NEW DELHI: A large glacier collapse near the Nepal-China border in the early hours of August 26 is believed to be the likely cause of the devastating flash floods in Nepal. The collapse, which may have triggered significant ground vibrations equivalent to a 5.2-magnitude earthquake, led to debris flows and floods that killed over 350 people and left thousands missing. However, the exact cause of the glacier's collapse remains unclear.
Initially, scientists at the United States Geological Survey (USGS) recorded ground vibrations resembling an earthquake of magnitude 4.4 on August 26 at 8:37 AM (local time). After further examination of data from additional seismic monitoring stations, an analysis of the types of seismic waves, and review of satellite images, the USGS revised its conclusion.
They determined that there was no earthquake; instead, a large mass of glacier or ice had collapsed in the mountains, producing seismic waves that mimicked an earthquake. This event triggered a debris flow, which is a fast-moving mixture of mud, rocks, ice, and water.
The National Disaster Risk Reduction and Management Authority of Nepal reported data from Planet Labs, an Earth-imaging company, indicating that a large mass of snow and debris fell after a section of the glacier on the northern side of Langtang Himal detached. This mass dropped from an elevation of nearly 5 km to the river surface at around 3 km.
A preliminary analysis by the International Centre for Integrated Mountain Development (ICIMOD) revealed that a significant volume of an ice-rock avalanche descended from high altitude into the Lende Khola river, a tributary of the Bhote Koshi. This sudden influx generated a surge of water mixed with sediments and large boulders, raising water levels up to nine meters high downstream within 30 minutes, which washed away villages, towns, bridges, six hydropower plants, and roads.
Experts from various institutes estimated the size of the ice chunk that dropped to be between 0.2 kms and 1.5 kms wide, descending to approximately 5 km above the river surface. However, Indian glaciologists have refrained from commenting on the initial size of the ice chunk.
Besides, Chinese authorities have warned Nepal of another impending disaster, as a large barrier lake containing 2 million cubic meters of water (equivalent to 800 Olympic-sized swimming pools) has formed. This lake could breach as more water flows into it in the coming days.
A recent analysis by ICIMOD showed that glaciers in the Hindu Kush Himalayas are losing ice at double the rate since 2000, increasing the risk of flash floods and avalanches.
