Nepal-Tibet Floods Were Likely Triggered by a Glacier-Side Landslide

A massive flash flood that struck near the Nepal-China border on August 26 appears to have begun with a landslide in Nepal’s Lāṅṭāṇ National Park, according to an August 27 update from the U.S. Geological Survey. The landslide may have carried part of a glacier downhill, releasing energy comparable to a magnitude-5.2 earthquake. The resulting mass of ice, rock and sediment then moved through river channels, gathering additional water and producing a debris flow that traveled roughly 62 miles. Scientists initially considered whether a glacial lake had burst, but satellite imagery and weather data did not show evidence that a large lake had formed in the area. Many researchers now favor the landslide explanation over the possibility that a glacier simply collapsed. Satellite images taken on the evening of the disaster showed what appeared to be a stripped section of mountain, which researchers said was consistent with a major landslide. The exact source of all the floodwater remains uncertain. Researchers cited by Smithsonian Magazine said the moving debris may have accumulated river water as it descended, though the scale of the resulting flow has made that question difficult to resolve. Authorities said the disaster had killed more than 900 people and left almost 5,000 missing by August 31. Rescue operations remained underway, including efforts to reach people stranded on buildings and hundreds of workers trapped in hydropower tunnels. Recovery could take weeks, followed by months of cleanup. Nepali officials estimated rebuilding costs at $4 billion to $5 billion. Scientists have not yet completed a formal attribution study linking this particular flood to climate change. However, researchers say warming temperatures are destabilizing Himalayan glaciers and thawing permafrost beneath mountain slopes. Those changes can make ice and surrounding terrain less stable, increasing the possibility of landslides and cascading floods. Researchers therefore expect similar glacier-related hazards to become more common as global temperatures rise, although they have not determined precisely how often such events will occur. Nepal’s foreign minister called for international action to protect the Himalayan ecosystem, noting that the country contributes relatively little to global greenhouse-gas emissions while facing severe effects from climate change.