An excellent historical perspective on Tsunamis from the New York Times.
When Nature's Wrath Is History's Reminder
By Dennis Smith
Scientists, like art teachers who have not mastered anatomy or drawing, often assume that what they do not know is not important. And, when it comes to earth science, what they do not know is the pattern of geologic time, particularly what has happened beneath the ground in the 4.5 billion years that we assume the earth has existed. What have been the consequences of large waves and water movement to whatever life existed on its surface?
Humans might know that the universe is theorized to be 15 billion years old, or that the Milky Way was formed 13 billion years ago, but the way we feel about ourselves in relation to a 4.5 billion-year-old earth is not much different from the way indigenous people studying a night sky might have felt about themselves anywhere on earth 10,000 years ago. The subject of what can possibly happen on earth is simply too big for most of us to handle if we are to continue to be an optimistic race. And so we hope for the best.
Yet there are some things we should be thinking about in a more serious manner. There are facts that we should not let pass into an obscure scientific history, for remembering them will undoubtedly help ensure a safer future for all on our planet. This is harder than it sounds.
We have a tsunami warning system in the Pacific Ocean because, in recent history, we've experienced tsunamis there. We don't have a similar system in the Indian Ocean. This has something to do with the technologies developing nations can afford, of course, But it also has to do with the fact that our experience with the giant waves in this region is less immediate. Yet the single worst explosion in our known geologic history - an eruption of a 20-by-60-mile caldera some 71,000 years ago - occurred on Sumatra, just 100 miles from the epicenter of Sunday's earthquake.
The earlier eruption left a 10,000 square-mile sheet of volcanic rock, more than a thousand feet thick, and so filled the sky with ash that it probably created our last ice age. Still, the eastern Indian Ocean is thought to be an area of infrequent tsunami activity. Earthquakes as a rule occur at the ridge of land and water, where plates usually meet and either slide, thrust or pull apart, releasing awesome power. But there are exceptions.
Americans believe that earthquakes are a West Coast problem. But the largest earthquake ever in the United States that we know of, probably at least as large as the one that destroyed most of San Francisco in 1906, occurred in the area of the Mississippi Valley in 1811. Boats were thrown over in the river and people drowned. Whole islands simply disappeared. This earthquake, and its aftershocks a year later, were so destructive that Congress passed the first federal relief act in 1815 to support the farmers whose previously healthy and farmable land was turned to swamp, sand and mud.
The quake covered a much larger area than the San Francisco catastrophe, but fewer people were killed, for in 1811 the area was sparsely settled by fewer than 10,000, most living in log houses that would have sustained the shaking well. However, the seismological activity that caused it has never been explained in definitive terms.
Scientists speculate that the earth here tried but failed to separate 600 million years ago, creating a weakness of some kind beneath the ground. The United States Geologic Survey vaguely refers to the area as a plate boundary zone, which simply means that the agency doesn't know if there are plate boundaries in the vicinity. But we do have historical evidence of many substantial earthquakes in a wide area of the southern Midwest, from St. Louis to Memphis - an area where more than 10 million people live today.
The greatest cliché in geology is the question, Can it happen again? Sure. Will it happen again? Well, nature is never overdue, and we simply don't know. The earth has had many configurations of land, water and living inhabitants over the ages, and if we think of an earth-changing event as being "overdue," we are failing to understand geologic time. It is mind-boggling to think that only 200 million years ago the earth was one gigantic continent, and one can only imagine the explosions that broke it into today's continents. The plates beneath these continents continue to creep, and they don't need an earthquake to move them along.
We know that Baja California is moving away from Mexico at the rate of two inches a year - and that it has been doing so for four to six million years. We know that Europe is moving away from the United States at the rate of one inch every year, and that Maui is moving away from South America at the rate of three inches a year. Geodesy is the science of the shape of the earth and, with the advent in the last decade of global positioning systems, the geodesists in future will be able to map every movement of the land and sea with authority and exactitude.
Our observation and reporting periods cover far too brief a period of time to allow us to see any pattern. What's more, there are physical realities in our world that we are not paying attention to. For instance, in 1971 an earthquake of 6.4 magnitude occurred in the San Fernando Valley in California. It occurred on a fault that had not been known to exist, and so surprised scientists, as well as the 80,000 people who lived there.
At one end of this valley is the Van Norman Dam, which lost 30 feet from its top, and tons of water, during the shaking. Behind it is a reservoir larger than the one that created the famous Johnstown, Pa., flood that killed 2,200 people in 1889. Given the damage, cracks and weaknesses that resulted, engineers concluded that the dam would have collapsed altogether had the quake lasted another eight seconds. Today, almost half a million people live in the valley.
Sunday's tragic earthquake occurred miles beneath the Indian Ocean, and despite its 9.0 magnitude it was hardly felt in Indonesia, and not at all in Sri Lanka. Yet the water displacement caused by the thrusting of the Indian plate beneath the Burma plate created 30-foot waves that were to kill people on the African coast more than 3,000 miles away. This distance may seem hard to believe, but after the Great Chilean Earthquake of 1960, tsunamis traveled more than 6,200 miles to Hilo, Hawaii, where they killed 61 people and destroyed many buildings with waves of more than 35 feet.
Oddly, a tsunami cannot be felt as it passes ships on the open ocean, for the wave is usually small, one to two feet, and traveling very fast, as fast as airliners. It is only as it approaches shallow water that it begins to break; as the bottom of the wave slows, the top keeps traveling at the higher speed and increases in height, hitting landfall at 30 to 40 miles an hour. In 1958, an earthquake in Lituya Bay, Alaska, caused a landslide into the ocean that created a tsunami 1,720 feet high, a wave that could have swept over the Empire State Building. Fortunately it headed into a wilderness area and did not travel across the ocean to Hawaii or Japan.
The possibility of great landmasses falling into the ocean is always with us, and recently scientists found vertical fault lines through a volcano on La Palma, one of the smaller and more westward Canary Islands. The volcano has a crater about five miles wide and a half-mile high, and erupts about every 200 years. The last eruption was in 1948, but the newly discovered fault lines have convinced some scientists that eventually the huge crater will break apart and slide into the ocean, bringing more than a half-trillion tons of rock with it.
Since tsunamis are created in proportion to the amount of land that has fallen into the water, this event would likely create a wave mass never before known to written history, many times bigger than the wave at Lituya Bay. The wave would diminish a little as it crossed the Atlantic, but if it hit the Atlantic Seaboard it could be higher than the skyscrapers of Boston, New York, Washington and Miami. Scientists do not know if it will take one, four, or 10 eruptions to separate the landmass, only that the separation is inevitable.
The only good news is that volcanoes usually send signals before they erupt, and it would take eight hours for the wave to travel from Africa to the United States' eastern shoreline. It is not sufficient time, however, to move all the people who would be in its path. In any event, surely the mountain on La Palma should be reduced in size, to lessen the impact should it ever slide into Atlantic. But, who will pay for such a huge reduction of a landmass?
BIG earthquakes occur infrequently, but when they do they usually come unexpectedly and with horrendous power. It is, of course, dangerous to live in an earthquake-prone area, but what area in the world can we say is earthquake-safe? Surely the people in the Mississippi Valley feel they are safe, as do the people in New York City. Yet, New York has a fault line going across 125th Street that I would guess 99 percent of the city's population does not know about.
And even if they did, they would likely be no more concerned about it than they are about La Palma. Americans have always lived in dangerous places - on the flat cyclone fields of the Midwest, on the hurricane battered coasts of Florida, on the flood plains of the South. We live in these places because we are uncertain about the time and place of the next disaster, and we are an adventurous culture. We believe that lightning never strikes twice in the same place, despite the many times it has.
I hope for the future in the same way I hope when I step on to an air-plane. I hope the people in control are of sound mind and body, and that they know what they are doing. Yet I know that simply wishing this is not enough. Terrible events in the future are in-evitable. But I also know that we will continue to be unprepared for them if we don't look more deeply into the past. By this, I don't mean a fire last year or a volcanic eruption a century ago. I mean another past, in geologic time, that we simply don't know enough about. Thinking about that ex-plosion on Sumatra 71,000 years ago is a good place to start.
Dennis Smith, a retired New York City firefighter, is the author of the forthcoming "San Francisco Is Burning," a history of the 1906 earthquake.