The box indicates the following close-up image:
They also link to this site, which is appreciated. Meanwhile, the NDMA site suggests that the lake level has dropped by about 3.5 inches (about 9 cm).
Wednesday, July 7, 2010
New EO-1 ALI satellite image of Attabad
NASA have released a new satellite image of the Attabad landslide and lake, collected by the Advanced Land Imager (ALI) instrument on the EO-1 satellite on Saturday 2nd July. The images are excellent, showing both the lake and the dam and spillway with only limited cloud cover (note that north is to the right on these images):
The box indicates the following close-up image:
They also link to this site, which is appreciated. Meanwhile, the NDMA site suggests that the lake level has dropped by about 3.5 inches (about 9 cm).
The box indicates the following close-up image:
They also link to this site, which is appreciated. Meanwhile, the NDMA site suggests that the lake level has dropped by about 3.5 inches (about 9 cm).
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The length of the spillway slope appears to be around 800m from this image, which suggests an overall gradient of no more than 15%. This relatively shallow slope ought to be a significant factor when considering possible failure mechanisms. The matrix appears heavily boulderised (NDMA should confirm by resistivity measurement). The white colour of the spillway (almost along its entire length) clearly indicates that the channel bed is now being armoured by boulders. As further fine materials are washed through, the interlock forces between remaining boulders will increase and, considering the relatively shallow slope, should provide more than enough resistance to shear (for that type of failure mechanism). I can not see how a shear surface (of any significant length) could possibly develop in this material.
ReplyDeletemakes sense..
ReplyDeleteBeforeGoreKneel- I've done a bit of hiking. The Rockies and Cascades (part of the Ring of Fire) both are geologically relatively new ranges. The Cascades have plenty of active volcanoes.
ReplyDeleteThat said, I have observed a good number of landslide lakes that exists. I have not hiked up the Hunza, so I have not taken a complete survey. I also never see the ones that failed and washed away.
My personal observations regarding the rocks in the dam is what lead me to believe that the dam would survive. A couple of months ago it was suggested that the river could move all the boulders, no matter how large. I brought up the issue of entrainment velocity.
In summary, I am considering far more than just one river. In fact, I've seen the dams in higher elevations (higher as contrasted to the general elevations for the area. The North American ranges are nothing compared to Himalayas.).
In geology, there is no such thing as permanent, and long-lasting is a question of magnitude. There are plenty of people who might suggest this dam is already long-lasting.
ReplyDeleteYou know, you just look at the impressive topography there in the photographs and videos, the steep slopes of bare rock angling down into narrow river channels from towering mountains, and it is hard to imagine that this sort of landslide and blockage has not been going on episodically for millions of years (interrupted only by being covered by glaciers). Many cubic kilometers of rock have already been removed from that area, and those mountains are still rising. You see the other villages precariously situated at the base of these steep slopes, like Attabad was, and it hard not to get the sense that what happened to Attabad is ultimately going to be the fate of all of them, sometime in the future. Like the threat of tsunamis for people who inhabit low lying coastal areas, it has be considered an ever present risk; not a matter of “if”, only a matter of “when”.
ReplyDeleteDave mentioned that the remnants of a recent prior landslide/blockage reside just downstream of the current one. I would think that if these sorts of natural dams had any sort of longevity, the region would be populated with lakes. It is not.
In 2004 there was a road sign just north of Zost on the KKH into China and only about 2 hours from Hunza Attabad lake. The sign read "Landsliding". At first I thought it was poor use of English. However the debris on the road and the periodic but continuous bouncing of stones and pebbles across the road, both when I traveled up and still when I traveled down again about 3 hours later, attests to Geology being well and truly in action in this area ....and visibly in action at that.
ReplyDeleteIn 2004 there was a road sign just north of Zost on the KKH into China and only about 2 hours from Hunza Attabad lake. The sign read "Landsliding". At first I thought it was poor use of English. However the debris on the road and the periodic but continuous bouncing of stones and pebbles across the road, both when I traveled up and still when I traveled down again about 3 hours later, attests to Geology being well and truly in action in this area ....and visibly in action at that.
ReplyDelete