Dendrogeomorphic reconstruction of past snow avalanche events in Bâlea glacial valley-Făgăraş massif (Southern Carpathians), Romanian Carpathians

The tree-ring based analysis of the 586 extracted increment cores allowed the identification of 853 growth disturbances related to past avalanche activity. The most frequent response is found as reaction wood (64.1%), followed by abrupt growth changes (20.6%), traumatic resin ducts (13%) and callus tissue (2.3%). A total of 77 event-years with AAI > 10% were reconstructed. The reconstruction revealed five high-magnitude avalanches (AAI > 30%), 25 medium-magnitude avalanches (20% ≤ AAI ≥ 30%) and 47 small-magnitude avalanches (10% ≤ AAI ≥ 20%). The return period values vary between 16.7 and 23.6 years. Based on the reconstructed chronologies, our analyses identified 13 cases of synchronicity of events with AAI > 10%. This synchronicity indicates the decisive role of local weather conditions, which are responsible for the occurrence of extreme snow avalanches. The weather conditions triggering extreme avalanche correspond with high amounts of snowfall and consequently thick snowpack, even if the largest snowfalls are not necessarily associated with extreme avalanches.