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| Humberhead Levels |
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| Habitat: Earth heritage (of local significance) |
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The rocks, fossils, minerals and landforms of geological interest, together with the natural geomorphological processes that continue to shape the landscape.
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In explaining the present-day features, geological history really began for the Humberhead Levels about 350 million years ago when the area was covered by a tropical sea. Then a coastal plain developed where the rivers flowed into the sea; luxuriant swamps became established, and the remains of these plants later formed coal. This period was followed by an arid one in which the Natural Area resembled the Sahara desert. It became covered by river-borne sands and later by a finer material which subsequently formed mudstone.
About 2 million years ago, the climate cooled to Arctic conditions, and the area was in the grip of the Ice Ages. During the ultimate ice age, about 18,000 years ago, a glacier blocked the Humber Gap (which was roughly where the Humber Bridge now is), beyond which the inland rivers flowed into the North Sea. Trapped water created a huge area of open water, Lake Humber, which filled with sediment to later form a huge plain - the Humberhead Levels. As the climate warmed and the ice retreated, the plain was initially colonised by a large forest, but 3,000 years ago, rising sea levels pushed the Humber Estuary further inland, causing rivers to back up and overflow into the forest. The waterlogging of the soil killed the trees and much of the Humberhead Levels became covered in reed swamps.
These special waterlogged conditions prevented the usual biological processes of decay, so when any plants died, they did not decompose completely. The fen plants formed the peat deposits which enabled acidic conditions to develop; these, together with certain areas of waterlogged heathland, gave rise to raised peat bogs, of which Thorne Moors and Hatfield Moors are the two largest remaining examples. In addition to the fen plants and acid bog plants such as Sphagnum mosses, the peat has also preserved trees from the original forest, Mesolithic boats and leather sandals, and pollen grains. All these enable us to develop a fascinating insight into local trade, agriculture, climate and the changes occurring in the vegetation over thousands of years.
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