Looks like this will be 'flood week' at WaterWired. Yesterday, the Lake Missoula floods, today, the... Pamir Mountains? Well, when it rains, it pours!
The Pamirs, long known as 'The Roof of the World,' are among the highest mountains on Earth. I've never seen them but have been in the general area (Central Asia - foothillls of the Tian Shan Mountains).
So what does this have to do with floods? Well, the story is similar to the Lake Missoula case in that a natural dam formed by landslide material has blocked a river forming a large lake, although nowhere near the volume of Lake Missoula - about 17 cubic kilometers, or 14 MAF, a little over half the size of a full Lake Mead. It's dissimilar in that the blockage occurred in the past century and the flood has not yet happened, but scientists are worried that a dam break or overtopping is inevitable, as the region is seismically very active; after all, it was a magnitude 7.4 earthquake that caused the landslide.
I stumbled upon this item in a news story from Science (18 December 2009), 'Peril in the Pamirs,' by Richard Stone.
The graphics below are from the article; the map is from the Wikipedia entry for the Pamir Mountains.
Here is the article's abstract:
Lake Sarez was born nearly a century ago, when a mountainside in Tajikistan crumbled during a magnitude-7.4 earthquake. The 567-meter-high landslide blocked an alpine river, forming the world's tallest dam. Since then, the valley behind it has filled with 17 billion cubic meters of snow and glacier melt. Experts fear that the natural dam could someday give way, unleashing a wall of water from the 56-kilometer-long lake on villages along the Bartang and Panj rivers and the great waterway they feed: the Amu Darya, Central Asia's largest river. Shoring up Usoi Dam is not feasible, experts concluded at a workshop last September. Rather, they agreed on the urgent need to draw down the lake, which last year reached its highest-ever water level. Several ideas have been floated for lowering the waterline. Meanwhile, researchers have proposed taking cores from Usoi.
The graphic below shows the path the water would take in the event of a dam break or overtopping. One of the fears is that a quake will trigger a landslide into Lake Sarez, which would cause a massive wave (seiche) that would overtop the dam, similar to what happened to Italy's Vaiont Dam in 1963. That dam was little damaged, but the massive wave killed many and destroyed villages downstream of the dam.
Below is a pdf of the article. It also contains a brief story by Stone about the battle over water rights in the region and other wonderful water legacies from the Soviet era.
Enjoy!
'Three may keep a secret, if two of them are dead." -- Dari/Tajik proverb
Michael,
Today, I read my new copy of Orion magazine with many photos by Carolyn Drake of the region along the Amu Darya. It is worth your readers taking the time to visit that online.
http://www.orionmagazine.org/index.php/articles/article/5331/
The narrated slide show is a bit more inclusive than the print magazine, but not annotated, so you miss knowing some important things. But, for this region in waiting, as Drake calls it, there is ample rationale for apprehension.
Posted by: Wes Rolley | Tuesday, 23 February 2010 at 07:09 PM