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Rare self-rolling giant snow balls found in UK
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.
Published: 9:45PM GMT 08 Jan 2010
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.
But this week's frozen weather has allowed the snow cylinders to make a freak appearance in the UK.
Ron Trevett, 55, and his wife Aileen, 54, readers of The Daily Telegraph, were stunned when they stumbled across the mysterious formations as they walked their dogs in a field near their home in Yeovil, Somerset.
"We saw them from a distance on the ridge of the field, and we thought some kids had been playing up there and making giant snowballs," said Mr Trevett.
"But when we got up there we saw there were no footprints and there were hundreds of them – too many for children to have done it. We realised it must have been the wind."
Mr Trevett, a builder, said he and his wife felt privileged to have witnessed such a rare phenomenon. "We feel very lucky. I'm the wrong side of fifty and I've never seen anything like it in my life. We were gobsmacked to look at them there in the sunlight. It was a really impressive sight, and I took some pictures so other people could share it," he said.
Frank Barrow, a lecturer in meteorology at the Met Office, said the rolls can only form in a precise set of unusual conditions.
"They start off with nice thick layer of snow, with the top snow just on the point of melting either because of general temperature or sunshine on the surface," he said.
"The top snow layer becomes a bit sticky, and you then need a fairly strong wind. The sticky layer can be peeled off the colder and more powdery snow underneath by the wind forming a roll. In the first picture you can see some of the powdery stuff sticking to the lower outside surface of the roll. I suppose it is a natural version of making a snowman."
After being formed, the rolls eventually become too large and heavy for the wind to move, or are halted by rising ground or a tuft of vegetation.
They are often hollow because the weak inner layers which form first can easily be blown away, and the fragile formations can collapse in the slightest change of temperature or gust of wind.
Liz Bentley, of the Royal Meteorological Society, said despite their rarity in the UK, there is a chance of more snow rolls appearing over the next few days.
"These rolls are unusual here because we don't tend to have major snow events like the one we're experiencing now. They happen with the combination of lying snow and high wind speeds, mostly in North America and Northern Europe, and they can be as small as a tennis ball or they can be as large as two feet across – depending on how strong the wind is and how smooth the surface of the snow is," she said.
"There are quite strong winds predicted this weekend as well as more snow, so if people keep a look out they might see a few more of these appearing around the country over the next few days."
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