August 27, 2007

Exploring Nevada’s sand dunes

Uncovering the mysteries of the hillsides in the Southwest

By Shirley Robinson, Staff Writer
The Rebel Yell
University of Nevada, Las Vegas

Sand that makes music; vast dunes frozen in time; a living tarnish that spreads like a rash across hillsides; aquatic animals that seem to spontaneously appear out of puddles; boulders that blow across the ground. Although these features may sound like something from an oddball alien planet, they’re not. They are all found in and around Southern Nevada – a scientist’s, a child’s and a mystery-lover’s playground.

Among Nevada’s and the Southwest’s most striking characteristics are those smooth, shadowed mounds of sorted sand known as sand dunes. Grains from past, disintegrated mountains are gathered by strong winds and are often deposited against natural barriers where the winds die down. Grains that are very small, such as fine silts, remain suspended in the air and are carried off and aloft.

Although the grains comprising most dunes are pale-colored quartz crystals, streams of black sediments are frequently seen feathered within the peaks. These darker minerals are often heavy and iron-rich, and they are able to be transported along with the quartz sand due to their fine-grain size. Twirling a simple kitchen magnet within the sand may quickly attract a mass of iron filings. One of the most enchanting aspects of sand dunes is the ability of a select few to emit sound. Reports of this phenomenon have poured from all corners of the globe for hundreds of years with some likening the sound to that of a kettledrum or low-flying aircraft and others to that of a trumpet or harp.

It is thought that the sound of these musical sands, which are often called “singing” or “booming sand dunes,” is created from the movement of the quartz crystals as avalanches are triggered either by the wind or by dune travelers. The synchronized sliding of the polished grains emits a rumble, squeak or roar that reverberates across the dunes and can be heard for miles.

More than 30 locations across the world, from Morocco to Hawaii, feature singing sand dunes and over a half dozen of those are found in Nevada and California. Located 100 miles southwest of Las Vegas in Southern California’s Mojave National Preserve, the 45-square-mile Kelso Dunes are among the West’s most popular and highly studied singing sands.

With the exception of the Nellis Sand Dunes, located north of Nellis Air Force Base, the Las Vegas Valley lacks extensive dunes. However, geologists have concluded that this was not always the case.

Vast, barren sand seas (ergs) comparable to those of the Sahara Desert are thought to have blanketed the Las Vegas Valley and much of the Southwest with thousands of feet of sand. Evidence for this lies in the fiery-red cliffs and rounded outcrops of the ever-popular Red Rock Canyon west of Las Vegas. (Although now solid sandstone, petrified over time, the area’s formations were once soft, spilling dunes.)

Las Vegans tend to treasure these “fossil” dunes as their area’s own unique attraction, but the sandstone that makes up Red Rock is also present in the Valley of Fire State Park in northeastern Clark County. It is also in Zion National Park and at Lake Powell in neighboring Utah. Although known as the Aztec Sandstone in Southern Nevada and the Navajo Sandstone in Utah, the red rock is all believed to have been part of the same giant desert dunes.

Distinctive characteristics held by the Aztec and Navajo Sandstone include the streaks of red, orange and purple that stain the outcrops. These color bands are thought to be caused by the circulation of water through the quartz grains after they were petrified; the water essentially rusted the iron-rich minerals within the solid dunes, creating oxidized works of art.

Water has also taken its toll on the structure of the petrified dunes. Rainwater dissolves the cementation between the grains. Moisture also hydrates wind-blown salts that work their way between the sand grains, which swell and consequently pry the sandstone apart. Bizarre geologic forms result, such as deep, smooth hallows, rounded piles of boulders and towering, but teetering, balanced rocks.

Although they no longer look like dunes, the solidified remnants show undeniable evidence of being deposited by wind. Sediments that are carried and laid down by water tend to be stacked into fairly flat-lying planes or beds. The grains of the Aztec Sandstone, however, lie in gently curving, multi-angled layers (or cross-beds), suggesting that shifting winds of the past swirled the once loose sands and deposited them upon the dynamic slopes of restless sand dunes.

One may notice that some surfaces of the old, smooth and sculpted Aztec Sandstone is blackened and almost charred-looking. Although wildfires frequently ravage the desert and can indeed darken rock outcrops, the most probable cause behind these coatings is a life form rather than a flame. It is theorized that microbes living on the rock surfaces trap wind-blown dusts (clay, pollen, etc.) and cement them together with dark manganese and iron oxides. The oxides are thought to be leached out of the host rock, mobilized and concentrated by the microbes, creating the black, laminated film which has been termed “desert varnish.”

As one can imagine, the environment on a dry Mojave Desert rock is far from hospitable – becoming searing hot during summer afternoons and freezing cold during winter nights. Despite the temperature extremes, the microbes stay alive by going into a state of dormancy. Research has shown that the hardy little life forms explode with activity and create layers of varnish only during times of rain. Since precipitation is scarce in the desert, there are only a handful of days out of the year during which the microbes work. It therefore requires many years for varnish to accumulate; the older the coatings are, the thicker and darker they become.

It sounds rather far-fetched that life can survive in a torpid state for extended periods of time without water in such a harsh climate, but the phenomenon occurs more often than people might think.

One of the most amazing and surprisingly prevalent examples of dormancy lies buried beneath the fine silts of the dry lakes and playas throughout the Southwest. Microscopic eggs of a crustacean, known as the long-tailed apus, withstand the drought and heat of sun-baked mud-cracks for months, hatching only when heavy rains bring life-giving puddles to the seasonal lake beds. Adults, which reach two inches in length, mature rapidly as they have very little time to lay their eggs before the water soaks into the thirsty ground and evaporates into the hot air.

Although they have hatched out of the soils of several areas for centuries, these ephemeral creatures were first discovered within the Dry Lake of Eldorado Valley in1936 by a girl from nearby Boulder City, Nev. The news of rain-puddles teeming with life quickly drew local children with jelly jars hoping to catch their own early version of “Sea Monkeys.” Specimens were also collected by curious adults and sent away to various scientific organizations. Definitive answers about the mysterious species came in 1947 when Swedish naturalist Folke Lind identified them as A ”pus Longicauditus,” a tadpole shrimp often found fossilized in sedimentary rock.

Dry lake beds and salt-crusted playas, which form at the base of broad, desert valleys where fine silts accumulate, are among the most level surfaces on the earth. Hence, they make for ideal landing strips and are sought-after for racing high-speed craft. The dry Groom Lake of Lincoln County, Nev., home of the remote test facility “Area 51,” has one of the world’s longest run strips, and the Black Rock Desert, in northwestern Nevada, served as the racetrack on which the current land speed record of over 760 mph was achieved.

One of the most famous playas, however, is known for the “racing” of something other than top-secret aircraft and jet-powered cars. Located within California’s Death Valley National Park, “The Racetrack,” attracts thousands of flabbergasted “spectators” each year with its evidence of cobbles and boulders sliding mysteriously across the playa surface. Although no one has ever actually seen the rocks move, undeniable tracks, left in the now desiccated mud, trail the scattered subjects, which weigh up to 80 pounds.

Individual tracks have measured over 2,000 feet in length and tend to indicate that the rocks follow a straight coarse while traveling. Some, however, have sudden hairpin turns, and many show signs of rolling, tumbling and colliding.

Some investigators propose that the rocks become frozen within thin sheets of ice that are driven across the playa by winter winds. Most scientists, however, believe that the gusty winds of any season which happen to blow across the playa after a recent rain can propel the rocks. It is believed that the slick mud washed in by flood waters create unbelievably smooth surfaces on the flat playas across which wind can travel incredibly fast at ground-level. Stones just a few inches high can be blown across the slippery surface.

Southern Nevada is in the heart of one of the most mysterious regions on earth. By stepping out and exploring its natural wonders, we may unlock the secrets of the Southwest.