Gardnos
Key facts
- Country
- Norway
- Diameter
- 5 km
- Age
- about 500 million years
- Location
- 60.65° N, 9.00° E
A forested valley side in Hallingdal with exposures of the dark Gardnos breccia, a black impact rock, along trails and roadsides; the crater outline is subtle on the ground.
Gardnos, in the valley of Hallingdal in southern Norway, is an ancient impact crater known for its unusual black rocks. It lies near the village of Nesbyen, in a landscape of forests, mountains and rivers, and it has been developed into a popular geological park.
The impact. About 500 million years ago, around the Cambrian period, an asteroid struck an area of ancient crystalline rock, probably covered by a shallow sea and layers of carbon-rich mud. The crater was about 5 km across. After the impact, the crater was filled with sediments and later buried by younger rocks. Over hundreds of millions of years, mountain-building and erosion, including the work of ice-age glaciers, removed the overlying rocks and exposed the crater's interior.
Black breccia. The most striking feature of Gardnos is the Gardnos breccia, an impact rock made of broken and melted fragments. Unusually, it is dark grey to black, because it contains a large amount of carbon. Scientists think the carbon came from organic-rich mud or shale that covered the area at the time of the impact, which was mixed into the breccia and transformed by the heat and pressure.
Recognising the impact. The strange black rocks of Gardnos had long puzzled geologists. Some thought they were volcanic, others that they were formed by movements in the crust. In 1990 the Norwegian geologists Johan Naterstad and Johannes A. Dons found shocked quartz and other evidence of an impact, confirming that Gardnos is an impact crater. Later studies have described its structure and the different types of impact rock in detail.
A geological park. Gardnos has been developed as a meteorite park, with trails, signs and guided tours that explain the impact and show visitors the black breccia, shocked rocks and features of the crater. It is part of efforts to promote geological heritage and tourism in Hallingdal. Visitors can see rocks that were shattered and melted by an impact half a billion years ago.
Why it matters. Gardnos shows how impact craters can be buried, preserved and later exposed by erosion. It also shows how an impact into a carbon-rich target can produce unusual rocks, which helps scientists understand impacts into similar targets on Earth and other bodies in the Solar System.
Visiting. The meteorite park lies a short drive from Nesbyen, which can be reached by road or rail from Oslo. Trails are open in summer. Visitors should stay on marked paths and leave rocks in place.
Did you know?
Gardnos is known for its black impact rock, coloured by carbon.
The crater's impact origin was confirmed in 1990.
Visitors can walk through the crater on trails in a meteorite park near Nesbyen.