May 02, 2016
Photographer: David K. Lynch
Summary Author: David K. Lynch
Nabkhas are eolian sand dunes formed when plants catch and accumulate wind-borne soil. They're called phytogenic mounds (phytogenic means originating from plants) and they're most common in desert and semiarid regions. Nabkhas are typically 3 ft to 16 ft (1-5 m) high and 30 ft to 200 ft (9-61 m) across. They're the only kind of dunes that are stationary. All other dunes move with the wind because there's nothing anchoring them to one spot.
A nabkha begins as a plant grows large enough to act as a windbreak and slows down passing air. Sand and dust accumulate around the plant along with spores, seeds and small insects. The mound grows larger and seeds germinate. Soon small animals join the party. Over the years, plants drop leaves and some die and decay, adding nutrients to the soil. The anchor plant grows larger, such as the mesquite tree shown here, and provides shade. Animals take refuge in the shade during the day. Burrowing animals aerate the soil. Larger predators arrive to hunt for rodents, all of whose droppings fertilize the growing mound. Some plants fix nitrogen and help other plants thrive. Eventually, the nabkha grows large enough to become self-sustaining and an entire ecosystem develops, all because of a single plant.
This photo one shows one of the many nabkhas in Death Valley National Park, west of Scotty’s Castle road and north of the Mesquite Flat Sand Dunes. It's about 13 ft (4 m) high and 82 ft (25 m) across. Note the rock hammer at lower left for purposes of scale. Photo taken on March 9, 2016.
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