guardian:

Unusual clouds caught on camera – clockwise from top left:

A steam ring being blown from the Bocca Nuova vent of Mount Etna, Sicily. Steam rings are generated when a pulse of steam is ejected from a near-cylindrical volcanic vent

Photograph: Science Photo Library/Rex Features

Von Karman cloud vortices above Alexander Selkirk Island, Chile. These naturally occurring vortices are crafted by wind patterns on the clouds

Photograph: Science Photo Library/Rex Features

Lenticular cloud, Mauna Kea, Hawaii. The lens-shaped clouds form at high altitude and are usually formed when air passes over mountain tops

Photograph: Science Photo Library/Rex Features

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