Loess in Scablands

7 Feb 2017

At https://earth-pages.co.uk/2016/10/14/scablands-megaflood-hypothesis-temp... ... which is last year's story. An adaptation of the megaflood theory into a succession of floods as a result of the discovery of a number of water level rims in the lake that is supposed to have emptied across the scablands. The article begins with a description of the channelled scablands ...

     ... described as a vast barren area scoured free of superficial sediments and soils. Notice - scoured free of previously laid down sediments. It is a landscape of wide canyons incised on a plateau formed by a prehistoric basalt flow (known as flood basalt, a flood of lava in this case). The canyons are pitted with numerous pot holes, megaripples, and erratic boulders. He says it marks the footprint of a massive flooding event (at the end of the Ice Age). However, the description adds that there are streamlined hillocks made of residual wind blown loess deposits. Was I reading him right? He had already said sediments had been washed away but here he is saying wind blown loess (laid down in the Ice Ages) has been left in smooth rounded hillocks. Is this guy having his slice of Victoria sponge cake with a double portion of clotted cream? Surely the existence of wind blown loess is apposite to the idea of a massive flooding event? In contrast, it suggests that loess is laid down by water - and has nothing to do with the wind whipping across the ice sheets and tundra. If it had been laid down previously it would have been washed away - with all the other sediments of the Pleistocene period. This fits in with evidence elsewhere - loess is commonly found in river flood plains and the terraces of former river levels. At Brentford in what is now the suburbs of London loess was farmed by market gardeners in the 18th and 19th centuries, and a vestige of that trade lingered into the 3early 20th century (and Brentford fruit and vegetable wholesale market flourished into the late 20th century, but was then relocated near Heathrow airport). At Brentord the loess is known as brick earth - but it was full of nutrients (as you might expect if it originated as water transported). The early farmers of Europe followed the loess trail up the river valleys such as the Danube, utilising the loess they found on the flood plains. The idea they went chopping down virgin forests with their stone axes doesn't wash - or even setting fire to swathes of countryside. Landscape fires in all likelihood have a different origin to the spread of farming (but see elsewhere) although contained fires to quickly clear an area for fields is not an unreasonable assumption. Wood ash provides potash - but loess has lots more goodies (including fossils). 

In the 1920s J Harlen Bretz, a geologist, proposed that the scablands landscape had been formed by a massive flood. This smacked of catastrophism (and water related catastrophism to boot) and you can imagine this did not go down very well at all. It fell like an iron anchor and got stuck in a sea of criticism. This post does not reflect the controversy or the fact that Bretz was not vindicated until he was a very old man. He spent most of his life ostracised by the big wigs - but presumably was able to make a living in his chosen field (working for a company rather than as a taxpayer funded academic). One of the reasons he was eventually embraced by the geological community was the claim that a huge lake of glacial water existed at the end of the Ice Age. When a theoretical ice dam burst the water rushed down and created the scablands, far below the heights of Montana's Rocky Mountain chain. Gradualists were still dissatisfied with this idea and have since watered this theory into a succession of smaller flooding events (without explaining how the melting ice sheet kept accumulating lakes of water in Montana's highlands for thousands of years after the Ice Age had come to an end). Bretz, in the end, was happy to settle for at least a prostituted version of his theory as for most of his life the idea had been ridiculed. I wouldn't have posted this version of events (as most of the story is missing) but for the mention of the loess. Is it water driven rather than wind blown? The evidence in the scablands would seem to suggest there is a good chance loess is water formed - and no doubt mainstream would disagree.