A field full of hundreds of rare self-rolling snow balls in Yeovil. Photo: Ron Trevett. They may look like winter's answer to crop circles, but these mysterious snow rolls are in fact a rare natural phenomenon usually found only in the world's most remote and frozen regions. Also known as snowrollers, snow bales and snow doughnuts, they form mostly in unusual conditions created by a precise combination of snow, ice, wind, temperature and moisture on the prairies of North America.
