Trips After the Meeting

428. Landscape and Hydrologic Recovery in the Williamson River Basin Following the Holocene Eruption of Mount Mazama to form Crater Lake, Cascade Volcanic Arc
Wed.–Fri., 21–23 Oct.
Sorry, this trip has been canceled.
429. Mesozoic Sedimentation, Magmatism, and Tectonics in the Blue Mountains Province, Central Oregon
Wed.–Sat., 21–24 Oct. US$572 (L, D, R, 3ON).
Cosponsored by GSA’s Sedimentary Geology Division
Leaders: Todd LaMaskin, University of Oregon; Joshua Schwartz; Rebecca Dorsey; Art Snoke; Ken Johnson.
This trip will examine Upper Triassic to Jurassic sedimentary rocks of the Izee terrane and associated Paleozoic basement and Jurassic magmatic rocks in the adjacent Baker terrane. This will provide an opportunity for wide-ranging discussions of Mesozoic sedimentation, magmatism, and tectonics of the western U.S. and Canadian Cordillera. We will depart Portland at 1 pm on Wednesday and drive about six hours to John Day, Oregon, USA. On Thursday, we will visit basement exposures of serpentinite-matrix mélange and overlying Triassic sedimentary strata. We will traverse up-section through Triassic and Jurassic rocks that include olistostromal slide blocks and volcaniclastic turbidites and examine new detrital-zircon data that have implications for the tectonic evolution of the region and possible links to the Klamath Mountains and southern British Columbia. On Friday, we will visit Late Jurassic plutons and associated volcanic rocks exposed in the Baker terrane east of John Day. We will examine two compositionally and geochemically distinct plutons that record magmatism 157 and 146 million years ago and examine host rocks, including basaltic andesite flows and volcaniclastic breccias. Discussion will focus on petrographic and geochemical characteristics of the Late Jurassic igneous rocks, their petrogenesis, and their relationship to orogenic events in the Blue Mountains. We will also examine Mesozoic volcanogenic sedimentary rocks in the Dixie Butte complex and compare them to sedimentary rocks observed on day one. We will depart John Day at ~8 a.m. on Saturday and return to Portland by about 2 p.m.
430. Geological and Geophysical Perspectives on the Magmatic and Tectonic Development of the Northwest Basin and Range
Wed.–Sat., 21–24 Oct. US$400 (L, R, 3ON).
Cosponsored by GSA’s Geophysics and Structural Geology and Tectonics Divisions and GSA’s Cordilleran Section.
Leaders: Andrew Meigs, Oregon State University; Anita Grunder; Tim Grove; Richard Carlson; Ray Weldon; Kaleb Scarberry.
High Lava Plains
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Late Cenozoic magmatism created the High Lava Plains (HLP) in southeastern Oregon, one of the great continental volcanic provinces on Earth. Thin, widespread Plio-Pleistocene lava flows of primitive basalt, along with a belt of silicic eruptive centers that are successively younger to the northwest, characterize the HLP. Age-progressive magmatism in the HLP mirrors the basalt plateau and rhyolite age progression of the Snake River Plain. Structurally, the HLP obliquely straddles both the small northwest-striking Brothers fault zone and the northern termination of major Basin and Range normal faults. Competing influences on the bimodal volcanism include active subduction and extension, the Yellowstone Plume, and western edge of the North American craton. Understanding the lithospheric evolution of this region by highlighting ongoing structural, geophysical, and petrologic research is the objective of this trip. On a grand tour from Bend through Burns, Oregon, USA, participants will travel from the eastern edge of the Cascade arc across the Basin and Range to the HLP volcanic plateau. Day 1 visits Newberry Caldera and ends on the western-most edge of Basin and Range. Day 2 begins with the early magmatic and extensional history along the Abert Rim fault and ends with the bimodal volcanism within the HLP and its relationship with to the major fault zones. Evening entertainment features new geophysical results from the HLP active source seismic experiment, the largest ever conducted in North America. On the last day, the onset of bimodal volcanism and extension in the eastern HLP are revealed from the proto-Harney Basin.
431. Terroir Tour of the Columbia Gorge
Thurs., 22 Oct. US$95 (L, R).  — FULL —
Cosponsored by GSA’s Engineering Geology, Hydrogeology, and Quaternary Geology and Geomorphology Divisions; GSA’s Cordilleran Section; the International Association of Hydrogeologists; and the Groundwater Resources Association of California.
Leader: Scott F. Burns, Portland State University.
Terroir is the relationship between geology, soils, hydrology, climate, and wine. We will explore the wineries of the Columbia Valley east of Portland where the climate is warmer than the Northern Willamette Valley so the wines can be made from both warm and cool climate grapes. See how the bedrock affects the wines and learn the effect the great Missoula Floods as well. Join nationally famous terroir specialist, Scott Burns, as he takes you to four wineries: Cathedral Ridge, The Pines, Naked, and Syncline. We will also enjoy the spectacular geology of the Columbia River Gorge on the way to the wineries.
Oxbow Park
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432. Eruption-Related Lahars and Sedimentation Response Downstream of Mount Hood
Thurs., 22 Oct. US$79 (L, R).
Cosponsored by GSA’s Quaternary Geology and Geomorphology and Sedimentary Geology Divisions.
Leaders: Thomas C. Pierson, USGS–Cascades Volcano Observatory; Patrick Pringle; W.E. Scott; James W. Vallance.
We will examine deposits of lahars and volcanic floods related to the last two (late Holocene) dome-building eruptions of Mount Hood, Oregon, USA. We will visit outcrops from about 15 to 85 km downstream from the volcano along the Sandy River to contrast and compare volcanic debris-flow, hyperconcentrated-flow, and water-flow deposits and to see how this fluvial system responded to volcanic sediment loading with significant channel aggradation.
433. Fluvial Response to Removal of Marmot Dam, Sandy River, Oregon
Thurs., 22 Oct. US$80 (L, R).
Cosponsored by GSA’s Quaternary Geology and Geomorphology Division.
Leaders: J. Rose Wallick, USGS-Portland; Charles J. Podolak; Jim O’Connor; Jon Major.
Participants of this one-day trip to the site of Marmot Dam on the Sandy River east of Portland will examine erosional and depositional features resulting from the dam’s 19 Oct. 2007 removal. This dam removal has been one of the most visible in a growing movement of decommissioning done in part to restore riverine ecosystems, and was especially notable for the large volume of reservoir sediment suddenly accessible for downstream transport by an energetic river. This trip will look at the fate of the former reservoir and downstream sedimentologic and geomorphic consequences two years after removal, as well as examine the host of ecologic, geomorphic, and sociologic issues involved with dam decommissioning.
434. Mega Breccias and Subglacial Meltwater Outburst: Evidence from Whidbey Island, Washington
Wed.–Fri., 21–23 Oct. US$368 (B, L, D, R, 2ON).
Cosponsored by GSA’s Quaternary Geology and Geomorphology Division and the American Quaternary Association (AMQUA).
Leaders: Eugene Domack, Hamilton College; David Sharpe.
The purpose of this trip is to examine the spectacular exposures of megabreccia gravels exposed along the sea cliffs of Whidbey Island. The goal is to develop a discussion and consensus on the origin of this stratigraphic unit as it relates to subglacial meltwater outburst during the closing stages of Fraser (Vashon Stade) Glaciation in the northern Puget Lowlands. Subglacial outburst flooding as fed by meltwater reservoirs beneath ice sheets and ice streams is a topic of much importance in understanding both the stability of current ice sheets in Antarctica and past behavior and water transfer to the oceans during the last deglaciation. The sediments examined on this field trip will be integrated with recent LIDAR topography provided by the Puget Sound LIDAR consortium and placed into a proper glacial to marine model.
435. Coastal Geomorphology, Hazards, and Management Issues along the Pacific Northwest Coast of Oregon and Washington
Thurs.–Fri., 22–23 Oct. US$305 (L, D, R, 1ON).
Leaders: Jonathan Allan, Oregon Dept. of Geology and Mineral Industry Newport Coastal Field Office; Peter Ruggiero; Robert Witter.
Development along the coasts of Oregon and Washington, USA, is threatened by a variety of natural hazards, including coastal erosion, landslides, earthquakes, and tsunamis. The impacts of hazards on development have increased significantly in recent years due to poor management practices and an intensification of the physical processes that drive coastal change. This field trip will visit a number of sites that illustrate the processes that shape Pacific Northwest coastal geomorphology and create hazards, including potentially catastrophic tsunamis generated by the Cascadia subduction zone (CSZ). We will discuss what we have learned about the ocean processes that produce elevated tides and high wave runup levels, resulting in the erosion of the coast, which leads to property losses. Also examined is the human response, which includes constructing coastal engineering structures and the establishment of coastal “erosion” hazard zones. At three sites, we will discuss new research findings on tsunamis and the effects of coastal subduction caused by great earthquakes on the CSZ, including examining efforts by public officials to prepare and mitigate for future events. The field trip will conclude on the southern Washington coast at Cape Disappointment State Park adjacent to the Columbia River, where researchers will discuss the response of the coast to the construction of the Columbia River jetties. Additional discussion will focus on the role of river flow regulation and dredging and disposal activities in influencing the sediment budget of the Columbia River littoral cell as well as current sediment management practices that aim to ensure more effective decision making within this cell.
436. Tuff Cones, Tuff Rings, and Maars of the Fort Rock–Christmas Valley Basin, Oregon: Exploring the Vast Array of Pyroclastic Features that Record Violent Hydrovolcanism at Fort Rock and the Table Rock Complex
Thurs.–Sat. 22–24 Oct. US$283 (L, R, 2ON).
Cosponsored by the University of Washington.
Leaders: Brittany D. Brand, Univ. of Washington; Grant Heiken.
Fort Rock
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Hydrovolcanic eruptions occur when rising magma violently fragments while mixing with shallow surface water or groundwater. These eruptions, among the most violent on Earth, generate hundreds to thousands of explosions throughout the course of an eruptive event. Each of these explosions ejects a mixture of juvenile and accidental clasts, gas, and water droplets. The solid materials either fall to the ground from tephra jets or collapse to form pyroclastic density currents (PDCs). The deposits of these eruptions build up rings of bedded tuff around the vent, recording both a wide variety of pyroclastic depositional mechanisms and important changes in the eruptive style with time. This field trip will explore the deposits of basaltic, hydrovolcanic eruptions in the Fort Rock–Christmas Valley basin, the location of a widespread Pleistocene lake. Basaltic volcanoes within the ancient lake are characterized by Surtseyan eruptions (standing water), along the lake margins by maar eruptions (groundwater), and beyond the lake margin by scoria cones. The focus of the trip will be Fort Rock (Surtseyan) and the Table Rock Complex (large Surtseyan-tuff cone, large maar, and seven minor eruptions). This trip offers the opportunity to examine (1) settings under which explosive hydrovolcanic eruptions occur; (2) depositional characteristics that infer eruptive conditions; (3) a wide variety of pyroclastic deposits (i.e., fallout through air or a body of water, eruption-fed subaqueous sediment gravity current deposits, PDC deposits); and (4) mega-dunes—200-m-wavelength dunes associated with large scale, dilute, PDCs from what may be one of the largest mafic hydrovolcanic eruptions ever documented.
437. Columbia River Basalts and Structure from the Gorge through the Forearc to the Washington-Oregon Coast: Tracing Subaerial Lavas to Lava Deltas, Submarine Pillow Breccias, and Mega-Invasive Flows
Thurs.–Sat., 22–24 Oct. US$335 (L, R, 2ON).  — FULL
Leaders: Ray E. Wells, USGS–Menlo Park; Alan Niem; Jonathan Hagstrum; Russ Evarts; Terry Tolan.
Miocene flood basalts of the Columbia River Basalt Group (CRBG) passed through the Cascade arc via a wide ancestral Columbia River valley, eventually reaching the Pacific Ocean. This three-day trip will follow these flows and examine the spectacular results of their interactions with the sea. Yakima fold belt-like structures, strike-slip faults, and rotating CRBG blocks in the forearc will also be examined. We will spend the first day in the scenic western Columbia River Gorge, along the margin of the Miocene paleovalley, viewing subaerial sheet flows and their interactions with tributary streams. We will also examine younger intra-canyon flows and discuss recent refinements to flood-basalt stratigraphy based on new chemical and paleomagnetic data. The second and third days follow these subaerial flow units down the modern (and ancestral) lower Columbia River to the Miocene shoreline, where geologic mapping and geochemical and paleomagnetic data allow individual flows to be traced into distal lava deltas, pillow breccia complexes, and a partly filled submarine canyon, now forming inverted topography. Mega-invasive flows formed peperites, 30-km-long dikes, and sills up to 300 m thick in Eocene, Oligocene, and Miocene marine and deltaic sedimentary rocks, baking the sediments up to 150 m away from the contact. Mechanisms for this will be discussed. Day 2 overnights in historic Astoria overlooking the waterfront, while Day 3 examines scenic coastal headlands and state parks of northwest Oregon, which are mostly mega-invasive “sills” and flows, along with rugged, 1000-m-high pillow breccia peaks not accessible to the casual visitor.
438. Paleobotany of the John Day Fossil Beds, Central Oregon
Thurs.–Sat., 22–24 Oct. US$300 (B, L, D, R, 2ON).
Cosponsored by the Evolving Earth Foundation, Western Oregon University, The Burke Museum of Natural History and Culture, and the University of Washington.
Leaders: Richard Dillhoff, University of Washington; Thomas Dillhoff; Regan Dunn; Caroline Stromberg; Jeff Myers.
The John Day Fossil Beds document almost 40 million years of Oregon prehistory, from the middle Eocene through the late Miocene (44–7 million years ago), recording the important environmental and biotic changes that shaped modern ecosystems. This will be a three day trip, surveying fossil plants from the middle Eocene Clarno formation, the late Eocene to early Oligocene John Day formation and middle Miocene Mascall formation. Participants will need hiking boots and should be prepared to walk about four miles at Camp Hancock on uneven terrain. The registration fee includes a shared cabin at Camp Hancock Thursday night and a double occupancy room at a John Day motel Friday night. The Camp Hancock cabins are heated but only provide a bare mattress, so you will need to bring a sleeping bag or blankets or rent a bag. With advance notice, we can rent sleeping bags from REI (liner provided) for a $25 fee. Cafeteria-style meals will be provided, and we will bring loaner tools; however, participants are encouraged to bring a backpack and their own hammer and chisel. No collecting will be permitted on national park lands, but specimens collected at the other localities may be kept for educational purposes. We will make provisions to have any significant finds deposited at an appropriate public institution.
439. Hydrogeology of the Columbia River Basalt Group (CRBG) in the Willamette Valley, Oregon
Thurs.–Fri., 22-23 Oct. US$206 (L).
Cosponsored by GSA’s Hydrogeology Division.
Leaders: Walt Burt, GSI Water Solutions Inc.; Larry Eaton; Ken Lite; Karl Wozniak; Terrence Conlon; Terry Tolan.
The flood basalts of the CRBG form the framework of some of the most utilized aquifers in the northern Willamette Valley, supplying water to cities, agriculture, and rural and suburban developments. Water level declines in areas with increasing development and sustained withdrawals illustrate the limitations of the CRBG aquifers as a groundwater resource. Recent success in testing and development of aquifer storage and recovery (ASR) systems highlight the continued importance of these aquifer systems to developing water resource management tools in the region. Stratigraphic characteristics and the effects of tectonic structures provide the key to understanding groundwater resources in the CRBG. Participants of this two-day trip will examine geologic features that control recharge, storage, and flow of groundwater in CRBG aquifers in the Willamette Valley. Each day of the field trip will begin and end in Portland. A mid-afternoon stop at a meeting room (e.g. at a winery or restaurant) will be scheduled for two of the days(remove) to present hydrogeologic information from the areas visited earlier in the day, summarize and discuss field observations, and view borehole samples.
440. Geothermal Geology and Utilization in Oregon
Thurs.–Sat., 22–24 Oct.
Sorry, this trip has been canceled.


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