Scientists from the HiRISK collective say satellite imagery showed several signs of glacier and slope instability days before the avalanche that triggered the devastating Nepal-Tibet flood.

 Warning signs of the devastating Nepal-Tibet flash flood may have been visible days before the disaster, according to scientists who analysed satellite imagery of the glacier and mountain slope involved in the avalanche.

Scientists from the HiRISK collective said satellite images showed what they described as “pre-event indications” of the avalanche, including changes in the glacier and surrounding terrain.

The findings have raised questions over whether these signals could have been detected and communicated to authorities early enough to warn communities living downstream.

Satellite images showed changes before disaster

According to the scientists, satellite imagery from the days before the flood indicated that water movement within the glacier had accelerated.

They said the change could have pointed to increasing instability inside the glacier and the surrounding rock.

Images captured two days before the disaster reportedly showed two additional signs. Scientists observed that meltwater had turned visibly brown and identified a crack developing in the surrounding bedrock slope.

Individually, such changes do not necessarily indicate that an avalanche or flood is imminent. But researchers said that, when considered together, they suggested increasing instability in the glacier and mountain slope.

Langtang Lirung collapse triggered avalanche

On August 26, a large section of the northern face of 7,234-metre Langtang Lirung mountain collapsed in Nepal.

The mountainside fell into the valley along with a substantial section of the glacier above it. The resulting rock-and-ice avalanche generated a massive debris flow that moved downstream and contributed to flooding across the Bhote Koshi-Trishuli-Narayani river system and the Nepal-Tibet border region.

The disaster has caused extensive destruction and a significant loss of life.

The latest figures cited in the source report put the death toll at 1,127, while 4,858 people remain missing.

Could earlier detection have helped?

The scientists stressed that identifying the satellite signals retrospectively does not mean the disaster could certainly have been predicted.

However, they said systematic monitoring of glaciers and unstable mountain slopes could help improve future early-warning systems.

The HiRISK assessment suggested that communities farther downstream could potentially have benefited from 10 minutes or more of warning time. Such advance notice, combined with an effective warning and evacuation system, could potentially have allowed people in vulnerable areas to move to safety.

This distinction is important: the satellite observations indicate that physical changes were detectable, but they do not establish that authorities could have confidently predicted the exact timing or scale of the avalanche before it occurred.

Scientists call for AI-assisted monitoring

Jakob Steiner, a geologist and co-author of the assessment, said AI-assisted satellite monitoring could help identify potential hazards across the vast and difficult terrain of High Mountain Asia.

Steiner told ABC News that there are thousands of glaciers across the region and that monitoring them would require scalable technological solutions.

The findings therefore point to a broader challenge for Himalayan disaster preparedness: detecting warning signals is only useful if those signals can be rapidly analysed, verified and converted into actionable alerts for people at risk.

For Nepal and other countries exposed to glacier-related hazards, the disaster could strengthen the case for combining satellite monitoring, AI-based analysis and local early-warning systems to reduce response times in future emergencies.