The Ms 8.0 earthquake that hit Wenchuan on May 12, 2008 caused a number of barrier lakes threatening lives and properties in the downstream. The early reported 34 lakes in the quake-hit area are scattered within a distance of 15 km to the central fault of the Longmenshan Fault Zone. These lakes are distributed along the faults. Emergency measures have been taken to the lakes with high risks. This paper reports the background, environment, damming structure, countermeasures, and its effects with particular interest to the Tangjiashan and Xiaogangjian barrier lakes. Finally, problems for future study are commented
Barrier lakes are usually formed by landslides, moraines, debris flows, and volcanic eruptions or flows when they run into and dam up rivers. Barrier lakes induced by earthquake are one of many secondary disasters of the earthquake. Historically, quake-induced lakes are common in mountain areas. These dams are formed by quick accumulations and usually unconsolidated, loose in structure, and likely to collapse due to seepage and erosion, resulting in catastrophic flood or debris endangering the downstream (Seismological Bureau of Sichuan Province, 1983).
Landslides, rockfalls, debris flows, and collapses induced by the Wenchuan earthquake on May 12, 2008, have formed many barrier lakes and 34 of high risk ones have been treated by emergent countermeasures, from the early report. This paper provides an outline of the barrier lakes, their distribution, and the countermeasures.
The Wenchuan earthquake has stricken the mountain areas with complexity of geology and geotectonics, making them prone to landslides and collapses. Many slopes are unstable and likely to fail under the vertical and horizontal forces of the quake, large landslides occur at some locations. The landslides and collapses poured into the streambed that dammed the flow and finally formed lakes (Cui Peng, 2008).
By May 19, seven days after the earthquake, 34 barrier lakes were reported (Figure 1, Table 1, 2).
The epicenter is located in the central faults of the Longmenshan fault zone, which consists of a group of faults in NE30°-40° of Yingxiu-Beichuan fault, Remote sensing data indicate that the major fracture stretches along the Yingxiu-Beichuan faults, from the Shuimo town of Wenchuan in the south through the Chaping village of Qingchuan in the north. The barrier lakes are distributed along the major fracture, all within 15 km to the major faults (Figure 2). Among them, 24 lakes are within 5 km; and the number of lakes along the front and back faults are 24 and 10 respectively.
(Table in full paper)
In rivers, the barrier lakes form strings of beads. For example, in the Tongkou (Jianjiang) River within 30 km lie 9 lakes; and in Mianyuan Rive there are 4 within 10 km(distribution density is 0.4 lakes/km); in Shiting River, 7 within 8 km(distribution density is 0.88 lakes/km).