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At least 1,351 records · Page 75Linked to original sources

USGS2015

Barrier Island Shorelines Extracted from Landsat Imagery

Introduction Changes to barrier islands occur at time scales that vary from the few hours it takes an individual storm to pass (Morton, 2008) to the millennia it takes for coastal systems to undergo geologic evolution. Developing an understanding of how barrier islands will respond to climate change, sea level rise, and major storms over a range of time scales is relevant to studies of physical, geological, ecological, and societal processes and will help to guide and improve management of our coastal resources (Sallenger and others, 1987). Observations of coastal processes made over a range of spatial and temporal scales and from a variety of instrument platforms (for example, in situ and remote remote sensing) are required to understand and eventually predict the evolution of coastal systems. The deployment of Landsat and other earth-observing satellites within the last few decades has provided an opportunity to observe barrier islands at frequent intervals, often many times a year. This sample frequency is much higher and the spatial coverage much greater than most routine high-resolution topographic surveys (Guy and others, 2014). In addition, the historical record of these datasets have become long enough to document shorter- (that is, annual) and longer-term (that is, decadal) changes from a single data source. Certain aspects of barrier island morphology, such as island size, shape, and position, can be determined from these images and can indicate erosion, land loss, and island breakup (McBride and others, 1989; Plant and Guy, 2013). The shoreline is a common variable used as a metric for coastal erosion or change (Himmelstoss and others, 2010). Although shorelines are often extracted from topographic data (for example, ground-based surveys and light detection and ranging [lidar]), image-based shorelines, corrected for their inherent uncertainties (Moore and others, 2006), have provided much of our understanding of long-term shoreline change because they pre-date routine lidar elevation survey methods. Image-based shorelines continue to be valuable because of their higher temporal resolution compared to costly airborne lidar surveys. A method for extracting sandy shorelines from 30-meter (m) resolution Landsat imagery is presented here.

Open-File Report↗

USGS2016

High-resolution geophysical data from the Inner Continental Shelf: South of Martha's Vineyard and north of Nantucket, Massachusetts

The U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management have cooperated to map approximately 185 square kilometers of the inner continental shelf south of Martha’s Vineyard and north of Nantucket, Massachusetts. This report contains geophysical data collected by the U.S. Geological Survey during a survey in 2013. The geophysical data include (1) swath bathymetry collected by using interferometric sonar, (2) acoustic backscatter from the interferometric sonar, and (3) seismic-reflection profiles from a chirp subbottom profiler. These spatial data support research on the Quaternary evolution of coastal Massachusetts, the influence of sea-level change and sediment supply on coastal evolution, and efforts to understand the type, distribution, and quality of subtidal marine habitats in the coastal ocean of Massachusetts.

Massachusetts↗

USGS2018

The Colorado River and its deposits downstream from Grand Canyon in Arizona, California, and Nevada

Understanding the evolution of the Colorado River system has direct implications for (1) the processes and timing of continental-scale river system integration, (2) the formation of iconic landscapes like those in and around Grand Canyon, and (3) the availability of groundwater resources. Spatial patterns in the position and type of Colorado River deposits, only discernible through geologic mapping, can be used to test models related to Colorado River evolution. This is particularly true downstream from Grand Canyon where ancestral Colorado River deposits are well-exposed. We are principally interested in (1) regional patterns in the minimum and maximum elevation of each depositional unit, which are affected by depositional mechanism and postdepositional deformation; and (2) the volume of each unit, which reflects regional changes in erosion, transport efficiency, and accommodation space. The volume of Colorado River deposits below Grand Canyon has implications for groundwater resources, as the primary regional aquifer there is composed of those deposits. To this end, we are presently mapping Colorado River deposits and compiling and updating older mapping. This preliminary data release shows the current status of our mapping and compilation efforts. We plan to update it at regular intervals in conjunction with ongoing mapping.

Arizona, California, Nevada↗

USGS2020

Development of a process-based littoral sediment transport model for Dauphin Island, Alabama

Dauphin Island, Alabama, located in the Northern Gulf of Mexico just outside of Mobile Bay, is Alabama’s only barrier island and provides an array of historical, natural, and economic resources. The dynamic island shoreline of Dauphin Island evolved across time scales while constantly acted upon by waves and currents during both storms and calm periods. Reductions in the vulnerability and enhancements to the resiliency of Dauphin Island—through offshore sand placement, breach closure, berm construction, and other means—have been used to protect the island and its vital resources. Planning for a resilient Dauphin Island requires predicting the long-term evolution of the barrier island system and the dominant, temporally varying processes that influence it, including littoral alongshore sediment transport under typical wave conditions, beach and dune erosion, the island overwash and breaching that occur rapidly during storm events, and the recovery of primary sand dunes through Aeolian transport over decadal time scales. Littoral sediment transport within the Dauphin Island decadal-scale framework was simulated using the Delft-3D modeling software suite. The influences of wind, waves, water levels, and sediment transport are incorporated into the model. Model skill in the prediction of waves, water levels, currents, volumetric flow rates through inlets, and shoreline position was assessed by using a set of deterministic and statistical hindcast simulations. The Delft-3D modeling application described here can be coupled with validated models of storm-response and dune recovery to predict the evolution of Dauphin Island on decadal time scales.

Alabama↗

USGS1957

Hydrology and water law: what is their future common ground?

We live in an age of social and economic evolution--evolution so deep reaching and rapid it constitutes ad revolution in numerous fields of human concern. Long-standing concepts of what is appropriate and orderly face drastic modification if they are to survive. To this situation the principles of applied hydrology and the tenets of water law are no exceptions. Their common ground, incomplete in the past, becomes tenuous when projected into the future. To hydrologists it is common knowledge that the Nation has some trouble spots tin water supply, occasioned by burgeoning population, by standards of living that seem luxurious to other peoples if not to us, and by tremendously dynamic industry whose voracious thirst for water seems insatiable. Seldom is the "trouble" a mere lack of water in a quantity sufficient to serve all real needs; rather, water usually is available only part of the time, at greater-than-customary cost, or under competition among several potential uses. We can expect only that such spots will increase in number and in geographic reach.

Open-File Report↗

USGS1977

Magmatic behavior of Cu, S, Cl, F, and H 2 O in igneous rocks associated with the Ray porphyry copper deposit, Arizona

Porphyry copper deposits are the subject of a large volume of literature indicating that controversy still reigns as to which model or combination of models explains their origin, and yet, over 70 years ago we reached agreement that the well-documented space-time relationship between the deposits and calc-alkaline plutons indicates a genetic tie between them. This genetic tie is generally assumed to indicate a causitive role for an exposed or nearby hidden pluton. There are many variants, but the two end-member models that incorporate this causitive assumption are the meteoric water model and the orthomagmatic model. It is my opinion that the controversy originates from use of indirect data and variant models to explain new observational data and experimental studies that threaten the survival of the basic end-member models. One of many examples of this is the end-stage magmatic evolution of chlorine-rich water required of the orthomagmatic model. This evolution is required because the low copper content of calc-alkaline plutons demands a large source magma, that, because it generally is not visible, has to be buried. Additionally, much of the ore minerals in porphyry deposits is along fractures. Both conditions require transportation of the ore components from the magma, and to transport enough ore components, given the limited amount of water soluble in a melt and the low solubility of base-metal sulfides in water without benefit of chloride complexing, we required of the original Lindgren magmatic model that the source pluton produced chloride-rich water. However, we did not investigate the rocks associated with deposits to substantiate the hypothesis. We went to the laboratory and found that sufficient water and chlorine could be dissolved in silicate melt in a gold capsule in a high-pressure high-temperature bomb to allow postulation of sufficient water and chlorine in the stocks associated with porphyry deposits; in other words, we invested in indirect rather than direct studies.

Arizona↗

USGS1983

Trace-element geochemistry of postorogenic granites from the northeastern Arabian Shield, Kingdom of Saudi Arabia

Concentrations determined for all of the trace elements included in this study of postorogenic granites from the northeastern Arabian Shield are best described by log-normal distributions. The trace elements are divided into two groups: (1) compatible lithophile and siderophile elements (strontium, cobalt, scandium, manganese, europium, and titanium) and (2) incompatible lithophile elements (uranium, thorium, tantalum, rubidium, and rare-earth elements, except europium). The compatible elements exhibit greatest concentrations in the metaluminous postorogenic granites, and concentrations decrease with increasing degree of magma evolution. Economic potential for these elements and other geochemically similar elements is considered to be low. The concentrations of the incompatible elements increase with increasing degree of magma evolution and are greatest in the peralkaline and peraluminous granites. There is some geologic evidence that pegmatite and vein-forming processes were operative toward the end stage of postorogenic magmatism in the northeastern Arabian Shield, and therefore there is some probability for economic potential for these elements. It is suggested that such potential is greatest where highly evolved postorogenic granites intruded volatile (generally water )-rich country rocks.

Open-File Report↗

USGS1985

Reconnaissance geology of the Al Hufayr Quadrangle, sheet 27/41A, Kingdom of Saudi Arabia

The Al Hufayr quadrangle (27/41 A) lies at the northern edge of the Arabian Shield between lat 27 30' and 28 00' N. and long 41 00' and 41 30' E. A cataclastically foliated syenogranite, the oldest rock exposed in the quadrangle, crops out in a restricted area in the south-central part of the quadrangle. Younger, weakly metamorphosed metarhyolite and minor metabasalt, arkosic sandstone, and conglomerate crop out north of the syenogranite and are correlated with lithologically similar rocks exposed to the south that comprise the Hadn formation. Most of the intrusive rocks in the quadrangle are peralkaline or have a peralkaline affinity and are characterized by the presence of soda pyriboles. A large mountain known as Jibal Aja extends into the southeast corner of the quadrangle and is composed of postorogenic peralkaline alkali granite plutons that form concentric rings around a core granophyre. A small plug of Tertiary alkali basalt crops out near the southeast corner of the quadrangle. Eighty percent of the quadrangle is covered by a thick accumulation of eolian sand that forms the southern edge of the An Nafud dune field. The plutons of the Aja suite represent samples of magma that depict the evolution of a batholith-scale magma body that solidified to the Aja suite. The major- and rare-earthelement chemical variation observed among the components of the suite is a consequence of a discontinuous process that involved chemical evolution via separation of silicate liquid from earlier formed crystals, and emplacement of batches of magma, whose compositions represent stages of the process. Resource potential in the quadrangle is low. No ancient mines are reported in this quadrangle. Geochemical data for a limited number of pan concentrates of wadi sediment from wadis draining the peralkaline rocks of Jibal Aja show distinctive associations of incompatible lithophile elements. A similar association of elements has previously been shown to be diagnostic of peralkaline granite in the northeast part of the Shield but does not imply high resource potential.

Open-File Report↗

USGS1985

Geochemistry of ground-water in two sandstone aquifer systems in the Northern Great Plains in parts of Montana and Wyoming, North Dakota, and South Dakota

The Kootenai Formation in the Judith Basin, Montana, and the Lance Formation and Fox Hills Sandstone in the Powder River Basin, Wyoming, constitute two important sandstone aquifer systems in the Northern Great Plains region. Ground waters in each of these systems evolve from low dissolved-solids concentration, near-neutral pH, predominantly calcium and magnesium bicarbonate types in their recharge areas, to high dissolved-solids concentration, high pH, predominantly sodium-bicarbonate types in the basins. Oxidation potentials decrease as the waters flow downgradient under confined conditions. Calculation of the saturation states of aquifer minerals suggests several groups of mineral phases that could control ground- water chemistry. Mass transfer modeling indicates, however, that the observed behavior of major and minor dissolved species in both systems can satisfactorily be explained only by equilibration with cal cite, dolomite, or calcite and dolomite. The geochemistry of these systems is probably controlled by the incongruent dissolution of dolo mite to form calcite. This reaction appears to be driven by cation ex change and the dissolution of carbon dioxide. Plausible carbon diox ide sources include organic carbon oxidation and lignite coalification. Aluminosilicates influence major element chemistry primarily as sub trates for cation exchange, which, in combination with carbonate equilibria, buffer ground water pH at values of 8.5 to 8.9. Dissolved- iron concentrations are controlled by equilibration with amorphous ferric oxyhydroxides in oxidizing waters, with amorphous ferric oxyhydroxides and siderite in moderately reducing waters, and with siderite and amorphous ferrous sulfide in strongly reducing waters. Measured variations in dissolved carbonate isotopic composition compare favorably with carbon isotopic evolution, calculated by assuming dedolomitization. Recharge areas of the two systems are characterized by ground waters with high tritium and carbon-14 activities and relatively low dissolved-solids concentrations, with calcium and magnesium as the predominant cations. Recharge temperatures, calculated from dissolved-argon concentrations and 5 18 0 and SD isotopic measure ments, indicate that recharge is derived primarily from spring snow- melt rather than late spring and summer storms. Ground-water flow directions are generally parallel to trends of increasing dissolved solids concentrations and decreasing divalent to monovalent cation concentration ratios. However, these trends are sometimes obscured in areas of leakage or mixing. Further indication of leakage between aquifers is provided by abrupt changes in major element and isotopic chemistry, which are not characteristic of normally observed geo chemical evolution. Ground-water flow rates, calculated by adjusting measured carbon-14 activities for carbonate mass transfer, are com parable to values calculated from aquifer tests and potentiometric data. These carbon-14 flow rates average 1.6 meters per year for the Second Cat Creek sandstone of the Kootenai Formation, and 1.3 meters per year for the Lance-Fox Hills aquifer.

Montana, North Dakota, South Dakota, Wyoming↗

USGS1991

Geochemistry of ground water in alluvial basins of Arizona and adjacent parts of Nevada, New Mexico, and California

Chemical and isotope analyses of ground water from 28 basins in the Basin and Range physiographic province of Arizona and parts of adjacent States were used to evaluate ground-water quality, determine processes that control ground-water chemistry, provide independent insight into the hydrologic flow system, and develop information transfer. The area is characterized by north- to northwest-trending mountains separated by alluvial basins that form a regional topography of alternating mountains and valleys. On the basis of ground-water divides or zones of minimal basin interconnection, the area was divided into 72 basins, each representing an individual aquifer system. These systems are joined in a dendritic pattern and collectively constitute the major water resource in the region. Geochemical models were developed to identify reactions and mass transfer responsible for the chemical evolution of the ground water. On the basis of mineralogy and chemistry of the two major rock associations of the area, a felsic model and a mafic model were developed to illustrate geologic, climatic, and physiographic effects on ground-water chemistry. Two distinct hydrochemical processes were identified: (1) reactions of meteoric water with minerals and gases in recharge areas and (2) reactions of ground water as it moves down the hydraulic gradient. Reactions occurring in recharge and downgradient areas can be described by a 13-component system. Major reactions are the dissolution and precipitation of calcite and dolomite, the weathering of feldspars and ferromagnesian minerals, the formation of montmorillonite, iron oxyhydroxides, and probably silica, and, in some basins, ion exchange. The geochemical modeling demonstrated that relatively few phases are required to derive the ground-water chemistry; 14 phases-12 mineral and 2 gas-consistently account for the chemical evolution in each basin. The final phases were selected through analysis of X-ray diffraction and fluorescence data, aqueous speciation and saturation data, and mass-balance and isotopic constraints and through chemical models developed from mineral combinations among the 27 phases that were considered realistic in these geologically and mineralogically complex basins. X-ray diffraction of basin-fill sediments confirm the presence of the postulated minerals and their weathering sequences. High partial pressures of soil CO2 and large concentrations of dissolved CO2 in recharge areas, and the rapid depletion of CO2 downgradient, accompanied by high weathering rates of the silicates which also decrease downgradient, indicate that carbonic acid is the impetus in the weathering process. Reactions in the soil zone and the unsaturated zone are influential and, in some instances, are as important as the mineralogy of the source rock in determining ground-water compositions. The basins can be divided geochemically into two general categories-closed systems, which evolve under closed hydrologic conditions, and open systems, which are open to CO2 and other constituents along the flow path. The ground-water chemistry of the unconfined aquifers in the eastern part of the study area and of the aquifers underlying the flood plain along the Colorado River generally evolves under open conditions. The ground-water chemistry of most basins in the central and western parts and of the confined aquifers in the eastern part evolves under closed conditions. The factors that determine whether a basin is an open or closed system are the amount of and the spatial and seasonal distribution of annual precipitation and the presence or absence of fine-grained confining units. The basins along the Colorado River are unique among basins in the region. Virtually all ground water underlying the flood plain originated as seepage or overbank flow from the Colorado River. Initial deuterium content of about -120 per mil is indicative of precipitation from the central part of Colorado. Using chemical m

Professional Paper↗

USGS1994

Geology of the Blue Mountains region of Oregon, Idaho, and Washington: Stratigraphy, physiography, and mineral resources of the Blue Mountains region

PART 1: Stratigraphic and sedimentological analysis of sedimentary sequences from the Wallowa terrane of northeastern Oregon has provided a unique insight into the paleogeography and depositional history of the terrane, as well as establishing important constraints on its tectonic evolution and accretionary history. Its Late Triassic history is considered here by examining the two most important sedimentary units in the Wallowa terrane-the Martin Bridge Limestone and the Hurwal Formation. Conformably overlying epiclastic volcanic rocks of the Seven Devils Group, the Martin Bridge Limestone comprises shallow-water platform carbonate rocks and deeper water, off-platform slope and basin facies. Regional stratigraphic and tectonic relations suggest that the Martin Bridge was deposited in a narrow, carbonate-dominated (forearc?) basin during a lull in volcanic activity. The northern Wallowa platform was a narrow, rimmed shelf delineated by carbonate sand shoals. Interior parts of the shelf were characterized by supratidal to shallow subtidal carbonates and evaporites, which were deposited in a restricted basin. In the southern Wallowa Mountains, lithofacies of the Martin Bridge are primarily carbonate turbidites and debris flow deposits, which accumulated on a carbonate slope apron adjacent to the northern Wallowa rimmed shelf from which they were derived. Drowning of the platform in the latest Triassic, coupled with a renewed influx of volcanically derived sediments, resulted in the progradation of fine-grained turbidites of the Hurwal Formation over the carbonate platform. Within the Hurwal, Norian conglomerates of the Excelsior Gulch unit contain exotic clasts of radiolarian chert, which were probably derived from the Bakei terrane. Such a provenance provides evidence of a tectonic link between the Baker and Wallowa terranes as early as the Late Triassic, and offers support for the theory that both terranes were part of a more extensive and complex Blue Mountains island-arc terrane. PART 2: Mesozoic rocks exposed along the Snake River in the northern Wallowa terrane represent a volcanic island and its associated sedimentary basins within the Blue Mountains island arc of Washington, Oregon, and Idaho. In the northern part of the Wallowa terrane, rock units include the Wild Sheep Creek, Doyle Creek, and Coon Hollow Formations, the (informal) Imnaha intrusion, and the (informal) Dry Creek stock. The volcanic rocks of the Ladinian to Karnian Wild Sheep Creek Formation show two stages of evolution-an early dacitic phase Gower volcanic faciesY and a late mafic phase (upper volcanic facies). The two volcanic facies are separated by eruption-generated turbidites of siliceous argillites and arkosic arenites (argillitesandstone facies). The two magmatic phases of the Wild Sheep Creek Formation may be recorded by the compositional zoning from older quartz diorite and diorite to younger gabbro in the Imnaha intrusion. Although the Late Triassic Imnaha intrusion is in fault contact with the Wild Sheep Creek Formation, it may be a subduction-related pluton and was the likely magma source for the Wild Sheep Creek Formation. Interbedded with the upper volcanic facies are eruption-generated turbidite and debris flow deposits (sandstone-breccia facies) and thick carbonate units (limestone facies). The limestone facies consists of two marker units, which may represent carbonate platform environments. Clast imbrication, fossil orientation, and cross-stratification in the Wild Sheep Creek Formation indicate a shoaling to subaerial volcanic island to the south and southeast; sediment was transported to the north and northwest. The Karnian Doyle Creek Formation consists largely of epiclastic conglomerate, sandstone, and shale that were deposited in welloxygenated basins. Vitric tuffs interbedded with these sediments suggest shallow or subaerial pyroclastic eruptions. Quartz diorite clasts in this formation may indicate uplift

Idaho, Oregon, Washington↗

USGS2005

Oceanic Pb-isotopic sources of Proterozoic and Paleozoic volcanogenic massive sulfide deposits on Prince of Wales Island and vicinity, southeastern Alaska

Volcanogenic massive sulfide (VMS) deposits on Prince of Wales Island and vicinity in southeastern Alaska are associated with Late Proterozoic through Cambrian volcanosedimentary rocks of the Wales Group and with Ordovician through Early Silurian felsic volcanic rocks of the Moira Sound unit (new informal name). The massive sulfide deposits in the Wales Group include the Big Harbor, Copper City, Corbin, Keete Inlet, Khayyam, Ruby Tuesday, and Stumble-On deposits, and those in the Moira Sound unit include the Barrier Islands, Moira Copper, Niblack, and Nichols Bay deposits. Pb-isotopic signatures were determined on sulfide minerals (galena, pyrite, chalcopyrite, pyrrhotite, and sphalerite) to constrain metal sources of the massive sulfides and for comparison with data for other deposits in the region. Except for the Ruby Tuesday deposit, galena is relatively rare in most of these deposits. Pb-isotopic signatures distinguish the mainly Cu+Zn±Ag±Au massive sulfide deposits in the Wales Group from the Zn+Cu±Ag±Au massive sulfide deposits in the Moira Sound unit. Among the older group of deposits, the Khayyam deposit has the widest variation in Pb-isotopic ratios ( 206 Pb/ 204 Pb=17.169–18.021, 207 Pb/ 204 Pb=15.341–15.499, 208 Pb/ 204 Pb=36.546–37.817); data for the other massive sulfide deposits in the Wales Group overlap the isotopic variations in the Khayyam deposit. Pb-isotopic ratios for both groups of deposits are lower than those on the average crustal Pbevolution curve (µ=9.74), attesting to a large mantle influence in the Pb source. All the deposits show no evidence for Pb evolution primarily in the upper or lower continental crust. Samples from the younger group of deposits have scattered Pb-isotopic compositions and plot as a broad band on uranogenic and thorogenic Pb diagrams. Data for these deposits overlap the trend for massive sulfide deposits in the Wales Group but extend to significantly more radiogenic Pb-isotopic values. Pb-isotopic ratios of samples from the massive sulfide deposits in the Moira Sound unit plot on a different trend ( 206 Pb/ 204 Pb=17.375–19.418, 207 Pb/ 204 Pb=15.361–15.519, 208 Pb/ 204 Pb=36.856–37.241) from the steep slope defined by the massive sulfide deposits in the Wales Group. In comparison, the Pb-isotopic ratios of Devonian polymetallic (Pb-Zn-Au-Ag) quartz-sulfide veins vary widely ( 206 Pb/ 204 Pb=18.339–18.946, 207 Pb/ 204 Pb=15.447–15.561, 208 Pb/ 204 Pb=37.358–38.354), straddling the slope defined by the massive sulfide deposits in the Moira Sound unit. The general decrease in 207 Pb/ 204 Pb ratio in these deposits, relative to the average crustal Pb-evolution curve, suggests that the most likely lead sources were those associated with oceanic volcanic rocks. The massive sulfide deposits in the Wales Group may have resided within an intraoceanic tectonic setting where the mantle was the predominant contributor of metals. Some contribution from reworked arc material or recycled older, hydrothermally altered oceanic crust (including pelagic sediment) is also possible. Lead sources of the massive sulfide deposits in the Moira Sound unit also included an older source region, possibly a Late Proterozoic or Cambrian volcanosedimentary sequence and the massive sulfide deposits in the Wales Group. Preliminary regional comparison of the Pb-isotopic data indicates that the Greens Creek (Admiralty Island, Alaska) and Windy Craggy (northern British Columbia) deposits probably did not share a common lead source with the VMS deposits on Prince of Wales Island. Other sulfide occurrences on Admiralty Island are also more radiogenic than those on Prince of Wales Island. Large differences in 207 Pb/ 204 Pb ratio suggest that the lead in the VMS deposits in different parts of the Alexander terrane evolved from sources with heterogeneous U/Pb ratios, resulting from mixing of mantle and crustal components.

Alaska↗

USGS2008

Plagioclase populations and zoning in dacite of the 2004-2005 Mount St. Helens eruption: Constraints for magma origin and dynamics

We investigated plagioclase phenocrysts in dacite of the 2004-5 eruption of Mount St. Helens to gain insights into the magmatic processes of the current eruption, which is characterized by prolonged, nearly solid-state extrusion, low gas emission, and shallow seismicity. In addition, we investigated plagioclase of 1980-86 dacite. Light and Nomarski microscopy were used to texturally characterize plagioclase crystals. Electron microprobe analyses measured their compositions. We systematically mapped and categorized all plagioclase phenocrysts in a preselected area according to the following criteria: (1) occurrence of zones of acicular orthopyroxene inclusions, (2) presence of dissolution surface(s), and (3) spatial association of 1 and 2. Phenocrysts fall into three main categories; one category contains four subcategories. The range of anorthite (An) content in 2004-5 plagioclase is about An 57-35 during the last 30-40 percent crystallization of plagioclase phenocrysts. Select microphenocrysts (10-50 μm) range from An 30 to An 42 . Anorthite content is lowest near outermost rims of phenocrysts, but zonation patterns between interior and rim indicate variable trends that correlate with textural features. Crystals without dissolution surfaces (about 14 percent of total) show steadily decreasing An content outward to the crystal rim (outer ~80 μm). All other crystals are banded as a consequence of dissolution; dissolution surfaces are band boundaries. Such crystals display normal outward An zoning within a single band that, following dissolution, is then overgrown abruptly by high-An material of the next band. Swarms of acicular orthopyroxene inclusions in plagioclase are characteristic of 2004-5 dacite. They occur mostly inward of dissolution surfaces, where band composition reaches lowest An content. The relative proportions of the three crystal types are distinctly different between 2004-5 dacite and 1980s dome dacite. We propose that crystals with no dissolution surfaces are those that were supplied last to the shallow reservoir, whereas plagioclase with increasingly more complex zoning patterns (that is, the number of zoned bands bounded by dissolution surfaces) result from prolonged residency and evolution in the reservoir. We propose that banding and An zoning across multiple bands are primarily a response to thermally induced fluctuations in crystallinity of the magma in combination with recharge; a lesser role is ascribed to cycling crystals through pressure gradients. Crystals without dissolution surfaces, in contrast, could have grown only in response to steady(?) decompression. Some heating-cooling cycles probably postdate the final eruption in 1986. They resulted from small recharge events that supplied new crystals that then experienced resorption-growth cycles. We suggest that magmatic events shortly prior to the current eruption, recorded in the outermost zones of plagioclase phenocrysts, began with the incorporation of acicular orthopyroxene, followed by last resorption, and concluded with crystallization of euhedral rims. Finally, we propose that 2004-5 dacite is composed mostly of dacite magma that remained after 1986 and underwent subsequent magmatic evolution but, more importantly, contains a component of new dacite from deeper in the magmatic system, which may have triggered the new eruption.

Washington↗

USGS2010

Augustine Volcano - The influence of volatile components in magmas erupted A.D. 2006 to 2,100 years before present: Chapter 16 in The 2006 eruption of Augustine Volcano, Alaska

The petrology and geochemistry of 2006 eruptive products of Augustine Volcano, Alaska, have been investigated through analyses of whole-rock samples, phenocrysts, silicate melt inclusions, and matrix glasses to constrain processes of magma evolution, eruption, and degassing. Particular attention was directed toward the concentrations and geochemical relationships involving the magmatic volatile components H 2 O, CO 2, S, and Cl. The analytical results for 2006 samples have been integrated with data for samples of Pleistocene basalt, prehistoric andesites, and 1986 andesites from Augustine to provide a broad view of volatile behavior in Augustine magmas. The observation of generally similar geochemical features for this range of eruptions indicates that magmatic and volatile degassing processes have been relatively consistent during the past 2,100 years. Augustine andesites range from low-silica to high-silica compositions and contain phenocrysts of plagioclase, orthopyroxene, and clinopyroxene, with lesser olivine, amphiboles, iron-titanium oxides, and apatite. The groundmass varies from strongly crystallized and/or oxidized to comparatively clear, microlite-poor vesicular glass. Coexisting iron-titanium oxides of 2006 rock samples, which are generally consistent with those of prior eruptive materials, indicate &fnof; O2 values of approximately NNO+1.5 to NNO+2.5 and oxide crystallization temperatures of 835 to 1,052°C. The compositions of matrix and melt-inclusion glasses range from rhyodacite to rhyolite and show relationships that reflect magma evolution involving fractional crystallization and multiple stages of mingling and/or mixing. In particular, melt inclusions of low-silica andesites express mixing of magmas with more widely varying compositions, than do melt inclusions of high-silica andesites and dacites. The melt inclusions of 2006, 1986, and prehistoric andesites contain moderate to high concentrations of H 2 O and Cl and lesser CO 2 and SO 2 . Comparing the abundances of H 2 O, CO 2 , and Cl in these melt inclusions with experimentally established volatile solubilities for felsic melts indicates that the 2006 and prehistoric samples are most consistent with the ascent of fluid-saturated magmas containing 1 weight percent of H 2 O-enriched vapor under closed-system conditions and that pressures of volatile phase exsolution range from 150 to less than 20 MPa. This closed-system behavior was maintained to quite shallow depths prior to eruption, and this pressure range is consistent with constraints derived from 2006 geodetic measurements indicating magma storage and crystallization at 4 to 6 km and upwards to near-surface depths. The magmatic fluids were relatively oxidizing and included H 2 O-enriched and HCl-, H 2 S-, S 2 -, and SO 2 ± CO 2 -bearing vapors; hydrosaline aqueous liquids largely enriched in Cl - , SO 4 2- , alkalis, and H 2 O; and moderately saline, H 2 O-poor liquids containing Cl - , SO 4 2- , and alkali elements.

Alaska↗

USGS2008

Precambrian basement structure map of the continental United States - An interpretation of geologic and aeromagnetic data

The Precambrian basement rocks of the continental United States are largely covered by younger sedimentary and volcanic rocks, and the availability of updated aeromagnetic data (NAMAG, 2002) provides a means to infer major regional basement structures and tie together the scattered, but locally abundant, geologic information. Precambrian basement structures in the continental United States have strongly influenced later Proterozoic and Phanerozoic tectonism within the continent, and there is a growing awareness of the utility of these structures in deciphering major younger tectonic and related episodes. Interest in the role of basement structures in the evolution of continents has been recently stimulated, particularly by publications of the Geological Society of London (Holdsworth and others, 1998; Holdsworth and others, 2001). These publications, as well as others, stress the importance of reactivation of basement structures in guiding the subsequent evolution of continents. Knowledge of basement structures is an important key to understanding the geology of continental interiors.

Scientific Investigations Map↗

USGS2009

Geologic Map of the southern Inyo Mountains and vicinity, Inyo County, California

The Inyo Mountains are located in east-central California between Owens Valley on the west and Saline Valley on the east. This map encompasses the southernmost part of the Inyo Mountains and vicinity, which is centered on the high plateau of Conglomerate Mesa and extends from Owens Valley on the west to the Santa Rosa Hills, Lee Flat, and the Nelson Range on the east. The area includes parts of the Cerro Gordo Peak, Nelson Range, Keeler, and Santa Rosa Flat 7.5' quadrangles. Sedimentary and volcanic rocks, unconformities, and structural features exposed in the southern Inyo Mountains region provide information critical for reconstructing the complex Paleozoic and Mesozoic tectonic evolution of the southwestern United States. Ordovician to Cretaceous rocks in the map area record a long geologic history during which the continental margin of the western United States gradually changed from a passive tectonic setting in the early and middle Paleozoic to an active tectonic setting in the Jurassic and Cretaceous. A major highlight of the map area is the unusually complete record of late Paleozoic to earliest Mesozoic (Pennsylvanian to Triassic) deformation and sedimentation that marked the transition between the passive and active margin settings. The area also provides an excellent record of Jurassic to Cretaceous deformation and igneous activity that characterized the middle to late Mesozoic active margin. This map provides a detailed depiction of all the Paleozoic and Mesozoic rocks and structural features known in the area. The area also contains important exposures of upper Cenozoic rocks related to the evolution of the Basin and Range province, although detailed mapping of these rocks was beyond the scope of this study.

California↗

USGS2005

Precipitation-runoff processes in the Feather River basin, northeastern California, and streamflow predictability, water years 1971-97

Precipitation-runoff processes in the Feather River Basin of northern California determine short- and long-term streamflow variations that are of considerable local, State, and Federal concern. The river is an important source of water and power for the region. The basin forms the headwaters of the California State Water Project. Lake Oroville, at the outlet of the basin, plays an important role in flood management, water quality, and the health of fisheries as far downstream as the Sacramento-San Joaquin Delta. Existing models of the river simulate streamflow in hourly, daily, weekly, and seasonal time steps, but cannot adequately describe responses to climate and land-use variations in the basin. New spatially detailed precipitation-runoff models of the basin have been developed to simulate responses to climate and land-use variations at a higher spatial resolution than was available previously. This report characterizes daily rainfall, snowpack evolution, runoff, water and energy balances, and streamflow variations from, and within, the basin above Lake Oroville. The new model's ability to predict streamflow is assessed. The Feather River Basin sits astride geologic, topographic, and climatic divides that establish a hydrologic character that is relatively unusual among the basins of the Sierra Nevada. It straddles a north-south geologic transition in the Sierra Nevada between the granitic bedrock that underlies and forms most of the central and southern Sierra Nevada and volcanic bedrock that underlies the northernmost parts of the range (and basin). Because volcanic bedrock generally is more permeable than granitic, the northern, volcanic parts of the basin contribute larger fractions of ground-water flow to streams than do the southern, granitic parts of the basin. The Sierra Nevada topographic divide forms a high altitude ridgeline running northwest to southeast through the middle of the basin. The topography east of this ridgeline is more like the rain-shadowed basins of the northeastern Sierra Nevada than the uplands of most western Sierra Nevada river basins. The climate is mediterranean, with most of the annual precipitation occurring in winter. Because the basin includes large areas that are near the average snowline, rainfall and rain-snow mixtures are common during winter storms. Consequently, the overall timing and rates of runoff from the basin are highly sensitive to winter temperature fluctuations. The models were developed to simulate runoff-generating processes in eight drainages of the Feather River Basin. Together, these models simulate streamflow from 98 percent of the basin above Lake Oroville. The models simulate daily water and heat balances, snowpack evolution and snowmelt, evaporation and transpiration, subsurface water storage and outflows, and streamflow to key streamflow gage sites. The drainages are modeled as 324 hydrologic-response units, each of which is assumed homogeneous in physical characteristics and response to precipitation and runoff. The models were calibrated with emphasis on reproducing monthly streamflow rates, and model simulations were compared to the total natural inflows into Lake Oroville as reconstructed by the California Department of Water Resources for April-July snowmelt seasons from 1971 to 1997. The models are most sensitive to input values and patterns of precipitation and soil characteristics. The input precipitation values were allowed to vary on a daily basis to reflect available observations by making daily transformations to an existing map of long-term mean monthly precipitation rates that account for altitude and rain-shadow effects. The models effectively simulate streamflow into Lake Oroville during water years (October through September) 1971-97, which is demonstrated in hydrographs and statistical results presented in this report.

Northeastern California↗

USGS2006

Ecology of bonytail and razorback sucker and the role of off-channel habitats in their recovery

The bonytail and razorback sucker are two of four endangered mainstem fishes found in the Colorado River. Unlike the Colorado pikeminnow and humpback chub, wild populations of the bonytail and razorback sucker are either extirpated from the mainstem river or are nearly so. Agencies are aggressively stocking these fish and while repatriated fish spawn, their young are rapidly eaten by introduced predators. A decade of predator removal efforts has proved ineffective in restoring natural recruitment. Today, the presence of these species is totally dependent on stocking, suggesting both species are worse off today than when recovery efforts began nearly two decades ago. In contrast, both species readily produce young in ponds where nonnative predators are absent. Evidence shows they evolved with the ability to spawn in both flowing and standing water, which suggests isolated oxbow communities may have been an essential feature in their evolution and survival strategy. Sustainable populations during the past few decades have only occurred in isolated ponds devoid of predatory nonnative fish. Efforts to force recovery in the main channel river continue to fail due to the presence of nonnative predators that may be economically important recreational species. Off-channel sanctuaries provide research and management opportunities on a scale that are both biologically and economically realistic. Effective management of these species in small habitats appears to be the most logical approach to advance recovery in larger river reaches. This report presents new findings, updates existing information, and describes what may well represent the only practical approach to these species’ conservation and recovery. Chapter 1 provides an overview of the Colorado River system from its origin to the Gulf of California and includes a description of propagation and stocking programs which have not been described elsewhere. The report also updates what is known or suspected on the life history and ecology of these two endangered fishes. Chapter 2 describes the successful recruitment of both species at an oxbow pond on the Cibola National Wildlife Refuge in Arizona, discusses factors that contribute to completion of the life cycle of both fishes, and provides recommendations for future management of the impoundment. Chapter 3 provides historical evidence that oxbow habitats were formed historically in years of high runoff and the importance of these habitats for survival and evolution of native fishes. It also summarizes key features of habitats that can serve as sanctuaries that enhance early survival of the endangered fishes and allow the fish to complete their entire life cycles.

Scientific Investigations Report↗