Slush flows can be more deadly than avalanches: How scientists are racing to stop this hidden hazard

Scientists in Norway are developing a tool to help predict slush flows - a significant yet under-researched problem.

These moving masses of snow and water are much more unpredictable than avalanches, moving faster and with more energy.

Slush flows happen regularly in Norway - particularly in the far northern county of Finnmark. There have already been 55 documented incidents with several of them proving fatal. But this is likely an underestimate with data on these deadly hazards severely lacking.

No effective tools currently exist to predict when and where they might happen leaving authorities with little space to react.

The EU-funded IMPETUS project is hoping to change that by collecting data on what makes slush flows more likely and mapping the risks to help prevent life-threatening events.

What is a slush flow?

A slush flow is a mass of snow saturated with water that moves over long distances at high speed. The way they start is different from an avalanche.

Whereas an avalanche requires a steep slope of somewhere between 30 to 45 degrees, slush flows start on those below 30 degrees where water can accumulate in the snow. Once it is oversaturated, it begins to move, rapidly picking up speed.

“To compare a slush avalanche to a dry snow avalanche, the slush flow has much more mass because it's water and snow mixed together, and you get a really high speed,” explains Trond Jøran Nilsen, Finnmark’s avalanche planning expert.

“So the speed and the mass makes it high energy and then also you get much more damage potential. And also because you have a longer runout because it's flowing like water, it can go in a flat terrain. It can go long out on the fields or out to the sea.”

Why are slush flows dangerous?

The worst case scenario is humans being in the direct path of a slush flow. But even when they are not fatal they can be incredibly destructive.

If a slush flow hits a lake, the lake can overflow. As they move across the landscape they gather mud and rubble along the way, damaging roads and villages as they roll through.

Closing roads after a slush flow can mean a detour of four to nine hours with major consequences for commuters, hospital access and the fishing industry. Communities can be left completely isolated.

“Finnmark is a really big county. It is almost 48,000 square kilometres. It has around 4,200 kilometres of roads. The roads in this county are like the lifeline for people because it's almost the only way to get around. So it is really important the work the road authorities are doing to keep the roads open,’’ Nilsen says.

He adds that though there are a number of tools that can be used to forecast and assess avalanche risks, few exist for slush flows because little is known about how they happen. Knowing when and where to expect one could, for example, help road authorities to minimise disruption.

Can scientists predict when slush flows will happen?

At the University of Tromsø, scientists are working on a digital tool to map areas at risk of slush flows.

Leading the research is Christopher D’Ambiose who previously helped develop a model for avalanche flows in Austria. He is now adjusting his model to predict slush flows in Norway.

“We have some of the necessary conditions, but it doesn't tell the whole story. So how can we forecast that better? How can we tell okay when we have water saturated? So when is it dangerous and when is it okay?” These are the questions D’Ambiose is looking to answer.

He says that taking a deep dive into the data on weather conditions, snowpack and terrain will help determine what makes a slush flow more likely.

“Hopefully we can kind of narrow down which of those starting conditions actually matter and which signals actually matter in the data.”

This would allow them to decide when a situation is dangerous and when it isn’t, something that is very difficult with what is currently known.

Building a data set for slush flows

Most of Norway has a maritime climate, which can lead to more snow building up over a season, known as a snowpack. Though they can happen anywhere there is a seasonal snowpack, slush flows are more common in Norway and Scandinavia than in other parts of Europe like the Alps.

The midnight sun in the Arctic keeps solar radiation constant. Warm nights allow water to accumulate in the snow. The last ice age also tore away most of the topsoil in Norway’s mountains, leaving only a thin layer. Since water can’t penetrate the bedrock, it accumulates.

Weather approaches from the ocean, bringing periods of warm weather and rain that also contribute to water pooling in the snow.

Testing the snowpack for wet snow hazards involves carrying out field tests to measure the water content of the snow. These field assessments have seen road authorities from Finnmark County collaborate with the UIT – the Arctic University of Norway, as part of the IMPETUS project.

They observe and document slush flow paths, uploading the data to the national database and updating information on potential release areas.

“It's an important part of the research because we expect warmer and wetter winters up here in the Arctic,’’ says D’Ambiose. ”So we expect more of this kind of wet snow hazard to come in. And wet snow hazard could be wet snow avalanches or also slush flows.’’

Data from these field tests - crucial to determining the stability of a snowpack - is being used to validate the slush flow risk simulation model D’Ambiose is creating.

If successful, this model could help protect lives and infrastructure in Scandinavia and other regions with a regional snowpack.