Ancestral Thames facts for kids
The Ancestral Thames was a very old river. It was like the River Thames we know today, but it existed a long, long time ago.
How the Ancestral Thames Connected to Other Rivers
Millions of years ago, during the Ice Age (called the Pleistocene period), there were two big rivers in southern Britain. These were the Bytham and the Ancestral Thames. Both were longer than 150 miles (240 km) (about 240 km).
For most of this early time, the Ancestral Thames was the main river. It collected water from a huge area. This area stretched into Wales, past the Chiltern Hills, and through southern East Anglia. Finally, it flowed into a land area called Doggerland, which is now under the North Sea. There, it joined the ancestral Rhine river.
At the start of the Ice Age, the Thames followed a path similar to the modern River Thame. It flowed through parts of Bedfordshire, Hertfordshire, and north-west Essex. Then, it took a path like the River Waveney along the border of Suffolk and Norfolk.
The Bytham River, which was further north, first flowed into the Thames. But as the climate got warmer, the Bytham River grew bigger. During a very cold period called the Anglian Stage, the Bytham River almost disappeared. This event also made the Thames change its path to flow through London, just like it does today.
The Loubourg River System
During the last big Ice Age, much of what is now the southern North Sea was dry land. Scientists call this area Doggerland. At that time, several major rivers likely joined together before flowing into the sea. These rivers included the Thames, the Meuse, the Scheldt, and the Rhine. This combined river system is known as the Loubourg or Lobourg River.
Scientists used to debate where this super-river flowed. Some thought it went south-west into what is now the English Channel. Others believed it flowed north into the North Sea, near modern Yorkshire. Today, most research suggests it flowed south-west. The Thames and Rhine probably met in a large lake. The water from this lake then flowed out near where the Straits of Dover are now.
Clues from the Past
Before the Thames changed its course, it and its smaller rivers formed a system that drained the Welsh mountains. This means they carried rocks from Wales to other areas. We can still see evidence of this today.
There's a thick layer of material called Kesgrave Sands and Gravels. These are the remains of the old riverbed. These ancient Thames gravels contain many unique pebbles. Some of these pebbles came all the way from North Wales! This shows us how far the ancient river system reached.
The gravels also contain large boulders of puddingstone and sarsens. Puddingstone is a very hard rock made of pebbles stuck together. Sarsens are very hard sandstones. Scientists believe these rocks came from layers of pebbles and sand in the Reading Beds (which later turned into hard rock). People in ancient times used these boulders as markers at road junctions.
Today, these gravels are very valuable. They are dug up in many pits between Harlow, Chelmsford, and Colchester. This is the area where the Ancestral Thames flowed over 600,000 years ago.
During that time, the River Medway flowed north across east Essex. It joined the Thames near Clacton. This left behind a line of special gravels. You can find these gravels between Burnham-on-Crouch and Bradwell-on-Sea.
Other rivers also flowed north into the early Thames. We know this because of patches of gravel found on top of small hills in south Essex. These include the Langdon Hills, Warley, and High Beach in Epping Forest.
