Q&A: Crop circles

As a new study claims some crop circles are created by shifts in the earth's magnetic field, George Bishop, of the Centre for Crop Circle Studies, expounds on the phenomenon.

According to Dr Colin Andrews, who has studied crop circles for 17 years, about 20% are caused by eddies in the earth's magnetic field - the rest are man-made. He thinks a mysterious shift in the electro-magnetic field creates a current that flattens the crops in its path.

Is it plausible?

"Yes - it's a nice rounded theory," says Mr Bishop. Like Dr Andrews, he says all but the simplest circles are hoaxes.

The theory could explain why in some circles, microphones and recording equipment hit interference, he says. Some years ago, a BBC crew had difficulty recording in a circle.

New theory: electro-magnetic eddies flatten the crops

"If the circles are formed by electro-magnetic eddies, there may be a residual charge of energy," Mr Bishop says.

But he does not think the new theory is the final word: "It doesn't explain why often the nodes of the plants have swollen up to 200 times the original size."

He thinks the currents may work in tandem with other environmental factors, possibly conducted via water in the air, such as mist, or in underground water tables.

Are they only in the UK?

No, the circles crop up around the world - in grass as well as grain fields.

Why so many in Wiltshire, south England?

As an area steeped in the mysteries of the ancients, this is where the hoaxers are most active, and where the majority of enthusiasts go circle spotting.

Many more circles around the country and abroad go unseen and unreported, Mr Bishop says.

"Ninety percent - and in some years, 98% - of the circles in the UK appear along the aquifer line (a layer of rock able to hold water), which runs from Dorset to Norfolk."

When do the circles date from?

One of the earliest reports was in Lyon in 815AD, and a late 16th Century woodcut depicts the devil mowing a field into patterns.

Wiltshire's ancient stone circles - which include Stonehenge and Avebury - could have been built on the sites of early crop circles, Mr Bishop says.

What of the other theories - aliens, for example?

Aliens are a modern-day obsession, so not surprisingly the circles have been attributed to little green men - either as messages, or the imprint of UFOs landing in the fields.

Message from afar, or homegrown hoax?

"People relate crop circles to what is going on around them, what concerns them," Mr Bishop says.

"People used to think it was witches and fairies; then it was aliens. Today, people think it might be electro-magnetic pollution, caused by the proliferation of radio masts and mobile phones."

And ancient ley lines?

"It may well be that the earth does have these energy lines, and it may well create some sort of current when these lines intersect with the magnetic fields."

What about freak weather patterns?

Mini-tornadoes are unlikely to create such intricate and symmetrical patterns, Mr Bishop says: "We know whirlwinds aren't static - they travel around."

But this you can guarantee - the circles will crop up again next summer.