A glacier collapse near Nepal’s Langtang Lirung appears to have triggered the devastating floods along the Nepal-Tibet border, according to scientific analysis. The initial explanation focused on an earthquake causing a landslide, but the US Geological Survey later identified the breaking of part of a glacier as the cause of the disaster.
Researchers who examined USGS data said the glacier’s impact on the valley floor was equivalent to an earthquake measuring 5.2 in magnitude. The collapse is believed to have released a large mixture of ice and rock, which moved into the Lende Khola, a tributary of the Bhotekoshi River.
The sudden surge then carried silt, large rocks and other debris downstream. An analysis by the International Centre for Integrated Mountain Development, or ICIMOD, found that water levels in lower areas rose by seven to nine metres within half an hour. Several water-monitoring stations were swept away or damaged.
How the flood developed
Dr Simon Cook, a glacier specialist at the University of Dundee, said his team had traced the event to the lower section of a glacier near Langtang Lirung in Nepal. The location is about 15 kilometres west of the area affected by the flooding.
The glacier appears to have broken towards the north-west before falling westward into the river’s flow, according to Cook’s assessment. ICIMOD described the event as possibly an avalanche made up of ice and rock.
Professor Mike Searle, an earth sciences expert at the University of Oxford, said the sequence may have involved several stages. A landslide could have blocked the river, allowing water to build up behind a temporary dam before the barrier failed and released a destructive flood.
The steep landscape around Langtang Lirung may have intensified the impact. The peak is located in the high Himalayas, where sharply inclined valleys on both sides of the mountain can channel water rapidly downhill.
Searle said the process from the initial landslide to the flood could have unfolded over hours or even several days, rather than necessarily occurring in a single instant.
Why the glacier broke
The precise reason for the glacier’s collapse on Wednesday remains unclear. Searle said Langtang Lirung, like other parts of the Himalayas, has been rising gradually because of tectonic activity.
That geological movement pushes one plate above another. As the mountains rise, glaciers become steeper, increasing the likelihood that sections will break away. In most cases, Searle said, the pieces are smaller and may temporarily block rivers before being carried away.
The scale of this event appears to have been unusual because what may have broken was a much larger section of the glacier. Searle said floods of this kind occur frequently, but rarely at such a large scale.
He suggested that two separate processes may have contributed: the tectonic forces lifting the Himalayas and the effects of climate change, including rising temperatures and glacier melt. Scientists have warned for years that climate change is accelerating the loss of ice and permafrost in the Himalayan region.
Wider glacier-related risks
An ICIMOD analysis earlier this year found that glaciers in the Hindu Kush are now losing ice at twice the rate recorded in the year 2000. The organisation said this increases hazards such as flooding.
Cook said similar floods and landslides linked to glacier collapses have occurred in India, Switzerland and Italy in recent years. In 2021, a large section of a Himalayan glacier broke away in northern India’s Chamoli Valley, sending a torrent of water and debris downstream. About 200 people died in that disaster.
Scientists later estimated that the collapse had an impact equivalent to 15 nuclear bombs. Nepal also experienced flooding last year after a glacial lake burst in Tibet.
The latest event underscores the danger created when unstable ice, steep Himalayan terrain and river channels combine. However, the exact chain of events behind Wednesday’s collapse has not yet been fully established.
