Motivation for slushflow classification

Abstract

Slushflows are a type of rapid mass movement where water saturated snow flows downhill. Slushflows come in many different sizes, have different triggering mechanisms, and contain debris ranging from simply snow and ice to soil, rock and vegetation. Slushflows are often misclassified as debris flows, wet snow avalanches or river/stream ice jam processes. <p>

<p>Norway reports 5 to 20 larger slushflows each year which have economic impacts such as damage to infrastructure, road closures, and even fatalities. For improved slushflow hazard assessment a robust classification system must be used to precisely describe what size and type of process is being forecasted, modeled, or investigated. A classification system would be beneficial for both scientific research, data collection, and operational hazard mitigation strategies. <p>

<p>Slushflows have been well defined as a sub-category of mass flows classified by the composition of the mass. However, they have not been systematically broken down into sub-categories that describe the formation, type of movement, size, and quantity of entrained material. These sub-categories are needed because the types of slushflow, the terrain from which they initiate, and the triggering mechanism can differ greatly. Extreme rain on snow or melt events have predictive power for slushflow activity when all slushflow types and sizes are analyzed together. However, many slushflow events occur during periods of moderate rain on snow or melt events, defying forecasts. Weather and snowpack data alone are not able to predict slushflow activity during moderate rates of melt or rain. Some of the nuances of slushflow formation may be uncovered when single slushflow types and/or sizes are investigated independently. Independently investigating slushflow types and sizes will also help define the spatial patterns of slushflow formation. <p>

<p>We propose a classification system which includes some traits of snow avalanche classification, such as size and release mechanisms, and build on this to include other unique traits such as water availability and indication of debris materials. A classification system will allow further research on precise sub-classes of slushflow, because as a whole slushflow behavior is too diverse to describe as a single process.