23 April 2020

The Rub' al Khali

The Arabian Peninsula's Empty Quarter, known as Rub' al Khali, is the world's largest sand sea, holding about half as much sand as the Sahara Desert. The Empty Quarter covers 583,000 square kilometers (225,000 square miles), and stretches over parts of Saudi Arabia, Yemen, Oman, and the United Arab Emirates. The Enhanced Thematic Mapper on NASA's Landsat 7 satellite captured this image of the Empty Quarter on August 26, 2001. (NASA/Robert Simmon, Landsat,USGS)
Text and photo from a Boston.com The Big Picture 2009 gallery. More info here.

9 comments:

  1. Why is it the second-largest sand sea, if it's but half the sand of the Sahara? Is the Sahara not a sand sea?

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    1. because it has half the sand of the Sahara... if it had more sand then the Sahara it would be the first largest ... if another desert had more sand then Rub al Khali then it would be number two, and Rub al Khali would be number three ... it's science

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    2. I think both of you are missing the point that a "sand sea" is not the same thing as a "desert":

      An erg (also sand sea or dune sea, or sand sheet if it lacks dunes) is a broad, flat area of desert covered with wind-swept sand with little or no vegetative cover.[1] The term takes its name from the Arabic word ʿarq (عرق), meaning "dune field".[2] Strictly speaking, an erg is defined as a desert area that contains more than 125 km2 (48 sq mi) of aeolian or wind-blown sand[3] and where sand covers more than 20% of the surface.[2] Smaller areas are known as "dune fields".[4] The largest hot desert in the world, the Sahara, covers 9 million square kilometres (3.5×106 sq mi) and contains several ergs, such as the Chech Erg and the Issaouane Erg in Algeria.[5]

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    3. No need to get snarky. 😎 I think AaronS meant to say, "Why isn't it the second-largest sand sea,..."

      The text in the post, and on science websites, says "The Arabian Peninsula's Empty Quarter, known as Rub' al Khali, is the world's largest sand sea, holding about half as much sand as the Sahara Desert."

      The scientific and geographic definition of a desert is an area that gets less than 25cm of precipitation a year, which is why Antarctica is scientifically considered the world's largest desert. A sand sea (erg) generally has no sand dunes or vegetation. Science defines a sand sea as a desert area with more than 125 square miles of wind-blown sand and sand covers more than 1/5 of the surface. There are sand seas in the Sahara, but none are larger than Rub' al Khali. It's science, and perhaps math when you consider a discussion of area.

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    4. Kolo, that is exactly what I meant. I didn't realize the typo, so when I read my question again today, I was wondering what in the world I had meant. THANK YOU!

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  2. Wonderful image - that could be almost anything.

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  3. Since you mentioned the Rub' al Khali, maybe someone can clear up a question that has puzzled me. In a late 1920s British story paper, the hero braves the Rub' al Khali, which is supposedly "known as the Desert of Stones." The author claims the desert isn't made of regular sand but of tiny pebbles. Of course British story papers aren't exactly a source of reliable information, but the specificity of the claim smacked of the author having run across it in research. Anyone ever heard of this?

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    1. There are a number of dried lake beds in the Rub' al Khali. The surface of these areas are covered by gypsum and marl (mostly clay and silt) that are the size of pebbles. Maybe what the story refers to?

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    2. I couldn't say in the case of the Rub' al Khali, but possibly reg (aka desert pavement)? It's a hard, compacted surface of interlocking pebbles that forms when all the sand between the pebbles is blown away. (At least this is the model of formation I learned. Apparently there are new competing models based on some form of heave lifting stones up to form the pavement.) https://en.wikipedia.org/wiki/Desert_pavement

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