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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.
Threat over 'forever' Every year hundreds of twisters tear through
communities in the great north-south corridor between the Rocky and Appalachian Mountain
ranges. The proposed walls would not shelter towns
- they would not be strong enough to block a tornado in motion.
Instead, they would soften the clashing streams of hot southern and cold northern air, which
form twisters in the first place, Prof Tao said.
"If we build three east-west great walls, one in North Dakota, one along the border
between Kansas and Oklahoma, and the third in the south in Texas and Louisiana, we will
diminish the threats in Tornado Alley forever," he said.
As evidence, he points to China - where only three tornadoes were recorded last year, compared
to 803 in the US. China too has flat plain valleys running north-south,
but the difference is they are broken up by east-west hill ranges.
Although only a few hundred metres high, they are enough to take the sting out of air currents
before they clash, Prof Tao believes.