Chris is not standing barefoot in snow. This is sand–incredible sand!
For years I have wanted to visit White Sands National Monument. There is nothing like it on the planet. The main geological feature here is sparkling white sand about the color of sugar. I had heard about it, but nothing really prepared me for it. This is the largest white gypsum dune field in the world. The glistening sand dunes are found in the Tularosa Basin at the northern end of the Chihuahuan Desert in New Mexico north of Las Cruces and south of Alamogordo.
It covers about 800 sq. km. (300 sq. mi). Gypsum, which is also found in Manitoba in a completely different form, is a water soluble mineral that is not often found as sand. Because there is no drainage from the Tularosa Basin surrounding the white sand dunes the sediment from the mountains that is washed by rains, even though infrequent, gets trapped in the basin. When the rain evaporates dry lakes form and strong winds blow the white gypsum up into huge fields of rippling white sand dunes.
Sand dune never remain in place. They are constantly on the move. At one point we saw dunes about to climb over the State highway we had driven to get here. What surprised me is that the water table here is very shallow and water can actually rise to the surface after heavy rains turning the interdune area into temporary large ponds.
Geology is always interesting. There is a lot of history in rocks. Millions of years ago, an ancient sea covered most of the southwestern United States and during this time layers of gypsum were deposited on the floor of the sea. Of course that sea was never static either. It rose and sank many times over millions of years. This started the process of the creation of gypsum.
Gypsum is created within layers of sedimentary rock often found in thick beds or layers. It forms in lagoons where ocean waters that are high in calcium sulfate content slowly evaporate but are regularly replenished with new sources of water. This is precisely what happened at White Sands.
Massive gypsum rock forms within layers of sedimentary rock, typically found in thick beds or layers. It forms in lagoons where ocean waters high in calcium and sulphate content can slowly evaporate and be regularly replenished with new sources of water. Because gypsum dissolves over time in water, gypsum is rarely found in the form of sand. That is why White Sands is unique.
Many factors led to the creation of this astonishing ecosystem. 280 to 250 million years ago (‘mya’) the continents of the world were welded together in one massive mega-continent now called Pangea. Part of what we today call the United States in the southwest, including the southern part of current New Mexico, were covered by what we now call the Permian Sea. When the sea rose and fell repeatedly thick layers of the mineral, gypsum, were left behind along with other minerals that were also dissolved on the seafloor.
About 70 mya when the earth’s tectonic plates started to shift they collided into each other. In some places the pressure from such movement pushed up land and created many mountain ranges including the Rocky Mountains and the mountains that now surround the Tularosa Basin.
30 mya ago the tectonic plates began to pull apart in the opposite direction creating many fault zones. Large portions of mountains were sometimes split apart causing sections of the Earth’s crust to drop thousands of feet, forming basins along the faults. At that time 2 distinct mountain ranges were formed in this region—the San Andres Mountains to the west that are shown in my photographs and the Sacramento Mountains that we could see to the east. Between the two mountain ranges, where we stood, the Tularosa Basin was formed.
About 2 to 3 mya the Rio Grande River flowed along the southern edge of the Tularosa basin bringing sediments and minerals into the basin. This eventually blocked the basin’s outlet to the sea. Water that was trapped at the blockage started to collect at the lowest point and eventually formed Lake Otero. This lake was about 1,600 sq. miles and covered much of today’s basin.
24,000 to 12,000 years ago the climate was much colder and wetter then it is today. About 12,000 years ago when the climate changed and the last ice Age ended, Lake Otero began to evaporate and when conditions became dryer a playa or dry lake bed was formed. Around 11,000 years ago, the rain and snowmelt carried dissolved gypsum from the surrounding mountain ranges into the Tularosa Basin. Much of that gypsum runoff settled in Lake Otero.
As the climate became even warmer and dryer the sun and winds combined to transform this area into the Chihuahuan Desert and almost all of Lake Otero dried up completely. The dry portions of the lakebed became what today is called Alkali Flat. When Lake Otero’s water disappeared selenite crystals formed on the bottom of the Alkali Flat. Small pieces of gypsum crystal were broken down by strong winds leaving small grains of white sand that were polished into a brilliant white color unlike anything I have ever seen anywhere. These Sands, unlike the white sand beaches of the Caribbean are really white. The sands were consistently pushed to the northeast by the prevailing winds from the west accumulating into massive dunes forming the white dune fields that we saw today.
Of course not all geology is old. Geology is today too. At the present time change occurs as well. Rain and snow melt from the surrounding mountains and even upwelling from the deep water within the basin from time to time fills Lake Lucero with water that contains gypsum. When the water in the lake evaporates again small selenite crystals (2cm to 3cm) are again formed on the surface of the temporary lake and Alkali Flat in the same was they have for thousands of years. It is usually when large floods concentrate the mineralized water about every 10 to 14 years that crystal formations again occur. After that the relentless forces of wind and water again attack those crystals of gypsum creating ever smaller particles of white sand until they are as fine as the sand we walked on today.
Of course it is not just the geology that is interesting in White Sands National Monument. A plant guy like me must pay some attention to the plants. One of the more interesting ones is Soaptree Yucca (Yucca elata). The plants and animals of White Sands are special because they must have special attributes to survive the harsh and changing conditions of the desert. The desert is not place for wimps. The landscape here is constantly changing, even more than most other environments. The sand moves. It never stays for long in one place. That is a characteristic of all dunes.
The Soaptree yucca adapts to these changing conditions by growing rapidly. Yucca first take root in the interdunal soil. Then when the sand piles up as it inevitably does, it elongates its stem to keep it’s leaves above the sand so that they can continue the important work of photosynthesis whereby light is miraculously turned to energy. What looks like a yucca of 4 to 6 feet, as many of those I saw, are actually much taller with a long stem that connects to the roots in the interdunal soil. Plants are smart!