Cochise College Student Papers in Geology

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Roger Weller, geology instructor

Aeolian Processes
Ann Vermillion
Fall 2004

Aeolian Processes

Sand dunes with some ripple marks in the front of the picture. This whole thing was caused by wind.

Aeolus is the Greek god of the wind. So since the English language is made up of words from other languages, it makes since that we turned Aeolus into Aeolian and gave it the definition of wind. Wind is a topic most people don’t even think about in their whole life, even though it could affect them from the food they eat to the buildings they live in.

The term Aeolian describes the process of wind erosion, deposition, and how it is transported. It also has to do with the deposits that wind leave behind, such as sand dunes. A sand dune is an elongated mound of sand formed by wind or water. In this paper we are only going to look at wind made dunes. We are also going to be talking about Aeolian processes, such as erosion, transportation, and deposition.

Now that you know more about what Aeolian entitles, here is some more background. Aeolian process normally happens in arid and semi-arid environments. This includes Arizona, Utah, California, Colorado, Nevada, and any desert environment. However, some of the most studied places in the U.S. are outside Flagstaff, Arizona, Southern California, Colorado, Nevada, and New Mexico. Utah has some labs, but not much is said about them and apparently they are not very important. White Sands Missile Range is an Army base outside Alamogordo, New Mexico. It is named White Sands for the gorgeous white sand dunes that surround it. This is also a much studied area. This is where they study a lot of dune movement. They have very little human contact, so most of the study is uncontaminated. Humans really ruin the things around them. On sand dunes they think it is fun to go four-wheeling, however, this causes the sand to loosen up and blow away in the next sand storm. This also causes the dunes to move faster. Dunes are constantly moving sand piles. Wind helps this along with Aeolian transportation.

Aeolian transportation is just saying that particles are being moved by wind. Transportation is when the wind picks up the particles of sand and dust and moves them. The wind can only pick up certain size particles of sand or dust. The faster the wind the heavier the particle can be. There are different names for the way different size particles are carried. The first is called suspension. Suspension is how the smallest dust particles are carried. Suspension is when the wind picks up the smallest particles and lifts them up into the air and then upward currents carry them. They can go on as long as there is wind to keep moving them forward. Then next is called saltation, which is the Latin word for leaping. Saltation moves small particles (but bigger than the smallest particles). Saltation is when the wind picks up, what we are going to call medium size particles, and starts to move them forward. They become too heavy and the current drops them. The particles then bounce and then the wind can start to carry them again for a short time. If the particles bounce off a bigger particle it causes them to move forward some and this becomes creep. Saltation is what we see as a fuzzy layer next to the ground. Creep is when the largest size particles can’t be picked up by the wind. However, they are hit by smaller particles and the smaller particles cause them to “creep” forward, very slowly. Aeolian transportation helps move soil around so that way new soil is brought to the top; it also helps move rich soil to lands that might not have such rich soil. When the wind stops blowing the particles they are dropped and make what they call deposits. While the wind is blowing the particles around, you have Aeolian erosion.

When you talk about erosion most people think about something that has been worn away by either water or wind. However, that is about all they think about and they think that that is the only thing involved. The wind erodes the surface by what they call deflation. Deflation, in this case, is when the wind carries away the loose, fine-grained material. As the wind is carrying these particles they rub up against other particles and start to wear off and that is actual erosion. Aeolian erosion is just wind erosion. The wind blows and moves the loose rock, sand, and dust that are on the top layer, which is transportation; however, when the rocks and sand blow into things they do what we call sandblasting. They also bump off one another and rub material off, which is called abrasion. These are all types of erosion. Aeolian erosion makes what we call stone pavement, which is when all the loose stuff on top blows away and you are left with a hard surface. This is kind of like pavement. Erosion also leads to blowouts, erosional troughs and depressions. Aeolian erosion is more likely to happen when there is lack of vegetation and then there is sand or other materials showing. This speeds up that erosion process. Erosion factors are wind speed, the size of the grain, and the amount of vegetation. Erosion has many factors, but those are the ones for Aeolian erosion.

The last process is Aeolian Deposition. Aeolian deposits are just sedimentary deposits of windblown dust. Easy, right? Well, for the definition, yes. However, there are so many different types of deposits that you could write a paper just on those. Some aeolian deposits are dunes, yardangs, and loesses.

This is a sand dune and in the background is the ridge of California.

This picture is of a yardang in White Sands, New Mexico.
loess

This is what a loess looks like.

Now that we have some visuals of what a dune, yardang, a loess are we can go into the actual definitions. A dune is an elongated mound of sand formed by, in this case, wind. Dunes are constantly moving when there is wind to move them. Yardangs are streamlined hill oriented parallel to the prevailing winds and produced by wind erosion of rock or soft sediment, normally sandstone and lacustrine. Yardangs, in my opinion, are just a new definition for a eroded away piece of sandstone or other material. O.K., moving on to what loess is. Loess is a, according to Amateur Geology website, buff- colored, wind blown deposit of silt, which is frequently exposed in bluffs with steep faces. The thickness can vary from 6 to 30 m. There is not much of this material in the United States, because is thought to come from glaciers.

This paper is just an overview of Aeolian processes. There is so many things about Aeolian that it is not possible to cover all of it. There are complex studies like Aeolian mapping and machines that are made just to see what areas of the world are at danger for this type of erosion. This paper is suppose to be informative, but not overwhelming. When I started this paper I thought it was going to be easy. I thought that since the topic was a hard one, there would be no info on it. However, when I started my research I found out that there is studies and information from all over the world. The pictures I saw where amazing and made me want to do the whole paper out of pictures. The pictures describe what wind has the power to do better than any person could describe with words.

The paper did a quick overview of Aeolian processes which are transportation, erosion, and deposition. I hope you learned something (or in your case, Mr. Weller, liked the pictures at least), but weren’t overwhelmed with information, like I was when I started my research. Wind is very powerful and can still make some of the most beautiful sculptures I have ever seen.