A rock-ice avalanche induced complex hazard cascade in the Suku River basin, southeastern Tibetan Plateau

In the Tibetan Plateau cryosphere, rock and ice avalanches are becoming more frequent due to climate warming. These events often trigger a cascade effect, resulting in catastrophic disasters. On July 2, 2018, a rock-ice avalanche occurred in the Suku River basin on the southeastern Tibetan Plateau, triggering an extremely complex hazard cascade. This cascade included eight processes: rock and ice avalanche, mass flow, barrier lake, outburst flood, debris flow, flood, debris flow, flood. The event caused significant damage to infrastructure within approximately 50 km downstream, inundating and destroying dozens of houses and 150 m roads. The hazard cascade event was reconstructed using optical images, digital elevation model data, field investigation, and numerical analysis. The rock-ice avalanche originated in the steep glacial bedrock area at the top of the right bank of the Suku River, with a 3.60 million cubic meters volume. The fractured rock and ice hit the lower slope, disintegrated, transformed into mass flow, and scoured the lower glacier and moraine. Eventually, these mixed materials accumulated in the Suku River and formed a barrier dam with a height of 68 m. After three days, the dam lake overtopped and burst, with the entire process lasting approximately two hours and reaching a peak flow of 195.16 m³/s. Subsequently, the outburst fluid underwent multiple transitions between flood and debris flow due to the input and output of loose solid materials downstream. Meteorological data indicates that rapid warming and prolonged heavy rainfall triggered the rock and ice avalanche. After the rock and ice failure, the transformation process was primarily controlled by the topography and the erosion and deposition of loose materials downstream. This study is crucial for understanding the complex hazard cascade process of the cryosphere and for mitigating disaster risk.