North West European Rivers
5. Elsterian / Anglian Stage
Map 5. Palaeogeography of the Elsterian / Anglian / Oka Stage (? Marine Isotope Stage 12; late Middle Pleistocene).
The advance of continental ice sheets into lowland northwest Europe in the Elsterian Stage had widespread effects. The area overridden by the ice was subjected to total landscape remodelling, with old river courses destroyed or buried. An entirely new landscape was formed beneath the ice by glacial and glaciofluvial erosion and deposition; the sculpturing of deep glacial valleys was to have a striking palaeogeographic impact after the ice retreat. At the ice margin, major river valleys were dammed all across the region. The Thames and its tributaries were diverted southwards, the Elbe was dammed and the North German rivers were deflected westwards. However, the most striking feature was the development of a massive ice-dammed lake in the southern North Sea, into which the Thames, Rhine, Meuse, Scheldt and possibly the Ems all discharged. Overspill of this lake initiated the Dover Straits and greatly enlarged the Channel River system. The latter was formed during low sea-level stands by confluence of the Somme, Seine, Solent and minor rivers of the Channel region. It discharged into the Hurd Deep graben, off Cotentin and ultimately into the North Atlantic between Cornwall and Bretagne (Brittany) at sea-level minima.
A substantial morainic barrier may have been formed across the southern North Sea - an extension of the Cromer Ridge onshore in northern East Anglia - at the end of this event. This ridge was constructed from combined meltwater accumulation (a delta moraine complex) and ice-pushed pre-glacial and glacial strata. These accumulations have been found on-land both in Norfolk and the Netherlands, as well as on the floor of the North Sea. The barrier undoubtedly had important implications for the palaeogeographical evolution of the region during the subsequent Holsteinian - Hoxnian high sea-level stand.