KATHMANDU, Oct 15: The Budhi Gandaki flood may have been triggered by the collapse of a glacier or a large mass of ice in the high Himalayas, according to a preliminary analysis, nearly six weeks after a similar disaster struck the Bhotekoshi area.
Although both events appear to be associated with ice and rock collapses in high mountain areas, researchers say the precise cause of the Budhi Gandaki flood remains unconfirmed.
Water resources and climate change researcher Dr Santosh Nepal said a glacier or a large mass of ice on the southern slopes of 7,100-metre-high Chamar Himal may have collapsed into the Syar River, potentially triggering the flood.
Dr Nepal, who has more than 16 years of experience in hydrological assessment, climate change and water resources management, has worked extensively across South Asia, particularly in the Hindu Kush Himalayan region.
He had previously served as a water and climate specialist at the International Centre for Integrated Mountain Development (ICIMOD) and led its Climate Change Hydrology group from 2012 to 2022.
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According to Dr Nepal, the preliminary assessment indicates that the ice mass may have descended from an elevation of around 5,000 metres to 2,000 metres, travelling five to six kilometres downhill. The affected glacier section is estimated to be 1.2 kilometres long and 600 metres wide.
However, the volume of ice, rock and debris involved remains uncertain. Further investigation and clearer satellite imagery are needed to establish the scale and nature of the collapse, according to Dr Nepal, who is currently affiliated with the International Water Management Institute.
Experts believe that rainfall may also have contributed to the disaster. An analysis of ERA5- Land data, a global dataset developed by the European Centre for Medium-Range Weather Forecasts (ECMWF) under the Copernicus Climate Change Service, indicates that a low-pressure system originating in the Bay of Bengal brought heavy rainfall to Nepal in late September. The ERA5 Land dataset provides historical estimates of land-based weather and environmental conditions. It provides detailed, historical estimates of land-based weather and environmental conditions Rainfall data show that Chamar Himal area received around 206 millimetres of rainfall between September 24 and 27. Much of the precipitation at such high elevations may have fallen as snow. Dr Nepal say that further analysis of satellite-derived snow-cover data is needed to determine whether snowfall contributed to the suspected ice collapse and subsequent flooding.
ICIMOD scientist Sudan Bikash Maharjan also argued that an avalanche and glacier collapse were the likely causes of the flood.
“Planet imagery clearly shows evidence of an avalanche and glacier collapse. The landslide occurred after this event,” Maharjan said in a social media post.
Similarities with the Bhotekoshi flood
Dr Nepal said the Budhi Gandaki and Bhotekoshi floods appear to share a possible link to ice and rock collapses in high mountain areas.
Heavy snowfall was reported in the Langtang Himalayan region before the Bhotekoshi flood in August, while data indicate heavy rainfall and possible snowfall before the Budhi Gandaki disaster. However, researchers have yet to establish whether snowfall directly contributed to either event.
The two floods also appear to have differed in the materials they carried downstream. Preliminary observations suggest that the Budhi Gandaki flood contained a relatively high proportion of fine, black clay particles, while the Bhotekoshi flood carried a mixture of rocks, soil and snow.
Need for stronger Himalayan monitoring
The two disasters occurred within roughly 45 days, with their suspected source areas about 40 kilometres apart. The events underscore the need for stronger monitoring of hazards across the Himalayan region.
High-altitude hazards, including ice and rock collapses, sudden river surges and intense rainfall, can pose serious threats to downstream communities and infrastructure.
Dr Nepal called for stronger international support to help vulnerable countries address climate-related risks. He said effective early warning systems, adequate climate finance, improved mountain monitoring and stronger institutional capacity were essential to reducing disaster risks.
Integrating satellite imagery, rainfall data, field investigations and river-flow measurements could help scientists better understand such hazards and provide timely alerts to vulnerable communities. “An early warning system that can deliver alerts faster than the flood travels has become essential for reducing disaster risks,” Dr Nepal said.