How Do Parabolic Dunes Form?

parabolic-dunes-form Credit: Larry/Flickr/CC-BY-2.0

As with all dunes, parabolic dunes are primarily shaped by the wind. Parabolic dunes tend to proliferate in places where wind blows predominantly in one direction and the movement of sand is restrained by vegetation.

In places where sand cover is thin and the wind blows in a constant direction, barchan dunes are the most common type observed. Barchan dunes require free-flowing sand to form and are therefore not as common as parabolic dunes. To form a classic parabola, the sand in a dune must be at least somewhat held in place by living vegetation.

As the wind blows over a sandscape, grains begin to accumulate in a ridge. In places where wind patterns are complex, star dunes form. If wind is comparatively steady, however, a vegetated area may erode into a cup-shaped depression. Sand from inside this depression is gradually blown over the edge and onto the reverse slope of the dune. Vegetation holds the sides of the dune in place while sand is scooped out and deposited leeward of the crest. As the parabolic shape forms, the "nose" of the dune advances in the direction of the prevailing wind. In Colorado's Great Sand Dunes national park, parabolic dunes eventually migrate into the main dunefield, where complex wind patterns shape them into star dunes.