Plate Tectonics

Norway is located on the western side of the Eurasian Plate, relatively close to the divergent plate boundary it shares with the North American Plate along the Mid-Atlantic Ridge. 400 million years ago, Norway was positioned in the tropics near the equator. The landscape was very different than it is today, covered in a dense tropical forest that was composed of some of the first trees to appear on Earth (Berry and Marshall 1043). The motion of the tectonic plates over hundreds of millions of years has caused Norway to steadily move around the surface of the Earth to its present location in the North.

Norway was separated from Greenland by the Iapetus Ocean until the ocean closed by subduction, causing the two landmasses to collide with each other about 425 million years ago. This collision formed the Caledonian Mountains on both Norway and Greenland. Sea floor spreading along the Mid-Atlantic Ridge once again separated them, opening the North Atlantic Ocean around 54 million years ago.The Caledonian Mountains rivaled the size of the Himalayas at the time of their formation, but have since been deeply eroded. This mountain range is thought to be part of the same range as the Appalachian Mountains in the United States, but it is debated whether the mountains in Norway are still the same that formed 400 million years ago or if they were eroded away and the current mountains were caused by different processes. The hypothesis put forth that the mountain range has survived for hundreds of millions of years relies on isostasy (Redfield). The Earth's crust floats on the mantle, similar to an iceberg floating on the ocean. When mountains erode, they get lighter and rise through isostatic uplift. Land will commonly be uplifted when the load is removed from the meltdown of glaciers, which is evident in Norway from the fjords. The rate of erosion would need to exceed the rate of uplifting for the mountains to disappear. The other side argues that the Caledonian Mountains were completely flattened before later tectonic events. Collision tectonics form mountain belts because the crust becomes thicker than normal, and forms a crustal root that will support the overlying mountains. Conversely, the crust under the highest mountains in Norway is of normal or even slightly reduced thickness. In addition, seismic data has not been able to find a root sufficient to support the present-day mountains (Jaspen and Chalmers 14). The hypotheses for how the geologically young mountain elevation came to be are varied, including a mantle plume below the crust and a cycle of uplift and subsidence, but no definitive evidence has been produced to explain the more recent uplift. It has been much debated among geologist and is still not well understood.

Although it lies on a passive margin, Norway does experience small earthquakes from time to time mainly due to ridge push stress caused by sea-floor spreading along the Mid-Atlantic Ridge. These earthquakes have actually been helpful to scientists in determining the movement of the Eurasian Plate. Researchers built a database of 109 earthquake stress mechanisms for Scandinavia, and were then able to calculate the stress directions for Norway and the Norwegian Sea, which indicated a clockwise rotation (Bungum et al. 429). On average, Norway experiences a magnitude 5 earthquake roughly every 10 years, and a magnitude 7 earthquake every 1,100 years.