The establishment and influence of Baimakou paleo-dam in an upstream reach of the Yangtze River, southeastern margin of the Tibetan Plateau

Abstract

Landslide damming is an important disturbance factor in the river evolution of mountain belts and may control river morphology at variable timescales. This temporal aspect is mostly discussed in terms of the spatial relationships between the dams and river longitudinal profiles within any given region. Largely lacking are detailed studies of the geomorphic response for individual dams. Here we present field evidence and 24 optically stimulated luminescence (OSL) ages that show the history of a landslide dam in an upstream reach of Yangtze River at the southeastern margin of the Tibetan Plateau and its influence on river evolution. The distribution of lacustrine ages suggests that there was only one long-term damming event, induced by landslide blocking the river. The dammed lake formed at 12.1 ka, and disappeared at 7.5 ka. The estimated dam height was 120 m, lake area was 96 km2, and lake volume was 7.5 km3. In addition, the grain size and distribution of lacustrine deposits indicate the dam failed cataclysmically when the lake finally drained. Today, the river long profile upstream of the dam site remains lower and the channel is wider in contrast to the downstream reach. Consequently, the former dam still influences channel morphology. Our study shows that the interaction of landslide dams with the rivers in the southeastern Tibetan Plateau may impeded valley incision and headward erosion in those cases where damming continued over periods of several thousand years.