showed up the following Reuters image, entitled: “Water from the Tangjiashan “quake lake” flows down in quake-hit Mianyang, Sichuan Province June 7, 2008. Chinese troops on Saturday eased pressure on a swelling “quake lake” threatening hundreds of thousands of people, but a smaller lake burst its banks in a show of destructive force.”

According to the caption this was taken on 7th June – i.e. yesterday.

Now, lets compare this to the earlier image that we had by putting them side by side, with the older one on the left and the newer one on the right:

A few things to note here (see annotated image below):
1. There does appear to be more flow in the second image, though not vastly so;
2. The activities of the excavators in the second image appear to be to deposit soil and rock, not to be excavating it (highlighted with the red circle below). Are they filling something in here?
3. The small waterfall adjacent to the blue trucks in the first image has eroded back a considerable distance in the second one (highlighted with a green circle below). This shows that erosion is occurring, but through a nick point.

The timing of the image is crucial here. If it was indeed taken yesterday, and the nick point eroded back that far during the day, then the erosion back of this nick point becomes a very possible failure mechanism for the dam.

Updated – here is another Reuters image that shows this more clearly: