What event in 1170 may have caused the creation of 5,000 km2 large shallow bay of the North Sea in the northwest of the Netherlands?
All Saints' Flood (1170) The All Saints' Flood of 1170 (Allerheiligenvloed) was a catastrophic flood in the Netherlands that took place in 1170. Large parts of the Northern Netherlands, and Holland territories were overflowed. This is the flood that created the Zuiderzee. "Lake Flevo" was once a fresh water lake, but after this flood a sea channel opened a connection from the North Sea into the lake through Creil Woods, and turned the lake into the salt-water sea known as the Zuiderzee. The Creiler Forest vanished forever under the waves.
Ancylus Lake Ancylus Lake is a name given by geologists to the body of fresh water that replaced the Yoldia Sea after the latter had been severed from its saline intake across central Sweden (with the eastern end of the channel near present Stockholm) by the isostatic rise of south Scandinavian landforms. The dates are approximately 9500–8000 BP calibrated, during the full Boreal period. The lake became the Littorina Sea when rising oceanic levels broke through the Great Belt.