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The Beaches Are Moving
A PERSON CAN live on a mountain, in a desert, or on a suburban lot, and after a few years he can say: "I know every inch of this place, every rock, tree, weed, and fold of earth." No one can say that about the shoreline or the beaches.
The beach is land which has given itself up to wind and wave. Every day throughout the life of the earth, the wind and the waves have been at work shaping and reshaping the beach, pushing and pulling almost microscopic grains of sand and sometimes boulders larger than cars. For practical purposes there may be days when no wind blows, but even on the stillest days, when the sea lies like a flawless mirror, a wave moves against the shore. This is the wave of the tide, a gigantic slow sloshing of the sea within the oceanic basins. As the sea and the wind move, the beaches move.
A glance at maps of the American coastline, from Vespucci to the U. S. Geological Survey, seems to show little change. There's the Florida peninsula, the familiar elbow of Cape Hatteras, the great fish form of Long Island, and the hook of Cape Cod. Yet, comparisons of detailed maps show that privateers, pirates, and adventurers sailed a different coastline than our Founding Fathers defended against Britain. The coast illumined by the "rockets' red glare" is not the coast of our Bicentennial. From map to map islands change shape, inlets appear and disappear, shoals shrink or grow, and capes of land stretch further and further out to sea. To know the beaches is to know the beaches are moving.
We ignore this when we build motels, pavilions, boardwalks, and even whole towns on the edge of the ocean. In our business hats we do not recognize any real estate as movable. Corners are staked, lines drawn, and neat rectangular lots are recorded in courthouses as if they would be true forever. But in our play we are guided by a different vision. On almost any summer day on any sandy beach in the United States, adults and children alike amuse themselves with sand castles, moats, road systems, arches, miniature towns, and statues of each other. Here at the beach is one of the few socially acceptable forms of carefree play for adults. In molded damp sand we build images of our dreams and hopes. The water takes them away, as time one day takes our very lives. Amateur engineers may be fascinated with what we build, but perhaps the more interesting question is, Why do we make these little sacrifices? Perhaps, freed of economic and social concerns, we set aside our passion for monuments, history, and permanence and admit we are part of the ceaseless change that is nature.
The waves and tides which accept our sacrifices of sand castles and statues are only a small part of the forces that keep the beaches in motion. One way of understanding the dynamic nature of the beach would be to imagine yourself a photographer setting out to do a photo essay and a film on the beach. An ordinary snapshot would reveal a static, stationary place. The picture would show no sign of motion unless it were taken on a day when wind, rain, or waves were so violently agitated that they registered as blurs on the film. Now suppose you go to the water's edge and snap a picture at an extremely fast speed, say 1/ 2000th of a second, and on very fine film. And you do the same at the top of a dune. Very likely the pictures would show thousands of minute sand grains tumbling in the water and blowing through the air. Finally you set up a small shelter and a time-lapse camera and take two or three pictures a day for several years. Then the pictures are shown like a movie. The film will show dunes rising, falling, and marching along the beach as if enormous whales were migrating beneath the sand. The foredune and the tidal area of the beach where bathers spread their blankets will expand and contract like a sheet of stretched rubber. At the same time the tidal zone as well as the beach seems to rise and fall like the gangplank of a boat riding the daily tides beside the dock. The sand of the beach may even turn miraculously into large cobbles, then back into sand, and so on. During stormy weather changes flash before us almost too fast for the eye to follow—a dune or an inlet here one second and gone the next, as the film moves on. Chances are that at some point in the film we would see a dark line cut across the beach not far from the camera—an inlet. It may advance in our direction, gnawing away at the beach before it and leaving new beach in its wake. Within a few minutes the film will stop short, the photographer having abandoned the camera as the whole lookout station collapses in the water.
Despite this incessant motion, beaches continue to border the continent with about the same area from one year to the next. But like a person constantly changing position in a large armchair, not everything will be in the same place all the time.
Beaches are not stable, but they are in dynamic equilibrium.
We say the site of New York City or Chicago or Atlanta is stable because even over several human lifespans there is little practical change in the land mass itself unless mankind so wills it. Dynamic equilibrium is not stability of this kind but a net balance among many changes. If you give a person a dollar in return for three loaves of bread, you have neither a net loss nor gain. Your assets change shape but their value is in equilibrium. The same is true if you eat the bread. You no longer have the loaves, but you have energy. You have been making "trade-offs." You trade off the convenient convertibility of stock for the comfort of a house, or you trade off the supply of bread for more physical stamina.
Nature maintains the dynamic equilibrium of the beaches through unceasing trade-offs of four factors:
MATERIALS: sand, silt, biological debris, flotsam.
ENERGY: the forces of winds, waves, and tides.
SHAPE OF THE BEACH: steepness and width.
SEA LEVEL: land rising or falling, seas gaining or losing water.
The simplicity of listing these four elements is deceptive. Great mysteries still surround the processes of shoreline evolution. We may never unravel the interworkings of the long slow rise of sea level and the daily work of wind, wave, and tide. Yet gradually we are learning how the beaches survive, so that the story of a particular event, limited to a short stretch of coast and span of time, can be told.
Today we understand how hurricane seas surrounded and leveled the island city of Galveston and killed six thousand people in 1900. We know how a resort town disappeared on Oregon's Tillamook Spit. We understand the evolution of Cape May, New Jersey, from a broad sandy beach resort frequented by the country's Founding Fathers in the eighteenth century to a rubble-walled town pleading for economic assistance from Washington. We can prove that Miami's once broad white beaches were destroyed by the hotels facing them. We know how in an Alaskan bay giant waves sheared trees from hills a thousand feet above the water. We can even predict where future disasters will occur.
Beach stories are too easy to find. In writing this book we amassed whole file cabinets full of stories. Some stories were a thousand years old—stories of native American coastal villages and beach encampments only revealed in this century by a changing shoreline or archeologist's trowel. Most of our stories are modern because today the number of people living within a mile of the beach is probably greater than the number of all Americans who lived anywhere in the nineteenth century. We can predict the headline stories for the next decade or two because mankind's presence and the elements of the dynamic equilibrium that write these stories will not have changed. We are tempted to tell too many of these stories because they embody so much spectacular action, so much complex human character, and, at least at a distance, so much amusing irony.
Yet accounts of houses falling over California cliffs, or Gulf Coast islands disappearing in hurricanes, are in themselves unimportant. Only idle curiosity wants to know how high the flood was and how many perished. Our higher intelligence asks: How did we face danger? How did we feel afterward? Why did we take the risk? What are we going to do now?CHAPTER 2
Who's Afraid of Sea Level?
FROM TIME TO time an article appears in the newspaper describing the various disasters which might end the world—collision with a comet, the moon tiring and falling out of orbit, the sun exploding or cooling, or the earth being drawn into the sun. Apocalyptical disaster can be fascinating. With the exception of a few people, however, motivated by an unusual prophetic perspective, no one's life is changed much, if at all, by the sure knowledge that the world will come to a spectacular end.
To those who contemplate it, rising sea level enjoys a status similar to the other visions of Apocalypse. We know the oceans rise and fall. We know the slow wrinkling of continents raises and lowers the earth itself. We acknowledge the marine fossils of the walls of the Grand Canyon and New York's Catskill Mountains. But it all happened too long ago to worry us by its return. There are no human bones in the Grand Canyon's fossil beds. Most people are unaware of whether sea level is rising, falling, or standing still. Those of us who have lived a few decades might dismiss any thought of danger by observing that in our lives we haven't heard about the ocean's rising into the streets. What have we heard? Something about a few hundredths of an inch a year? Certainly neither New York nor San Francisco will follow Atlantis, at least not for several centuries or millennia—unless, of course, air pollution really does create the "greenhouse" effect and the icecaps melt completely. Even without accelerated melting of icecaps some shores will drown before others. Rising sea level could cause the destruction of Galveston County, Texas before the year 2000. The water is already in the streets. In Bay City the fish in Henry's Fish Market are almost back in the sea, and the buyers at high tide are walking in the water as they shop. You will understand why when we have explained the character of sea level.
If we think of rising sea level as merely the addition of water to the ocean basins from the continents and melting icecaps, we do not have the whole story, but we do have one fundamental cause. During the greatest expanse of the last glacier so much water was locked up as ice that sea level fell to four hundred feet below our present shoreline. Divers, research vessels, and remote-control cameras have filled laboratories with evidence that under the waves a hundred miles seaward from New York or Boston fertile plains and valleys once grew lush and dry. There is no other way to explain beach rocks, coral reefs, salt-marsh peat, and oysters on the deep ocean floor. Much of the landscape trekked and hunted over by our cave-dwelling ancestors nineteen thousand years ago is now flooded.
Since then sea level has risen, but geologists argue about how steady the rise has been—whether there were pauses and during what periods the rise was most rapid. In general, the rise seems to have slowed down about five thousand years ago. Since that time the rise in sea level may have speeded up, paused, or even fallen for brief periods. For the first part of this century sea level was rising very slowly. Then in 1971, from the National Oceanographic Survey, Dr. Stacey Hicks, a physical oceanographer, published evidence that the rise of sea level had begun to speed up. Measuring against the New England coastline, he documented an increase from one foot a century to three feet a century. Even that dramatic increase amounts to only three inches every ten years. What's more, this figure is a generality full of exceptions. In some places sea level is rising much faster, and in other places it is falling. Anyone who knows much about water knows it always seeks its own level, and that of its own accord the sea can't be higher in Massachusetts than in Alabama. In fact it is.
One problem of cutting a sea-level canal across the Central American isthmus would be a current running continually from Pacific to Atlantic, sweeping along alien plants and animals. Sea level is higher on the Pacific side of the Panama Canal. Here, as all over the world, the sea's level is affected by winds, tides, weather trends, currents, and even water density and temperature. The effects of wind may last only a few days, while a current as steady as the Gulf Stream or Japan Current may push water shoreward for many years. So sea level has many causes. Sea level is not an absolute measure, a uniform horizontal surface, like water level in a bucket. We can only measure sea level as it exists in a given locale. And we can only measure it relative to other things which may themselves be in motion. The land against which we measure sea level moves. Canada and upper New England are rebounding from the weight of the glaciers. All of the great crustal plates of the earth are in motion, rising and falling as they move against each other. Parts of the floor of the Gulf of Mexico are sinking under the weight of the Mississippi's delta. Little, if any, of these motions are evident to the observer who notices only that the water is higher or lower on the cliffs, beaches, bridges, piers, and seawalls.
Steady, long-term changes in sea level can usually be explained by one of three events: more water entering the oceans; the seafloor rising or sinking; and the edge of the continent rising or sinking. If only we could measure the volume of water in the oceans, we would have a steady reference point and we might know which of the three events is changing sea level. With a steady volume local differences in sea level would clearly indicate motions of the continental plates. A worldwide rise in sea level would mean either the unlikely syncopated falling in the motions of all the continents, or a rising of the seafloor. The latter would act something like a dent or growth in the bottom of a bathtub.
Most geologists agree, in spite of the measuring difficulties, that measured against most landmarks, sea level is generally on the rise. They disagree about the causes. A minority argue that the seafloor is rising in places, displacing water. Every ocean has a mid-ocean ridge where the earth's crust is spreading apart. The Mid-Atlantic Ridge, for instance, is so active that recently volcanic ruptures created Surtsey, a new island off the coast of Iceland. Growth in one or more mid-ocean ridges, or an immeasurably slight bulge over hundreds of thousands of square miles of seafloor, would displace enough water to create a significant rise in sea level.
Most geologists think the polar icecaps are still melting. Thousands of years of precipitation are still stored around both poles.
The arguments over cause are interesting, but not so important to coastal residents as the simple fact that the water is rising. Should you prepare for the floods? The answer may depend on where you live.
The rates cited by Dr. Stacey Hicks are only general, and in some places sea level is rising much faster and people are responsible. Along the northeast Texas coast underground shale layers are expanded by thin layers of trapped water. To slake the thirst of cities around Galveston Bay, including Houston, Galveston, and Texas City, local governments have been pumping some six hundred million gallons of this fresh water a day. As the water leaves, the shale collapses and the land sinks. At some point the rock will be compressed to stability, but by that time the rise in sea level may turn the space city of Houston into a sea city. Over the past fifty years or so some thirteen hundred square miles of coastal plain in Texas has subsided or sunk more than one foot.
Many large, lavishly built homes near Baytown have protected themselves with expensive flood walls. Even so, storms now flood the streets and hold the residents prisoners in their own homes. Some homes are now permanently surrounded by water and have been abandoned. The Humble Oil Refinery, a major user of the ground water, protected itself in 1965 with a 13.5-foot-high levee. Already storm water tops the structure. At San Jacinto Battleground Park a sign which says NO FISHING FROM BRIDGE is near a lot of water, but the bridge is out of sight—submerged. The San Jacinto monument no longer towers higher than the Washington monument. In some places subsidence has reached nine feet.
Readings taken from very accurate tidal gauges in New York City show the relentless sea level rise that is behind the inevitable erosion of the world's beaches.
To the house on the shore, feeling no fall, the land sinking means the sea is rising. Geologists estimate that by the year 2000 this sinking of the land and rising sea level will mean a loss of some twenty thousand acres of shoreline property. But even this year or next, in a hurricane equal to 1961's Carla, high water and waves, rising on top of the higher sea level, may flood seventy square miles of land that stayed dry a generation ago. Here is the real importance of rising sea level—a small rise may bring water far inland.
Excerpted from The Beaches Are Moving by Wallace Kaufman, Orrin H. Pilkey Jr.. Copyright © 1983 Wallace Kaufman and Orrin H. Pilkey, Jr.. Excerpted by permission of Duke University Press.
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