Monitoring and Modeling Dune Mobility
The Native Navajo and Hopi peoples of the southwestern United States are currently challenged by an increasingly dry climate. Increased aridity from warmer temperatures, combined with recurring drought, has resulted in a large amount of migrating sand that threatens housing, health, and transportation. More than one-third of Native lands on the Navajo Nation and Hopi Tribal Lands of the Colorado Plateau are covered with sand dunes and sand sheets.
Such dunes and sand sheets are common features of arid and semiarid environments across the globe, where specific conditions of abundant sand supply, wind, and minimum vegetation cover promote their occurrence. Existing dunes can be grouped into three climatic threshold classes (Lancaster, 1988): immobile (fully stabilized by vegetation), partly active (exposed dune crests with some vegetation cover), and fully active (wind-driven with no vegetation cover).
U.S. Geological Survey (USGS) scientists are conducting research with the aim of providing critical data to the Native peoples of the region in response to growing dune activity, diminished vegetation cover, and an increasingly arid environment (Redsteer, 2002). The USGS interdisciplinary studies are focused on understanding the processes responsible for initiation of eolian (wind-blown) sand movement, including the influence of source sediment availability, climate, vegetation, and land use.
Reactivation of inactive dunes could have serious consequences on human and animal populations, agriculture, grazing, and infrastructure on the Navajo Nation and similar areas of the Southwest. Annual rainfall in the western Navajo Nation has fallen below 75 mm (3 in) during the most recent drought (Redsteer and others, 2010). As a result, the areal extent of sand susceptible to mobilization has increased significantly. Moreover, regionally significant sand and dust storms are becoming commonplace during the spring, which is typically dry and windy.
Initial data from this study indicate that sand-dune migration rates are currently about 35 m/yr (115 ft/yr) or more in the arid southwestern portion of the Navajo Nation. Fieldwork and data from photo archives show growth of active dune fields and present reactivation of formerly stabilized surfaces. The formation and movement of active dunes on the downwind side of stream-bed sand sources is presently endangering housing and transportation, potentially jeopardizing native plants and grazing lands, increasing health hazards to humans and animals, and impacting regional air quality.
A more complete understanding of the complex environmental processes that have such a profound influence on the Navajo Nation requires more detailed datasets. USGS scientists, with the cooperation of Navajo communities, are working to expand the sensor network in the southwestern Navajo Nation and concurrently develop new analysis techniques. The resulting analyses will provide the Navajo people with a deeper understanding of the processes driving dune migration and will help identify possible techniques for mitigating hazards from sand and dust transport.
- Lancaster, N., 1988, Development of linear dunes in the southwestern Kalahari, southern Africa: Journal of Arid Environments, v. 14, p. 233-244.
- Redsteer, M.H., 2002, Factors effecting dune mobility on the Navajo Nation, Arizona, USA, in 5th International Conference on Aeolian Research and The Global Change & Terrestrial Ecosystem-Soil Erosion Network, Lubbock Texas, July 22-25, 2002 Proceedings: Lubbock Texas, Texas Tech University, International Center for Arid and Semiarid Lands Studies, Publication number 02-2, p. 385.
- Redsteer, M.H., Bogle, R., Vogel, J., Block, D., Velasco, M., and Middleton, B., 2010, The history and growth of a recent dune field at Grand Falls, Navajo Nation, NE Arizona [abs.]: Geological Society of America Abstracts with Programs, v.42, no. 5, p. 416.