MONITORING ACTIVE SAND DUNES AT GREAT SAND DUNES NATIONAL PARK AND PRESERVE, COLORADO

Great Sand Dunes National Park and Preserve (GSDNPP), located immediately west of the Sangre de Cristo Mountains in central Colorado, is a wonderful natural laboratory for investigating the movement of active sand dunes. We have initiated a study of some specific sand dunes on and adjacent to the southern margin of the main dune mass at GSDNPP. A handheld Trimble GeoXH unit was used to document both the crest and the basal margins of several dunes in an effort to track movement of the crest of the dunes, as well as to constrain the volume of sand involved in any detected movement of the dunes. The GeoXH makes use of both US Global Positioning System (GPS) satellites and other international satellites available through the Global Navigation Satellite System (GNSS) to record positional information that, after post-processing (which is a free service), locations are produced with a horizontal precision where >96% of the points are located to better than 15 cm (6 inches). This accuracy is sufficient to monitor changes to the dunes on a horizontal scale >0.5 m. GeoXH surveys were conducted at GSDNPP in June of 2015 and 2016, which provides an early assessment of the yearly movement of some of the dunes. Initial results indicate that the movement of the dunes at GSDNPP may be less systematic than had been previously anticipated. One dune on the sloping southern side of the main dune complex appears to show a rather complex motion of the dune crest, with portions of the dune crest moving >2 m to the east during the same time interval when other crest portions moved up to 1 m to the west. Vertical precision of the location data is less well constrained than is the horizontal precision, but it is still sufficient to allow a determination of the volume of mobile sand associated with each monitored dune. Future efforts will relate GeoXH results to previous survey-grade differential GPS measurements of other dunes along the southern margin of the GSDNPP dune field, as well as to measurements of sand dunes on Mars obtained from data derived from the High Resolution Imaging Science Experiment (HiRISE).