Dune Types

The dunefield as seen from the foothills of the Sangre de Cristo Mountains. The long ridges that comprise much of the dunefield are reversing dunes.

NPS/Patrick Myers

The main dunefield at Great Sand Dunes is 30 square miles (78 square km), comprised primarily of reversing dunes and star dunes. Around the dunefield's edges and in the grassy sand sheet are barchan dunes, parabolic dunes, and nebkha dunes.

 

NPS/Kris Illenberger

Reversing Dunes

Comprising the majority of the 30-square-mile dunefield, reversing dunes are the result of two opposing wind directions. The predominate wind direction is from the southwest, pushing the dunes in the dunefield toward the mountains, but storm winds off the mountains from the northeast sometimes flip the crest of the dunes backward, forming a sharp ridge.

 

The pyramid-shaped Star Dune is one of the tallest dunes in the dunefield.

NPS/Patrick Myers

Star Dunes

Star dunes have three or more ridges descending from their summit, creating a star shape when viewed from above.

The prominent Star Dune, visible from the park entrance, is the tallest of the star dunes in the dunefield. However, it's an isolated star dune, separate from the star dune complex located in the northwest part of the dunefield.

 

Star dunes have three or more arms, formed from multiple wind directions.

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Star dunes form only in locations where there are multiple wind directions over the course of a year. At Great Sand Dunes, the large star dune complex in the northwest portion of the dunefield is the result of scattered wind directions from the shape of the nearby mountains.

 

Aerial view of parabolic dunes showing how vegetation holds back their long arms while the nose of the dune moves forward toward the dunefield.

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Parabolic Dunes

Much of the sand sheet is covered with vegetation. If strong winds erode a section of the vegetated sand (commonly referred to as a blowout), a parabolic dune may form. Leeward motion occurs if sand from the blowout is deposited on the opposite slope of the parabolic dune. Vegetation holds the "arms" of the dune in place as the leeward "nose" of the dune migrates forward toward the main dunefield. Parabolic dunes are common in the sand sheet southwest of the main dunefield.

 

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In the foreground of this aerial photo, on the sand sheet, parabolic dunes are slowly migrating toward the main dunefield. Vegetation on the valley floor causes them to become parabolic dunes rather than barchan dunes (below).

 

Barchan ("BAR-kahn") dunes form in areas with only one wind direction, and little or no vegetation.

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Barchan Dunes

The term 'barchan' is arabic for 'horns', indicating the simple arc shape of this dune type with two angular arms pointing forward. These develop in areas where winds blow only one direction, and there is little or no vegetation. Look for classic barchan dunes directly across from the main Dunes Parking Area, at the base of the tall dunes. Barchan dunes can begin to connect with others, forming barchanoid ridges.

 

This nebkha dune has formed around cottonwood trees near Medano Creek.

NPS/Patrick Myers

Nebkha Dunes

Nebkha dunes (also known as coppice dunes) are simple dunes that form around vegetation, either on the sand sheet or in cottonwood trees along Medano Creek and Sand Creek. Shrubs or trees begin to gather windblown sand; as the sand gets deeper, the plants also grow taller, allowing more sand to gather around them.