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Volume XXIII |

Snow avalanche activity in the Țarcu Mountains, Southern Carpathians. Comparative analysis based on tree ring studies

Abstract: Snow avalanches are a major natural hazard threatening human life and infrastructure in mountainous areas. They have a sudden onset and involve the rapid transport of large masses of snow and ice down on steep slopes. Thus, it is essential for risk management activities to understand avalanche activity, frequency and triggers. In this study, the dendrogeomorphic method was used to analyse an avalanche path in the Țarcu Mountains (the Southern Carpathians) in order to reconstruct the spatio-temporal activity of past snow avalanches. The reconstruction was based on the dating of growth disturbances caused by the mechanical impact of snow avalanches on trees. A total of 186 increment cores were analysed, resulting in the identification of 374 growth disturbances, including traumatic resin ducts, reaction wood, growth suppression and scars. In a chronology spanning 101 years in Picea abies, 13 events with It between 10-20% and 6 events with It between 20-40% were reconstructed over the period 1965-2021. The frequency of snow avalanche events was calculated, resulting in an average of 17.7 years. The climatic parameters were analysed for the event years exhibiting the strongest signal. The occurrence of avalanches was associated with warmer weather and rainy days. Event year 2010 is evidenced by a tragic incident in which two individuals lost their lives in the vicinity of the Țarcu weather station. Eleven events are synchronous with those analysed in other avalanche paths, while the event year 2005 is synchronous in nine other avalanche paths.

Volume XIV |

Near surface thermal characteristics of alpine steep rockwalls in the Retezat Mountains

Abstract: The characteristics of the near surface thermal regime of two rockwalls with different aspect in the Retezat Mountains were investigated using two miniature thermistors. Three one-year (2012-2013; 2013-2014 and 2014-2015) rock surface temperature time series were available for the north facing rockwall, whereas only two seasons were analyzed for the south facing rockwall. The mean annual rock surface temperature (MARST) values were with 1.5-2°C colder on the northern rockwall compared with the southern steep bedrock face. Due to long daily exposure to sunshine, the south facing rockwall experienced more diurnal freeze-thaw cycles during the cold season compared to the north facing rockwall. Overall, the thermistor with a southern aspect recorded 40 and 55 more freeze-thaw cycles than the northern one. A greater number of effective freeze-thaw cycles were measured on the south facing rockwall. The maximum daily amplitude on the southern rockwall is three times higher than on the north-facing location (39.1°C compared to 13.6°C). Based on our findings it seems that the MARST values recorded on the shaded face of the steep bedrock suggest a quite likely absence of permafrost, whereas the MARST values at TPR indicate a quite certain absence of permafrost.