Mont Terri
Mont Terri is a mountain in the Jura Mountains in Switzerland. It rises to 804 meters (2,638 feet) and lies south of Cornol in the canton of Jura. The summit features a prehistoric site called Mont-Terri Castle.
The mountain is the northernmost anticline of the folded Jura. The sedimentary rocks there dip about 42 degrees toward the southeast. An old limestone quarry on the site was used for lime production until the 1980s.
The Mont Terri tunnel is 4,068 meters (about 2.5 miles) long. It was built between 1988 and 1998 for the Transjuranne A16 motorway. The tunnel has one main tube with two directions of traffic and a safety/evasion gallery. A smaller pilot gallery was first dug to help with construction. The tunnel intersects the Opalinus Clay Formation, a Jurassic claystone.
The tunnel connects the towns of Saint Ursanne and Courgenay, and also links Delémont and Porrentruy.
In 1995, the Mont Terri Rock Laboratory was created from the security gallery, with expansions in 1998, 2008, and 2018. The site hosts an international research project, the Mont Terri Project, started in 1996.
The underground lab studies Opalinus Clay, a 130-meter-thick, watertight claystone dating to the Middle Jurassic around 174 million years ago. The research team includes partners from Switzerland, Europe, Japan, Canada, and the USA. The goal is to understand the properties of this deep clay and to develop methods for site characterization, focusing on thermal, hydraulic, mechanical, and biochemical processes that matter for the long-term safety of disposing highly radioactive waste.
More recently, research at Mont Terri has also covered seismology, carbon capture and storage, and deep geothermal energy. By agreement with the canton of Jura, Mont Terri is not used for radioactive waste disposal.
Funding for the project comes from Nagra, ENSI, Swisstopo, and the partner organizations.
This page was last edited on 2 February 2026, at 05:44 (CET).