Skip to comments.Researchers Plot Course Of Ancient American Tsunami (902AD)
Posted on 10/28/2002 4:27:53 PM PST by blam
Researchers plot course of ancient American tsunami
Researchers have calculated the scale of a giant wave that devastated the north west coast of America 1,100 years ago.
Japanese scientists used computer modelling to recreate the devastation from the ancient tsunami.
The team from the Disaster Reduction and Human Renovation Institution in Kobe say the work will help planners minimise the impact of any future wave.
The researchers took clues from silt deposits found in the Puget Sound, a Pacific inlet above earthquake fault lines in the Seattle area.
Experts say the tsunami could have reached up to seven metres in height and penetrated 300 metres inland.
They say it's possible a tsunami of similar scale could hit the Puget Sound in the event of a future quake.
Nature says that the research will be incorporated into maps predicting the areas most at risk.
Story filed: 11:06 Monday 28th October 2002
Ditto. This is the first time I recall seeing a date.
eh--is there a problem with scale here, like maybe a misplaced decimal? because a 25 ft wave penetrating 1000 ft inland doesn't sound like much to me.
If it is 23 feet out in the deep ocean and covers a large area, it represents a huge mass of water. By the time it reaches shore and piles up on itself it can be hundreds of feet high and crash far inland.
Near New Madrid, the epicenter of the biggest 'quake in the contiguous United States...
October 18 2000
IT looked like a scene from Hollywoods latest summer blockbuster. But the image of a giant tsunami engulfing Manhattan island published in last weeks Insurance Day did not come from the over-active imagination of an eager scriptwriter.
It was, in fact, an artists impression of a very real threat. One that has been established through years of authoritative research from scientists at the Benfield Greig Hazard Research Centre at University College, London.
Their work has established that much of La Palma, the most volcanically active of the Canary Islands, is now inherently unstable.
Another eruption could cause half the island to simply fall away and crash into the ocean. The resulting impact would generate a giant wave big enough to sweep westwards across the Atlantic and devastate the entire eastern seaboard of the United States.
Such theories of enormous tsunamis being generated by island landslides first emerged from studies of the seabed around Hawaii in the Pacific. Here great slabs of rock were identified which, it was suggested, had slipped below the surface after detaching themselves from the main islands as a result of volcanic activity.
Meanwhile, in the Canaries Dr Simon Day, of the Benfield Greig Centre, began mapping La Palma in 1994.
His studies of the summit area gradually uncovered dozens of volcanic vents formed over a period of hundreds of thousands of years by various volcanic eruptions.
All the evidence pointed to one startling conclusion - that the western half of the volcano is gradually separating itself from the eastern half.
Another important realisation was the influence of water within the rock. When this is heated by magma rising to the surface it expands and adds to the pressure on the island to fragment.
This particular effect may well prove significantly more crucial in years to come, speculates Dr Day. He believes the process of global warming could contribute to the heating of water and make the set of conditions necessary for a landslide more likely.
There is an interesting possibility that the collapse may become much more likely over the next century or so because of global warming, he warned.
So what happens when the fracture does take place? Well, quite simply, 500bn tonnes of rock plunge straight into the ocean.
In an attempt to determine the nature and impact of such an event Dr Day co-operated with researchers from the Swiss Federal Institute of Technology in Zurich.
Here a laboratory model was constructed of La Palma island in a wave tank. The collapse was then reconstructed and recorded by a high-speed camera.
The results were incredible. They showed that as the rock crashed into the ocean it would in real life generate a wave up to 650 m tall.
The models still have a lot of uncertainty attached to them, but the wave height is estimated at around 650 m and that is in my view using a number of conservative assumptions, explained Dr Day.
Other methods have predicted anything from 1 km to 3 km.
As the wave spreads out it looses its strength, but it will still be several tens of metres high as it strikes the United States.
But it would not be just the eastern seaboard of America to suffer. The wave would spread out in a circular pattern like the ripples generated by dropping a stone into a pond.
They would reach as far as Florida and the Caribbean as well as bending back to hit Western Europe.
The big question of course is how probable is this nightmare scenario? It is one which is answered simply by Professor Bill McGuire, also from the Benfield Greig Centre.
Theres no if about it, he stated. It will happen, its just a question of when.
But when exactly? Here at least there is some comfort. While the landslide will be caused by volcanic activity it will not necessarily happen the very next time the island erupts.
Indeed, it may take many more eruptions before the split finally occurs.
And eruptions do not happen on a regular basis.
The last one was in 1971 and those in the future may only strike at intervals of anything from a few decades to a couple of centuries.
The probability of a giant tsunami being generated in any one century, therefore, is estimated by Dr Day at 5%.
When it does finally happen, however, there may be little opportunity for New York and the rest of the eastern coast of the United States to head for the hills.
No volcano ever erupts without some warning, said Professor McGuire.
The difficult thing is determining whether that particular eruption will be the one to cause the landslide or not.
When it does go it will go in a matter of minutes and I wouldnt like to be around measuring things at that point.New York (right) and much else could be devastated by a tsunami emanating from the eruption of La Palma, the most volcanic of the Canary islands, whose main port is Las Palmas (below). A volcanic eruption (left) last came on La Palma in 1971 - and those in future may come at any time The difficult thing is determining whether that particular eruption will be the one to cause the landslide or not.
Was some time earlier, and might be again. Probably won't be real soon, though. Long term investment.
North of the rapids on the Brazos river, I trust? (They were formed 65 mya by the impact tsunami from the strike at Chicxulub that wiped out the dinosaurs)...
Here you go:
Tree-ring study enables researchers to link massive American earthquake to Japanese tsunami in January 1700
Stumps of long-dead western red cedar trees are revealing new details of a cataclysmic earthquake along North America's west coast more than 100 years before the arrival of the first European occupants.
Two University of Washington researchers believe that evidence in the dead wood confirms that in the year 1700 a great earthquake struck the Pacific Northwest coast and set off a tsunami, a train of massive ocean waves, that flooded coastal Japan.
The scientists are reporting in tomorrow's Nature magazine (Oct. 30) that they have dated the demise of six trees, along 60 miles of the Washington coast, by "reading" the annual ring patterns in the trunks and roots of the stumps. They found that each of the trees produced its final ring in the 1699 growing season. No further rings were evident, indicating that the trees were dead by the spring of 1700.
"We are saying this huge earthquake really happened," says David Yamaguchi, a UW dendrochronologist, or tree-ring analyst. Last year Japanese scientists reported that a tsunami that hit Honshu island on January 27, 1700, was probably caused by an earthquake on the Cascadia subduction zone, a 600-mile coastal fault stretching from British Columbia to northern California.
Based on the size of the tsunami, the Japanese researchers estimated the earthquake at magnitude 9, even though no Cascadia fault earthquake of magnitude 5 or above has ever been recorded by seismologists. The Nature article concludes that the tree dates "mean that the northwestern United States and adjacent Canada are plausibly subject to earthquakes of magnitude 9."
The second author of the paper, Brian Atwater of the U.S. Geological Survey and an affiliate UW professor, says the new dates clinch the argument that massive earthquakes can occur where the Juan de Fuca plate, an Oregon-sized slab of crust, collides with a large block of continental crust called the North America plate. The Cascadia fault forms the boundary between the two plates.
Over the past decade, Atwater and other researchers have discovered geologic evidence of repeated magnitude 8 or larger earthquakes along the Cascadia fault. However, the size of the 1700 earthquake remains a subject of much debate, which the tree-ring dates do not resolve, says Atwater. Some scientists have proposed a ceiling of magnitude 8; others have suggested a maximum magnitude of 9.5.
Only a handful of magnitude 9 earthquakes have occurred globally this century. The largest earthquake in the Pacific Northwest in historic times was a magnitude 7.4 in the north Cascade mountains in 1872. This was not on the Cascadia fault.
Yamaguchi first "read" the cedar stumps to show that a great earthquake happened some time after 1690. UW researcher Minze Stuiver then pinned the earthquake to between 1695 and 1710 with precise radiocarbon dating. This led the Japanese scientists to propose the Cascadia fault as the likely origin for the 1700 tsunami.
To test the Japanese theory, the UW researchers dug up the roots of a dozen cedar stumps from the Copalis River south to the Columbia River. In half of these stumps, the dating was inconclusive, but in six they found evidence that the trees had died before the start of the 1700 growing season.
Then they all moved to Columbus and founded Ohio State...
(grin) Go Blue!
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Channeled Scablands Theory
But this one only came in about a 1000 feet.
Now that we have seen an actual major tsunami, it seems Fairbanks would be safe even if it were a foot above mean high tide.
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Note: this topic is from 10/28/2002. Thanks blam.