Tuesday, October 16, 2007

Deadly Evapotranspiration

So, I seem to have missed the boat on this volume of the geologic carnival, as it has been published and lithified over at Shear Sensibility. But I’ll post anyway, as a philosophical exercise.

There are two endmember philosophies used to look at geologic processes, particularly those related to geomorphology. One is catastrophism, the idea that sudden, discontinuous, dramatic events are the driving force in shaping Earth history. The opposite is uniformitarianism. This school of thought suggests that the processes we can observe happening regularly today can explain all the geological events worth investigating. The dramatic nature of the current accretionary theme lends itself to catastrophism, so I will try to shift the balance by describing a process that is common, widespread, and deadly.

Evaporation, and its biological buddy, transpiration, are the basis for the hydrologic cycle. Without evaporation, we would have no rain, snow, rivers, glaciers, or humidity, and the earth would be a cold, dry, and barren place to live. But too much of anything can kill, and transpiration is no exception.

The playas shown above are an instance where persistent evaporation can become unhealthy. Here, on the northern edge of the Simpson Desert, evaporation reigns supreme, and there is little or no available surface water for most of the year. In such a climate, a person will transpire readily. However, without a source of water to rehydrate, this transpiration can rapidly turn fatal.

There are two ways transpiration can kill. The first is heat stroke. As the body loses water, it becomes more difficult to maintain a constant body temperature in hot conditions. If the body starts to overheat, and there is no available water for evaporative cooling, death can come quickly, as the brain starts to sustain permanent damage at temperatures much over 40 C.

Even if temperatures aren’t so hot, dehydration caused by transpiration can still cause death. Loss of fluids thickens the blood, and puts strain on a number of bodily organs, particularly the kidneys. Left untreated, it can cause organ failure and death.

I’m off for the final field campaign of the season (I hope). Working in the middle of a stable craton with very subtle relief, it is unlikely that volcanoes, earthquakes, mass wasting, or other catastrophic events will kill me. But every summer people in Australia are killed by the toasty end of the hydrologic cycle. I’ll try to make sure my crew doesn’t suffer that fate.

Later, y’all.

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