Spectacular pictures of nature at its wildest, captured by the storm chasers who risk their lives to follow twisters

Last updated at 11:57 31 March 2008

The violent winds howl, announcing the arrival of the twister.

Grapefruit-sized hailstones rain down and the huge funnel of the tornado swings menacingly on the horizon.

These are the most violent storms on earth, wreaking havoc wherever they whirl.

For most, the sight of an approaching "twister" is a vision of hell on earth.

But for a few, experiencing a tornado in full flow is their idea of heaven.

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Independence Day II: A cloud over Sioux City, Iowa, is whipped into a massive, spaceship-like doughnut a mile in diameter

Bolts from the blue: A violent swirling mass darkens the skies over Grand Island, Nebraska and creates a mini electrical storm

They are the storm chasers, a rare breed of adventurers who delight in tracking tornados and watching them unfold.

And as these pictures taken by storm chasers Mike Hollingshead and Eric Nguyen show, tornados can be both deadly - and hypnotically beautiful.

Storm chasers, who think nothing of driving 500 miles a day in the hope of finding a "big one", are a motley bunch of research scientists, local TV journalists competing to be first with the tornado warnings (not only saving lives but boosting viewer ratings, too) and adrenaline junkies.

Up to 800 twisters are reported in the U.S. every year and most of them are to be found in the Mid-West prairieland or, as the chasers have named it, "Tornado Alley".

The storms there are triggered by the unique weather of the Mid-West.

It has a constant low pressure system that draws moist, warm air from the southern Gulf of Mexico towards the cool dry air of the Northern Rockies and the warm dry air of the Western deserts.

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Touchdown: A funnel of rotating air leaps from the cloud to the ground and a twister is born over the fields of Attica, Kansas

Heaven's Hammer: A monster tornado unleashes its wrath across Alvo, Nebraska, travelling at over 70mph

These conflicting air systems produce large, violently rotating masses of air, called supercells.

In some, especially in the sultry heat of mid-afternoon, huge updraughts are created and begin to spin.

The distinctive dark snout of cloud is formed, and when it touches the ground a tornado is born, with winds that can reach up to 300mph.

Chasers soon learn to read the signs. Towering cumulus - or fluffy clouds - usually mean something is brewing. But the most hopeful sight is a "gust front", an angry black wall of indigo cloud.

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