Driven by southwesterly winter winds, dust from the White Sands dune field in New Mexico rises thousands of feet from the valley floor and drifts over the snowy peaks of the Sacramento Mountains. White Sands National Monument lies in the 50 kilometer (31 mile) wide Tularosa valley, between the dark rocks and forested slopes of the Sacramento Mountains and the San Andres Mountains. The lower and warmer ridge line of the San Andres was without snow on the day this photograph was taken. The striking black lava flows of the Carrizozo lava field also occupy the valley floor (image top). The darker tones of agriculture in the Rio Grande floodplain can be seen along the left margin of the image.
The dust plumes in this astronaut photograph stretch more than 120 kilometers (74 miles). The vigor of the winds also can be judged from the fact that they are lifting dust particles from the valley floor to more than 1200 meters over the mountains. The winds channel the dust through a low point in the mountains, about 800 meters lower than the ridge crests to north and south (image right). The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite also captured a wider, regional view of the plumes on the same day.
In most parts of the world, blowing dust is some shade of light brown or red. In this image, two different colors can be seen in the dust plume: redder dust from the hillsides north of White Sands and white dust from the dune field itself.
The sand dunes of this national monument are white because they are composed of gypsum, a relatively rare dune-forming mineral. The gypsum is deposited during the evaporation of mineral-rich waters in an ephemeral lake in the western part of the Monument. Erosion of the deposits, together with wind transport, provides the granular material for the dunes. The dunes’ brilliance, especially contrasted against the nearby dark mountain slopes, makes them easily identifiable to orbiting astronauts. The white speck of the dunes was even visible to astronaut crews looking back at Earth on the way to the Moon.