An intense video surfaced on YouTube this afternoon showing a powerful dust devil destroying tents, umbrellas, and even an inflatable slide during pre-game festivities at Pasadena, California's Rose Bowl on Wednesday. Four people sustained minor injuries as the whirlwind launched debris in the air.
Dust devils can appear similar to tornadoes—especially when they kick up dust and dirt—but they form through completely different processes. Dust devils form as a result of rapidly rising air at the surface. Direct sunlight causes the surface of the Earth to heat much more quickly than the air. As the surface warms, air immediately above the surface is able to warm up faster than the atmosphere above it due to conduction.
This layer of warm air is usually capped by cooler, more stable air above it, preventing it from rising and mixing with the rest of the atmosphere. Sometimes if a pocket of warm air is able to break through the cap, it will rapidly begin to rise. Light winds can cause the rising column of air to begin rotating, and as the column grows and stretches out, the air will rotate more quickly thanks to the conservation of angular momentum (think of a figure skater pulling her arms in during a spin).
Dust devils are most common over large areas of hot surfaces such as parking lots, large gravel fields, or even the desert. Dust devils are usually weak, with maximum winds equal to that of a breezy day, but some stronger dust devils can cause structural damage with winds equivalent to those found in EF-0 tornadoes.