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Understanding the passive microwave emissions of a snowpack, as observed by satellite sensors, requires knowledge of the snowpack properties: water equivalent, grain size, density, and stratigraphy. For the snowpack in the Upper Colorado River Basin, measurements of snow depth and water equivalent are routinely available from the U.S. Department of Agriculture, but extremely limited information is available for the other properties. To provide this information, a field program from 1984 to 1995 obtained profiles of snowpack grain size, density, and temperature near the time of maximum snow accumulation, at sites distributed across the basin. A synoptic basin�wide sampling program in 1985 showed that the snowpack...
Sulfate is a major component of bulk atmospheric deposition (including dust, aerosol, fog, and rain). We analyzed sulfur and oxygen isotopic compositions of water-soluble sulfate from 40 sites where year-round dust traps collect bulk atmospheric deposition in the southwestern United States. Average sulfur and oxygen isotopic compositions (?34S and ?18O) are 5.8 � 1.4 (CDT) and 11.2 � 1.9 (SMOW) (n = 47), respectively. Samples have an oxygen 17 anomaly (?17O), with an average value of 1.0 � 0.6?. Except for a weak positive correlation between ?18O and ?17O values (r2 ? 0.4), no correlation exists for ?18O versus ?34S, ?17O versus ?34S, or any of the three isotopic compositions versus elevation of the sample site....
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Scientists vigorously debate the degree to which rock varnish is formed through the actions of microorganisms. To investigate this enigma, we utilized a three-pronged approach that combined (1) culture-independent molecular methods to characterize bacterial communities associated with varnish that coats the rhyolitic volcanic rocks of Black Canyon, New Mexico, and rocks with no visible varnish; (2) culturing of varnish in media supplemented with reduced forms of manganese and/or iron and no or low amounts of carbon to isolate bacteria capable of precipitating iron and/or manganese oxides; and (3) scanning electron microscopy (SEM) of varnish and nearby rock that lacks macroscopically visible varnish. Our culture-independent...
Cloud-to-ground (CG) lightning flash parameters collected by the National Lightning Detection Network were analyzed in conjunction with rainfall observations near Mitchell Creek (MC) at the Coal Seam Wildfire site in western Colorado, USA. Nine thunderstorms produced significant CG flashes in the area surrounding MC from 28 June (fire containment) to 5 August 2002. A debris flow was generated at MC by one of these storms at ?2058 LT on 5 August 2002. This study compares the CG flash parameters and rainfall characteristics of the 5 August thunderstorm with the eight thunderstorms (control group) that did not produce a hazardous hydrologic response at MC. The CG flash patterns and a synoptic analysis suggest that...
Insect outbreaks are significant disturbances in forests of the western United States, with infestation comparable in area to fire. Outbreaks of mountain pine beetle (Dendroctonus ponderosae Hopkins) require life cycles of one year with synchronous emergence of adults from host trees at an appropriate time of year (termed “adaptive seasonality�) to overwhelm tree defenses. The annual course of temperature plays a major role in governing life stage development and imposing synchrony on mountain pine beetle populations. Here we apply a process-based model of adaptive seasonality across the western United States using gridded daily temperatures from the Vegetation/Ecosystem Modeling and Analysis Project (VEMAP)...
Drag coefficients (Cd ) for the desert shrub greasewood (Sarcobatus vermiculatus) were developed from force versus wind speed data collected with an omnidirectional force balance. The average Cd for a small (0.6 m high, 0.5 m wide) shrub and a larger (1.6 m high, 1.3 m wide) shrub were 1.425 (�0.103) and 0.435 (�0.200), respectively. These values are much larger than similarly shaped solid elements and previously reported values for creosote bush (Larrea tridentata, Cd = 0.485) and an artificial tree (0.4). The greater Cd value for greasewood probably results from factors related to porosity and vegetation structure that gives this shrub-type greater momentum extracting potential. The drag coefficients for the greasewood...
We use cosmogenic radionuclide (CRN) exposure ages from polished, striated bedrock to constrain numerical simulations of deglaciation in the Middle Boulder Creek Valley, Colorado Front Range, and the Animas River Valley, San Juan Mountains, Colorado. In both valleys, the cosmogenic ages suggest initiation of deglaciation ?20 ka and ongoing retreat until 12?13 ka. While the first-order trend in CRN concentrations in each valley suggests a monotonic glacial retreat, we evaluate other retreat scenarios with different implications for post-Last Glacial Maximum regional climate. We use a 2-D numerical glacier simulation with a CRN layer to investigate how CRN-based deglaciation records are affected by retreat histories...
The Needles District in Canyonlands National Park, Utah, is known for its well-exposed array of extensional faults, which are thought to be produced by gravity-driven extension and downward flexure of a thin sandstone plate into the Colorado River canyon in response to dissolution and flow of underlying evaporites (halite and gypsum). Owing to a lack of precise geodetic data, however, it remains uncertain if and to what extent those extensional faults are currently deforming. In this study we use synthetic aperture radar (SAR) data to search for ongoing, decadal ground displacements, by applying both a stacking interferometric SAR (InSAR) analysis and Interferometric Point Target Analysis (IPTA). Our results show...
The forest-alpine tundra ecotone in the Front Range of Colorado typically occurs as a gradual transition from the treeless tundra to the closed canopy coniferous subalpine forest. We evaluated the patterns of snow, deposition inputs, and soil properties at three spatial scales: across the entire ecotone, with distance from tree limit in the transitional krummholz zone, and around individual trees. Snow depth was deepest in the krummholz zone and lowest in the alpine tundra and upwind of trees near tree limit, but was not predictive of most soil properties except for surface litter decomposition. Inorganic deposition ranged from 0.7 to 7.7 g m−2 yr−1 across the ecotone and tended to be higher downwind than upwind...
The paleomagnetism of the ?147 Ma (Tithonian) Brushy Basin Member of the Morrison Formation was analyzed to obtain a Late Jurassic paleomagnetic pole for North America. A total of 200 samples were collected from 25 sedimentary horizons (sites) at Norwood Hill in southwest Colorado. At Montezuma Creek in southeast Utah, 184 samples were collected from 26 sites. Detailed thermal demagnetization (up to nine temperature steps between 600�C and 680�C) and principal component analysis were required to confidently isolate characteristic remanent magnetization (ChRM) directions carried by hematite. Demagnetization behavior for many horizons is erratic and does not allow isolation of a high unblocking-temperature ChRM. Data...
A physical model was developed to explain threshold friction velocities u*t for particles of the size 60–120 μm lying on a rough surface in loose soils for semiarid and arid parts of the United States. The model corrected for the effect of momentum absorption by the nonerodible roughness. For loose or disturbed soils the most important parameter that controls u*t is the aerodynamic roughness height z 0. For physical crusts damaged by wind the size of erodible crust pieces is important along with the roughness. The presence of cyanobacteriallichen soil crusts roughens the surface, and the biological fibrous growth aggregates soil particles. Only undisturbed sandy soils and disturbed soils of all types would...
Nonerodible elements on erodible surfaces have the effect of absorbing part of the wind momentum flux (stress) and thus protect the erodible surface to a degree, depending on the geometry of the mixture. Experiments measuring the effect of nonerodible elements show that these elements increase the apparent threshold velocity of erosion an that the functional form of the mass flux (of erodible sand particles) in terms of friction velocity follows an Owen function. The partitioning of momentum flux by the nonerodible elements is smaller in our experiments than measured in the experiments of Marshall; however, in those measurements for which nonerodible geometry in similar, our results are roughly consistent with the...
Radiative forcing induced by soot on snow is an important anthropogenic forcing affecting the global climate. In this study we simulated the deposition of soot aerosol on snow and the resulting impact on snowpack and the hydrological cycle in the western United States. A year-long simulation was performed using the chemistry version of the Weather Research and Forecasting model (WRF-Chem) to determine the soot deposition, followed by three simulations using WRF in meteorology-only mode, with and without the soot-induced snow albedo perturbations. The chemistry simulation shows large spatial variability in soot deposition that reflects the localized emissions and the influence of the complex terrain. The soot-induced...
Glen Canyon Dam has caused a fundamental change in the distribution of fine sediment storage in the 99-km reach of the Colorado River in Marble Canyon, Grand Canyon National Park, Arizona. The two major storage sites for fine sediment (i.e., sand and finer material) in this canyon river are lateral recirculation eddies and the main-channel bed. We use a combination of methods, including direct measurement of sediment storage change, measurements of sediment flux, and comparison of the grain size of sediment found in different storage sites relative to the supply and that in transport, in order to evaluate the change in both the volume and location of sediment storage. The analysis shows that the bed of the main...
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The Needles District in Canyonlands National Park, Utah, is known for its well-exposed array of extensional faults, which are thought to be produced by gravity-driven extension and downward flexure of a thin sandstone plate into the Colorado River canyon in response to dissolution and flow of underlying evaporites (halite and gypsum). Owing to a lack of precise geodetic data, however, it remains uncertain if and to what extent those extensional faults are currently deforming. In this study we use synthetic aperture radar (SAR) data to search for ongoing, decadal ground displacements, by applying both a stacking interferometric SAR (InSAR) analysis and Interferometric Point Target Analysis (IPTA). Our results show...
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Aeolian dust strongly influences ecology and landscape geochemistry over large areas that span several desert ecosystems of the southwestern United States. This study evaluates spatial and temporal variations and trends of the physical and chemical properties of dust in the southwestern United States by examining dust deposited in natural depressions on high isolated surfaces along a transect from the Mojave Desert to the central Colorado Plateau. Aeolian dust is recognized in these depressions on the basis of textural, chemical, isotopic, and mineralogical characteristics and comparisons of those characteristics to the underlying bedrock units. Spatial and temporal trends suggest that although local dust sources...
This study investigates the causes for, and distribution of, unimodal versus bimodal seasonal cycle of vegetation greenness in the Southwest United States using extensive site observations, climate data, satellite data, and the Lund-Potsdam-Jena (LPJ) vegetation model. Peak vegetation greenness is achieved in a clockwise manner across the Southwest, beginning in spring in the Sonoran Desert following winter rains, then in Utah-Colorado with snowmelt/summer rains, and finally in New Mexico?eastern Arizona with late summer monsoon rains. At high elevations, spring-summer snowmelt is critical for supplying the necessary soil moisture to trigger vegetation growth. A bimodal seasonal cycle of vegetation greenness is...
To study certain aspects of the climatology of precipitation integrated over the Colorado River basin, daily precipitation values recorded at weather stations in the basin were gummed with an area weighting method to yield a daily mean basin value. Several checks were performed to test the reliability of the procedure within the limits needed for this analysis. A good correlation was obtained between computed annual precipitation and annual river discharge. It was found that 50% of annual precipitation is produced by 16 per cent of the number of days having precipitation per year (about 260). A correlation exists between daily precipitation and fraction of area receiving precipitation, so that large amounts of basinintegrated...
A reservoir analysis of the Denver earthquakes: A case of induced seismicity, credited to Hsieh, Paul a., published in 1981. Published in Journal of Geophysical Research, volume 86, issue B2, on pages 903 - 903, in 1981.
Poroelastic stressing and induced seismicity near the Lacq gas field, southwestern France, credited to Segall, Paul, published in 1994. Published in Journal of Geophysical Research, volume 99, issue B8, on pages 15423 - 15423, in 1994.
map background search result map search result map Diversity of rock varnish bacterial communities from Black Canyon, New Mexico Compositional trends in aeolian dust along a transect across the southwestern United States The effects of snowpack grain size on satellite passive microwave observations from the Upper Colorado River Basin Active salt tectonics in the Needles District, Canyonlands (Utah) as detected by interferometric synthetic aperture radar and point target analysis: 1992–2002 Diversity of rock varnish bacterial communities from Black Canyon, New Mexico Active salt tectonics in the Needles District, Canyonlands (Utah) as detected by interferometric synthetic aperture radar and point target analysis: 1992–2002 Compositional trends in aeolian dust along a transect across the southwestern United States The effects of snowpack grain size on satellite passive microwave observations from the Upper Colorado River Basin