Five Ways to Trigger a Natural Disaster

This caused water to pour into the mine, filling the shafts and dissolving the salt, as the oil rig and eleven barges were sucked down. The event is said to have looked like a giant bathtub emptying down a drain.

Incredibly, no-one was hurt. But the lake's ecosystem was permanently altered. Just days after the event, water flowed backwards from the Gulf of Mexico into Lake Peigneur, turning the freshwater lake into a brackish, saltwater one.

Flooding

Cloud-seeding is an increasingly common form of weather modification – but is it possible to push the method one step too far and bring on a biblical flood?

On June 9, 1972, more than 35 centimetres of water – nearly a year's worth of rain – fell in six hours over the Black Hills of Western South Dakota. The rainfall caused Rapid Creek to overflow and the Canyon Lake Dam to burst, resulting in huge floods in downstream Rapid City.

More than 200 people died and 3000 were injured. About 1300 houses were destroyed, some simply lifted by the water and carried away. In all, the floods caused over $160 million in damage to the city.

On the day of the storm, scientists had been carrying out cloud-seeding experiments nearby, and were later blamed for the floods.

The principle of cloud seeding is relatively simple. The skies are peppered with a chemical – usually silver iodide – which draws the moisture out of clouds by providing something for water to condense on. But it is difficult, if not impossible, to establish how much rainfall is a direct result of cloud seeding.

Don Griffith, of North American Weather Consultants, says it is highly unlikely that cloud seeding could trigger a flood on the scale of the one that devastated Rapid City in 1972.

"In truth it was probably a bad idea for the scientists to be cloud seeding while a storm was building," says Griffith. "But man's ability to modify the weather in some small measure can in no way match power of nature."

Kerry Emanuel of Massachusetts Institute of Technology agrees that humans probably cannot influence such a large storm. "Cloud seeders often have the opposite problem: they don't know whether they've had an effect at all," he says.

Hurricanes

Worryingly, hurricanes can also be seeded. In the 1960s, US scientists involved in a project called Stormfury sought to demonstrate that they could disrupt the structure and energy of a hurricane by seeding the atmosphere.

After two decades, some scientists suggested that Stormfury had failed to induce any change and the project was cancelled. But hurricane expert Kerry Emanuel says controlling the path of a hurricane is something that "we know how to do theoretically".

Emanuel explains that two-thirds of the hurricanes on course to make landfall in the US are knocked off course by another weather system. So scientists know what temperature and pressure disturbances in the atmosphere will help divert a raging hurricane. "The evolution of the atmosphere is very sensitive to small perturbations," Emanuel adds.

One way to create the necessary disturbances would be to release a trail of black carbon – tiny soot particles – into the sky. This should absorb enough of the Sun's energy to create a temperature disturbance.

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