Quaternary boreholes – learning from the past to prepare for the future

Deposits of unconsolidated rock from the Quaternary – the most recent geological time period from around 2.5 million years ago to the present – provide information on past erosion processes and tectonic activity. For this reason, Nagra has investigated these unconsolidated rocks by drilling boreholes. The drilling procedure has been completed, but investigations of the rock samples obtained are ongoing.

Interactive map

The data from the Quaternary boreholes can be used to better reconstruct and understand past processes, allowing for more reliable statements on the future evolution of the landscape. The issue at stake is the long-term safety of a deep geological repository and how well it will be protected against the removal of rock layers (erosion). In comparison, Nagra’s deep boreholes are mainly used to investigate deeper layers of consolidated rock.

Where were boreholes drilled?

The Quaternary boreholes were used for the geological investigation of scientifically selected areas of Northern Switzerland. The exact locations of the boreholes depended on where the Quaternary deposits of unconsolidated rocks occur and on information from previously conducted seismic measurements. Unconsolidated rocks can mainly be found near present-day river courses that often follow troughs once formed by glaciers and re-filled again later. Nagra investigated troughs such as these in the lower Aare Valley, the “Riniker Feld” and the Thur Valley from 2018 to 2020. In total, Nagra drilled eleven Quaternary boreholes.

Drill site of the Adlikon-Dätwil Quaternary borehole

Further investigations of drill cores

The borehole campaign to investigate the geology of the Quaternary Period has now been completed. However, Nagra and its partners will continue to investigate the drill cores they obtained. The Institute of Geological Sciences of the University of Bern is conducting chemical and geotechnical analyses. These provide information on what type of unconsolidated rock fills the troughs and what properties the rocks have. The drill cores are also dated, which involves a very complex process.

Opened orange tube with a drill core consisting of unconsolidated rock from one of Nagra’s Quaternary boreholes.