The Sichuan earthquake in China occurred on May 12, 2008, along faults
within the mountains, but near and almost parallel the mountain front,
northwest of the city of Chengdu. This major quake caused immediate and
severe damage to many villages and cities in the area. Aftershocks pose a
continuing danger, but another continuing hazard is the widespread
occurrence of landslides that have formed new natural dams and
consequently new lakes. These lakes are submerging roads and flooding
previously developed lands. But an even greater concern is the possible
rapid release of water as the lakes eventually overflow the new dams. The
dams are generally composed of disintegrated rock debris that may easily
erode, leading to greater release of water, which may then cause faster
erosion and an even greater release of water. This possible "positive
feedback" between increasing erosion and increasing water release could
result in catastrophic debris flows and/or flooding. The danger is well
known to the Chinese earthquake response teams, which have been building
spillways over some of the new natural dams.
This ASTER image, acquired on June 1, 2008, shows two of the new large
landslide dams and lakes upstream from the town of Chi-Kua-Kan at 32º12'N
latitude and 104º50'E longitude. Vegetation is green, water is blue, and
soil is grayish brown in this enhanced color view. New landslides appear
bright off-white. The northern (top) lake is upstream from the southern
lake. Close inspection shows a series of much smaller lakes in an
elongated "S" pattern along the original stream path. Note especially the
large landslides that created the dams. Some other landslides in this
area, such as the large one in the northeast corner of the image, occur
only on the mountain slopes, so do not block streams, and do not form
lakes.