When the water level of the Chaun River rises, the water clean the beaches from loose material and vertical walls with frozen soil get exposed. Its like these walls are made for historical sampling. Photo: Peter Mortensen

With higher water flows new areas gets exposed. But it does not taker too long before the surface dries and collapses, and the permafrost becomes difficult to access again. Photo: Peter Mortensen

By taking samples from the top down to the bottom of the permafrost, you get a time series that goes back thousands of years back. Photo: Rasmus Erlandsson

Sergej hands over a sediment core to Peter, who run back and forth between Sergej and the cooling box. Photo: Rasmus Erlandsson