White Sands National Monument

1/26/09
White Sands National Monument is a part of the White Sands Desert, the largest field of gypsum sand dunes in the world. It is located in the Tularosa Basin, 150 miles long and up to 60 miles wide, surrounded entirely by mountains, the highest being the San Andreas Mountains on the west and the Sacramento Mountains on the east. All of this runs parallel north and south between the Rio Grande and the Pecos River, the two major drainages of New Mexico. Telaroso Basin, though, drains nowhere; it is a true basin. The water that flows down from the mountains or falls as occasional rain either evaporates, soaks into the ground, or accumulates in shallow intermittent lakes, called  playas, whose eventual evaporation plays an important role in the formation of the gypsum dunes.

Gypsum is not a particularly rare mineral, and large gypsum strata lie in the mountains surrounding Tularosa Basin. But gypsum sand is rare. This is because gypsum dissolves in water when it erodes and thus flows to wherever the stream is flowing, eventually the ocean. In Tularosa Basin, though, water pools up in shallow lakes in the wet season and gradually evaporates in the long, hot, dry season, leaving the gypsum in its mineral form on the dry floor of the playa. Still not sand, this gypsum precipitate covers the ground in crystal beds up to three feet long. Freezing and thawing break the crystal down to sand particles, at which point the wind takes over the job of building sand dunes.

White Sands is no misnomer. The gypsum dunes are blindingly, brilliant white in the bright blue sunny sky. I had to don my shades for the first time of my entire trip. It looked like the first sunny day after a blizzard, with big banks of white reflective sand rising up from roads, themselves covered in white. To round out the illusion, people were out sledding! This was the first National Park unit I'd ever been to where the dominant visitors were families with small children out to play. The visitor center even rented plastic sleds. It was Sunday and by afternoon the entire picnic area was filled with cars and picnickers at the 60s-style space age picnic tables, the surrounding dunes alive with sledding children. It was a hoot. (I have no idea why I didn't take a picture of some sledders.)

White Sands National Monument covers about 10 acres, nearly subsumed by the 2.2-million acre White Sands Missile Range, the largest military installation in the country (and the site of the Trinity test, world’s first hydrogen bomb explosion.) Nearly half of the monument is a “Zone of Cooperative Use” with the Defense Department, with restricted access and requiring permits required to visit, The entire monument as well as a stretch of US 70 are closed for an hour or two an average of twice a week during tests. It would seem we are lucky to have White Sands National Monument at all.

The monument is primarily a day-use facility. It has no campground and closes for the night at 6:30. The park does allow what it calls “backcountry” camping, really just walk-in camping, the closest site being 0.7 miles from the parking lot. I decided to give that a try, digging out my backpack for the first time since the Sierra. Before issuing my overnight permit the ranger showed me photos of unexploded ordinance that I could conceivably come upon in the dunes, devices that I should report and decidedly not touch. As with the Franklin State Park, campers are alone in the park once the gates were locked, though unlike the Texas State Park, White Sands did not give campers the code. In emergencies we could dial 911.

Once I had my overnight permit I had a few hours to kill before heading out, so I hunkered down in the shade and resumed my sand dune studies.

Most of the world’s sand is made of quartz, but sand can be basalt, or sea shells, or gypsum. Sand is not a particular material, it is a size, or rather a condition: small and light enough to be moved easily by wind or water but too large or heavy to remain suspended in the air. Anything lighter would be dust or silt. Anything heavier would be a pebble.

It takes wind above 15 mph to move much sand. Above that sand volume is a cubed function of wind velocity, which is to say a 10 MPH increase in wind velocity would move 1000 times more sand.. Winds pick up to 45 MPH at White Sands in the  spring so that is when dunes are on the move, and why I didn‘t want to be there then.

I’d often wondered why sand dunes form where they do, and the answer turned out quite simple. Other than sand and wind all it takes is an obstruction of any sort  - a rock, a mound of earth -  to block the flow of sand. After that the built-up sand serves as the barrier, and the dune builds itself. Once started sand dunes take on a fairly predictable life of their own, and scientists have come up with some pretty interesting observations.

A dune’s windward face rises gently at a 3 to 10 degree slope. Sand creeps or bounces up the face. As the dune gets higher relative to its neighbors it sticks up too much and absorbs too much direct wind to keep building, so sand starts going down the lee side, called a slipface, at a 34 degree angle, the angle of repose for dry sand. In entirety, the dune slides on over, occupying a space and then abandoning it, creating an interdune.

slipface

The first mounds of sand, the embryonic dune, move 30‘-38 feet/year. Strong winds tend to mold growing sand dunes into a crescent shaped, with two downwind horns stemming from an upwind ‘nose’. With enough sand these crescent dunes join to form long ridges, perpendicular to the prevailing wind, called Transverse Dunes, which will move 12-13’/year. Where plants gain a foothold, they anchor sand and invert the shape of the dunes. With the arms anchored, the mobile center moves downwind, These are called Parabolic Dunes. These are the slowest moving, maybe 2-8’/year.

parabola

Most plant life takes root in the soils that develop in the interdune areas. But to survive any length of time a species has to develop a method of overcoming this (moving) obstacle. Plants such as the soaptree yucca and the skunkbush sumac send their stems and roots down the sand fast enough to continue growing above the emerging dune. These plants may appear to be 4-5 feet high but are in fact 35-45’ high, most of which is buried by sand. When the sand moves along the exposed soaptree yucca root is too unstable and the bush collapses. But the skunkbush sumac has dense and thick branches that trap enough sand to form a pillar when the rest of the dune moves on. These become oases of life in the dune fields.

soaptree yucca

interdune

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skunktree sumac?

Jackrabbits, kangaroo rats, pocket mice, rattlesnakes, lizards, beetles, and porcupine all live in the dunes. Some have adapted by turning whitish. The kit fox is the top predator, as larger mammals such as coyotes wouldn't find enough food in the dunes. They do lurk around the edges should the kit fox wander.

I ate dinner before heading out to my camp and planned to come back to my car for breakfast, so the only provisions I needed to carry were an energy bar and some soy milk for my midnight snack. The ranger instructed me to start for my site an hour before sunset to avoid stumbling around lost once dusk set in, as it is very easy to become disoriented in sand dunes. The ranger also told me that the only one other party out there that night was a young couple from North Carolina and their two dogs.

While White Sands is the largest gypsum dune field, the dunes in the monument are not themselves large. Walking 0.7 miles in the Kelso Dunes at Mojave National Preserve for example might be grueling, but my walk was rather modest. The camp sites were all located in separate interdunes and consisted of nothing but numbered sticks identifying which was which. After setting up my tent (Setting up I broke one of my tent polls. It would be doomed if the night got windy.) I wandered about the dunes taking pictures, careful not to get lost or disoriented. I got lost and disoriented anyway, but eventually spotted the North Carolina couple who were able to orient me to my own interdune.

Once it got dark the sense of isolation was enormous. Just me and the kit foxes, which I never saw. Of course the isolation was mostly an illusion given the surrounding military infrastructure, but still, it was a mystical sort of evening, I must say. The morning began with the most fiery sunrise I'd ever seen but then turned mostly cloudy, depriving me of my hopes for doing some amateur photography with the early morning light.

As I hiked back to my car I saw what appeared to be a rocket take off from nearby Holloman Air Force Base  Noteworthy enough for an ersatz backpacking trip, but then a  jet emerged from the vertical tailings of the rocket blast and flew off, horizontally. It was, I since learned, an F-22A Raptor, the most advanced fighter aircraft in the world according to the United States Air Force. It's not all cacti and sand storms in this desert.