I’m dreaming of a White Christmas, but if you live in a place where snow isn’t guaranteed, you can visit one of these locations for a geologic blizzard of white.
Sharon Lyon
Editor, GeoLifestyle
White Sands National Park, New Mexico
Zack Frank/ Shutterstock.com
White Sands is the world’s largest gypsum dune field, towering more than 50 feet tall on its western side. Why are the sand dunes located so far from the ocean?
Formation:
Two hundred and eighty to 250 million years ago, part of the southwestern United States was covered by the shallow Permian Sea. Rising and falling sea levels and hypersaline conditions left behind thick layers of the evaporite mineral gypsum, interbedded with limestones and sandstones.
During the Laramide orogeny 70 million years ago, the land was uplifted, forming the once-contiguous San Andres and Sacramento Mountains.
Down-faulting due to extension of the continent in the Oligocene 30 million years ago, caused the development of the Tularosa Basin, splitting the mountains into two bordering ranges.
Precipitation in the mountains dissolved the gypsum layers, and streams carried the minerals into the Tularosa Basin, where the water ponded to form Lake Otero. When the last Ice Age ended, Lake Otero began to evaporate, becoming a playa, or dry lakebed.
As the climate became warmer and drier, the area transformed into the modern Chihuahuan Desert. As Lake Otero dried up, gypsum (selenite) crystals formed an Alkali flat. Winds broke up the crystals into small grains, polished them by abrasion, and blew them into large dunes. The 275-square miles of dunes are comprised of more than 4.5 billion tons of white gypsum sand.
What remains of the lake is today known as the much-smaller Lake Lucero. The process of gypsum crystal formation and destruction continues, with selenite crystals up to 3-ft-long found along the lakeshore.
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The historic visitor center, an example of Spanish Pueblo-style adobe architecture, was constructed onsite in the 1930s using local materials.
Wander through the native plant garden, learn about the daily programs, view the orientation film, and explore the interactive museum.
Take the 16-mile round-trip Dunes Drive into the heart of the gypsum dune field. The first four miles are paved, and the last four miles are a hard-packed, gypsum road.
For the adventurous, sled down the slopes of the sand dunes on a waxed plastic saucer, available at the gift shop.
Human Footprints at White Sands
During the Pleistocene, the Tularosa Basin contained streams, grasslands, and Lake Otero. Large Ice Age mammals lived along the lakeshore, including mammoths, ground sloths, camels, dire wolves, lions, and saber-toothed cats. Paleolithic human footprints have been found interacting with the footprints of these mammals.
More than 60 fossilized footprints, buried in layers of gypsum soil, were dated between 21,000–23,000 years old.
Controversy over this dating stems from the use of an aquatic plant, which may have taken up carbon from old groundwater; however, further dating of terrestrial pollen and the use of optically stimulated luminescence dating of quartz grains within the footprint layers support this age.
Why it matters: If the date holds up, the footprints at White Sands would potentially be the oldest in North America. The recent data support the fact that humans were present in North America during the Last Glacial Maximum.
Next, we’ll fly across the pond to the famous White Cliffs of Dover, 300-foot-tall bluffs overlooking the Strait of Calais. On a clear day, these striking white cliffs are visible from the French coast, and similar features are found in France. How did they form?
The cliffs are made of chalk, a rock composed of coccoliths, fragments of tiny pelagic algae. During the late Cretaceous, 85–89 million years ago, a continuous rain of these calcium carbonate microorganisms settled through the ocean water, which covered this part of Europe.
The calcareous ooze on the ocean floor formed the “Middle and Upper Chalk” seen at the cliffs. Small amounts of silica from siliceous sponges within the ooze became bands of flint during diagenesis.
The chalk was uplifted, faulted, and folded during the late Paleogene and Miocene, due to distant effects of the Alpine orogeny, as the African and Arabian plates to the south collided with the Eurasian plate to the north.
Britain and mainland Europe were physically connected by the Weald-Artois Anticline which acted as a natural dam to a vast glacial lake, into which the ancestral Thames and Rhine rivers flowed. Between 450,000–180,000 years ago, the dam broke, causing a catastrophic flood through the collapsing chalk—perhaps the largest geological flood in Europe.
With rising sea levels 10,000 years ago, Britain became fully cut off from its last land connection with continental Europe. The English Channel was born, completing the separation of the cliffs of England and France.
Erosion has exposed the chalk at the land surface, where it forms a characteristic topography of rolling hills and valleys, known as the Downs. The White Cliffs form where the downs meet the sea.
The dark-colored flint within the chalk is mostly composed of the remains of sponges and siliceous microorganisms, but the silica has also filled cavities left by dead marine creatures to create molds, especially of echinoids. Crinoids, bivalves, and ammonites are also present in the chalk deposits.
You can locate fossils at the base of the cliff. Flint nodules and chalk boulders dot the shore, but chiseling fossils out of rocks and cliffs is prohibited. Instead, collect loose fossils on the shore or in the smaller rocks.
Low tide is the safest time of the day to hunt. Fossil hunters with less experience should seek advice prior to approaching a recent cliff face.
Whether you are celebrating the holidays in a snowy locale, on a tropical beach, or somewhere in between, I wish you a Happy Holiday. See you in the New Year!
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