Many things happening at once
It is hard to know where to begin to tell the story of the meltdown of the last Ice Age, because it is really many different stories woven together into a single fabric.
Part of it concerns large-scale climate flips, sudden radical thaws and equally radical freezes, volcanism on a planetary scale, earthquakes of unparalleled ferocity and mass extinctions of animal species.
Part of it, which I’ve already touched on, is the huge loss of habitable land, of low-lying coastal plains and fertile river deltas that occurred as the sea-level rose – a ‘lost continent’ scattered around the world like the pieces of a jigsaw puzzle with a combined land area of 25 million square kilometres.
Part of it concerns the speed and the sheer magnitude of the post-glacial flooding.
Part of it is the need to understand the processes that led the earth into this devastating cycle of inundations.
Part of it is a complexity: yes, global sea-level did rise by about 120 metres between 17,000 and 7000 years ago; no this ‘eustatic’ rise (i.e. pertaining to sea-level alone) has not been uniformly reflected in changing shorelines through time. Thus, in some parts of the world sea-level relative to ancient shorelines has remained quite stable for millennia; in others, submersion of a particular locality may be deeper than expected from eustatic changes; in yet others submersion may be shallower than expected from eustatic changes. Such variations can be caused by local land subsidence or land rise following earthquakes or volcanic activity; however, a much more potent and extensive agent of changing land-levels is known to geologists as isostacy.
Kicking the gel-filled football
The earth’s surface, which seems solid beneath out feet, can yield and deform when subjected to sufficiently large pressures. It behaves a bit like a football that has been loosely filled with a thick, heavy gel: pressure at one point on the gel-filled ball will result in an indentation in that area, a displacement of the fluid mass within and a corresponding rise in a roughly circular area surrounding the indentation. Geologists call this process isostacy, and it plays an important role not only during Ice Ages but also for thousands of years after all the ice has melted away. The reason it does so is that the vast weight of the ice-caps is sufficient to force down the earth’s crust into great basin-like depressions beneath them. When the ice melts, that pressure is suddenly removed and the floors of the basins begin to rebound; they will, if sufficient time is allowed, rise again to their original levels.
Ice-loading causes a depression in crust under ice, and an isostatic bulge effect beyond it. Based on Wilson and Drury (2000).
At the LGM 17,000 years ago, the ice-caps over large parts of North America and northern Europe were between 2 and 4 kilometres thick and applied loads of thousands of billions of tonnes to the continental landmasses on which they had formed.13 Thomas Crowley and Gerald North, both oceanographers at Texas A&M University, observe that North America’s Laurentide ice-sheet
extended from the Rocky Mountains to the Atlantic shore and from the Arctic Ocean southward to about the present positions of the Missouri and Ohio rivers. In Europe the Fennoscandian Ice Sheet reached northern Germany and the Netherlands. The weight of the massive ice sheets depressed the crust by as much as 700–800 metres, resulting in gravity anomalies that are still detectable.14
The post-glacial world showing regions of isostatic rebound (light shade) and submergence (dark shade). Based on Wilson and Drury (2000).
On average it has been found that 100 metres of ice-loading depresses continental crust by 27 metres.15 But this is only part of the story. The water of the world’s oceans also has weight; indeed it is denser than ice. Thus, 100 metres of water-loading depresses the sea-bed beneath it by 30 metres.16 Since all the ice formed on land during the last Ice Age was made out of water extracted from the sea, it follows that while the crust was pressed down beneath the continents, it actually rose up beneath the oceans (as the water-burden above it lightened). Conversely, after all the ice had melted and returned to the oceans as water, the burden on the sea-bed would have again increased. R. C. L. Wilson, Professor of Earth Sciences at Britain’s Open University, calculates that a layer of water 165 metres deep was subtracted from the oceans to make the great ice-caps of the last glaciation. This, however, only produced a net drop in relative sea-level of around 115 metres between the onset of glaciation 125,000 years ago and the onset of LGM 104,000 years later – the reason for the discrepancy being that reduced water-loading in the oceans during the Ice Age allowed the sea-bed to rise by 50 metres through the process of isostatic compensation.17
Let’s stop for a moment and take another look at this see-saw system swing by swing:
125,000 years ago the most recent glacial surge begins, turning a worldwide layer of ocean 165 metres deep into ice-caps thousands of metres high piled up (for the most part) in North America, Greenland, northern Europe, South America and the Himalayas.
The maximum extent of ice formation is reached 21,000 years ago and largely maintained until 17,000 years ago; by this time the continental crust beneath the big ice-caps has been depressed into huge basins nearly a kilometre deep.
Simultaneously, as the ice-burden on the land increases, the water-burden on the sea-bed decreases; by the Last Glacial Maximum this had allowed the ocean-floor around the world to rise by 50 metres.
Soon after the LGM the ice begins to melt and to flow back as water to the oceans, a process that is substantially over within 10,000 years.
Since a layer of water 165 metres deep was taken out of the oceans to begin with to make up the ice-caps, it follows that a layer of water 165 metres deep is returned to the oceans with the complete melting of the ice-sheets.
Professor Wilson observes that the rate at which the crust and mantle respond to loading and unloading is ‘much slower than the build-up or melting of ice caps. This is why areas that were buried beneath several kilometres of ice 18,000 years ago are still rising today, thousands of years after the ice sheet melted away.’18
It also follows that the average 50 metre rebound of the ocean floor between 125,000 and 17,000 years ago would take thousands of years to be forced down again by isostatic subsidence to its original level.
Measured at a warm point in a long interglacial, and after 17,000 years of isostatic subsidence, today’s sea-level is probably quite close to the final balance in the equation of rising seas and sinking sea-beds. But there must have been many times during the meltdown of the Ice Age when the speed of the former far outstripped any compensating effects of the latter.
Is it not possible, perhaps even probable, that this combination of a higher sea-floor than today’s and rapid influxes of meltwater from the decaying ice-caps could have produced relative temporary rises in sea-level much greater than the average annual rate projected over the full period of the meltdown?
See-saw
Examples of segments of continental crust that continue to rise through isostatic rebound since the removal of the ice-sheets include the highlands of Scotland19 (where the ice-cap that once covered most of Britain was at its thickest), the floor of the Gulf of Bothnia in what is now the Baltic Sea (reported to be rising at a rate of a metre per century),20 large parts of the coasts and mainland of Sweden, Denmark and Norway, the north-east coast of Canada,21 and parts of southern Chile.22
Complicating the picture is the fact that around each zone of ‘post-glacial rebound’, there lies what geologists call a ‘peripheral zone of submergence’-which is always larger than the zone of rebound.23 Thus, while it is not uncommon to find such phenomena as raised beaches in the highlands of Scotland24 (demonstrating graphically that areas that were once at sea-level, and formed an ancient coastline, have now been lifted well above it), other areas of the British Isles are visibly sinking into the sea. This is because the downward pressure of the Fennoscandian ice-sheet on the northern European continental crust at the LGM was transformed by the mechanism of isostatic com
pensation into a huge ‘forebulge’ several hundred kilometres beyond the ice-margin-literally as though one end of a see-saw had been forced down, pushing the other end up. As the ice melted the weight that was holding the end of the ‘see-saw’ down was released, allowing it to rise again and causing the other end – the ‘forebulge’ – to fall.
This is exactly what is happening in the English Channel today, which we’ve seen was entirely dry at the LGM. The Isle of Wight stood on the forebulge of the Fennoscandian ice-sheet, forced upwards by isostatic compensation. Then when the ice-sheet melted, the dynamics of isostacy again came into play and the forebulge began to subside – taking the Isle of Wight (and much of southern England) down with it.
Isostatic Atlantis
An ingenious theory of the lost land of Atlantis, the first that I am aware of that is explicitly based upon the relationship between isostacy and rising sea-levels, was put forward in the late 1990s by Vitacheslav Koudriavtsev, a member of the Russian Geographical Society of the Russian Academy of Sciences.
It is well known that the story of Atlantis was set in writing in the fourth century BC by the Greek philosopher Plato – in his dialogues Critias and Timaeus. But before that, Plato tells us, it had been an oral tradition passed down within his family from his ancestor Solon, the revered Athenian lawmaker. Solon had been told it during a visit that he had made to Egypt at around 600 BC. His informant, in turn, had been an elderly Egyptian priest at the Temple of Sais in the Delta, who said that he had drawn the information from written records, then more than 8000 years old, lodged in the temple’s archives.
There are four essential ingredients in Plato’s story:
Atlantis was a relatively advanced, well-organized and prosperous civilization.
It flourished and was destroyed 9000 years before Solon’s time – in other words, approximately 11,600 years before our time.
It was located on a large island ‘opposite the Pillars of Hercules’ – presumed to be the modern Straits of Gibraltar.
Its destruction was the result of a global cataclysm: ‘There were earthquakes and floods of extraordinary violence, and in a single dreadful day and a night … the island of Atlantis was … swallowed up by the sea and vanished.’25
There have been a thousand theories about the location of lost Atlantis, moving it around in time according to individual researchers’ whims and placing it everywhere from the Mid-Atlantic Ridge to Indonesia and from the Andes mountains to Crete. What Koudriavtsev is suggesting is just another theory. Nevertheless, it has the great merit of requiring no liberties to be taken with Plato’s text either in respect of the location of ‘Atlantis’ (beyond the Straits of Gibraltar in the Atlantic Ocean) or of the date of its submergence – 11,600 years ago.
Koudriavtsev’s location is an area known to fishermen as the Little Sole Bank, situated on a vast underwater plateau called the Celtic Shelf, 200 kilometres to the south-west of the British Isles and Ireland. Although the shallowest part of Little Sole Bank is now 57 metres beneath the waves, and thus might be expected to have been about 60 metres above sea-level just before the end of the last Ice Age, Koudriavtsev’s research shows that it and a large area of the surrounding shelf may have been tilted dramatically upwards during the build-up to the Last Glacial Maximum by the see-saw effect of isostatic forces emanating from the continental ice-mass. In brief, his theory is that there was an unusually rapid collapse of the forebulge in this area around 11,600 years ago, coinciding with a ferocious episode of ice-melting and global flooding – the sudden inundation of Atlantis described by Plato.
‘In my opinion,’ states Koudriavtsev,
the most serious argument in favour of the assumption that Atlantis was not invented by Plato is that the time when it vanished, as indicated by Plato – about 11,600 years ago – and the circumstances of its vanishing described by him (the sinking into the deep of the sea), coincide with the findings of modern science about the end of the last Ice Age and the substantial rise of the level of the World Ocean that accompanied it.26
Three global superfloods
Anyone who has read the Timaeus and Critias carefully knows that what Plato describes in his account of the destruction of Atlantis is indeed a global flood that took place approximately 11,600 years ago and that swallowed up huge landmasses as far apart as the eastern Mediterranean and the Atlantic Ocean. I would have thought that a first line of approach for scholars investigating Plato’s claims would be to find out whether anything on this scale might actually have happened in the world 11,600 years ago. So far as I can discover, however, not a single historian or prehistorian has ever made the effort to do so – although many of them have put forward theories, usually widely applauded by their peers, locating Atlantis anywhere but in the Atlantic, where Plato says it was, and any time within the epoch of recorded history, rather than considering the prehistoric date of 9600 BC given by Plato. One of the ludicrous (but positively peer-reviewed) claims put forward to divert the debate endlessly into trivia is that Plato meant 9000 months before Solon’s time, not 9000 years, when he spoke of the submergence of Atlantis.
In my experience historians and archaeologists will go through Houdini-like contortions of reason and common sense rather than consider the possibility that their paradigm of prehistory might be wrong – so I am not surprised that they have never attempted to investigate at face value the Atlantis tradition of a devastating global flood 11,600 years ago. However, there are scholars – trained in other disciplines and not hobbled by the same preconceptions – who are more open to the possibility that the flood tradition in general, and the Atlantis story specifically, might be rooted in the real events of the meltdown of the last Ice Age. This view has been entertained positively by the late Cesare Emiliani, for example, former Professor in the Department of Geological Sciences at the University of Miami27 – one of the pioneers of the isotopic analysis of deep-sea sediments as a way to study the earth’s past climates.28 Moreover, Emiliani’s fieldwork in the Gulf of Mexico has produced striking evidence of cataclysmic global flooding ‘between 12,000 and 11,000 years ago’.29 Robert Schoch, Professor in the Department of Geology at Boston University, observes that there was also a dramatic warming of the earth’s climate in the same period30 – the ‘Preboreal’ – and that overall there is a
stunning line-up in time between the sudden warming of 9645 BC, Emiliani’s scenario of a massive freshwater flood pouring into the Gulf of Mexico, and the date Plato ascribed to the sinking of Atlantis. Whatever the accuracy of specific details, this curious coincidence points to the effect sudden climatic changes can have – and no doubt have had – on civilization.31
Science writer Paul LaViolette likewise argues that ‘there may be much truth to the many flood cataclysm stories that have been handed down to modern times in virtually every culture of the world. In particular, the 9600 BC date that Plato’s Timaeus gives for the time of the deluge happens to fall at the beginning of the Preboreal at the time of the upsurge of meltwater discharge.’32
Before rejecting the possibility of a lost civilization of the last Ice Age, therefore, I urge historians and archaeologists to take a close look at the mass of data that now exists about the sequence of cataclysmic floods that swept the earth between 17,000 and 7000 years ago.
Yet this too is a contentious area of debate. For while scientists now agree on the approximate figure of 120 metres for sea-level rise during the 10,000 years of post-glacial flooding, many do not accept that these were ‘floods’ at all – and certainly not in the cataclysmic sense. Averaging the rise over the time-span as we did earlier, they see a fairly gradual and distinctly non-cataclysmic process in the range of a metre a century. This remains the majority view. But since Emiliani’s findings first began to undermine it in the 1970s there has been more and more research to show how very cataclysmic the meltdown of the Ice Age could in fact have been.
In brief what is being suggested is that during the long span of the meltdown �
�� in addition to countless episodes of smaller-scale flooding – there were three global superfloods which have been dated within the following approximate time-bands: 15,000–14,000 years ago, 12,000–11,000 years ago and 8000–7000 years ago. I have found that estimates of these dates vary by more than a thousand years either way, depending upon which authority you consult, but the general point is clear enough: there now exists a strong case that nearly half the total meltwater release at the end of the last Ice Age was concentrated into these three relatively short episodes, creating conditions of concentrated damage after long periods of stability – precisely the combination of circumstances and bad luck that could have led ultimately to the destruction of an antediluvian culture.33
Professor Emiliani’s ice dams
Cesare Emiliani made many original contributions to scientific understanding of the meltdown of the last Ice Age. He was also among the first to work out the precise mechanism behind the characteristic ‘rhythm’ of this 10,000-year period – millennia of slow melting and gradual sea-level rises interrupted, apparently randomly, by much shorter episodes of extremely severe global flooding and rapid, destructive oceanic transgressions:
Underworld: The Mysterious Origins of Civilization Page 9