Search

Search Results

• 1. [Article] Structure and evolution of the Horse Heaven Hills in south-central Washington

  The Horse Heaven Hills uplift in south-central Washington consists of distinct northwest and northeast trends which merge in the lower Yakima Valley. The northwest trend is adjacent to and parallels the ...

  Citation × Citation Citation Abstract Copy Title: Structure and evolution of the Horse Heaven Hills in south-central Washington Author: Hagood, Michael Curtis Year: 1985 The Horse Heaven Hills uplift in south-central Washington consists of distinct northwest and northeast trends which merge in the lower Yakima Valley. The northwest trend is adjacent to and parallels the Rattlesnake-Wallula alignment (RAW; a part of the Olympic-Wallowa lineament). The northwest trend and northeast trend consist of aligned or en echelon anticlines and monoclines whose axes are generally oriented in the direction of the trend. At the intersection, folds in the northeast trend plunge onto and are terminated by folds of the northwest trend. Title: Structure and evolution of the Horse Heaven Hills in south-central Washington Author: Hagood, Michael Curtis Year: 1985 The Horse Heaven Hills uplift in south-central Washington consists of distinct northwest and northeast trends which merge in the lower Yakima Valley. The northwest trend is adjacent to and parallels the Rattlesnake-Wallula alignment (RAW; a part of the Olympic-Wallowa lineament). The northwest trend and northeast trend consist of aligned or en echelon anticlines and monoclines whose axes are generally oriented in the direction of the trend. At the intersection, folds in the northeast trend plunge onto and are terminated by folds of the northwest trend. Close

• 2. [Article] Shear development and overprinting in a back-arc basin, Klamath Falls, Oregon

  Celebration of Undergraduate Excellence (2013)

  Citation × Citation Citation Abstract Copy Title: Shear development and overprinting in a back-arc basin, Klamath Falls, Oregon Author: Meigs, Andrew, Waldien, Trevor Celebration of Undergraduate Excellence (2013) Title: Shear development and overprinting in a back-arc basin, Klamath Falls, Oregon Author: Meigs, Andrew, Waldien, Trevor Celebration of Undergraduate Excellence (2013) Close

• 3. [Article] Geophysical and geological analysis of a fault-like linearity in the lower Clackamas River area, Clackamas County, Oregon

  A fault-like linearity along the lower Clackamas River is evaluated by analysis of physiographic and structural alignments, geological relationships, and by gravity and magnetic data. The study has resulted ...

  Citation × Citation Citation Abstract Copy Title: Geophysical and geological analysis of a fault-like linearity in the lower Clackamas River area, Clackamas County, Oregon Author: Schmela, Ronald Jay Year: 1971 A fault-like linearity along the lower Clackamas River is evaluated by analysis of physiographic and structural alignments, geological relationships, and by gravity and magnetic data. The study has resulted in the verification of a structural feature extending along the Clackamas River and the eastern front of the Portland Hills. Physiographic alignments were examined in twelve 15 minute and two 7-1/2 minute quadrangle maps. A significant northeasterly morphologic trend, N. 20⁰ W. and N. 40° W., and other secondary trends, namely, the N-S, E-W, and N. 50-60° E., has developed in the Portland area. The consistent northwest trend is observed throughout the entire area studied which strongly suggests that the alignments are very good indicators of underlying structural features. Structural alignments show that approximately 60% of the known mapped faults and fold axes concur with the dominant northwest physiographic trend. Seismic first motion analysis supports the established morphologic trend. A series of regionally co-aligned morphologic and structural features striking S. 40 -50⁰ E. across the state of Oregon suggest the presence of a major structural fault system aligned with the Portland Hills-Clackamas River structural alignment. The geologic cross sections developed from map and well data generally lack any tangible evidence as to the nature of the physiographic alignment. An apparent offset of the lower Pliocene Sandy River mudstone suggests movement as recent as middle Pliocene. Geophysical information was obtained from six gravity traverses and three magnetic traverses. The consistency of the size and shape of the gravity anomaly, 2.18 milligals/O. 2 mile, downdropped to the east, across the physiographic alignment defines the zone of a fault or a steep fold developed in the Columbia River basalt. The magnetic anomalies show a consistent change in the magnetic gradient corresponding to the structural zone. Title: Geophysical and geological analysis of a fault-like linearity in the lower Clackamas River area, Clackamas County, Oregon Author: Schmela, Ronald Jay Year: 1971 A fault-like linearity along the lower Clackamas River is evaluated by analysis of physiographic and structural alignments, geological relationships, and by gravity and magnetic data. The study has resulted in the verification of a structural feature extending along the Clackamas River and the eastern front of the Portland Hills. Physiographic alignments were examined in twelve 15 minute and two 7-1/2 minute quadrangle maps. A significant northeasterly morphologic trend, N. 20⁰ W. and N. 40° W., and other secondary trends, namely, the N-S, E-W, and N. 50-60° E., has developed in the Portland area. The consistent northwest trend is observed throughout the entire area studied which strongly suggests that the alignments are very good indicators of underlying structural features. Structural alignments show that approximately 60% of the known mapped faults and fold axes concur with the dominant northwest physiographic trend. Seismic first motion analysis supports the established morphologic trend. A series of regionally co-aligned morphologic and structural features striking S. 40 -50⁰ E. across the state of Oregon suggest the presence of a major structural fault system aligned with the Portland Hills-Clackamas River structural alignment. The geologic cross sections developed from map and well data generally lack any tangible evidence as to the nature of the physiographic alignment. An apparent offset of the lower Pliocene Sandy River mudstone suggests movement as recent as middle Pliocene. Geophysical information was obtained from six gravity traverses and three magnetic traverses. The consistency of the size and shape of the gravity anomaly, 2.18 milligals/O. 2 mile, downdropped to the east, across the physiographic alignment defines the zone of a fault or a steep fold developed in the Columbia River basalt. The magnetic anomalies show a consistent change in the magnetic gradient corresponding to the structural zone. Close

• 4. [Article] The geology of the Floras Creek area, Curry County, Oregon

  The Floras Creek area, east of the town of Langlois, near the southwest Oregon coast, includes Colebrooke Schist (a klippe of metamorphosed pelitic sediments of Jurassic age), Jurassic Otter Point Formation ...

  Citation × Citation Citation Abstract Copy Title: The geology of the Floras Creek area, Curry County, Oregon Author: Bounds, Jon Dudley Year: 1982 The Floras Creek area, east of the town of Langlois, near the southwest Oregon coast, includes Colebrooke Schist (a klippe of metamorphosed pelitic sediments of Jurassic age), Jurassic Otter Point Formation (a melange complex), and lower the middle Eocene Roseburg and Lookingglass Formations, part of a sandstone-shale sequence occurring more extensively in other areas. The Colebrooke Schist occurs in the south-central part of the area, bounded on the Otter Point and Roseburg. The Lookingglass is exposed as a small (1.5 sq. km) block in the north-north-west part of the area. Two major structural trends are found in the Floras Creek area; an older Mesozoic east-west normal fault trend which is truncated by younger serpentinitefilled, north-south shear zones. The younger fault trend was active into the Tertiary as the faults cut the Eocene. Detrital modal analyses of sandstones suggest that the Otter Point is related to the coeval Dothan Formation of the interior Klamath Mountains, in the same way that the Franciscan is related to the Great Valley sequence in California. The detrital modal analysis indicates that the Otter Point is trench-slope deposited sediments as is the Franciscan and the Dothan is forearc basin deposits similar to the Great Valley. Title: The geology of the Floras Creek area, Curry County, Oregon Author: Bounds, Jon Dudley Year: 1982 The Floras Creek area, east of the town of Langlois, near the southwest Oregon coast, includes Colebrooke Schist (a klippe of metamorphosed pelitic sediments of Jurassic age), Jurassic Otter Point Formation (a melange complex), and lower the middle Eocene Roseburg and Lookingglass Formations, part of a sandstone-shale sequence occurring more extensively in other areas. The Colebrooke Schist occurs in the south-central part of the area, bounded on the Otter Point and Roseburg. The Lookingglass is exposed as a small (1.5 sq. km) block in the north-north-west part of the area. Two major structural trends are found in the Floras Creek area; an older Mesozoic east-west normal fault trend which is truncated by younger serpentinitefilled, north-south shear zones. The younger fault trend was active into the Tertiary as the faults cut the Eocene. Detrital modal analyses of sandstones suggest that the Otter Point is related to the coeval Dothan Formation of the interior Klamath Mountains, in the same way that the Franciscan is related to the Great Valley sequence in California. The detrital modal analysis indicates that the Otter Point is trench-slope deposited sediments as is the Franciscan and the Dothan is forearc basin deposits similar to the Great Valley. Close

• 5. [Article] Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica

  A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative ...

  Citation × Citation Citation Abstract Copy Title: Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica Author: Obryk, Maciej K., Doran, Peter T., Hicks, Jared A., McKay, Christopher P., Priscu, John Charles Year: 2016 A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 a (between 1996 and 2012) of ice thickness changes for the west lobe of Lake Bonney (average ice thickness = 3.53 m) and Lake Fryxell (average ice thickness = 4.22 m). Long-term ice thick-ness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or fa-cilitate ice thickness change depending on the predominant climatic trend (cooling or warming). As such, shallow (columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation. Title: Modeling the Thickness of Perennial Ice Covers on Stratified Lakes of the Taylor Valley, Antarctica Author: Obryk, Maciej K., Doran, Peter T., Hicks, Jared A., McKay, Christopher P., Priscu, John Charles Year: 2016 A 1-D ice cover model was developed to predict and constrain drivers of long-term ice thick-ness trends in chemically stratified lakes of Taylor Valley, Antarctica. The model is driven by surface ra-diative heat fluxes and heat fluxes from the underlying water column. The model successfully reproduced 16 a (between 1996 and 2012) of ice thickness changes for the west lobe of Lake Bonney (average ice thickness = 3.53 m) and Lake Fryxell (average ice thickness = 4.22 m). Long-term ice thick-ness trends require coupling with the thermal structure of the water column. The heat stored within the temperature maximum of lakes exceeding a liquid water column depth of 20 m can either impede or fa-cilitate ice thickness change depending on the predominant climatic trend (cooling or warming). As such, shallow (columns) perennially ice-covered lakes without deep temperature maxima are more sensitive indicators of climate change. The long-term ice thickness trends are a result of surface energy flux and heat flux from the deep temperature maximum in the water column, the latter of which results from absorbed solar radiation. Close

• 6. [Article] Geology and hydrothermal alteration, Glass Buttes, Southeast Oregon

  The Glass Buttes volcanic complex consists of many domes and individual vents that erupted both rhyolitic and basaltic lavas during the late Miocene to early Pliocene. The east half of the complex, in ...

  Citation × Citation Citation Abstract Copy Title: Geology and hydrothermal alteration, Glass Buttes, Southeast Oregon Author: Berri, Dulcy Annette Year: 1982 The Glass Buttes volcanic complex consists of many domes and individual vents that erupted both rhyolitic and basaltic lavas during the late Miocene to early Pliocene. The east half of the complex, in the vicinity of Little Glass Butte, contains interfingering, finely flow-banded rhyolite and black obsidian flows. The youngest unit, an obsidian, has been dated at 4.9 m.y. East of Little Glass Butte lie two northwest-trending ridges, Antelope and Cascade Ridges, composed of two or more overlapping exogenous domes that formed along northwest-trending faults. Title: Geology and hydrothermal alteration, Glass Buttes, Southeast Oregon Author: Berri, Dulcy Annette Year: 1982 The Glass Buttes volcanic complex consists of many domes and individual vents that erupted both rhyolitic and basaltic lavas during the late Miocene to early Pliocene. The east half of the complex, in the vicinity of Little Glass Butte, contains interfingering, finely flow-banded rhyolite and black obsidian flows. The youngest unit, an obsidian, has been dated at 4.9 m.y. East of Little Glass Butte lie two northwest-trending ridges, Antelope and Cascade Ridges, composed of two or more overlapping exogenous domes that formed along northwest-trending faults. Close

• 7. [Article] A seismic refraction study of a portion of the northeastern margin of the Tualatin Valley, Oregon

  The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) ...

  Citation × Citation Citation Abstract Copy Title: A seismic refraction study of a portion of the northeastern margin of the Tualatin Valley, Oregon Author: Nazy, David John Year: 1987 The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) which are a faulted, northwest-trending asymmetrical anticline. Topographic and geophysical evidence have defined the Portland Hills fault, which occurs along the northeast side of the Tualatin Mountains. The possibility that a fault or fault zone occurs along the southwest side of the Tualatin Mountains was investigated in this study. Title: A seismic refraction study of a portion of the northeastern margin of the Tualatin Valley, Oregon Author: Nazy, David John Year: 1987 The Tualatin Valley is a well defined elliptical basin centered at Hillsboro, with a major axis trending roughly N65°W. The valley is bordered on the northeast by the Tualatin Mountains (Portland Hills) which are a faulted, northwest-trending asymmetrical anticline. Topographic and geophysical evidence have defined the Portland Hills fault, which occurs along the northeast side of the Tualatin Mountains. The possibility that a fault or fault zone occurs along the southwest side of the Tualatin Mountains was investigated in this study. Close

• 8. [Article] The stratigraphy and structure of the Columbia River basalt in the Clackamas River drainage

  The Clackamas River drainage within the western Cascade Range is approximately aligned with a northwest trending lineation defined by the Portland Hills and the Brothers Fault zone. This area is occupied ...

  Citation × Citation Citation Abstract Copy Title: The stratigraphy and structure of the Columbia River basalt in the Clackamas River drainage Author: Anderson, James Lee Year: 1978 The Clackamas River drainage within the western Cascade Range is approximately aligned with a northwest trending lineation defined by the Portland Hills and the Brothers Fault zone. This area is occupied by an extensive Columbia River Basalt sequence that is deeply incised by the Clackamas River and its tributaries. Two major basalt units of the Yakima Basalt Subgroup, including the Grande Ronde Basalt and the Frenchman Springs Member of the Wanapurn Basalt, are distinguishable in a 515 meter to 550 meter accumulation. Of particular interest is the presence of five trending right-lateral strike-slip faults is consistent with a stress model of north-south compression and east-west extension. Title: The stratigraphy and structure of the Columbia River basalt in the Clackamas River drainage Author: Anderson, James Lee Year: 1978 The Clackamas River drainage within the western Cascade Range is approximately aligned with a northwest trending lineation defined by the Portland Hills and the Brothers Fault zone. This area is occupied by an extensive Columbia River Basalt sequence that is deeply incised by the Clackamas River and its tributaries. Two major basalt units of the Yakima Basalt Subgroup, including the Grande Ronde Basalt and the Frenchman Springs Member of the Wanapurn Basalt, are distinguishable in a 515 meter to 550 meter accumulation. Of particular interest is the presence of five trending right-lateral strike-slip faults is consistent with a stress model of north-south compression and east-west extension. Close

• 9. [Article] A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon

  The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie ...

  Citation × Citation Citation Abstract Copy Title: A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon Author: Haas, Nina Year: 1982 The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie River along the same trend, through Columbia County, Oregon. The possibility that this lineament follows a fault or fault zone was investigated in this study. Geophysical methods were used, with seismic refraction, magnetic and gravity lines run perpendicular to the lineament. The seismic refraction models indicate the near surface basalt is broken in many places, with 15 - 30 meters (50 - 100 feet) vertical displacement, down to the west, at Bunker Hill along the Alder Creek fault. Gravity models required a faulted zone approximately two kilometers wide across the lineament. The proposed fault zone is more clearly defined in the south, becoming more diffuse and branching in the northern part of the study area. The Bouguer gravity values from this study distort the -40 milligal contour farther to the northwest than is shown on the Complete Bouguer Gravity Anomaly Map of Oregon {Berg and Thiruvathukal, 1967b). The existence of sharp topographic features and the geophysical evidence indicate fault activity along the zone. Title: A geophysical study of the North Scappoose Creek, Alder Creek, Clatskanie River lineament, along the trend of the Portland Hills fault, Columbia County, Oregon Author: Haas, Nina Year: 1982 The Portland Hills fault forms a strong northwest trending lineament along the east side of the Tualatin Mountains. An en echelon lineament follows North Scappoose Creek, Alder Creek, and the Clatskanie River along the same trend, through Columbia County, Oregon. The possibility that this lineament follows a fault or fault zone was investigated in this study. Geophysical methods were used, with seismic refraction, magnetic and gravity lines run perpendicular to the lineament. The seismic refraction models indicate the near surface basalt is broken in many places, with 15 - 30 meters (50 - 100 feet) vertical displacement, down to the west, at Bunker Hill along the Alder Creek fault. Gravity models required a faulted zone approximately two kilometers wide across the lineament. The proposed fault zone is more clearly defined in the south, becoming more diffuse and branching in the northern part of the study area. The Bouguer gravity values from this study distort the -40 milligal contour farther to the northwest than is shown on the Complete Bouguer Gravity Anomaly Map of Oregon {Berg and Thiruvathukal, 1967b). The existence of sharp topographic features and the geophysical evidence indicate fault activity along the zone. Close

• 10. [Article] Igneous Dikes at Long Valley, CA: Emplacement Mechanisms and Associated Geologic Structures

  Two hypotheses for dike emplacement are: (1) magma flows into and dilates pre-existing fractures; or (2) magma flows into and dilates self-generated fractures. In the first case dikes should be parallel ...

  Citation × Citation Citation Abstract Copy Title: Igneous Dikes at Long Valley, CA: Emplacement Mechanisms and Associated Geologic Structures Author: Pollard, David D., Fink, Jonathan H., Delaney, Paul T. Year: 1984 Two hypotheses for dike emplacement are: (1) magma flows into and dilates pre-existing fractures; or (2) magma flows into and dilates self-generated fractures. In the first case dikes should be parallel to an element of the rock fabric; in the second, they should be perpendicular to the least compressive stress. The two hypotheses suggest different dike intrusion and fissure eruption mechanisms and therefore different strategies for monitoring igneous events at Long Valley. We derive a method to distinguish the two mechanisms, a priori, from in-situ stress measurements and estimates of magma pressure. Estimates of relative dilation and slip across a dike plane from models constrained by surface displacement data provide a method to distinguish the two mechanisms, a posteriori. Joints cluster near dike contacts just as microcracks cluster near laboratory fractures. Such clusters define a process zone of secondary cracking that forms at the tip of a primary crack. For basaltic dikes in sedimentary host rocks of the Colorado Plateaus, the process zone size is about 10 m and the number of joints is in the range 10 to 100. The mechanical energy release rate for propagation of these dikes is estimated to be 10 to 100 times that for a single laboratory fracture. Data from .proposed drill holes through rhyolite dikes under the Inyo Domes will elucidate propagation mechanisms and process zone characteristics. As a dike nears the Earth's surface, two sets of ground cracks open parallel to the dike trend. A "rule of thumb" is that the depth to the dike top is one-third to one-half the spacing between the innermost surface cracks of each set. Surface structures on and near the Inyo Domes suggest a NNE trend for shallow (< several hundred meters) dike segments, but dome alignment suggests a NNW trend for the feeder dikes at depth. Title: Igneous Dikes at Long Valley, CA: Emplacement Mechanisms and Associated Geologic Structures Author: Pollard, David D., Fink, Jonathan H., Delaney, Paul T. Year: 1984 Two hypotheses for dike emplacement are: (1) magma flows into and dilates pre-existing fractures; or (2) magma flows into and dilates self-generated fractures. In the first case dikes should be parallel to an element of the rock fabric; in the second, they should be perpendicular to the least compressive stress. The two hypotheses suggest different dike intrusion and fissure eruption mechanisms and therefore different strategies for monitoring igneous events at Long Valley. We derive a method to distinguish the two mechanisms, a priori, from in-situ stress measurements and estimates of magma pressure. Estimates of relative dilation and slip across a dike plane from models constrained by surface displacement data provide a method to distinguish the two mechanisms, a posteriori. Joints cluster near dike contacts just as microcracks cluster near laboratory fractures. Such clusters define a process zone of secondary cracking that forms at the tip of a primary crack. For basaltic dikes in sedimentary host rocks of the Colorado Plateaus, the process zone size is about 10 m and the number of joints is in the range 10 to 100. The mechanical energy release rate for propagation of these dikes is estimated to be 10 to 100 times that for a single laboratory fracture. Data from .proposed drill holes through rhyolite dikes under the Inyo Domes will elucidate propagation mechanisms and process zone characteristics. As a dike nears the Earth's surface, two sets of ground cracks open parallel to the dike trend. A "rule of thumb" is that the depth to the dike top is one-third to one-half the spacing between the innermost surface cracks of each set. Surface structures on and near the Inyo Domes suggest a NNE trend for shallow (< several hundred meters) dike segments, but dome alignment suggests a NNW trend for the feeder dikes at depth. Close