Oslo Graben
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The Oslo Graben or Oslo Rift is a graben formed during a geologic rifting event in Permian time. The rift formation was accompanied by volcanic activity and associated rhomb porphyry lava flows. It is located in the area around the Norwegian capital Oslo.
The lava production was high when the rhomb porphyry lavas were deposited. The lavas reflect a period of abundant earthquake-related movements, when strong forces tore the crust apart.
In the Vestfold district, one lava flow was deposited on average every 250,000 years, resulting in a 3000 metre thick sequence of mainly volcanic material. In the Oslo area, lavas were deposited on average every 800,000 years. Only a few plant remains have been found between these lavas. The bedrock in this area, roughly from Skien to Oslo and Mjøsa, results in soil rich in nutritients important for plant growth.
