Ergs

Namib Naukluft National Park, Namibia. (Photo by Michael Poliza)

Once again I have been thinking about the Namib Desert–the world’s oldest desert–which calls to me for reasons I cannot fully explain. I wrote about some of the Namib’s strange animals and plants…but one thing I did not mention was its ergs. This is because I did not know what an erg is, but today I looked it up and the concept is simultaneously horrifying and beautiful. An erg is a sea of wind-blown sand. This geographic feature is not unique to the Namib Desert—or indeed to planet Earth—but they do tend to be found only in vast & mighty deserts. Such a landscape is characterized by vast dunes—mountain-like sand hills composed of immense numbers of individual sand grains.

A sand dune in the Rub al Kali Desert

Geographers have seemingly fixed certain parameters on how large a sandbed must be to count as an erg—but I will let you look these up on your own—I think the word “sea” covers the scope of ergs. We are not talking about a child’s sandbox here.

Issaouane Erg, Algeria (photo from the International Space Station)

The word erg derives from an Arabic word “arq” which means dune landscape. The Rub al Kali Desert “the empty quarter” of Saudi Arabia is a vast erg—the world’s largest. There are a multitude of ergs throughout the Sahara (as seen on the map below) and they can also be found in central Asia, the middle of Australia, and the Atacama Desert (which I also really need to write about). Ergs are less common in North America than in Asia and Africa, but there a few notable examples mostly in the Sonoran Desert, but also including the unimaginatively named “Great Sand Dunes” in Colorado.

The geology of ergs is quite fascinating as the dominant agent of erosion and change is wind rather than water. When wind activity shapes the surface of the Earth (or another planet), geologists describe the varying sorts of erosion, deposition, and weathering as “Aeolian processes” in homage to the ancient Greek god of the winds who crops up in the Odyssey and the Aeneid. Ergs do not just feature great dunes but also strange sand sculpted rocks and dry river beds.

White Sands, New Mexico

As noted, ergs are not a phenomena exclusive to Earth, but can be found on other planetary bodies too (if they have silica and atmospheres). Ergs have been discovered on Mars where vast erg fields ring the polar caps. The Martian winds blow the ergs into bizarre patterns and shapes (usually I would say “otherworldly”, but that seems too pedestrian a word here). Venus also has ergs (discovered by the Magellan probe) and Cassini’s radar spotted huge parallel ergs on Saturn’s great moon Titan. Indeed ergs may be the dominant surface feature of Titan.

Martian Polar Dunes (photographed by the Mars Odyssey Spacecraft)

I have never been to an erg. There are none in Brooklyn (yet). However I would like to see one…although I admit to a certain amount of trepidation. They do not seem like places for life, and indeed they are among the most lifeless places on all of Earth. Ergs are beautiful but also terrible and dangerous. At least they should stay free of suburban sprawl for long enough for me to visit one (and it will probably be a very long time indeed before we cover the ergs of Titan with strip malls).

Erg Chebbi in Morocco (Bjørn Christian Tørrissen)

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