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• 21. [Article] Stratigraphy, Structure, and Petrology of the Snoqualmie Pass area, Washington

  The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are ...

  Citation × Citation Citation Abstract Copy Title: Stratigraphy, Structure, and Petrology of the Snoqualmie Pass area, Washington Author: Chitwood, Lawrence A. Year: 1976 The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are recognized in the area. They were deformed and later intruded by granodiorite and quartz monzonite porphyry of the Snoqualmie batholith (middle Miocene). The oldest unit, the Denny Formation (Permian), 7000 ft (2100 m) thick, consists of interstratified basalt, andesite and dacite volcanic rocks and limestone and chert beds. This formation is unconformably overlain by a thick conformable sequence of early Tertiary strata which are subdivided, from oldest to youngest, into the Guye Formation, Mount Catherine Tuff, and Naches Formations (Paleocene to early Oligocene). The Guye Formation, 6500 ft (1980 m) thick, consists of carbonaceous mudstone, quartzofeldspathic siltstone and sandstone, and chert conglomerate. The Mount Catherine Tuff, 900 ft (274 m) thick, consists of interstratified dacitic and rhyolitic crystal-vitric welded tuff. The Naches Formation, more than 6000 ft (1830 m) thick, is composed of carbonaceous mudstone and quartzofeldspathic siltstone and sandstone with interstratified andesitic lava and pyroclastic rock. The Denny Mountain Formation, informally named, 1800 ft (550 m) thick,(Oligocene or early Miocene) overlies the Guye Formation along a major angular unconformity. This unit consists of interstratified dacitic and andesitic tuff, volcanic breccia, and intercalated andesitic lava. The rocks of all stratified formations except the Denny Mountain Formation were deformed at different times before emplacement of the Snoqualmie batholith. During batholithic emplacement, four stages of deformation are recognized: (1) development of an anticline in the Guye, Mount Catherine Tuff, and Naches Formations, (2) break-up of this anticline and downfaulting of limbs with displacements up to 2 mi (3.2 km), (3) uplift of blocks of the Denny Formation and juxtaposition of these with younger formational units, and (4) uplift of additional blocks of the Denny Formation along trends that cut obliquely across stratigraphic contacts and previous structural trends. Intrusion of the Snoqualmie granodiorite and quartz monzonite porphyry into limestone beds of the Denny Formation has formed local deposits of skarn containing principally magnetite and lesser amounts of chalcopyrite. Title: Stratigraphy, Structure, and Petrology of the Snoqualmie Pass area, Washington Author: Chitwood, Lawrence A. Year: 1976 The Snoqualmie pass area lies about 50 mi (80 km) east of Seattle, Washington, along the crest of the Cascade Range. Five stratified units, forming a composite section over 22,000 ft (6700 m) thick, are recognized in the area. They were deformed and later intruded by granodiorite and quartz monzonite porphyry of the Snoqualmie batholith (middle Miocene). The oldest unit, the Denny Formation (Permian), 7000 ft (2100 m) thick, consists of interstratified basalt, andesite and dacite volcanic rocks and limestone and chert beds. This formation is unconformably overlain by a thick conformable sequence of early Tertiary strata which are subdivided, from oldest to youngest, into the Guye Formation, Mount Catherine Tuff, and Naches Formations (Paleocene to early Oligocene). The Guye Formation, 6500 ft (1980 m) thick, consists of carbonaceous mudstone, quartzofeldspathic siltstone and sandstone, and chert conglomerate. The Mount Catherine Tuff, 900 ft (274 m) thick, consists of interstratified dacitic and rhyolitic crystal-vitric welded tuff. The Naches Formation, more than 6000 ft (1830 m) thick, is composed of carbonaceous mudstone and quartzofeldspathic siltstone and sandstone with interstratified andesitic lava and pyroclastic rock. The Denny Mountain Formation, informally named, 1800 ft (550 m) thick,(Oligocene or early Miocene) overlies the Guye Formation along a major angular unconformity. This unit consists of interstratified dacitic and andesitic tuff, volcanic breccia, and intercalated andesitic lava. The rocks of all stratified formations except the Denny Mountain Formation were deformed at different times before emplacement of the Snoqualmie batholith. During batholithic emplacement, four stages of deformation are recognized: (1) development of an anticline in the Guye, Mount Catherine Tuff, and Naches Formations, (2) break-up of this anticline and downfaulting of limbs with displacements up to 2 mi (3.2 km), (3) uplift of blocks of the Denny Formation and juxtaposition of these with younger formational units, and (4) uplift of additional blocks of the Denny Formation along trends that cut obliquely across stratigraphic contacts and previous structural trends. Intrusion of the Snoqualmie granodiorite and quartz monzonite porphyry into limestone beds of the Denny Formation has formed local deposits of skarn containing principally magnetite and lesser amounts of chalcopyrite. Close

• 22. [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

• 23. [Article] Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon

  The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica ...

  Citation × Citation Citation Abstract Copy Title: Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon Author: Whitson, David Neale Year: 1988 The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica rhyolites of the formation were erupted over an irregular highland of eroded pre-Tertiary metamorphic rocks locally overlain by intracanyon, Eocene Clarno-type basalt flow(s) . The Dooley Rhyolite Braccia is exposed in a tectonically disrupted, north-south trending graben across the Elkhorn Range. The formation is variable in thickness with maximum thickness exceeding 660 meters in the south and 600 meters in the north half of the quadrangle. Volumetrically the formation is dominated by block lava flows with lessor associated volcaniclastic and pyroclastic rocks. Although initial and waning phases of eruption of the formation produced ash-flow tuffs which extend well beyond the quadrangle boundaries, volcanism within the quadrangle appears to have been primarily effusive. At least nine geochemically distinct rhyolite subunits belonging to four related chemical groups have been identified in the formation stratigraphy which appear to represent unique eruptive episodes. Chronologic geochemical patterns within the formation are consistent with a petrogenetic model of repeated partial melting and eruption from multiple silicic magma chambers in an attenuated continental crust. Basalts correlative with the Powder River Basalt and the Strawberry Volcanics overlie the Dooley Rhyolite Braccia on the north flank of Dooley Mountain. Cale-alkaline basalts correlative with the Strawberry Volcanics are overlain by thoeliitic basalts of uncertain affinity on the south flank of the mountain. These basalt flows on respective flanks of the mountain were not continuous across the quadrangle. Rhyolitic volcanism in the Dooley Mountain quadrangle is contemporary with the strawberry Volcanics and the Picture Gorge Basalt of the Columbia River Basalt Group. Title: Geochemical stratigraphy of the Dooley rhyolite breccia and Tertiary basalts in the Dooley Mountain quadrangle, Oregon Author: Whitson, David Neale Year: 1988 The Dooley Rhyolite Breccia in northeast Oregon was erupted between 12 and 16 million years ago, from central vents and linear feeder dikes within the Dooley Mountain quadrangle. The peraluminous, high-silica rhyolites of the formation were erupted over an irregular highland of eroded pre-Tertiary metamorphic rocks locally overlain by intracanyon, Eocene Clarno-type basalt flow(s) . The Dooley Rhyolite Braccia is exposed in a tectonically disrupted, north-south trending graben across the Elkhorn Range. The formation is variable in thickness with maximum thickness exceeding 660 meters in the south and 600 meters in the north half of the quadrangle. Volumetrically the formation is dominated by block lava flows with lessor associated volcaniclastic and pyroclastic rocks. Although initial and waning phases of eruption of the formation produced ash-flow tuffs which extend well beyond the quadrangle boundaries, volcanism within the quadrangle appears to have been primarily effusive. At least nine geochemically distinct rhyolite subunits belonging to four related chemical groups have been identified in the formation stratigraphy which appear to represent unique eruptive episodes. Chronologic geochemical patterns within the formation are consistent with a petrogenetic model of repeated partial melting and eruption from multiple silicic magma chambers in an attenuated continental crust. Basalts correlative with the Powder River Basalt and the Strawberry Volcanics overlie the Dooley Rhyolite Braccia on the north flank of Dooley Mountain. Cale-alkaline basalts correlative with the Strawberry Volcanics are overlain by thoeliitic basalts of uncertain affinity on the south flank of the mountain. These basalt flows on respective flanks of the mountain were not continuous across the quadrangle. Rhyolitic volcanism in the Dooley Mountain quadrangle is contemporary with the strawberry Volcanics and the Picture Gorge Basalt of the Columbia River Basalt Group. Close

• 24. [Article] The Bedrock Geology of the Southwest Part of the Kachess Lake Quadrangle, Washington

  The southwestern part of the Kachess Lake quadrangle lies between Lakes Cle Elum and Kachess, on the east flank of the central Cascade Range of Washington. The region lies between the North and South Cascade ...

  Citation × Citation Citation Abstract Copy Title: The Bedrock Geology of the Southwest Part of the Kachess Lake Quadrangle, Washington Author: Lofgren, David Carl Year: 1973 The southwestern part of the Kachess Lake quadrangle lies between Lakes Cle Elum and Kachess, on the east flank of the central Cascade Range of Washington. The region lies between the North and South Cascade petrologic provinces, and includes rocks typical of each. Pre-Tertiary Easton Schist (called the Shuksan Suite farther north), and the Late Cretaceous-Paleocene Swauk Formation occur widely in the North Cascades, while the Tertiary Silver Pass Volcanics and Teanaway Basalt are typical of South Cascade volcanic sequences. Diabasic dikes of the Teanaway dike swarm occur throughout the vicinity. The area is bounded on the west by a major fault, the Kachess, and bot.h folding and faulting have occurred in the area proper. Folding is represented by southeast plunging Thorp Mountain anticline; to the north, and Domerie Creek syncline to the south. Several faults have been recognized, the most important being northwest-southeast trending Thomas Mountain fault, which diagonally bisects t.he folds and complicates stratigraphic relationships. The region has been geologically active during most of its history. Eugeosynclinal rocks were metamorphosed to blueschists and greenschists during a late Paleozoic-early Mesozoic orogeny, and folding, faulting, and unconformable relationships involving Tertiary strata indicate continued diastrophism during the Cenozoic. Title: The Bedrock Geology of the Southwest Part of the Kachess Lake Quadrangle, Washington Author: Lofgren, David Carl Year: 1973 The southwestern part of the Kachess Lake quadrangle lies between Lakes Cle Elum and Kachess, on the east flank of the central Cascade Range of Washington. The region lies between the North and South Cascade petrologic provinces, and includes rocks typical of each. Pre-Tertiary Easton Schist (called the Shuksan Suite farther north), and the Late Cretaceous-Paleocene Swauk Formation occur widely in the North Cascades, while the Tertiary Silver Pass Volcanics and Teanaway Basalt are typical of South Cascade volcanic sequences. Diabasic dikes of the Teanaway dike swarm occur throughout the vicinity. The area is bounded on the west by a major fault, the Kachess, and bot.h folding and faulting have occurred in the area proper. Folding is represented by southeast plunging Thorp Mountain anticline; to the north, and Domerie Creek syncline to the south. Several faults have been recognized, the most important being northwest-southeast trending Thomas Mountain fault, which diagonally bisects t.he folds and complicates stratigraphic relationships. The region has been geologically active during most of its history. Eugeosynclinal rocks were metamorphosed to blueschists and greenschists during a late Paleozoic-early Mesozoic orogeny, and folding, faulting, and unconformable relationships involving Tertiary strata indicate continued diastrophism during the Cenozoic. Close

• 25. [Article] Geology, Alteration and Mineralization of a Silicic Volcanic Center, Glass Buttes, Oregon

  Glass Buttes, a Pliocene silicic volcanic complex within the High Lava Plains province of Oregon, was erupted approximately 5.0 to 5.8 million years ago. Geologic mapping revealed that the eastern portion ...

  Citation × Citation Citation Abstract Copy Title: Geology, Alteration and Mineralization of a Silicic Volcanic Center, Glass Buttes, Oregon Author: Johnson, Michael James Year: 1984 Glass Buttes, a Pliocene silicic volcanic complex within the High Lava Plains province of Oregon, was erupted approximately 5.0 to 5.8 million years ago. Geologic mapping revealed that the eastern portion of the complex is underlain by rhyolitic glass domes, flows and rare pyroclastis flows. Basalt flows are interlayered with and onlap the silicic glass. Younger basalt flows, erupted from local vents, overlie silicic glass and onlapping basalts. The eastern end of Glass Buttes is hydrothermally altered at the surface; a weak geothermal anomaly coincides with the altered areas. Alteration, localized by northwest trending normal faults, occurs primarily as opalite replacement of rhyolite glass with associated cinnabar, alunite, clay-rich vein material, hematite, and hyalite. Alteration paragenesis at the surface was defined, and physicochemical conditions during hydrothermal activity were inferred from alteration minerals and assemblages and trace element content of alteration minerals. Alteration identified in the subsurface is interpreted to be related to an older hydrothermal system. Carbonate, pyrite, quartz, and minor smectite and chlorite occur in vugs and fractures, and partially replace subsurface basalt. Abundant fine-grained disseminated pyrite occurs in permeable units. Pyrite separates from disseminations and veins within basalt and permeable glassy units contain up to 13 ppm Au. The pyrite samples are also anomalous with respect to arsenic and antimony. Title: Geology, Alteration and Mineralization of a Silicic Volcanic Center, Glass Buttes, Oregon Author: Johnson, Michael James Year: 1984 Glass Buttes, a Pliocene silicic volcanic complex within the High Lava Plains province of Oregon, was erupted approximately 5.0 to 5.8 million years ago. Geologic mapping revealed that the eastern portion of the complex is underlain by rhyolitic glass domes, flows and rare pyroclastis flows. Basalt flows are interlayered with and onlap the silicic glass. Younger basalt flows, erupted from local vents, overlie silicic glass and onlapping basalts. The eastern end of Glass Buttes is hydrothermally altered at the surface; a weak geothermal anomaly coincides with the altered areas. Alteration, localized by northwest trending normal faults, occurs primarily as opalite replacement of rhyolite glass with associated cinnabar, alunite, clay-rich vein material, hematite, and hyalite. Alteration paragenesis at the surface was defined, and physicochemical conditions during hydrothermal activity were inferred from alteration minerals and assemblages and trace element content of alteration minerals. Alteration identified in the subsurface is interpreted to be related to an older hydrothermal system. Carbonate, pyrite, quartz, and minor smectite and chlorite occur in vugs and fractures, and partially replace subsurface basalt. Abundant fine-grained disseminated pyrite occurs in permeable units. Pyrite separates from disseminations and veins within basalt and permeable glassy units contain up to 13 ppm Au. The pyrite samples are also anomalous with respect to arsenic and antimony. Close

• 26. [Article] Chemical and Petrographic Survey of Large, Igneous-Textured Inclusions in Ordinary Chondrites

  Our inventory of material from the early solar system includes large, igneous-textured inclusions in O chondrites, whose origin and relationship to their host meteorite is unclear. These inclusions occur ...

  Citation × Citation Citation Abstract Copy Title: Chemical and Petrographic Survey of Large, Igneous-Textured Inclusions in Ordinary Chondrites Author: Armstrong, Katherine Year: 2014 Our inventory of material from the early solar system includes large, igneous-textured inclusions in O chondrites, whose origin and relationship to their host meteorite is unclear. These inclusions occur in approximately 4% of O chondrites, and are mineralogically, petrographically, and chemically diverse. Petrographic and chemical data from 29 inclusions from 23 host meteorites were collected with optical light and scanning electron microscopy, allowing for the determination of major phase modal abundance and major element bulk chemistry. No correlation between any inclusion property and host meteorite type were found, but some trends were observed. Nine of the inclusions show strong evidence, such as radial variations in texture and chemistry, for having crystallized as a free-floating droplet in a space environment, and may share the same formation process as chondrules. One inclusion is almost certainly shock-melted material that intruded into the host material. Thirteen inclusions have bulk chemistry patterns that suggest the material was vapor fractionated; the remaining sixteen are essentially chondritic, i.e., unfractionated. Broadly, the data support the conclusions of Ruzicka et al. (1998, 2000), which divided large inclusions into Na-poor (vapor fractionated) and Na-rich (unfractionated) groups, suggesting at least two different origins. There is no evidence that any of the inclusions studied formed by igneous differentiation. Title: Chemical and Petrographic Survey of Large, Igneous-Textured Inclusions in Ordinary Chondrites Author: Armstrong, Katherine Year: 2014 Our inventory of material from the early solar system includes large, igneous-textured inclusions in O chondrites, whose origin and relationship to their host meteorite is unclear. These inclusions occur in approximately 4% of O chondrites, and are mineralogically, petrographically, and chemically diverse. Petrographic and chemical data from 29 inclusions from 23 host meteorites were collected with optical light and scanning electron microscopy, allowing for the determination of major phase modal abundance and major element bulk chemistry. No correlation between any inclusion property and host meteorite type were found, but some trends were observed. Nine of the inclusions show strong evidence, such as radial variations in texture and chemistry, for having crystallized as a free-floating droplet in a space environment, and may share the same formation process as chondrules. One inclusion is almost certainly shock-melted material that intruded into the host material. Thirteen inclusions have bulk chemistry patterns that suggest the material was vapor fractionated; the remaining sixteen are essentially chondritic, i.e., unfractionated. Broadly, the data support the conclusions of Ruzicka et al. (1998, 2000), which divided large inclusions into Na-poor (vapor fractionated) and Na-rich (unfractionated) groups, suggesting at least two different origins. There is no evidence that any of the inclusions studied formed by igneous differentiation. Close

• 27. [Article] A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica

  We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave ...

  Citation × Citation Citation Abstract Copy Title: A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica Author: Hunt, H. W., Fountain, Andrew G., Doran, Peter T., Basagic, Hassan J. Year: 2010 We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave and longwave radiation. Water fluxes included snowmelt, freezing/thawing of soil water, soil capillary flow, and vapour flows among atmosphere, soil, and snow. The model accounted for 96-99% of variation in soil temperature data. No long-term temporal trends in soil temperature were apparent. Soil water vapour concentration in thawed surface soil in summer often was higher than in frozen deeper soils, leading to downward vapour fluxes. Katabatic winds caused a reversal of the usual winter pattern of upward vapour fluxes. The model exhibited a steady state depth distribution of soil water due to vapour flows and in the absence of capillary flows below the top 0.5 cm soil layer. Beginning with a completely saturated soil profile, soil water was lost rapidly, and within a few hundred years approached a steady state characterized by dry soil (,0.5% gravimetric) down to one metre depth and saturated soil below that. In contrast, it took 42,000 years to approach steady state beginning from a completely dry initial condition. Title: A Dynamic Physical Model for Soil Temperature and Water in Taylor Valley, Antarctica Author: Hunt, H. W., Fountain, Andrew G., Doran, Peter T., Basagic, Hassan J. Year: 2010 We developed a simulation model for terrestrial sites including sensible heat exchange between the atmosphere and ground surface, inter- and intra-layer heat conduction by rock and soil, and shortwave and longwave radiation. Water fluxes included snowmelt, freezing/thawing of soil water, soil capillary flow, and vapour flows among atmosphere, soil, and snow. The model accounted for 96-99% of variation in soil temperature data. No long-term temporal trends in soil temperature were apparent. Soil water vapour concentration in thawed surface soil in summer often was higher than in frozen deeper soils, leading to downward vapour fluxes. Katabatic winds caused a reversal of the usual winter pattern of upward vapour fluxes. The model exhibited a steady state depth distribution of soil water due to vapour flows and in the absence of capillary flows below the top 0.5 cm soil layer. Beginning with a completely saturated soil profile, soil water was lost rapidly, and within a few hundred years approached a steady state characterized by dry soil (,0.5% gravimetric) down to one metre depth and saturated soil below that. In contrast, it took 42,000 years to approach steady state beginning from a completely dry initial condition. Close

• 28. [Article] Post-Stagnation Behavior in the Upstream Regions of Ice Stream C, West Antarctica

  The region where two active tributaries feed into the now stagnant Ice Stream C (ISC), West Antarctica, is thickening. In this region, we observe a correlation between faster ice flow (the tributaries) ...

  Citation × Citation Citation Abstract Copy Title: Post-Stagnation Behavior in the Upstream Regions of Ice Stream C, West Antarctica Author: Price, Stephen F., Bindschadler, R. A., Hulbe, Christina L., Joughin, Ian R. Year: 2001 The region where two active tributaries feed into the now stagnant Ice Stream C (ISC), West Antarctica, is thickening. In this region, we observe a correlation between faster ice flow (the tributaries) and elevated topography. We conclude that stagnation of ISC resulted in compression and thickening along the tributaries, eventually forming a "bulge" on the ice-sheet surface. Modern hydraulic potential gradients would divert basal meltwater from ISC to Ice Stream B (ISB). These gradients are primarily controlled by the bulge topography, and so likely formed subsequent to trunk stagnation. As such, we argue against "water piracy" as being the cause for ISC's stagnation. Kinematic-wave theory suggests that thickness perturbations propagate downstream over time, but that kinematic-wave speed decreases near the stagnant trunk. This and modest diffusion rates combine to trap most of the tributary-fed ice in the bulge region. Using interferometric synthetic aperture radar velocity measurements, we observe that half of the ice within ISC's southern tributary flows into ISB. That flow pattern and other observations of non-steady flow in the region likely result from stagnation-induced thickening along upper ISC combined with a longer period of thinning on upper ISB. If current trends in thickness change continue, more ice from upper ISC will be diverted to ISB. Title: Post-Stagnation Behavior in the Upstream Regions of Ice Stream C, West Antarctica Author: Price, Stephen F., Bindschadler, R. A., Hulbe, Christina L., Joughin, Ian R. Year: 2001 The region where two active tributaries feed into the now stagnant Ice Stream C (ISC), West Antarctica, is thickening. In this region, we observe a correlation between faster ice flow (the tributaries) and elevated topography. We conclude that stagnation of ISC resulted in compression and thickening along the tributaries, eventually forming a "bulge" on the ice-sheet surface. Modern hydraulic potential gradients would divert basal meltwater from ISC to Ice Stream B (ISB). These gradients are primarily controlled by the bulge topography, and so likely formed subsequent to trunk stagnation. As such, we argue against "water piracy" as being the cause for ISC's stagnation. Kinematic-wave theory suggests that thickness perturbations propagate downstream over time, but that kinematic-wave speed decreases near the stagnant trunk. This and modest diffusion rates combine to trap most of the tributary-fed ice in the bulge region. Using interferometric synthetic aperture radar velocity measurements, we observe that half of the ice within ISC's southern tributary flows into ISB. That flow pattern and other observations of non-steady flow in the region likely result from stagnation-induced thickening along upper ISC combined with a longer period of thinning on upper ISB. If current trends in thickness change continue, more ice from upper ISC will be diverted to ISB. Close

• 29. [Article] Variability in the Mass Flux of the Ross Sea Ice Streams, Antarctica, over the last Millennium

  We synthesize previously published remote-sensing observations, radar data and model output to obtain a ~1000 year ice flow history for the Siple Coast ice-stream system in West Antarctica to investigate ...

  Citation × Citation Citation Abstract Copy Title: Variability in the Mass Flux of the Ross Sea Ice Streams, Antarctica, over the last Millennium Author: Catania, Ginny, Hulbe, Christina L., Conway, Howard, Scambos, Ted A., Raymond, C. F. Year: 2012 We synthesize previously published remote-sensing observations, radar data and model output to obtain a ~1000 year ice flow history for the Siple Coast ice-stream system in West Antarctica to investigate the timing and magnitude of changes in mass flux. The synthesized history shows significant short-term variability in ice-stream shear margin and grounding line position due to internal variability of the coupled system. The chronology highlights the interplay between adjacent ice streams, which implies that the behavior of any individual ice stream should not be examined in isolation. Furthermore, individual events cannot be fully interpreted without an understanding of the broad-scale, long-term variability in the ice sheet. In the context of this millennium-scale history, we interpret the relatively recent stagnation of Kamb Ice Stream (KIS) as just one stage in the thermodynamic cycle of an ice stream in this region. The changes in mass balance that result from the KIS stagnation may thus be viewed as century-scale ?noise? relative to the longer-term trend. Understanding and characterizing this noise is a necessary step before accurate model-based predictions of ice-sheet mass balance for the next century can be made. Title: Variability in the Mass Flux of the Ross Sea Ice Streams, Antarctica, over the last Millennium Author: Catania, Ginny, Hulbe, Christina L., Conway, Howard, Scambos, Ted A., Raymond, C. F. Year: 2012 We synthesize previously published remote-sensing observations, radar data and model output to obtain a ~1000 year ice flow history for the Siple Coast ice-stream system in West Antarctica to investigate the timing and magnitude of changes in mass flux. The synthesized history shows significant short-term variability in ice-stream shear margin and grounding line position due to internal variability of the coupled system. The chronology highlights the interplay between adjacent ice streams, which implies that the behavior of any individual ice stream should not be examined in isolation. Furthermore, individual events cannot be fully interpreted without an understanding of the broad-scale, long-term variability in the ice sheet. In the context of this millennium-scale history, we interpret the relatively recent stagnation of Kamb Ice Stream (KIS) as just one stage in the thermodynamic cycle of an ice stream in this region. The changes in mass balance that result from the KIS stagnation may thus be viewed as century-scale ?noise? relative to the longer-term trend. Understanding and characterizing this noise is a necessary step before accurate model-based predictions of ice-sheet mass balance for the next century can be made. Close

• 30. [Article] Temporal and Crustal Effects on Differentiation of Tholeiite to Calcalkaline and Ferro-trachytic Suites, High Lava Plains, Oregon, USA

  Strongly bimodal, basalt-rhyolite volcanism of the High Lava Plains Province of Oregon followed the Middle Miocene flood basalts of the Pacific Northwest and extends to recent time. During the 8 m.y. of ...

  Citation × Citation Citation Abstract Copy Title: Temporal and Crustal Effects on Differentiation of Tholeiite to Calcalkaline and Ferro-trachytic Suites, High Lava Plains, Oregon, USA Author: Streck, Martin J., Grunder, Anita L. Year: 2012 Strongly bimodal, basalt-rhyolite volcanism of the High Lava Plains Province of Oregon followed the Middle Miocene flood basalts of the Pacific Northwest and extends to recent time. During the 8 m.y. of volcanism recorded in the central High Lava Plains, in western Harney Basin, three distinct mafic magmatic trends originate from primitive high-alumina olivine tholeiites (HAOT); they are tholeiitic, calcalkaline and ferro-trachytic. Tholeiitic basalts occur throughout the history and their compositions are derived by crystal fractionation while traversing the crust and mixing with evolved mafic magmas. Scavenging of apatite from crustal rocks and minor contamination with felsic melts accounts for P, incompatible element enrichments and increasing tilts of incompatible element patterns with differentiation. The calcalkaline mafic suite occurs in temporal association with abundant silicic volcanism and is the only suite with Fe decreasing with Mg. Calcalkaline compositions are derived from evolved tholeiitic basalt by crystal fractionation coupled with assimilation of felsic crust or crustal melts. The ferro-trachytic suite occurs mainly late, is highly enriched in incompatible element with patterns parallel to tholeiites from which it is derived by protracted fractionation and recharge. The three suites primarily reflect changes in magma flux and crustal interactions in time. High magma flux promotes crustal melting and contamination of tholeiite to make the calcalkaline suite. On the other hand, ferrotrachytic magmas erupted mainly late in the sequence, during magmatic waning and after significant basaltification of the crust. Title: Temporal and Crustal Effects on Differentiation of Tholeiite to Calcalkaline and Ferro-trachytic Suites, High Lava Plains, Oregon, USA Author: Streck, Martin J., Grunder, Anita L. Year: 2012 Strongly bimodal, basalt-rhyolite volcanism of the High Lava Plains Province of Oregon followed the Middle Miocene flood basalts of the Pacific Northwest and extends to recent time. During the 8 m.y. of volcanism recorded in the central High Lava Plains, in western Harney Basin, three distinct mafic magmatic trends originate from primitive high-alumina olivine tholeiites (HAOT); they are tholeiitic, calcalkaline and ferro-trachytic. Tholeiitic basalts occur throughout the history and their compositions are derived by crystal fractionation while traversing the crust and mixing with evolved mafic magmas. Scavenging of apatite from crustal rocks and minor contamination with felsic melts accounts for P, incompatible element enrichments and increasing tilts of incompatible element patterns with differentiation. The calcalkaline mafic suite occurs in temporal association with abundant silicic volcanism and is the only suite with Fe decreasing with Mg. Calcalkaline compositions are derived from evolved tholeiitic basalt by crystal fractionation coupled with assimilation of felsic crust or crustal melts. The ferro-trachytic suite occurs mainly late, is highly enriched in incompatible element with patterns parallel to tholeiites from which it is derived by protracted fractionation and recharge. The three suites primarily reflect changes in magma flux and crustal interactions in time. High magma flux promotes crustal melting and contamination of tholeiite to make the calcalkaline suite. On the other hand, ferrotrachytic magmas erupted mainly late in the sequence, during magmatic waning and after significant basaltification of the crust. Close