Forecasting method of ice blocks fall using logistic model and melting degree–days calculation: a case study in northern Gaspésie, Québec, Canada

Ice blocks fall is a serious natural hazard that frequently happens in mountainous cold region. The ice blocks result from the melting and collapse of rockwall icings (ice walls or frozen waterfalls). Environment Canada weather data were analyzed for 440 cases of ice blocks fall events reported in northern Gaspésie by the “Ministère des Transports du Québec.” The available meteorological variables were used to develop an ice blocks fall forecasting tool. The analysis shows that the ice blocks falls are mainly controlled by an increase in the air temperature above the melting point of ice. The temperature variations and the heat transfer into the ice bodies can be expressed by the melting degree – days (DD melt ). The best logistic model was derived by testing a number of combinations of variables against the database (ice blocks fall events and meteorological data). Feeding this model with the meteorological data and using the recorded evolution of DD melt as a complementary predictive tool allow the forecast of the most hazardous periods on a regional scale, i.e., along the northern Gaspésie roads and on a local scale, i.e., the collapse of some of the most problematic rockwall icings. We also discuss the effects of large daily temperature changes such as drastic drops of temperature below 0 °C and freeze–thaw cycles on the opening of cracks and the collapse of unstable ice structures such as freestanding ice formations.