Tsunami & Mega-Tsunami

EnolaGaia

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#31
markrkingston1 said:
I can't help feeling that the possibly greater-than-generally-expected prevalence of tsunamis in this area might be relevant to analysis of the 1607 Bristol Chanel Flood.
That's been put forward as a hypothesis already ... See the 2005 / 2007 postings earlier in this thread.

However ... Based on a number of factors (including similar flooding in Norfolk at the same time), this 2006 paper argues it was a storm surge ....

Horsburgh, K.J. and M. Horritt (2006) The Bristol Channel floods of 1607 - reconstruction and analysis. Weather, Vol. 61, 10, 272-277.

The first page of the paper can be viewed at:

http://onlinelibrary.wiley.com/doi/10.1 ... 5/abstract
 

markrkingston1

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#32
EnolaGaia said:
markrkingston1 said:
I can't help feeling that the possibly greater-than-generally-expected prevalence of tsunamis in this area might be relevant to analysis of the 1607 Bristol Chanel Flood.
That's been put forward as a hypothesis already ... See the 2005 / 2007 postings earlier in this thread.

However ... Based on a number of factors (including similar flooding in Norfolk at the same time), this 2006 paper argues it was a storm surge ....

Horsburgh, K.J. and M. Horritt (2006) The Bristol Channel floods of 1607 - reconstruction and analysis. Weather, Vol. 61, 10, 272-277.

The first page of the paper can be viewed at:

http://onlinelibrary.wiley.com/doi/10.1 ... 5/abstract
Yup, I'm aware of that. My point is that, despite the evidence for a storm surge (which, as I recall is not at all conclusive, merely suggestive), the balance of probabilities suggests that a (seismic or landslide) tsunami is not as unlikely an explanation as it might seem.

To put it another way, the evidence in favour of a storm surge is not evidence against the existence of a tsunami.

Some of the damage that was apparently caused by the 1607 event seems impossible for a storm surge (or even a so-called meteotsunami) to have caused.

It is possible, althought unlikely, that a storm surge and tsunami (a non-meteotsunami I mean) coincided.

In summary, I do not deny the evidence in favour of a storm surge occurring at that time but such evidence does not necessarily provide an adequate explanation for all aspects of the event. The greater than commonly realised preponderance of tsunamis offers reasons to consider a larger set of possible explanations.


**edit**
Corrected strained phraseology.
 

EnolaGaia

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#33
True ... Given the paucity of detailed evidence on the context (weather, etc.) it will probably never be possible to conclude exactly what caused the flooding.

The strongest clue tending toward the tsunami theory is the alleged existence of accounts describing the sea receding before the wave / surge. The strongest clue in favor of a meteorologically-induced surge is the alleged coincidence of flooding on both the west and east coasts.

There's little or no way to differentiate between the two theories based on the stratigraphic evidence. Both involve an incursion of water and the laying down of sediment.

A peripheral issue is that the event occurred during usage of the Julian calendar, and one must be careful in correlating contemporary records' dating with the eventual calendar.
 

rynner2

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#34
Scientists batshit crazy for tsunami research! ;)

Sumatra coastal cave records stunning tsunami history
By Jonathan Amos, Science correspondent, BBC News, San Francisco

A cave on the northwestern coast of Sumatra holds a remarkable record of big tsunamis in the Indian Ocean.
The limestone opening, close to Banda Aceh, retains the sandy deposits washed ashore by huge, earthquake-induced waves over thousands of years.

Scientists are using the site to help determine the frequency of catastrophes like the event of 26 December 2004.
This is being done by dating the cave's tsunami-borne sediments, which are easy to see between layers of bat droppings.
"The tsunami sands just jump right out at you because they're separated by guano layers. There's no confusing the stratigraphy (layering)," explains Dr Jessica Pilarczyk.
"It makes for interesting field work; I'm not going to lie to you. The bats get very excited when people are disrupting their space. But from a geologist's point of view, this cave has the most amazing stratigraphy," she told BBC News.

Dr Pilarczyk was speaking here in San Francisco at the American Geophysical Union (AGU) Fall Meeting, the world's largest annual gathering of Earth scientists.
She is part of a team of researchers - led by Prof Charles Rubin - from the Earth Observatory of Singapore, an institute of Nanyang Technological University that is investigating the coastal history of Indonesia's largest island.

Sumatra's proximity to the Indo-Australia and Sunda tectonic plate boundary, and the giant earthquakes that occur there, means its shores are at risk of major inundations.
Understanding how often these occur is important for policy and planning in the region.
The Acehnese cave lies about 100m back from the swash zone at current high-tide. Its entrance is also raised somewhat, and this prevents all waters from getting into the opening - apart from tsunamis and severe storm surges.

Dr Pilarczyk and colleagues have dug trenches through the alternating bands of bat guano and sand to piece together the cave's history.
The scientists know they are looking at tsunami deposits because they can find debris in the sediments of seafloor organisms such as microscopic foraminifera. Only the most energetic waves could have lifted and carried this material into the cave.

The investigations are ongoing but the team thinks it can see deposition from perhaps 7-10 tsunamis. The geometry of the cave means these events would likely have been generated by earthquakes of Magnitude 8, or more. By way of comparison, the devastation wrought by 26 December 2004 stemmed from a M9.2 tremor.

Dating the old deposits is obtained by radiocarbon analysis of organic debris caught up in the bands, such as molluscs and pieces of charcoal from old human-lit fires.
Work is under way to date even the insect remains eaten by the bats and now immersed in the guano layers.

Today, the cave is so full of sand and bat droppings that any new event will essentially overwash and erode the most recent deposits. "The 2004 tsunami completely inundated the cave," comments Prof Rubin.
Nonetheless, the stratigraphy from about 7,500 to 3,000 years ago is impeccable.
"What we think we have is actually a near-complete sequence of late-Holocene deposits. This is amazing because usually the records we have are fragmentary at best. This coastal cave is a unique 'depot centre', and it's giving us a remarkable snapshot of several thousands of years, allowing us to figure out every single tsunami that would have taken place during that time," said Dr Pilarczyk, who is affiliated also to Rutgers University, US.

The team's other investigations along the Acehnese coast are filling in the period from 3,000 years ago to the present.
And the take-home message from all this research is that the biggest tsunamis are not evenly spaced through time. Yes, there can be long periods of quiescence, but you can also get major events that are separated by just a few decades.

Co-investigator Prof Kerry Sieh says this is a cautionary story.
"2004 caught everybody by surprise. And why was that? Because nobody had been looking back to see how often they happen, if they'd ever happened," he told BBC News.
"In fact, because people thought they had no history of such things, they thought it was impossible. Nobody was prepared, nobody had even given it a second thought. So the reason we look back in time is so we can learn how the Earth works and how it might work during our watch."

http://www.bbc.co.uk/news/science-environment-25269698
 
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#35
Even in Switzerland. Images and audio at link.

Scientists study Swiss lake tsunamis

How do you prepare for tsunamis that come only every 1,000 years or so?

This is the issue Swiss geoscientists are wrestling with as they study the country's big lakes.

Some of these water bodies around the Alps have been known to experience huge waves that were driven by sub-surface landslides, which were themselves triggered by earthquakes.

The researchers' work indicates such hazards still exist but the likelihood of future events is very small.

"These incidents happen much less frequently than flooding or avalanches, which makes tsunamis a very hard-to-grasp hazard that is simply not in the minds of the population. But as geoscientists we have a duty to look at the problem and to let people know the risks," explained Prof Flavio Anselmetti from the University of Bern.


He was speaking here in Vienna at the European Geosciences Union General Assembly.

The professor recalled the estimated Magnitude 5.9 quake in the Alps region in AD 1601 that prompted sediment on sub-surface slopes in Lake Lucerne to slide down on to the lake basin floor.

As the muds descended, they alternately made the water column above slump and then rise, setting off a sequence of waves that inundated coastal communities.

The chronicles from the time talk of mountains of water appearing in the middle of the lake, and of water reaching inland to a distance of 1,000 steps or three gunshots. This would be about a half to one kilometre.

Floating debris was described also to have been caught in trees to the height of two halberds. The weapon famously associated with Medieval Swiss soldiers features an axe on the end of a long staff and measures about 2m.

Lake Lucerne
The shores of Lake Lucerne are today far more populated than in AD 1601
Prof Anselmetti and colleagues have studied the collapsed sediments in the lake, and have simulated the likely tsunami waves they generated.

They can show how the waves move and how they can be reflected off opposite shores in a complex pattern.

"Those slopes that were triggered in 1601 - they will need quite a while to be 'recharged'," explained Prof Anselmetti.

"But there are other areas where we can see metres of soft sediment that are more or less ready to be released, so to speak. And we do geotechnical analysis in order to quantify just how much we need to shake these slopes in order to make them unstable.

"So, actually, we can predict to a certain degree what sort of earthquake is required to trigger which kinds of slopes, and because our numerical codes then allow us to calculate the resulting tsunami wave, we are somehow able to say which areas will be mostly affected."

The major qualification here is that the frequency of quakes of sufficient magnitude occurring in the region is small.

Those same collapsed sediments in Lake Lucerne can be used like ancient seismograms to time the reoccurrence of big tremors.

This reveals there were six destabilisation events in the past 15,000 years similar in size to 1601.

A recurrence interval of 1,000 to 2,000 years is too long for one generation of people to pay much attention to, concedes Prof Anselmetti. Nonetheless, the risks need to be quantified, he says.

"Somehow it is our duty as geologists to remind society that this is natural hazard - we may have tsunami waves, they occur rarely, but it is a natural hazard they should be aware of without making of course too much of a panic."

The summation of the research is being presented to the EGU meeting this week by the University of Bern's Michael Hilbe.
http://www.bbc.com/news/science-environment-27196759
 
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#36
A new NASA study is challenging a long-held theory that tsunamis form and acquire their energy mostly from vertical movement of the seafloor.

An undisputed fact was that most tsunamis result from a massive shifting of the seafloor—usually from the subduction, or sliding, of one tectonic plate under another during an earthquake. Experiments conducted in wave tanks in the 1970s demonstrated that vertical uplift of the tank bottom could generate tsunami-like waves. In the following decade, Japanese scientists simulated horizontal seafloor displacements in a wave tank and observed that the resulting energy was negligible. This led to the current widely held view that vertical movement of the seafloor is the primary factor in tsunami generation.

In 2007, Tony Song, an oceanographer at NASA's Jet Propulsion Laboratory in Pasadena, California, cast doubt on that theory after analyzing the powerful 2004 Sumatra earthquake in the Indian Ocean. Seismograph and GPS data showed that the vertical uplift of the seafloor did not produce enough energy to create a tsunami that powerful. But formulations by Song and his colleagues showed that once energy from the horizontal movement of the seafloor was factored in, all of the tsunami's energy was accounted for. Those results matched tsunami data collected from a trio of satellites -the NASA/Centre National d'Etudes Spatiales (CNES) Jason, the U.S. Navy's Geosat Follow-on and the European Space Agency's Environmental Satellite. ...

https://phys.org/news/2017-04-nasa-long-held-tsunami-formation-theory.html
 

EnolaGaia

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#37
This Forbes article:

World's Tallest Tsunami Hit An Alaskan Bay In 1958 And It Was Not The First Of Its Kind

... describes the 1958 Lituya Bay (Alaska) tsunami, which involved a massive rockfall spawning a mega-wave surging out to sea rather than the other way around.

This event has sometimes been cited as the tallest (demonstrable) wave event in the historical record, based on evidence of the initial inland 'splash' reaching a height of over 1,700 feet. :eek:

(By the time it cleared the coastline and menaced boats, it had diminished to a 'mere' 50 - 75 feet according to the few, and very lucky, survivors who'd been in its path.)

This article goes on to outline evidence indicating the 1958 event wasn't unique, and that there may well have been as many as five similar events there from the mid 19th century onward.
 

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#38
I think the 1958 incident is the one where a father & son miraculously survived the tsunami in their fishing boat isn't it?
 

EnolaGaia

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#39
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#40
My Bunnie Lies Over The Ocean...

The deadly tsunami that struck north-east Japan in 2011 has carried almost 300 species of sea life thousands of miles across the Pacific Ocean to the west coast of the United States.

In what experts are calling the longest maritime migration ever recorded, an estimated one million creatures – including crustaceans, sea slugs and sea worms – made the 4,800-mile (7,725km) journey on a flotilla of tsunami debris.

“This has turned out to be one of the biggest unplanned natural experiments in marine biology – perhaps in history,” said John Chapman, an expert at Oregon State University who co-authored a study of the creatures published this week in the journal Science.

The towering tsunami, triggered by a 9.0 magnitude earthquake on the afternoon of 11 March 2011, generated five million tonnes of debris from the three prefectures of Iwate, Miyagi and Fukushima.

About 70% sank quickly to the ocean floor, according to experts, but countless buoys, docks, boats and other items with buoyancy were swept out to sea.

Between June 2012 and February this year 289 Japanese species attached to 600 pieces of debris washed up on beaches in the states of Washington, Oregon, California, Alaska and Hawaii, as well as in the Canadian province of British Columbia,according to the study. ...

https://www.theguardian.com/world/2...japan-to-us-west-coast?CMP=Share_iOSApp_Other
 

EnolaGaia

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#41
Submarine landslides are blamed for circa 20% of all tsunamis and a significant proportion of really big historical tsunamis. Strangely, paleo-geological evidence doesn't support the obvious notion these slides were caused by quakes shaking precariously positioned material sliding down steep angles of descent. This new study suggests one of the most elementary marine life forms - diatoms - may facilitate such mega-slides.

Sea Slime Can Trigger 65-Foot Mega-Tsunamis
A layer of ooze made of microscopic fossils may underlie Earth's biggest landslides, a new study finds.

The biggest landslides on Earth are not on dry land but rather on the seafloor. ...

Submarine landslides are not just perils for life underwater; they can trigger catastrophic tsunami that can wreak havoc on land. For example, prior work suggested that the Storegga megaslide triggered a tsunami that deluged surrounding coasts with waves up to 65 feet (20 meters) high. ...

Oddly, the largest submarine landslides happen on nearly flat slopes inclined less than 3 degrees. Prior work found the kind of terrain left in the aftermath of these landslides suggests great expanses of seafloor glided over weak layers of material embedded within more-stable layers of sediment.

Scientists have proposed many possibilities for what material could make up these weak layers, including liquefied sand and "flammable ices" known as clathrates ... However, it was nearly impossible to say what these weak layers were because they were typically destroyed along with the landslides.

Now, in a first, [ ... researchers ... ] have identified the weak layer behind a submarine megaslide — a layer of ooze made of microscopic fossils. ...
FULL STORY: https://www.livescience.com/61756-sea-slime-mega-tsunamis.html

ABSTRACT of the Published Research: https://pubs.geoscienceworld.org/gs...for-the-generation-of?redirectedFrom=fulltext
 

EnolaGaia

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#42
Here's a recent story including a photo illustrating the effect of a meteotsunami (a meteorologically-induced wave or rise in shoreline water level).

Meteotsunami spotted on Lake Michigan near Traverse City
... A large complex of thunderstorms that parked out over Lake Michigan on Saturday afternoon produced what's known as a meteotsunami.

Translated literally, a meteotsunami means a large wave caused by weather.

Strong winds combined with a drop in pressure pushed water toward the eastern Lake Michigan shoreline and then rippled south, into Grand Traverse Bay.
636649019627763356-metrotsunami.jpg

SOURCE: http://ux.freep.com/story/news/loca...ake-michigan-traverse-city/709328002/?ref=yfp

SEE ALGO: https://en.wikipedia.org/wiki/Meteotsunami
 
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#43
Ancient graves provide evidence of tsunamis.

UNSW scientists have shown – for the first time – that a series of high-profile burial sites in the Pacific, Mediterranean and northern Scotland were likely related to catastrophic tsunamis. The work was published in the Journal of Archaeological Method and Theory.

Honorary Professor James Goff from the PANGEA Research Centre at UNSW Sydney, who co-authored the paper, says the research provides new insights into past human-environment interactions and a new perspective on past catastrophic events.

"Tsunamis have never been considered as explanations for burial sites before – which is why no prehistoric coastal mass graves have ever been identified in the archaeological record as tsunami-related.

"Proving that a site is related to a past tsunami could lead to a fundamental rewrite of how we interpret coastal human settlement in prehistory, and change what we thought we knew about the culture and people living in the region at the time. It could also have dramatic implications for how archaeologists analyse a site."

The researchers looked at coastal mass burial sites in the Solomon Islands and Vanuatu as well as in Orkney and Shetland. The mass graves cover a long timeframe of human history – they are from about 5000 years ago to as recent as about 500-600 years ago.

"We already know that tsunamis have occurred in all the areas that we explored in this study, and the ages for mass burials match those of the geological evidence for past events," Professor Goff says.

"Looking at the evidence from the burial sites considering the potential of tsunamis, we were able to make a strong case for many of these sites being related to major tsunamis, as opposed to more standard explanations like warfare or an epidemic.

"For example, at the site in the Solomon Islands, the method of burial and the age of the people buried is consistent with what we'd expect after a tsunami – people were buried in atypical positions, and they're uncharacteristically young."

https://phys.org/news/2018-08-prehistoric-mass-graves-linked-tsunamis.html
 

EnolaGaia

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#44
Mega-tsunami? Ha! Merely a splash ...

This new research modeled the tsunami triggered by the 'dinosaur-killer' Chicxulub impact, and it suggests the wave was on the order of 3 times as tall as the tallest known historical wave (Alaska; 1958; see post #37), and it propagated worldwide.

Dinosaur-Killing Asteroid Triggered Mile-High Tsunami That Spread Through Earth's Oceans

When the dinosaur-killing asteroid collided with Earth more than 65 million years ago, it did not go gently into that good night. Rather, it blasted a nearly mile-high tsunami through the Gulf of Mexico that caused chaos throughout the world's oceans, new research finds.

The 9-mile-across (14 kilometers) space rock, known as the Chicxulub asteroid, caused so much destruction, it's no wonder the asteroid ended the dinosaur age, leading to the so-called Cretaceous-Paleogene (K-Pg) extinction.

"The Chicxulub asteroid resulted in a huge global tsunami, the likes of which have not been seen in modern history," said lead researcher Molly Range, who did the research while getting her master's degree in the Department of Earth and Environmental Sciences at the University of Michigan. ...

Range and her colleagues presented the research, which has yet to be published in a peer-reviewed journal, at the American Geophysical Union's annual meeting on Dec. 14 in Washington, D.C. And the research, first reported by EOS, is novel. "As far as we know, we are the first to globally model the tsunami from impact to the end of wave propagation," Range told Live Science. ...
FULL STORY: https://www.livescience.com/64426-dinosaur-killing-asteroid-caused-giant-tsunami.html

SEE ALSO: https://eos.org/articles/huge-global-tsunami-followed-dinosaur-killing-asteroid-impact
 

EnolaGaia

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#45
The disastrous tsunamis triggered by the 2018 Anak Krakatoa eruption were notably tall. New research indicates they were significantly taller prior to hitting land.
Deadly Tsunami Unleashed by 'Child of Krakatoa' Volcano Surged Up to 150 Metres Tall

The Anak Krakatoa volcano in Indonesia - the so-called "Child of Krakatoa" - was formed by one of the most deadly volcanic disasters in modern history. Last year, unbeknownst to the world, it was close to unleashing something similar.

In 2018, as Anak Krakatoa violently erupted, its middle suddenly collapsed, triggering a tsunami that claimed more than 400 lives on the islands of Sumatra and Java.

When the waves reached civilisation less than an hour after the trigger, this wall of water was more than 10 metres (32 feet) high. And yet, researchers from Brunel University London and the University of Tokyo say, this was a mere fraction of its former glory.

At its peak, they estimate, the tsunami was anywhere between 100 and 150 metres tall (330 to 490 ft), which is larger than the Statue of Liberty and at least as high as London's Big Ben.

As these huge waves sped across the ocean, like ripples in a pond, they gradually shrank from gravity and friction until, at some 80 metres high, they finally hit land. ...
FULL STORY: https://www.sciencealert.com/the-20...atoa-volcano-was-taller-than-london-s-big-ben
 
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