Abstract:On 12 May 2008

a devastating mega earthquake of magnitude 8.0 struck the Wenchuan area

northwestern Sichuan province

China. Wenchuan earthquake with Seismic has intensity 11 inevitably impaired the stability of mountains in the course of massive reverse thrust strike slip motion in the fault zone. Geohazards approaching of about 20 thousands were triggered with the types of rock fall

rock avalanches

landslides

debris flows

and earthquake lakes. The features of the debris dams were examined using the 124 breadth of ADS40 images obtained by airplane during 15 to 28 May 2008

which figured out the 256 dammed lakes with the features of distributing along ruptured zone and river channel. The farther analysis found that the number of dammed lakes reduce with the increase of distance to rupture and obey exponential relation with the correlation coefficient of 0.9699. According to the investigation data

a quick risk evaluation on the potential of outburst of dammed lakes was performed using the indices of material composition of dam

dam height

and water storage capacity of the dam. The dammed lakes were classified as extremely high risk

high risk

medium risk and low risk. The failure risk of 21 debris dams were evaluated according to the indices as 1 with an extremely high danger risk

7 with a high danger

5 with a medium danger and 8 of low danger. The risk evaluation result was totally accepted by state earthquake disaster relief office. And emergency dam treatment for risk reduction was planned based on the assessment which was carried out in successful. The earthquake destroyed the stability of the slopes and produced numerous loose soil and debris in tributaries

which resulting in a prolonged geo hazards for the area. Landslides and debris flows will continue to develop for at least five to ten years after the Wenchuan earthquake and will cause additional dammed lakes. After then

the probability of dammed lake formation will go down as less activation of landslides and debris-flows.