Footage: Slush found – Norway’s dangerous slush flows get mapped

A slush flow is a mass of water-saturated snow that moves over long distances at high speed. A major difference between these and avalanches is how they start. Whereas avalanches need a steep slope of 30 to 45 degrees, slush flows normally start on slopes below a 30-degree angle where water can saturate the snow. Oversaturation of the snow leads to movement within the watery mass which starts a slush flow.  

In Norway, particularly in the far northern county of Finnmark, slush flows happen regularly, with 55 incidents already documented - some of them proving fatal.  

In a series of new, free-to-use interviews, experts explain the science behind these wet snow hazards, and the new mapping techniques that could help road authorities avoid communities from costly and time-consuming closures. 

Closing roads after a slush flow often means a detour of between four and nine hours. This has major consequences for Finnmark’s commuters, access to hospitals, and the fishing industry.   

“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,’’ says Trond Jøran Nilsen, the avalanche planning expert of Finnmark County. 

He says that although there are many tools to make avalanche forecasts and assessments, few exist for slush flows because there’s little known about the process behind them. If the road authorities know when and where to expect a slush flow, they could minimise these disruptions.  

NEW SLUSH MAP 

At the University of Tromsø, a digital tool to map slush flow hazards is now in development under the EU-funded IMPETUS project. This hazard map shows the area at risk of slush flows. A forecast of extreme weather conditions such as heavy rain, high temperatures or wind shows the increasing levels of danger in a particular area. 

For example, if the slush flow hits a lake it will overflow, gathering mud and rubble on the way and hitting roads and villages. Predicting these events will save lives through timely warnings.   

Leading the research is Christopher D’Ambiose of the University of Tromsø, who has already helped develop a model for avalanche flow in Austria. He is now adjusting the parameters of the same model for slush-flows.   

“I'm currently in validation mode. I have the simulation working. I've come up with a method for automatically identifying potential release areas. Now I need to make sure that the simulations actually match reality,’’ says Christopher. 

UNIQUE FACTORS 

But weather is not the only fluctuating variable required for the calculation. Slush flows can happen anywhere there's a seasonal snowpack, but they're more common in Norway and Scandinavia than other parts in the world like the Alps further south.  

In the Arctic the midnight sun keeps solar radiation constant, even at night. These warm nights allow water to accumulate in the snow. In comparison, nighttime temperatures in the Alps drop to or below freezing. This helps water to drain, lowering the snow’s water content.   

Likewise, any residual water in the Alps can also seep into its thick layer of soil. The last ice age tore away most of the topsoil in Norway’s mountains, leaving only a thin layer of soil beneath the bedrock. Since the water cannot refreeze nor penetrate the adjacent bedrock, it continues to accumulate.   

Warm periods and winter rain also contribute to this water pooling, caused by weather approaching from the ocean. 

FIELD TESTS 

Most of Norway has a maritime climate, which can lead to more snow building up over a season, known as a snow pack. Evaluating a snowpack for wet snow hazards involves field tests to measure the water content of the snow.   

In field-assessments, the 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 Christopher. “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.’’ 

“In practice everybody does this wet snow test. So, if it’s moist you can make a snowball. If it’s soaking, you can squeeze the water out. If it’s very wet, you can see water between the snow grains. That’s how we classify it in the field,’’ he says.  

These field tests for assessing the water content of snow are crucial for confirming the stability of a snowpack. By using updated field data to validate their simulation model, the researchers aim to create a national hazard map for slush flows. If successful, this model could help protect lives and infrastructure in Scandinavia and other regions with a regional snowpack.    

For more information, visit the IMPETUS website