First visit to the Grotte Agressive

A group of four from Neuchâtel university, composed of Tanguy, Lucas, Elie and Charlotte drove to Tsanfleuron to accomplish several tasks. The first was to continue building the rating curve for the Glarey estavelle, using the salt dilution method. This time, they also characterised the conductivity and temperature of the Morge river before its confluence with the estavelle and downstream. The preliminary results are clear: the Glarey estavelle rating curve will be built more precisely by using the difference of discharges downstream and upstream of the Morge / Estavelle confluence.

The second task was to investigate a short cave located near the centre of the Tsanfleuron limestone pavement and as well as to take in the local geology, in particular, the various karstifiable limestone facies which outcrop there. After parking at the Sanetsch pass, the team walked up to an altitude of about 2300 m asl and found the entrance to “Grotte Agressive”, a steeply descending canyon-like cave.One of the project tasks is to characterise flow in the unsaturated zone of the karst, and to do so we plan to monitor drip water dynamics and conduit flow in shallow caves.

From the entrance, the team surveyed the cave using a laser disto, and measured a depth of 46 m, for a total length of 66 m. Notably, the floor canyon is very clean. Due to the lack of rain in the preceding week and absence of snow patches on the surface, the passage was mostly dry. It looks as though it can carry a small stream in response to surface hydrological events. Some hydrologically active soda straws were also found: these may provide a valuable insight into the response of fracture flow to local precipitation events.