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Could a tsunami hit the U.S.?

/ Source: Dateline NBC

When the tsunami hit, many Americans, especially those living near the ocean, couldn't help worrying about the vulnerability of coastal communities. The West Coast is known to be at risk for quakes and, therefore, tsunamis. There's also a radical theory predicting that a tsunami, with waves far larger than the ones we've just seen, could hit Miami, Washington and New York.

Our fears of tsunamis hitting home are formed largely by movies like "The Day After Tomorrow,” the nation's proudest manmade empires crumbling under nature's whims. And with two such populated coastlines, the question is inevitable: Could it happen in the United States?

Dr. John Rundle is the director of The Center for Computational Science and Engineering at U.C. Davis.

Dr. John Rundle: “We need to think about this. The risk for tsunamis like the one we saw in Sumatra is very real and very present and very possible.”

Scientists do warn there are several active undersea areas, called subduction zones, off both coasts, that could trigger a tsunami. And before you dismiss that as doomsday talk in academic jargon, consider this. It has already happened. Alaska has been hit repeatedly, as has Hawaii.

And then, there's Crescent City, not some ancient megalopolis swallowed by the sea, but a sleepy waterfront town on the northern edge of California. Forty years ago it was struck by a killer tsunami. It was March 27, 1964, at 5:36 p.m. A 9.2 magnitude earthquake shook the seafloor under Valdez, Ak, triggering a tsunami that went hurtling down the West coast.

Gary Clawson: “We just happened to be in the wrong place, the very worst place.”

Gary Clawson, then 27 years old, owned a waterfront tavern in Crescent City, on around midnight after the initial wave hit and passed, he rushed to shore to check on his property. Along came both his parents and his fiancée.

Clawson: “It just seemed like that it was over with.”

Mack McGuire: “You don't forget something like that.”

After hearing the monster wave had receded, Mack McGuire also headed to the shore, to check on his fishing boat. He couldn't find it, so he too stopped by the waterfront tavern, where he and the Clawson gang all marveled at the damage, assuming the worse had come and gone.

But they were about to learn one of the most important lessons in handling a tsunami. Contrary to what you would often imagine, the first wave may not be the deadly one.  

Suddenly a second wave hit.

McGuire: “Yes, very much surprised. I never had a wave like that hit me.”

Clawson: “All of a sudden, I heard just kind of heard a rumble. And the whole west wall of that tavern just disappeared. It just crushed it in. Then all of a sudden the building itself, the whole tavern, left its foundation.”

All were trapped on the tavern's roof, now barely above water. These two, then younger men, swam off. Mack Maguire returned home to his wife, after lending a spare row-boat to Gary Clawson, who rushed to rescue his stranded parents and fiancée. They climbed onto the boat. The water was calm. Again, they all assumed the worse was behind them.

Clawson: “I had never been through a tsunami. Had no idea that when the water went down, it would go back out as fast as it come in.”

They had almost reached dry land, when the tsunami's huge force sucked them back toward the ocean. The water was pulling them violently at speeds upwards of 300 mph, toward a small underpass under the flooded highway.  Within seconds, the boat crashed into the metal grate.

Gary's father, mother, fiancée, and 3 other people on board all died. he was the sole survivor.

Four waves struck crescent city that night. The largest was over 20 feet high. The tsunami washed away 29 city blocks and killed 11 people.

Today there are still constant reminders of the tsunami here. Yes, it can happen again. The next one may be far bigger.

Dr. Rundle: “The West Coast of the United States is at risk.”

Dr. Rundle has created a model that predicts with a high rate of accuracy where earthquakes may strike in the next 10 years. Tsunamis are often a result of earthquakes, when one undersea earth plate slips beneath or on top of another, violently pushing water in its wake.

Dr. Rundle: “This plate gets lifted up and this plate goes down. It's that vertical motion of the seabed that produces the tsunami itself.”

He says Washington, Oregon and Northern California are vulnerable to waves generated by earthquakes as far off as Alaska.  And, in fact, he and others agree the Northwest states are at even greater risk from an active earthquake zone in the Pacific just 50 miles off the coast.

Dr. Rundle: “This is an area called the Cascadia subduction zone, where a plate-- the Pacific Ocean plate-- is actually diving down underneath the North American continent.”

Experts fear a rupture along the 600-mile undersea fault could set off a deadly wave that would sink the coast of Oregon within 30 minutes. 300 years ago, a massive earthquake in that same area generated a wave so powerful it scarred trees deep inland in California and reached all the way to Japan. An ancient Japanese diary actually pinpoints the time: 9 p.m., January 26, 1700.

Such an earthquake occurs in the north Pacific every 300 to 500 years. That means we're due for one, sometime in the next 200 years.

And what about the East Coast? A tsunami is statistically much less likely to hit the East Coast. There're far fewer earthquakes. Once you get out in the Atlantic, the scenarios tend to be, literally, outlandish, like an asteroid falling into the sea and generating a wave. And yet, there are precedents there, too.

In 1929, a giant wave we now know was a tsunami pounced on Newfoundland, Canada, killing some 50 people. And even Atlantic City was hit by a tsunami twice, once after World War I, once after World War II.

Now, there's concern that an area of instability 1,400 miles south of Miami, in the Caribbean, may trigger the next big wave. 

Dr. Rundle: “If a large earthquake of magnitude 7 or larger were to happen either here or there, you could see there's an unobstructed path to the Eastern coast to the United States.”

Such a wave could engulf Miami and reach as far north as Washington, D.C.

And what about New York City? How realistic is that movie image, in "Deep Impact," of the Big Apple submerged? Well, if you ask Dr. Steven Ward of U.C. Santa Cruz, it's certainly possible. In 2001 he and a colleague published a paper. It may read like a movie script, but it's science.

According to Ward, a huge chunk of a volcano on the Canary Islands, near Morocco, is on the verge of chipping off and sliding into the Atlantic. Another volcanic eruption, and it might go.

Dr. Steven Ward: “This particular volcano has vertical layers of rock inside it filled with water, like vertical dams. When the eruption occurs, hot material will come up and heat this water. And it-- almost like a popcorn seed, it's going to pop off the side. And when this happens, it'll make a big wave.”

Think of a rock almost the size of Manhattan falling into the sea.

Dr. Ward: “It's going to be 20 times, 15 times more than this than in the earthquake which you saw. So we're talking seriously. It's equivalent to all of the nuclear bombs and earthquake at once.”

In this computer model he designed, the gigantic tsunami starts fanning out immediately. Within nine hours the wave would wallop the Atlantic shore, drowning everything in its path, with 80-foot waves engulfing New York City.

The island of Manhattan would be underwater?

Dr. Ward: “Yes.”

Does he really believe that that might happen?

Dr. Ward: “Absolutely. Because as a geologist, you're not just making things up. You look at previous examples.”

But before New Yorkers start heading for the hills, keep in mind other scientists aren't so concerned. They point out the volcanic rock may just crumble gradually, not fall in one big plop. And they say an eruption strong enough to dislodge the rock may be tens of thousands of years away.

Dr. Ward: “Do I think it's likely? No. If you want statistics, somewhere in the world such an event's happened about every 5,000 to 10,000 years.”

Yes, for all the doomsday scenarios, scientists agree, odds are these will never happen in our lifetime. But then, they warn, you never know. While there's a growing body of knowledge about where tsunamis may hit, the pertinent question of when is still, pretty much, anyone's guess.

Sophisticated deep sea tsunami warning system for the West Coast is currently in operation. Emergency officials say it is subject to false alarms, but many consider it effective. They believe the disaster in south Asia could prompt the building of a similar system for the East Coast.