This work, named for Aeolus, the Greek god of winds, suggests how fluids and wind interact with sand and rock to sculpt landscapes on terrestrial planets.  The sand dunes of Earth and Mars are stunning examples of this interaction.  Duning also takes place on ocean and river bottoms, in snow, and even in ice.  Glaciers are rivers of ice that pick up rock, slowly transport it, and deposit it in dune-like formations.  The blowing ice formations on the Martian poles are another example of the interaction of fluids and solids in the process called flow dynamics.

The duning process observable in “Aeolian Landscape” involves the interplay of several physical forces.  For duning to occur in sand, three conditions are necessary.  The wind must rise to a speed sufficient to lift and move sand grains.  The air must be dense enough to push and carry the sand.  And the grains of sand must not be too heavy. 

Photo Credit: Rex Burress

Dunes form on both Earth and Mars, but the interplay of processes is unique on each planet.  For dunes to form on Mars, winds must blow much faster than on Earth because the air on Mars is less dense than the air on Earth.  Duning does not occur on Venus.  Scientists speculate that although the air is much denser on Venus than on Earth, wind speeds may not be high enough to form dunes, or perhaps the sand is too heavy.

Dunes form when air carrying sand climbs over an obstacle such as a peak or a ridge.  Deposition, the process in which wind drops some of the sand as it passes over the ridge, causes sand to pile up, forming a dune.  The height and steepness of the dune increase until the underlying sand can no longer support more, at which point the top of the dune slips in an avalanche or landslide that causes the side of the dune to grow wider and shallower.  The maximum angle at which the underlying sand can support the piling up of sand is called the angle of repose.  The landslide causes the top of the dune to drop, allowing the wind to continue the process by placing more sand on top of the dune.

Depending on the direction of the wind, one side of the dune may collapse faster than the other.  The side that is avalanching at a faster rate moves into the landscape more quickly.  As a result, the dune’s peak migrates in that direction, seeking equilibrium between the slopes and the wind.  Over time, this process may cause the dune to march across the landscape.

As sand slumps off the peaks of dunes, it can begin to flow like a river, and continue to flow through a formerly stable area on its own momentum. The flow channels cut new features into the landscape.  Eventually sand fills up the area, the slope becomes too shallow, and the flow ceases.

Duning can sculpt a variety of landscapes.  U-shaped or long valleys may appear in the duning area depending on how the peaks and ridges are arranged.  Or a repetitive pattern of spacing between the dunes can result in the dunes’ taking on the appearance of waves. 

Photo Credit: NASA