Why hanging glaciers matter after Nepal

Nepal's flood began with a glacier collapse on Wednesday. That is the warning.

Hanging glaciers are ice on steep slopes. They can detach. When they do, the ice can become an avalanche. It can also set off a glacial lake outburst flood downstream.

A Nature study in April 2026 counted 219 hanging glaciers in the Alaknanda basin of the Garhwal Himalayas. Ashim Sattar of IIT Bhubaneswar and Nandu Krishnan of IISc were among the authors.

The ice covers 71.7 plus or minus 3.5 square kilometres. The ice volume is 2.39 plus or minus 0.42 cubic kilometres. Of that, 0.74 plus or minus 0.14 cubic kilometres is hanging ice.

Simulations said avalanche flows could exceed 50 metres in height in the Badrinath-Mana stretch. There is a secondary risk of glacial lake outburst floods.

Exposure of buildings and infrastructure is projected to rise 120 percent by 2030 against 2000. The number of people in those zones is projected to rise 17 percent.

The Alaknanda basin holds towns as well as ice. Badrinath and Mana sit in the stretch the models flagged. A 50-metre flow is a wall of debris.

Nepal's collapse is a live case of ice coming off a steep face. The Indian study is an inventory of ice that can fall in one basin. The authors mapped hanging glaciers. They did not forecast a flood in Badrinath this week.

The volume numbers are small on a planetary scale and large on a valley scale. Less than one cubic kilometre of hanging ice can still bury a town if it detaches above the wrong slope. The 219 count tells you how many of those slopes the authors found in this one basin.

Chamoli in 2021 showed what a sudden ice-and-rock collapse can do in this range. Warning was thin. Blatten in Switzerland showed the other end. People were moved before the slope came down. The contrast is about preparedness.

Pam Pearson, director of the International Cryosphere Climate Initiative, has said these glaciers need systematic identification and monitoring. The study's own numbers point the same way. You cannot watch what you have not listed.

The exposure figures matter because buildings are growing as well as ice risk. Buildings and infrastructure in the hazard zone are projected to more than double against 2000. People in those zones rise more slowly, at 17 percent. The land is filling faster than the population print.

A secondary glacial lake outburst flood is the cascade. Ice falls. It dams a river, or it hits a lake. The water then goes. That is how a hanging glacier above one valley becomes a problem kilometres downstream.

Nepal is still counting the dead and the missing. The rebuild estimate is already in the billions.

For India, the work is the list. Officials need to know which hanging glaciers sit above towns, roads, and pilgrimage routes. They need to know who is watching them, and what the warning looks like if one moves.

The Nature count is a start for the Alaknanda. Monitoring is the next step Pearson and the study both point to.