Eolian Processes and Deposits in the Southwestern United States

Eolian sand covers extensive areas over the southwestern United States, and much of this sand is presently stabilized by vegetation. Reactivation of this sand due to future climate change or land-use practices could have serious consequences on human and animal populations, agriculture, grazing and infrastructure. Studies in the Mojave Desert, the Sonoran Desert, the Colorado Plateau (northern Arizona and southeastern Utah), and the Southern High Plains (southeastern New Mexico and west Texas) aim to understand the processes responsible for initiation of eolian sand movement, including controls from source-sediment availability, climate, vegetation, and land use.

Previous studies have suggested that, in the Mojave Desert, climate plays a major role in eolian sand dynamics, but more recent studies have suggested that source-sediment availability could be more important than climate controls. On the other hand, in the Southern High Plains, eolian sediment movement may be more a function of climate controls. Thus, each subregion of the southwestern U.S. may have different processes controlling the degree of eolian sand movement and dune activity. Detailed stratigraphic, geomorphic, geochemical, and mineralogic studies are needed to understand the most critical controls on eolian sediment movement.
 

Although dust emission in the southwestern United States today is minor on a global scale, it is further important regionally for management of lands vulnerable to wind erosion, for issues of human health and safety, and for potential damage to equipment and infrastructure, as well as for ecosystem function. Moreover, some National Parks and Federally designated wilderness areas in the western United States have protected viewsheds and thus are required to maintain certain high standards of visibility. Such standards, however, are commonly exceeded, but the causes of visibility degradation are still poorly understood. In particular, it is difficult to reconstruct the contributions of distant sources of haze caused by mineral or non-mineral aerosols, and to determine the relative roles of natural processes and human activities in producing atmospheric haze. Moreover, if models of dust emission can be developed for southwestern United States, they can also be applied to deserts elsewhere.

Today, dust continues to be emitted from natural surfaces but also from many previously stable surfaces now exposed through development or water diversion, such as at Owens Lake, California. However, we know little about how much dust was generated under different climatic conditions in the past, how much dust is naturally generated today, how much dust is related to human activities, and how much dust will be generated under different climatic and land-use scenarios in the future.

Using a combination of ground-based geologic and biologic studies, remote sensing techniques, and weather monitoring, USGS scientists are developing new methods to:

• detect and track dust events from satellite and remote camera images,
• distinguish between mineral-dust haze and industrial/urban pollution,
• determine soil conditions leading to wind erosion and dust emission,
• detect eolian dust in soils and estimate past rates of deposition,
• characterize modern dust and calculate current rates of dust emission and deposition in ecologically sensitive areas,
• evaluate the roles of eolian dust in ecosystem function, including possible effects on exotic-species invasion, especially conditions of cheatgrass invasion
• evaluate how wind erosion might affect human health, including the spread of infectious disease, such as Coccidiodomycosis (Valley Fever)
• model future dust emission and transport.