It was a wall of water and mud traveling at such speed that it engulfed buildings in seconds. In the wake of the Nepal flood disaster, questions were being asked about whether the deadly torrent could have been predicted or detected quicker to give communities downstream more time to evacuate.

Geologists say they believe the flash floods in Nepal and Tibet were set off by a dual high-altitude landslide and glacial avalanche that unleashed huge volumes of water. Disaster experts say such events are difficult to forecast.

Most monitoring and early-warning systems for glacial hazards focus on a specific area of risk. For example, water levels in flood-prone glacial lakes — which form when a glacier retreats and meltwater fills the hole left behind — can be monitored for unexpected rises.

Eran Hood, professor of environmental science at the University of Alaska, has spent years studying glacial lake outburst floods from the Mendenhall Glacier and their impact on the city of Juneau, where flooding occurs annually.

He said that scientists relied on real-time video monitoring, laser measurements of water levels and frequent field observations to try to predict when the area might flood and what the risks might be to communities downstream.

But experts in disaster response said the Nepal flooding would have been harder to predict because the collapse was sudden. Forecasting such an event would have required intensive and resource-heavy monitoring across vast areas, they say.

One way to improve monitoring could be to measure seismic activity and use remote sensing technology to build a 3-D image of the area, Professor Hood said. Over time, scientists might be able to look at deformations in the area and assess them for risk of collapse, he added.

“But the Himalayas are very remote. It’s not easy to get in there with drones or helicopters,” he noted.

Preparing for the Worst

There are 2,070 glacial lakes in Nepal, 21 of which are classified as high risk, according to a 2020 report by an intergovernmental body for mountain monitoring. There are many more glacial lakes in the surrounding Himalayan areas of China and India.

Although Nepal has a flood warning system, the country relies on a conventional network of river and lake gauges that is not equipped to issue alerts about the sudden collapse of part of a mountain, according to scientists and disaster response researchers.

The river gauges are designed to detect slower-rising water levels that typically precede floods from monsoons or glacial lakes, not the sort of fast-moving torrents that crashed through on Wednesday, experts said.

Shushil Kumar Shrestha, senior divisional engineer at the National Disaster Risk Reduction and Management Authority of Nepal, said the country does have a warning system in the region, but “the flood developed so rapidly that people simply did not have enough time to get to safety, even though the system was functioning.”

China has not said what kind of monitoring it undertakes.

Alton Byers, a glacier hazards expert at the University of Colorado, Boulder, said that the authorities needed to look at other measures, such as avoiding building on floodplains and ensuring that evacuation paths were developed and clearly marked.

He pointed to Japan’s tsunami warning system as an example. There, signs and broadcasts in different languages tell people what to do if a risk is detected. When a disaster strikes, he added, that information is crucial to increase survival chances.

Mr. Byers visited Nepal after an earthquake in 2015 to help assess the risk posed by three glacial lakes there.

He said that the Nepali government had installed a warning system but that locals reported not knowing what it sounded like or what to do if it went off.

Ensuring greater understanding about warning systems, as well as avoiding building in areas of risk such as flood plains, could improve safety, he said.

“It is no longer a question of if these floods are going to happen, but when the next flood will happen,” he added.