Dust devils can be found over much of the earth. Several years ago I saw one at the summit of Hawaii's Mauna Kea nearly 14,000 feet over the Pacific. They're even found on Mars.

Recently Minnie and I spotted a large dust devil (or whirlwind, which is remolino in Spanish) as we drove near Seguin.

This dust devil distinguished itself by sucking up large quantities of shredded corn leaves. As it approached, I switched the camera to movie mode to capture its arrival. Suddenly the wind arrived with a roar, and the center of the whirlwind crossed the fence just 20 feet away. It then blew across the highway, striking two cars on its way.

Based on a fence in one of the photographs, the dust portion of this whirlwind was about 15 feet across at the ground and 30 feet across at the top of the fence posts. The whirling vegetation at the top of the fence posts was more than 75 feet across. The flying debris in the movie suggests that the wind at the core of the dust devil was moving faster than the passing cars.

Flying corn leaves are relatively benign compared to what I experienced while bicycling along a gravel road in New Mexico. The wind pelted me with gravel and sand and nearly knocked me over.

If you want to photograph dust devils, head west on Interstate 10 on a hot summer day. As you enter West Texas, you may see half a dozen at a time. Their dusty plumes may reach a thousand feet into the sky.

Minnie and I once experienced a monster dust devil near Carlsbad, N.M. The whirling vortex of orange sand shook the car as it passed over. Large dust devils like this can damage sheds and roofs.

The National Weather Service office in Flagstaff, Ariz., is in prime dust devil country. Its Web site explains how dust devils often form along the boundary between a meadow or an irrigated field and an adjacent road or bare soil.

The air over the road or soil rises as it is heated, creating plumes of warm air. When the conditions are right, one or more plumes will begin to rotate and move across the ground.

A dust devil needs a hot surface to survive and will rapidly dissipate if it passes over an irrigated field.
