National Geographic : 1935 Aug
THE WHITE SANDS OF ALAMOGORDO A Dry Ocean of Granular Gypsum Billows Under Desert Winds in a New National Playground BY CARL P. RUSSELL Chief, Eastern Museum Division, National Park Service A ONE stands upon the heights of the San Andres Mountains in the neighborhood of Rhodes Pass, New Mexico, one looks out upon an ocean of white. South and east stretches a vast sea on which the glint of whitecaps appears as real as the rocky shores. The view is a startling mirage. Closer inspection reveals that the billowing snowy expanse is the White Sands of Alamogordo.* The windrowlike dunes seem velvety in their softness, yet many of them are firm enough to permit motorists to roll their cars from one crest to the next in roller coaster fashion. Some of the hills have attained a height of 100 feet, but 50 feet probably represents the average. Curious stories of the origin of the sands have circulated since they have been known to Americans, but the truth is not less inter esting than the fanciful explanations. The processes of making are going on constantly. WATER CARRIES GYPSUM TO THE SURFACE Underlying the Tularosa Basin are beds of Permian limestone and sandstone, be tween the layers of which are interspersed thick beds of gypsum. Borings made in recent years reveal that the gypsum is hun dreds of feet below the present valley floor and that water is encountered at depths of a thousand feet or less. The nature of the sedimentary rocks above the water-bearing sands is favorable to upward seepage. As the water on its upward course passes through the gypsum deposits, it dissolves that material and car ries a rather full load to the surface. The limestone through which the solution passes is not readily soluble; very little in addition to gypsum is carried by the rising water. When evaporation takes place at the surface a fairly pure crust of gypsum is deposited, which, under action of the atmosphere, crumbles to form crystalline grains. * See The National Geographic Society Map of the United States, NATIONAL GEOGRAPHIC MAGA ZINE, May, 1933. The prevailing southwest wind sweeps these crystals from the surface upon which they were formed and piles them in huge drifts to the north and east of the point of origin. The wind erosion excavates basins, the flat floors of which may be 10 to 30 feet below the surface of the plain and 50 feet or more below the tops of the dunes. Nearly everywhere in the basin floors moist sands are encountered at a depth of a few inches. Ordinarily sand erosion does not develop flat surfaces, but the flatness of these floors is manifestly caused by the water table which limits the depth to which the sand can erode (pages 252, 256). The largest of the basins from which the sands are blown is a boggy lake bed at the south end of the dune area, but many of the smaller flat-floored depressions are scat tered through the area. The size of the depression apparently affects the height of the sand piles built up to the lee of it. Hills and mountains surrounding the Tularosa Basin contain gypsum, and it is evident that some of the deposit is brought from this source by surface waters that feed it to the large natural evaporation pan at the south end of the sands. Whether the source is the deeply buried beds or the visible deposits in the mountains, the proc esses of evaporation, crumbling, and drift ing with the wind are the same. The end product is invariably beautiful, white, winnowed, and clean. ZOOLOGISTS STUDY COLOR ADAPTATION The picture afforded in this expanse of white sand is unlike anything known. The white environment has produced a notable effect upon the limited animal life of the sands, and zoologists look to this natural laboratory for possible answers to questions bearing upon adaptation. Botanists long ago turned to the White Sands as a field in which to study the responses of plants to unusual physical influences.* * See "The American Deserts," by Frederick V. Coville, NATIONAL GEOGRAPHIC MAGAZINE, April, 1904.