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• 1. [Article] Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon

  The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream ...

  Citation × Citation Citation Abstract Copy Title: Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon Author: Weatherford, Jonathan Michael Year: 2015 The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream relocation, and the formation of biologically diverse fens and seasonal wetlands. The pumice aquifer at Round Meadow, an 8.6 km2 basin, hosts both a fen and seasonally ponded wetlands. The Round Meadow watershed lies within a closed basin between the upper Klamath and Deschutes river basins. As the highest meadow at Walker Rim, it is a relatively well-constrained system to study the effects of hydrological disruption. A water budget was calculated for the basin, hydraulic conductivity was evaluated for the three main sediment layers in the meadow, recharge sources and evaporative trends were studied using stable isotope analysis, and aquifer residence times were estimated using CFC tracer water age dating. Water year 2014 was a drought year and observation of the system under stressed conditions allowed discrimination of four independently functioning components of the hydrogeologic system. These were the meadow, which is by far the largest component in terms of water storage, the fen where iron cementation and up to 1 m of peat holds water in a berm above the meadow, three springs which are sourced from deeper groundwater hosted in the bedrock which underlies the pumice deposit, and the outflow area. In all cases, the aquifer material is pumice, but the influence of the pre-eruption landscape and post-eruption modifications of the aquifer material have resulted in partial isolation of the components. The water budget analysis indicated that the basin lost 44 cm of water storage during WY 2014. Hydraulic conductivity values of 1x10-6, 2x10-2, and 4x10-5 cm/s, were determined for the diatomaceous silt underlying the pumice, the Plinian pumice fall aquifer, and for the diatomaceous silt overlying the pumice, respectively. The pumice is characterized as a perched, weakly confined aquifer and residence times in the pumice are much longer (decades) than for water near the surface of the meadow. Water discharging at the springs is isotopically different (lighter) than either the surface water or groundwater in the pumice aquifer. The fen at Round Meadow appears dependent on seasonal precipitation to recharge water, and responds to fluctuations in annual precipitation. The wetland meadows are volumetrically the main water-storing features at Round Meadow, and these are not homogenous features, but a combination of discrete components. Title: Hydrogeologic Investigation of a Pumice Aquifer, Fremont/Winema National Forest, Oregon Author: Weatherford, Jonathan Michael Year: 2015 The middle Holocene cataclysmic eruption of Mount Mazama blanketed Walker Rim, in south central Oregon, with 270 cm to 300 cm of pumice, causing capture of surface water systems by groundwater, stream relocation, and the formation of biologically diverse fens and seasonal wetlands. The pumice aquifer at Round Meadow, an 8.6 km2 basin, hosts both a fen and seasonally ponded wetlands. The Round Meadow watershed lies within a closed basin between the upper Klamath and Deschutes river basins. As the highest meadow at Walker Rim, it is a relatively well-constrained system to study the effects of hydrological disruption. A water budget was calculated for the basin, hydraulic conductivity was evaluated for the three main sediment layers in the meadow, recharge sources and evaporative trends were studied using stable isotope analysis, and aquifer residence times were estimated using CFC tracer water age dating. Water year 2014 was a drought year and observation of the system under stressed conditions allowed discrimination of four independently functioning components of the hydrogeologic system. These were the meadow, which is by far the largest component in terms of water storage, the fen where iron cementation and up to 1 m of peat holds water in a berm above the meadow, three springs which are sourced from deeper groundwater hosted in the bedrock which underlies the pumice deposit, and the outflow area. In all cases, the aquifer material is pumice, but the influence of the pre-eruption landscape and post-eruption modifications of the aquifer material have resulted in partial isolation of the components. The water budget analysis indicated that the basin lost 44 cm of water storage during WY 2014. Hydraulic conductivity values of 1x10-6, 2x10-2, and 4x10-5 cm/s, were determined for the diatomaceous silt underlying the pumice, the Plinian pumice fall aquifer, and for the diatomaceous silt overlying the pumice, respectively. The pumice is characterized as a perched, weakly confined aquifer and residence times in the pumice are much longer (decades) than for water near the surface of the meadow. Water discharging at the springs is isotopically different (lighter) than either the surface water or groundwater in the pumice aquifer. The fen at Round Meadow appears dependent on seasonal precipitation to recharge water, and responds to fluctuations in annual precipitation. The wetland meadows are volumetrically the main water-storing features at Round Meadow, and these are not homogenous features, but a combination of discrete components. Close

• 2. [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

• 3. [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

• 4. [Article] Accommodation Space in a High-Wave-Energy Inner-Shelf During the Holocene Marine Transgression: Correlation of Onshore and Offshore Inner-Shelf Deposits (0–12 ka) in the Columbia River Littoral Cell System, Washington and Oregon, USA

  The Columbia River Littoral Cell (CRLC), a high-wave-energy littoral system, extends 160 km alongshore, generally north of the large Columbia River, and 10–15 km in across-shelf distance from paleo-beach ...

  Citation × Citation Citation Abstract Copy Title: Accommodation Space in a High-Wave-Energy Inner-Shelf During the Holocene Marine Transgression: Correlation of Onshore and Offshore Inner-Shelf Deposits (0–12 ka) in the Columbia River Littoral Cell System, Washington and Oregon, USA Author: Peterson, Curt D., Twichell, Dave C., Roberts, Michael C., Vanderburgh, Sandy, Hostetler, Steven Year: 2016 The Columbia River Littoral Cell (CRLC), a high-wave-energy littoral system, extends 160 km alongshore, generally north of the large Columbia River, and 10–15 km in across-shelf distance from paleo-beach backshores to about 50 m present water depths. Onshore drill holes (19 in number and 5–35 m in subsurface depth) and offshore vibracores (33 in number and 1–5 m in subsurface depth) constrain inner-shelf sand grain sizes (sample means 0.13–0.25 mm) and heavy mineral source indicators (> 90% Holocene Columbia River sand) of the inner-shelf facies (≥ 90% fine sand). Stratigraphic correlation of the transgressive ravinement surface in onshore drill holes and in offshore seismic reflection profiles provide age constraints (0–12 ka) on post-ravinement inner-shelf deposits, using paleo-sea level curves and radiocarbon dates. Post-ravinement deposit thickness (1–50 m) and long-term sedimentation rates (0.4–4.4 m ka− 1) are positively correlated to the cross-shelf gradients (0.36–0.63%) of the transgressive ravinement surface. The total post-ravinement fill volume of fine littoral sand (2.48x1010m3) in the inner-shelf represents about 2.07x106 m3 yr− 1 fine sand accumulation rate during the last 12 ka, or about one third of the estimated middle- to late-Holocene Columbia River bedload or sand discharge (5–6x106 m3 yr− 1) to the littoral zone. The fine sand accumulation in the inner-shelf represents post-ravinement accommodation space resulting from 1) geometry and depth of the transgressive ravinement surface, 2) post-ravinement sea-level rise, and 3) fine sand dispersal in the inner-shelf by combined high-wave-energy and geostrophic flow/down-welling drift currents during major winter storms. Title: Accommodation Space in a High-Wave-Energy Inner-Shelf During the Holocene Marine Transgression: Correlation of Onshore and Offshore Inner-Shelf Deposits (0–12 ka) in the Columbia River Littoral Cell System, Washington and Oregon, USA Author: Peterson, Curt D., Twichell, Dave C., Roberts, Michael C., Vanderburgh, Sandy, Hostetler, Steven Year: 2016 The Columbia River Littoral Cell (CRLC), a high-wave-energy littoral system, extends 160 km alongshore, generally north of the large Columbia River, and 10–15 km in across-shelf distance from paleo-beach backshores to about 50 m present water depths. Onshore drill holes (19 in number and 5–35 m in subsurface depth) and offshore vibracores (33 in number and 1–5 m in subsurface depth) constrain inner-shelf sand grain sizes (sample means 0.13–0.25 mm) and heavy mineral source indicators (> 90% Holocene Columbia River sand) of the inner-shelf facies (≥ 90% fine sand). Stratigraphic correlation of the transgressive ravinement surface in onshore drill holes and in offshore seismic reflection profiles provide age constraints (0–12 ka) on post-ravinement inner-shelf deposits, using paleo-sea level curves and radiocarbon dates. Post-ravinement deposit thickness (1–50 m) and long-term sedimentation rates (0.4–4.4 m ka− 1) are positively correlated to the cross-shelf gradients (0.36–0.63%) of the transgressive ravinement surface. The total post-ravinement fill volume of fine littoral sand (2.48x1010m3) in the inner-shelf represents about 2.07x106 m3 yr− 1 fine sand accumulation rate during the last 12 ka, or about one third of the estimated middle- to late-Holocene Columbia River bedload or sand discharge (5–6x106 m3 yr− 1) to the littoral zone. The fine sand accumulation in the inner-shelf represents post-ravinement accommodation space resulting from 1) geometry and depth of the transgressive ravinement surface, 2) post-ravinement sea-level rise, and 3) fine sand dispersal in the inner-shelf by combined high-wave-energy and geostrophic flow/down-welling drift currents during major winter storms. Close

• 5. [Article] The Geology, Geochemistry, and Alteration of Red Butte, Oregon: A Precious Metal-Bearing Paleo Hot Spring System

  Red Butte is located 60 km south of Vale, Oregon, about 20 km west of the Oregon/Idaho border. The butte is within the Owyhee Upland physiographic province of eastern Oregon which lies at the intersection ...

  Citation × Citation Citation Abstract Copy Title: The Geology, Geochemistry, and Alteration of Red Butte, Oregon: A Precious Metal-Bearing Paleo Hot Spring System Author: Evans, Carol Susan Year: 1986 Red Butte is located 60 km south of Vale, Oregon, about 20 km west of the Oregon/Idaho border. The butte is within the Owyhee Upland physiographic province of eastern Oregon which lies at the intersection of the Western Snake River Plain, the High Lava Plains, and the Northern Basin and Range provinces. The butte is composed of Miocene to Pliocene lacustrine and fluvial volcaniclastic sediments. The topography of the butte is controlled by silicification of the sandstones and mudstones which cap it. Silicification and hydrothermal alteration are both structurally and stratigraphically controlled. North-trending normal faults dominate the area, and show progressively less offset in younger units. Strong northwest and minor northeast faults also cut the area. Anomalous concentrations of Au, As, Sb, and Hg occur in banded quartz, quartz-adularia veins and rarely in calcite-quartz veins cutting basalts. The silicified mudstones at the butte top are generally barren. An hydrothermal explosion crater exposed on the southeast side of the butte lies at the intersection of north and northwest-trending faults. Banded quartz veins, quartz-adularia veins, and quartz-cemented breccias are exposed in the walls of the explosion crater. There is evidence of multiple brecciation events. A few mudstones exposed in the crater wall have an exhalative texture, contain pyrite des seminated along bedding, and contain trace amounts of Au. The Red Butte system developed as a hot spring venting into a lake, possibly within a caldera. Periodic influxes of air fall tuffs and coarser clastic sediments diluted accumulating fine grained clastic and chemical sediments. As hot, silica saturated fluids rose into cooler lake waters they were cooled and diluted, resulting in silica flocculation near the vents and silicification of the lake sediments as they were deposited. Faults cutting the butte acted as conduits for the hydrothermal fluids. Overpressuring, caused by silica sealing of open fractures, resulted in explosions, generally followed by resealing of the system. Simultaneous faulting, sedimentation, and hot spring activity occurred at different rates throughout the life of the system. Late in the life of the system, the local water table dropped, and the lake was replaced by a high-energy fluvial system. As the water table dropped below the surface, zones of low pH alteration and bleaching were developed above the hydrothermal vents, implying boiling at depth. The large explosion crater and bedded explosion breccia on the southeast side of the butte were formed in these last stages of hydrothermal activity. Title: The Geology, Geochemistry, and Alteration of Red Butte, Oregon: A Precious Metal-Bearing Paleo Hot Spring System Author: Evans, Carol Susan Year: 1986 Red Butte is located 60 km south of Vale, Oregon, about 20 km west of the Oregon/Idaho border. The butte is within the Owyhee Upland physiographic province of eastern Oregon which lies at the intersection of the Western Snake River Plain, the High Lava Plains, and the Northern Basin and Range provinces. The butte is composed of Miocene to Pliocene lacustrine and fluvial volcaniclastic sediments. The topography of the butte is controlled by silicification of the sandstones and mudstones which cap it. Silicification and hydrothermal alteration are both structurally and stratigraphically controlled. North-trending normal faults dominate the area, and show progressively less offset in younger units. Strong northwest and minor northeast faults also cut the area. Anomalous concentrations of Au, As, Sb, and Hg occur in banded quartz, quartz-adularia veins and rarely in calcite-quartz veins cutting basalts. The silicified mudstones at the butte top are generally barren. An hydrothermal explosion crater exposed on the southeast side of the butte lies at the intersection of north and northwest-trending faults. Banded quartz veins, quartz-adularia veins, and quartz-cemented breccias are exposed in the walls of the explosion crater. There is evidence of multiple brecciation events. A few mudstones exposed in the crater wall have an exhalative texture, contain pyrite des seminated along bedding, and contain trace amounts of Au. The Red Butte system developed as a hot spring venting into a lake, possibly within a caldera. Periodic influxes of air fall tuffs and coarser clastic sediments diluted accumulating fine grained clastic and chemical sediments. As hot, silica saturated fluids rose into cooler lake waters they were cooled and diluted, resulting in silica flocculation near the vents and silicification of the lake sediments as they were deposited. Faults cutting the butte acted as conduits for the hydrothermal fluids. Overpressuring, caused by silica sealing of open fractures, resulted in explosions, generally followed by resealing of the system. Simultaneous faulting, sedimentation, and hot spring activity occurred at different rates throughout the life of the system. Late in the life of the system, the local water table dropped, and the lake was replaced by a high-energy fluvial system. As the water table dropped below the surface, zones of low pH alteration and bleaching were developed above the hydrothermal vents, implying boiling at depth. The large explosion crater and bedded explosion breccia on the southeast side of the butte were formed in these last stages of hydrothermal activity. Close