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Roger Weller, geology instructor
White Sands, New Mexico
by Christen Bailey
White Sands National Monument
Photos courtesy of (L-R) Wikipedia Shared Images, National Park Services, and Christen Bailey..
President Herbert Hoover proclaimed and established White Sands as a National Monument back in January 18, 1933. In its first year the park attracted 12,000 people; today more than 500,000 people visit White Sands each year. The sand dunes cover approximately 275 square miles making it the largest white sand desert on our planet. It is an active, constantly changing environment.
Sunbathers at White Sands in 1934-Photo by National Park Service Historic Photograph Collection
THE ORIGIN OF WHITE SANDS NATIONAL PARK
White Sands National Monument is situated between the cities of Las Cruces and Alamogordo located in New Mexico. To the east of the monument are the Sacramento Mountains and to the west the San Andres. Thousands of years ago these mountains were once steep cliffs which rain water and melting snow poured down into what is now known as the Tularosa Basin and formed a shallow sea. The rain water became saturated with gypsum dissolved from the cliffs. Thousands of years later, as the climate changed from wet and cold to warm and dry the lake began to evaporate. This occurrence caused the gypsum to be deposited around the shrinking lake close to the base of the San Andres Mountains. For about 20,000 years the winds have been moving the gypsum as the deposit breaks up into sand grains.
WHAT IS THIS THING CALLED GYPSUM?
a mineral compound called calcium
sulphate dihydroxide, or sulphate of lime. This mineral is generally found
underground near deposits of limestone or other minerals formed by evaporation.
One of the most common forms of raw gypsum is a pure white crystal called
alabaster. Another form of unprocessed gypsum forms in desert terrain and its
crystals resemble the petals of a flower. For this reason, many people refer to
it as the 'desert rose'. As a matter of fact, if you take the word Tularosa and
break it down, in spanish “tu” means you or your and “la rosa” means the rose.
Gypsum is rarely found in the form of sand because it is soluble in water.
Normally, gypsum would be carried by rivers to the sea but no river drains the
Tularosa Basin where White Sands is located.
‘Desert Rose’-Photo courtesy of Christen Bailey.
HOW DO YOU GET GYPSUM SAND?
The gypsum saturated water becomes trapped within the Tularosa Basin as it has no other means of passage. With no outlet to the sea the water either sinks into the ground or pools up in low spots. One of the lowest points in the basin is a large playa (beach) called Lake Lucero. Occasionally this dry lake bed fills with water. As the water evaporates the dissolved gypsum is deposited onto the surface. During wet periods, water evaporating slowly on the playa floor causes gypsum to form in a crystalline structure called selenite. Beds of selenite, some three feet tall, cover the ground. Weather, freezing, thawing, wetting, and drying, eventually break down the crystals into sand-sized particles, light enough to be moved by the wind, thus creating what we call white sand.
Aerial View of Lake
Lucero-Photo by National Park Service.
Selenite Crystals at Lake Lucero.-Photo by National Park Service.
Three key ingredients needed to make a sand dune include a source of sand, wind sufficient to pick up sand and move it, and changes in wind direction and speed. Wind can move sand in several ways. Creeping occurs when grains hit other grains, nudging them slightly out of place. The majority of sand grains bounce, hop, or jump along the surface, a movement known as saltation. In strong winds saltating grains will form a flurry of sand about a foot or so above the surface of a dune. The smallest grains are carried high into the air often mixing with dust.
Photo by National Park Service.
Wind is a part of everyday life in White Sands. During the spring months of March, April, and May gusts often exceed 30 miles per hour. These strong winds wafting across the playa pick up the gypsum particles and carry them downward. As the sand encounters an obstacle such as a rock the grains fall to the ground and begin to collect around the obstruction. Over time the obstacle is buried by a building dune, which itself obstructs the wind. The wind continues to carry the sand grains as they bounce up the dune’s windward slope it creates ripples in its surface. At the dunes steep edge sand builds up until gravity ultimately pulls it down, moving the dune forward.
There are several different types of dunes created. The first dunes to form downwind of Lake Lucero are low mounds known as dome dunes that move up to 30 feet per year. Crescent-shaped dunes, barchan dunes, form in areas with strong winds and a limited supply of sand. Areas where there is sufficient sand barchan dunes join together and create transverse dunes with long ridges of sand. On the dune field edges plants will anchor the arms of barchans and invert their shape creating parabolic dunes.
Slump marks of transverse gypsum dune. Geologist for scale.
Photographer: D. E. McKee, provided by National Park Service.
LIFE IN THE DUNES
One wonders how anything can live in such an extreme environment. There is not much rain, the heat in the summer is intense, and the sand is constantly shifting. Yet almost 400 types of animals live in White Sands National Monument. Most of them are birds or insets. There are also 26 types of reptiles such as rattlesnakes and lizards and more than 40 types of mammals including rabbits, foxes, and coyotes.
A Juvenile Indigo Bunting.
Photo by R. Martinez-Chavez, provided by National Park Service.
Animals often adapt in order to live in extreme environments. For instance, they may change color to protect themselves form enemies which is what many of the animal that live at White Sands have done. A lot of the animals are white, making it difficult to see the animals against the sand.
A whiptail lizard Photo by National Park Service.
Many of the animals remain underground during the day when it is hot and come out at night when it is much cooler. If you are lucky you may be able to see traces of animals by finding their footprints in the sand.
Animal Tracks in white sand-Photo courtesy of Christen Bailey.
Even without much water or nutrients plants do grow in the White Sands dune field. These plants struggle to survive in this hazardous desert. A major cause for this is that the dunes bury any plants in their way as they move along the desert. A few plants have developed techniques to avoid being buried by moving sand.
Soaptree yucca plants in dunes-Photo courtesy of Christen Bailey
Cottonwood Tree in Dune. Photo courtesy of Christen Bailey.
A soaptree yucca plant can appear to be 3-4 feet tall. In reality the majority of the yucca plant has been buried under the sand over time. It has adapted by growing upward to as much as a foot per year keeping its leaves above the sand. At first glance what may appear to be a small bush is in fact a cottonwood tree that has had 30 or more feet of ittaken over by sand, it too has adapted in order to survive. Other plants such as the Skunkbush Sumac create what are called pedestals. These plants grow taller to avoid burial while their roots and stems lengthen and tangle, securing part of a dune in place. When the dune moves some and remains around the plant, allowing it to hold onto its home for a little while longer.
Skunkbush Sumac pedestal with person for scale. Photo courtesy of Christen Bailey.
With animals and plants continually adapting to the dunes constant motion White Sands National Monument truly is an active, constantly changing environment.