– I expect more slush avalanches if the weather continues to vary in winter, because rain on snow is particularly dangerous, says Christopher D’Amboise. He has a doctorate in the field and is one of the few researchers working with slush avalanches in Norway and worldwide. – We expect more landslides, but at the same time there are still many open questions about mudslides. In October, D’Amboise started at UiT Norway’s Arctic University in October 2022 to research slush avalanches. Through mapping and modelling, he hopes to be able to put in place better assessments of when mudslides may occur and a better warning system. Christopher D’Amboise researches slush avalanches. His goal is to find a method that makes it possible to predict even better where slush avalanches can go. Photo: Siri Vilberg / UiT A slush avalanche occurred in the Tour de France It is unusual for slush avalanches to occur in northern Norway, but avalanche researcher Christopher D’Amboise says that milder winters, which alternate between plus and minus degrees, make the risk of more slush avalanches even greater in the following years. Monica Sund is chief engineer in the Hydrological Department of the Norwegian Directorate of Water Resources and Energy (NVE). She states that there are slush avalanches all over the country. – Basically, slush avalanches can occur in the whole country and in general anywhere in the world with snow, but areas with alternations between snow and mild weather, such as Western Norway and the coastal areas to the north, are probably more exposed than, for example, the inland areas in the east, writes Sund in an e -mail to news. – Southern avalanches are observed more or less everywhere in the world with snow, and in all seasons. For example, a slush avalanche was triggered on stage 19 during the Tour de France on 26 July 2019. First came snow that settled on bare asphalt, followed by intense rain. It was unleashed as a small slush avalanche on the asphalt, but then dragged a lot of soil down with it, since the soil was not frozen. Triggered naturally The aim of Christopher D’Amboise’s research project, which is financed by EU funds, is to make it safer for people to travel along the roads in winter. – Many avalanches are triggered by a skier, but this type of avalanche happens when people do not know they are in danger, says Christopher D’Amboise about the form of avalanche that he is researching. Because while avalanches often occur on slopes of 25–30 degrees, slush avalanches can be triggered in places with a smaller slope. It is also easier to see in the terrain where an avalanche can go on steep terrain. – Sørpeskred does not follow the same rules, he continues. For the researcher, the whole of Northern Norway is the coverage area. – And I always have a bag packed and am ready to go out to study slush avalanches. – Interesting Geologist in Troms and Finnmark County Municipality, Trond Jøran Nilsen, says that it is difficult to predict where and when slush avalanches will be triggered. New research and better warning systems are therefore something he welcomes. – It is certainly interesting. New knowledge is always good in relation to avalanche warning, says Nilsen. Monica Sund states that warning of avalanche danger on a regional scale is a relatively new service, which Norway is probably the only one to have. – There are probably several reasons why there has not been an established warning of the danger of avalanches earlier. One is that slush avalanches have often been mixed together with other types of avalanches, writes the NVE hydrologist. – As a result, there has been little awareness of this type of avalanche, even though there are other processes that lead to slush avalanches than, for example, avalanches. The second is that the process is complex and it became clear early on that slush avalanches were challenging to warn. Trond Jøran Nilsen states that one of the biggest challenges with landslide assessments today is having enough data. It is not always the case that you have enough information about local conditions to be able to make a good landslide assessment. – Sørpeskred is not something that happens very often and then it is difficult to get enough knowledge about it. It is therefore important to know whether there are any factors, beyond those we know today, that can help make better assessments. In collaboration with the contractors, assessments are made as to whether road sections should be closed due to an increased risk of landslides. Trond Jøran Nilsen is a geologist in Troms and Finnmark County Municipality. He states that slush avalanches are rare in Finnmark, but that this year there have been more than normal. Photo: Kristian Sønvisen Bye / news Facts about slush avalanches Slurp avalanches differ from wet snow avalanches, among other things, in that they start on gentle slopes or depressions where water collects. Wet snow avalanches will typically start on slopes above 30 degrees. In a slush avalanche, there will be free water between the snow particles in large parts of the avalanche mass, while this is the case to a lesser extent in a wet snow avalanche. Another characteristic of slush avalanches is that they often take all the snow with them in the course of the avalanche. Further down the run, however, it can be difficult to trace the origin of an avalanche that started as a mudslide, as they can tear loose and transport with them large quantities of loose masses, boulders and trees in and along the run. They can therefore look like a flood slide or a landslide in the lower part of the slide course. The southern avalanches vary in size. Some extend several kilometers downwards in great width over a water-saturated area. Triggering of slush avalanches Slurp avalanches are most often triggered during periods of heavy rain and/or intense snowmelt due to sudden temperature increases. The avalanches are usually triggered in areas with a snow depth of at least 0.5 m. With a smaller amount of snow – the melting process takes place so quickly that there is not enough snow left when full water saturation is reached. Fresh snow or coarse-grained snow with little firmness is most at risk. The water-saturated snow is almost liquid where the slush avalanche is released. Southern avalanches can also be triggered when an avalanche dams up a river. When the snow is saturated with water, the snow dam will break like a slush avalanche. In such cases, a slush avalanche could be triggered, even if the weather conditions do not indicate it Danger sign Blue or gray slivers in the upper parts of the snow cover or open water breaking through the snow show that the snow has a high water content. Range and speed Sørpeskred can have a large range even in relatively flat terrain. They often do not stop until they reach water or a fjord. The speed is often relatively high and can reach over 100 km/h. Safety measures Controlling the drainage to reduce the accumulation of water in exposed areas can be a measure. Another possibility is to set up nets or front buildings to keep the snow in place. By keeping streams open so that the water runs away, you can often avoid it accumulating in the snow masses. As mudslides move like a viscous liquid, they are difficult to stop with terrain measures. In depressions, check dams can still have a reducing effect. Barrier embankments and brake fronts can also be an option. (Source: NVE) Data from 1873 NVE is currently working on improving the data base, which are good records of mudslides from where they start to where they end, in order to be able to further develop the warning they have today. – Historical sources where it is clear that there has been a slush avalanche are also interesting. An example is a slush avalanche in Ofjordbukta on Sørøya in Finnmark where a slush avalanche occurred on 16 March 1873 where a house with seven people, several outbuildings with 40 small cattle and 2 cows were swept into the sea. Observations of snow type and weather conditions where slush avalanches have occurred or are signs of danger are also of great interest to NVE. Then preferably observations from areas with gentler terrain and not just from steep terrain where observations for avalanches are made. – Here we depend on contributions from people around. Observations of avalanches, even if you are unsure of the type of avalanche, and possible danger signs such as a lot of stormwater in the snow can be submitted to Regobs.no. This is then included in the warning assessment, and also stored as data that is later used to develop better warning tools. Large backlog The county roads in Troms and Finnmark have around 200 avalanche points and on a national basis there are around 1,500 avalanche points. Transport council in Troms and Finnmark county municipality, Agnete Masternes Hanssen (Ap), states that work is being done to contribute to new avalanche technology. Today, there is a backlog of 17 billion on avalanche protection in Troms and Finnmark. County councilor for transport in Troms and Finnmark county municipality, Agnete Masternes Hanssen, says that the county council has an extra focus on avalanche protection, but that they lack funds. Photo: Frode N. Børfjord / news Masternes Hanssen says that it is not just avalanches that are a challenge on the road section in the region. In addition, there is a risk of rock falls, soil and slush landslides on several stretches of road. – We are working on using less costly measures and we are working on getting increased frameworks for avalanche and landslide protection, says the Transport Council, who adds that avalanches and landslides are a major societal challenge in her region.
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Climate change means that slush avalanches may become more common in the future – news Troms and Finnmark
