Please pardon the pun, but my publisher tells me we have been inundated with questions since the recent Tsunamic catastrophe in southern Asia. Some time back, I wrote a Secrets of the Sea column on tsunamis that you might have missed. Therein I explained that the term “tidal wave” is a misnomer for the devastatingly large waves such as the one that has recently caused so much death and destruction. In fact, the correct terminology is “tsunami”, which in Japanese (who have the most problems with these natural disasters) means “harbor wave.” I have responded to emails about the phenomena, and the biggest question is how they occur and are created. This column will, I hope, answer in lay terms, that question.
            First, let’s clear up one misconception. A tsunami is a huge wave that, once it reaches shore, causes unspeakable calamity. However, the fact that it is a wave has absolutely nothing to do with the tidal occurrences in our oceans. The positioning of cosmic bodies, primarily the moon and sun, causes tides.  Tsunamis find their causation in oceanic disturbances such as earthquakes. So, exactly what happens out there in the depths that can cause problems on land? Well, it has to do with the earth’s “plates” and the movement thereof. 
            Geologically speaking, a “plate” is a large, rigid hunk of rock. These are constantly moving, although at a speed indiscernible to the naked eye. But they are moving. This movement is a good way to describe the word tectonics, which comes from the Greek verb meaning “to build.” Earth has a dozen or so plates that kind of slip and slide along a layer of liquid beneath them. This liquid acts as kind of a geological ski slope on which the plates glide. Prior to our gaining knowledge of plate tectonics, it was believed that continents “drifted” over the oceans, which was the theory of “continental drift.” In fact, one theory, long held, is that the world originally had a super-continent called Pangaea, which eventually broke apart and formed various landmasses that drifted and shifted around until they reached present day status. 
            The theory of plate tectonics is only about thirty years old. However, it is now widely accepted, and has combined many areas of science, including geology, geography, paleontology, archaeology and seismology.  This theory has given us valid explanations for questions such as why earthquakes occur where they do, volcanoes erupt when they do, and how mountain ranges are formed. And remember, this is all still going on as we speak. 
            In 1912, a young scientist named Alfred Wegener introduced the idea that continents were moving. He postulated that two hundred million years ago, Pangaea began to split apart. Wegener froze on an expedition before fully developing his theory, but one of his disciples further developed the idea, stating that Pangaea initially split in two, forming two world continents, one in the northern hemisphere and another in the southern. What a war these guys could have had. Of  course, there were no such things as humans at the time. These two continents, so the theory went, continued to divide, drifting over the millennia until we reached the present day situation. If you look at a world map, you will notice the uncanny fit of the coasts of South America and Africa, now an ocean apart. Also, there are identical fossils on each coast, which could mean that they were once attached. Of course, Wegener’s guys knew that this all took millions of years. It did not occur overnight. Prior to this time, the prevailing view had been that the position of the world’s landmasses had been caused by a catastrophic event, most likely the Biblical flood. You go, Noah! But such is not the case. Continents were not, nor are they now, permanent fixtures. Now, can you guess what the problem with the theory of gradual drift might be? Well, what force is there on earth that would move these continents? Gravity? No, that goes up and down. Wind or water? Uh uh. Not strong enough. So continental drift as an explanation was debunked and set aside. The thing is, though, that Wegener’s theory led the modern world to the supposedly correct theory, which is that of plate tectonics. 
            In the 1950’s, four things were learned that brought Wegener and his ideas back to the forefront of earth science. First, technology made it known how rugged and youthful the ocean floor is. Before the 19^th century, everyone believed that the ocean floor was flat, with no topography. Now we know that most of the occurrences of a geological nature on land are directly or indirectly linked to ones on the ocean floor and that the seabed is anything but flat. There are deep valleys, mountains higher than Everest, craters, rills, ridges and anything else you might see up top. Additionally, in 1947 it was learned that the sediment atop the ocean floor was much thinner than earlier believed. Scientists’ best guess was the oceans are about 4 billion years old. If so, how could there be such a thin layer of sediment. It should have been very thick. Plate tectonics provide an answer. 
           There also have been many reversals of the earth’s magnetic fields in the past. It is a difficult scientific explanation, but basically there are two different types of magnetic rock on the sea floor, laid out in stripes like on a Zebra. This is called “magnetic striping.” They form along ocean ridges. There are weak spots in between the stripes that allow molten magma to rise to the surface. The rising of this magma is known as “sea floor spreading.” This has formed what is known as the mid-ocean ridges, which is important to the theory of plate tectonics. The most significant thing about sea floor spreading is that new earth crust is constantly being formed. This crust has to go somewhere. So it moves. It pushes. Are you starting to get it?              The third thing that happened was the development of seismic instrumentation. This enabled us to find that earthquakes happen in some areas a great deal more often than in others. It was found that earthquakes were much more common along oceanic ridges. Scientists now believe that sea floor spreading, and the constant “recycling” of the ocean floor, is one of the causes of all these earthquakes concentrated parallel to the oceanic ridges. 
            Finally, satellite imagery shows beyond a doubt that things down there are moving all the time. There are processes known as convergence and divergence, and subduction. Subduction is apparently the real big deal. Plates grind up against each other, bump each other, and contend to be “top dog.” When one plate slips underneath the other, subduction occurs, and quakes are likely. Additionally, the subduction process causes the formation of volcanoes beneath the water. Eventually, after such volcanoes erupt enough, they build themselves up to the point they become island volcanoes, like Hawaii. 
            So, scientists now believe that it is the process of plate tectonics, the shifting of the earth’s crust, and the dynamics thereof, that cause the problems. When things down there start bumping and grinding, slipping and sliding, something’s got to give, and usually that involves an earthquake. So then what happens? 
            When a major earthquake occurs along a subduction zone, then is the time to watch out! This is especially hazardous, because the formation of a Tsunami is likely to occur. Tsunamis are seismic events, waves, if you will, caused by the quakes, volcanic eruptions, and underwater avalanches. The latter two are very rare. Normally the culprit is that earthquake. When a large earthquake happens down below, the seabed crust can move several meters. This may not sound like a great deal, but the results are. Enormous quantities of water are set into motion, rocking back and forth for hours. This rocking causes a series of waves, which can race across open expanses of water at speeds exceeding 700 mph. That’s about how fast passenger jets go. They travel for great distances, often unobserved, until they find shallow water, rise to heights of up to 100 feet, and do their thing to the land.
            Let me tell you this. Prior to the most recent tsunami, the worst catastrophe in terms of human life was some time ago, in which 26,000 lives were lost. That, friends, is miniscule to what we are experiencing right now. Some reports have the death toll at 150,000 and rising. Property and environmental damage cannot possibly be assessed at present. Lots of people are talking about the fact that these poor people were not warned. But, in reality, you tell me. What could have been done? We are a long way from preventing small tropical storms, much less earthquakes and resulting tsunamis. There are all kinds of relief funds through which we can help these unfortunates. Think about it.
            Interestingly, where do you think would be the safest place when a tsunami is approaching?  Well, what do you naturally do when a wave is about to crest right on top of you? Dive under, right? So, if you have enough warning (unlikely), put on your scuba gear and go out to Crocker’s. You’ll most likely be the safest person in the Keys. Of course, there won’t be anything left when you come up.
            But now, you know how they happen. It was right there on your plate. Thanks for reading, and keep it up. We love those emails and other contact with the paper. It let’s us know you’re there.