How deep is the desert? Depending on the desert, the sand is between 1 m and 43 m deep. Although, if you count to the top of the largest sand dunes, they could be several hundred meters deep. Also, if we are talking about deserts and not just sandy deserts, the ice on Antarctica is several kilometers thick.
A desert is an area of land that receives less than 25 centimeters of precipitation a year. Precipitation doesn’t necessarily mean rain. My question is about the sand on a desert, but the majority of deserts don’t have sand. Only about 10% of the world’s deserts have sand, the rest are generally covered in mountains, rock, thin sand, or salt. Deserts are created by different conditions and there are five different types of deserts.
The first type are subtropical deserts. They are in a band between 15 and 30 degrees north and 15 and 30 degrees south of the equator. The Sahara is a subtropical desert. The air over the equator is heated, pushing it up into the atmosphere. As it gets higher, it cools and drops its rain. This happens before the 15 degree line. Between 15 and 30 degrees, the cooing air with no moisture drops, picking up water and warming again. At about 30 degrees it carries that moisture up again, so no rain falls between 15 and 30 degrees. The second type are coastal deserts. They are next to the sea and the air that blows in is cooled down by the sea, producing fog, but it never produces rain. The third type are rain shadow deserts, which are almost always in the rain shadow of a mountain range. Warm, moist air is pushed upwards by the mountain range. As it gets higher it cools and drops all of its moisture as rain. Once it clears the mountains, it has no moisture left and descends, creating a desert. Death Valley is a rain shadow desert. The fourth type are interior deserts. They are in the center of continents and are too far for any moisture carrying air to reach them. The Gobi Desert is an interior desert. The fifth and last type of desert are polar deserts. People always think that deserts have to be hot and sandy, but the classification is less than 25 cm of precipitation and there is no precipitation in the Arctic or Antarctic because it is too cold. All of the water is frozen and there is no evaporation. The Antarctic is the world’s largest desert.
So, how deep is the sand on sandy deserts? On most of them, the sand layer is very thin and they are more rock than anything else. The large sandy deserts that we think of are called ergs. They are “broad, flat areas covered with wind-swept sand.” The Sahara Desert has more ergs than any other desert, but even the Sahara is not only sand. About 25% of the Sahara is covered in sand, and is an erg. The sand comes from the rocks in the bedrock. There is no water, but deserts get pretty cold at night because there is no cloud cover to keep the heat in. This warming and cooling cracks the rocks and the rocks are slowly ground down by the wind and the flying sand. This sand is blown around by the wind, forming dunes. On average the depth of the sand in the Sahara Desert is about 5 meters. If you dig down through it, you will find bedrock that is similar to the parts of the desert that are not covered by sand.
The sand in deserts tends to accumulate in certain areas, just like water accumulates in dips. The ergs are areas where the sand has accumulated and they might be in a natural dip, or they might be surrounded by hills. The wind blows the sand in, and it builds up. In the Sahara, some of the ergs have a depth of up to 41 meters. This is not the average depth and is the point where the sand has built up the most. In the same way, a lake has different depths. The tallest sand dune in the world is Duna Frederico Kirbus in Agerntina. It is 1,230 m tall, so the sand there is 1,230 m deep!
Deserts used to be much thicker than they are today. During the Mesozoic era, about 251 million years ago, there was a desert belt around the equator that could have had an average depth of hundreds of meters. Deserts on other planets are very deep as well because they have had more time to build up and there is no continental drift to alter them.
The Antarctic is actually the world’s largest and deepest desert. It has different depths depending on what is below it, but at some points it is between 2 and 3 km deep. And this is what I learned today.
Photo by Greg Gulik: https://www.pexels.com/photo/green-grasses-on-sahara-desert-1001435/
Sources
https://www.asoc.org/learn/antarctic-ice
https://www.physicsforums.com/threads/third-equatorial-desert-belt-during-mesozoic-era.461636
https://www.iflscience.com/whats-underneath-sand-and-desert-sand-69708
https://moroccanjourneys.com/sahara-desert-facts
https://education.nationalgeographic.org/resource/desert
https://www.lbc.co.uk/radio/special-shows/the-mystery-hour/how-deep-is-the-desert
https://books.google.co.jp/books?id=k1vv3wU28QMC&pg=PA155&redir_esc=y#v=onepage&q&f=false