LiDAR Surveys of Gypsum Dune Fields in White Sands National Monument, New Mexico

Kocurek, Gary; Kohrig, Mike; Baitis, Elke; Ewing, Ryan; Smith, Virginia; Peyret, Aymeric; Lewis, Ann; Reiser, M.

LiDAR (Light Detection and Ranging) surveys were conducted over a representative 39 km2 area of the gypsum dune field at the White Sands National Monument during June 2007 and June 2008. Study objectives were to (1) establish the base physical parameters that characterize the dune field, (2) identify spatial variability in the dune pattern, (3) determine the cause of pattern variability, (4) ascertain dune activity over a year, and (5) gauge the potential for long-term monitoring via LiDAR surveys. Digital elevation models (DEMs) created from LiDAR data using ArcGIS allowed for accurate measuring of an unprecedented range of dune-field parameters from dunes selected (1) at random, (2) along transects in the net transport direction, and (3) within zones where the pattern is visually different. In order to investigate the cause of pattern variability, dunes were computationally removed to reveal the base surface over which they are migrating. Dune activity over the year was determined from a difference map in which the June 2007 topography was subtracted from the June 2008 topography. Results show that the dune field is best characterized by dune height, spacing, dune length, crest sinuosity, and dune orientation, but there is marked variability among most measured parameters and little correlation exists between parameters. Pattern emerges at White Sands because of the strong trend in dune orientation. Dune-field variability is real and is thought to occur because of the young age of the field, ubiquitous dune-dune interactions that rearrange the pattern, and field-scale boundary conditions. However, the nature of LiDAR data forces the recognition of pattern variability, which exists in most dune fields, but that has been deemphasized by traditional measurements. The primary boundary condition that causes pattern heterogeneity at White Sands is antecedent relict topography from paleo-shorelines formed during the episodic retreat of Lake Otero. Disguised beneath the dune field new paleo-shorelines were discovered at elevations of 1203, 1205.5, and 1211 m on the base surface. Dune activity varies significantly over the dune field, from high rates of dune migration and pattern ordering within the first 0.5 km of the field, to low levels of dune activity within the parabolic dunes at the downwind end of the field. Dune growth occurs on sand build-ups lee of the paleo-shorelines, in contrast to dunes in the central portion of the field where the water table is just below the surface. Although the dunes migrate about 3.5 m/yr to the ENE in response to dominate winds from the WSW, streamwise lineations, superimposed stoss bedforms, and both crescentic and parabolic dunes show a component of lateral migration to the south because of winter north winds. The impact of dune migration upon park infrastructure is evident, and LiDAR emerges as a powerful tool for monitoring vital signs within the park and for maintaining park functions.

LiDAR Surveys of Gypsum Dune Fields in White Sands National Monument, New Mexico

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