Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Thursday, June 6, 2024

Altered flow

John McPhee's wonderful book The Control of Nature describes three attempts to alter naturally-occurring geological processes: the shift of the course of the Mississippi River into the Atchafalaya River (which would leave New Orleans without a port); the lava flow from the 1973 eruption of Eldfell Volcano on the Icelandic island of Heimaey, which threatened to seal off the main town's only harbor; and the ongoing problem with landslides in the San Gabriel Mountains of California, which have been exacerbated by people's insistence on building multi-million-dollar homes in steep-sided canyons.

Of the three, only the Icelanders had a success story.  They halted the lava flow by pumping cold seawater onto it, and stopped it before it closed off the harbor completely; the tongue of solidified rock actually created a useful seawall.  The other two were, and still are, drastic failures.  The levee/spillway system in Louisiana, intended to keep the Mississippi in its channel and prevent it from switching over to the Atchafalaya's shorter and more direct path to the Gulf of Mexico, has caused more silting of the channel and subsidence of the land, both of which were direct contributors to the severity of the Hurricane Katrina disaster in 2005.  California still deals with landslides, despite their best efforts to contain them with various slope stabilization devices -- and rich people are still building their mansions right in harm's way.

33% is not a great success rate, but it's pretty reflective of our attempts to control natural processes.  It's not that I'm saying what we do has no effect; the unfortunate part is most of what we've tried hasn't worked, or has actually made the situation more dire.  The obvious example (anthropogenic climate change) is only one of many examples of times we've messed around with things and come off very much the worse.

Although we're unique in the animal world in being able to control our environments to some extent, we're still very much at the mercy of the natural world.  Big, sudden cataclysms -- events like major earthquakes, volcanic eruptions, hurricanes, tornadoes, or floods -- are the most obvious examples, but sometimes slow, gradual processes can alter the course of history just as profoundly.  The fall of the Roman Empire, about which I've written a couple of times recently, may well have been triggered by a climatic shift causing freezing drought in the central Asian steppes, inducing the Huns to migrate west and starting a domino effect of invasions.  Certainly the rising and lowering of sea level as ice ages came and went altered migration patterns; both Australia and the Americas were colonized during periods when the areas now at the bottom of (respectively) the Gulf of Carpentaria and the Bering Sea were dry land.

The idea that climate has been a major driver for history has gone out of vogue, and is sneeringly referred to as "climate determinism" despite the fact that (1) there's no denying the vagaries of climate have had obvious and dramatic effects, and (2) no one has ever claimed that climate was the only thing affecting the course of events.  Consider, for example, some new research out of the University of Southampton that came out in Nature Geoscience this week.

Life in Egypt has always been dicey -- the valley of the Nile is thickly-inhabited, but go more than a few miles east or west from it and you're in marginally-inhabitable desert.  We all learned in elementary school how the ancient Egyptians survived by learning how to manage what are always called the Nile's "life-giving floods" through irrigation channels and catchment basins, but the truth is, all it took was a dry year or two and the entire civilization was in deep trouble.

The situation changed -- for once, for the better -- about four thousand years ago, when the Nile shifted course and created the floodplain around Luxor.

The reason was the same as what John McPhee explains about the Mississippi, but with a happier outcome.  As rivers flow, they pick up sediment, and when they reach the sea and the water velocity slows down, that sediment is deposited on the river bottom.  This raises it, creating an impediment to water flow, slowing down the water further and making it drop more sediment, and so on and so forth.  Eventually the delta becomes impassible, and the water is forced into another channel (unless people step in and try to stop it, like what is happening with dubious success in Louisiana).

In southern Egypt, though, the switch in paths brought the flow of the Nile out over a broad, flat plain that prior to that had been high and dry.  The outflow into the Mediterranean moved east as well, and the outgoing river broke up into dozens of outflow channels.  This proved extraordinarily beneficial to the people living all along the river's northern half.  "The expansion of the floodplain greatly enlarged the area of arable land in the Nile Valley near Luxor (ancient Thebes) and improved the fertility of the soil by regularly depositing fertile silts," said Benjamin Pennington, who co-authored the paper.  "The Egyptian Nile we see today looks very different from how it would have been throughout much of the last 11,500 years.  For most of this time, the Nile was made up of a network of interwoven channels that frequently changed their course.  Around four thousand years ago, the Nile abruptly shifted and there was rapid floodplain aggradation, where the river began depositing large amounts of sediment, building up the valley floor.  This created a more expansive and stable floodplain."

The result was that the New Kingdom -- which included the reigns of famous pharaohs such as Ahmose I, Hatshepsut, Thutmose III, Amenhotep III, Akhenaten, and Tutankhamun -- had the resources to become one of the significant political powers of the region.

[Image licensed under the Creative Commons Mohammed Moussa, Ramses II in Luxor Temple, CC BY-SA 3.0]

Like McPhee's one-out-of-three success rate for humans trying to control nature, however, it bears keeping in mind that for every example of a natural event benefitting humans, there's one that didn't turn out so well for us.  The collapse of classical Mayan civilization in the eighth century C.E. was largely triggered by a prolonged drought; the onset of the Little Ice Age in the fourteenth created a perfect storm of conditions that fed into the Black Death killing one-third of the population of Europe.

However confident we are in our comfortable high-tech world keeping us safe, it's always good to remember how tenuous it is -- and the fact that in the long haul, Mother Nature is still very much in charge.


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