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Landforms along the Pacific, Gulf of Mexico, and Atlantic coastlines for the conterminous United States are attributed with the relative vulnerability of horizontal erosion due to sea-level rise to characterize coastal zone stability. The position and extent of landforms are geospatially indexed as line-events where these coastal zone features are intersected by the linear-referenced 2013 - 2014 U.S. Geological Survey National Hydrography Dataset Coastline, which corresponds to the National Oceanic and Atmospheric Administration (NOAA) 2013 - 2014 mean high water level datum delineated in intertidal zones open to oceans, behind barrier coasts in bays, lagoons, and estuaries, and sometimes where tidal currents reach...
Aeolian processes are of particular importance in dryland ecosystems where ground cover is inherently sparse because of limited precipitation. Dryland ecosystems include grassland, shrubland, savanna, woodland, and forest, and can be viewed collectively as a continuum of woody plant cover spanning from grasslands with no woody plant cover up to forests with nearly complete woody plant cover. Along this continuum, the spacing and shape of woody plants determine the spatial density of roughness elements, which directly affects aeolian sediment transport. Despite the extensiveness of dryland ecosystems, studies of aeolian sediment transport have generally focused on agricultural fields, deserts, or highly disturbed...
Eolian deposits of the Chaco dune field cover a broad expanse of the southeastern Colorado Plateau in New Mexico and comprise a large part of the late Quaternary sedimentary record in this region. The primary eolian landforms include sand sheets, parabolic and modified parabolic dunes, barchan-barchanoid dune complexes, and ridge dunes. Many of the eolian landforms in the Chaco dune field have remained stable over a sufficiently long time to permit soil development. Weakly to moderately developed calcic soils, which formed in eolian deposits of mid-Holocene and latest Pleistocene age, possess clay-enriched, weak argillic B horizons. These soils have been buried progressively by younger eolian sediments, forming...
Categories: Publication; Types: Citation, Journal Citation; Tags: Geomorphology
Channel responses to flow depletions in the lower Duchesne River over the past 100 years have been highly complex and variable in space and time. In general, sand-bed reaches adjusted to all perturbations with bed-level changes, whereas the gravel-bed reaches adjusted primarily through width changes. Gravel-bed reaches aggraded only when gravel was supplied to the channel through local bank erosion and degraded only during extreme flood events. A 50% reduction in stream flow and an increase in fine sediment supply to the study area occurred in the first third of the 20th century. The gravel-bed reach responded primarily with channel narrowing, whereas bed aggradation and four large-scale avulsions occurred in the...
The vulnerability of dryland surfaces to wind erosion depends importantly on the absence or the presence and character of surface roughness elements, such as plants, clasts, and topographic irregularities that diminish wind speed near the surface. A model for the friction velocity ratio has been developed to account for wind sheltering by many different types of co-existing roughness elements. Such conditions typify a monitored area in the central Mojave Desert, California, that experiences frequent sand movement and dust emission. Two additional models are used to convert the friction velocity ratio to the surface roughness length (zo) for momentum. To calculate roughness lengths from these models, measurements...
This study used three cross-sections along a subalpine channel to examine associations between flow and sand and gravel bedload transport in a cobble-bed channel. At each section, velocity was measured at 0.2, 0.4, 0.6, and 0.8 of flow depth for ten increments across the section. At each increment, velocity measurements were immediately followed by 10-min bedload samples with a 7.6 cm Helley-Smith sampler. Linear regressions between bedload and flow variables suggest that grain shear stress, stream power, near-bed velocity, average velocity, and the Froude number are the most relevant indicators of bedload transport, particularly when regressed against the Dmax or D84 of the bedload grain-size distribution. No significant...
Ice surface topography of a late Pleistocene glacier complex, herein named the Taylor River Glacier Complex (TRGC), was reconstructed on the basis of detailed mapping of glacial landforms combined with analyses of aerial photos and topographic maps. During the last glacial maximum (LGM), the TRGC covered an area of 215 km2 and consisted of five valley or outlet glaciers that were nourished by accumulation in cirques basins and/or upland ice fields. Equilibrium-line altitudes (ELAs) for the glaciers of the TRGC were estimated using the accumulation-area ratio method, assuming that ratio to be 0.65���0.05. ELAs thus derived ranged from about 3275 to 3400 m, with a mean of 3340���60 m. A degree-day model (DDM) was...
Over the past 100 yr, several hypotheses have been proposed for the origin and age of the Great Sand Dunes. These hypotheses differ widely in the descriptions of dune morphometry, the immediate source of eolian sand, and when sand transport occurred. The primary purpose of this paper is to evaluate these hypotheses and, where warranted, to present new ideas about the origin and age of the Great Sand Dunes. To evaluate the previous hypotheses, we had to develop more detailed information about the surficial geology of the northern San Luis Valley. Thus, we mapped the surficial geology of an area extending several tens of kilometers north, south, and west of the Great Sand Dunes and examined subsurface stratigraphy...
map background search result map search result map Linear-referenced Geomorphology and Relative Vulnerability to Erosion at the 2013 – 2014 conterminous U.S. Pacific Ocean National Hydrography Dataset Coastline Linear-referenced Geomorphology and Relative Vulnerability to Erosion at the 2013 – 2014 conterminous U.S. Pacific Ocean National Hydrography Dataset Coastline