Stirring Up Dust
On Earth in the spring, dust devils can blow through a field flattening green crops. Often on hot summer days you can see dust devils racing across the wheat fields and stirring up dust in plowed fields. Even in cities one can find dust devils as they twirl down alleys, streets and vacant lots.
NASA scientists have found dust devils spinning across Mars. The image at right shows the track of a dust devil, the plume of dust, and the shadow of the plume on the surface of Mars. The scientists had seen tracks on Mars but were not sure how they had been created until the Mars Orbiter Camera captured a dust devil as described below.
Dust Devils on Mars
A NASA press release contained this description of a dust devil on Mars:
"In December 1999, the MOC (Mars Orbiter Camera) team finally had an answer! A dust devil, shown in the above figure, was caught in the act of creating a swirly, dark streak! An eerie sensation washed over the first team members who saw this picture---here was an event on Mars "caught in the act" just hours before the picture was played back to Earth…
The first dust devil seen making a streak---located in Promethei Terra---was traveling from right (east) to left (west). A columnar shadow was cast by sunlight coming from the upper left. This shadow indicates the true shape of the dust devil. The bright dust devil itself does not look like a column because the picture was taken from a camera looking straight down on it. The dust devil is less than 100 meters (less than 100 yards) wide…
Dust devils are spinning, columnar vortices of wind that move across the landscape, pick up dust, and look somewhat like miniature tornadoes. Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. They form when the ground heats up during the day, warming the air immediately above the surface. As the warmed air nearest the surface begins to rise, it spins. The spinning column begins to move across the surface and picks up loose dust (if any is present). The dust makes the vortex visible and gives it the "dust devil" or tornado-like appearance. On Earth, dust devils typically last for only a few minutes."
Photo Credit: NASA/JPL/Malin Space Science Systems
When dust devils land in tall grass or fields of growing crops they flatten their stalks in a swirling pattern as they bounce through the field. This can be seen in the photo at right of a wheat field. Click on the image or here for a closer look. During the summer months after harvest many bare fields have dust devils spinning across.
As described above the warming air spins as it rises and carries dust and debris with it. In New England and Great Britain where it is more moist they are called "hay devils". Although they may look like it they are really not tornadoes. Tornadoes are caused by huge masses of cold air interacting with warm air and are associated with storm clouds. Dust devils form most often in hot weather with few clouds in the sky.
|"The dust devils in this family (below) were racing each other just south of Ritzville. These little whirlwinds move very fast through the fields. The amount of dust they carry along changes almost from plowed furrow to furrow making it very hard to get a good picture!" [Draggoo]|
Here are some basic terms used in the tour. Find more geology terms in the Glossary.
- Lifting and removal of rock, dirt, sand and the like caused by wind, water, or glacial ice.
- The study of the changes in landforms due to volcanoes,
earthquakes, weather, floods, etc.
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