Hunt’s incredulity at the notion of an ice dam more than 2,000 feet high and 7 miles long receives support from studies which argue that “at a lake depth of approximately 200 meters (656 feet), the hydrostatic pressure exerted on the damming ice is sufficient to begin to force a hole through the ice. Once formed this hole will enlarge by frictional melt-widening, enabling the drainage of ice-dammed lake water to occur.”14
At more than thrice 200 meters in height, therefore, the hypothetical Clark Fork ice dam does, indeed, begin to look “impossible.”
Yet, as noted, Hunt accepted the USGS statistics. The surface of Lake Missoula certainly did at one point stand 4,150 feet above sea level and the lake therefore must indeed have reached around 2,100 feet deep in the Clark Fork Valley between the Bitteroot and Cabinet mountain ranges. That it did so is confirmed by an ancient strandline at that altitude, and other strandlines have been found at lower altitudes which clearly show many subsequent lower water levels after the high one.15 Hunt’s solution, however, since he continued to regard the Clark Fork dam as a geological impossibility, was to propose that a gigantic flood, thousands of feet deep, must have washed over the entire region at the end of the Ice Age, in the process filling the various basins of Glacial Lake Missoula up to the 4,150 foot level where the highest strandline is found and leaving the lower strandlines as it receded.16
As the source of his proposed region-wide flood, Hunt suggested that:
tidal inundation brought on by some form of gravitational attraction from a celestial source, the nature of which is beyond the competence of the writer, must have resulted in a … tide … rising to 5,000 feet (1,600 meters) above present sea level … The waters were held there several weeks … during which there was much surging, partial floating of glaciers, and development of the highest beaches in “Lake Missoula.” The tidal ebb and flood with successive lower beaches developing allowed sweeping of the canyons, removal of previous glacial deposits, fans and talus, scouring of the “Scablands,” ice-rafting, polishing of standing rock obstructions to tidal surge, aggradation of valley and “by-pass” floors, and discharge of boulders into submarine deltas and fans. Lastly, a layer of silt was left in the wake of the tide, especially in the quieter waters of cul-de-sac estuaries.17
In other words, Hunt had very much gone “back to Bretz” in proposing a single gigantic flood as the source of all the damage on the Columbia Plateau. His 1977 notion that it was a tidal inundation of sea-water rushing up estuaries (and brought on by the gravitational attraction of some hypothetical celestial body)18 is, however, untenable, and Hunt himself recognized this when he revisited the subject some years later in his 1990 book Environment of Violence. Conceding that “the tidewater solution is weakened by the great distance to tidewater and the absence of a trail of evidence along the possible routes,”19 he sought out other possible sources of water in sufficiently vast quantities to inflict the damage to the landscape that he had observed in the field. In the process, he briefly considered John Shaw’s theory of a subglacial reservoir of 100,000 cubic kilometers of meltwater, but asked some pertinent questions:
How could such melting take place without a heat source such as the volcanic heat which precipitates Icelandic jökulhlaups? What climatic regimen would allow such melting in the first place? Why would the water not have lifted the periphery of the ice sheet and emerged without accumulating soon after it was produced by melting? What containment mechanism would allow accumulation of a great under-ice lake … beneath 3,000 meters of ice? And would not water beneath the maximum ice thickness tend to escape toward the lesser confining pressures under peripheral areas of the ice sheet? Is there any possible way such a huge under-ice chamber of water could accumulate?20
To cut a long story short, Hunt reasoned that there was not. Besides the 100,000 cubic kilometers that Shaw’s theory offered was, in his opinion, insufficient. Almost ten times as much water would be needed to account for all the field evidence. With a tidal source, Glacial Lake Missoula and Shaw’s under-ice reservoir all dismissed, therefore, Hunt found himself left with only one possible—though startlingly catastrophist—solution. Somehow, in some way, very rapid, cataclysmic melting of an immense area of the North American ice cap must have taken place. After doing the necessary calculations Hunt concluded that 840,000 cubic kilometers of ice, i.e. about ten percent of the entire glaciated area, “would have had to melt.”21
The reader will recall that Bretz originally envisaged something similar but was defeated by the inability of either radical global warming or sub-glacial volcanism (quite simply, neither happened) to account for the vast quantities of meltwater “his” flood called for. In the end, as we saw, he settled for outburst floods from Glacial Lake Missoula as the answer. In 1990, Hunt faced the same dilemma—with the exception that he had already ruled out Lake Missoula—but showed himself to be an extraordinarily competent and prescient innovator when, without any preamble, he wrote:
Earth heat cannot have melted continental ice to produce floodwaters in the volumes required … A cometary heat source could have served the purpose.22 (Emphasis added.)
To melt ten percent of the North American ice cap, Hunt calculated that the kinetic energy of a half-kilometer diameter comet would be sufficient:
A comet of the type that exploded above the Tunguska site in 1908 could have provided this heat. The great lake it might have created in the middle of the ice sheet would rapidly have tunneled under the remaining glacier and emerged as catastrophic floods in many directions. Cometary melting of the ice seems necessary to yield so much water in such a short time.23 (Emphasis added.)
Anticipating the objection that no crater had been found, Hunt pointed out that the Tunguska event—an airburst—likewise left no crater or ejecta blanket. Furthermore, in the case of a hypothetical comet impact on the North American ice cap:
all ejecta and cometary matter would likely have been swept away in the ensuing flood, coming to rest widely dispersed in the drift blanket far from its source. Thus diluted and mixed with other debris, direct evidence for either the exploded projectile or ejecta from the site could be difficult to recognize, if not lost to science permanently.24
Last but not least—and again the prescience is almost eerie!—Hunt noted that “glass spherules if found in glacial debris could support the theory.”25
He could not have known then, writing a quarter of a century ago, that from 2007 onward a team of leading scientists would champion the cause of comet impacts on the North American ice cap and, in the absence of obvious craters, would derive much of their evidence from microspherules, fused glass and nanodiamonds.
How to change global climate in an instant
Hunt’s suggestion was that a single relatively small half-kilometer diameter object would have packed sufficient kinetic energy to set off the melting of approximately one tenth of the North American ice cap, producing a cataclysmic flood. Twenty-five years on, the proponents of the Younger Dryas comet hypothesis, as we have seen, are proposing that “multiple two-kilometer” objects may have impacted the ice cap.26 If they are correct, the scale of the ensuing floods must have been almost unimaginably large. Nor would they have been confined only to the Channeled Scablands of the Columbia plateau. The comet hypothesis envisages a rain of impacts right across the ice sheet from the Pacific to the Atlantic coasts of North America, so we should find evidence of flooding everywhere.
We do. The Columbia plateau displays flood-ravaged scablands but so too does the state of New Jersey much farther to the east. The Columbia plateau is notable for its fields and hillsides strewn with huge ice-rafted erratics but so, too, is the state of New York. Indeed, perched on the bare rock surfaces of Manhattan’s Central Park are many imposing erratic boulders, including diabase from the Palisades Sill along the Hudson River and shist from even farther afield. Interestingly, too, just as the Columbia plateau has its coulees, so New York State has its Finger Lakes. These latter were long thought to have bee
n carved by glaciers but their geomorphology closely parallels that of the coulees and some researchers now believe they were cut by glacial meltwater at extreme pressures—a process linked by sediment evidence to “the collapse of continental ice sheets.”27
Figure 22
Likewise in Minnesota, on the Saint Croix River where Randall Carlson and I finished our long road trip across North America, there is a spectacular array of more than eighty giant glacial potholes. One is 10 feet wide and 60 feet deep, making it the deepest explored pothole in the world. Others, as yet unexcavated, are even wider, suggesting the probability that they may be deeper as well. And all of them, without exception, were carved out by turbulent floods at the end of the Ice Age—floods emanating, Randall believes, from the superior lobe of the Laurentide ice cap.
“You could spend a lifetime,” he tells me, “traveling this land and still not see it all. The effects of mega-scale flood flows have been extensively documented in the eastern foothills of the Rocky Mountains in both Canada and the US, across the prairie states, in the vicinity of the Great Lakes, in Pennsylvania and western New York, and in New England. All the Canadian provinces preserve large-scale evidence of gigantic water flows. All regions within or proximal to the area of the last great glaciation show the effects of intense, mega-scale floods.”
But the question that remains concerns the source of these floods.
Having been dragged kicking and screaming into conceding that flooding occurred at all, gradualist science, as we have seen, subsequently engaged in a love affair with Glacial Lake Missoula, elevating it and its epic jökulhlaups to serve as the sole explanation for all the astonishing diluvial features of the Channeled Scablands of the Columbia plateau. It is not surprising, therefore, that other Ice Age floods, wherever they are admitted to have occurred, are also attributed to jökulhlaups from glacial lakes.
More than that, it is the floodwaters from these glacial lakes—rather than anything so vulgarly catastrophist as a comet—that are presently regarded by mainstream science as the most likely cause of the Younger Dryas cold event. The giant Glacial Lake Agassiz, which lay across most of Manitoba, northwestern Ontario, northern Minnesota, eastern North Dakota and Saskatchewan, is particularly implicated. Around 13,000 years ago—i.e. immediately before the onset of the Younger Dryas—Lake Agassiz is thought to have covered an area as great as 440,000 square kilometers (170,000 square miles) when an ice dam broke and allowed a substantial fraction of its contents, perhaps as much as 9,500 cubic kilometers, to spill out along a flood path running through the Mackenzie River system in the Canadian Arctic coastal plain, and thence into the Arctic Ocean.28 There the anticyclonic circulation of a current known as the Beaufort Gyre would have gradually moved it onward into the subpolar North Atlantic in the Transpolar Drift:
The slow release of meltwater south through Fram Strait provides a mechanism unique to the Arctic that is capable of turning a short-duration, high-magnitude meltwater discharge into a significantly longer, more moderated and sustained meltwater rerouting event to the North Atlantic.29
What made matters worse, however, was that at the same time huge quantities of icy meltwater were also being dumped into the North Atlantic from the other glacial lakes and directly off the Laurentide ice sheet itself.30 The combined effect, so the theory goes, disrupted ocean circulation to such an extent that it radically affected global climate:
A great gush of cold freshwater derived from the melting Laurentide ice sheet swept across the surface of the North Atlantic. It prevented warm, salty water from the southern ocean flowing deep beneath the surface (the Gulf Stream) from rising to the surface. The normal overturning of the ocean water stopped. As a consequence the atmosphere over the ocean, which would normally have been warmed, remained cold and so, in consequence, did the air over Europe and North America.31
These are highly technical matters, with which we do not need to concern ourselves at too great length here. In brief, though, the Atlantic meridional overturning circulation, also known as the thermohaline circulation, is the great ocean conveyer belt32 that not only carries warm salty equatorial water to the surface and thence northward where it eventually cools and sinks off the coasts of Greenland and Norway, but also carries the resultant cold North Atlantic deep water south, returning it slowly to the equator where it mixes with warmer water, rises again to the surface and thus continues the cycle:
It transports large amounts of water, heat, salt, carbon, nutrients and other substances around the globe and connects the surface ocean and atmosphere with the huge reservoir of the deep sea. As such it is of critical importance to the global climate system.33
It was the shutting down of this delicately balanced, intricately interconnected, hugely complex, critical cycle, scientists agree, that caused the dramatic global cooling of the Younger Dryas. That the shutdown was the result of colossal meltwater floods out of glacial lakes, and directly off the Laurentide ice cap, is also agreed. A major puzzle, however, as S.J. Fiedel points out in a keynote paper in the journal Quaternary International, is why this should have happened 12,800 years ago, rather than say 800 or 1,000 years earlier at the height of the warm phase—known as the Bølling–Allerød interstadial—that immediately preceded the Younger Dryas.34 Intuitively one feels the meltwater floods should have been at their peak during the warming phase. In reality however it was only at the Bølling–Allerød/Younger Dryas Boundary that the meltwater releases occurred.
The solution to the mystery seems transparently obvious to Richard Firestone, Allen West, Jim Kennett and other proponents of the Younger Dryas impact hypothesis. Quite simply, there is no mystery! In their reckoning, the huge meltwater floods that so radically affected global climate were caused by multiple large fragments of a comet ripping through the earth’s atmosphere and smashing down into the ice cap—not just one fragment of half a kilometer or so as envisaged by C. Warren Hunt, but as many as eight fragments, and possibly more, including some that might have been as much as two kilometers in diameter.35
The colossal heat generated by such impacts, with a combined explosive power estimated as we have seen at ten million megatons, provides all the energy needed to set off a truly cataclysmic meltdown of huge sectors of the North American ice cap. The gigantic flood that would have followed, after scouring the land in its path, would indeed have entered the oceans as “a great gush of freshwater” and provided the shock to the Atlantic meridional overturning circulation that kept global climate savagely cold for the next 1,200 years. The situation would have been worsened by the injection of dust and immense quantities of smoke into the upper atmosphere “blocking sunlight for an extended period of time,” which would, of course, have had the effect of lowering temperatures even further. Moreover:
The impact event, followed by extensive fires and sudden climate change, likely contributed together to the rapid extinction of the megafauna and many other animals.36
The reader will recall that no less than thirty-five genera of North American mammals became extinct during the Younger Dryas.37 We are therefore, by definition, looking for “an extinction mechanism that is capable of wiping out up to thirty-five genera across a continent in a geologic instant.”38 Nor is it just North America that we must consider—for most of the diverse megafauna of South America that had flourished before the Younger Dryas also suffered extinction by 12,000 years ago, i.e, before the Younger Dryas came to an end.39
Could it have been “overkill” by human hunters? The question touches upon a contentious issue—namely when, in fact, and from where, did human beings first arrive in the Americas? Whatever the answer, it seems implausible that bands of nomadic hunter-gatherers would have been either motivated, or ruthlessly efficient enough, to wipe out so many animals, including giants like the Columbian mammoth, in so short a time across two continents. Moreover there is much to suggest that human beings in the Americas themselves entered a period of deep distress during the Younger Dryas that would have fur
ther reduced their motivation and efficiency. Archaeological evidence from South America is limited, but in North America, this was the time when the Clovis culture, with its sophisticated stone weapons technology, abruptly vanished from the record. Indeed, all available indicators point to “a significant decline and/or reorganization in human population during the early centuries of the Younger Dryas.”40
Once again, therefore, the only explanation that makes complete sense of the evidence is the comet-impact hypothesis of Firestone, Kennett, West and their large group of colleagues and co-authors.
In the light of their findings, which we have reviewed extensively in the preceding chapters, I propose the following:
1 There was indeed cataclysmic flooding in North America at the end of the Ice Age.
2 It was not primarily caused by outburst floods from glacial lakes but rather by the rapid, almost instantaneous, meltdown of a large area of the ice cap.
3 The heat source needed to initiate this meltdown came from the kinetic energy of a series of impacts from fragments of a giant comet that entered the earth’s atmosphere over North America 12,800 years ago and bombarded the North American ice cap.
4 North America, while being the epicenter of the disaster, was by no means the only region hit. Other fragments of the disintegrating comet, including some particularly large objects, appear to have smashed into the European ice cap. In this connection it may be of relevance that recent high-resolution sonar scans of the English Channel, the floor of which was above water during the Ice Age, have revealed evidence of cataclysmic flooding there in the form of a 400-kilometer-long network of submerged and partially infilled valleys carved into the bedrock. “The data show a collection of landforms that, taken together, indicate a catastrophic flood origin,” state the authors of a study published in Nature. The study specifically likens these now submerged landforms to “the Cheney–Palouse terrain of the Channeled Scabland of Washington, USA.” The authors state that they “cannot resolve the absolute timing of the flooding events.” They do conclude, however, that their study “provides the first direct evidence that a megaflood event was responsible for carving the English Channel valley network. Our observations are consistent with erosion by high-magnitude flows, as in the Channeled Scabland.”41