Ancestral Thames

The Ancestral Thames is the name given to the geologically ancient precursor to the present day River Thames.

During the Early and Middle , central and southern Britain had two main rivers of more than 150 miles (240 km): the Bytham and the Ancestral Thames. For most of the Early Pleistocene the Ancestral Thames was the main river with, at its maximum extent, a catchment area that extended into Wales alongside the Chiltern Hills, through southern East Anglia and finally into lowlands in what is now the North Sea, where it joined the ancestral Rhine. In the early Ice Age the Thames took a line similar to the present-day River Thame, through parts of Bedfordshire, Hertfordshire and north-west Essex, then took a course resembling that of the River Waveney along the Suffolk/Norfolk border.

Initially the more northerly Bytham River was a tributary of the Thames but as the climate warmed it progressively extended its catchment. During the Anglian Stage the Bytham river more or less disappeared and the Thames was diverted to its present course through London.

During the last glacial maximum, much of what is now the southern part of the North Sea was land, known to palaeogeographers as Doggerland. At this time, the Thames, the Meuse, the Scheldt and the Rhine probably joined before flowing into the sea, in a system known as the Loubourg or Lobourg River. There is some debate as to whether this river would have flowed south-west into what is now the English Channel, or north into the North Sea close to modern Yorkshire. Current scientific research favours the former opinion, with the Thames and Rhine meeting in a large lake, the outflow of which was close to the present-day Straits of Dover.

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