An Investigation of Cornice Development Control at Kvannberget, Norway

Abstract

Snow cornices develop along mountain ridges and plateaus in areas with seasonal snow cover and are recognized as a natural hazard endangering life and infrastructure in mountainous areas. At Kvannberget, Western Norway, the horizontal extent of a large continuous cornice has previously interfered with power lines that transport electricity from hydropower installations above Fortunsdalen. In 2019 five wind baffles were installed at the location to permanently mitigate the hazard posed by the cornice structure. During the 2019/2020 winter season the area previously subject to the development of a large continuous snow cornice, as well as a reference cornice, was monitored using time-lapse imagery and an automatic weather station (AWS). The temporal resolution of the images capturing cornice development and local meteorological data acquired, enabled detailed observation of cornice accretion events, analysis of the meteorological controls of cornice accretion, and a visual evaluation of the effectiveness of the installed wind baffles. The results of the investigations provide reinforcement to the existing conceptual models of cornice development. Cornice accretion at Kvannberget is a response to distinct meteorological events: North-Easterly winds with hourly wind speed averages of 10 m/s and temperatures below 0°C, with snow available for transport. The local wind regime at Kvannberget deviates from the wind regime at the meteorological station at Sognefjellet and accretion events are likely connected to local fall winds. Cornice accretion rates of up to 46mm/hour were observed, significantly higher than measurements made in previous studies. Cornice accretion events could become more frequent in a future climate with increased winter precipitation and wind speeds if the average winter temperature remains below freezing. The wind baffles effectively mitigated the development of a continuous cornice and prove to be proficient as a cornice mitigation measure in areas with a prevailing wind direction, although the effectiveness of 2 of the baffles could be optimized with a more ridge ward placement.