Dogerland and Viking-Bergen were immersed after the end of the last glaciation, at various stages:

(1) 8500 years ago Dogerland was an area of land between current coast of Germany and Great Britain (so that the Rhine and the Thames flowing together in the same estuary) and Viking-Bergen was an island east of present Islands Shetland in Scotland.

(2) A large ground motion (sliding Storegga) 8200 years ago sank part of the territory, became Dogerland on an island and made disappear Viking-Bergen under water of the North Sea

(3) 7000 years ago Dogerland Island is definitely flooded due to rising sea level.

This information is confirmed by the appearance of scrap wood from a forest off the coast of Norfolk County today at a depth of 150 m from the current level of the North Sea.