Spatio-temporal reconstruction of snow avalanche activity using dendrogeomorphological approach in Bucegi Mountains Romanian Carpathians

- Dendrogeomorphologic approach delivers a chronology of avalanches in Bucegi Mountains.
- 32 and 27 winter avalanches, respectively, were noticed in the chosen 2 stands.
- 4 major events in each of the 2 stands had an activity index over 20% and 30%.
- Return periods had an average of 15.2 years and 13.7 years, respectively.
- Most of the high snow avalanche activity occurs in cold winters.

Snow avalanches cause damage to tourism infrastructure and loss of human life. In mountain areas where snow avalanches are less scientifically documented, the dendrogeomorphological approach is the best way for snow-avalanche activity reconstruction and to investigate the magnitude and frequency of the avalanches. Our study was conducted in the Bucegi Mountains located in the eastern part of the Southern Carpathians (Romanian Carpathians) in the Sinaia ski area, the most important ski area in the Romanian Carpathians. The mountains are characterised by high elevations of over 2400-2500 m, a harsh climate (− 2.5 °C mean annual air temperature above 2500 masl, over 130 days with snowfall on average, over 185 days with deep snow on average and 10-12 months with a snow layer). Snow avalanche activity is marked by tilted trunks, scars and broken trees. Therefore, we applied the dendrogeomorphological approach. We performed a dendrogeomorphic analysis based on 66 Picea abies and 48 Larix decidua Mill. We sampled trees in two snow avalanche tracks, 43 in one and 71 in the other, and obtained 86 and 142 samples, respectively. Our results from tree-ring records yielded 32 snow avalanche winters in the 1963-2011 chronology in one track and 27 snow avalanche winters in the 1963-2012 chronology in the other track. Thus, we obtained important information about the spatial and temporal characteristics of snow avalanche activity. The small and medium snow avalanches cover the central and lateral parts of the stands, whilst the large snow avalanches reach the runout zone of the stands. We dated past snow avalanches and obtained a return period ranging from 13.7 to 15.2 years. The analysis revealed that 14 winters had an activity index over 10% 4 winters had an activity index over 20% in the first avalanche track, 10 winters had an activity index over 10% and 4 winters had an activity index over 20% in the second avalanche track. On the other hand, to determine the relationship between snow avalanches and winter temperatures we use the Winter Standardized Index (WSI) between 1963 and 2012. We obtained a correlation between these parameters and our dendrogeomorphological results; the probability of major snow avalanche occurrence was highest during cold winters.