If I asked you to name the driest spots on Earth, I wonder if this one would come to mind -- even though it's a top contender for the number one spot.
You might have thought of Chile's Atacama Desert, or possibly somewhere in the Gobi, Sahara, or the Rub' al Khali (Empty Quarter) of Saudi Arabia. All good guesses, and certainly they're not what I'd call wet climates. In fact, parts of the Atacama come in second; the high elevation and perpetual clear skies are why it's such a great spot for astronomical observatories -- it's currently home to three of the best, and a fourth is being built. The La Silla Observatory, the Paranal Observatory (which includes the Very Large Telescope), the Llano de Chajnantor Observatory (which hosts the ALMA international radio observatory), and the Cerro Armazones Observatory (site of the future Extremely Large Telescope), are all in the Atacama Desert.
As an aside, can astronomers please try to come up with better names for their observatories? I mean, what the hell? The "Very Large Telescope" and the "Extremely Large Telescope"? What's next, the "Abso-fucking-lutely Humongous Telescope, No Really I'm Totally Serious You Won't Believe How Big It Is"?
Probably not. AflHTNRITSYWBHBII would be hard to fit on a grant application.
But I digress.
Anyhow, the top spot for the driest climate on Earth is the McMurdo Dry Valley region of Antarctica, and beats most of the other possibilities by a significant margin. Some studies indicate the place hasn't had any significant accumulated precipitation in over two million years. What small amount does fall -- estimates are in the range of a hundred millimeters per year -- almost all evaporates before it reaches the ground because of the fierce katabatic winds. Katabatic winds occur because air density is strongly dependent upon temperature, and the McMurdo Dry Valleys are surrounded by mountains. Air masses above the mountaintops lose heat faster, making them become more dense; the air then flows downhill, easily reaching hurricane speed, and pools in the valleys. Most of the air already started out dry; any humidity it originally had was precipitated out as snow on the windward side of the mountains. This drops the relative humidity to only a few percent and keeps it there.
Any snowflakes falling into that don't stand a chance. They don't melt; it's too cold for that. They sublimate -- turn from a solid to a gas without passing through the liquid phase.
That's how cold and dry it is.
The result is that the McMurdo Dry Valleys are basically nothing but a vast expanse of extremely cold rock, gravel, and sand.
The exposed rocks are mostly of Triassic age, and belong to the Beacon Formation, which is largely made of sandstone. There are a few volcanic intrusions only a few million years old, but by and large, the whole place is just one big bunch of very old wind-eroded sandstone, quartzite, and pebble conglomerate.
And yet... there are living things there.
Not many, of course, but the McMurdo Dry Valleys are home to endolithic bacteria, which live in the cracks and fissures inside rocks, subsisting on the minerals therein and the tiny amount of water in the soil (supplemented from time to time by trickles of glacial meltwater). They're still poorly understood, but are thought to be metabolically similar to the mid-ocean vent bacteria, which are able to use minerals like sulfur, iron, and manganese as the basis of their metabolism.
All of which makes me wonder if Mars hosts life. McMurdo has been described as "the most Mars-like environment on Earth;" the site has been used to test equipment for the Mars rover missions. Hell, if bacteria can survive in McMurdo, it's not much of a stretch to surmise that there might be life underground on Mars -- perhaps a holdover from the distant past, when Mars was a much warmer, wetter place.
I find places like this fascinating. The idea that we have here on our (mostly) temperate and green planet a spot so profoundly inhospitable is pretty astonishing. I wonder how (or if) climate change will alter things there? The entire continent is climatically isolated by the Antarctic Circumpolar Current, one of the hugest oceanic water transporters in the world -- the amount of water flowing through the Drake Passage, between South America and Antarctica, is estimated at around 130 times the volume of all the world's rivers put together -- so it's hard to imagine this shifting in any significant way.
But given that many oceanographers fear that meltwater from Greenland is going to block the Atlantic Meridional Overturning Circulation -- the best-known part of which is the Gulf Stream -- maybe I shouldn't speak too soon.
So that's our look at the Earth's answer to Mars. Not, I'm afraid, a locale I'm eager to visit, given how little I like the cold. I'm adventurous, but I draw the line at a place that hostile.
Plus, I like rocks as much as the next guy, but when there's nothing else to see -- well, I can think of a few other places that are higher on the destinations list. I'm content to appreciate McMurdo from afar.
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