OBSERVATIONS ON DUNE BEHAVIOR AT GREAT SAND DUNES NATIONAL PARK, COLORADO

Great Sand Dunes National Park & Preserve, CO, is the site of a complex aeolian system and varies along a topographic gradient [1]. The dunefield is at the high end of the gradient and it contains a variety of dune forms at a variety of scales. Some are small and typical of unimodal wind regimes while others are large and the type found in bimodal or complex regimes. The National Park Service (NPS) manages Great Sand Dunes and is interested in understanding the behavior of the sand dunes and how the aeolian system works. Essential to that is monitoring dune movement and growth.

The NPS has used GPS and traditional surveys to map dune position and height beginning in 1992 on a few index dunes. There is also aerial imagery of the dunefield from 1998, 2005, and 2011 it was used map changes in dune location for other dunes.

The results show that regardless of dune type or size, there has been next migration toward the NE. The smaller dunes doe migrate faster, but not proportionally. These results match sand drift potential calculated from wind data and agree with previous work on dune migration rates [2].

Vertical dune growth for the largest dune is dependent on the direction of migration as accommodation space varies on either side of the dune. On large dunes in general, an increase in dune high will require the migration of smaller dunes to the crest or the migration of a large ridge up the slope of a mega dune.

References:

[1] Valdez, A. D., Development and Eolian Geomorphology of Great Sand Dunes in Quaternary Geology of Great Sand Dunes, USGS Open File Report 2007-1193 p 7-10, 2007

[2] Foreman, S. L., Episodic Late Holocene dune movements on the sandsheet area, Great Sand Dunes National Park and Preserve, San Luis Valley, Colorado, USA. Quaternary Research 66 p 97–108, 2006