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Articles 61 - 90 of 138
Full-Text Articles in Geology
Analysis Of Carbon Dioxide And Cloud Effects On Temperature In Northeast China, Hyunsoo Lee
Analysis Of Carbon Dioxide And Cloud Effects On Temperature In Northeast China, Hyunsoo Lee
Geosciences Faculty Publications
With the observed rise in temperature, many researchers have tried to identify the causes of such climate change to help mitigate its effects. The objective of this study is to determine whether, under the same carbon dioxide (CO2) concentrations, CO2 with lower cloud coverage would raise the temperature at a greater rate than CO2 with higher cloud coverage. The hypothesis was tested through data analysis and modeling. The relationships between the temperature and the CO2 emissions, the temperature and the cloud coverage, and the CO2 emissions and the cloud coverage were identified using Pearson's correlation test. The data analysis concluded …
Geostatistical And Statistical Classification Of Sea-Ice Properties And Provinces From Sar Data, Ute C. Herzfeld, Scott Williams, John Heinrichs, James Maslanik, Steven Sucht
Geostatistical And Statistical Classification Of Sea-Ice Properties And Provinces From Sar Data, Ute C. Herzfeld, Scott Williams, John Heinrichs, James Maslanik, Steven Sucht
Geosciences Faculty Publications
Recent drastic reductions in the Arctic sea-ice cover have raised an interest in understanding the role of sea ice in the global system as well as pointed out a need to understand the physical processes that lead to such changes. Satellite remote-sensing data provide important information about remote ice areas, and Synthetic Aperture Radar (SAR) data have the advantages of penetration of the omnipresent cloud cover and of high spatial resolution. A challenge addressed in this paper is how to extract information on sea-ice types and sea-ice processes from SAR data. We introduce, validate and apply geostatistical and statistical approaches …
Mantle-Derived Helium In Hot Springs Of The Cordillera Blanca, Peru: Implications For Mantle-To-Crust Fluid Transfer In A Flat-Slab Subduction Setting, Dennis L. Newell, Micah J. Jessup, David R. Hilton, Colin Shaw, Cameron Hughes
Mantle-Derived Helium In Hot Springs Of The Cordillera Blanca, Peru: Implications For Mantle-To-Crust Fluid Transfer In A Flat-Slab Subduction Setting, Dennis L. Newell, Micah J. Jessup, David R. Hilton, Colin Shaw, Cameron Hughes
Geosciences Faculty Publications
Fault-controlled hot springs in the Cordillera Blanca, Peru provide geochemical evidence of mantle-derived fluids in a modern flat-slab subduction setting. The Cordillera Blanca is an ~200km-long mountain range that contains the highest peaks in the Peruvian Andes, located in an amagmatic reach of the Andean arc. The Cordillera Blanca detachment defines the southwestern edge of the range and records a progression of top-down-to-the-west ductile shear to brittle normal faulting since ~5Ma. Hot springs, recording temperatures up to 78°C, issue along this fault zone and are CO2-rich, near neutral, alkaline-chloride to alkaline-carbonate waters, with elevated trace metal contents including …
The Science And Practice Of River Restoration, Ellen E. Wohl, Stuart N. Lane, Andrew C. Wilcox
The Science And Practice Of River Restoration, Ellen E. Wohl, Stuart N. Lane, Andrew C. Wilcox
Geosciences Faculty Publications
River restoration is one of the most prominent areas of applied water-resources science. From an initial focus on enhancing fish habitat or river appearance, primarily through structural modification of channel form, restoration has expanded to incorporate a wide variety of management activities designed to enhance river process and form. Restoration is conducted on headwater streams, large lowland rivers, and entire river networks in urban, agricultural, and less intensively human-altered environments. We critically examine how contemporary practitioners approach river restoration and challenges for implementing restoration, which include clearly identified objectives, holistic understanding of rivers as ecosystems, and the role of restoration …
Foreland-Directedpropagation Of High-Grade Tectonism In The Deep Roots Of A Paleoproterozoic Collisionalorogen, Sw Montana, Usa, Cailey B. Condit, Kevin H. Mahan, Alexis K. Ault, Rebecca M. Flowers
Foreland-Directedpropagation Of High-Grade Tectonism In The Deep Roots Of A Paleoproterozoic Collisionalorogen, Sw Montana, Usa, Cailey B. Condit, Kevin H. Mahan, Alexis K. Ault, Rebecca M. Flowers
Geosciences Faculty Publications
The study of deeply exhumed ancient collisional belts offers important constraints on geologic processes and properties complementary to inaccessible portions of the crustal column in active orogens. The ca. 1.8−1.7 Ga Big Sky orogeny in southwest Montana is a major convergent belt associated with the Proterozoic amalgamation of Laurentia. New structural, petrologic, and geochronologic data from the Northern Madison Range, crossing the NE-SW trend of the belt, record key information about the internal dynamics of the orogen. At least two phases of Big Sky−related deformation are preserved, both nearly coeval with peak metamorphic conditions of ∼0.9−0.8 GPa and >700 °C. …
Forecasting The Response Of Earth's Surface To Future Climatic And Land Use Changes: A Review Of Methods And Research Needs, Jon D. Pelletier, A. Brad Murray, Jennifer L. Pierce, Paul R. Bierman, David D. Breshears, Benjamin T. Crosby, Michael Ellis, Efi Foufoula-Georgiou, Arjun M. Heimsath, Chris Houser, Nick Lancaster, Marco Marani, Dorothy J. Merritts, Laura J. Moore, Joel Pederson, Michael J. Poulos, Tammy M. Rittenour, Joel C. Rowland, Peter Ruggiero, Dylan J. Ward, Andrew D. Wickert, Elowyn M. Yager
Forecasting The Response Of Earth's Surface To Future Climatic And Land Use Changes: A Review Of Methods And Research Needs, Jon D. Pelletier, A. Brad Murray, Jennifer L. Pierce, Paul R. Bierman, David D. Breshears, Benjamin T. Crosby, Michael Ellis, Efi Foufoula-Georgiou, Arjun M. Heimsath, Chris Houser, Nick Lancaster, Marco Marani, Dorothy J. Merritts, Laura J. Moore, Joel Pederson, Michael J. Poulos, Tammy M. Rittenour, Joel C. Rowland, Peter Ruggiero, Dylan J. Ward, Andrew D. Wickert, Elowyn M. Yager
Geosciences Faculty Publications
In the future, Earth will be warmer, precipitation events will be more extreme, global mean sea level will rise, and many arid and semiarid regions will be drier. Human modifications of landscapes will also occur at an accelerated rate as developed areas increase in size and population density. We now have gridded global forecasts, being continually improved, of the climatic and land use changes (C&LUC) that are likely to occur in the coming decades. However, besides a few exceptions, consensus forecasts do not exist for how these C&LUC will likely impact Earth-surface processes and hazards. In some cases, we have …
Linking Hematite (Uth)/He Dating With The Microtextural Record Of Seismicity In The Wasatch Fault Damagezone, Utah, Usa, Alexis K. Ault, Peter W. Reiners, James P. Evans, Stuart N. Thomson
Linking Hematite (Uth)/He Dating With The Microtextural Record Of Seismicity In The Wasatch Fault Damagezone, Utah, Usa, Alexis K. Ault, Peter W. Reiners, James P. Evans, Stuart N. Thomson
Geosciences Faculty Publications
Techniques directly dating fault slip are few, limiting the ability to interpret the rock record of seismicity. Hematite is commonly found in fault zones, amenable to (U-Th)/He dating, and slip surface hematite may be reset by shear heating events and/or recrystallization. Glossy hematite-coated fault surfaces in the Wasatch fault footwall damage zone, Utah (USA), exhibit evidence of hematite cataclasis and preserve Pliocene hematite (U-Th)/He dates. Apatite (U-Th)/He and fission track data from the host gneiss indicate footwall unroofing through ∼2 km by ca. 4.5 Ma. Internally reproducible but disparate hematite (U-Th)/He dates 4.5 Ma and younger from isolated locations on …
Active Salt Deformation And Rapid, Transient Incision Along The Colorado River Near Moab, Utah, Andrew P. Jochems, Joel L. Pederson
Active Salt Deformation And Rapid, Transient Incision Along The Colorado River Near Moab, Utah, Andrew P. Jochems, Joel L. Pederson
Geosciences Faculty Publications
In certain settings, erosion is driven by and balanced with tectonic uplift, but the evolution of many landscapes is dominated by other factors such as geologic substrate, drainage history, and transient incision. The Colorado Plateau is an example where these controls are debated and where salt deformation is hypothesized to be locally active and driven by differential unloading, although this is unconfirmed and unquantified in most places. We use luminescence-dated Colorado River terraces upstream of Moab, Utah, to quantify rates of salt-driven subsidence and uplift at the local scale. Active deformation in the study area is also supported by patterns …
Pleistocene Relative Sea Levels In The Chesapeake Bay Region And Their Implications For The Next Century, Benjamin D. Dejong, Paul R. Bierman, Wayne L. Newell, Tammy M. Rittenour, Shannon A. Mahan, Greg Balco, Dylan H. Rood
Pleistocene Relative Sea Levels In The Chesapeake Bay Region And Their Implications For The Next Century, Benjamin D. Dejong, Paul R. Bierman, Wayne L. Newell, Tammy M. Rittenour, Shannon A. Mahan, Greg Balco, Dylan H. Rood
Geosciences Faculty Publications
Today, relative sea-level rise (3.4 mm/yr) is faster in the Chesapeake Bay region than any other location on the Atlantic coast of North America, and twice the global average eustatic rate (1.7 mm/yr). Dated interglacial deposits suggest that relative sea levels in the Chesapeake Bay region deviate from global trends over a range of timescales. Glacio-isostatic adjustment of the land surface from loading and unloading of continental ice is likely responsible for these deviations, but our understanding of the scale and timeframe over which isostatic response operates in this region remains incomplete because dated sea-level proxies are mostly limited to …
Reply To Simon And Reed: Independent And Converging Results Rule Out Historic Disturbance And Confirm Age Constraints For Barrier Canyon Rock Art, Joel L. Pederson, Harriet Cornachione, Steven R. Simms, Reza Sohbati, Tammy M. Rittenour, Andrew S. Murray, Gary Cox
Reply To Simon And Reed: Independent And Converging Results Rule Out Historic Disturbance And Confirm Age Constraints For Barrier Canyon Rock Art, Joel L. Pederson, Harriet Cornachione, Steven R. Simms, Reza Sohbati, Tammy M. Rittenour, Andrew S. Murray, Gary Cox
Geosciences Faculty Publications
We welcome this further discussion of our results on the age of the Great Gallery rock art in the Canyonlands of Utah. The comment by Simon and Reed (1) focuses on just one of the three components of our study (2), which is presented in greater technical detail in ref. 3 and is surely our best-constrained and least-surprising result: the dating of a rock-fall that removed some of the art and thus provides a minimum age. Simon and Reed (1) point out that the Great Gallery panel is not pristine and relate the sordid human history of visitation and possible …
Drilling The Solid Earth: Global Geodynamic Cycles And Earth Evolution, John W. Shervais, Nicholas Arndt, Kathryn M. Goodenough
Drilling The Solid Earth: Global Geodynamic Cycles And Earth Evolution, John W. Shervais, Nicholas Arndt, Kathryn M. Goodenough
Geosciences Faculty Publications
The physical and chemical evolution of the Earth is driven by geodynamic cycles that are global in scale, operating over 4.57 Ga of Earth’s history. Some processes are truly cyclic, e.g., the Wilson Cycle, while others are irreversible (e.g., core formation). Heat and mass transfer between the lowermost mantle (e.g., core-mantle boundary) and the surface drives these global geodynamic processes. Subduction of lithospheric plates transfers cool fractionated material into the lower mantle and leads indirectly to the formation of new oceanic lithosphere, while the rise of thermochemical plumes recycles the remnants of these plates back to the surface, driven by …
A New Ankylosaurid Dinosaur From The Upper Cretaceous (Kirtlandian) Of New Mexico With Implications For Ankylosaurid Diversity In The Upper Cretaceous Of Western North America, Victoria M. Arbour, Michael E. Burns, Robert M. Sullivan, Spencer G. Lucas, Amanda K. Cantrell, Joshua Fry, Thomas L. Suazo
A New Ankylosaurid Dinosaur From The Upper Cretaceous (Kirtlandian) Of New Mexico With Implications For Ankylosaurid Diversity In The Upper Cretaceous Of Western North America, Victoria M. Arbour, Michael E. Burns, Robert M. Sullivan, Spencer G. Lucas, Amanda K. Cantrell, Joshua Fry, Thomas L. Suazo
Geosciences Faculty Publications
A new ankylosaurid (Ankylosauria: Dinosauria), Ziapelta sanjuanensis, gen. et sp. nov., is based on a complete skull, an incomplete first cervical half ring, a possible fragment of the second cervical half ring, and additional fragmentary osteoderms. The holotype specimen is from the Upper Cretaceous (Upper Campanian, Kirtlandian Land-Vertebrate Age) Kirtland Formation (De-na-zin Member) at Hunter Wash, San Juan Basin, in northwestern New Mexico, USA. Diagnostic characters of Ziapelta include: a large, prominent triangular median nasal caputegulum; a mixture of flat and bulbous frontonasal caputegulae; ventrolaterally oriented squamosal horns with a sharp, prominent dorsal keel; and the ventral surface of basicranium …
Age Of Barrier Canyon-Style Rock Art Constrained By Cross-Cutting Relations And Luminescence Dating Techniques, Joel L. Pederson, Harriet Cornachione, Steven R. Simms, Reza Sohbati, Tammy M. Rittenour, Andrew S. Murray, Gary Cox
Age Of Barrier Canyon-Style Rock Art Constrained By Cross-Cutting Relations And Luminescence Dating Techniques, Joel L. Pederson, Harriet Cornachione, Steven R. Simms, Reza Sohbati, Tammy M. Rittenour, Andrew S. Murray, Gary Cox
Geosciences Faculty Publications
Rock art compels interest from both researchers and a broader public, inspiring many hypotheses about its cultural origin and meaning, but it is notoriously difficult to date numerically. Barrier Canyon-style (BCS) pictographs of the Colorado Plateau are among the most debated examples; hypotheses about its age span the entire Holocene epoch and previous attempts at direct radiocarbon dating have failed. We provide multiple age constraints through the use of cross-cutting relations and new and broadly applicable approaches in optically stimulated luminescence dating at the Great Gallery panel, the type section of BCS art in Canyonlands National Park, southeastern Utah. Alluvial …
Composition, Alteration, And Texture Of Fault-Related Rocks From Safod Core And Surface Outcrop Analogs: Evidence For Deformation Processes And Fluid-Rock Interactions, Kelly Keighley Bradbury, Colter R. Davis, John W. Shervais, Susanne U. Janecke, James P. Evans
Composition, Alteration, And Texture Of Fault-Related Rocks From Safod Core And Surface Outcrop Analogs: Evidence For Deformation Processes And Fluid-Rock Interactions, Kelly Keighley Bradbury, Colter R. Davis, John W. Shervais, Susanne U. Janecke, James P. Evans
Geosciences Faculty Publications
We examine the fine-scale variations in mineralogical composition, geochemical alteration, and texture of the fault-related rocks from the Phase 3 whole-rock core sampled between 3,187.4 and 3,301.4 m measured depth within the San Andreas Fault Observatory at Depth (SAFOD) borehole near Parkfield, California. This work provides insight into the physical and chemical properties, structural architecture, and fluid-rock interactions associated with the actively deforming traces of the San Andreas Fault zone at depth. Exhumed outcrops within the SAF system comprised of serpentinite-bearing protolith are examined for comparison at San Simeon, Goat Rock State Park, and Nelson Creek, California. In the Phase …
Rapid Reservoir Erosion, Hyperconcentrated Flow, And Downstream Deposition Triggered By Breaching Of 38 M Tall Condit Dam, White Salmon River, Washington, Andrew C. Wilcox, Jim E. O'Connor, Jon J. Major
Rapid Reservoir Erosion, Hyperconcentrated Flow, And Downstream Deposition Triggered By Breaching Of 38 M Tall Condit Dam, White Salmon River, Washington, Andrew C. Wilcox, Jim E. O'Connor, Jon J. Major
Geosciences Faculty Publications
Condit Dam on the White Salmon River,Washington, a 38m high dam impounding a large volume (1.8 million m3) of fine-grained sediment (60% sand, 35% silt and clay, and 5% gravel), was rapidly breached in October 2011. This unique dam decommissioning produced dramatic upstream and downstream geomorphic responses in the hours and weeks following breaching. Blasting a 5 m wide hole into the base of the dam resulted in rapid reservoir drawdown, abruptly releasing ~1.6 million m3 of reservoir water, exposing reservoir sediment to erosion, and triggering mass failures of the thickly accumulated reservoir sediment. Within 90 min …
Late Quaternary Faulting History Of The Carrizal And Related Faults, La Paz Region, Baja California Sur, Mexico, Paul J. Umhoefer, Sara J. Maloney, Beverly Buchanan, J. Ramón Arrowsmith, Genaro Martinez-Gutiérrez, Graham Kent, Neal Driscoll, Alistair Harding, Darrell Kaufman, Tammy M. Rittenour
Late Quaternary Faulting History Of The Carrizal And Related Faults, La Paz Region, Baja California Sur, Mexico, Paul J. Umhoefer, Sara J. Maloney, Beverly Buchanan, J. Ramón Arrowsmith, Genaro Martinez-Gutiérrez, Graham Kent, Neal Driscoll, Alistair Harding, Darrell Kaufman, Tammy M. Rittenour
Geosciences Faculty Publications
The southwest margin of the Gulf of California has an array of active normal faults despite this being an oblique-divergent plate boundary with spreading centers that localized deformation along the plate boundary 2–3 million years ago. The Carrizal and Centenario faults form the western border fault of the Gulf of California marginal fault system within and south of La Paz Bay, and ∼20–30 km west of the capital city of La Paz, Baja California Sur, Mexico. Geologic and geomorphic mapping, optically stimulated luminescence (OSL) geochronology, and paleoseismic investigations onshore, compressed high-intensity radar pulse (CHIRP) profiling offshore, and analysis of uplifted …
Hot Faults:Iridescent Slip Surfaces With Metallic Luster Document High-Temperature Ancientseismicity In The Wasatch Fault Zone, Ut, Usa, James P. Evans, Mitchell R. Prante, Susanne U. Janecke, Alexis K. Ault, Dennis L. Newell
Hot Faults:Iridescent Slip Surfaces With Metallic Luster Document High-Temperature Ancientseismicity In The Wasatch Fault Zone, Ut, Usa, James P. Evans, Mitchell R. Prante, Susanne U. Janecke, Alexis K. Ault, Dennis L. Newell
Geosciences Faculty Publications
We document new geological indicators of ancient seismicity in the form of highly reflective, iridescent, hematite-coated fault surfaces. Small faults that cut the Paleoproterozoic Farmington Canyon Complex in the footwall damage zone of the Brigham City segment of the Wasatch fault (Utah, USA) are smooth to striated surfaces, tens of square centimeters to 30 m2 in area. The dull-rusty to high-metallic luster and moderate- to high-gloss surfaces exhibit multicolored elliptical iridescent patches ∼0.5–3 cm across. Preexisting hematite crystals were deformed during slip on 1–200-mm-thick slip surfaces. Textural observations, X-ray diffraction, X-ray photoelectron spectroscopy, electron backscattered diffraction analysis, surface metrology, and …
Climate And Topographic Controls On Simulated Pasture Production In A Semiarid Mediterranean Watershed With Scattered Tree Cover, J. Lozano-Parra, Marco P. Maneta, S. Schnabel
Climate And Topographic Controls On Simulated Pasture Production In A Semiarid Mediterranean Watershed With Scattered Tree Cover, J. Lozano-Parra, Marco P. Maneta, S. Schnabel
Geosciences Faculty Publications
Natural grasses in semiarid rangelands constitute an effective protection against soil erosion and degradation, are a source of natural food for livestock and play a critical role in the hydrologic cycle by contributing to the uptake and transpiration of water. However, natural pastures are threatened by land abandonment and the consequent encroachment of shrubs and trees as well as by changing climatic conditions. In spite of their ecological and economic importance, the spatiotemporal variations of pasture production at the decadal–century scales over whole watersheds are poorly known.We used a physically based, spatially distributed ecohydrologic model applied to a 99.5 ha …
Diversion(S) Of The Lower Bear River In Gem Valley, Southeast Idaho, By A Tectono-Volcanic Valve, Susanne U. Jänecke, Robert Q. Oaks Jr.
Diversion(S) Of The Lower Bear River In Gem Valley, Southeast Idaho, By A Tectono-Volcanic Valve, Susanne U. Jänecke, Robert Q. Oaks Jr.
Geosciences Faculty Publications
The lower Bear River of Utah and Idaho was once a tributary of the Snake River that flowed along the NE edge of the Great Basin. Similar biological communities in the upper Bear and Snake Rivers attest to this phase of its history. Basalt flows in Gem Valley, Idaho, diverted the lower Bear River southward into the Bonneville Basin during the late Pleistocene [1] [2] [3]. However, there is no consensus about the timing, location, and mechanism of this major diversion [4] [5]. Landscape and image analysis reveals previously unmapped active normal faults and characterizes Late Pleistocene to Holocene(?) volcanic …
A Tree-Ring Based Reconstruction Of Logan River Streamflow, Northern Utah, Eric B. Allen, Tammy M. Rittenour, R. Justin Derose, Matthew F. Bekker, Roger Kjelgren, Brendan M. Buckley
A Tree-Ring Based Reconstruction Of Logan River Streamflow, Northern Utah, Eric B. Allen, Tammy M. Rittenour, R. Justin Derose, Matthew F. Bekker, Roger Kjelgren, Brendan M. Buckley
Geosciences Faculty Publications
We created six new tree‐ring chronologies in northern Utah, which were used with preexisting chronologies from Utah and western Wyoming to reconstruct mean annual flow for the Logan River, the largest tributary of the regionally important Bear River. Two reconstruction models were developed, a “Local” model that incorporated two Rocky Mountain juniper chronologies located within the basin, and a “Regional” model that also included limber pine and pinyon pine chronologies from a larger area. The Local model explained 48.2% of the variability in the instrumental record and the juniper chronologies better captured streamflow variability than Douglas‐fir collected within the Logan …
Rapid River Incision Across An Inactive Fault - Implications For Patterns Of Erosion And Deformation In The Central Colorado Plateau, Joel L. Pederson, Neil Burnside, Zoe Shipton, Tammy M. Rittenour
Rapid River Incision Across An Inactive Fault - Implications For Patterns Of Erosion And Deformation In The Central Colorado Plateau, Joel L. Pederson, Neil Burnside, Zoe Shipton, Tammy M. Rittenour
Geosciences Faculty Publications
The Colorado Plateau presents a contrast between deep and seemingly recent erosion and apparently only mild late Cenozoic tectonic activity. Researchers have recently proposed multiple sources of epeirogenic uplift and intriguing patterns of differential incision, yet little or no quantitative constraints exist in the heart of the plateau to test these ideas. Here, we use both optically stimulated luminescence (OSL) and uranium-series dating to delimit the record of fluvial strath terraces at Crystal Geyser in southeastern Utah, where the Little Grand Wash fault crosses the Green River in the broad Mancos Shale badlands of the central plateau. Results indicate there …
Phanerozoic Surface History Of The Slavecraton, Alexis K. Ault, Rebecca M. Flowers, Samuel A. Bowring
Phanerozoic Surface History Of The Slavecraton, Alexis K. Ault, Rebecca M. Flowers, Samuel A. Bowring
Geosciences Faculty Publications
New apatite (U-Th)/He (AHe) thermochronometry data and key geologic constraints from Slave craton kimberlites are used to develop a model for the Phanerozoic burial, unroofing, and hypsometric history of the northwestern Canadian shield. AHe dates range from 210 ± 13 to 382 ± 79 Ma, are older in the eastern Slave craton and decrease westward, and resolve the spatial extent, thickness, and history of now-denuded sedimentary units. Results indicate Paleozoic heating to temperatures ≥85–90°C, suggesting regional burial beneath ≥2.8 km of strata while the region was at sea level, followed by the westward migration of unroofing across the craton. This …
Paleoseismology Of The Southern Panamint Valley Fault: Implications For Regional Earthquake Occurrence And Seismic Hazard In Southern California, Lee J. Mcauliffe, James F. Dolan, Eric Kirby, Chris Rollins, Ben Haravitch, Steve Alm, Tammy M. Rittenour
Paleoseismology Of The Southern Panamint Valley Fault: Implications For Regional Earthquake Occurrence And Seismic Hazard In Southern California, Lee J. Mcauliffe, James F. Dolan, Eric Kirby, Chris Rollins, Ben Haravitch, Steve Alm, Tammy M. Rittenour
Geosciences Faculty Publications
[1] Paleoseismologic data from the southern Panamint Valley fault (PVF) reveal evidence of at least four surface ruptures during late Holocene time (0.33–0.48 ka, 0.9–3.0 ka, 3.3–3.6 ka, and >4.1 ka). These paleo‐earthquake ages indicate that the southern PVF has ruptured at least once and possibly twice during the ongoing (≤1.5 ka) seismic cluster in the Mojave section of the eastern California shear zone (ECSZ). The most recent event (MRE) on the PVF is also similar in age to the 1872 Owens Valley earthquake and the geomorphically youthful MRE on the Death Valley fault. The timing of the three oldest …
White Papers: Drilling Active Tectonics And Magmatism (Volcanics, Geoprisms, And Fault Zones Post-Safod), John W. Shervais, James P. Evans, Amanda Clark, John C. Eichelberger, James Kirkpatrick, Virginia Toy
White Papers: Drilling Active Tectonics And Magmatism (Volcanics, Geoprisms, And Fault Zones Post-Safod), John W. Shervais, James P. Evans, Amanda Clark, John C. Eichelberger, James Kirkpatrick, Virginia Toy
Geosciences Faculty Publications
No abstract provided.
Drilling Active Tectonics And Magmatism (Volcanics, Geoprisms, Fault Zones Post-Safod) Proceedings Of A Workshop, John W. Shervais, James P. Evans, Virginia Toy, John Eichelberger, James Kirkpatrick, Amanda Clarke
Drilling Active Tectonics And Magmatism (Volcanics, Geoprisms, Fault Zones Post-Safod) Proceedings Of A Workshop, John W. Shervais, James P. Evans, Virginia Toy, John Eichelberger, James Kirkpatrick, Amanda Clarke
Geosciences Faculty Publications
No abstract provided.
Understanding Greenland Ice Sheet Hydrology Using An Integrated Multi-Scale Approach, A. K. Rennermalm, S. E. Moustafa, J. Mioduszewski, V. W. Chu, R. R. Forster, B. Hagedorn, Joel T. Harper, T. L. Mote, D. A. Robinson, C. A. Shuman, L. C. Smith, M. Tedesco
Understanding Greenland Ice Sheet Hydrology Using An Integrated Multi-Scale Approach, A. K. Rennermalm, S. E. Moustafa, J. Mioduszewski, V. W. Chu, R. R. Forster, B. Hagedorn, Joel T. Harper, T. L. Mote, D. A. Robinson, C. A. Shuman, L. C. Smith, M. Tedesco
Geosciences Faculty Publications
Improved understanding of Greenland ice sheet hydrology is critically important for assessing its impact on current and future ice sheet dynamics and global sea level rise. This has motivated the collection and integration of in situ observations, model development, and remote sensing efforts to quantify meltwater production, as well as its phase changes, transport, and export. Particularly urgent is a better understanding of albedo feedbacks leading to enhanced surface melt, potential positive feedbacks between ice sheet hydrology and dynamics, and meltwater retention in firn. These processes are not isolated, but must be understood as part of a continuum of processes …
Dynamically Downscaled Winter Precipitation Over Complex Terrain Of The Central Rockies Of Western Montana, Usa, Nicholas Loren Silverman, Marco P. Maneta, S.-H. Chen, Joel T. Harper
Dynamically Downscaled Winter Precipitation Over Complex Terrain Of The Central Rockies Of Western Montana, Usa, Nicholas Loren Silverman, Marco P. Maneta, S.-H. Chen, Joel T. Harper
Geosciences Faculty Publications
We evaluate the results of dynamically downscaled winter precipitation over Western Montana using the weather research and forecasting (WRF) model through comparison with estimates from the observationally based parameter-elevation regressions on independent slopes model (PRISM). Seven years (six winters) from 2000 to 2006 are simulated at 4 km resolution to assess the similarities and differences between the two models as well as the implications for hydrologic modeling. Inherent biases in both approaches are apparent, highlighting the difficulty in climate model validation. Results show general agreement between the two models in the spatial distribution of winter precipitation. A principal component analysis …
Compressional And Em Wave Velocity Anisotropy In A Temperate Glacier Due To Basal Crevasses, And Implications For Water Content Estimation, John Bradford, Joshua Nichols, Joel T. Harper, Toby W. Meierbachtol
Compressional And Em Wave Velocity Anisotropy In A Temperate Glacier Due To Basal Crevasses, And Implications For Water Content Estimation, John Bradford, Joshua Nichols, Joel T. Harper, Toby W. Meierbachtol
Geosciences Faculty Publications
We have conducted a series of experiments designed to investigate elastic and electromagnetic (EM) velocity anisotropy associated with a preferentially aligned fracture system on a temperate valley glacier in south-central Alaska, USA. Measurements include a three-dimensional compressional wave (P-wave) seismic reflection survey conducted over a 300 m x 300 m survey patch, with uniform source grid and static checkerboard receiver pattern. Additionally, we acquired a multiazimuth, multi-offset, polarimetric groundpenetrating radar (GPR) reflection experiment in a wagon-wheel geometry with 94 degrees of azimuthal coverage. Results show azimuthal variation in the P-wave normal-moveout velocity of less than 3% (3765 and 3630 ms …
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, K. Van Wijk, M. M. Haney, J. H, Bradford, H. P. Marshall, Joel T. Harper
Monitoring Glacier Surface Seismicity In Time And Space Using Rayleigh Waves, T. D. Mikesell, K. Van Wijk, M. M. Haney, J. H, Bradford, H. P. Marshall, Joel T. Harper
Geosciences Faculty Publications
Sliding glaciers and brittle ice failure generate seismic body and surface wave energy characteristic to the source mechanism. Here we analyze continuous seismic recordings from an array of nine short-period passive seismometers located on Bench Glacier, Alaska (USA) (61.033N, 145.687W). We focus on the arrival-time and amplitude information of the dominant Rayleigh wave phase. Over a 46-hour period we detect thousands of events using a cross-correlation based event identification method. Travel-time inversion of a subset of events (7% of the total) defines an active crevasse, propagating more than 200 meters in three hours. From the Rayleigh wave amplitudes, we estimate …
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Georadar-Derived Estimates Of Firn Density In The Percolation Zone, Western Greenland Ice Sheet, Joel Brown, John Bradford, Joel T. Harper, W. Tad Pfeffer, Neil Humphrey, Ellen Mosley-Thompson
Geosciences Faculty Publications
Greater understanding of variations in firn densification is needed to distinguish between dynamic and melt-driven elevation changes on the Greenland ice sheet. This is especially true in Greenland’s percolation zone, where firn density profiles are poorly documented because few ice cores are extracted in regions with surface melt.We used geoader to investigate firn density variations with depth along an about 70 km transect through a portion of the accumulation area in western Greenland that partially melts. We estimated electromagnetic wave velocity by inverting reflection travel times picked from common midpoint gathers. We followed a procedure designed to find the simplest …