Nepal Faces Secondary Flash Flood Threat as Debris Forms Temporary Dam Following Avalanche

NEW DELHI / KATHMANDU — Nepal remains vulnerable to secondary flash floods as debris from a recent ice-rock avalanche accumulates at river confluences, creating a temporary dam. Mohd Farooq Azam, a senior cryosphere specialist at the International Centre for Integrated Mountain Development (ICIMOD), issued the warning as search and rescue operations entered their third day.

The disaster, which has affected both Nepal and Tibet, has resulted in a death toll exceeding 470, with approximately 1,000 people still reported missing as of Friday. Researchers at ICIMOD, based near Kathmandu, have been investigating the event and indicate that an ice-rock avalanche originating from a high-altitude location likely triggered the initial floods.

According to Azam, the disaster involved a detachment of bedrock from beneath a glacier, which descended into the valley. The resulting debris has created a temporary barrier at the river confluence, collecting water. Experts anticipate that water will continue to accumulate in the temporary pond or lake over the next three days, increasing the probability of secondary flash flooding in the valley.

However, Azam noted that there is also a possibility that the temporary lake could breach gradually, releasing water without triggering a sudden flash flood. He drew parallels to the February 2021 disaster in Chamoli, Uttarakhand, where mass movement blocked the Rishi Ganga river. In that instance, the secondary lake breached slowly without causing a flash flood, a scenario authorities hope will repeat in Nepal.

Following the rising water levels at the affected site, Nepal's National Disaster Risk Reduction and Management Authority (NDRRMA) issued a fresh flood warning. Azam cautioned that even a minor secondary flash flood could prove devastating because the valley is already highly vulnerable and sensitive.

Addressing the predictability of such events, Azam stated that while preventing these disasters is difficult, advance understanding is possible—particularly for glacial lake outburst floods, where expanding lakes are visible. Monitoring these lakes and sharing data can help develop regional-scale strategies.

Highlighting the cross-border nature of upstream disasters, Azam pointed out that the recent event originated in the Nepal Himalaya, entered the Tibetan boundary where it impacted infrastructure, and then moved back toward Nepal. He emphasized the necessity of regional cooperation and data-sharing policies to better understand and prepare for such cross-border environmental risks.

"Environmental disasters and infrastructure risks pose significant operational challenges for businesses operating in vulnerable geographical corridors. This situation in Nepal highlights the critical need for robust business continuity planning, supply chain resilience, and cross-border risk assessment. Companies with regional footprints must integrate environmental monitoring and proactive data sharing into their risk management frameworks to mitigate unforeseen disruptions." — Dr. Shishir Gupta, Founder & CEO, StartupLanes