There are increasing signs that the outer sloping edge of the continental shelf along the East Coast has the potential to cave in, possibly abruptly enough to send destructive "tidal waves", or tsunamis, speeding toward shore. The latest evidence comes in a study published in Science (July 14, 2000) which found that sediment buried nearly 2,000 feet under the seabed off New Jersey is so porous that it is actually mostly water.
As stated in the New York Times (7/14/2000):
Just as stepping on a water-filled balloon can cause its sides to bulge and burst, so too could the weight of rock over the soggy sediments cause the water to blow out the side of the continental slope, potentially causing an underwater landslide and subsequent giant waves, the authors say.
The report says the area studied, about 100 miles east of Atlantic City, is particularly waterlogged, and thus particularly unstable, because the deep layers of the shelf were formed in the last Ice Age, when the Hudson River was a turbid torrent, laying down enormous amounts of silt that trapped water as successive layers accumulated.
"It's a system that's in a critical state because of those fluid pressures," said Dr. Peter B. Flemings, a geologist at Pennsylvania State University who wrote the paper with Brandon E. Dugan, a doctoral candidate at the university. What is not yet known, Dr. Flemings said, is if this condition will result in a succession of small crumbling failures or in occasional canyon-carving, wave-spawning collapses."
Now here, courtesy of the BBC, is information that captures another giant-wave-generating source, this time from a collapsing volcano.
The wave would sweep up to 20 km inland. 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.
Swiss researchers who have modelled the landslide say half a trillion tonnes of rock falling into the water all at once would create a wave 650 metres high (2,130 feet) that would spread out and travel across the Atlantic at high speed.
The wall of water would weaken as it crossed the ocean, but would still be 40-50 metres (130-160 feet) high by the time it hit land. The surge would create havoc in North America as much as 20 kilometre (12 miles) inland.
Dr Day told BBC Science's Horizon programme: "This event would be so huge that it would affect not only the people on the island but people way over on the other side of the Atlantic Ocean - people who've never heard of La Palma.
Day's latest work on the subject has been published in the Journal of Volcanology and Geothermal Research.
On the back of this work, the Geological Society of London is to write to the UK science minister, Lord Sainsbury, to make him aware of the dangers posed by so-called mega-tsunami in the Atlantic.
The society hopes he will take the issue as seriously as he has the threat from asteroid strikes.
Scientists have known of the destructive power of tsunami - huge tidal waves - for many centuries. As recently as 1998, over 2,000 people were killed by a large wave hitting the coast of Papua New Guinea.
This was caused by an offshore earthquake. But researchers believe far bigger phenomena can be created by giant landslides.
The largest wave in recorded history, witnessed in Alaska in 1958, was caused by the collapse of a towering cliff at Letuya Bay. The resulting wave was higher than any skyscraper on Earth and gouged out soil and trees to a height of 500 metres (1,640) feet) above sea level.
Geological studies have found evidence of giant landslides elsewhere in the world such as Hawaii, the Cape Verde Islands and Reunion in the Indian Ocean.
Dr Day has identified dozens of volcanic vents in the Cumbre Vieja volcano that have been formed by successive eruptions over the past 100,000 years.
He thinks water trapped between dykes of impermeable rock could create pressures that eventually lead to the western flank of the mountain falling away during some future eruption.
Hermann Fritz, of the Swiss Federal Institute of Technology, which has equipment to model waves created by landslides, said: "If the Cumbre Vieja were to collapse as one single block, it would lead to a giant mega-tsunami with an initial wave height of 650 metres.
"It would have a wavelength of 30 to 40 kilometres (18 to 25 miles) travelling westwards across the Atlantic at speeds up to 720 km/h (450 mph) towards America."
But researchers caution that such a catastrophe may not occur for many decades.
"There could be five more summit eruptions of the Cumbre Vieja before the western flank collapses," said Professor Bill McGuire, of the Benfield Greig Hazard Research Centre.
"There could be 10 or there could be 20 - we simply don't know. But put it this way: if I was living in Miami or New York and I heard that the Cumbre Vieja was erupting, I would keep a very close eye on the news."
Now consider this passage from the New International Version of the Bible (Luke 21), under the heading "Signs of the End of the Age:"
There will be signs in the sun, moon, and stars. On the Earth, nations will be in anguish and perplexity at the roaring and tossing of the sea. Men will faint from terror, apprehensive of what is coming on the world, for the heavenly bodies will be shaken. At that time they will see the Son of Man coming in a cloud with power and great glory. When these things begin to take place, stand up and lift up your heads, because your redemption is drawing near.
Tsunamis cause the sea to begin "tossing" when they mound up over the shallow continental shelf as they move toward shore. And they often cause "roaring" when they begin to overtop the coastline itself.
What do the Edgar Cayce readings say about the possibility of tsunamis along Atlantic shorelines? In a word, nothing. But we must remember that nobody ever asked. And like many potentially unbelievable subjects in Cayce's time, such as men landing on the moon, the readings are mute because no one ever asked about the possibility. However, a Cayce reading does mention that "inundations" from earthquakes will affect the coast of southern California, after "greater activities" in the volcanoes Vesuvius or Pelee. Such inundations would come from two main sources: undersea "landslides offshore of southern California and undersea landslides in the Hawaiian Islands.
Returning to the threat to Atlantic shores from tsunamis originating in the Canary islands, note that six geoscientists have just published a paper on the subject that indicates that this threat is much greater than inferred by previous studies. Sebastian Krastel And Others (Jour. Geophysical Research, v. 106, no. B3, 3110/2001) surveyed the submarine flanks of the Canary islands with the GLORIA long-range side-scan sonar system, bathymetric multibeam systems, and sediment echo sounders. They identified twelve geologically young (less than two million years old) giant landslides, and several older ones. Most slides were on the flanks of La Palma, E1 Hierro, and Tenerife. The ages of the five youngest slides range from 13 to possibly 536 thousand years old. The estimated volumes of these slides are huge, ranging between 25 to 1000 cubic kilometers (16-620 cubic miles). The destruction to Atlantic shores rendered by the tsunamis generated by these landslides must have been tremendous. If the Cayce readings' predictions about pole shift and Earth changes come true, it seems quite probable that there will again be mega tsunami in the future of the coastal communities of the Atlantic. Two of the main sources of such tsunamis will be the Hawaiian ridge and the Canary islands.
But many other tsunami sources from former or potential underwater landslides have recently been identified. Among these are 1) the giant tsunami waves that hit Scotland about 7,000 years ago due to an underwater landslide off Storegga, southwest Norway; 2) the colossal wave that smashed Papua New Guinea's coast on `17 July 1998; 3) a tsunami that hit Puget Sound 1000-1100 years ago; 4) a series of three slides - perhaps triggered by earthquakes - that generated catastrophic tsunamis 110, 450, and 1,210 thousand years ago off southern Oregon; and 5) a giant landslide off Tahiti that undoubtedly generated some enormous tsunamis some 650 to 850 years ago.
Is it any wonder that, as Christ said, On the Earth, nations will be in anguish and perplexity at the roaring and tossing of the sea?
Tsunamis are a true threat to the Caribbean region and, depending upon their strength and travel direction, to North Atlantic shores beyond. According to Jim Lander of the University of Colorado, "since 1530, tsunamis have caused more deaths in the Caribbean than in Alaska, Hawaii, and the U. S. east coast combined" (EOS, 12/16/97). Tsunami sources include volcanic activity, submarine landslides, and tectonic movements of the seabed. If reading 3976-15 is correct, that "new lands seen off the Caribbean Sea," rising of the sea floor might well cause large tsunamis that could wreak destruction on shorelines and low-lying lands at various places around the North Atlantic and Caribbean ocean basins.
This speculation should be tempered, perhaps, by a reading (1602-3) in 1939, in which Cayce was asked, "Is Atlantis rising now?" The answer was that "In 1998 [emphasis added] we may find a great deal of the activities as have been wrought by the gradual changes that are coming about "....[and that]...."this [Atlantis rising] is a gradual, not a cataclysmic activity in the experience of the Earth in this period."
If we consider a worst-case scenario for tsunamis originating in the Puerto Rico Trough, we can reason that the greatest damage to U.S. and Canadian shores would occur on those shorelines that trend perpendicular to the directions of tsunami-wave travel. Thus, northward- propagating tsunami waves from strong subsea movements in the Puerto Rico Trough would be most devastating to shores trending east-west, like those in eastern Maine and eastern Nova Scotia. Such tsunami waves would have the least effect on the Atlantic coast of Florida because of the long diagonal approach of waves coming from the trough. This causes the waves to lose energy in crossing the long distance of shallow water before coming to shore. Shorelines trending off-perpendicular to tsunami wave travel would suffer less, but harbors and bays oriented as funnels to wave travel would be strongly affected. Narragansette Bay and harbors, and the Bay of Fundy come to mind, as perhaps also New York Bay and harbor.
If we switch to California for a moment, note that tsunami waves originating from the giant (M9.5) earthquake in Chile in 1960, produced some damage to yachts and coastal engineering works in both San Diego and Los Angeles harbors, even though the waves traveled diagonally through shallow water for hundreds of miles. Both of these harbors face south, and thus the waves had a more direct approach.
"The amplitude of the waves coming into San Diego reached at least 5 ft and continued to be measurable for the entire day with considerable variation in heights. Strong currents moved up the entrance of both harbors and caused ships to break their lines and crash into the pier pilings."(Shepard, F.P., and Others, 1963, Submarine Geology, Harper & Row, New York).
Giant waves emanating from the Cumbre Vieja volcano in the Canary Islands is not the hazard it seems when compared to the possibility of a surprise tsunami generated off Virginia's coast. Coastal communities around the North Atlantic basin will have fair warning of any Canary Island tsunami waves by paying attention to geophysical monitoring services that track eruptions and potential landslides.
But for U. S. mid-Atlantic communities there is the possibility for surprise tsunamis that may be generated locally and without warning. As presented at the beginning of this article, sediments along the outer continental margin are so soggy and gas charged that they can slump spontaneously. Marine geologists identified fresh slump scars last year off New Jersey, and Driscoll, and others, recently found a 25-mile-long system of cracks along the shelf edge off southern Virginia. These cracks lie just north of the approximately 16,000-year-old (Albemarle) submarine landslide.
Should an Albemarle-like slide occur tomorrow off Virginia, how big might the tsunami waves be? Steven Ward (Univ. Calif. at Santa Cruz) has modeled the case of a hypothetical slide moving down Norfolk Canyon, whose headwall is around 62 miles due east of Virginia Beach. He traced the edge of the Albemarle debris field and transported the outline northward so that the head scarp overlies the newly found shelf-edge cracks. Using data for slump speeds and volumes inferred from studies of former slides, Ward's model was able to simulate the sea-surface disturbance for the hypothetical Norfolk Canyon slide. The slide would run out to a point about 140 miles from shore.
Thirty minutes after the slide began, peak waves 32 feet high would be generated. Deep ocean water to the east would allow the waves to travel at speeds of around 375 miles per hour. But to the west, shallows barely 165 feet deep keep the waves to a comparative crawl (about 50 mph). After two hours, waves reach Virginia Beach. Ward concluded that although waves along the shore from North Carolina to Long Island would vary from 13 to 23 ft in amplitude, most visitors to this stretch of the shoreline would experience only a very few peak waves of 6 to 13 ft.
A tsunami wave striking Virginia Beach would most likely appear as flooding. If its amplitude were 20 ft that means that the height of the flooding would be 20 ft above local mean water level at the time. If the trough of the wave arrives first, the water level will drop rapidly to minus 20 ft, exposing the bottom. This may be the only warning to residents that a large tsunami is approaching and it may move so quickly that people who wandered out on the bottom could be drowned. Although there may be an interval of minutes - to perhaps an hour - between the arrival of flooding waves, the second, third, or later waves can be more destructive than the first.
Tsunami-wave run-up distance and damage to structures depends upon a variety of factors such as the angle of slope of the beach, tide height, and building-construction. While Ward's wave amplitudes, if realized, would be somewhat less damaging than those expected from a Cumbre Vieja slide, tsunami waves' ability to surprise is the greatest danger. A two-hour warning for a Norfolk Canyon slide would not be enough for most people to get out of harms way, even if seismic detection of the slide could somehow be broadcast quickly. And what if the slide occurred at midnight? How many would hear the broadcast?
Unlike the U.S. Pacific rim, the U.S. east coast has no tsunami-warning system in place. It is time for NOAA to install a tsunami-detection system on Virginia's continental shelf, such as it has done in the Gulf of Alaska, and off Oregon and Washington. Data on tsunami waves could then be sent in real-time to mid-Atlantic coastal communities. It would then be up to each community to warn vulnerable residents via strategically placed sirens, as is done now in Hawaii.