New findings regarding the ground air circulation by chimney effect in low-altitude permafrost susceptible porous screes (Detunata Goală, Romanian Carpathians)

Seasonally differentiated ground air circulation in low altitude porous talus slopes from temperate regions known as chimney circulation creates the conditions for permafrost development in their lower parts well below the regional permafrost altitudinal limit. So far it was shown that the cold air adsorption and warm air exfiltration areas during winter correspond to the lower and upper areas respectively of talus slopes and that they are quite stable and regular in extent and shape. New aerial survey in early winter at Detunata Goală scree with a complex talus slope-rock glacier morphology performed immediately in the days following light snow falls allowed the precise detection of warm air areas positions, shape and temporal changes within hours and days. Several triangular-shaped stripes were found to occur continuously from lower to upper parts of talus slopes and morphometric analysis on a high resolution UAV-derived DEM revealed that they correspond to 1the central longitudinal axis of debris cones composing the talus slopes. Thermal monitoring of air between the blocks was also performed at the location of these stripes where a thermal gradient was found to occur: the atmospheric/ground air temperature contrast increases upwards and towards the axis of talus cones reaching a maximum of >10 °C (+5.3 °C in the ground versus -5 °C outside). In the rock glacier lobe area, the warm air evacuation is different and presents a linear configuration. This work discusses the relation between the morphometry of the deposit and warm air evacuation areas and their short term thermal regime. Also, it discusses new geophysical investigations results (electrical resistivity tomography and seismic refraction tomography) performed at the end of the warm season of 2020 in the coldest area of the scree.