About 26 km southwest of Alamogordo and just south of the White Sands Missile Range, in the state of New Mexico, the United States, is an immense area of snow-white sand. But unlike other desert, the sand here is not composed of quartz, but gypsum crystals.
Gypsum is one of the most common mineral compounds found on Earth but is rarely found in the form of sand, as it easily dissolves in water. Gypsum is often found in hot springs and in lake and sea water, and can occur as deposits when the water evaporates. And that’s precisely how the gypsum dunes at White Sands were formed.
The Tularosa Basin, where White Sands is located, is a shallow basin surrounded by the Sacramento and San Andres Mountains. About 100 million years ago, rainwater and melt water came from the mountains dissolving gypsum from the sedimentary rocks and the concentrated solutions were washed down the mountainsides, and accumulated in Lake Lucero in the Tularosa Basin. As the water evaporated away it left behind a layers of crystallized gypsum. Weathering then reduced these crystals to fine, sandy grains, which were carried farther up the basin by the winds, and deposited in what is now the White Sands. Lake Lucero is today a dry bed but its lowest portion occasionally fills with shallow water after recent rains.
The White Sands cover an area of over 700 square kilometers with dunes that often reach as high as 15 meters. It is the largest gypsum dune field in the world. The dunes are constantly changing as they are moved by the steady southwest winds.
Unlike other desert sands, gypsum crystals do not absorb heat from the sun rays due to which they are cool to the touch. One can easily walk upon the sand with bare feet, even in the hottest summer months, which makes it suitable for sand boarding.
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