Slushflows: Large discrepancy between reported and actual incidents

Abstract A key challenge in advancing slushflow management is the limited record of past incidents. Identifying their starting points and enhancing the quality of slushflow documentation are important in order to improve the regional early warning and develop slushflow numerical runout models and susceptibility maps. Here we investigate three major slushflow events at Kistrandfjellet, northern Norway and quantify the differences between registered slushflows in the national rapid mass movement database and the actual events. We use unique image datasets from the events in February 2021, January 2023 and January 2024, and identify slushflow starting points and flow paths. The curvature of the starting point locations is examined to assess how local topography influences slushflow release at the field site. Our mapping reveals 25 slushflows across the three events, whereas only five were registered in the database. For the 2021 event, we found six times as many slushflows as were officially registered. Comparison of our mapped slushflows to modeled drainage pathways and FKB-Vann (the official surface water dataset of Norway), yielded an average overlap of 35%. To improve slushflow management, we recommend establishing a standardized protocol for future data collection.