The geology of the bedrock is the key to history

The geology of the bedrock in the area between Karmøy and Kristiansund is the key to understanding the geological history of West Scandinavia.

The mountains are formed in several time epochs, and the marks left behind are clear when you study the landscape and the individual types of rock. The last ice age, which in geological terms was recent, removed all traces of the effect of wind and weather, and left a beautiful surface that was polished and ground down by the ice.

The fjords, which cut deep into the fresh bedrock, provide a unique view into geological history because they provide a continuous profile through the mountain massif. In this respect the fjords are important because they make it possible to investigate the bedrock, which has a very complex developmental story to tell.

Gneiss

The bedrock in the Geirangerfjord area mainly contains Precambrian gneiss from the Western Gneiss Region, and most of it is of igneous origin. Occurrences of coarse-grained granite gneiss features like a relatively uniform mass in the otherwise stratified and varied gneisses.

Mica and schist occurs in some places. These rock types represent sedimentary rock that was transformed into crystalline stone through metamorphism – high pressure and high heat.

High pressure, high heat

Various occurrences of eclogite and olivine rich peridotite are found locally. A large area in the East contains Augen gneiss with some quartzite, garnet mica gneiss and several fields of olivine-rich rock. This part of the mountain was pushed over the underlying gneiss through the Caledonian collision.

Unlike the Nærøyfjord area the bedrock in the Geirangerfjord area does not retain evidence of the Sweconorwegian orogeny (1130–900 million years ago), but the Scandian plate collision (a phase of the Caledonian mountain range folding, 420 million years ago) led to transformation of rock types under very high pressure and great heat.

Processes deep down

This geological process gave us eclogite, among other things. This is a rock that only forms under high pressure. It is a striking and rather unusual rock, which mainly consists of reddish to pink granite and green pyroxene (omphacite). Particularly interesting is the local occurrence of microscopic remains of the mineral coesite, which is a form of quartz that forms under very high pressure and moderately high heat (700 °C). This has occurred 100 km deep in the earth’s crust.