Galveston: A History of the Island

Chapter 2

2 ONE HUNDRED thousand years ago when there were no boundaries or known civilizations and when strange creatures wandered the face of the earth, the sea level was about the same as it is today. Then a cataclysm of unknown duration and origin altered the earth's angle to the sun. Maybe Zeus sneezed, or maybe some cosmic upheaval caused the earth to wobble slightly on its axis. More likely, the cataclysm was the product of an arcane blip of physics, an aberration within the earth's own rotation sufficient to tilt the planet a degree or two away from the sun and affect temperatures over a large part of the earth's surface. This sort of aberration happens from time to time, and is called the Milkanvotich Cycle in recognition of the scientist who first observed the relationship of the earth's climate to variations in its rotation. Whatever happened one hundred thousand years ago, it caused the earth's temperature to drop a few degrees, which was enough to freeze the planet from its poles halfway to its equator. The big freeze extracted enormous volumes of moisture from the atmosphere, dropping sea levels all over the world and creating glaciers and ice sheets of unimaginable size and form. In the northern hemisphere the glacier field spread as far south as the present states of Illinois and Kansas. As the earth's supply of water was redistributed to form glaciers, what had been ocean bottom became dry land. The shoreline of what we now call Texas would have been 14 Gary Cartwright 150 miles out into the Gulf of Mexico, compared to its present location. Then the cycle began reversing itself about eighteen thousand years ago. The earth warmed, melting glaciers and elevating sea levels. Trillions of tons of water rushed down ancient riverbeds, flooding coastal valleys along the Atlantic and Gulf coasts: the Pacific coast, because it was mostly lined with mountain ranges, had few coastal plains to flood. In time, the coastal valleys became jagged inlets called bays. Nature's relentless response to a jagged shoreline is to straighten it out, and that's what happened: the pounding surf began eroding piles of river sediment (called headlands ) that had collected between the bays. Longshore currents carried the sand from these headlands laterally along the coast, forming dunes and sandbars. The sea level continued to rise, flooding the low areas behind these sandbars, or spits of sand, and separating some of them from the mainland. The spits of sand that remained attached to the mainland became peninsulas like Bolivar, and those that were separated became barrier islands like Galveston. One of the interesting things about barrier islands is that they are constantly migrating toward the mainland. When Galveston Island was formed at the end of the last ice age, it was located a hundred miles or more south of its present location. Because the sea level was rising, the Island was constantly eroding on the ocean side and building up on the bay side, always advancing toward the mainland-which was also eroding. Then about five thousand years ago the acceleration of the tides slowed and the Island stopped migrating. That is to say, it stopped eroding. But it continued to grow on its bay side, becoming wider and higher. In 1930 scientists made a surprising discovery: not only was the sea level rising again, it was accelerating at an amazing pace, a foot or more each century. This was particularly significant to lowlying islands along the Gulf coast because their gently sloping coastal plains caused the tide to move more rapidly than it would up a steeper incline. A one-foot rise in sea level can gobble up a thousand feet of Galveston shoreline. Evidence of the Island's inexorable march toward the shore is scattered along any beach. Those oyster, clam, and snail shells that you see are native to the brackish waters ofthe bay. So what are they doing over here on the Gulf side? Answer: the Island moved, liter- GALVESTON 15 ally passed over the lagoon where they were born. The majority of the shells found on the beaches of any barrier island are fossils, revealed by radio carbon dates to be prehistoric. To measure exactly how far Galveston Island has traveled since the last section of the seawall was completed in 1962, drive to where the wall ends, near 7-Mile...