Thunderstorms produce a lot of weird things, which are often easy to miss amid the urgency of tornadoes, floods and lightning. But before a storm arrives, or sometimes out of the blue, rare "roll clouds" like this one command attention as they float ominously overhead.
"It was amazing," photographer Rob Sharrock told ZUMA Press in 2010, after shooting this roll cloud over Warrnambool, Australia. "I just looked up in the sky and said, 'Bloody hell, what on Earth is that?' It seemed to go on for miles."
To see more, and to find out what causes these stormy spindles, check out the following gallery of nine rockin' roll clouds from around the world. (Text: Russell McLendon)