Welcome to the Ice Age Coast
The Ice Age in East Yorkshire, UK
by Mike Horne FGS
The Quaternary was a time when huge glaciers covered vast areas of northwestern Europe.
The most obvious feature of our Quaternary geology are the boulder clays (tills or diamicts) of Holderness. We can see them on the coast, being rapidly eroded by the sea. We observe a mass of brown clay containing pieces of rock (erratics) brought here by the glaciers. Occasionally we get to see amazing geological structures in the tills, we can make out differences between parts of the boulder clay, we can see coloured streaks and observe beds of sand, gravel, silt and peat. And often when we go back to look again the feature is covered over by beach sand, hidden by a mudslide or has been washed away by the sea.
We are really looking at the latest boulder clay, most of the time. Trying to understand what is really going on is like trying to calculate how many times a blackboard has been wiped clean. We mainly see the most recent cleaning, but occasionally we catch glimpses of bits that have been missed or faint impressions of ancient sentences! Similarly the last Ice Age probably gathered up the remnants of earlier boulder clays and other deposits, and then moved them around and incorporated them in the most recent boulder clay.
We need to also think of different stages of the Ice Age. Before the ice arrived; when it was cold and the ice sheet had arrived; the melting of the ice and subsequent events.
Before the ice arrived - Sea level was much lower because a lot of water was trapped in the glaciers. The "North Sea" was not covered by sea, but was land with lakes and rivers and estuaries.
When the ice arrived - everything was very cold. To the east of the Wolds there was a huge glacier one or two kilometers thick. This had traveled from Scandinavia, Scotland, the Lake District and Northeast England. We know this from studying the erratic rocks that were left behind in the boulder clay. And also it brought rocks from the bed of the North Sea, both solid bedrock and frozen lumps of the morn recent deposits ('drift'). So do bear that in mind - when we see a fossil that we now find at Whitby, for example, it does not mean that that fossil came from Whitby it may have come from an exposure in the North Sea! From time to time the glacier melted a bit, retreated depositing boulder clay, then advanced again perhaps pushing the boulder clay in front of it.
During that time, when almost everything was frozen, because there was little water around, sand was blown around by desert winds, we can find some examples of this wind-blown sand at the buried cliff and on the western edge of the Wolds. The soil on top of the Wolds was frozen, any water was around could not run into the porous Chalk so we find river valleys cut into the Wolds. The glacier dammed the mouths of rivers so water flowed inland into large lakes in the Vale of York and Vale of Pickering.
As the Glacier began to melt, rivers started to flow out from underneath it, often fast flowing, and these washed the finer fractions of the sediment away leaving gravels and sands. Sometimes huge quantities of water were released from the glacier or the lakes, rapidly eroding "overflow channels".
After the deposition of the boulder clay, hollows formed as lumps of ice trapped in it melted. This Holderness landscape potted with meres started to weather, layers of clay were washed into the meres and as they filled peat deposits were formed as they became shallow.
Quaternary time scale:
2.4 Ma BP [million years Before Present (1950 BCE)]- Ice sheets had grown in the northern hemisphere, with fluctuations on a 41 000 year cycle..
2.0 - 1.8 Ma BP - start of the Pleistocene.
900 ka [thousand years] BP - Fluctuations in environmental conditions become more pronounced and are on a 100 ka cycle, with slow periods of cooling and rapid thawing after reaching "full glacial conditions" or a "glacial maximum". Within each cycle there may be slight returns to warmer conditions ("interstadials") and periods of more extreme cold ("stadials").
117 ka BP - start of the most recent Ice Age (the "Wisconsin" in North America, "Wurm" or "Weichsel" in Europe and "Devensian" in the U.K.)
22 - 18 ka BP - the Ice Age reached its glacial maximum.
16-15 ka BP - glaciers were melting and retreating.
11 - 10 ka BP - Loch Lomand stadial [equivalent of the "younger Dryas" in Europe] a short period of cooling and ice growth.
10 ka BP - start of the Holocene
10 - 7 ka BP - rapid melting of glaciers.
6 ka BP - sea level had roughly reached present day levels
[ reference - " Quaternary Environments "]
DATES FROM HOLDERNESS
Blown sand above the raised beach at Sewerby by : 120.84 ± 11.82 ka (Bateman and Catt 1996)
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(c) Mike Horne & Hull Geological Society 1999 + 2020