BY HALF A MILLION YEARS ago many generations of people had made Britain their home. They had adapted to the temperate climates and developed new tools and technologies to cope with the longer, colder winters of northern Europe, but big changes were about to disrupt their daily lives. As the trajectory of the earth around the sun began to change, ice caps on the poles grew and sea-levels fell. Northern Europe had experienced glaciations before – a particularly severe one about 650,000 years ago – but Britain was about to suffer the coldest of all. Its name was the Anglian.
Although the Anglian Glaciation was one of the most influential forces in shaping the Britain that we see today, we actually know comparatively little about it. We do know that it started about 480,000 years ago and lasted some 55,000 years. Most climate curves show a steady decline in temperatures with occasional very brief rises and reaching extreme cold conditions between 470,000 and 430,000 years ago. The eventual warming in climate was very rapid, taking only a few thousand years. During the maximum cold Britain was largely covered by ice, but there would have been tens of thousands of years when there was a periglacial or even more temperate climate with permanent ice limited to more northern areas. Southern lowland Britain would have had seasonal snows with frozen ground, but summer thaws that allowed hardy plants and animals to survive. Much of the time there would have been permafrost with only the upper levels of the ground thawing, causing defrosted sediments to slide down even the gentlest slopes across the frozen ground beneath. Of course one of the problems of understanding these periods is the general lack of animal and plant life to enable reconstruction, and even when present, it rarely survives. But there are two sites that give a glimpse into the cold beginnings.
COLD BEGINNINGS
The cooling at the beginning of the Anglian can be measured as rapid in geological time, though on the human generational scale, it was a slower decline with short periods of warming. Some human groups may have retreated to the south, but at Boxgrove we know that people stayed on as the climate began to deteriorate.
Boxgrove
We have already seen in Chapter 5 how humans thrived beneath the coastal cliffs at Boxgrove during a temperate climate with a good supply of flint for making handaxes, ready for butchering the abundant game (Roberts & Parfitt, 1999). But soon there were the first visible signs of a deterioration in climate – the receding sea. As temperatures dropped ice became locked up on the poles and sea-level dropped. At the same time vegetation began to change. Warm-loving plants struggled to cope with the colder winters and the deciduous trees began to diminish. The vegetational changes were accompanied by shifts in the native fauna and the arrival of more northerly taxa. Harsher winters led to longer periods of frost. As frozen ground thawed on the slopes above the coastal plain, water-logged soils and underlying silts, clays and chalk gravels slid downhill as muddy sludge, burying the cliff beneath. For humans their prime source of flint raw material was buried and instead they had to rely on nodules brought downslope in the sludgy gravel and mud. But they continued to knap these nodules, making similar handaxes and leaving scatters of flakes, just like their forebears (Figure 73).
FIG 73. Section at Boxgrove showing marine deposits and raised beach in the lower part of the section with overlying slope deposits of sands and gravels from the nearby chalk cliff and downs. (Courtesy of Boxgrove Project)
From the fauna within the slope deposits or equivalent beds on the plain below, we know that there was not a simple decline in climate, but an initial cooling, followed by amelioration and then the more steady deterioration to much colder conditions (Parfitt, 1999). Many of the animals had wider tolerances and continued to survive in the first cooling. Some of the extinct shrews and voles, such as Sorex rutonensis, Sorex savini and Pliomys episcopalis were still inhabitants, probably reflecting good ground cover. The presence of the water vole (Arvicola cantiana) indicates that there were streams or ponds in the area, while Pine Vole and Wood Mouse suggest some woodland. The real indications of a cooler climate come from the first appearance of Narrow-skulled Vole (Microtus gregalis), which today occupies dry, open areas of central and northern Asia, while the Northern Vole (Microtus oeconomus) is found in the boreal zone of northern Eurasia, inhabiting riverbanks or marshland and more open grassland (Figure 74). Although the climate was undoubtedly colder, there are unlikely to have been extended periods of frozen ground as shown by the occurrence of moles. Today they venture no further than central Scandinavia because of the difficulties of burrowing into frozen soil in more northerly environments and the rarity of their principal nourishment of earthworms. No doubt the shrews, voles and moles were preyed on by a range of carnivores, but the only remains so far found are from Weasels (Mustela nivalis). Larger herbivores, such as horse and bison, would also have populated the more open landscapes and provided important hides and meat for the human survivors.
FIG 74. Boreal forest in Sveg, central Sweden. (Robin Dennell)
A brief return to warmer conditions is signalled by the stabilisation of the land surface and the slowing down of hill-wash deposits from the slopes above the plain. A thin soil developed, indicating the return of thicker vegetation cover with shrubs and trees. We also see the retreat of the more northerly taxa as Northern Vole and Narrow-skulled Vole disappeared from the landscape. The extinct shrews and voles remained and were joined by Water Shrew (Neomys fodiens), Pygmy Shrew (Sorex minutus), Field Vole and Common Vole (Microtus arvilis). Hazel Dormouse also made a reappearance as did the Slow Worm (Anguis fragilis), and among the birdlife we have the Robin (Erithacus rubecula). This is only a partial picture of the wildlife reconstructed from the scant remains, but it seems that conditions had returned to those enjoyed by humans during the heyday of the Boxgrove interglacial.
The respite was brief, but still people clung on as climate deteriorated once more. Increased cold brought new thick deposits of muddy, chalky gravel down the buried slopes of the cliff. Occasional larger bones and teeth have been found of horse, bison, extinct rhinoceros and extinct bear (Ursus deningeri). The latter is an early form of cave bear with a distinctive domed head. Wolf would have been one of their predators. Finally the telltale signs of humans disappear as a deeper cold set in and people were no longer able to cope with the harshness of an arctic Britain. The ice was building in the north, but more southerly areas were yet to suffer the full glaciation, as we can see at Ostend.
Ostend
As you drive out of Happisburgh heading west you pass a byroad signposted to Ostend. Visitors to Norfolk might be a little confused. In fact it is not a short-cut to Belgium, but a tiny hamlet barely worthy of a name. The byroad takes you back to the coast and it was here that Clement Reid of the Geological Survey noted an ‘Arctic Freshwater Bed’ in the cliffs on the beach (Reid, 1882). Similar deposits had been found at Mundesley a short distance to the north and as far as Beeston some 23 km around the coast. At Mundesley Reid noted the occurrence of arctic plants such as Dwarf Willow (Salix polaris), Dwarf Birch (Betula nana) and Common Mare’s Tail (Hippuris vulgaris), together with taxa indicating open conditions such as moss (Hypnum turgescens).
While we were working at Happisburgh in 2008, new exposures of the ‘Arctic Bed’ were revealed at Ostend and my friend and colleague, Simon Parfitt, would stride off along the beach of an evening to investigate. The extra-curricular work paid dividends and we now have a clearer insight into a cold episode as Anglian ice was building further north (Parfitt et al., 2010).
The exposure was about 30 m in length and consisted of 0.8 m of organic silts and fine sand underlying the Anglian glacial till. Pollen and plant remains show a dominance of herbaceous taxa with grasses (Poaceae), sedges (Cyperaceae) and Bog-moss (Sphagnum), coloured in summer with flowers of the pink or carnation family (Carophyllaceae) and Dandelion (Taraxacum spp.). Arboreal pollen from birch, willow, pine and spruce suggest occasional trees in the area, although some of the pollen might have been reworked from the underlying Cromer Forest-bed.
The molluscs are dominated by the gastropods, Stagnicola palustris and Anisus leucostoma that live in fresh water and the terrestrial Succinella oblonga that thrives in damp, sparsely vegetated areas. They can all survive cold conditions through their ability to hibernate or aestivate in winter. Gyraulus rossmaessieri is no longer found in Britain and has a distribution from central Europe through to eastern Siberia. It often lives in snow-melt-filled, shallow pools on poorly vegetated floodplains. The diversity of the assemblage is low with only 12 other taxa, but has been likened to those found around Lake Baikal today, and able to survive long, cold winters.
Ten beetle taxa were identified. The only abundant species is Helophorus obscurellus which lives under stones in sandy substrates. Today it is distributed from the Kanin Peninsula in arctic Russia through to Siberia and across the Tibetan Plateau. Two of the other beetles have distinctly northern distributions; Pterostichus brevicornis is a predatory carabid that lives under leaves and mosses on open tundra, while its cousin Pterostichus middendorffi prefers dry, sandy river banks. Five of the species can be used to estimate temperatures and they suggest that summers were about 10°C, while average winters lay somewhere between −36 and −10°C. Even the upper limit shows an extremely cold winter climate.
Bones from Ground Squirrel (Citellus citellus) were also found in the recent work with just three other taxa of collared lemming (Dicrostonyx), Field Vole (Microtus agrestis/arvalis) and Narrow-skulled Vole. The combination is typical of the northern tundra or steppe of central and northern Asia with dry grasslands. Collared lemmings are well adapted to cold northern environments, digging extensive burrows during winter and having specialised winter claws adapted for digging through snow and frozen ground. There is also an unknown predator, as many of the remains have been attacked by stomach acids and one bone has a tooth puncture mark. The culprit was a probably a small carnivorous mammal and the remains deposited as a scat on the edge of the pond.
The picture that emerges from Ostend is of a seasonally flooded pool, surrounded by marsh and occasional reed beds. Open tundra stretched for miles beyond a floodplain of sedge, grass and moss with small stands of Dwarf Birch and Dwarf Willow. Summers would have been cool, similar to those found in the Arctic Circle, while winters dropped to extreme Siberian cold. The barren landscape supported little animal life other than the hardier voles, Ground Squirrel and lemmings. But what of the larger mammals? There are very few, but for this we have to look to other sites.
Other Arctic faunas
There are only a handful of other animal remains that probably date to the Anglian. Among these is an extinct form of Musk Ox, called Praeovibos priscus, remains of which were found just 10 km up the coast from Ostend at Trimingham (Stuart, 1982). It is not quite clear in which deposit the remains were found or indeed whether they had the same ecology as today’s Musk Ox (Ovibos moschatus). The modern species are predominantly found in Arctic North America, but have been reintroduced into parts of northern Eurasia. Their name is taken from the strong smell that is emitted by males during mating. They are characterised by their long, curved horns and short tail, protected by a long, thick coat. The soft undercoat provides qiviut, which is much valued as a soft, warm wool. Standing up to 1.5 m high, the larger males can weigh over 400 kg. They usually congregate in herds of 10 to 20 individuals, feeding on grasslands in lowland valleys during summer. In winter they seek areas of reduced snow cover, such as windswept uplands, browsing off taller shrubs such as Dwarf Willow. Today their main predators are wolves and occasionally bears, which would probably have also been the case during the early part of the Anglian.
Back down the coast a few kilometres to Mundesley another cold-adapted species was found, the Wolverine or Glutton (Gulo gulo) (Figure 75). They are the largest of the land-based mustelids, but with their short legs, stocky bodies and broad head, they have more resemblance to small bears than others in that family. The heavier males can grow up to a metre in length, stand about 40 cm in height and weigh between 20 and 30 kg. Their thick, dark fur is rich in oils, repelling water and of course cold, while their broad five-toed paws are excellent for traversing snow. They are well known for their fearless, vicious nature, often attacking prey several times their own weight, even as large as elk. They also scavenge and have been known to steal from other larger carnivores such as wolves. To help tear meat from their prey they have a pair of opposing molars at right angles to other teeth. Their modern distribution is in northern boreal forests or Arctic areas of Eurasia and Canada.
FIG 75. Wolverine (Gulo gulo), Kamchatka, Russia. (Sergey Gorshkov/Minden Pictures/FLPA)
There are also occasional records of Reindeer from Anglian or slightly earlier deposits. We are all very familiar with Reindeer, although today there are several subspecies with a great deal of variation in size and behaviour. The larger males can weigh up to 180 kg and females 120 kg, and they are the only deer where both sexes have antlers. Compared to other deer their antlers are particularly large and can be used to brush away snow. There are other characteristics that make them well adapted to cold conditions. Like the Musk Ox the fur has two layers with a thick undercoat and a longer overcoat with hollow hairs providing greater insulation. The nostrils are also adapted by having longer turbinate bones that warm the air as it enters the lungs. During winter they have hardened hooves which provide grip on ice or snow and can also be more effective for digging through to reach their food beneath. Their digestion system is adapted to tundra vegetation. In winter they are largely dependent on lichens, particularly Reindeer Moss (Cladonia rangiferina), which uniquely for mammals is broken down to glucose by the enzyme lichenase. They also graze and browse on grass, sedge and shrubs such as birch and willow. It is unclear whether the huge herds that we see today were a regular part of the early Anglian, but in the last glaciation they would have been a very familiar sight in the open landscapes of Britain (see Chapters 10 and 11).
As we saw from Boxgrove, bison were also a part of the early Anglian fauna. Although this example has not been identified to species, a likely candidate would have been the now extinct steppe bison (Bison priscus). It seems to have been similar to present-day bison, being up to 2 m in height, weighing some 900 kg with 1 m wide horns. More clues come from the last known survivor from about 10,500 years ago as frozen remains in Siberia (Boeskorov et al., 2014). Yakutia in eastern Siberia is well known for the carcasses that are revealed seasonally during spring thaws. Indeed the local Yukagir tribal community add commercial gathering of mammoth tusks to the more traditional hunting and fishing. In August 2011 the complete corpse of a steppe bison was found on the shore of Lake Chukchalakh (Figure 76). It is still being analysed but initial reports describe it as a four-year-old male weighing an estimated 500 to 600 kg with horns about 75 cm across. The comparatively low weight and horn breadth suggests that it is a smaller subspecies of other steppe bison and its attribution to this species has been confirmed from DNA. Its organs and stomach contents are also still intact so further work should reveal more about its diet. At the time of its death about 9,300 years ago the landscape would have been similar to today with low-lying steppe-tundra dissected by rivers and scattered with small lakes. Whether extreme winter temperatures or malnourishment led to the bison’s premature death is as yet unknown. But it does seem to have died from natural causes as there is no damage from predators and it was found in a sleeping position with neck and head stretched out and legs tucked under the belly.
FIG 76. Mummified bison from Yukagir, Siberia. (Alexei Tikhonov)
The steppe bison had a long history, but other cold-adapted mammals had a more recent introduction to Britain. As we will see in subsequent chapters the typical mammals of the cooler, more open phases developed and changed with new arrivals from central Eurasia. As the climatic oscillations became more accentuated over the last 500,000 years, conditions became more continental, leading to the adaptation of a suite of animals on the ‘mammoth steppe’ (Guthrie, 1990). Horse and bison were already residents, but the first signs in Britain of other animals able to cope with colder winters were the appearance of woolly rhinoceros (Coelodonta antiquitatis) from about 300,000 years ago, soon followed by woolly mammoths. For the last cold episode after 100,000 years we can add Mountain Hare (Lepus timidus), Steppe Pika (Ochotona pusilla) and Arctic Fox (Alopex lagopus) to the typical open tundra or steppes of Britain. To return to the Anglian, the steppes, tundras and any biological life were about to disappear as ice descended from the north.
ICE AGE BRITAIN
As most animals, including humans, began to retreat from southern Britain, ice built in the north. The first signs would have been the growing snow and ice in the Highlands of Scotland, followed by the other mountainous areas of Britain. Within a few thousand years glaciers had developed across large parts of the landscape, enveloping river valleys and sweeping broader paths as it headed to the lower lands of the south. The base of the ice sheet eroded large swathes of land, grinding and churning the underlying sediments into stony clays, or tills, with only the harder rocks surviving (Figures 77 and 78). The frontal lobes were areas of summer melt with huge volumes of water carving out deep valleys that rapidly filled with sands and gravels. Doubtless the ice sheet expanded and retreated several times through slight shifts in climate, but their most southerly extent is marked by the distribution of tills. In East Anglia, these consist of chalky, flint-rich clays, reflecting the underlying bedrock (Figure 79), whereas in the Midlands they are often characterised as red and brown clays with large erratics of Leicestershire syenite and carboniferous conglomeratic sandstone. In south Wales glacial sands contain rocks of Millstone Grit, basalt, rhyolite and coal. A line can be drawn that starts near the northern end of the Essex coast, passes through Hornchurch and Finchley in North London, skirts to the north of the Chilterns and then heads down to the coast of South Wales (Figure 80; Lee et al., 2016).
FIG 77. The Burren, County Clare, showing glaciated limestone pavement. (Peter Hoare)
FIG 78. Glacially striated sandstone cobble from Chalk Hill, near Barton Mills, Suffolk. (Peter Hoare)
FIG 79. Glacial till or ‘chalky boulder clay’ at base of section at Barnham, Suffolk (see Chapter 7).
FIG 80. Map of southern Britain showing palaeogeography about 450,000 years ago, illustrating the most southerly extent of ice. (Illustration: Craig Williams)
To the south of the line would have been treeless, wind swept, polar desert, almost devoid of plant or animal life (Figure 81). To the north lay a trail of destruction. One of the major casualties was the Bytham River. Overrun by ice it would never flow as a river again with its network of tributaries and valleys gone for ever. Instead the ice had carved out a large basin choosing an easy path through the soft Jurassic clays and sands between the limestone and the chalk. When the ice melted it would become the Wash. Rivers in the future would flow from east and west into this basin.
FIG 81. Polar desert: glacier reaches the ocean, South Georgia Island. (Flip de Nooyer/Minden Pictures/FLPA)
The Bytham was not the only river to be affected. The Thames had been flowing from the northwest, through the Goring Gap in the Chilterns and eastward through the Vale of St Albans to the Essex coast. But ice blocked its eastward course to the north of Watford and created an ice-dammed lake. As the lake level rose, the river found an easier route to the south, forcing a passage eastwards to what we now know as London. Without the Anglian, our capital city would be situated 40 km to the north.
However, the biggest impact was yet to happen and was caused by the Scandinavian ice sheets. As the ice grew in northern Europe it expanded to the south and west across the North Sea Basin until it reached the ice from the British mainland. The evidence can be seen today on the Norfolk and Suffolk coasts. If you walk along the beach at Happisburgh you will see the grey sandy clays at the base of the cliffs with occasional specks or larger fragments of chalk. If you look harder you will find more exotic stones, such as rhomb porphyry, which is an igneous rock that originates from around Oslo in Norway (Figure 82). It had probably arrived in Britain from earlier glaciations, but was now being dragged south as part of the new advance. The clay is called Happisburgh Till and is the residue from the ice sheet that swept across the soft sediments of the eastern seaboard of Britain and the North Sea Basin, bringing with it an unusual suite of rocks.
FIG 82. Norwegian erratic of rhomb porphyry from the Happisburgh Till at Happisburgh. (Peter Hoare)
FIG 83. Rafts of glacially transported chalk within Happisburgh Till near Sidestrand, Norfolk. (Tony Sutcliffe)
If you were to continue walking along the coast to the northwest you would pass the villages of Walcott, Bacton and Mundesley, eventually reaching the long stretch of deserted beach with 50 m high cliffs between Trimingham and Sidestrand. Here too the Happisburgh Till can be seen. But more impressive is an excellent demonstration of the sheer power of the glaciation. High up in the cliff you will see huge chalk rafts that were lifted from the bedrock and then dumped as the ice proceeded on its way (Figure 83). Clement Reid gives the following description in his Memoir of the Geological Survey: The Geology of the Country around Cromer.
The bending has been so violent as to squeeze up a ridge of Chalk; of which, judging from the dips on the foreshore, the two Chalk bluffs seen in the cliff appear to be the last remnants. In all probability about 200 years ago there was a continuous cliff of disturbed Chalk, at least half a mile long, though the greater part of this must have been denuded long before the first scientific account of the coast was written … The northern Chalk bluff was 106 yards in length when Lyell measured it, but is now less than 40 yards, and the part where he saw Boulder Clay extending for 7 feet under the Chalk has been destroyed. This mass has been forced up till its surface is 40 feet above high-water, and probably about 60 feet above its original level. (Reid, 1882, p. 95)
But the violence of these glacial forces was as nothing compared to what was yet to come.
THE ANGLIAN MEGAFLOOD
Higher in the cliffs around parts of the Norfolk coast can be seen laminated silts and clays, very different from the less structured Happisburgh Till below. These are in fact lake deposits, which have a story of their own and provide clues to one of Britain’s most dramatic events. As the Scandinavian ice expanded it met the British ice forming a solid wall across the northern part of the North Sea Basin. To the south the Kent–Artois Anticline was a continuous chalk ridge between southeast England and northern France, linking Britain to mainland Europe. As the climate began to warm towards the end of the glaciation, meltwaters poured off the ice sheets into the southern North Sea Basin to form a rapidly filling lake. The swollen rivers of northern Europe added to the lake with rivers such as the Rhine bringing meltwaters from the Alps. The lake must have been approaching the size of Belgium, some 30,000 km2, with an incredible 500 billion tonnes of water. The wall of ice to the north was solid, but the comparatively lower chalk ridge to the south, perhaps 30 or 40 m high, was more vulnerable. As the lake reached the top of the chalk, it began to tip over the edge and drop to the dry floor of the Channel valley below. The soft rock of the chalk rapidly eroded and like a dam breaking, the pent-up water of the lake burst through, carving a gorge several kilometres wide. Within days or perhaps even hours the chalk had been breached to create what we now call the Strait of Dover (Figure 84; Smith, 1985; Gibbard, 1995).
The scars of this event can of course be seen in the white cliffs of Dover and, on the opposite side, in Calais. There are other signs, though, in the floor of the Channel. Immediately to the south of the Strait are basins over 100 m deep that were scoured out by the impact of the water hitting the valley floor. As water poured down the ever-widening gorge it carved out new channels, leaving elongated, cigar-shaped islands in its wake. These have been examined by my colleague Sanjeev Gupta from Imperial College using bathymetry to map the Channel floor (2007). The morphology of the islands is of particular interest, as similar features are characteristic of the megafloods caused by the repeated breaching of the ice-dammed Lake Missoula in western Montana during the last glaciation. It is estimated that at the peak of the flood there was a volume of 40 to 60 km3 of water flowing at a rate of over 30 metres per second. It is easy to see how the power of an even greater volume of water could create the Strait of Dover. To travel even further afield, Sanjeev is now working on the Mars Space Programme and has identified similar features as evidence of a super-flood on Mars (Warner et al., 2009).
FIG 84. Map of southern Britain showing formation of the Strait of Dover. (Craig Williams)
For Britain, the megaflood was the most momentous event in its geographic history. From now on at times of high sea-level there was no longer the land link between southeast England and northwest France, and Britain was soon to become an island for the first time in its human history. As climate warmed, people were soon to return, but to a totally new landscape.