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• 1. [Article] Melting in the Mantle Wedge: Quantifying the Effects of Crustal Morphology and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone

  Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting ...

  Citation × Citation Citation Abstract Copy Title: Melting in the Mantle Wedge: Quantifying the Effects of Crustal Morphology and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone Author: Yang, Jiaming Year: 2017 Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting and decompression melting due to upward flow. The distribution of melting is sensitive to temperature, the pattern of flow, and the pressure in the mantle wedge. The arc front is the surface manifestation of partial melting in the mantle wedge and is characterized by a narrow chain of active volcanoes that migrate in time. The conventional interpretation is that changes in slab dip angle lead to changes in the arc front position relative to the trench. We explore an alternative hypothesis: evolution of the overlying plate, specifically thickening of the arc root, causes arc front migration. We investigate the effects of varying crustal morphology and viscous decoupling of the shallow slab-mantle interface on melt production using 2D numerical models involving a stationary overriding plate, a subducting plate with prescribed motion, and a dynamic mantle wedge. Melt production is quantified using a hydrous melting parameterization. We conclude: 1) Localized lithospheric thickening shifts the locus of melt production trenchward while thinning shifts melting landward. 2) Inclined LAB topography modulates the asthenospheric flow field, producing a narrow, well-defined arc front. 3) Thickening of the overriding plate exerts increased torque on the slab, favoring shallowing of the dip angle. 4) Viscous decoupling produces a cold, stagnant forearc mantle but promotes arc front melting due to reduction in the radius of corner flow, leading to higher temperatures at the coupling/decoupling transition. Title: Melting in the Mantle Wedge: Quantifying the Effects of Crustal Morphology and Viscous Decoupling on Melt Production with Application to the Cascadia Subduction Zone Author: Yang, Jiaming Year: 2017 Arc magmatism is sustained by the complex interactions between the subducting slab, the overriding plate, and the mantle wedge. Partial melting of mantle peridotite is achieved by fluid-induced flux melting and decompression melting due to upward flow. The distribution of melting is sensitive to temperature, the pattern of flow, and the pressure in the mantle wedge. The arc front is the surface manifestation of partial melting in the mantle wedge and is characterized by a narrow chain of active volcanoes that migrate in time. The conventional interpretation is that changes in slab dip angle lead to changes in the arc front position relative to the trench. We explore an alternative hypothesis: evolution of the overlying plate, specifically thickening of the arc root, causes arc front migration. We investigate the effects of varying crustal morphology and viscous decoupling of the shallow slab-mantle interface on melt production using 2D numerical models involving a stationary overriding plate, a subducting plate with prescribed motion, and a dynamic mantle wedge. Melt production is quantified using a hydrous melting parameterization. We conclude: 1) Localized lithospheric thickening shifts the locus of melt production trenchward while thinning shifts melting landward. 2) Inclined LAB topography modulates the asthenospheric flow field, producing a narrow, well-defined arc front. 3) Thickening of the overriding plate exerts increased torque on the slab, favoring shallowing of the dip angle. 4) Viscous decoupling produces a cold, stagnant forearc mantle but promotes arc front melting due to reduction in the radius of corner flow, leading to higher temperatures at the coupling/decoupling transition. Close

• 2. [Article] The structural controls of the Vale Rhinehart Buttes complex, Vale KGRA, Malheur County, Oregon

  The Vale KGRA is characterized by high heat flow, two to five times higher than the worldwide average, and by numerous hot springs. The hot springs are aligned along faults. This phenomena is typical of ...

  Citation × Citation Citation Abstract Copy Title: The structural controls of the Vale Rhinehart Buttes complex, Vale KGRA, Malheur County, Oregon Author: Doerr, John Timothy Year: 1986 The Vale KGRA is characterized by high heat flow, two to five times higher than the worldwide average, and by numerous hot springs. The hot springs are aligned along faults. This phenomena is typical of a Basin and Range type geothermal system. The hot geothermal fluids migrate upward along the more permeable, fault planes. The rocks exposed in the Vale area are the Pliocene Chalk Butte formation and the Pleistocene beds of Captain Keeney Pass. Both units are composed of volcaniclastic siltstones, sandstones and conglomerates. The units are differentiated by color, texture and degree of lithification. About 200 meters of the Chalk Butte formation and 100 meters of the beds of Captain Keeney Pass are exposed in the area. Silicification is wide spread in the rocks of the Chalk Butte formation. Title: The structural controls of the Vale Rhinehart Buttes complex, Vale KGRA, Malheur County, Oregon Author: Doerr, John Timothy Year: 1986 The Vale KGRA is characterized by high heat flow, two to five times higher than the worldwide average, and by numerous hot springs. The hot springs are aligned along faults. This phenomena is typical of a Basin and Range type geothermal system. The hot geothermal fluids migrate upward along the more permeable, fault planes. The rocks exposed in the Vale area are the Pliocene Chalk Butte formation and the Pleistocene beds of Captain Keeney Pass. Both units are composed of volcaniclastic siltstones, sandstones and conglomerates. The units are differentiated by color, texture and degree of lithification. About 200 meters of the Chalk Butte formation and 100 meters of the beds of Captain Keeney Pass are exposed in the area. Silicification is wide spread in the rocks of the Chalk Butte formation. Close

• 3. [Article] Geometry of Silicic Dikes Beneath the Inyo Domes, California

  Structural geologic evidence in the vicinity of the Inyo Domes indicates that the youngest extrusive products were erupted from a silicic dike that divided into at least three segments which underwent ...

  Citation × Citation Citation Abstract Copy Title: Geometry of Silicic Dikes Beneath the Inyo Domes, California Author: Fink, Jonathan H. Year: 1985 Structural geologic evidence in the vicinity of the Inyo Domes indicates that the youngest extrusive products were erupted from a silicic dike that divided into at least three segments which underwent up to 30° of clockwise rotation as they neared the surface. The geometry of ground cracks, explosion craters, and surface structures on the domes suggest that the dike may have propagated laterally from a source beneath Mammoth Mountain, with both the overall-dike and the individual segments rising as they moved northward. Structural evidence and tephrochronology also imply that the actual vents may have migrated northward along individual dike segments as the activity evolved from explosive eruptions to more quiet emplacement of lavas. Monitoring of changing patterns of ground cracks and faults may assist in predicting the sites and timing of future eruptions. Title: Geometry of Silicic Dikes Beneath the Inyo Domes, California Author: Fink, Jonathan H. Year: 1985 Structural geologic evidence in the vicinity of the Inyo Domes indicates that the youngest extrusive products were erupted from a silicic dike that divided into at least three segments which underwent up to 30° of clockwise rotation as they neared the surface. The geometry of ground cracks, explosion craters, and surface structures on the domes suggest that the dike may have propagated laterally from a source beneath Mammoth Mountain, with both the overall-dike and the individual segments rising as they moved northward. Structural evidence and tephrochronology also imply that the actual vents may have migrated northward along individual dike segments as the activity evolved from explosive eruptions to more quiet emplacement of lavas. Monitoring of changing patterns of ground cracks and faults may assist in predicting the sites and timing of future eruptions. Close

• 4. [Article] Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks

  Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. ...

  Citation × Citation Citation Abstract Copy Title: Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks Author: Hiester, Justin Year: 2013 Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. Recent satellite observations of ice surface elevation changes have given researchers new insights into how subglacial water is stored and transported. Localized uplift and settling of the ice surface implies that lakes exist beneath the ice sheet that are being filled and drained on relatively short time scales. %At the base of an ice sheet water can be transported through a variety of drainage networks or stored in subglacial lakes. Here, a numerical investigation of the mechanisms of transport and storage of subglacial water and the associated time scales is presented. Experiments are carried out using a finite element model of coupled ice and water flow. The first experiment seeks to understand the relationship between the depth of a basal depression and the area over which the feature affects basal water flow. It is found that as the perturbation to a topographic depression's depth is increased, water is rerouted in response to the perturbation. Additionally it is found that the relationship between perturbation depth and the extent upstream to which its effects reach is nonlinear. The second experiment examines how the aspect ratio of bed features (prolate, oblate, or equidimensional) influences basal water flow. It is found that the systems that develop and their interactions are mediated by both the topography and the feedbacks taken into account by the coupling of the systems in the model. Features oriented parallel to ice and water flow are associated with distributed fan systems that develop branches which migrate laterally across the domain and interact with one another on monthly and yearly timescales. Laterally oriented features develop laterally extensive ponds. As the ratio of longitudinal to lateral dimension of the topography is increased, a combination of these two water distributions is seen. Title: Investigations into the Regional and Local Timescale Variations of Subglacial Drainage Networks Author: Hiester, Justin Year: 2013 Subglacial water plays an important role in the regulation of an ice sheet's mass balance. It may be the dominant control on the velocities of ice streams and outlet glaciers on scales of months to millennia. Recent satellite observations of ice surface elevation changes have given researchers new insights into how subglacial water is stored and transported. Localized uplift and settling of the ice surface implies that lakes exist beneath the ice sheet that are being filled and drained on relatively short time scales. %At the base of an ice sheet water can be transported through a variety of drainage networks or stored in subglacial lakes. Here, a numerical investigation of the mechanisms of transport and storage of subglacial water and the associated time scales is presented. Experiments are carried out using a finite element model of coupled ice and water flow. The first experiment seeks to understand the relationship between the depth of a basal depression and the area over which the feature affects basal water flow. It is found that as the perturbation to a topographic depression's depth is increased, water is rerouted in response to the perturbation. Additionally it is found that the relationship between perturbation depth and the extent upstream to which its effects reach is nonlinear. The second experiment examines how the aspect ratio of bed features (prolate, oblate, or equidimensional) influences basal water flow. It is found that the systems that develop and their interactions are mediated by both the topography and the feedbacks taken into account by the coupling of the systems in the model. Features oriented parallel to ice and water flow are associated with distributed fan systems that develop branches which migrate laterally across the domain and interact with one another on monthly and yearly timescales. Laterally oriented features develop laterally extensive ponds. As the ratio of longitudinal to lateral dimension of the topography is increased, a combination of these two water distributions is seen. Close

• 5. [Article] West Antarctic ice stream discharge variability: mechanism, controls, and pattern of grounding line retreat

  West Antarctic ice streams show pronounced flow variability in their downstream reaches, with changes stranding formerly fast-flowing ice and redirecting discharge. A simple model, in which the temperature ...

  Citation × Citation Citation Abstract Copy Title: West Antarctic ice stream discharge variability: mechanism, controls, and pattern of grounding line retreat Author: Hulbe, Christina L., Fahnestock, Mark A. Year: 2004 West Antarctic ice streams show pronounced flow variability in their downstream reaches, with changes stranding formerly fast-flowing ice and redirecting discharge. A simple model, in which the temperature gradient in basal ice provides control of fast sliding in the downstream reach, can explain this behavior. Downstream thinning steepens the temperature gradient near the bed, increasing upward heat flow and the tendency toward basal freezing. The basal temperature gradient is steepest and the tendency toward basal freezing the strongest in ice that has experienced the most rapid downstream thinning, that is, the fastest-flowing ice. The most ?successful? rapid outflows are regions where basal water from elsewhere is likely to be consumed. Freezing here leads to episodic slow-downs and redirections of flow, the history of which appears in satellite imagery as ice rises, distorted streaklines, and margin jumps created when discharge migrates to areas with more favorable basal conditions. One compelling consequence of this process is that it makes catastrophic collapse less likely; if discharge currents are forced to slow when they become too fast (thin), then there may be an upper bound on the retreat rate and discharge flux of the West Antarctic ice sheet (WAIS) ice-stream system under the present climate. Title: West Antarctic ice stream discharge variability: mechanism, controls, and pattern of grounding line retreat Author: Hulbe, Christina L., Fahnestock, Mark A. Year: 2004 West Antarctic ice streams show pronounced flow variability in their downstream reaches, with changes stranding formerly fast-flowing ice and redirecting discharge. A simple model, in which the temperature gradient in basal ice provides control of fast sliding in the downstream reach, can explain this behavior. Downstream thinning steepens the temperature gradient near the bed, increasing upward heat flow and the tendency toward basal freezing. The basal temperature gradient is steepest and the tendency toward basal freezing the strongest in ice that has experienced the most rapid downstream thinning, that is, the fastest-flowing ice. The most ?successful? rapid outflows are regions where basal water from elsewhere is likely to be consumed. Freezing here leads to episodic slow-downs and redirections of flow, the history of which appears in satellite imagery as ice rises, distorted streaklines, and margin jumps created when discharge migrates to areas with more favorable basal conditions. One compelling consequence of this process is that it makes catastrophic collapse less likely; if discharge currents are forced to slow when they become too fast (thin), then there may be an upper bound on the retreat rate and discharge flux of the West Antarctic ice sheet (WAIS) ice-stream system under the present climate. Close

• 6. [Article] Hydrogeology of Pumice-Hosted Fens in the Winema-Fremont National Forest, Oregon, USA

  Subaerial fallout from the Holocene eruption of Mount Mazama in the Oregon Cascade Range was deposited upon relatively low permeability volcanic and volcaniclastic bedrock and regolith. In the Walker Rim ...

  Citation × Citation Citation Abstract Copy Title: Hydrogeology of Pumice-Hosted Fens in the Winema-Fremont National Forest, Oregon, USA Author: Cummings, Michael L., Weatherford, Jonathan Michael, Mowbray, Leslie A Year: 2014 Subaerial fallout from the Holocene eruption of Mount Mazama in the Oregon Cascade Range was deposited upon relatively low permeability volcanic and volcaniclastic bedrock and regolith. In the Walker Rim study area, erosion by ephemeral streams shortly after the eruption disrupted the lateral continuity of the 270 to 300 cm-thick pumice deposit. Co-evolution of the surface- and ground-water systems in a low-relief, low-slope landscape allowed diffuse groundwater discharge from the banks of the evolving stream system. Accumulation of organic material from groundwater dependent ecosystems at these sites of discharge allowed peat deposits to form on gently sloping erosion surfaces cut into the pumice deposit. Following early stream incision, fine-grained, silt-rich deposits accumulated in valleys and contributed permeability barriers to the lateral migration of water in the pumice aquifer. Fens discharge from the pumice aquifer through gently sloping surfaces patterned after the slope of the erosion surface cut into the pumice deposit and overlain by approximately 1 m of peat on the sloping surface and alluvium or iron-cemented pumice overlain by alluvium at the toe of the slope. The predominant source of groundwater is snowmelt which infiltrates the pumice deposit during the freshet. However, shallow groundwater flow also takes place along permeable pathways in bedrock units. Locally, low volume discharge takes place along faults. The snowmelt-dependent hydrologic system that supports the fens of the Walker Rim study area occurs at elevations primarily above 1585 m. Title: Hydrogeology of Pumice-Hosted Fens in the Winema-Fremont National Forest, Oregon, USA Author: Cummings, Michael L., Weatherford, Jonathan Michael, Mowbray, Leslie A Year: 2014 Subaerial fallout from the Holocene eruption of Mount Mazama in the Oregon Cascade Range was deposited upon relatively low permeability volcanic and volcaniclastic bedrock and regolith. In the Walker Rim study area, erosion by ephemeral streams shortly after the eruption disrupted the lateral continuity of the 270 to 300 cm-thick pumice deposit. Co-evolution of the surface- and ground-water systems in a low-relief, low-slope landscape allowed diffuse groundwater discharge from the banks of the evolving stream system. Accumulation of organic material from groundwater dependent ecosystems at these sites of discharge allowed peat deposits to form on gently sloping erosion surfaces cut into the pumice deposit. Following early stream incision, fine-grained, silt-rich deposits accumulated in valleys and contributed permeability barriers to the lateral migration of water in the pumice aquifer. Fens discharge from the pumice aquifer through gently sloping surfaces patterned after the slope of the erosion surface cut into the pumice deposit and overlain by approximately 1 m of peat on the sloping surface and alluvium or iron-cemented pumice overlain by alluvium at the toe of the slope. The predominant source of groundwater is snowmelt which infiltrates the pumice deposit during the freshet. However, shallow groundwater flow also takes place along permeable pathways in bedrock units. Locally, low volume discharge takes place along faults. The snowmelt-dependent hydrologic system that supports the fens of the Walker Rim study area occurs at elevations primarily above 1585 m. Close

• 7. [Article] A Morphologic Proxy for Debris Flow Erosion With Application to the Earthquake Deformation Cycle, Cascadia Subduction Zone, USA

  In unglaciated steeplands, valley reaches dominated by debris flow scour and incision set landscape form as they often account for > 80% of valley network length and relief. While hillslope and fluvial ...

  Citation × Citation Citation Abstract Copy Title: A Morphologic Proxy for Debris Flow Erosion With Application to the Earthquake Deformation Cycle, Cascadia Subduction Zone, USA Author: Penserini, Brian D., Roering, Joshua J., Strieg, Ashley Year: 2017 In unglaciated steeplands, valley reaches dominated by debris flow scour and incision set landscape form as they often account for > 80% of valley network length and relief. While hillslope and fluvial process models have frequently been combined with digital topography to develop morphologic proxies for erosion rate and drainage divide migration, debris-flow-dominated networks, despite their ubiquity, have not been exploited for this purpose. Here, we applied an empirical function that describes how slope-area data systematically deviate from so-called fluvial power-law behavior at small drainage areas. Using airborne LiDAR data for 83 small (~ 1 km2) catchments in the western Oregon Coast Range, we quantified variation in model parameters and observed that the curvature of the power-law scaling deviation varies with catchment-averaged erosion rate estimated from cosmogenic nuclides in stream sediments. Given consistent climate and lithology across our study area and assuming steady erosion, we used this calibrated denudation-morphology relationship to map spatial patterns of long-term uplift for our study catchments. By combining our predicted pattern of long-term uplift rate with paleoseismic and geodetic (tide gauge, GPS, and leveling) data, we estimated the spatial distribution of coseismic subsidence experienced during megathrust earthquakes along the Cascadia Subduction Zone. Our estimates of coseismic subsidence near the coast (0.4 to 0.7 m for earthquake recurrence intervals of 300 to 500 years) agree with field measurements from numerous stratigraphic studies. Our results also demonstrate that coseismic subsidence decreases inland to negligible values > 25 km from the coast, reflecting the diminishing influence of the earthquake deformation cycle on vertical changes of the interior coastal ranges. More generally, our results demonstrate that debris flow valley networks serve as highly localized, yet broadly distributed indicators of erosion (and rock uplift), making them invaluable for mapping crustal deformation and landscape adjustment. © 2017 Elsevier B.V. Title: A Morphologic Proxy for Debris Flow Erosion With Application to the Earthquake Deformation Cycle, Cascadia Subduction Zone, USA Author: Penserini, Brian D., Roering, Joshua J., Strieg, Ashley Year: 2017 In unglaciated steeplands, valley reaches dominated by debris flow scour and incision set landscape form as they often account for > 80% of valley network length and relief. While hillslope and fluvial process models have frequently been combined with digital topography to develop morphologic proxies for erosion rate and drainage divide migration, debris-flow-dominated networks, despite their ubiquity, have not been exploited for this purpose. Here, we applied an empirical function that describes how slope-area data systematically deviate from so-called fluvial power-law behavior at small drainage areas. Using airborne LiDAR data for 83 small (~ 1 km2) catchments in the western Oregon Coast Range, we quantified variation in model parameters and observed that the curvature of the power-law scaling deviation varies with catchment-averaged erosion rate estimated from cosmogenic nuclides in stream sediments. Given consistent climate and lithology across our study area and assuming steady erosion, we used this calibrated denudation-morphology relationship to map spatial patterns of long-term uplift for our study catchments. By combining our predicted pattern of long-term uplift rate with paleoseismic and geodetic (tide gauge, GPS, and leveling) data, we estimated the spatial distribution of coseismic subsidence experienced during megathrust earthquakes along the Cascadia Subduction Zone. Our estimates of coseismic subsidence near the coast (0.4 to 0.7 m for earthquake recurrence intervals of 300 to 500 years) agree with field measurements from numerous stratigraphic studies. Our results also demonstrate that coseismic subsidence decreases inland to negligible values > 25 km from the coast, reflecting the diminishing influence of the earthquake deformation cycle on vertical changes of the interior coastal ranges. More generally, our results demonstrate that debris flow valley networks serve as highly localized, yet broadly distributed indicators of erosion (and rock uplift), making them invaluable for mapping crustal deformation and landscape adjustment. © 2017 Elsevier B.V. Close

• 8. [Article] Holocene History of Deep-Seated Landsliding in the North Fork Stillaguamish River Valley From Surface Roughness Analysis, Radiocarbon Dating, and Numerical Landscape Evolution Modeling

  Documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution. While landslide inventories can map spatial distributions, ...

  Citation × Citation Citation Abstract Copy Title: Holocene History of Deep-Seated Landsliding in the North Fork Stillaguamish River Valley From Surface Roughness Analysis, Radiocarbon Dating, and Numerical Landscape Evolution Modeling Author: Booth, Adam M., LaHusen, Sean R., Duvall, Alison R., Montgomery, David R. Year: 2017 Documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution. While landslide inventories can map spatial distributions, lack of dateable material, landslide reactivations, or time, access, and cost constraints generally limit dating large numbers of landslides to analyze temporal patterns. Here we quantify the record of the Holocene history of deep-seated landsliding along a 25 km stretch of the North Fork Stillaguamish River valley, Washington State, USA, including the 2014 Oso landslide, which killed 43 people. We estimate the ages of more than 200 deep-seated landslides in glacial sediment by defining an empirical relationship between landslide deposit age from radiocarbon dating and landslide deposit surface roughness. We show that roughness systematically decreases with age as a function of topographic wavelength, consistent with models of disturbance-driven soil transport. The age-roughness model predicts a peak in landslide frequency at ~1000 calibrated (cal) years B.P., with very few landslide deposits older than 7000 cal years B.P. or younger than 100 cal years B.P., likely reflecting a combination of preservation bias and a complex history of changing climate, base level, and seismic shaking in the study area. Most recent landslides have occurred where channels actively interact with the toes of hillslopes composed of glacial sediments, suggesting that lateral channel migration is a primary control on the location of large deep-seated landslides in the valley. Title: Holocene History of Deep-Seated Landsliding in the North Fork Stillaguamish River Valley From Surface Roughness Analysis, Radiocarbon Dating, and Numerical Landscape Evolution Modeling Author: Booth, Adam M., LaHusen, Sean R., Duvall, Alison R., Montgomery, David R. Year: 2017 Documenting spatial and temporal patterns of past landsliding is a challenging step in quantifying the effect of landslides on landscape evolution. While landslide inventories can map spatial distributions, lack of dateable material, landslide reactivations, or time, access, and cost constraints generally limit dating large numbers of landslides to analyze temporal patterns. Here we quantify the record of the Holocene history of deep-seated landsliding along a 25 km stretch of the North Fork Stillaguamish River valley, Washington State, USA, including the 2014 Oso landslide, which killed 43 people. We estimate the ages of more than 200 deep-seated landslides in glacial sediment by defining an empirical relationship between landslide deposit age from radiocarbon dating and landslide deposit surface roughness. We show that roughness systematically decreases with age as a function of topographic wavelength, consistent with models of disturbance-driven soil transport. The age-roughness model predicts a peak in landslide frequency at ~1000 calibrated (cal) years B.P., with very few landslide deposits older than 7000 cal years B.P. or younger than 100 cal years B.P., likely reflecting a combination of preservation bias and a complex history of changing climate, base level, and seismic shaking in the study area. Most recent landslides have occurred where channels actively interact with the toes of hillslopes composed of glacial sediments, suggesting that lateral channel migration is a primary control on the location of large deep-seated landslides in the valley. Close

• 9. [Article] Evaluation of strain rates on Ice Stream B, Antarctica, obtained using differential GPS

  The "stop-and-go" kinematic Global Positioning System (CPS) technique was used to survey 270 stations twice within a 25 km by 10 km strain grid on the surface of Ice Stream B. One or two geodetic quality ...

  Citation × Citation Citation Abstract Copy Title: Evaluation of strain rates on Ice Stream B, Antarctica, obtained using differential GPS Author: Hulbe, Christina L., Whillans, I. M. Year: 1994 The "stop-and-go" kinematic Global Positioning System (CPS) technique was used to survey 270 stations twice within a 25 km by 10 km strain grid on the surface of Ice Stream B. One or two geodetic quality receivers operated as reference pivots, while two similar receivers traveled to grid stations. Each station was occupied for 25 s. The method is rapid and reliable. Each survey was completed within 2 weeks. Calculated horizontal strain rates are accurate to 1%. Relative vertical velocities are accurate to 20 mm kmI a-1. Maps of the four horizontal velocity gradients, relative vertical velocity and surface elevation are presented. The vertical velocity pattern is used to identify the part of the topography that forms stationary waves and that which is migrating. No strong quantitative link is found between the pattern in horizontal strain rate and surface topography. In particular, there is no evidence that the topography is relaxing toward isostasy. None of the "weir-type" sticky spots, which are commonly observed with other glaciers, is found but there could be two of the "submerged-boulder type", which cause lateral flow diversion. Evidence for "hot stripes" and zones of preferred crystal orientation is not found. Title: Evaluation of strain rates on Ice Stream B, Antarctica, obtained using differential GPS Author: Hulbe, Christina L., Whillans, I. M. Year: 1994 The "stop-and-go" kinematic Global Positioning System (CPS) technique was used to survey 270 stations twice within a 25 km by 10 km strain grid on the surface of Ice Stream B. One or two geodetic quality receivers operated as reference pivots, while two similar receivers traveled to grid stations. Each station was occupied for 25 s. The method is rapid and reliable. Each survey was completed within 2 weeks. Calculated horizontal strain rates are accurate to 1%. Relative vertical velocities are accurate to 20 mm kmI a-1. Maps of the four horizontal velocity gradients, relative vertical velocity and surface elevation are presented. The vertical velocity pattern is used to identify the part of the topography that forms stationary waves and that which is migrating. No strong quantitative link is found between the pattern in horizontal strain rate and surface topography. In particular, there is no evidence that the topography is relaxing toward isostasy. None of the "weir-type" sticky spots, which are commonly observed with other glaciers, is found but there could be two of the "submerged-boulder type", which cause lateral flow diversion. Evidence for "hot stripes" and zones of preferred crystal orientation is not found. Close

• 10. [Article] Hydrogeochemical Evaluation of the Uinta Formation and Green River Formation, Piceance Creek Basin, Northwestern Colorado, USA

  The Piceance Creek Basin in northwestern Colorado contains extensive oil shale deposits that produce natural gas and which could potentially yield ~1.5 trillion barrels of shale oil. However, much of the ...

  Citation × Citation Citation Abstract Copy Title: Hydrogeochemical Evaluation of the Uinta Formation and Green River Formation, Piceance Creek Basin, Northwestern Colorado, USA Author: Masterson, Megan E. Year: 2016 The Piceance Creek Basin in northwestern Colorado contains extensive oil shale deposits that produce natural gas and which could potentially yield ~1.5 trillion barrels of shale oil. However, much of the oil shale lies at depths too great for traditional mining practices and various innovative approaches for in situ conversion of kerogen to oil have been proposed. A firm understanding of the existing hydrogeochemistry is needed as resulting mineralogical changes or rock-fluid reactions may affect rock porosity and permeability. Using an existing database complied by the USGS, the water chemistry of 267 surface and groundwater samples in the Piceance Creek primary drainage basin have been evaluated by mapping major ion concentrations and mineral saturation indicies with respect to hydrostratigraphic units and geologic structures. Controlling processes have been further assessed using statistical correlation and factor analysis. Results indicate that shallow waters in recharge zones are dominated by mixed cations (Na, Ca, Mg) and bicarbonate anions but with increased depth, groundwater transition to nearly 100% sodium bicarbonate type water. The chemistry of lower aquifer waters are principally controlled by nahcolite dissolution, but evidence of sulfate reduction and cation exchange aid in maintaining a sodium-bicarbonate water type. Ion evolution in surface and upper aquifer waters are influenced by an increase in sulfate concentration which is necessary to evolve water to an intermediate stage with sulfate-dominant anions. The source of sulfate is speculative, but likely due in part to the oxidation of sulfide-enriched groundwater and possible dissolution of sulfate-bearing carbonates. Surface and upper aquifer water chemistry in the northern portion of the basin is the result of discharge of deeper groundwater which is controlled to some degree by preferential pathways created by faults. Lower aquifer water migrates upward and mixes with the less-concentrated near-surface water, resulting in sodium bicarbonate type water in all hydrologic units. Title: Hydrogeochemical Evaluation of the Uinta Formation and Green River Formation, Piceance Creek Basin, Northwestern Colorado, USA Author: Masterson, Megan E. Year: 2016 The Piceance Creek Basin in northwestern Colorado contains extensive oil shale deposits that produce natural gas and which could potentially yield ~1.5 trillion barrels of shale oil. However, much of the oil shale lies at depths too great for traditional mining practices and various innovative approaches for in situ conversion of kerogen to oil have been proposed. A firm understanding of the existing hydrogeochemistry is needed as resulting mineralogical changes or rock-fluid reactions may affect rock porosity and permeability. Using an existing database complied by the USGS, the water chemistry of 267 surface and groundwater samples in the Piceance Creek primary drainage basin have been evaluated by mapping major ion concentrations and mineral saturation indicies with respect to hydrostratigraphic units and geologic structures. Controlling processes have been further assessed using statistical correlation and factor analysis. Results indicate that shallow waters in recharge zones are dominated by mixed cations (Na, Ca, Mg) and bicarbonate anions but with increased depth, groundwater transition to nearly 100% sodium bicarbonate type water. The chemistry of lower aquifer waters are principally controlled by nahcolite dissolution, but evidence of sulfate reduction and cation exchange aid in maintaining a sodium-bicarbonate water type. Ion evolution in surface and upper aquifer waters are influenced by an increase in sulfate concentration which is necessary to evolve water to an intermediate stage with sulfate-dominant anions. The source of sulfate is speculative, but likely due in part to the oxidation of sulfide-enriched groundwater and possible dissolution of sulfate-bearing carbonates. Surface and upper aquifer water chemistry in the northern portion of the basin is the result of discharge of deeper groundwater which is controlled to some degree by preferential pathways created by faults. Lower aquifer water migrates upward and mixes with the less-concentrated near-surface water, resulting in sodium bicarbonate type water in all hydrologic units. Close