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Birth of the river Mersey

This video shows how the coastline has changed over thousands of years, eventually leading to the birth of the river Mersey.

The key stages in the process are explained below, select each thumbnail to find out more:

20,000 BC: Ice hundreds of metres thick covers the Liverpool area. Britain has become uninhabitable. Over the next few thousand years the ice begins to melt.

14,000 BC: Still very cold. The ice has gone from the Irish Sea. The sea level rises, but is still much lower than it is today. There may have been a swampy 'land' bridge between England and Ireland.

12,500 BC: A warmer 'inter-glacial' period, with summers as warm as today. Britain is inhabitable again. The land is covered in birch woodland. There is evidence of people living on the Fylde coast, near what is now Blackpool. Then the sea was about 15 miles further out than it is today.

10,500 BC: A mini Ice Age returns to Britain, with glaciers in mountain areas. Locally, arctic-type grassland replaces the birch woodland of the previous warm period. Frozen ground is common. Reindeer reappear in Britain.

8,200 BC: The ice has gone from Britain. The earliest local people settle on the Wirral. The sea level has risen enough for the coastline to be about 10 miles further out than it is today.

6,300 BC: Britain is an island. The Irish Sea has risen high enough to be close to the present coastline, making the tidal River Mersey.

3,800 BC to the present: By about 3,800 BC the sea reaches its present position. The coastline has remained fairly stable since then. The oldest sand dunes, near Southport, are from this date. The sand dunes at Formby became fixed about 2,000 years ago, in the Iron Age.