Impacts of landslide dams on mountain valley morphology

Landslide dams can influence mountain-valley morphology significantly in the vicinity of the dam sites, as well as upstream and downstream. The effects are: (1) impoundment of lakes that results in changes in stream gradients, (2) deposition of lacustrine and deltaic sediments in these impoundments that causes changes in surficial morphology and geologic materials upstream from the dams, (3) diversion of stream channels at and near the dam sites, (4) formation of avulsively-shifting channels downstream from the dams by the introduction of high sediment loads from erosion of landslide deposits or sediments in the landslide-dammed lakes, and (5) secondary landslide activity along the shores of the impounded lakes due to rapid drawdown when the dams fail. Often, by construction of channel spillways or outlet tunnels, human remedial efforts affect the longevity of landslide dams and their impoundments, and thus influence the long-term effects of these natural features on mountain-valley morphology.