The deadly flooding in Nepal on Wednesday was likely set off at least in part by an enormous chunk of ice snapping off a glacier and cascading thousands of feet to the valley below, according to an initial assessment by a group of geologists and glaciologists. The phenomenon is known as an ice avalanche.

“It looks like a glacier in the area basically snapped off in a clean break, allowing it to fall just over a vertical kilometer to the valley bottom,” said Daniel Shugar, a geologist at the University of Calgary in Canada who studied satellite imagery to analyze what happened. “The bottom looks like a bomb exploded — it’s just deposits from the broken-up glacier.” But he said that it was too early to rule out other possible factors behind the flash flooding.

Hundreds of people are missing in Nepal and the Chinese territory of Tibet after floodwaters cascaded through river valleys on Wednesday morning. Warming temperatures caused by climate change may have accelerated the glacier’s collapse, scientists said, but they added that it was too early to determine a precise cause.

According to the group’s analysis, the flow of ice moved northwest along the valley toward the Bhotekoshi River, at the border between Nepal and the Chinese territory of Tibet. Dr. Cook said the ice avalanche recalled a similar event in India in 2021, when a Himalayan glacier broke and caused major flooding in the northern Indian state of Uttarakhand, killing more than 100 people.