Snow avalanche formation and dynamics

Snow avalanches— a type of fast-moving mass movement— occur in snow covered mountain areas throughout the world and may cause property damage and loss of life as they interfere with human activities. Within the last ten winters (1996–1997 to 2005–2006) about 1020 people were killed in the European Alps by avalanches. Worldwide, the number of fatalities per year is estimated to about 250. Economic costs due to property damage can be considerable. In Switzerland, for example, the direct and indirect costs of the avalanche disaster in February 1999 amounted to about EUR 500 million. Due to avalanche protection works constructed in recent decades, the damage to infrastructure and residential areas has been reduced, so that today most of the fatalities involve personal recreation on public land (Jamieson and Stethem, 2002; Schweizer et al., 2003). Whereas the population and recreation pressure in many regions of the European mountains is still increasing, the financial means for avalanche protection works appear to be declining. Cost–benefit considerations increase the relevance of temporary protection measures such as road closures. However, preventivemeasures heavily rely on reliable avalanche forecasting; i.e. the prediction of location and time of avalanche occurrence. Since snow avalanches are rare events — as are many other natural hazards — possibilities to study their causes and dynamics with field observations are limited. Moreover, due to the complexity of avalanches, many processes are not amenable to laboratory or numerical studies. Nevertheless, a better understanding of the underlying processes is considered as a prerequisite for improved prediction. The General Assembly of the European Geosciences Union (EGU) in Vienna, 15–20 April 2007, included — within the Natural Hazards Division — two sessions on “Snow avalanche formation and dynamics” with a total of 27 contributions. This Special Issue of Cold Regions Science and Technology contains six papers based on EGU contributions. Remote sensing of the cryosphere is a very active research topic. Data acquired by satellites are essential to obtain, for example, the snow cover extent which is an important input for climate models as well as for hydrological applications. Many snow related applications are based on the reflectance properties of snow in the near-infrared band (e.g. Tedesco and Kokhanovsky, 2007). Whereas, data from space-born instruments have rarely been applied for avalanche research, ground-based remote sensing techniques have been extensively explored, especially in the last couple years. Terrestrial laser scanning (TLS) has created the most interest. The potential for its application as well as the limitations is now described in two contributions (Prokop, 2008—this issue; Schaffhauser et al., 2008— this issue). These two studies and a complementary one (Prokop et al., in press) clearly show the applicability of terrestrial laser scanning. The application of TLS for snow depth sounding will certainly provide