Some sciences capture the public imagination, others don’t. Sadly, geology seems to fall into the latter category. The monotonous cycles of erosion and deposition are quite boring, and the interminable timeframes involved in geological processes are quite difficult for people to truly comprehend.
What people don’t realize, however, is that many of the events they find most interesting and exciting – volcanic eruptions, landslides, floods, and other natural disasters – are actually geological processes, altering the landscapes around us in real time. Geology is a combination of occasional, extremely dramatic events against a backdrop of slow, incremental change.
One such dramatic event is the Spokane (or Missoula) Flood, which occurred relatively recently – about 14,000 years ago, at the end of the last Ice Age. The changes this flood wrought on the U.S. inland northwest are still extremely obvious if you know what to look for. Its discovery back in the 1920s was central to a great scientific debate that was raging at the time, pitting the Church against science, and scientists against scientists.
Up until the second half of the 18th century, when James Hutton and others laid the foundations of modern geology, the Church had held a monopoly on the origins of the Earth; in the western world, anyway. The physical realm in which we lived – mountains, canyons, oceans, plains, and rivers – were said to have been created by events described in the Bible, most notably the great flood featured in the Book of Genesis. Hutton, a Scottish farmer, and one of the leading lights of the Scottish Age of Enlightenment, concluded that many of the rocks he saw in Scotland were most likely formed by the slow, seasonal erosion and deposition processes he observed on his farm. From this grew the theory of uniformitarianism – that slow, cyclical processes repeating over unfathomable periods of time could explain many of the physical features of our world’s landscapes. This theory was in direct conflict with the Church, which held that the world was created in 7 days or some other extremely short period, versus the millions of years the uniformitarians were calculating, based on rates of soil deposition.
The Church’s intellectual dominance was under assault on many fronts, most notably from Charles Darwin and the theory of evolution. We know how its battle with geology turned out – few people today literally believe the Book of Genesis. Throughout the 1800s, the science of geology matured, uniformitarianism became very entrenched, and any consideration of the role catastrophes might play in geology became scientific heresy. Today, the role catastrophes play in shaping our world are very well understood, thanks in great part to the great Spokane Flood and the man who explained it first.
J. Harlan Bretz was a Seattle science teacher, who, inspired by the landscapes of the U.S. northwest, obtained a PhD in geology from the University of Chicago. With doctorate in hand, he returned to Eastern Washington to apply what he had learned. He became convinced that many of the features that had always intrigued him – such as giant ripple marks, scoured landscapes (which he named scablands), massive deposits of sediment, and oddly positioned boulders – could only have been formed by flooding on a huge scale. Over seven years of painstaking field work, and aided by bird’s-eye views recently made possible by the use of airplanes for crop dusting, he formed a solid theory with hard geological evidence to back it up. In 1923, Bretz published a paper, and immediately found himself under attack for apparently promoting a catastrophist theory along former Church lines.
Scientific camps on both sides of the argument formed, and this at times nasty debate carried on for more than 40 years. V.R. Baker describes the geological establishment’s reaction to Bretz’s paper:
“Bretz’s flood theory was so despicable that even circular reasoning could be employed to erect an alternative hypothesis… One cannot but be amazed at the spectacle of otherwise objective scientists twisting hypotheses to give a uniformitarian explanation to the Channeled Scabland. Undoubtedly these men thought they were upholding the very framework of geology as it had been established in the writings of Hutton, Lyell, and Agassiz.”
Ironically, the scientists had become dogmatic and inflexible in their thinking, just as they had accused the Church of being 100 years earlier. This is a good reminder that scientists are as prone to human failings as anyone.
In 1925, another geologist, Joseph Pardee, began working on the Spokane Flood theory. The work of Bretz and Pardee, along with an increasingly better understanding of the last ice age and its processes, resulted in the basically unanimous acceptance of Bretz’s Spokane Flood theory by the 1950s. Bretz died in 1981, so he did enjoy the sweet taste of vindication. Eventually, the geology community had to admit that catastrophism also had a place within the science. Today, the interplay between both processes – short and violent, and slow and incremental – are well understood, and the great Spokane Flood is one of the main reasons why.
Figure 1 shows a Google Maps image of Eastern Washington, with key components of the flood superimposed. During the last ice age of 17,000 to 11,000 years ago, the Cordilleran Ice Sheet covered much of the Canadian Rockies. Tongues of ice ran down the valleys and at times extended into northern Washington, Idaho, and Montana. At some point, a massive wall of ice blocked the Clark Fork River in the vicinity of Sandpoint. With the Bitterroot Mountains running to the south, there was nowhere for the water to go, and so a huge lake formed, called Glacial Lake Missoula.
Numerical estimates attached to Glacial Lake Missoula and the Spokane Flood are staggering. At its maximum size, the lake is calculated to have been approximately 10,000 km2 in area, with a water volume of about 2,184km3, roughly equal to the combined volumes of Lakes Erie and Lake Ontario. Near Sandpoint, the depth of the lake would have been about 650 metres, 350m at Flathead, and 200m at Missoula. When the ice dam burst, the flow of water at its peak was ~ 40-60 km3/hour (or up to 10 times the current flow rate of all the world’s current rivers combined), with water flowing at speeds of up to 130 km/hour. Simple math gives the duration of the flood as only three to five days, yet in this brief period the flood waters removed some 210 km3 of sediment further to the west. Prior to the flood, the Spokane Basin contained approximately 75m of soil overlying basalt sheets. After the flood, the loose sediment had mostly been scoured away.
Dry Falls (Figure 2), a popular tourist attraction near Coulee City, Wash., is known for its 5.6-km escarpment and enormous plunge pools, formed by the explosive power of the flood. Throughout the Glacial Lake Missoula area, giant ripples can be seen, formed by the exiting waters. Some are almost 15m high, the largest such ripples known on earth.
Figure 3 is an aerial view of Markle Pass, Mont.
How did the ice dam burst? Contemporary answers can be found in Iceland, where sudden draining – known as a jökulhlaup – of glacial lakes occurs occasionally. Icelandic ice dams usually rupture due to sub-glacial volcanic activity melting the ice above, but sometimes another mechanism is at play. As the ice near the base of the dam is subjected to greater and greater pressure from the weight of the water and ice above it, its melt temperature is lowered. Small cracks due to melting begin to form, and as these cracks connect to form networks, water begins to move through the ice. The friction of the water against the ice further enlarges the passages, and so on. Suddenly, a point is reached at which there is a catastrophic failure in the structural integrity of the dam at its base, and the dam collapses. This is most likely what happened near Sandpoint.
When the ice dam holding back Glacial Lake Missoula ruptured, its massive volume of water exploded out to the west and southwest, blasting through channels of least resistance, taking boulders, earth, and everything else with it. Figure 1 shows the many routes the water took as it rushed through the Spokane Basin – with no soil, these scoured channels can’t support agriculture, so they show up as a purplish brown. The water did not drain toward the Pacific in a traditional fashion; at pinch points, walls of water flowed violently backward up river valleys such as the Palouse Canyon, then finding no way out, slopped back down the direction from which they came. The Wallula Gap just southeast of Kennewick also presented such a bottleneck. Water backed up at this point, and as it blasted out the other side, it created the windsurfing mecca now known as the Columbia Gorge. At Portland, some water headed north to the sea, while some was forced south, up the Willamette Valley all the way to Eugene, Oregon. The rich fertility of the soil in this valley, some of the best farmland in the U.S., is thanks to the Spokane Flood.
Geological work on the Spokane Flood has continued to the present, and revisions to Bretz’s original theory have been made. New geological data do not jibe with a single flood theory. For example, thin layers of volcanic ash, which are deposits of once-airborne particles, have been identified between thick floodwater deposits, meaning there must have been periods between floods where the deposits were exposed to the open air. Recent water flow studies suggest that the high-water marks seen in various canyons in the Spokane Basin cannot be adequately explained by the draining of only Glacial Lake Missoula – some additional sources of water must have contributed. Some possible candidates include several pulses of water from jökulhlaups further upstream in Canadian valleys, or additional drainage of a massive lake or lakes lying underneath glaciers in those same valleys.
The current consensus is that many floods of varying sizes have occurred over the millennia. The series of alternating mountain ranges and valleys to the north, overlain by vast bodies of melting ice, the gap represented by the Columbia River system and Spokane Basin, and the continuation of mountain ranges to the south, combine to form a perfect setting for jökulhlaup-type floods, which appear to have occurred many times.
The Spokane Flood story features several interesting aspects. The constant revision of theories is an excellent example of the scientific method in action. As new data is collected, the model is revised or replaced to better explain it.
While the flood was a point of dispute between Church and science, in a curious way it also shows how science and religion have some things in common. Both have at times become rigid and dogmatic, stuck in their beliefs, and unwilling to contemplate alternate views. Both are motivated by a human desire to explain the world in which we live. The entire northern hemisphere would have experienced similar late glacial flooding around the time of the Spokane Flood, and surely the Book of Genesis and many other Middle Eastern creation myths were originally inspired by descriptions of catastrophic flooding events caused by the retreat and melting of the great ice caps of the last ice age.
Most of all, the Spokane Flood is an excellent example of just how exciting geological processes can be. Contemplating the huge, rushing torrents of water that created the jarring landscapes of Eastern Washington is awe inspiring, and makes one wonder whether we may witness some such cataclysmic event in our lifetimes, perhaps an earthquake or volcanic eruption of Biblical proportions.
Baker, V. R. (2008, December 30). The Channeled Scabland: A Retrospective. Reviews in Advance .
Diamond, J. (1997). Guns, Germs, and Steel: The Fates of Human Societies. W. W. Norton.
Henrich, J. (2020). The WEIRDest People in the World: How the West Became Psychologically Peculiar and Particularly Prosperous. New York: Farrar, Straus and Giroux.
Saul, J. R. (2009). A Fair Country : Telling Truths About Canada. Toronto: Penguin Canada.
United States Geological Survey. (1976, January 1). Missoula Floods. From Wikipedia.
Wikimedia Foundation, Inc. (2011, August 4). Dry Falls. From Wikipedia.
Figure 1 – Spokane Flood region. (Based on Google Maps image)
Figure 2 – Dry Falls, WA. Used under Attribution-ShareAlike 3.0 Unported CC BY-SA 3.0. (Wikimedia Foundation, Inc., 2011)
Figure 3 – Giant ripple marks at Markle Pass, MT. Public Domain. (United States Geological Survey, 1976)