INSIGHTS INTO RECENT ACTIVITY IN THE ST. ANTHONY DUNE FIELD, NORTHEASTERN SNAKE RIVER PLAIN, IDAHO Rachael H. Hoover 1, David G. Gaylord 1, Richard A. Rupp 2 and William M. Phillips 3 1: School of Earth and Environmental Sciences, Washington State University 2: Crop and Soil Sciences, Washington State University 3: Idaho Geological Survey, University of Idaho INTRODUCTION: o Eolian dune deposits are proxies for past regional and local climate fluctuations and are useful for assessing the duration and intensity of climate events such as droughts (Forman et al, 2001) o Deposition and mobilization of sand dunes reflect atmospheric interactions with the Earth’s surface and are controlled by complex interactions between precipitation, temperature, and vegetation (Nickling, 1989; Lancaster, 1997; Hugenholtz and Wolfe, 2005 and 2006) o The primary purpose of the research presented here is to: Quantify the threshold climatic conditions that control the expansion and contraction of active, St. Anthony dunes o Results of this research will assist in efforts to evaluate dune reactivation potential in this agriculturally sensitive part of the eastern Snake River Plain METHODS: o TEXTURAL ANALYSIS: Collected dune samples at 30 cm depth and 1km intervals to investigate textural trends Trace amounts of silt and clay allowed for standard sieve techniques to determine grain size o DUNE MIGRATION: Used archival air photos ( ) to calculate dune movement Georegistered air photos and mapped dune crest changes over time o DUNE TOPOGRAPHY: Quantified current dune thickness and underlying topography using Digital Elevations Models o METEOROLOGICAL EVALUATION: Analyzed data (1912-present) to assess historical weather patterns and fluctuations Weather stations located throughout Idaho include St Anthony, Rexburg, Idaho Falls and Juniper Buttes TEXTURAL ANALYSIS: o Mean grain size ranges from phi Coarsest located in the south Finest located in the north and northeast o Dune complex appears to consists of two separate fining downwind subcomplexes o All but one sample is very well sorted or well sorted ARCHIVAL AIR PHOTOS: o Dune complex is comprised of barchan, parabolic and linear dunes o Average migration rates of the dunes range from m/yr from Highest rates are located in the northeast part of the dune complex between following a period of increased temperature and decreased precipitation Lowest migration rates located in the southeast occur between following a period of increased precipitation o Preliminary analysis indicates that variations in migration rates are related to surface roughness most directly correlated with vegetation cover and basalt exposures Higher migration rates attributed to migration across relatively smooth unvegetated dunes and interdune basalt Lower migration rates are attributed to the influence of relatively rough, shrub- dominated vegetation o Dune wavelengths are longest in the central portion Exposed basalt in interdunes may promotes sediment bypass o Dune heights are greatest in the east Lack of basalt exposures and sediment bypass may cause net dune aggradation DIGITAL ELEVATION MODEL: o Minimum thickness of dune cover above underlying basalt varies from m with an average thickness of 6m o Thin dune cover interpreted as an artifact of net sediment bypass o Thick dune cover reflect net dune climbing and aggradation o Topographic profiles indicate northern and eastern (downwind) margins are higher than the upwind margins Increased elevation of underlying topography may influence positions of the dune margin by slowing rates of migration and by limiting long-term accumulation Position of active dune complex may reflect topographic funneling by a topographic low in Island Park Caldera approximately 25km downwind METEOROLOGICAL DATA AND VEGETATION: o Average wind speeds decreased from and increased between Correlate positively with rates of dune migration from o Increased amounts of precipitation in 1998 were followed by a decreased in migration rates beginning in 1999 o Increase in temperature and decrease in precipitation from associated with increased migration rates beginning in the earl 1990s These climatic conditions may decrease the amount of vegetation cover which in turn would increase the migration rates o Increased amount of vegetation cover results in an increased dune stability REFERENCES: Forman, S.L., Oglesby, R., Webb, R.S., Temporal and spatial patterns of Holocene dune activity on the Great Plains of North America: megadroughts and climate links. Global Planetary Climate Change.29, Hugenholtz, C.H., and Wolfe, S.A., 2005, Biogeomorphic model of dunefield activation and stabilization on the northern Great Plains: Geomorphology.70, Hugenholtz, C. H. and Wolfe, S. A., 2006, Morphodynamics and climate controls of two aeolian blowouts on the northern Great Plains, Canada. Earth Surf. Process. Landforms.31, 1540–1557. Lancaster, N., Response of eolian geomorphic systems to minor climate change: examples from the southern Californian deserts. Geomorphology. 19, Nickling, W.G., Prediction of soil loss by wind. In: Rimwanich, S. (Ed.), Land Conservation for Future Generations. Ministry of Agriculture, Bangkok, SUMMARY AND CONCLUSIONS: o Larger dune complex may represent the amalgamation of two smaller dune subcomplexes Both dune subcomplexes fine downwind Both dune subcomplexes contain dunes with different orientations that reflect different migration directions o General trends have been identified between migration rates and changes in temperature, precipitation and wind speeds o Additional meteorological analyses (e.g., 3 year running averages) is necessary to identify the threshold climatic conditions associated with episodes of dune expansion and contraction o Dune wavelengths and heights vary according to the underlying topography and basaltic substratum o Dune migration rates have varied systematically since the 1940’s potentially in response to expansion and contraction of vegetation cover, which grossly reflects episodes of varying evapotranspiration and evaporation o We anticipate that continued evaluation of the long- and shorter-term trends in temperature, precipitation and wind speed will help identify general and perhaps even more specific threshold climatic conditions responsible for the stabilization and activation these eastern Snake River Plain dunes Division of subcomplexes