Devastating Ice Age Floods That Occurred in the Pacific Northwest Fascinate Scientists

The Earth seems to be unchanging. In a year, the continents shift by half an inch. Sea levels rise in a quarter of an inch. The mountains seem to stand the same as they did yesterday and the day before, even though they are constantly being eroded. Our planet's geological history seems to be one of slow, grinding change. That's not the whole story. Sometimes geological change comes startlingly, violently fast, leaving scars on the Earth's surface. The Channeled Scablands of the Pacific Northwest, a landscape full of flat-topped plateaus that rise between steep-walled canyons, is one of the vastly-altered landscapes that have caused researchers to rethink what they previously assumed. Dramatic evidence shows that rapid and catastrophic changes have shaped our planet.

The signs of an Ice Age event can be seen in the Scablands. The glaciers burst from their natural dams and went over the landscape, dropping huge stones as they went. Entire hills were washed away as the floods dumped gravel, boulders and sediment in new places. This is a new understanding that has been accepted since the 1970s. It took decades for geologists to figure out what the Scablands represent, a realization that turned out to be a turning point for science. If intense floods could carve such features once in Earth's history, surely they could have changed the landscape elsewhere.

The story of the Scablands was picked up by geologists a century ago. The strange basins and odd channels of the area were descriptive papers written by J Harlen Bretz in the 1920s. The way the water flowed through the area seemed to make no sense.

They were not ready for that conclusion. The concept of uniformitarianism has influenced geology since it came into its own as a science in the 19th century. That is an excellent rule. The Earth is still changing, and many of those alterations from erosion to volcanic eruptions occurred in the past. The older idea's additional stipulations were taken as truth. The Earth is changing at a slow, gradual rate and that is not possible in a hurry. The idea of how the Scablands formed flew in the face of what many geologists accepted. Other geologists thought that the channels were carved by rivers over a long period of time.

The evidence was clear. There were layers of gravel hundreds of feet high. Slow- moving streams couldn't have left such a large amount of accumulateements. Gravel is heavier than sand or silt and requires faster moving water to pick it up and transport it. It must have taken a lot of fast-flowing water to make the Gravel deposits as tall as skyscrapers. The underlying geology of the area was consistent with the pattern. The volcanic rock beneath the flood deposits was easily broken and carved. The floods were able to rip out channels and canyons because of the fragility of the rock layers. Evidence of similar events, such as Ice Age flood beds found in Montana, caused many to dismiss the idea of a source of the floods. By the 1970s, geologists began to change their tune. The Scablands were created by something catastrophic.

There are lots of outstanding questions and many people are thinking carefully about the Scablands. The precise volumes of the repeated floods are unknown, and the timing of the dozens of outbursts has yet to be determined in detail.

The tools available to scientists have changed a lot since the time of Bretz. The salty water in the northern Pacific was reduced for years by the influx of freshwater, and the way in which water in the deep ocean layers changed. The floods affected more than the land they ran over, and have acted as models for how our glaciers might alter ocean circulation as they melt due to global warming. There aren't modern examples of flooding like the ones that created the Scablands, but new, broad scale methodologies can offer some of these insights.

The landscape was reconstructed by Lehnigk and his colleagues after the floods created the Scablands. She notes that water carves can be used to start with the current topography and work backwards to estimate what the starting conditions were like and detect variables like where rock was more likely to erode. It is a way to replay floods that we can no longer witness.

New techniques, such as LiDAR scans to map terrain and numerical models used to estimate water discharged by glaciers, are turning up more evidence for various outburst floods in other time periods and places from the Mississippi River to the Himalayas. The landscapes on the Red Planet are very similar to the Scablands. Before NASA missions found evidence of liquid water on Mars, geologic scars left no doubt that water once rushed over the planet's surface. The research helps researchers understand how such events occurred through space and time, as well as an understanding that change can occur quickly and at scales completely unfamiliar to us.