From EurekAlert.com a look at the starting and ending factors of the last ice age in Britain from Dr. David Evans.
Egg-shaped legacy of Britain’s mobile ice-sheet
The ice sheets that sculpted the landscape of northern Britain moved in unexpected ways and left distinctive egg-shaped features according to new research.
Scientists from Durham University have deciphered the landforms and created a model of the British and Irish Ice Sheet (BIIS) which reveals for the first time how glaciers reversed their flows and retreated back into upland regions from where they originated.
These ice sheet flow patterns created a unique ‘overprinting’ of British glacial landforms 26,000 to 16,000 years ago, leaving distinctive egg-shaped features called ‘drumlins’ across our fields and valleys.
Drumlin-strewn landscapes can be seen along the A66 road through the Eden Valley (near Appleby) and across the Solway and Lake District lowlands, the Northern Pennines, and through the Tyne Gap and the valleys of southern Scotland.
The research, funded by the Natural Environment Research Council, is published in the Journal, Quaternary Science Reviews.
During the last glacial maximum, around 21,500 years ago, the BIIS built up on the high land of the Lake District, north Pennines and Scottish Southern Uplands; as more snow fell in these areas and local ice caps thickened, glaciers flowed into surrounding lowlands as expected.
The new reconstruction of the movement of the ice sheet, compiled by the Durham University research team, reveals an unusual twist once the glaciers filled lowland areas. As the ice sheet evolved from the coalescence of the upland ice caps, it flowed out towards the Irish Sea, eventually becoming so thick over the Solway Lowlands that it reversed its flow back up the valleys, re-adjusting the landforms it had created during earlier stages of growth.
The rolling terrain that walkers can see along many parts of the Pennine Way and that drivers can see along the route of the M6 motorway provide examples of this glacial landscape.
The research team led by Dr David Evans, from the Department of Geography at Durham University plotted the progress of the ice sheet between 26,000 and 16,000 years ago. Using maps of superimposed drumlins, ancient temperature records, and computer modeling, the team profiled the size, extent and flow directions of the ice-sheet, and reconstructed its movement through time.
Dr Evans said: “The stereotypical image of Ice-age Britain is of ice rolling in from the Arctic but this is not an accurate description of what happened. Britain was cold enough for ice to form in the uplands, growing and coalescing to produce an elongate, triangular-shaped dome over NW England and SW Scotland around 19,500 years ago.
“The Ice sheet then moved downhill, as one would expect. Our findings show that the lowland ice became so thick that it began to move in unexpected ways – the ice moved back uphill from where it originally came. Recession and a series of complex ice flow directional switches took place over relatively short timescales.”
Four major ice flows have been identified across northern Britain and Dr Evans’ team has produced case studies of drumlin and lineation mapping that show that these glacier flow directions switched significantly through time.
The pressure of the ice flows became sufficient to deform sediments at the base of the ice sheet, resulting in the moulding of the sediment into streamlined landforms like drumlins.
Many of the fields of northern England and southern Scotland have been cleared of their boulders during hundreds of years of agricultural improvement. This stony, unworkable material was called ’till’, the term now used by glacial researchers to describe sediment laid down at the base of ice sheets and glaciers.
A close look at many of the distinctive stone walls in the region of the North Pennine chain, often reveals the use in their construction of Scottish and Lake District ‘erratics’, stones which are quirks of glacial ice flows. Many of these erratic stones were transported hundreds of miles away from their origin by the complex and often reversed movement of the glaciers.
Dr Evans says: “The Durham model shows that an ice sheet can reverse its flow in a hundred or so years and when this happens, it creates unique features in our landscape. Elongated drumlins and meltwater channels in northern England and southern Scotland provide evidence of this unique phenomenon. ”
“The ice sheet had no real steady state but rather was mobile and comprised constantly migrating dispersal centres and ice divides which triggered significant flow reversals. The occurrence of Lake District material in Pennine dry-stone walls is a clear indication that during the last glaciation of Britain, ice sheet flow directions were at times reversed.”
Five stages of glaciation in Northern Britain:
Build up of snow and ice on higher ground.
Ice thickening results in ice flow down valleys that drain the uplands.
Valley ice from different upland sources fuse or coalesce.
Ice thickens in the lowlands and the ice sheet dispersal centres migrate, forcing ice flows to become independent of the underlying hills and valleys.
In some areas the ice flows reverse and in places (e.g. Vale of Eden) actually move back uphill.
Four flows of glaciation in northern Britain:
Phase I flow was from a dominant Scottish dispersal centre, which transported Criffel granite erratics to the Eden Valley and forced Lake District ice eastwards over the Pennines at Stainmore. Prior to this phase local ice caps over the Lake District and North Pennines forced ice to flow into the lowlands, the reverse of Phase I flow.
Phase II involved easterly flow of Lake District and Scottish ice through the Tyne Gap and Stainmore Gap with an ice divide located over the Solway Firth.
Phase III was a dominant westerly flow from upland dispersal centres into the Solway lowlands and along the Solway Firth due to draw down of ice into the Irish Sea basin;
Phase IV was characterised by unconstrained advance of Scottish ice across the Solway Firth. At this time, and ice sheet had started to uncouple again to produce localized ice retreat back on to the high land of the Lake District and North Pennines (the ice retreated from whence it came). This period saw: a) the development of a vast lake (Glacial Lake Carlisle) over the Solway Lowlands dammed by the Scottish ice advance; b) the cutting of the Melmerby meltwater channels on the Pennine Escarpment by water draining along a glacier margin retreating up the Eden Valley; and c) the deposition of the Brampton kame belt, the largest accumulation of glacial sand and gravel in England.
So,
a) Nice to know that the theory of drumlins as taught in school fifty years ago is still OK science [ /snork]
b) What does this tell us about relying on ice-core strata?
Ahem, Clew Bay is in Ireland, not Great Britain (caption).
REPLY: fixed thanks
Extract from “Druid Times”, 15,000 BC.
“Destructive new technology, such as fire and animal husbandry are producing a new kind of aether that that is destroying our perfect climate, that has not changed in time immemorial. The ice is retreating. The situation is worse than we thought.
We must control and limit the use of fire and kill all the sheep or we reach a tipping point. This is where we tip all the herders and fire freaks over a cliff.”
The fact that glaciers developed on the British Isle for me is a new approach which makes perfectly sense.
I expect similar events to have happened on the European Continent and the US.
This conclusion has consequences for the speed of a glaciation.
It will happen much faster, compared to the old theory that suggested that glaciation started in the arctic.
Ice thickening in the lowlands would be due to changes in precipitation patterns, i.e., climate change during the ice age.
Surely the advances and retreats coincided with various stages of human evolution / migration. I can’t wait for someone to show me the evidence. For surely humans were to blame for these unexpected reversals. Surely…
Now, if we could only rid the planet of the scourge that is humanity, then the climate will stabilise and never ever fluctuate again.
And then the polar bears will be fine.
Interesting, but I’d like to see some photographic / topographic evidence of this, and even if correct, I doubt glaciers would start to reverse direction anywhere there was a significant gradient. But I suppose that there are few areas of Albion’s Plain where this is the case.
1) How far back does the extended hockey stick handle go? Does the Totally Undisturbed Unchanging Until Just Now Climate Period go back 25,000 years?
2) Is there a statistical link between belief in AGW and residing in an area likely to be reclaimed by glaciers if the Ice Age returns? Are the people of New England, Canada and Northern Europe, for example, just manifesting a defense mechanism against the deep latent fear of a possible return of Big Ice by indulging obsessive belief in the power of CO2 that folks in more southern climes do not share?
If you want to see the spectacular power of glaciers, take a trip to Yosemite. It’s mind-boggling. I have a pic I will post later today.
jlc (11:01:39) :
Extract from “Druid Times”, 15,000 BC.
“Destructive new technology, such as fire and animal husbandry are producing a new kind of aether that that is destroying our perfect climate, that has not changed in time immemorial. The ice is retreating. The situation is worse than we thought.
We must control and limit the use of fire and kill all the sheep or we reach a tipping point. This is where we tip all the herders and fire freaks over a cliff.”
OK, but you left out reading the entrails of sheep and predicting the end of the universe.
George Tobin (11:14:52) :
just manifesting a defense mechanism against the deep latent fear of a possible return of Big Ice by indulging obsessive belief in the power of CO2 that folks in more southern climes do not share?
Very intelligent and deep sarcastic observation.
jlc (11:01:39) :
Extract from “Druid Times”, 15,000 BC.
“Destructive new technology, such as fire and animal husbandry are producing a new kind of aether that that is destroying our perfect climate…
You have forgot our new age Merlin wizards and their fantastic “pebbles’ universe”, who after consulting their stone circles, say “climate is changing”, Oh!, how wise they are!
I would think that the place from which ice was flowing uphill must have been higher than the uphill destination.
The standard textbooks have not explained the formation of drumlins in a satisfactory manner – or, if so, I’ve not seen it. This is an interesting explanation but it would have to be shown to be true elsewhere, such as in New York State along its northern coast and in the US mid-west. The depression caused by thick ice (a couple of miles) might cause a reversal but near the ice front the ice would have to stay intact. If it were to melt away and fall apart at the ice front then it would not move as described. Ice could move down a mountain, into and across a valley, and up the next ridge. If the valley ice were to melt away, then the ice that had been pushed up a ridge could move back down. This would also imply that the original source of ice had stagnated.
Note that the usual use of the word “retreat” when referring to glaciers has not had the meaning of “reversing” their direction of flow as used in this paper.
Ron De Haan
“The fact that glaciers developed on the British Isle for me is a new approach which makes perfectly sense.”
The old theory – that glaciers formed in the arctic and flowed southward – always seemed a bit suspect. For one thing, there just isn’t a downward sloping gradient that stretches for a thousand miles. I read an interesting book several years ago called “When the earth nearly died” by Allan & Delair. They argued that the movement of ice sheets postulated by glaciologists is physically impossible, and they quote Howorth:
“it is not possible to pile up a mass of ice to an idenfinite height, or to force a mass of ice of greater length than about seven miles along a level surface by any pressure, however obtained, without its crushing, and without, therefore the thrusting force being dissipated.”
Unfortunately, the thesis of the book was that the ice ages as we know them never actually happened, and the empirical data can be interpreted by flooding. They give a good account of this, but they then used the flooding to argue for a catastrophe, that the earth was nearly destroyed by an interstellar object, with a description that even trumps Hollywood. However, their skepticism of ice sheet movement, as explained, may have something in it.
OK. One picture is posted.
Just watched an episode of “How the Earth Was Made” about the Great Lakes. They spoke of an area of drumlins in Ontario (hundreds as I remember) all oriented in the same direction, north. An other episode was on how Loch Ness was formed due to ice and a fault in which the loch lies. Enjoyable TV.
It’s also worth recalling that, even today, the south of England is falling, as the decreased pressure on the northern part of the tectonic plate on which the UK sits, lets that part rebound upwards. Evidence is that the area around Manchester is the ‘hinge’ for this movement, as there are earthquakes in this region quite frequently. We experienced one such earthquake in August 2007, while cruising the Peak Forest Canal in a narrowboat. No tsunami resulted.
I was at a schools exhibition at the Cavendish Lab at cambridge uni today and got talking to a man from the british antarctic survey. I was talking about the surfacestations survey and he said those are not the sites used in the global temperature measurements. He said they are just used for the USA and are not the ones which are used as usa contribution to global temperatures. He might have meant only the best are used or meant something else… I could have misunderstood as well… The bell went and we had to move on to the next exhibitor. But it did make me think. I had assumed that the USHCN network was the US contribution to GISS or Hadley? Can anyone enlighten me?
Neil McEvoy (10:55:27) :
“Ahem, Clew Bay is in Ireland, not Great Britain…”
Which for some reason reminded me of an old Irish joke:
Paddy was anxiously driving up and down the street because he had a very important meeting, and he couldn’t find a parking place. Looking up to heaven he said, “Lord, take pity on me. If you find me a parking place I will go to Mass every Sunday for the rest of me life, and give up Irish Whiskey!”
Miraculously, a parking place appeared.
Paddy looked up again and said, “Never mind, I found one.”
Now we know why golf courses are the way they are.
Folks
Google Fimbul Winter – the old Norse story about a sudden ice climate. It’s the suddenness of these climate shifts in which the clue to their mechanisms might lie.
So much for the science is settled. Even this glaciation thingie is a tad more complicated than it seems at first blush. Who’d a thunk that, on geologic time-scales, a glacier could turn on a dime. Next thing you know folks will be saying that climate is far more complicated than we thought, that we don’t understand what’s happening with the sun, and that CO2 is good for the environment.
Apparently, it was theoretically possible during the last ice age to walkfrom London to New York across ice, as the glaciers came down as far as Watford. According to this new theory, we’d have ended up in Inverness, after doing a 2000 rotational rollercoast tour of the northern hemisphere.
P Wilson (15:28:30) :
Apparently, it was theoretically possible during the last ice age to walkfrom London to New York across ice, as the glaciers came down as far as Watford. According to this new theory, we’d have ended up in Inverness, after doing a 2000 rotational rollercoast tour of the northern hemisphere.
My Geography teacher taught us (in the 1960s) that the southernmost deposits of terminal moraine were found at Staples Corner on the North Circular Road, so maybe the glaciers just managed the extra five or so miles South from Watford!
Anyone with greying hair who took geography A level at school, which normally included field work could probably still recall and draw diagrams of the origin of drumlins, moraines hanging valleys and so on. Geologically they have been studied in great detail ever since Darwins time. The digitised archive of Geikie’s landmark treatise The Great Ice Age (1874, 3d ed. rev. 1894) is available as a google archive in all its 43 chapters but must be some kind of auto text recognition transcript because its chock full of typo’s.
http://www.archive.org/stream/greaticeageandi02geikgoog/greaticeageandi02geikgoog_djvu.txt
Right click for print preview is best for reading it. The last chapter debating possible drivers of climate change are entertaining, particularly the dismissal of polar wandering/continental drift, but also impressive in scope.