During the Pleistocene an ice sheet blocked the flow of rivers including the Thames and Rhine to the North Sea, resulting in a large proglacial lake to the northeast of the ridge. To the southwest, low-lying land connected the island that is now Great Britain to continental Europe. Overtopping of this ridge at two separate times resulted in the severing of this peninsular connection. The first glacial lake outburst flood occurred approximately 425,000 years ago, resulting in a waterfall of up to a million cubic meters per second that gouged out the Straits of Dover and flooded the low-lying land. The second, which may have been larger than the first, occurred approximately 225,000 years ago and finally severed the slender peninsula.[2][3]
