**2.2.4 Geological conditions and spatial distribution of the barrier lakes**

The Wenchuan earthquake triggered many geological hazards, including collapses and landslides along river valleys. Some of the large masses of land fell into the river valleys and formed a number of barrier lakes. Figure 1 shows the distribution of 51 barrier lakes through the interpretation of remote sensing images. From the distribution map, the barrier lakes were apparently along the Yingxiu-Beichuan fault, and the distribution was consistent with the direction of the fault zone. There were a series of high-risk barrier lakes distributed along the rivers such as the Jianjiang River's upstream in Beichuan County, the Mianyuan River's upstream in Mianzhu City, and the Pingshui River in Shifang City.

### **2.3 Remote sensing monitoring and analysis of roads damaged by Wenchuan earthquake**

High-resolution ADS40 optical airborne remote sensing images and other data were used to analyze and locate some national and provincial highways in seriously damaged areas. The process included analyzing qualitatively, orientatively and quantitatively different factors and classes of blocked and damaged roads from landslip, debris flows, river bank collapse, barrier lakes, earthquake disruption and ground fissuring. These monitoring and analysis results may give transportation department powerful information support.
