Also known as dust devils, willy-willies are dust filled vortices that can spiral upwards from the ground, varying in height from a few feet to over 1000 feet. <br /><br />They are usually several metres in diameter at the base - then narrowing for a short distance before expanding again. <br /><br />They mainly occur in desert and semi-arid area where the ground is dry and high surface temperatures produce strong updraughts. <br /><br />The initial rotation may be caused by irregularities in the surface. <br />
