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loess (2)

13 October 2015

At the recent study group meeting in Willesden we discussed Ellsworth Huntington's research in central Asia and his book, 'The Pulse of Asia' – from the early 20th century. He claimed that wet and arid periods can be seen in the rise and fall of the levels of the Caspian and Aral seas, going back to the Greek era in the first millennium BC (where various authors with known dates and lives wrote contradictory accounts of the lake levels. Sometimes the water level was high – but another author would describe the Caspian in dimensions little different to those of today – so what was going on?

Huntington's conclusion was that rainfall was to blame and he used agriculture as one of the yardsticks. In arid phases farming retreated – but in wet periods it expanded once again. These episodes of high lake levels, and moisture suitable for agriculture, coincide with known warming and cooling periods of the climate. Huntington didn't know this as he was writing a hundred years prior to modern climate science. His views did dovetail with those of HH Lamb who outlined a similar set of events – but in north western Europe (but he was writing in mid 20th century). Obviously, the Atlantic did not play much of a role in the climate of central Asia but the jet stream did. During cool periods of climate the jet stream seems to move from northern Asia (roughly) to central Asia (or a great deal to the south of its normal track). Excessive rainfall can be induced by the jet stream – just the sort of thing to overflow the Caspian basin.

Huntington claimed a huge area from western China and Kashmir in the east (where his research project began) to the Caspian and beyond was all part of this pulse of wet and dry climate. For example, during the Little Ice Age, a few centuries ago, the level of water in the Caspian and Aral seas was much higher than today. In fact, the environmentalists are consistent in blaming human activity for the modern decline – another deluded scare mongering. Going back to the first post on 'loess'  (from yesterday) we may note the paper in Nature Communications (October, 2015) on loess formation in China, has shown it was erosion of the Tibetan Plateau that created the layer cake of loess in China. The formation is very old as it has fossil beds within it – fossils that were laid down and preserved by being buried in loess. That means erosion of the Tibetan Plateau by the Yellow River must have been rather dramatic at times – which makes you wonder if the loess has any connection with Ice Ages and wind blown dust from tundra like northern climes (the textbook explanation). It may very well have a connection with cold periods of climate – and increased rainfall as it would seem we might be able to extend Huntington's pulse beyond those regions he travelled to for the sake of research, to include the Tibetan Plateau  and the Yellow River and its tributaries. If the jet stream is capable of overflowing the Caspian shore and creating a vast body of water so too might it have increased erosion of the plateau and created loess in a very quick manner (which may undermine the Uniformitarian position on loess as it has become something of a prop to glaciation expansions and contractions). Indeed, glacial episodes are themselves cooler periods of global temperature – but instead of the wind and dry dust being moved over incredible distances we may perhaps replace this with the idea of water driven loess as a result of flooding and heavy precipitation. That appears to be one way of looking at what the authors came up with in their paper – and we don't know what was left out for publication.

In all likelihood they had no intention of upsetting the geological applecart – but their research has in one way confirmed Ellsworth Huntington's 1906 research, but has also provided us with a more localised origin of loess in China. Therefore what is good for the goose must be for the gander – and loess deposits elsewhere in the world. One of the more attractive ideas of Allan and Delair in their book .'When the Earth Nearly Died' was the idea that loess was created by water flow rather than being wind blown in origin.

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