Figure 42. Evolution of Shelf Valleys. The upper panel depicts the seafloor shortly after glaciers have left, and the ocean level is 80 m deeper than today. Glacial-marine mud mantles most of the seafloor. In the middle panel, the seafloor has isostatically rebounded following melting of the ice, and the former seafloor is up to 60 m above the shoreline at that time. Some of the glacial sediment was eroded during emergence, and forest covered much of the area then. Bluff erosion and stream incision has begun to expose the Shelf Valleys. In the lower panel, sea level has risen to its present position and drowned the Shelf Valleys. During submergence, erosive processes removed mud from some areas and deposited modern, Holocene mud in deeper places. Natural gas is forming in some thick mud deposits, and gas has destabilized mud and led to submarine landslides in other places.

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Last updated on October 6, 2005

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