It is believed there have been three previous major ice ages in Earth's history and several minor ones.
The first was the Huronian Ice Age which lasted from 2400 to 2100 Ma
(million years ago)note1
The second was the Cryogenic period that lasted from 850 to 635 Ma. note2
The third was the Karoo Ice Age which lasted from 360 to 260 Ma.
The first two ice ages did not affect the Lake District because it did
not exist! The oldest rocks from which the Lake District is built (the
Skiddaw Slates) were laid down as sediments about 490Ma.
The Karoo Ice Age did not affect the Lake District because Britain was
in the tropics at that time.
The present ice age, the fourth, is called the Pliocene or Quaternary note3 Ice Age and started 2.58 million years ago, i.e. it has only just started and may have another 100 million years to go.note4
This may not feel like an ice age, with global warming and all, but
that is because we are in a warm inter glacial period
Ice Ages are not unremittingly cold. The current Ice Age, particularly
over the last half million years, has consisted of cold glacials lasting
70 to 90 thousand years alternating with warm interglacials lasting 10
to 30 thousand years note5.
Within the glacials there are shorter warm periods called interstadials
and within the interglacials there have been short cold snaps called
stadials.
Recent glacial and interglacial periods have names - in fact they
have multiple names in different parts of the world. In Britain the last
glacial which lasted from 110,000 to 11,650 years ago is called
the Devensian (Würm in the Alps) and the interglacial that preceded it,
from 130,000 to 110,000 years ago, is called the Ipswichian (Eemian in
northern Europe). The glacial that preceded the Ipswichian interglacial
was the Wolstonian (Illinoian in North America, Riss in the Alps) and
lasted from 200,000 to 130,000 years ago. The interglacial before that
was the Hoxnian.. Wikipedia has a table
of recent glacials and interglacials and their various names
Recent stadials and interstadials also have names ref1.
The Devensian glaciation reached is maximum about 18,000 years ago and
was followed by a warm period called the Allerød interstadial from 14
thousand to 13 thousand years ago. (In Britain the Allerød is known as
the Windermere). This was followed by a cold stadial called the Loch
Lomond Advance in Britain (called the Younger Dryas elsewhere) which
started abruptly (in the space of about 100 years), lasted 1,300 years
and ended even more abruptly (in about 20 to 70 years) about 11,650
years agonote6
The present interglacial, since the Loch Lomond Advance, is known as the Flandrian in the context of Britain glaciation, or more generally as the Holocene.
About the glacials there is not much to be said - there were no plants or animals let alone people. The Lake District was buried under about 3,000 feet (900 m) of ice which flowed over it and swept away not only the flora and fauna and soil but also a modest amount note7 of bedrock. However the appearance of the summit plateaus, on Helvellyn for instance, suggest that the highest peaks may have protruded above the ice as nunataks ref2. The ice cap does not keep growing indefinitely because the outflow of ice increase with the depth of ice. Also, as the global ice cover increases, precipitation falls virtually to zero. There is less warmth to evaporate the water and less open water to be evaporated.
During the previous interglacial (the Ipswichian or Eemian, 130,000
to 110,000 years ago) a previous Lake District would have existed with a
climate similar to or warmer than today. To be precise 3°C warmer at
its peak 125,000 years ago but then declining. (Temperature
Chart)
This Lake District would have been similar in general shape to ours. A
little higher since ours has suffered a further 100,000 years of erosion
by glaciers. The lakes would have been slightly different but there
would still have been lakes since the glacial mechanism that excavated
our lakes during the Devensian would have operated similarly during the
Wolstonian. There would have been different animals - hippopotamuses for
instance. There may have been people but they would not have been modern
humans (who at that time had only just evolved in Africa) and probably
not Neanderthals.. If there were hominins they would have
been homo erectus note8
Whatever animals or people there may have been in the Lake District
then, all traces have been swept away by the Devensian glaciation.
However the Devensian ice sheet was not as extensive as the Wolstonian
that preceded it and only reached the middle of England. Consequently
traces of the Ipswichian interglacial may be found further south,
particularly in East Anglia.
Before the Wolstonion glaciation another version of the Lake District existed in the Hoxnian interglacial. (424,000 to 374,000 years ago).
Another version of the Lake District existed in the Cromerian
interglacial 620,000 to 455,000 years ago
There were people in the Lake District in the Cromerian. Hand Axes
made of Lakeland volcanic rock have been found in Cromerian
deposits at Waverley Wood Farm quarry pit, near Bubbenhall in
Warwickshire.
In all, as many as twenty incarnations of the Lakes may have existed
in successive interglacials within the present ice age.
The Lake District 2.6 million years ago, before the onset of the
ice age, would have looked quite different. The pattern of valleys would
have been similar but they would have been narrow V shaped valleys
rather than the U shapes we see today. The highest peaks would have been
only a few metres higher since they were above the ice and suffered
little erosion but the valley floors would have been 100m to 200m
higher. The transition from the fell tops to the valley floor would have
been more gradual with few crags and the gradients of the rivers from
their source down to the sea would have been gradual - there would have
been few, if any, lakes.
Exactly which subset of the Eurasian fauna colonises Great Britain and the other British islands in a particular interglacial depends on the time span between the retreat of the ice and the inundation of the land bridges.
The remains of the following animals have been found in Ipswichian deposits in the south of England. These animals would also have roamed the Ipswichian Lake District but their remains have been swept away by the subsequent Devensian ice sheet.
Common Shrew (Sorex araneus), Lesser White Toothed Shrew (Crocidura suaveolens), Wood Mouse (Apodemus sylvaticus), Water Vole (Arvicola terrestris cantiana), Field Vole (Microtus agrestis), Tundra Vole (Microtus oeconomus), Mountain Hare (Lepus timidus), Fox (Vulpes vulpes), Badger (Meles meles), Fallow Deer (Dama dama), Verticornis Deer (Premegaceros verticornis), Red Deer (Cervus elaphus), Wild Boar (Sus scrofa), Spotted Hyaena (Crocuta crocuta), Wild Horse (Equus ferus), Brown Bear (Ursus arctos), Lion (Panthera leo), Aurochs (Bos primigenius), Steppe Bison (Bison priscus), Merck’s Rhinoceros (Stephanorhinus kirchbergensis), Narrow-nosed Rhinoceros (Stephanorhinus hemitoechus), Hippopotamus (Hippopotamus amphibius), Straight-tusked Elephant (Palaeoloxodon antiquus), Woolly Mammoth (Mammuthus primigenius). (The mammoth was able to cope with warm conditions which makes its extinction in the present interglacial all the more mysterious)
The periglacial zones ( - in the south of England* - the Lake
District being under the ice cap) during the whole ice age up to the
holcene were populated with lemmings, musk ox, woolly mammoths, woolly
rhinos, giant deer, aurochs, sabre tooth cats, cave bears and cave
lions. All but the first two species are now extinct. The last mammoth
died about 1700 BC on Wrangle island in the Siberian Arctic. The last
aurochs died in 1627.in
Poland.
There is no satisfactory explanation as to why all these megafauna
should have become extinct towards the end of the last glacial and into
the current interglacial when they survived all the previousnote9
interglacials some of which which were warmer and longer than this one.
The evolution and expansion of homo sapiens is one possible explanation
but there are objections to this and the whole topic is still being
debated in palaeoecological circles.
The novels of Jean M Auel give an excellent picture of life in the
prehistoric periglacial environment.note10
* Sea levels during the Devensian were about 100m lower than at present so the British Isles were part of the Eurasian continent
The ice sheets were at their maximum (about 900m thick) about 18,000 years ago and then began to recede. This would not have been a rapid process even if global air temperatures had suddenly switched to interglacial levels, which they could not have done because of the albedo effect of all the ice. It would have taken maybe a thousand years to melt 900m of ice. The bigger continental ice sheets were several kilometers thick and would have taken several thousand years to melt. In any event, it is believed that all the ice had gone from the Lake District by the time of the Windermere interstadial 14,000 years ago.
However, after a thousand years the ice returned, during the Loch Lomond Advance from about 13,000 to 11,650 years ago. The build-up of ice would have been as slow as the melting had been. The glaciers would have started to accumulate first in the cirques* at the tops of the mountains and then gradually worked their way down to lower levels. Alan Smith ref2 suggests that in the thousand to 1,300 years of the Loch Lomond the glaciers extended down to the valley floors and for some distance along them. Fairly conclusive evidence of how far they reached is in the form of the terminal moraines they left behind for example in the Langdale valley and at Rosthwaite in the Borrowdale valley.
* Smith points out that the bigger Lakeland cirques or corries are mainly east to north facing. An east facing corrie facilitates accumulation of snow from a prevailing westerly wind and a north facing corrie better retains the winter snowfall through the summer.
The Naddle valley has its own terminal moraine which is rather neglected in the literature. It is ESE of the stone circle. It is quite broad - 200 to 400m and 10m to 15m high. The Naddle beck cuts through it in the vicinity of the bridge, known locally as the 'Cement' bridge, at OS NY29792340 (54.6009444,-3.08836111 in Google Earth). The moraine is delineated most clearly by the 500 foot contour on old OS maps. It is not quite so clearly shown by the 150m contour on the current OS maps. There is a corresponding moraine in St John's Vale, also shown by the 500 foot contour, which extends from just north of Bridge House to Hill Top Farm. These may be contemporary with Loch Lomond terminal moraines such as the Rosthwaite moraines mentioned in ref2. They are further down their valleys than those at Rosthwaite because they are at a higher altitude (150m versus 100m).
There would have been a moraine lake which initially would have been quite extensive possibly joining up with the moraine lake in St John's in the Vale and with Thirlmere. The loose moraine material would have been cut through very quickly by the floodwaters from the melting glacier so that the extended lake may not have lasted even as long as the glacier. However, once the Naddle beck had cut through the moraine down to the bedrock the rate of erosion would have slowed dramatically and a small lake would have remained in the hollow carved out of the rock by the glacier.note11 It is known that this lake was in existence until about 1800 BC ref9. It has since disappeared (as most of our lakes would disappear in time, if this interglacial lasted long enough) due to the combined effects of being filled with sediment and its outlet being lowered by the erosion of the river.
Another glacial feature in the Naddle valley is a Kettle Hole. This is where a huge block of ice (about 20m by 30m) broke off the face of the retreating glacier and become embedded in the outwash of sediment from the glacier. When it finally melted it left behind a marshy depression which is visible on satellite images at NY29572203 {54.5886,-3.09139 in Google Earth).
Excavations at various places on the farm have revealed beds of boulder clay just beneath the topsoil. It has been found both at low elevations, e.g. at 150m beside the Naddle beck where the lake used to be and at higher elevations e.g. at 200m when constructing a new water tank in the field above the house. This clay is a startling blue colour.
Erratic pieces of rock deposited by the glacier litter the surface of the fields. The technical term for this glacial debris is clitter note12. In the meadows most of the rocks have been removed note13 and incorporated in stonewalls. In some of the pastures some large pieces remain, one particular field adjacent to the stone circle field has extensive clitter deposits note14 . Another field has a small group of quite large rock fragments of the order of tens of tons each note15. There are also large boulders just below the surface which are encountered when ploughing; the largest of which is more than 20 feet in length. It is notable that, whereas the subsurface boulders are rounded, the surface clitter is angular. This may be due to either frost action or the application of sledgehammers and dynamite.
note1 Ma ( = Mega
annum = million years (ago)) is a proper unit of time recognised by the IAU.
Likewise ka (= thousand years).
However other SI prefixes are not used, e.g. ha for 100 years, Ga for
1,000 Ma are not used.
a in this context is the Julian year of 365.25 days of 24 hours.note16
note2 Within the Cryogenic Period there were two episodes of intense glaciation - the Sturtian from 720 to 700 Ma and the Marinoan from 660 to 635 Ma During these severe glaciations the ice sheets extended almost to the equator - verging on 'Snowball Earth' conditions.
note3 Quaternary does not refer
specifically to the ice age but to the geological era which followed the
Tertiary Era and happens to coincide with this, by some reckoning, the
fourth ice age. The Tertiary has been renamed the Cenozoic Era in modern
geological
time charts.
Quaternary survives when the terms Primary, Secondary, Tertiary have
been abandoned as geological eras only because there are so many
departments for Quaternary Research at universities around the world.
The starting date for for the Quaternary has been the subject of
considerable debate which still continues. The interested parties agree
that the term Quaternary should be retained and that its start date
should correspond with the onset of the current ice age - but that was a
gradual process as noted below. The latest thinking is that the most
suitable marker is the Gauss - Matuyama magnetic reversal which occurred
2.588 Ma. The advantage of this marker as a reference point is that it
is global and easily detectable in rock strata and the date agrees with
other more localised markers such as the first occurrence of ice-rafted
debris in mid-latitude Atlantic sediments. ref 6
note4 It is supposed
that an ice age is caused by a continent drifting across the south pole
by tectonic plate movement allowing a build up of snow and ice and
blocking the circulation of warm water from the equator to the pole.
This appears to have been the case with the Karoo Ice Age which
coincided with Panagea being over the south pole. If this hypothesis is
correct then we may have to wait many tens of millions of years for
Antarctica to drift away from the pole before we can expect the present
ice age to end.
Although this ice age is reckoned to have started 2.588 or 2.6 million
years ago it is the culmination of maybe 15 million years of declining
temperatures which probably reflects the tectonic movement of
Antarctica to its present position over the south pole.
A continent drifting over the north pole would have the same effect but,
as far as is known, this has never happened - the Arctic Ocean has
always been there.
note5 Since the current interglacial has lasted 11,650 years (or 14,000 years if the Younger Dryas is reckoned as a stadial within this interglacial) the next glacial would be imminent were it not for man-made global warming.
note6 These remarkably
precise dates are due to the Greenland ice cores in which individual
winters are discernible.
For more details see ref 3
note7 The erosion of bedrock by a glacier is disappointingly slow. A study of glaciers in the Pyrenees ref 7, gives a maximum basal erosion rate of 60mm per century when the glacier is retreating and only 5mm per century when the glacier is advancing. If glaciers are assumed to have been active for 2 million years in this ice age (the other 600,000 years being allotted to interglacials) then 5mm per century adds up to 100m of erosion. A cursory glance at the hanging valley of Watendlath in Borrowdale indicates the total glacier erosion at the place which is now the middle of Derwentwater was about 160m which gives an erosion rate of 8mm per century.
note8 Tempting though it is to imagine that a civilisation similar to ours might have existed in the Ipswichian interglacial (complete with farms, roads and towns, even a tourist industry?), it cannot have been. Those early hominins were stone-age hunter gatherers, they lacked the rudimentary technologies (metal smelting, writing, language?) and were too busy fending off the giant predators and marauding packs of hyenas to develop a civilisation as our more recent ancestors have done in the holocene.
note9 Actually there were a few earlier extinctions but the rate of extinctions increased dramatically from one species every 73,000 years before 50ka to one species every 4000 years after 50ka ref8. Earlier extinctions include the giant beaver Trogontherium cuvieri and the giant hyena Pachycrocuta brevirostris.
note10 The Mammoth Hunters is one of a series of novels by Jean M Auel which give a fabulously detailed and well researched account of periglacial life about 30,000 years ago. This was in the glacial period so the novels are set well to the south around the Black Sea and the Balkans. The first book in the series is Clan of the Cave Bear.ref4
note11 There are a
couple of problems with the Naddle valley moraine and lake.
Firstly, why is the moraine so broad compared with the other Loch Lomond
moraines such as at Rosthwaite?.
Secondly, why was the lake carved into the bedrock when the other LL
moraines show no signs of such excavation?
The Loch Lomond Advance was too brief for the excavation anyway; Note7,
above, shows that a typical erosion rate is 8mm per century so that in
the thousand years of the Loch Lomond Advance the total erosion should
have been only about 8cm. It would have taken the whole 100,000 years of
the Devensian to have carved a basin deep enough for a lake. A partial
explanation may lie in the fact that the lower part of the valley where
the lake was (including Birks wood ref10)
is underlain by soft Skiddaw Sates whereas the rest of the valley is on
harder Borrowdale Volcanic rock.
Another explanation which may account for both the hollow in the bedrock
and the size of the moraine could be that during most of the Devensian
the Naddle Valley glacier was in collision at this point with other
glaciers moving in a different direction. This may have given rise to a
medial moraine which the subsequent Loch Lomond terminal moraine was
built on top of or adjacent to. The Naddle valley glacier could have
been forced up by the opposing glaciers allowing the carving of the
basin for the lake.
note12 The word clitter has acquired an unfortunate new meaning recently. If looking up clitter using a search engine it is advisable to specify 'glacial clitter'.
note13 grandfather was enthusiastic about using dynamite to reduce the larger rocks to manageable proportions.
note14 This clitter field was first noted by T. Clare. ref11
note15 This assemblage of huge clitter blocks is in a wood at NY29272253 (54.59297222N,-3.09611111E)
note16 In defining the Julian year the day length of 24 hours needs to be specified because we are dealing with astronomical and geological time scales. The length of a day is slowly increasing as the tidal drag of the moon slows the Earth's rotation. This is proved by 370 million year old fossil corals with daily and annual growth rings that show that each year then had about 400 days of about 22 hours ref5
general note The
global temperature changes which start and end a glacial period are
remarkably small, maybe 4°C to 6°C. This is why climatologists
get so excited about apparently small temperature changes due to
man-made greenhouse gases.
A few degrees drop in temperature is all it takes for the snow that
lasts until June on the mountains of Scotland and Cumbria to last right
through to autumn and so begin to accumulated year on year until it
becomes a glacier. Then this snow and ice cover on our mountains (and
all the other high altitude and high latitude parts of the world)
reflect solar radiation back into space causing global cooling to
accelerate by positive feedback.
Wikipedia has a graph
of global temperature changes over the last 65 million years.
ref 1 Global
environments through the Quaternary, By
David E. Anderson, Andrew Goudie, Adrian Parker
Oxford University Press 2007
ref 2 The Ice Age in the Lake District by Alan Smith, The Landscapes of Cumbria Series Vol. No. 3, Rigg Side Publications 2008
ref
3 A
Quick Background to the Last Ice Age by Quaternary
Environments Network (QEN) 1998
Adams J.M. & Faure H. (1997) (ed.s), QEN members. Review and Atlas
of Palaeovegetation: Preliminary land ecosystem maps of the world since
the Last Glacial Maximum. Oak Ridge National Laboratory, TN, USA.
ref 4 Clan of the Cave Bear by Jean M Auel, Crown 1980
ref 5 Scrutton, C. T., 1964. Periodicity in Devonian coral growth. Palaeontology 7(4): 552-558.
ref 6 The Pleistocene and Holocene Epochs, P. Gibbard and T. Van Klofschoten
ref 7 Variability of Quaternary glacial erosion rates – A global perspective with special reference to the Eastern Pyrenees. Delmas, Magali; Calvet, Marc; Gunnell, Yanni. Quaternary Science Reviews, v. 28, iss. 5-6, p. 484-498.
ref 8 Extinctions in near time By R. D. E. MacPhee
ref 9 Clare, T., Wilkinson, D.M. & Pile, S.R. (2002) Environmental change and Castlerigg stone circle. Transactions of the Cumberland and Westmorland Antiquarian and Archaeological Society II: 302-305.
ref 10 Wilkinson, D.M., Clare, T. & Corkish, J. (1999) The history of carr woodland at Birks Wood, northern Lake District. Naturalist 124: 157-162
ref 11 Clare, T. (1999) The environs of the Castlerigg stone circle: an analysis of the landscape of the Naddle Valley near Keswick, Transactions of the Cumberland and Westmorland Antiquarian and Archaeological Society XCIX:67-87.
general ref An absolute chronology for the raised beach and associated deposits at Sewerby, East Yorkshire, England, M. D. BATEMAN , J. A. CATT
Look-up OS map reference. Convert between OS map reference and latitude,longitude
The converter gives a map reference in metres relative to the OS origin. To convert this to the NY sheet origin it is necessary to subtract 300km from the eastings and 500km from the northings. i.e. drop the leading 3 and the leading 5.
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