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T270 Atlas Pg. 11, 12 Texas Gulf Coast, Texas Coastal features, rivers and deltas, urban and agricultural land use patterns Significance: This is a splendid example of a "trailing-edge coast," in plate-tectonic terminology. The Balcones fault system that separates central Texas from the coastal plains was active about 25 million years ago. Since then the only structural movements have been around salt domes in and around the Gulf. Because of the abundance of oil, natural gas, sulphur, and ground water within the sediments, this is an excellent area in which to study geologic processes on a trailing coast. Many effects of an increasing human population, unpredictable climate, and changes in technology leave their mark on the land surface and coastal waters and can be readily tracked from space. Physical Characteristics: The Texas Gulf Coast is a low-lying, nearly flat region formed from sand and mud; gradual uplift through geologic time has raised deltaic and shallow-marine sediments above sea level. A major chain of barrier islands and lagoons joins the deltas of the Rio Grande and the combined Brazos/Colorado Rivers. Old coastal features that apparently formed during a stand of sea level about 6 meters higher than present during the last interglacial period are prominent--the Brazos/Colorado River delta, and the Live-Oak Ridge barrier chain near Corpus Christi. The climate is variable. Average temperature is warm, but hard freezes occur every few years as far south as the Rio Grande. Rainfall varies from 50 inches or so per year at Beaumont to 30 inches or less nears Brownsville; it is equable (based on monthly averages) near Houston but highly seasonal in the south. Severe droughts occur unpredictably; the population of the coastal plain has tripled since the last severe drought in the 1950's, so the environmental effects of the next drought may be severe. Hurricanes occur every few years; again, the population of low-lying areas subject to tidal flooding has increased greatly during the past two decades. Native coastal prairie and brushland is largely replaced by agricultural fields: rice and cotton in the northeast, small grains and improved pasture in the Coastal Bend, and citrus and vegetables in the Rio Grande Valley. Parts of the coastal plain north and northeast of Houston are still in timber: conifer on the uplands and deciduous along river bottoms. Urban sprawl is replacing agricultural land in Houston, Corpus Christi, and Rio Grande Valley sections of the coastal plain. Industrial development is also conspicuous from space, particularly near Houston, Beaumont, and Corpus Christi. An increasing percentage of the remaining natural areas is being purchased and preserved for the use of wildlife, from the Big Thicket through the Aransas Refuge to the lower Rio Grande Valley. Observation Techniques: Different surface features of the low-relief coastal plain, and of the water bodies, will be emphasized by different lighting and weather conditions, from different viewing directions and sun angles, at different seasons. Oblique and near-vertical views using a short-focal-length lens are useful for regional understanding and for teaching purposes. Near-vertical views using the 250 mm lenses are appropriate for recording interesting features that stand out during a pass. In particular, look for coastal features such as hurricane channels and washovers, patterns of tidal sediment plumes, patterns of natural vegetation, striking agricultural and urban features, and, sooner or later, the effects of large oil spills. We have little CIR photography of the Texas Gulf coast; in particular, 250 mm CIR photographs of the bay systems are desired. Center Point: 28ºN,97ºW 101
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