Landslides caused by Wenchuan earthquake are distributed in
mountain regions mainly along the Yingxiu-Beichuan fault. Landslides
blocked the rivers and resulted in dozens of barrier lakes in
the quake-hit areas. Tangjiashan barrier lake was one of the largest
barrier lakes. Fig. 4 shows the development of a barrier lake located
to northwest of Beichuan county seat, which is a part of Tangjiashan
barrier lake. The barrier lake was caused by a massive landslide
which blocked the Jianjiang River (Fig. 4b). Fig. 4a and b is the
pre- and post-earthquake backscattering intensity images of ALOS
PALSAR, respectively, acquired on February 17, 2008 and May 19,
2008. Because of specular reflection from water surface, water body
is shown as dark target in a SAR image. Pre-earthquake backscattering
intensity image of PALSAR acquired on February 17, 2008 shows
the location of Jianjiang River as a narrow line (see cyan line shown
in Fig. 4a, which is the original riverway obtained from visual
interpretation of pre-earthquake backscattering intensity image