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Posted on 10/04/2015 7:00:40 PM PDT by SeekAndFind
Waves the size of the Chrysler building may seem like they belong in a movie trailer, but scientists have recently found that megatsunamis are all too real.
Scientists say that 73,000 years ago, a large flank (or slope) from the volcanic island Fogo in the Cape Verde islands off the coast of Africa fell into the ocean and triggered a tsunami that could – quite literally – move mountains.
“You’re displacing a huge mass, which must generate movement of water,” Ricardo Ramalho, the lead researcher behind the study, told The Washington Post. “And in the case of volcanic flank collapses they can be very acute, because you have all the mass collapsing basically into the oceans.”
Waves the size of the Chrysler building may seem like they belong in a movie trailer, but scientists have recently found that megatsunamis are all too real.
Scientists say that 73,000 years ago, a large flank (or slope) from the volcanic island Fogo in the Cape Verde islands off the coast of Africa fell into the ocean and triggered a tsunami that could – quite literally – move mountains.
“You’re displacing a huge mass, which must generate movement of water,” Ricardo Ramalho, the lead researcher behind the study, told The Washington Post. “And in the case of volcanic flank collapses they can be very acute, because you have all the mass collapsing basically into the oceans.”
So what was Dr. Ramalho’s proof for a megatsunami? Rocks. Really, really big rocks.
When Ramalho was on Santiago in 2007, he found large boulders on top of a high plateau, near a sheer, vertical cliff. Ramalho and his colleagues were able to trace the boulders’ origin to the cliff below because the rock types “exclusively crop out on the cliff faces and lower slopes of the plateau,
(Excerpt) Read more at csmonitor.com ...
I recall reading that there are signs of tsunamis on the east coast. Around Chesapeake or down into the Carolinas. I think the assumption was either a comet hit or ocean floor uplift.
While I’m hardly an expert, that result is a lot closer to what I’d expect based on the raw physics.
When energy starts as a central source and radiates outward, the energy is spread out proportionately... it does not amplify, for that’s impossible without more energy.
This is why tsunami forecasts are lower for more distant target zones...anybody who says this event would be different is simply hyping disaster shows (looking at you, Discovery Channel).
You had me and then you lost me. An expanding wave on a surface must necessarily diminish in linear intensity as 1/d, since the wave has a certain amount of energy which is distributed over a perimeter of length 2pi d.
I saw a show some time ago depicting this type of wave, but confined to a channel, somewhere in Alaska. Of course, the narrative did not point this out explicitly, but it was quite clear that this was the case. They were just angling for hype. I took due notice!
It could have been hype, I don’t know. Just because a thing is on Nat Geo does not mean a thing is true.
However, tsunamis created by ocean floor displacement also travel huge distances without losing any significant energy.
They don’t even stop once they have hit land.
The program I saw, which I have looked for on youtube for any highlights but could not find, discussed high speed land slides, which was cliff face breaking off straight down into water, and they also discussed long run out landslides hitting water, where a large mass of land travels downhill and then into water, also displacing a large amount of water greater than the amount of land actually hitting it because of air pulled in behind it.
They gave the impression that whatever land event may have caused Hawaiian fossils to appear on Australian mountains would have been pretty epic, and I think, though I may be mistaken, that they associated it with volcanic activity and island creation.
bmp4L8R—like after breakfast and coffee.
EQ’s have only been shown to show maximum waves of about 30 meters iirc - due to the “limited” amount of uplift in any one event (on the order of tens of meters). Whereas a landslide can fall from hundreds of meters. Of course the landslide is a pinpoint as you say, and a fault can run for miles.
The following paper gives a rebuttal against the huge landslide tsunami. The probability is that a landslide would occur over a period of time, rather than one huge single block of rock.
http://blogs.agu.org/landslideblog/2013/12/13/canary-islands-tsunami/
I have read of the Alaskan wave - a man and his son rode it out in a boat. Got swept over a peninsula that was hundred+ feet tall iirc!! Quite the ride. And yes - it was a fairly tight fjiord. I think they also said the natives had stories of this happening in this fjiord - and so their camps were around a bend near the ocean.
I find it hard to believe that these huge boulders were tossed 800 feet up by a tsunami. Volcanic activity they say - I wonder if they are huge pyroclastic “bombs”? Although I would think there would be additional evidence for that.
Worker ants.
You lost me on the math! But one thing - the tsunami (either due to submarine EQ or landslide) doesn’t show much if anything on the water surface mid-ocean. But it is the shallowing of the water at the shelf that concentrates the energy. Is your math more for waves at the surface?
EQ’s have only been shown to show maximum waves of about 30 meters iirc - due to the “limited” amount of uplift in any one event (on the order of tens of meters). Whereas a landslide can fall from hundreds of meters. Of course the landslide is a pinpoint as you say, and a fault can run for miles.
The following paper gives a rebutal against the huge landslide tsunami. The probablity is that a landslide would occur over a period of time, rather than one huge single block of rock.
http://blogs.agu.org/landslideblog/2013/12/13/canary-islands-tsunami/
I have read of the Alaskan wave - a man and his son rode it out in a boat. Got swept over a pennisula that was hundred+ feet tall iirc!! Quite the ride. And yes - it was a fairly tight fjiord. I think they also said the natives had stories of this happening in this fjiord - and so their camps were around a bend near the ocean.
I think that's correct, since a wavelength much less than the depth is what defines this term ( i.e. surface wave.) Tsunamis originate from broad upheavals of the ocean floor, and have a long wavelength and high speed of propagation.
A landslide can produce a high amplitude, but not a long wavelength, as far as I understand it.
That was it.
I guess like dumping a rock into the kiddie pool produces a different type/size of wave than trying to lift one edge to move the pool produces a whole ‘nother kind of wave. (That usually ends up with your shoes getting wet).
I call Bull Crap on this. Calculate the volume of land that will slide into the water and displace water. It’s not ANYWHERE near the displacement that occurs in major underwater earthquakes. The following linked article...
... explains somewhat the size of displacement that occurs to cause a Tsunami the size of the 2011 Japanese tsunami.
EXTRACT FROM LINKED ARTICLE:
“... Experts calculate the fault—or the boundary between two tectonic plates—in the Japan trench slipped by as much as 164 feet (50 meters). Other similarly large magnitude earthquakes, including the 9.1 Sumatra event in 2004, resulted in a 66-to-82 foot (20-to-25 meter) slip in the fault.
“We’ve never seen 50-meter [slips],” said Kelin Wang, a geophysicist with the Geological Survey of Canada in British Columbia.
The next largest slip would probably be the Chile earthquake in 1960, said Wang, who was not involved in the research. Based on the limited data recorded from that earthquake, the fault slipped by 98 to 131 feet (30 to 40 meters).
Most of the movement occurred horizontally, he explained. But because the plates are wedged together at this trench, that horizontal displacement still managed to thrust up enough seawater to produce the killer tsunami that hit Japan. ...”
I would agree with that.
Note: this topic is from . Thanks SeekAndFind.
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Note: this topic is from . Thanks SeekAndFind.
Yep, that was quite an "instant irrigation project." It really changed the morphology of the region. I don't know how old you are but maybe you recall a huge patch of tumbled and rounded basalt rocks that the receding waters dumped near Bliss, ID. The guy who owned the Fearless Ferris gas stations posted a sign for weary tourists to enjoy: "Petrified watermelons -- take one home to your mother-in-law."
There were many similar floods during the Big Melt when the Pleistocene glaciers turned back to liquid water. I'm sure that's the source of the "Great Flood" stories that persist in many cultures around the world.
The date 73,000ya is pretty close to the 74,000ya date for the eruption of Toba leaving a crater 16 x 65 miles. I wonder if these events were somehow connected. Was the earth in a particularly restless mode in that millenia?
Apparently after a major Alaskan earthquake in the 1900s there was a tsunami that ran 1,000 feet high up a fiord.
The Alaskan event you mentioned was at Lituya Bay -- a tributary to the fjord suffered a massive ice landslide, which blooped right into the water, and sent a big wave in both directions. There were actually a number of campers along the Bay, some of whom survived the event. The debris line reached inland to 1700 feet elevation (roughly a third of a mile). There was no significant tsunami in the Pacific, AFAIK.
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