Great Walls of America 'could stop tornadoes'

Building three "Great Walls" across Tornado Alley in the US could eliminate the disasters, a physicist says.

The barriers - 300m (980ft) high and up to 100 miles long - would act like hill ranges, softening winds before twisters can form.

They would cost $16bn (£9.6bn) to build but save billions of dollars of damage each year, said Prof Rongjia Tao, of Temple University, Philadelphia.

He unveiled his idea at the American Physical Society meeting in Denver.

However critics say the idea is unworkable, and would create more problems than it solves.

- BBC.co.uk