The theory that the dramatic landscapes of the Columbia River Plateau were caused by massive flooding in the distant past might not sound too controversial. But, as Sanjeev Gupta told us in our British Science Festival event yesterday, the theory, first proposed in 1923 by American geologist J Harlen Bretz, was so controversial it sparked a debate that lasted more than three decades.
By the time his ideas were finally accepted, Bretz was in his eighties. The story goes that he received a telegraph from researchers in the 1963 which ended with, ‘we are all now catastrophists.’
Back in 1923, making reference to ‘megafloods’ was loaded with controversy. Geology, by then, had left the days of biblical flood theories behind. Uniformitarianism – Lyell’s famous ‘the present is the key to the past’ – was the unifying theory, first proposed as an antidote to catastrophism.
Catastrophism, popularised in the early nineteenth century, argued that the Earth has been shaped by sudden, violent events in its past. Not only floods, but volcanic eruptions, earthquakes and rapid mountain building have all left their mark, in ways we can’t imagine by looking at today’s world.
Lyell’s arguments for more slow, incremental changes over geological time prevailed, and by the time Bretz suggested in 1923 that the unusual erosion features in the Columbia River Plateau could be explained by a cataclysmic flooding event, such a theory suggested a regression to the catastrophist theories of old. The geological establishment was resistant, and Bretz continued his research for another thirty years before he was vindicated.
Now, geologists recognise evidence for past ‘megafloods’ all over the world. Sanjeev showed us some amazing images of the landscape beneath the English channel, produced by high resolution sonar waves, showing deep scour marks and valleys.
The landscape is thought to have been produced by torrents of water, released when a lake, fed by the Rhine and the Thames, bounded to the north by glaciers and the south by the Weild Artois chalk ridge, overspilled. The resultant flooding, taking place between 200,000 and 450,000 years ago, would have displaced an estimated one million cubic metres of water per second, lasting potentially several months.
We also saw evidence that megafloods might have happened on other planets, too – with a flythrough of a Martian landscape which showed deep, meandering valleys carved by water flowing billions of years ago.
On Mars, the situation is more complicated – water frozen deep beneath the surface is thought to have burst, volcano like, through fissures and ruptures, producing flooding events many times the size of those we have seen on Earth. Though initially this was thought to be the main cause of Martian flooding, high elevation flood channels suggest surface water was shaping the landscape too, in the same way, though on a bigger scale, to Earth’s megaflooding.
All of which, for Sanjeev, suggests we have to be careful with Lyell’s uniformitarianism. Yes, present processes can tell us a lot about what happened in the past. But it’s becoming increasingly clear that events also occurred in our geological past that we’d find unimaginable today.