Snow avalanche and debris flow activity in the High Tatras Mountains: New data from using dendrogeomorphic survey

The High Tatras Mountains are known for frequent occurrences of hazardous geomorphic processes. Many occur at the same localities. This similarity of occurrence is typical of snow avalanches and debris flows, as snow avalanches tend to use debris flow channels. Dendrogeomorphic methods allow for the intraseasonal dating of scars left on stems and branches and hence the distinction of processes. Past scars on four tali in the Great Cold Valley were dated. Together, 189 individuals of Pinus mugo var. mugo with scars were sampled using increment cores and cross sections. The dating was supported by visual analysis of three historical orthophotos. Twenty-seven events since 1959 (17 certain events and 10 probable events), including snow avalanches (19 events) and debris flows (eight events), were dated. Historical archives provided evidence for approximately nine snow avalanches, and four of them were confirmed dendrogeomorphically. Debris flows and snow avalanches identified by spatial distribution of scarred trees in individual years correspond to the extent of events visible on orthophotos. Debris flows are of small magnitude, and their geomorphic effect is restricted to the elongation of current tracks. Snow avalanches often use debris flow tracks. The chronology of events (particularly debris flows) clearly shows a significant increase in debris flow activity during the last ca. 10 years. This finding corresponds to the observation of debris flow frequency trends from different localities in the High Tatras Mountains. Thus, future focus should be aimed at determining the potential influence of environmental changes on debris flow frequency in the High Tatras Mountains.