Pick your cataclysm: A tsunami washes over Miami. A massive quake rips Los Angeles. Or the volcano under Yellowstone erupts, spewing ash across America and ushering in a new Ice Age.

Surprised by Hurricane Katrina's destruction of New Orleans and the problem-plagued recovery, experts are revisiting with a new concern the risks posed by everything from killer asteroids to ocean-shaking landslides.

They also are considering a haunting new question: How can a disaster as widely predicted and slow-moving as a storm still pack such a devastating surprise in the United States?

"Hurricanes happen with some regularity and we can't deal with them. How can we deal with an earthquake?" said Nassim Nicholas Taleb, a specialist in uncertainty and risk at the University of Massachusetts. "We have a problem."

The potential catalog of calamities considered by scientists starts with the near-certainty of a major earthquake on California's San Andreas fault, and proceeds to far-shot catastrophes such as an Atlantic Ocean tsunami triggered by a volcanic landslide.

Then there are the "near-earth objects" and "supervolcanoes" -- seen as tiny risks now despite a geologic record of life-altering catastrophe.

NASA's Jet Propulsion Laboratory, which tracks asteroids at risk of hitting Earth lists three for "careful monitoring."

Those include a mass 350 yards in diameter given a 1-in-5,560 chance of crashing here in April 2036, the nearest collision window of the asteroids most closely watched.

Steve Chesley, a NASA astronomer, said none of the 1,200 or so near asteroids that are larger than 1,100 yards are on the watch list -- good news since it is believed it would take an object of that size to deliver a climate-changing blow to the planet.

Many scientists believe that an impact near Mexico's Yucatan peninsula led to the extinction of the dinosaurs, by ejecting dust and particles into the atmosphere which chilled the planet for several years.

Even so, Chesley said, a medium-sized asteroid of the kind that top NASA's watch list would be "absolutely capable of causing damage across several states, for example."

'THESE THINGS DO HAPPEN'

Asia's deadly tsunami in December focused attention on the risk from the huge waves triggered by earthquakes and other events of equal power.

Steven Ward, a geophysicist at the University of California, Santa Cruz, has studied the threat of a tsunami if the Cumbre Vieja volcano erupted in the Canary Islands.

Such an outburst, he projects, could cause a steep block of the island of La Palma to break off and crash to the ocean floor, touching off a rare Atlantic tsunami.

The worst-case rupture could send waves of up to 300 feet

to the African coast within an hour and 75 feet

tall to the beaches of Florida after nine hours. "These things do happen," Ward said.

Then there is the scenario in which a little-recognized volcano under Yellowstone National Park in Wyoming erupts again. The volcano spit out enough debris in a massive burst 2.1 million years ago to bury Texas with 12 feet of ash.

The risk of any eruption in the next hundreds of years is seen as very small, but the prospect of a killer blast drew attention after a 2003 BBC "docudrama" on the subject.

"My dad always used to joke that more people probably die of tripping on their shoelaces than from volcanoes," said Smithsonian Institution volcano expert Rick Wunderman. "But we'd like to look ahead and know what's coming -- just like with this hurricane."

The closest thing to a sure-bet U.S. disaster awaits in California, experts agree.

A magnitude 7.5 quake under Los Angeles could kill as many as 18,000 and cost $250 billion, according to computer models.

Meanwhile, the state's San Andreas fault is seen certain to at some point set off a magnitude 8 quake, possibly more powerful than the quake that destroyed San Francisco in 1906.

That would cut off the water and natural gas flows into Los Angeles, sever road and rail ties and effectively strand a region with 10 times the population of New Orleans, said Lucy Jones, a scientist with the U.S. Geological Survey.

"It is absolutely when and not if," she said, urging residents to take steps now to recognize the risk and prepare. "I'll bet most people in L.A. don't have a store of water."

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