Mong and basalt corridors

The youngest rocks in Magma Geopark are found in the many basaltic passages called Eigersund swarm of basalts.

Geology and nature

What is a basalt corridor?
A fault is a sheet of rock that was once melted and has crystallized (solidified) in a fracture of a pre-existing rock. The rock in a passage is usually different from the pre-existing rock. The aspect ratio of a dyke is high, which means that its thickness is small in relation to its length and width. The thickness can vary from one centimeter to several meters, and lateral extension can be many kilometers, which is the case for the basalt passages in the Magma Geopark.

What is basalt?
Basalt is the most common type of volcanic rock on our planet. It can occur on the earth's surface (basalt), in dykes (diabase/dolerite) and as large masses below the earth's surface (gabbro).

How and when were these hallways formed?
Around 900 million years ago, all the land masses on Earth were brought together in a large supercontinent called Rodinia. 750 million years ago, the continent began to slip apart - continents were separated and new oceans opened up. This was a slow process, and it wasn't until 650 million years ago that the continent Norway belonged to began to drift away. The continent was called Baltica (Scandinavia + Russia + Ukraine), and it began to drift away from the continents Laurentia (North America + Greenland + Scotland) and Amazonia forming the ocean Lapetus (the predecessor of the Atlantic) between them. As the continents began to split, volcanic activity started. This activity led to tunnels penetrating the bedrock here in Magma Geopark. Dating the rocks in these tunnels gives an age of 616.3 million years - that's 300 million years younger than the surrounding anorthosite.

Where do we find basaltic tunnels in Magma Geopark?
There are a total of 11 parallel basalt passages in the ESE-WNW direction. These can be found in several places in the geopark, but they are easily accessible in Mong, Tengs, Gaudland, Koldal and Tellenes.