Tsunami of dirt: What caused Nepal’s deadly glacial flood?

An enormous wave of water, ice, mud and rock swept down the Bhote Koshi River valley in Nepal, killing over 150 people and leaving hundreds more missing. The disaster, which struck without warning, is believed to have been caused by the abrupt collapse of a glacier. As climate change intensifies, glaciers worldwide, including those in the Himalayas, are rapidly melting, making them increasingly unstable.

Early analysis suggests that a large ice-and-rock landslide, triggered by the melting glacier, swept down a mountain pass, gathering up ice, water, rock, trees and dirt to form a massive debris flow. The landslide was so extensive that it initially appeared to be an earthquake when it was detected by seismographs. Despite its magnitude, the wave resembled a "tsunami of dirt" upon reaching Gyirong Port, a border crossing between China and Nepal.

Satellite imagery indicates that the landslide may have carved out significant sections of a glacier, causing its collapse. While the exact cause of the glacier's collapse remains unknown, the widespread retreat of glaciers due to climate change has led to a growing number of flood and debris flow disasters worldwide. A smaller flood in the same district of Nepal last year claimed nine lives, while a melting glacier in Switzerland triggered a devastating debris flow in a village earlier this year.

In 2023, a landslide and subsequent flood in Georgia killed 33 people at a mountain resort. This disaster is among the largest ever recorded. The high-altitude glaciers of the Himalayas respond differently to climate change than those at lower elevations or in warmer regions. As permafrost thaws, it can weaken the ice that holds together rock and soil on steep Himalayan slopes, making them more susceptible to landslides and other forms of ground movement.

If an earthquake or other disturbance occurs, it could trigger a rapid downslope movement of debris. Early warning systems can help mitigate the impact of such disasters by monitoring rapidly rising river levels, intense rainfall, and seismic waves to alert authorities before a catastrophe strikes. However, the installation and maintenance of these systems require significant investment, posing a challenge for lower-income and developing countries.

The Green Climate Fund recently announced funding for improved monitoring systems in Nepal. While increased glacier melt can temporarily boost river flows and contribute to flood risk in some areas, as glaciers continue to diminish, their contribution may eventually wane, leading to reduced water availability, particularly during the dry season.

To prepare for these challenges, rapidly reducing greenhouse gas emissions, investing in early warning systems, and monitoring vulnerable mountain regions are crucial. While these measures cannot prevent every disaster, they can save lives and enhance communities' ability to adapt to a changing climate.