Quaternary landscape development
The bedrock basement and the large scale landforms that we see today in Norway were formed during Caledonian mountain building era that took place over 400 million years ago during the Paleozoic era. The Caledonian mountain chain arose and the characteristic nappes appeared. Because the various rock types have a different resistance to erosion, today we often see resistant rocks in the highest areas and less resilient in lower terrain.
The next important phase in the formation of the landscape started after the Caledonian Orogeny in the Mesozoic era, when the continents began to break up and drift apart to give birth to what is now the Atlantic Ocean. 200 million years ago, fault zones formed and still remain part of the modern Norwegian landscape. Many deep fjords and valleys follow along these ancient fault lines because here the bedrock tends to be easily eroded and weak. The climate was hot and humid in the Mesozoic, and the land was covered by tropical swamp forests. Under such conditions the bedrock was subjected to heavy erosion and evidence of this is found in the shape of the underlying rock.
Then in the Cenozoic (ca. 67 million years ago), the climate became cooler and the river processes eroded the mountain range down to a hilly landscape. Towards the end of the Cenozoic, close to the time of ice ages in the Quaternary era (2.6 million years ago) the Norway's landscape was subjected to more drastic cooling. Glaciers formed which speeded the erosion of the mountains and rivers carried glacial sediments to the Norway's continental shelf. Once the weight of the glaciers and sediments was removed, large surfaces of land lifted up. This often happened along the old Mesozoic faults.
In the Quaternary era, glaciers and inland ice sheets were the force behind the changes in the landscape when glacial cirques, deep valleys and fjords were formed. Moving glaciers can erode a lot of bedrock in a relatively brief period of geologic time. If a glacier is frozen solid to the ground, which often the case in higher latitudes or interior areas of Norway, glacier erosion can be minimal. Hence, during the Quaternary, the presence or absence of glacier processes and inland ice sheets served to accentuate contrasts in the Norwegian landscape. Glacial processes have eroded bedrock effectively where we now find steep mountains and fjords, and where we find gently sloping plains glacial erosion has been less effective. Large amounts sand and gravel (debris) suggest a glacier was not moving and stayed frozen to the ground, while areas with less debris suggests there has been greater glacial erosion. The exception is where marine deposits are found.
In low-lying areas in Norway we often find thick layers of marine deposits. These deposits are the result of isostatic pressure created by the heavy inland ice on the ground's surface. Once the ice retreated, the land near the coast line remained below sea level. Glacial streams transported fine material from the melting glacier and deposited it in the ocean. Land uplift after deglaciation raised areas containing marine sediments above the current sea level. Occasionally these marine deposits become unstable and liquefy to run out as quick clay landslides (see quick clay landslides). In many low lying areas of Eastern Norway and Trøndelag, we find such marine deposits, as well as old ravines and landslide pits.