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RE: Ancient New York Tsunami
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Could an earthquake hit New York City? History says yes, but not like 9.0 magnitude Japan earthquake

Could a major earthquake shake the Big Apple to its core?
If the past is any indication, the answer is yes, says John Armbruster, a seismologist at Columbia University's Lamont-Doherty Earth Observatory.
Based on historical precedent, Armbruster says the New York City metro area is susceptible to an earthquake of at least a magnitude of 5.0 once a century.

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New Jersey Tsunami
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66-Foot Waves Hit New York in Ancient Asteroid Splashdown

Cosmic impacts have been known to cause tsunamis in the past. For instance, scientists have found evidence that the Chicxulub impact in Mexico, which may have ended the age of dinosaurs, triggered gigantic waves.
Now researchers have evidence suggesting that an asteroid roughly 183 meters wide crashed off the coast of New Jersey and sent tsunamis surging toward what is now New York City some 2,300 years ago.

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L

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RE: Ancient New York Tsunami
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While most tsunamis result from subduction zone earthquakes in deep trenches, they can also occur where oceanic volcanoes erupt catastrophically or where large landslides run down steep underwater slopes. The biggest tsunamis that might ever occur come from asteroid impacts, but so far, no large ones have struck since humans have been on the scene. The 6-mile-wide asteroid that smashed into the Gulf of Mexico 65 million years ago was travelling at 45,000 mph and created waves hundreds of feet high that ran up a then inland sea as far as South Dakota. No worries though, asteroid impacts even one-one hundredth that size hit Earth only once in about a million years.

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A huge wave crashed into the New York City region 2,300 years ago, dumping sediment and shells across Long Island and New Jersey and casting wood debris far up the Hudson River.
The scenario, proposed by scientists, is undergoing further examination to verify radiocarbon dates and to rule out other causes of the upheaval.

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Long Island Oceanic Impact
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Title: Evidence for a Tsunamigenic Impact Event in the New York Metropolitan Area Approximately 2300 B.P.
Authors: Cagen, K. T.; Abbott, D.; Nitsche, F.; West, A.; Bunch, T.; Breger, D.; Slagle, A.; Carbotte, S.

Oceanic impacts are a growing source of concern for the scientific community. Though the Earth is ~70 percent covered with water, and logic would therefore dictate that ~70 percent of impacts occur in the oceans, scientific investigations have focused on continental events. This is in part due to the difficulties inherent in examining submarine impact structures. Oceanic impacts lack many of the known features of continental events; however, oceanic impacts, unlike their continental counterparts, produce catastrophic tsunami events that may be used to identify them. Recent discoveries point to a tsunami event that affected the New York metropolitan area approximately 2300 years ago (Goodbred et al. 2006). Here it is shown that impact ejecta found in the tsunami deposit layer indicate an oceanic impact as the source of the tsunami. The sharp resolution of the stratigraphic study of the cores suggests that the sediment containing the impact ejecta was deposited in a tsunami-like event, rather than reworking from an older event. Samples were taken from the layer in sediment cores CD01-01, CD01-02, SD30, and VM32-2 from the Hudson River. Layer thickness ranged from approximately half a meter in CD01-02 to four centimeters in VM32-2. Individual ejecta grains were identified through an examination of the tsunami layer samples with optical and electron microscopy, as well compositional analysis via energy dispersive X-ray spectroscopy. Carbon and aluminium silicate impact spherules were found in the samples. Also present in the samples were shock-metamorphosed phases of feldspar, ilmenite, and olivine exhibiting planar deformation features and shock lamellae consistent with studies of known impact ejecta. TEM studies of the spherules revealed the presence of associated hexagonal nanodiamonds, also known as lonsdaleite, which are uniquely related to shock formation. In addition, the New York area lacks the extreme seismic and volcanic activity that might produce similar results, leaving a hypervelocity bolide impact as the most likely source for the tsunami event and associated impact ejecta. As oceanic impacts pose a serious threat to coastal communities around the world, it is necessary to understand both their frequency and effects. It is hoped that this method of identifying an oceanic impact via the ejecta found in tsunami deposits will improve our understanding of submarine impact events.

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RE: Ancient New York Tsunami
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The evidence included deformed rocks; rare microscopic "nanodiamonds"; and microscopic, perfectly round rocks called spherules, which form when molten and vaporised rock are flung into the air by a space impact and then solidify in the temporary vacuum created by the blast.
Nothing as big as a crater has been found, but Dallas Abbott, a Columbia University impact expert, estimates that the space rock would have had a diameter of between about 50 metres and 150 metres. Any smaller, and a major wave would not have formed and the rock would have exploded before hitting Earth. Any bigger, and the strike would have created "impact glass" - forged in the extreme heat of an impact blast - which has not been found as of yet.

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Did a big wave hit the Big Apple way back when? Scientists say a tsunami struck the New York City area 2,300 years ago, possibly as a result of a meteorite crashing into the Atlantic Ocean.

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Ancient New York Tsunami
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The tsunami washed over Fire Island and, to the west, waves perhaps as high as 20 feet spilled into Lower Manhattan. The furious onrush of water left sediment a foot and a half deep on the Jersey Shore, and debris cascaded far up the Hudson River.
No, theres no need to rush to higher ground, commandeer a rowboat in Central Park or empty the closet to grab the rubber boots. This disaster occurred about 2,300 years ago, though how bad it was, or even if it was a tsunami, remains in dispute.

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Ancient New York Tsunami
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Long before New York City was the Big Apple, or even New Amsterdam, a giant tsunami crashed ashore.
It was 2,300 years ago. The Palisades that frame the Hudson River were whisper-quiet, the sandy beaches of Long Island and New Jersey empty, and Manhattan was still just an unbroken sylvan carpet.
Then came the mammoth wave, roaring into the serenity. No one knows for sure what caused it, but new clues found in the Hudson's silt suggest an asteroid 100 meters in diameter slammed into the Atlantic Ocean nearby.
While sifting through samples, Katherine Cagen of Harvard University and a team of researchers found carbon spherules -- perfectly round particles that form in the extreme pressures of an impact.

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