In late August, a devastating natural disaster struck northern Nepal, claiming over 1,200 lives and leaving countless others missing. The unexpected severity of the rock, mud, and water flow took experts by surprise, highlighting the unpredictability of geological events in the region.
Geological engineer Ranjan Dahal from Tribhuvan University in Kathmandu shared his disbelief: “The victims, their pain and all the ruined towns … it is almost impossible to believe. I don’t think even Hollywood could make such a movie.”
Satellite images have provided crucial insight into the disaster. The collapse of a massive bedrock and ice slab from Langtang Lirung initiated a debris flow that raced downstream toward India, reaching speeds exceeding 160 kilometers per hour and obliterating villages in its path.
Mountain geographer Alton Byers of the University of Colorado Boulder remarked, “I’ve never seen anything remotely as large as this,” underscoring the scale of the catastrophe.
Underlying Causes
While the exact trigger of the bedrock collapse remains uncertain, scientists suggest a combination of geological, glacial, and climatic factors. The event highlights the growing risks in high mountain areas due to changing climate conditions. Glaciologist Ulyana Peña, also from the University of Colorado Boulder, warned, “The mountains are crumbling globally.”
Initially, it was thought a collapsing glacier caused the debris flow. However, satellite images soon revealed a newly exposed slope on Langtang Lirung’s north face at around 5,150 meters elevation. A 2.2 square kilometer slab of bedrock had detached, carrying ice into the valley below.
The volume of the detached glacier and bedrock is estimated at approximately 110 million cubic meters, roughly 40 times the volume of the Great Pyramid of Giza.
Copernicus Sentinel, Landsat-9, ESA
These processed satellite images, taken a couple of days before (left) and a couple hours after (right) the avalanche, show how flood water and debris spread downstream from the glaciated area where the rock and ice fell.
Copernicus Sentinel, Landsat-9, ESA
The 2015 Gorkha earthquake, which caused significant damage, may have weakened the bedrock, according to mountain hydrologist Walter Immerzeel of Utrecht University. Additionally, climate warming has softened much of the permafrost in the region, as illustrated by the analogy of leaving a stick of butter out of the refrigerator, Byers noted.
The recent warming of the area has been significant. The region’s temperature has risen by about 2 degrees Celsius since preindustrial times, according to World Weather Attribution. The days leading up to the collapse were particularly warm, with temperatures exceeding historical averages.
Moreover, the glacier above the bedrock had receded significantly, altering stress on the mountain face. Meltwater infiltration and subsequent refreezing may have worsened the situation by expanding rock fractures, noted geologist Jeffrey Kargel of the Planetary Science Institute.
Vulnerable Rock Structures
The type of rock involved, identified as metasedimentary, could have amplified the disaster. These rocks, originating from mud and sand layers, have inherent weaknesses that may have facilitated the rock’s disintegration. This increased frictional heating, transforming the debris into a fluid mass that rapidly descended the mountain.
Kargel highlighted the presence of similar rock types in past avalanches, such as the 2021 Chamoli disaster in India, which claimed over 200 lives. However, in Nepal’s case, the initial breakage seems more linked to existing fractures and climate-induced stress.
Byers emphasized the undeniable connection between climate change and such events, stating, “If you believe that warming temperatures melt ice, then I think you can make the connection.”
Beyond Nepal
Other Himalayan regions may face similar threats, especially where fractured and weathered rocks coincide with glaciers. More detailed geological mapping is needed to identify high-risk areas, Kargel suggested, as climate change continues destabilizing these regions.
The hazards are not limited to rock-ice avalanches. Glacial lake outburst floods (GLOFs) are becoming more frequent due to melting glaciers. A 2023 study in Nature Communications indicated that 15 million people live near glacial lakes, within potential flood paths.
High-risk areas like the Andes and European Alps are also experiencing increased glacial hazards. The Andes, for instance, have seen a doubling of glacial lakes, posing significant risks to nearby populations.
Dahal calls for international cooperation to implement early warning systems across the Himalayas, aiming to prevent future tragedies. “Let’s work together,” he urged, “and let’s save the lives of the people.”
Original Story at www.sciencenews.org