Satellite imagery showed pre-event indications of Nepal-Tibet disaster, scientists say

A rapid hazard assessment of the Nepal-Tibet disaster by a group of international scientists says there were "pre-event indications" of the avalanche, including satellite imagery showing a change in the surface of the collapsed glacier.

The initial findings prepared by HiRISK on August 28 have raised questions about whether better disaster preparedness may have prevented hundreds of construction workers from becoming trapped at several hydropower projects after the deadly floods on Wednesday.

Jakob Steiner, a co-author of the report and a geologist who has been advising the Nepali government on disaster risk in the Himalayas, also told the ABC that early warning systems for construction workers were "very weak".

In the past decade, China and Nepal have launched a number of high-altitude infrastructure projects, including highways, dams, tunnels and hydropower plants along the border.

Several of those projects were damaged by the massive flash flood that tore through the valley last Wednesday.

The number of people missing has risen to more than 3,900 with at least 1,000 people known to have died.

Among the missing are believed to be hundreds of Nepali, Chinese and Indian construction workers building roads, hydro-electric dams and their tunnels along the Trishuli River.

On Monday, the Nepali government said at least 933 workers were believed to be trapped at about half a dozen hydropower projects.

They have so far evacuated about 300 workers from a collapsed Upper Trishuli tunnel.

Satellite imagery reveals early warning signs

In May, experts and officials from Nepal and China met in Kathmandu to discuss the risk of disasters in the border area, according to a Reuters report.

They discussed floods and glacier-related hazards, as well as monitoring and response measures, according to a meeting agenda prepared by the Nepali side.

The participants called for joint risk-reduction steps, including monitoring glacial lakes and mapping the hazards.

However, according to the HiRISK report, no early warning system for glacier-related hazards had been set up in the affected area so far.

"Given the rapid speed of the initial avalanche, warning time from conventional … systems would have been minimal and likely insufficient for successful evacuation at the Nepal-China border check point at Rasuwagadhi [Gyirong Port]," it said.

"Further downstream, with warning times of 10 minutes or more, comprehensive and well-capacitated systems could have saved a significant number of lives."

The HiRISK report was penned by experts from the Asian Mountain Academic Alliance, the Stimson Center, and China's Institute of Mountain Hazards and Environment.

When the experts analysed satellite imagery of the affected area days before the glacier collapse, they found "there were some pre-event indications" of the avalanche.

According to the report, one sign was a change in the glacier's surface.

Satellite observations suggest the water in the glacier accelerated before the collapse, a sign that something was shifting inside and that the surrounding rock was destabilising.

The satellite imagery from August 24 also showed that meltwater in the area had turned visibly brown, while the scientists also identified a crack propagating into the surrounding bedrock slope in the days before the avalanche.

Mr Steiner said AI-assisted satellite monitoring could help scientists identify risks across vast and difficult mountain terrain.

"This is where I think we need to invest more," he said.

"There are thousands and thousands of glaciers in High Mountain Asia, so we have to find scalable solutions."

'We can't say … nobody knew'

For scientists studying the Himalayas region, natural disasters like the flash flood last week have become more frequent over the past decade.

In July last year, a glacial lake outburst flood sent floodwaters through the Nepal-China border checkpoint — known in China as the Gyirong port — destroying roads and a bridge linking the two countries.

It left at least nine people dead.

Last Wednesday, the Gyirong port was again hit by floodwaters but was this time completely flattened.

There were also similar incidents in previous years.

A rock-ice avalanche affected the same area in July 2024, and there was an earthquake-triggered ice avalanche in April 2015.

"The magnitude of all of [these events] coming together and then happening after each other in the same location is a concerning thing, and this is what we call multi-hazard events," said Mr Steiner, who has surveyed the valley where the avalanche occurred.

Mr Steiner said the previous disasters should have provided enough warning, and that authorities need to be questioned why "very little" had been done to prepare since.

Zhang Maoming, Chinese Ambassador to Nepal, told NTV news last week that both Nepal and China "can learn a lot from responding to this disaster".

"It is imperative for China and Nepal to further strengthen cooperation in disaster prevention, mitigation and emergency management, and continuously enhance our capacity to respond to natural disasters," he said.

The ABC has approached the Nepal Ministry of Foreign Affairs, the Nepal Electricity Authority and Chinese embassy in Canberra for comment.

Workers need more protection

China was involved in building at least four hydro-electric dam and tunnels projects about 35 kilometres down the river from Gyirong port.

Three of them, Upper Trishuli-1, Upper Trishuli-3A and Upper Trishuli-3B, have reportedly been severely damaged by the flood, with rescue works ongoing.

In total, 12 hydropower facilities and a solar plant, about 10 per cent of Nepal's total operational capacity, have been shut down. Seven of them have been damaged or destroyed, according to the report.

Mr Steiner said every construction project underwent detailed environmental and risk assessments, but what was not clear was whether they had been followed precisely.

The construction workers were "more exposed" because they lived in barracks close to the hydropower infrastructure, he said.

Mr Steiner said considering hundreds of people worked in each "cave" and the risk of natural disasters, the early warning systems were still "very weak".

He said after the 2025 rock-ice avalanche, he met with local authorities and advocated for ongoing training for staff and for disaster management authorities to monitor early warning signs of potential disasters in the area.

But he said there had been "no investment" in those capabilities.

"To put it … cynically, there was a lot of hot air, but very little was [done]," he said.

He said both Nepali and Chinese governments needed to do more to protect construction workers in the region.

Risk beyond project boundaries

While experts agree on the value of building early warning systems in the Himalayan valley, they also concede there is little that can be done on the project management level.

Arnold Dix, an Australian geologist and an engineer, is helping with the Nepali rescue work at the collapsed tunnel at hydropower station Trishuli-3A.

He estimated the flood waters would have been travelling at more than 160 kilometres an hour, which would have left only about 10 minutes for a response.

"There were people at the construction camp, 10 minutes wouldn't be long enough to run from camp to the tunnels [which were more resilient to the flood]," he said.

Professor Dix said that in retrospect, other measures could have also been put in place.

"We might make access points to underground caverns. We might be able to build something man-made to try and slow down a huge amount of energy like that.

"But at the moment, I'm just scratching my head."

Professor Dix said the engineering design of hydropower station Trishuli-3A looked reasonable and had already factored in potential risks.

However, he said the flash flood last week was "really the equivalent of like a bomb".

Tunnel expert Chris Cooper, who is also helping with rescue work in Nepal, said people also needed to plan for risks outside the project boundaries.

"At the moment when you do a project, you know what your annual flood levels are and you design the project around the maximum flood levels," he told the ABC's The World.

He said what happened along Trishuli River was "catastrophic", and he doubted that any project would have factored that into its project risk.

Moving forward, Mr Cooper said there needed to be a better monitoring system and cross-border data sharing system between relevant countries.