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When Nature's Wrath Is History's Reminder
By DENNIS SMITH
Published: December 28, 2004
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 airplane. 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 inevitable. 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 explosion on Sumatra 71,000 years
ago is a good place to start.
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