Ice Age Story

Glacial Prehistory 

 Ice Age Story

 

  Introduction 

This is a story of Britain, and north-west Europe, as it passed through several periods of extreme cold, Ice Ages, the formative events that created the landscape that we live with.

It is not authoritative, and may be taken with a pinch of salt, but it is my best attempt, using current evidence, to understand the ice age of Britain. 

The general territory that the story covers is very roughly the Atlantic coast of Europe, but includes the Alpine mountains of southern France, and the northern mass of Scandinavia. 

Specific areas that are covered are Britain, Norway, and the North Sea. These constitute an area that academia deems to have been covered by thick ice sheets, the British and Irish Ice-Sheet (BIIS) and the Fenno-scandinavian Ice-Sheet (FIS). These ice sheets are thought by some to have been joined across the North Sea for part of the last ice age.

The theory that is proposed, studied, taught and learned, in universities, is that the ice sheets over northern Europe, and elsewhere flowed as solid ice Formations along glacial valleys, shaping them as they progressed.

Beginning 

The evidence tells a more nuanced story that has to start several million years ago with the movement of Britain away from Europe.

As the Atlantic Ocean opened up a great chasm between Europe/Africa and North/South America developed, so that Britain pulled away from Norway. The result was that a portion of the earth's crust between Britain and Norway remained open, a vast crack in the earth's surface, to be filled by sediments from surrounding lands. 

Ultimately, as the oceans filled up with sediments, and the ice-sheets melted, the seas invaded the space between Norway and Britain, forming the North Sea. 

In the last million years, and possibly before, the planet was cold, reflecting the sun's rays off from polar ice caps. There were brief periods of warmth in which ice sheets collapsed crashing into underlying geology, cutting impact valleys and dumping huge volumes of sediments across landscapes, and eventually into offshore waters. (Impact Valleys)

This process would have raised average sealevel on a continuous basis from a million years ago right up to the present day. 

It is difficult to assess what effect this carving out of geology had on landscapes of today, but evidence of sediments in the Trent Valley confirm that some of them go back a long way into prehistory, with sand and gravel beds dated up to a million years, and more.

Nascent North Sea

The period formally assigned to the last ice age period began at 120,000BP, and lasted until about 10,000 years ago. 

Before 120,000BP, there occurred the earliest significant event that is recorded in the geology of the North Sea. An extended warm period melted polar ice sheets causing Sea levels to rise allowing an insurgence of sea water to flood the area now the North Sea. 

After this warm interglacial period snow began to fall from 120,000BP, continuing until around 70,000BP when there was a sharp thaw. At this time ice sheets on the Pennine Hill of Northern England and the mountains of Scotland collapsed, cuttimg impact valleys, and sending tidal waves across what was probably dry land in the North Sea area, to deposit huge volumes of sediments as Dogger Bank. (Dogger Bank)

Cold, but not that cold!

There followed a relatively mild period from around 50,000BP to around 23,000BP (Tattershall).

In this period the ice sheets remained at high altitude on the mountains of England Scotland, Wales and Ireland. But in the lowland regions of southern Britain and Ireland meltwater rivers flowed through a cold, and probably wooded landscape with marshy areas near the coasts. These places were home to cold tolerant creatures like the woolly rhinocerous, and to people using Upper Palaeolithic flint tools making technologies. (Dorset Barrow)

Also at this time, the ice sheet on Shetland was collapsing, and some of the meltwater from that event (Capeshore Formation) flowed south along the Scottish coast into a lagoon that had been formed by the after-wash from glacial meltwater, the Marr Bank lagoon. (Marr Bank Formation). There two additional deposits were laid with the Marr Bank Formation, the Wee Bankie Formation  and the Bolders Bank Formation. (Wee Bankie Formation) (Bolders Bank Formation)

Snowing again!

Cold weather and heavy snowfall returned to lowland Britain, possibly as late as 23,000BP,  laying a variable thickness of snow/ice across the British Isles and the North Sea. Very little snow built up on the south coast of England, though the South Downs in Kent, the east coast of England,  including London, (Levallois Flake) may have had considerable thicknesses of snow on them.

Additional thickness of snow over the pre-existing mountain ice-sheets of, Scotland, Wales, northern Ireland and northern England  raised those ice-sheets further.

The mainland ice sheets on England and Scotland extended off present coastlines a short distance and a high ridge of land joining Dogger Bank in the southern North Sea to the Atlantic Ocean at a peninsula east of, and separate from Shetland, but separated from Norway by the Norwegian Channel.

The Marr Bank lagoon lying off the Scottish coast, near Aberdeenshire remained unfrozen throughout this return to freezing conditions, supporting vegetation and wildlife. 

The ice-sheet spread across from Norfolk, linking up with Dogger Bank, to enclose the Marr Bank lagoon from the south. 

It is likely,  but cannot be proved, that the ice sheet also lay thickly around the North edge of the Marr Bank lagoon, where the Swatchway Formation is to be found.

Everything, everywhere, melts!

From about 21,000BP the very brief cold period at the end of the ice age ended, and a 10,000 year long deglaciation began.

Between 21,000BP and 15,000BP the ice sheets retreated rapidly across all low-lying areas, causing seasonal collapse differences to leave parallel valleys across many areas.(Parallel Valleys) 

Ice sheets on the French Alps collapsed sending meltwater North to the English Channel and the southern North Sea, where the speedy retreat of ice-sheets progressed northwards at a rate of roughly a kilometre per year.

At these intial stages of the melt the Lobourg Channel of the Dover Strait was cut, the Outer Silver Pit, at Dogger Bank also, and the Norfolk Banks. The South Wales valleys were cut around this time, and the Black Mountains of Brecon and Herefordshire. 

At about 15,000BP those ice-sheets on the high mountains began to fall, the meltwater causing Ice-streams to cut wide rivers and palaeovalleys across southern England. (Ice Streams)

These ice streams, containing varying proportions of stones, sludge, ice, and meltwater flowed across England and coastal waters leaving geological features where they passed.

These include glacial lineations,  moraines, and potholes. (Striations) (Moraines) (Pot-Holes) (Erratic Boulder) (Drumlins)

An ice sheet on Dogger Bank and the peninsula that bordered the west coast of the Norwegian channel in the North Sea also retreated, leaving huge gullies in the north of the area, as the Witch Ground, and the Devil's Hole, off the Scottish coast. (Swatchway Formation)

These edge collapses would have caused the release of meltwater, possibly in the region of half a cubic kilometre of water every day, with peak melt in summer and least melt in winter. This release, repeated on several coasts around the region caused the sea levels at those local coastlines to oscillate, up and down annually, as seasons changed.().

All Melted

At around 11,000BP the last of the mountain ice sheets had collapsed, and water from that event was mostly draining away with little effect on local sea levels.

In the highland valleys that had been gouged out by the collapse of ice sheets there remained rivers of ice, valley glaciers. These, like the ice-sheets, were static, and where the sun was less able to reach in the valley floors they remained as glacial rivers of solid ice. 

The glaciers carried the stones and sands that had been gouged out of the mountains and it wasn't until about 9000BP that these began to melt.

Again local sea levels rose as the ice melted in the valleys, and the debris that had been stored within the glacier simply gravitated to the floor of the valley, remainng now as hummocky moraine. (hummocky moraine)

North Sea develops

The spine of land that divided the North Sea, north to south was available to mesolithic wildlife and people.

As sea levels rose the spine of land was gradually whittled away until in a series of collapses in the 4th millennium BC, more recent, softer sediments in the northern North Sea were easily flushed aside, opening up the whole North Sea. (Archaeology in the North Sea)

There was a coastal inlet east of Shetland that had a southern shoreline just east of Orkney.

Two tidal waves were triggered by submarine landslides in the North Sea north of Norway. The first was the Nyegga Slide in 18,000BP, the second the Storegga Slide  in around 8200BP. These may both have been funneled along this inlet, between Shetland and the extension of Doggerland from the south, to hit the Aberdeenshire coastline.

Migrations 

During the mesolithic,  and early neolithic eras, Ireland was connected to Scotland by land; England was connected to Holland; and Scotland was connected to both Orkney and Shetland. 

Forest, heaths, and marshes formed with the inward migration of animals, plants, birds, and insects from Europe. 

During the 4th millennium BC the strands of land that connected these locations were stripped away by rising sea levels. The geological anomaly at the north West coast of Europe became the British and Irish archipelago.  (Walkable Land in the North Sea)

Between Caithness in Scotland, and south Ronaldsay in Orkney, land in the North Sea was removed.

The beach that connected these two places remains, vestigially, as the island of the Pentland Skerries, and there is a submarine raised landform attached to it, called the Sandy Riddle. 

The story of how the people who watched sea levels separate Orkney from Scotland reacted to this catastrophic event is told in "Orkney Riddle"

Jeffery Nicholls 

South Ronaldsay 

Orkney 

 #BIIS #Britice-Chrono #Quaternary #glaciation #LGM #neolithic #prehistory #archaeology #Orkney #Scotland