The Wenchuan earthquake on May 12, 2008, triggered many secondary disasters, among which the barrier lakes formed by landslides were extremely serious. We monitored the number and spatial distribution of the barrier lakes in the earthquake-hit area from ADS40 airborne images, which covered areas of about 23,700 km2. The results showed that there were 51 barrier lakes in the monitored area; among these, 10 were large-scale lakes and 14 were middle-sized lakes. The barrier lakes were distributed along the Longmen Mountain fault from the northeast to southwest direction. We used the dimensionless blockage index (DBI) to assess the potential risk of the barrier lakes. A small DBI value indicated a stable barrier lake, but the lake might have a higher risk with potential accumulative secondary disasters. Our study emphasized the monitoring and analysis of the high-risk Tangjiashan Barrier Lake from the multitemporal ADS40 airborne images acquired on May 16, 19, 23, and 27. We found that the water level at this barrier lake reached 66 m within 15 days after the barrier lake was formed, and the reservoir storage capacity reached 1.2 × 108 m3 with an increase of 8 × 106 m3 of water per day. Therefore, it faced a very real and urgent risk of dam break and overflow, considering the predicted storm rainfall and the continuous aftershocks. According to the analysis results, airborne remote sensing demonstrated the advantages of being intelligent, being able to maneuver, and providing high resolution. These advantages allowed us to quickly monitor and assess the distribution and dynamic changes of the barrier lakes in the earthquake-hit region using multitemporal airborne remote sensing images.
Collapsing houses are one of the indicators to assess earthquake damage intensity. We monitored and analyzed the house collapse ratio and its spatial distribution in the Wenchuan Earthquake of May 12, 2008 by interpreting the aerial images. The results show that the houses were widely damaged, especially in Wenchuan County, Mianzhu City, Shifang City, and Pengzhou City in which Wenchuan County experienced the severest damage. We analyzed the spatial variation of the house collapse ratio and its relationship with earthquake intensity, geological structure, and stratum lithology. The results demonstrate that the house collapse ratio and the earthquake intensity have a positive relationship, which is controlled by the geological structure, stratum lithology, and building structure. Analysis of the collapsed houses over an extensive earthquake-damaged region using aerial images provides not only an effective assessment for the damages and losses, but also the foundation data for the analysis of earthquake intensity.
The secondary disasters induced by the Wenchuan earthquake of May 12, 2008, such as landslides, collapsing rocks, debris flows, floods, etc., have changed the local natural landscape tremendously and caused heavy soil erosion in the earthquake-hit areas. Using thematic mapper images taken before the earthquake and airborne images taken after the earthquake, we extracted information about the destroyed landscape by utilizing remote sensing and geographical information system techniques. Then, taking into account multi-year precipitation, vegetation cover, soil type, land use, and elevation data, we evaluated the soil erosion area and intensity using the revised universal soil loss equation. Results indicate that the soil erosion in earthquake-hit areas was exacerbated, with the severe erosion area increasing by 279.2 km2, or 1.9% of the total statistical area. Large amounts of soil and debris blocked streams and formed many barrier lakes over an area of more than 3.9 km2. It was evident from the spatial distribution of soil erosion areas that the intensity of soil erosion accelerated in the stream valley areas, especially in the valleys of the Min River and the Jian River.