The first time I recall seeing a dust devil was in the Palouse Region of Washington State back in 2003. They were quite common on the arid rolling landscape and captivated all of our attention and intrigue. This past Saturday and again on Monday, I observed dust devils for the first time in my home state of Indiana. All were within five miles of the family’s lake cottage near Syracuse. Two were seen in a farm field on Saturday and one very large one (probably 75-100 feet in height) was seen on Monday afternoon. Below is a photograph of one of them seen on Saturday afternoon.
I must say that dust devils (and their smaller winter counterparts – snow devils) are one of those very special aspects of nature that make me think – “Wow!”
Below is background information from Wikipedia on the formation of dust devils:
“Dust devils form when hot air near the surface rises quickly through a small pocket of cooler, low-pressure air above it. If conditions are just right, the air may begin to rotate. As the air rapidly rises, the column of hot air is stretched vertically, thereby moving mass closer to the axis of rotation, which causes intensification of the spinning effect by conservation of angular momentum. The secondary flow in the dust devil causes other hot air to speed horizontally inward to the bottom of the newly forming vortex. As more hot air rushes in toward the developing vortex to replace the air that is rising, the spinning effect becomes further intensified and self-sustaining. A dust devil, fully formed, is a funnel-like chimney through which hot air moves, both upwards and in a circle. As the hot air rises, it cools, loses its buoyancy and eventually ceases to rise. As it rises, it displaces air which descends outside the core of the vortex. This cool air returning acts as a balance against the spinning hot-air outer wall and keeps the system stable.”
“The spinning effect, along with surface friction, usually will produce a forward momentum. The dust devil is able to sustain itself longer by moving over nearby sources of hot surface air.”
“As available extreme hot air near the surface is channelled up the dust devil, eventually surrounding cooler air will be sucked in. Once this occurs, the effect is dramatic, and the dust devil dissipates in seconds. Usually this occurs when the dust devil is not moving fast enough (depletion) or begins to enter a terrain where the surface temperatures are cooler, causing unbalance.”
“Certain conditions increase the likelihood of dust devil formation.”
- “Flat barren terrain, desert or tarmac: Flat conditions increase the likelihood of the hot-air “fuel” being a near constant. Dusty or sandy conditions will cause particles to become caught up in the vortex, making the dust devil easily visible.”
- “Clear skies or lightly cloudy conditions: The surface needs to absorb significant amounts of solar energy to heat the air near the surface and create ideal dust devil conditions.”
- “Light or no wind and cool atmospheric temperature: The underlying factor for sustainability of a dust devil is the extreme difference in temperature between the near-surface air and the atmosphere.”
Fortunately, dust devils rarely cause damage or injury, though one should be cautious, especially skydiving near one. Generally, a dust devil is spinning at approximately 45 miles per hour, but can accelerate up to 60 mile per hour.
The next time you see one of these whirling miracles of nature, take just a moment to appreciate its awesome beauty and delicate design. While the dust devils I have seen have been relatively small, the following photographs show they can become quite large. The photograph at the end shows one traversing the Martian landscape.