Permafrost station at Sommeiller Pass (NW Italy): from the monitoring to reference site and methods

The Sommeiller Pass permafrost monitoring station, at about 3000 m of altitude, is the key site of the regional network installed in 2009 during the European Project "Permanet" in the Piedmont Alps (NW Italy). The station consists of 3 vertical boreholes 5, 10 and 100 m deep with different characteristics, equipped with thermometric chains for a total of 34 Pt100 sensors. Due to infiltration and freezing of water inside the instrumentation and boreholes, the station became operational in 2011 after recovering. The collected data shows a constant active layer 8-9 m of thickness, while the permafrost temperature curves show a degradation of the base at approximately 65 m of depth since 2014. In order to verify this variation (about 0.4 °C), considering the station history, a sensor calibration was carried out in laboratory and on site aimed to understand the reliability of the measurements in progress.