White Sands N.P., NM | GeologyVirtualTrips

WHITE SANDS N.P.

FIELD TRIP STOPS – THE LARGEST GYPSUM SAND DUNE FIELD IN THE WORLD (275 sq. mi.)

LOCATION: Route 70, 15 miles southwest of Alamogordo, NM and 52 miles northeast of Las Cruces NM.

GEOLOGIC FEATURES: Sand Dune development from grains made of the evaporite mineral Selenite Gypsum.

DESCRIPTION: About 250 mya a shallow Permian Sea covered parts of the U.S. interior that was part of the supercontinent, Pangaea. Due to high rates of evaporation, layers of gypsum were left behind. Nearly 30 mya, the part of New Mexico currently occupied by White Sands N.P. tectonically downdropped to form the Tularosa Basin between the San Andreas Mts. to the west and the Sacramento Mts. to the east. Subsequently, rivers dissolved the gypsum in these mountains and carried it to the Basin where it accumulated in the former Lake Otero. About 10,000 years ago, evaporation of this former playa lake caused the precipitation of Selenite Gypsum crystals as the lake dried to form the present Alkali Flat.

Winds blowing from the southwest initiated the dune system that we see today. Lake Lucero is a playa lake currently found at White Sands. Periodically it will become saturated with gypsum. Since there is no outlet, evaporation will periodically cause selenite crystals to precipitate from these playa lake waters to provide an additional source of gypsum to the alkali flat dunes.

STUDENT QUESTIONS:

(1) What is a Playa Lake?

(2) Define an Evaporite Mineral.

(3) Sand dunes move over time. Identify the windward and leeward sides of a sand dune and describe the process by which the dune moves.

(4) CHALLENGE: Compare the Selenite crystals formed at White Sands with the crystals formed in the Crystal Cave discovered in Naica, Chihuahua, Mexico. What is the major difference, and why is that so?

SELECTED REFERENCES:

-National Park Service. Geology of White Sands. White Sands National Park New Mexico. Accessed on May 13, 2020: https://nps.gov/whsa/learn/geology-of-white-sands.htm

-National Park Service. White Sands National Park - Nature and Science. Accessed on May 15, 2020: https://nps.gov/whsa/learn/nature/index.htm

PHOTOS:

Figure 1 - Gypsum sand dunes in the Tularosa Basin, White Sands N.P. (Photo by Explorer Eric Marintsch)

Figure 2 - The Visitor Center rents "sleds" for people to slide down the slopes of the dunes. Bulldozers periodically push the drifting sands to the side of the road to keep the park roads clear for traffic.

Figure 3 - Gypsum dunes are pervasive and continually migrate with the winds.

Figure 4 - Winds blow the loose sand into ripples on the dune faces.

Figure 5 - Explorer and Naturalist Eric Marintsch traverses the dunes. Vegetation must be hearty enough to tolerate the nutrient-poor soil and temperatures that can vary from below freezing to above 100 degrees F. In parts of the park where the winds and dune movement are high, plants cannot take root. (Photo by renowned world traveler, Johnny Lish)

Figure 6 - Sunsets at White Sands are famous. (Photo by Johnny Lish)

Figure 7 - The evening cools as the sun sets. Another day of exploring and observing come to a close for Eric Marintsch. (Photo by Johnny Lish)