Earthquakes and Climate Change - Related?

Here is another example of a bright student trying to put things together. Sometimes there are things that are big and in the same place - but are still unrelated:

Q:
I am training to become a teacher, and my professor wants us to become more familiar with supplemental resources, such as this website. So he has asked us to generate a question and submit it to you and then give him the answer we get back. I thank you in advance for your feedback! Question: Are earthquakes, like storms are said to be, tied to climate change? Can you explain why or why not? Thank you so much! 
-Sarah S

A: 
No, earthquakes are not tied to climate change, and the main reason is because of they are not coupled (or very poorly coupled): Other than very temporary shaking of the ground, which is connected very poorly with the atmosphere, the huge energies involved in earthquakes are generated in, released in, and remain below the Earth's surface. Permanent surface manifestations of earthquakes (cracks or displacements) are uncommon except for the largest events, and are generally small and limited in scope, at least in terms of the scope of weather fronts moving across the Earth.


For a long time earthquake scientists have tried to find an association between earthquakes and syzygy (Solar and Lunar tides), but the correlation is just not there. Nor is there any correlation between volcanic eruptions and tides. Weather *IS* correlated with the orientation of the Earth's axis of course: when the north pole is oriented towards the Sun in the northern hemisphere summer, there is different weather than with the opposite orientation. Hurricanes and typhoons occur between June and November in the northern hemisphere, and the timing appears to be a heat latency effect. It takes awhile for the summer solar heat to accumulate in the upper ocean realm (water has a high heat coefficient, so it takes awhile to warm it up), and hurricanes derive their energy from the heat in warm ocean water. Hurricane Sandy was an unusual late-season event, because of the way pressure fronts interacted with each other to drive the storm backwards from the usual trade wind tracks and onto the New Jersey coastline.

Weather also correlates with the amount of CO2 and methane in the atmosphere, and also with the amount of energy that the Sun produces, but the critical geological record on the latter is distant in time and thus difficult to resolve clearly (see http://en.wikipedia.org/wiki/Snowball_Earth). Among scientists, the anthropogenic (human-caused) contribution to climate is now widely accepted as the evidence keeps piling up: the increasingly severe weather events of the past half century are caused in no small part by fossil fuel combustion. Of the hottest 10 years in the past century, 9 of them have been since 2000, and that correlates well with the growing levels of CO2 in the atmosphere. A good article to pursue this topic further is here:
http://en.wikipedia.org/wiki/Climate_change

Interestingly, methane is approximately 37 times more potent than CO2 as a greenhouse gas, and the amount of methane produced/converted by a single cow from the vegetation it eats is quite large. With the burgeoning human population and its increasing affluence, more people seek protein, and thus the number of meat-producing animals has skyrocketed in the past century. By itself this new methane is frightening. However, there is a huge amount of sequestered methane in what are called methane clathrates or methane hydrates - methane bound up in water ice beneath the ocean seafloors (see http://en.wikipedia.org/wiki/Methane_clathrate). This methane remains stable (and sequestered) as long as the pressure and cold temperatures around them don't change. However, with increasing temperatures caused by global climate change, it appears that these clathrates could become unstable, freeing more methane into the atmosphere, which will then get hotter, freeing ever more methane in a potential runaway feedback cycle.

Welcome to the increasingly interesting 21st Century!

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Earthquakes: How Often?

Until the following question arrived, I had only thought of earthquakes as being relatively localized features, mainly occurring along continental margins and ocean-floor spreading centers or transform faults. The San Andreas fault is a mostly on-land transform fault. I hadn't really thought about how MANY earthquakes there are in the world as a whole.

Q:
Hello, I was wondering how many earthquakes happen typically in a year?
-Lauren J

A:

The USGS estimates that several million earthquakes occur in the world each year. Many go undetected because they hit remote areas or have very small magnitudes. The National Earthquake Information Center in Denver, CO, now locates about 50 earthquakes each day, or about 20,000 a year. There are far fewer large events than small earthquakes, and this website will show you how these are parsed out according to magnitude:
http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php

There are lots of fascinating stats here, including an interesting table (below). Like asteroid impacts and frequency, or volcanic eruption magnitude and frequency, these all seem to follow an inverse log law:

The bigger the event, the less common it is.

Frequency of Occurrence of Earthquakes

Magnitude	Average Annually
8 and higher	1
7 - 7.9	15
6 - 6.9	134
5 - 5.9	1319
4 - 4.9	13,000 (estimated)
3 - 3.9	130,000 (estimated)
2 - 2.9	1,300,000 (estimated)

Extinctions: Asteroid Impacts vs. Volcanic Eruptions

The following question indicates that someone was thinking about things - a large step beyond just going to school and memorizing facts.

Q: 
Hello, I am 20 years old and from Portugal. My question arose when studying for school and noticing that these two events happen, more or less if it can be said on this matter, at the same time. Can a major impact like the one at Chicxulub have enough power to send shock-waves trough the mantel causing the major eruption at the Deccan traps? like if you "squeezed" the Earth and at its weakest point it broke, or like when you give a very strong hit on the top of the bottle and the bottom breaks away because of the pressure and strength that traveled until it finds a blockage it has the power to break through ... We know that earthquakes can be felt thousands of miles away but what happens inside the earth on the mantel at that time? If this is correct where would one get proof?
-Diogo C

A:

You have observed an interesting timing association that has intrigued geologists for a long time.

From Wikipedia (http://en.wikipedia.org/wiki/Deccan_Traps): The Deccan Traps formed at the end of the Cretaceous period. The bulk of the volcanic eruption occurred at the Western Ghats (near Mumbai) some 65 million years ago. This series of eruptions may have lasted less than 30,000 years in total. The original area covered by the lava flows is estimated to have been as large as 1.5 million km², approximately half the size of modern India. The Deccan Traps region was reduced to its current size by erosion and plate tectonics; the present area of directly observable lava flows is around 512,000 km2 (197,684 sq mi).

One website (http://palaeoblog.blogspot.com/2011/10/smaller-ka-boom-chicxulub-impact-did.html) offers this observation: "Researchers have simulated the meteorite strike that caused the Chicxulub crater in Mexico, an impact 2 million times more powerful than a hydrogen bomb that many scientists believe triggered the mass extinction of the dinosaurs 65 million years ago. The team's rendering of the planet showed that the impact's seismic waves would be scattered and unfocused, resulting in less severe ground displacement, tsunamis, and seismic and volcanic activity than previously theorized. "

Also from Wikipedia (http://en.wikipedia.org/wiki/Deccan_Traps) is even more specific information about the source of the Deccan Traps: "A geological structure exists in the sea floor off the west coast of India that has been suggested as a possible impact crater, in this context called the Shiva crater. It has also been dated at approximately sixty-five million years ago, potentially matching the Deccan traps. The researchers claiming that this feature is an impact crater suggest that the impact may have been the triggering event for the Deccan Traps as well as contributing to the acceleration of the Indian plate in the early Paleogene. However, the current consensus in the Earth science community is that this feature is unlikely to be an actual impact crater."

The short answer is that the Deccan Traps probably did not cause the extinction that wiped out most of the non-avian dinosaurs, though it may have contributed to making life even more difficult. There appears to be no connection between the Deccan Traps and the Chicxulub event.

On a related tack, the even larger Siberian traps (http://en.wikipedia.org/wiki/Siberian_Traps) formed 250 million years ago, and may have contributed to or even caused the Great Dying, the Permian-Triassic extinction event, the most complete extinction event in Earth's history. More than 90% of all species living in the Permian era abruptly disappeared at this time.

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Coral Reefs as Resources

The US Geological Survey expends a lot of time and manpower on resource estimation: energy, minerals, biological (in several ways). The following question came at me sideways, and caused me to really think.

Q: 
What are some resources that coral reefs provide?
What are some topographical features around coral reefs?
- Maya R

A.
The main resources that coral reefs provide - that most people talk about at least - is biodiversity. This is a hard thing to quantify or explain, but if reefs all die from acidification and heat related to climate change, then much of the food-chain in the oceans would be severely disrupted. Some new drugs have already been derived from unique reef species, so that is another potential future resource. I believe that there are some entities that have mined reefs for the calcium carbonate that they contain, but this is like the Spaniards four centuries ago melting down precious Aztec and Incan gold artifacts. Trying to capture a "resource" this way destroys 95% of its value.

Coral can only grow where there is light, so this generally means the fringe waters of islands and coastlines, and only in tropical latitudes. In the Pacific, this often means that there are reef rings around volcanic islands or below-the-surface guyots. As the original core rocks of the volcanic island weather and crumble down, this generally means that the remaining topographic feature is an atoll: a coral ring with a shallow lagoon inside. There is very little topographic relief above the water line. The topographic fall-off of an island reef system tends to be steep, however. I've Scuba-dived some of these and the reef "wall" looks like it just goes straight down into the black depths. There are also reef systems on continental margins, and the Great Barrier Reefs of Australia and Belize are examples. Bathymetry tends to follow this characterization as one moves outward: the continental margin, then shallow water, then a reef system, than a steep fall-off to the continental shelves or in some cases the oceanic abyssal plain.

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Rock Classes - from the forthcoming book "Ask a Geologist"

Rocks can be generally classified into one of three general rock classes. The first two of the three classes are easy to recognize:
1. Sedimentary rock, formed in layers by the accumulation of weathered rock fragments and/or chemical precipitates, usually under, or under the influence of water (and sometimes wind),
2. Igneous rock, which includes volcanic lava, as well as related (coarse-grained) intrusive rocks such as granite, diorite, and (the usually-very-dark) gabbro.
3. Metamorphic rock. This is generally more difficult to characterize and understand because it is modified – a derivative of - one of the other two.

About 90% of the queries we receive on Ask-a-Geologist, typically accompanied by a photo and asking "what is this rock", we cannot usually answer. In general, the photos have no scale and are blurry, and the light doesn't show the finer structures well. A geologist would want to turn the rock sample over in sunlight with a hand-lens, looking for mineral grains and their distinctive crystalline form or "habit", and perhaps scratch visible crystals with a knife-blade to check their hardness to aid her identification effort.

The following is a rare case of a query accompanied by a good quality photo (it even had a coin to provide scale!) and enough additional context information to allow me to identify the rock.

Q:
Last weekend I climbed Mount Mansfield in Vermont. The higher we got, the more silvery the rocks looked. Attached is a picture, but it doesn't really do justice to the silvery tone. My friend wanted to know what caused the rocks to look so silvery.  I said I'd ask the expert.
--Valerie W

A:
That's a schist. As in, that's a Gneiss Pile of Schist.  ;=)

Bear with me here – there is a point to this.

The silvery-ness that you see is caused by metamorphism, that is, a change to the character of the rock and its inclusive minerals. The word derives from metamorphosis – literally, change of form. Metamorphism usually is caused by the original igneous or sedimentary rocks being buried by tectonic forces at some time in their ancient past, but it could also be caused by hot fluids from a nearby heat-source (like an intruding granite body). Old-time miners would say that metamorphic rocks had been “stewed and cooked” – which is remarkably prescient.

The deeper a rock is buried, the greater the consequent increase in pressure - and also temperature – that it will experience. The photograph shows a complex rock that under great pressure has been deformed plastically – in this case, it is a schist. According to several sources (here's one: http://en.wikipedia.org/wiki/Blueschist ) this means depth of burial at one time reached 15 - 30 km before it was uplifted by tectonic processes and then exposed by weathering. The result of this high pressure/high temperature transformation process is that the original minerals are converted into several new minerals in a schist, commonly including glaucophane and muscovite - the latter is usually called white mica. Typically, there is plastic flowage going on, which leads to the alignment of the glaucophane and muscovite in the flow direction - and you can see this in your photo. The muscovite in these rocks, however, is usually very fine-grained - sometimes not easily visible even in a hand-lens. The net effect is to give the rock an over-all glossy look, and if you ran your hands over it, a slightly greasy feel sometimes. By the way, there are blueschist (blue-gray in color) and greenschist varieties of this rock. The latter are prominently greenish in color, because this kind of schist is loaded with chlorite and epidote: green, chlorine-rich minerals both derived from original black minerals such as pyroxene, and dispersed throughout the resulting rock as a whole by the metamorphic (“stewing and cooking”) process.

You describe the rock becoming more silvery with increasing elevation. That could be because the entire mountain is upside down from its original emplacement, and as you rise in elevation you are in fact walking deeper in time and burial depth. While this sometimes happens during tectonic processes, it is not very common. Though it seems more deformed, I suspect that in fact you are seeing a gradational change from an even more strongly metamorphosed rock, called a gneiss, found at the lower elevations of your hike. This kind of rock does not have the muscovite “sheen”, but instead is typically devoid of chlorite and platy minerals. Gneiss commonly has much larger crystals - this is because the rock was so hot, and maintained for such a long time a great depth of burial, that everything re-crystallized. The longer a hot, fluid mush is held in place, the larger the crystals can grow. Gneiss is typically formed at 15-50 kilometer depths. I suspect that the original rock mass is still more or less upright, and that you were in fact climbing up from deeply metamorphosed gneiss to less-metamorphosed schist above it.

~~~~~

Mount Lemmon is a spectacular uplifted mountain range located far to the south and west of Mount Mansfield - it lies just north of Tucson, Arizona. From the city, the face of the mountain has the broad texture and layering of the original sedimentary rock that it was made out of. However, up close it is coarsely crystalline and very much NOT (any longer) a sedimentary rock. As you move farther north in that complex you are moving ever deeper in original burial depth, and the gneiss turns gradually to granite – back to an original plutonic form. The original sediment probably was weathered out of a nearby, much more ancient granite complex. There is a famous story of a PhD student (Dr. Ed McCullough, who eventually became the geology department head at the University of Arizona) finding a blastoid (head) of a Paleozoic crinoid in the metamorphic rock while mapping the complex with other faculty. This story – and Mount Lemmon - neatly tie all three rock types together in one package.

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He Should Have Known

What do Baitullah Mehsud, Osama bin Laden, Anwar al-Awlaki, and Isoroku Yamamoto have in common?

Eleven years ago today, I was chairing a conference on unusual applications of geophysics at a large geophysics convention in San Antonio, Texas. I had just given the keynote talk in a room with about 1,500 people in it when my co-chair, Chris Liner, handed a piece of paper to me. His hands were shaking. It said that “planes had hit the World Trade Center and both towers had collapsed”. This did not compute with me: they were HUGE towers. A small plane had crashed into the smaller Empire State Building in the 1930’s and just stuck in the side. Chris asked me what we should do? I stood up and announced to the audience what we had just read, and said that the session would continue - but for people with family in that area to please feel free to step out and try to get in touch with them. I then excused myself, and after 9 tries finally connected with Louise, and learned that it was a lot worse than I had thought. She was still trying to get out of Washington, DC – her office was a block and a half from the White House - and had been walking in huge crowds for 2 hours already. She now considers the passengers on Flight 93, who forced down their aircraft near Shanksville, PA, as saviors. 

The rest of my story is like most other peoples’: After three days of staring at the Trade Towers collapsing over and over and over again on TV, I bought an American Flag tie, and took a taxi to the airport for my flight home. I soon realized that I was not going to be able to fly home. I walked out to the Hertz desk and the agent kindly offered me a car, said there would be no drop-off charges, and I started driving. It took me seven hours just to get out of Texas. Every two hours I would get a call from my Palestinian-Saudi son-in-law… who was worried about me. I was worried about him. No, people were not giving Hamed a bad time, in fact if anything they were being overly-protective of him in his home town of Charlotte, NC. The phone-calls depleted my phone battery, however, so I stopped in a Radio Shack to get a car-charger, and struck up a conversation with a police officer. We talked about our respective training in dealing with people wielding knives. Neither of us could believe that people were cowed by half-inch box-cutter blades into being passive sheep and waiting to fly into a building. “THAT’s not even a KNIFE!” he said, angrily.

I was full of anger. It kept me awake for 20 hours, until I finally stopped in eastern Tennessee, figuring I was probably becoming a danger to other people on the road by now. That anger got me all the way home – but then it stayed with me. How DARE someone take advantage of and then abuse our national hospitality to attack us, murder nearly 3,000 innocent people, for…what? Salifist jihadism? Why was it so important to be like the Old Ones (what Salafi means)? What could possibly make it important enough to murder 3,000 innocent people? There are harsh words for people who murder innocents - right in the Qu'ran. 

Before anyone attributed the truck-bomb attacks in Kenya and Tanzania in 1998, the name “bin Laden” came to my mind. I had probably walked past him in the late 1970’s in the souq in Jeddah, Saudi Arabia. I fancy that I had seen a tall, slack-jawed young guy who wore the red-and-white Saudi style shmaugh on his head but without the black aighal to keep it in place - to be just like the prophet Mohammed. I had camped with my children in the Asir region, the high scarp mountains of western Saudi Arabia, where 11 of the 19 hijackers had come from. I had seen the hatred in the eyes of the aighal-less Muttawah, aimed at me, a non-muslim. These religious police gave me and my family looks that could kill, as they herded unwilling young men into the mosques at prayer time. I couldn’t comprehend that hatred then, and I don’t understand it now. 

For years, however, the ‘righteous anger’ stayed with me. I would clip out news headlines that had anything to do with bin Laden and 9/11. I have a stack in the map-drawer in my office. I read every entry in The Long War Journal, memorizing names, keeping track of all the 3^rd-in-commands in al-Qaeda who seemed to last about two months on average. Ah… they finally popped the murderous Beitullah Mehsud with a Hellfire missile. Al-Awlaki was another one of those persistent, "Let's you and him fight" kind of guys, but he met his own Hellfire last year, not long after the SEALS shot bin Laden in the eye.

Yesterday I was reading “No Easy Day,” about the Navy SEAL team who flew to Abbotabad, Pakistan, and in 35 minutes assaulted bin Laden’s compound and then flew his body back to Jalalabad, Afghanistan. Two things stuck out to me: (a) how quick and efficient - and inexorable - the assault had been, and (b) that bin Laden encouraged thousands of people to commit suicide, to become shaheed, martyrs. A rather large percentage of these martyrs have been 12-to-14-yr-old boys. Someone else's children. But when the SEAL’s assaulted his compound, he was the only male present who did not take up a weapon and try to fight. He never touched his AK-47, nor his Makharov. They were found in easy reach, but not even loaded. When it came down to it, bin Laden didn’t have the courage to man up to what he had preached to his poor followers.

The anger finally left me.

How does Yamamoto figure in the title? Isoroku Yamamoto (1884 – 1943) was a Naval Marshal General, the commander-in-chief of the Japanese Combined Fleet during the decisive early years of the Pacific War, and was thus responsible for major battles such as Pearl Harbor and Midway. He died during an inspection tour of troops in the Solomon Islands when his aircraft was shot down during an ambush by American P-38 Lightning fighter planes. His death was a major blow to Japanese military morale during World War II.

He should have known.

Yamamoto was not a bad man. He had opposed the invasion of Manchuria in 1931, the subsequent colonization of China (1937-45), and the 1940 Tripartite Pact with Nazi Germany and Fascist Italy. As Deputy Navy Minister, he even apologized to United States Ambassador Joseph C. Grew for the bombing of the USS Panay in December 1937. These issues made him a target of assassination by pro-war militarists. In 1924, at the rank of captain, he was part of the Japanese delegation visiting the U.S. Naval War College. Afterwards, he toured the industrial heartland of the US. When the militarists forced the confrontation with the United States, which by then was embargoing fuel oil supplies to stop the expanding imperialism in China and southeast Asia, Yamamoto argued that they would awaken a sleeping giant. He said that Japan would not win this war. His argument did not prevail, of course. However, he was right in the end.

Anwar al-Awlaki, like Yamamoto, had spent time in the United States, had been welcomed, treated with courtesy. Like Yamamoto, he should have known. Bin Laden had spent a large part of his waking hours from 1996 onward studying the United States. This was the country that had landed a man on the Moon, and later obliterated the 4^th largest army on the planet – on the other SIDE of the planet – in just two weeks in 2003.

He should have known. 

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Tsunamis, Rogue Waves, and Tidal Waves

Geology started out as the science of uniformitarianism: What we could see in the rock record is what we could expect to see in the future. The initial assumption of Lyell and other early geology pioneers was that the “Great Flood” of the Bible was not to be taken seriously, and that every geologic phenomenon in the past was like what we observe today: calm and steady and slow – like weathering.  However, in the past several generations, geologists have come to recognize that there have been short-lived, phenomenally catastrophic events that have changed the face of the landscape. One of these is the tsunami, a word of Japanese origin where it was first described scientifically. The word was chosen about a generation ago to distinguish one kind of wave event (a tsunami) from a tidal wave or a hurricane storm surge. A tidal wave is a twice-daily feature associated with Lunar and Solar cycles. In Southeast Alaska and the Bay of Fundy in eastern Canada, these can reach 15 meters in height – especially if focused into an east-west-oriented narrow bay or fjord such as at Fundy. A “tidal bore” is a wave that moves in with a rising tide, and in shallow estuaries like Turnagain Arm in Southeast Alaska, these can be walls of water several meters high – sufficient to overturn or “pitch-pole” a medium-sized boat.

Q:

What causes tsunamis? Can one happen in the US?

-Jared W

A:

There are four different kinds of events that have caused tsunamis in the past:

1.       Asteroid impacts. There are huge tsunami deposits on Haiti stemming from an asteroid impact 65 million years ago.  This was the dinosaur-era-ending Chicxulub asteroid, which impacted on what is now a small village of that name on the northern tip of the modern Yucatan peninsula of Mexico. Fragments of this explosion apparently also went sub-orbital and landed as far away as Montana and the mid-Pacific ocean. Estimates of a mega-tsunami wave in the Caribbean up to 3 kilometers in height have been suggested – enough to completely inundate a large island such as Madagascar.

2.       Landslides. The face of a mountain fell off into Lituya Bay in southern Alaska in 1958. It created a wave at least 500 meters high, judging from surrounding mountains stripped of trees to at least that elevation. Surviving witnesses describe their vessel being floated over a large raft of logs, and the modern coastline remains largely denuded. http://en.wikipedia.org/wiki/Megatsunami

3.       Volcanoes. When the volcano Krakatau exploded in 1883, 45-meter-high waves reached as far as 10 kilometers inland on Sumatra, and swept people, animals, and debris back into the Sunda Strait. More than 36,000 people died in this event, and contemporary descriptions report that a person would walk across the Sunda Strait on bodies and logs without getting their feet wet. http://www.csmonitor.com/World/Global-Issues/2010/1028/Japan-tsunami-is-small-compared-to-five-of-world-s-biggest-tsunamis/1883-Krakatoa-tsunami The tsunami from the catastrophic eruption of Thera volcano (modern Santorini in the Aegean) 3,500 years ago apparently ended the Minoan civilization on nearby Crete. The language of modern science is substantially Greek-based (with Latin) as a result of that single event.

4.       Earthquakes. In January 1700 AD, a subduction earthquake in the Cascadia region of northwestern North America sent a tsunami across the Pacific Ocean that devastated villages on the Sendai coast of Japan. The earthquake sunk a forest in Puget Sound below sea level. The wave that reached Japan was called the “Orphan Tsunami”, since it was not associated with any locally-felt earthquake or typhoon – it arrived without warning under a clear blue sky. In 1946 a subduction earthquake off the Chilean coast of South America caused what one geologist friend referred to as “unplanned urban renewal” many hours later in Hilo, Hawaii. I have personally seen signs marking the wave run-up on telephone poles 5 meters above my head in the modern downtown area. The Great Sumatra Earthquake of December 2004 killed over 250,000 people from Indonesia to India. The wave reached Sri Lanka many hours after it was initially triggered, but there was no infrastructure in place at the time to warn the millions of affected people in its path. The Great Tohoku Earthquake of 2010 triggered a tsunami that devastated northeastern Japan, directly led to a melt-down at the Fukushima Dai-Ichi nuclear plant - and destroyed docks and ships many hours later on the Oregon coast.

It is important to understand that relatively few earthquakes cause tsunamis. The basic requirement is that the causative fault must have a normal or reverse component to it - part of the seafloor must drop or lift suddenly. Modern tsunami warning systems are based on a two-tiered approach: an initial earthquake beneath an ocean floor or ocean margin is detected. If the fault system is well known (for instance is understood to be a subduction fault), then an initial warning is issued. Deep ocean buoy systems are then monitored – these waves may travel at more than 500 kilometers per hour, so they take a relatively long time to cross an ocean. If a wave-front is noted passing through this system, then warning sirens light up on the threatened coast. http://en.wikipedia.org/wiki/Tsunami_warning_system

Technically, hurricanes (Atlantic Ocean) and typhoons (Pacific Ocean) do not cause tsunamis, but they DO generate low-pressure-driven storm-surges that could top 10 meters above normal sea level in the worst cases. These are not sharp-edged waves like a tsunami, but instead are long-wavelength, very broad surges of seawater tracking the eye of the hurricane or typhoon as it hits land. Hurricane Katrina in 2005 did most of its damage with a huge storm-surge that overwhelmed the levees and barriers designed to protect New Orleans, a city that over time since its founding has sunk below sea level.

There is another class of large water waves called “Rogue” or “freak” waves. There is a long history of “disappeared” ships in the history of humankind, and anecdotal stories of waves exceeding 30 meters in amplitude that somehow left survivors. Recently, sea-height-measuring radar satellites have allowed this sort of feature to be quantified. The physics concept of constructive interference of waves comes into play, but there may also be other factors involved, including diffractive focusing and non-linear effects. For instance, the southwest-flowing Agulhas current in the western Indian Ocean has long been known to interfere with westerlies to create a zone of dangerous rogue waves of unusual frequency and intensity.  http://en.wikipedia.org/wiki/Rogue_wave

By the way: that Biblical story of the Great Flood? As scientists we must be careful and not just dismiss something out of hand - like this one was. Geologic evidence now suggests that the Black Sea was a huge, populated continental basin that flooded catastrophically around 5,600 B.C.E.  

- due to waters from the Mediterranean Sea breaching a volcanic sill in the Bosporus Strait.

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