Already, some communities along the Atlantic Seaboard are setting up tsunami warning systems. The threat of tsunamis isn't as great as with Japan or Indonesia but it is most certainly real and prudent to plan ahead because landslides happen on the East Coast as well as the Canary Islands.
By RUSS BYNUM, Associated Press Writer Mon Feb 5, 10:43 AM ET
MIDWAY, Ga. - Standing outside his home along the Medway River 8 miles upstream from the Atlantic Ocean, John T. Woods III has a hard time imagining a towering tidal wave one day crashing over the dock where a lone fisherman stands casting his line.
Yet emergency managers here in Liberty County soon plan to post a warning sign near Woods' house depicting a stick man running uphill from a monstrous wave and declaring the surrounding area a " Tsunami Hazard Zone."
I have seen small tsunamis caused by distant storms or close-by giant container ships. These usually only discomfort swimmers and suntanning beach-goers. But when the earth heaves and shakes, great tsunamis can form and they can travel across entire oceans and swamp and destroy everything well inland. The East Coast of the USA doesn't get the heroic, big waves that crash into California, for example. Most of the big waves are winter storm waves. Icy as the oceans off Alaska, they hammer the rocks that protect the beaches around NYC during high winds coming from the backside of blizzards.
The other source of great waves is hurricanes in summer and fall. The backside of the eye of a hurricane is the most dangerous portion of these mighty storms. But hurricanes hearld their coming with many signs and significant displays. The high cirrus clouds, the brilliant sun rises or sun sets, sea birds fleeing inland, these and the rising seas well before the first puffs of wind, give warning.
But earthquakes give little to no warning. Like we witnessed so clearly in Indonesia with many people filming this horrific event, the earthquake caused some damage and killed people in Ache but then within a mere few minutes, the sea came rushing in, killing hundreds of thousands of people. All over the world between Asia and Africa, the seas rose up in many places and swept away helpless people.
The most dangerous zones are places where the continental shelf falls into deep trenches. These places, if there is a landslide, can heave the water upwards and produce a tsunami thanks to prevailing winds if they are blowing landwards. High tides are more dangerous than low tides, of course.
April 28, 2000
Woods Hole, Mass.
Potential landslides on the outer continental shelf and slope along the Mid-Atlantic coast could trigger tsunamis that might have devastating effects on populated coastal areas. In a paper published in the May 2000 issue of the journal Geology,Neal Driscoll of the Woods Hole Oceanographic Institution and colleagues Jeffrey Weissel of Columbia University’s Lamont-Doherty Earth Observatory and John Goff of the University of Texas at Austin say newly discovered cracks along the edge of the continental shelf could be an early warning sign that the seafloor is unstable in these areas.
These cracks, together with evidence of past landslides in the same area, indicate the sea floor could slump, or slide downhill like an avalanche, triggering the waves. Wave heights similar to the storm surge from a category 3 or 4 hurricane, up to several meters above normal, could occur along the Virginia-North Carolina coastline and lower Chesapeake Bay, the areas of highest risk.
Before the Great Boxing Day Quake showed us clearly how dangerous tsunamis from underwater landslides can be, scientists have been speculating about this here in America. Some geologists think large bolders found in the hills of the Bahama Islands came there via tsunamis caused by earthquakes, for example.
The researchers recently discovered a system of en echelon cracks along a 40-kilometer (25-mile) section of the outer continental shelf off southern Virginia and North Carolina, north of Cape Hatteras. The en echelon cracks, a series of cracks offset like the shingles on a roof, are located in water depths of 100 to 200 meters (about 300 to 600 feet) between the Norfolk Canyon and the Albemarle-Currituck submarine slide, which occurred approximately 16,000 to 18,000 years ago
In that article, they show marine photos of these cracks. I dig a lot, using backhoes and such. When I see these sorts of cracks, I warn people to stay back, the bank is going to give way. Any event like a heavy rainstorm can free up the earth and cause a collapse. This is the same with avalanches in snow country: usually there are deep fissures before the snow lets loose and goes flying down the valley.
I live in the mountains and I patrol for such cracks in the hillsides above me. In California, many people ignore such cracks prefering the 'monkey no see/monkey no need to do' ethos. This fatalism reaps its own rewards eventually.
Published 22 March 2005.
The magnitude Mw *= 9.3 Sumatra earthquake of 26 December 2004 claimed the lives of an estimated 300,000 people living in coastal areas of seven different countries around the Indian Ocean. This event raised the question of whether similar far-traveled tsunamis generated by plate boundary faulting could affect the estimated 150 million people living in coastal areas of the United States, including Alaska, Hawaii, Puerto Rico, and the U.S. Virgin Islands. Aside from the Pacific plate margin of North America, the North America-Caribbean plate boundary is the closest (˜ 2000 km) active plate boundary to coastal areas in the Gulf of Mexico and the U.S. Atlantic seaboard. Researchers also have proposed that other possible tsunami-generating sources that could affect coastal areas of the United States include slumping of the shelf margin along the Virginia-North Carolina margin [Driscoll et al., 2000] and slumping of volcanic edifices in the Canary Islands [Ward and Day, 2001].
Unlike the collapse of the subsiding seabed in Indonesia off Sumatra, the Eastern Sea board's landscape isn't as prone to earthquakes. The dangers for us is much more invisible and insidious.
The U.S. East Coast continental slope from Norfolk Canyon south to Cape Lookout, North Carolina represents a dramatic physiographic and sedimentological transition between the Middle Atlantic Bight (MAB) province of major submarine canyons and the South Atlantic Bight province of the Blake Plateau (BP)
The central portion of this region, just north of Cape Hatteras, isunique hydrographically: 1) as the zone where the northward flowing Gulf Stream meets the southward flowing Virginia current and 2) as the zone where the Gulf Stream crosses the underlying southward flowing Western Boundary Undercurrent
For quite a few years, geologists and people like me have fretted about the possibility of a great landslide from distant volcanoes causing giant tsunamis. I used to live in one of the most exposed parts of Long Island: Coney Island, and only one block from the ocean. Kept me awake some nights.
BBC News, Wednesday, 4 October, 2000
A collapsing volcano in the Atlantic could unleash a giant wave of water that would swamp the Caribbean and much of the eastern seaboard of the United States, a scientist has claimed.
Dr Simon Day, of the Benfield Greig Hazard Research Centre at University College London, UK, believes one flank of the Cumbre Vieja volcano on the island of La Palma, in the Canaries archipelago, is unstable and could plunge into the ocean.
The only good thing about this is, as Africa rotates into Europe and causes volcanic activity on the Atlantic northern edge, at least any tsunami triggered by a collapse of one of these volcanoes will give us a long warning. But emptying out much of NYC takes many hours since the entire place is a series of islands. With only a handful of bridges. And all the bridges in Brooklyn lead to other islands! There are no others!
If everyone in Manhattan evacuates to the upper floors of the towers there, and there are many such, that would probably be sufficient. But most of Brooklyn is lowlands except for Park Slope where I used to own a brownstone. That might (maybe) be safe. All of Long Island would be doomed. And they have only two bridges into the lowlands of Conn. Everyone in Conn would have to flee north and west and we are talking what? 10 million people here? And up to the Watchung Ridge in New Jersey! Another couple million. We have the same problem Indonesia has: it is nearly impossible to evacuate the huge populations that lie in the path of tsunamis.
More than any community on the entire East Coast, NYC and Long Island are the very hardest to evacuate in case of war or natural disaster.
We have the services of many good geologists but there is a problem; we like living on volcanic rifts, next to ocean cliffs about to collapse into trenches, causing tsunamis, we love California, one of the world's most dangerous geological places outside of Sumatra, we love hurricane zones and other things that are dangerous because in between moments of great destruction there are long periods of pleasant living. Who can resist that?
Frankly, I loved living right next to the ocean. Even during hurricanes, I was one of the last to evacuate. I even swam in the wild seas before a hurricane years ago. Nearly got killed. It was most exhilarating. But I will admit to having dreams of the ocean suddenly rising up and filling the house, we lived on the third floor of this Victorian summer retreat...and engulfing us. I never have that dream here on my mountain (it is replaced with dreams of being snowed under or blown off!).