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At least 1,423 records · Page 79Linked to original sources
USGS2024

Where ice gave way to fire: Deglacial volcanic activity at the edge of the Coast Mountains in Milbanke Sound, BC

Kitasu Hill and MacGregor Cone formed along the Principe Laredo Fault on British Columbia’s central coast as the Wisconsinan ice sheet withdrew from the Coast Mountains. These small-volume Milbanke Sound Volcanoes (MSV) provide remarkable evidence for the intimate relationship between volcanic and glacial facies. The lavas are within-plate, differentiated (low MgO < 7%) Ocean Island Basalts, hawaiites, and mugearites that formed from ∼1% decompression melting of asthenosphere with residual garnet. Kitasu Hill, on glaciated bedrock, formed between 18 and 15 cal ka BP. Dipping, poorly stratified, admixed hyaloclastite, and glacial diamicton with large plutonic clasts and pillow breccia comprise its basal tuya platform (0–43 masl). Subaerial nested cinder cones, with smaller capping lava flows, sit atop the tuya. New marine samples show McGregor Cone formed subaerially but now sits submerged at 43–200 mbsl on an eroded moraine at the mouth of Finlayson Channel. Seismic data and cores reveal glaciomarine sediments draping the cone’s lower slopes and show beach terraces. Cores contain glaciomarine diamictons, ice-rafted debris, delicate glassy air fall tephra, and shallow, sublittoral, and deeper benthic foraminifera. Dates of 14.1–11.2 cal ka BP show volcanism spanned ∼2000 years during floating ice shelf conditions. The MSV have similar proximal positions to the retreating ice sheet, display mixed volcano-glacial facies, and experienced similar unloading stresses during deglaciation. The MSV may represent deglacially triggered volcanism. The dates, geomorphic and geological evidence, constrain a local relative sea level curve for Milbanke Sound and show how ice gave way to fire.

Milbanke Sound↗
USGS1997

Effect of stream acidification and inorganic aluminum on mortality of brook trout (Salvelinus fontinalis) in the Catskill Mountains, New York

Juvenile brook trout (Salvelinus fontinalis) were exposed in cages to fluctuating chemical conditions in four Catskill Mountain streams during the spring and fall of 1989 and the spring of 1990. Specific chemical constituents and characteristics of acidic episodes that correlated with increased fish mortality were identified. Mortality increased during acidic episodes in one poorly buffered stream when inorganic monomeric aluminum (Al(im)) concentrations increased; mortality was low in three other streams during acidic episodes of shorter duration and smaller magnitude than measured in the poorly buffered stream. Variation in mortality was attributed primarily to differences in concentrations of both Al(im) and dissolved organic carbon. Linear and logistic regression analyses indicate that either mean or median Al(im) concentrations could account for 73-99% of the variability in mortality. Regression analyses suggest that mortality was highly related (in order of importance) to Al(im), pH, dissolved organic carbon, calcium, and chloride concentration. Brook trout mortality was also highly related to durations of exposure above 0.225 and 0.250 mg/L Al(im) during test periods. Characteristics of acidic-Al(im) episodes that are critical to mortality of caged brook trout appear to be (i) Al(im) concentrations of at least 0.225 ?? 0.025 mg/L and (ii) exposure to these toxic Al(im) concentrations for at least 2 days.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2022

Can’t see the flowers for the trees: Factors driving floral abundance within early-successional forests in the central Appalachian Mountains

Silviculture can be a powerful tool for restoring and enhancing habitat for forest-dependent wildlife. In eastern North America, regenerating timber harvests support abundant wildflowers that provide essential forage for native pollinators. Factors driving floral resource availability within regenerating forests remain almost entirely unstudied. Recent efforts to increase the area of regenerating forests (<10 years old) through overstory removal harvest in the central Appalachian Mountains provide an opportunity to investigate the development of forest wildflower communities following canopy removal. We conducted 1208 surveys of blooming plants across 143 harvests, recording 1 525 245 flowers representing 220 taxa spanning 47 families. The number of flowers within recently harvested stands was negatively associated with fern and sapling cover but positively associated with grass and bramble ( Rubus spp.) cover. Early in the growing season, more flowers bloomed in older regenerating stands (e.g., >5 years old), but this pattern reversed by the end of the growing season. Ultimately, our study demonstrates that the abundance of flowers available to pollinators within regenerating hardwood stands varies with factors associated with advancing succession. Recognizing the potential trade-off between woody regeneration (i.e., saplings) and pollinator forage availability may benefit forest managers who intend to provide floral resources to flower-dependent wildlife like pollinators via silviculture.

Pennsylvania↗
USGS2011

Sedimentary response to orogenic exhumation in the northern Rocky Mountain Basin and Range province, Flint Creek basin, west-central Montana

Middle Eocene through Upper Miocene sedimentary and volcanic rocks of the Flint Creek basin in western Montana accumulated during a period of significant paleoclimatic change and extension across the northern Rocky Mountain Basin and Range province. Gravity modelling, borehole data, and geologic mapping from the Flint Creek basin indicate that subsidence was focused along an extensionally reactivated Sevier thrust fault, which accommodated up to 800 m of basin fill while relaying stress between the dextral transtensional Lewis and Clark lineament to the north and the Anaconda core complex to the south. Northwesterly paleocurrent indicators, foliated metamorphic lithics, 64 Ma (40Ar/39Ar) muscovite grains, and 76 Ma (U-Pb) zircons in a ca. 27 Ma arkosic sandstone are consistent with Oligocene exhumation and erosion of the Anaconda core complex. The core complex and volcanic and magmatic rocks in its hangingwall created an important drainage divide during the Paleogene shedding detritus to the NNW and ESE. Following a major period of Early Miocene tectonism and erosion, regional drainage networks were reorganized such that paleoflow in the Flint Creek basin flowed east into an internally drained saline lake system. Renewed tectonism during Middle to Late Miocene time reestablished a west-directed drainage that is recorded by fluvial strata within a Late Miocene paleovalley. These tectonic reorganizations and associated drainage divide explain observed discrepancies in provenance studies across the province. Regional correlation of unconformities and lithofacies mapping in the Flint Creek basin suggest that localized tectonism and relative base level fluctuations controlled lithostratigraphic architecture.

Canadian Journal of Earth Sciences↗
USGS1991

U–Pb geochronology of Late Cretaceous and early Tertiary plutons in the northern Coast Mountains batholith

U–Pb geochronologic studies demonstrate that steeply dipping, sheetlike tonalitic plutons along the western margin of the northern Coast Mountains batholith were emplaced between ~83 and ~57 (perhaps ~55) Ma. Less elongate tonalitic–granodioritic bodies in central portions of the batholith yield ages of 59–58 Ma, coeval with younger phases of the tonalitic sheets. Large granite–granodiorite bodies in central and eastern portions of the batholith were emplaced at 51–48 Ma. Trends in ages suggest that the tonalitic bodies generally become younger southeastward and that, at the latitude of Juneau, plutonism migrated northeastward across the batholith at ~0.9 km/Ma. Variations in the age, shape, location, and degree of fabric development among the various plutons indicate that Late Cretaceous – Paleocene tonalitic bodies were emplaced into a steeply dipping, dip-slip shear zone that was active along the western margin of the batholith. Postkinematic Eocene plutons were emplaced at shallow crustal levels. Inherited zircon components in these plutons range in age from mid-Paleozoic to Early Proterozoic and are coeval with detrital zircons in adjacent metasedimentary rocks. These old zircons, combined with evolved Nd isotopic signatures for most plutons, record assimilation of continental crustal or supracrustal rocks during the generation and (or) ascent of the plutons.

Alaska↗
USGS2005

Stream acidification and mortality of brook trout (Salvelinus fontinalis) in response to timber harvest in Catskill Mountain watersheds, New York, USA

Effects of clear-cut and timber-stand improvement (TSI) harvests on water chemistry and mortality of caged brook trout (Salvelinus fontinalis) were evaluated in a study of three Catskill Mountain streams, 1994-2000. Harvests removed 73% of tree basal area (BA) from a clearcut subbasin, 5% BA from a TSI subbasin, and 14% BA at a site below the confluence of both streams. A fourth nonharvested site served as a control. Water quality and trout mortality were affected only in the clearcut stream. Acidity and concentrations of nitrate and inorganic monomeric aluminum (Alim) increased sharply during high flows after the first growing season (fall 1997). Acid-Alim episodes were severe during this period and decreased steadily in magnitude and duration thereafter. All trout at this site died within 7 days during spring 1998 and 85% died during spring 1999. Only background mortality was observed in other years at this site and at the other three sites during all tests. The absence of mortality in TSI watersheds indicates that limited harvests should not harm brook trout populations in acid-sensitive streams. Effects of tree harvests on fish communities are of concern, however, because many stream-dwelling species are more sensitive to acidified waters than brook trout. ?? 2005 NRC.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2009

Foods and nutritional components of diets of black bear in Rocky Mountain National Park, Colorado

We used scat analysis to determine diets and relative nutritional values of diets for black bears (Ursus americanus Pallas, 1780) in Rocky Mountain National Park, Colorado, from 2003 to 2006, and compared foods consumed and nutritional components to identify important sources of fecal gross energy (GE), crude fat (CF), and fecal nitrogen (FN) in annual and seasonal diets. Patterns of use of food classes followed typical seasonal patterns for bears, although use of animal matter was among the highest reported (>49% annually). Use of animal matter increased after spring, although crude protein levels in bear diets were always >25%. GE was typically lowest for grasses and other herbaceous plants and highest for ants and ungulates; FN was strongly positively related to most animal sources, but negatively correlated with vegetative matter; and CF showed the strongest positive relationship with ungulates and berries, with the latter likely influenced by the presence of seeds. Compared with historic data (1984-1991), contemporary diets included substantially greater prevalence of anthropogenic foods, which likely contributed to increases in size, condition, and productivity of the contemporary bear population. Management strategies are needed to increase quantity and quality of natural foods while minimizing dependence on anthropogenic sources.

Canadian Journal of Zoology↗
USGS1990

Early-winter diet of woodland caribou in relation to snow accumulation, Selkirk Mountains, British Columbia, Canada

Woodland caribou (Rangifer tarandus caribou) in the southern Selkirk Mountains of British Columbia shift from a diet of primarily vascular taxa during snow-free months to an arboreal lichen – conifer diet during late winter. We present evidence that caribou diets, during the early-winter transition period, are influenced by snow accumulation rates. Caribou shift to an arboreal lichen – conifer diet earlier during winters of rapid snow accumulation and forage extensively on myrtle boxwood (Pachistima myrsinites), an evergreen shrub, and other vascular plants during years of slower snow accumulation. The role of coniferous forage in early-winter food habits is examined. Forest management strategies can be developed to provide habitat that will enable caribou to forage in response to varying snow accumulation rates.

Selkirk Mountains↗
USGS1998

Relationship between deer mouse population parameters and dieldrin contamination in the Rocky Mountain Arsenal National Wildlife Refuge

A small-mammal capture-recapture study was conducted in the Rocky Mountain Arsenal National Wildlife Refuge to quantify the effects of soil contamination with dieldrin on demographic parameters of deer mouse (Peromyscus maniculatus) populations. Increased dieldrin concentrations were significantly associated with larger deer mouse populations, although the size of populations on contaminated sites decreased during the study. The most parsimonious model for estimating survival rates was one in which survival was a decreasing function of dieldrin concentration. A significantly higher proportion of female deer mice in the populations residing on the more highly contaminated sites exhibited signs of reproductive activity. Development of genetic resistance in P. maniculatus to chronic chemical exposure is suggested as a possible mechanism responsible for the species' observed dominance and relatively high densities on contaminated sites. Under the additional stress of unfavorable environmental conditions, however, these populations may suffer disproportionately greater mortality. The design and analytical methods presented offer a rigorous statistical approach to assessing the effects of environmental contamination on small mammals at the population level.

Canadian Journal of Zoology↗
USGS2015

Soil geochemical survey of abandoned mining sites in the Eastern-Central Peloritani Mountains, Sicily, Italy

This investigation focused on topsoils ( n = 122) and vertical profiles ( n = 6) distributed over an area of 250 km 2 in the eastern-central Peloritani Mountains, northeastern Sicily. Georeferenced concentration of 53 elements (including potentially harmful ones), determined by ICP-MS after an aqua regia leach, were used to produce geochemical maps by means of a GIS-aided spatial interpolation process. Results show that there are two distinct areas: the larger, located between the Fiumendinisi, Budali and Ali villages, and the other between C. Postlioni and Femmina Morta, which contain anomalous As (up to 727 mg/kg), Sb (up to 60 mg/kg), Ag (up to 1 mg/kg) and Au (up to 0.1 mg/kg) concentrations. Most of the investigated areas have high contamination levels for As, Zn, Sb, and Pb that exceed the threshold values (As = 20 mg/kg, Zn = 150 mg/kg, Sb = 10 mg/kg and Pb = 100 mg/kg) established for soils by the Italian Environmental Law ( Decreto Legislativo 2006 , number 152). The isotopic ratios of 206 Pb/ 207 Pb and 208 Pb/ 207 Pb have been measured in selected soils on both leaches [using 1M HNO 3 –1.75M HCl (50:50)] and residues thereof. Soil leach reflects possible anthropogenic contamination, whereas soil residues indicate geogenic contributions. Results suggest that most of contamination in the soils is related to the presence of sulphide and sulphosalt rock-forming minerals in the surveyed area. The soil fraction contains a Pb value >1600 mg/kg and has ratios of 1.1695 for 206 Pb/ 207 Pb and 2.4606 for 208 Pb/ 207 Pb. Only one soil leach isotopic composition could reflect possible anthropogenic contamination. The correlation among As, Zn, Pb contents v. Pb isotopic signatures of 206 Pb/ 207 Pb indicates that surface and deep soils collected from profiles are dominated by geogenic compositions.

Peloritani Mountains, Sicily↗
USGS2012

Magnetostratigraphy susceptibility for the Guadalupian Series GSSPs (Middle Permian) in Guadalupe Mountains National Park and adjacent areas in West Texas

Here we establish a magnetostratigraphy susceptibility zonation for the three Middle Permian Global boundary Stratotype Sections and Points (GSSPs) that have recently been defined, located in Guadalupe Mountains National Park, West Texas, USA. These GSSPs, all within the Middle Permian Guadalupian Series, define (1) the base of the Roadian Stage (base of the Guadalupian Series), (2) the base of the Wordian Stage and (3) the base of the Capitanian Stage. Data from two additional stratigraphic successions in the region, equivalent in age to the Kungurian–Roadian and Wordian–Capitanian boundary intervals, are also reported. Based on low-field, mass specific magnetic susceptibility (χ) measurements of 706 closely spaced samples from these stratigraphic sections and time-series analysis of one of these sections, we (1) define the magnetostratigraphy susceptibility zonation for the three Guadalupian Series Global boundary Stratotype Sections and Points; (2) demonstrate that χ datasets provide a proxy for climate cyclicity; (3) give quantitative estimates of the time it took for some of these sediments to accumulate; (4) give the rates at which sediments were accumulated; (5) allow more precise correlation to equivalent sections in the region; (6) identify anomalous stratigraphic horizons; and (7) give estimates for timing and duration of geological events within sections.

Texas↗
USGS2013

Three new Psammothidium species from lakes of Olympic and Cascade Mountains in Washington State, USA

Populations of several Psammothidium species were found in core sediments from nine remote, high elevation, ultraoligotrophic and oligotrophic, Olympic and Cascade Mountain lakes. Three of these species, P. lacustre, P. alpinum , and P. nivale , are described here as new. The morphology of the silica frustules of these species was documented using light and scanning electron microscopy. We discuss the similarities and differences with previously described Psammothidium species.

Washington↗
USGS1992

Precipitation estimation in mountainous terrain using multivariate geostatistics. Part I: structural analysis

Values of average annual precipitation (AAP) are desired for hydrologic studies within a watershed containing Yucca Mountain, Nevada, a potential site for a high-level nuclear-waste repository. Reliable values of AAP are not yet available for most areas within this watershed because of a sparsity of precipitation measurements and the need to obtain measurements over a sufficient length of time. To estimate AAP over the entire watershed, historical precipitation data and station elevations were obtained from a network of 62 stations in southern Nevada and southeastern California. Multivariate geostatistics (cokriging) was selected as an estimation method because of a significant (p = 0.05) correlation of r = .75 between the natural log of AAP and station elevation. A sample direct variogram for the transformed variable, TAAP = ln [(AAP) 1000], was fitted with an isotropic, spherical model defined by a small nugget value of 5000, a range of 190 000 ft, and a sill value equal to the sample variance of 163 151. Elevations for 1531 additional locations were obtained from topographic maps to improve the accuracy of cokriged estimates. A sample direct variogram for elevation was fitted with an isotropic model consisting of a nugget value of 5500 and three nested transition structures: a Gaussian structure with a range of 61 000 ft, a spherical structure with a range of 70 000 ft, and a quasi-stationary, linear structure. The use of an isotropic, stationary model for elevation was considered valid within a sliding-neighborhood radius of 120 000 ft. The problem of fitting a positive-definite, nonlinear model of coregionalization to an inconsistent sample cross variogram for TAAP and elevation was solved by a modified use of the Cauchy-Schwarz inequality. A selected cross-variogram model consisted of two nested structures: a Gaussian structure with a range of 61 000 ft and a spherical structure with a range of 190 000 ft. Cross validation was used for model selection and for comparing the geostatistical model with six alternate estimation methods. Multivariate geostatistics provided the best cross-validation results.

Nevada↗
USGS2008

Detection and attribution of temperature changes in the mountainous Western United States

Large changes in the hydrology of the western United States have been observed since the mid-twentieth century. These include a reduction in the amount of precipitation arriving as snow, a decline in snowpack at low and midelevations, and a shift toward earlier arrival of both snowmelt and the centroid (center of mass) of streamflows. To project future water supply reliability, it is crucial to obtain a better understanding of the underlying cause or causes for these changes. A regional warming is often posited as the cause of these changes without formal testing of different competitive explanations for the warming. In this study, a rigorous detection and attribution analysis is performed to determine the causes of the late winter/early spring changes in hydrologically relevant temperature variables over mountain ranges of the western United States. Natural internal climate variability, as estimated from two long control climate model simulations, is insufficient to explain the rapid increase in daily minimum and maximum temperatures, the sharp decline in frost days, and the rise in degree-days above 0??C (a simple proxy for temperature driven snowmelt). These observed changes are also inconsistent with the model-predicted responses to variability in solar irradiance and volcanic activity. The observations are consistent with climite simulations that include the combined effects of anthropogenic greenhouse gases and aerosols. It is found that, for each temperature variable considered, an anthropogenic signal is identifiable in observational fields. The results are robust to uncertainties in model-estimated fingerprints and natural variability noise, to the choice of statistical down-scaling method, and to various processing options in the detection and attribution method. ?? 2008 American Meteorological Society.

Journal of Climate↗
USGS2019

Mountain plant communities: Uncertain sentinels?

Mountain plant communities are thought to be sensitive to climate change and thus able to reveal its effects sooner than others. Two plant communities examined here, alpine treeline ecotones and alpine tundra, have been observed to respond to climate change in recent decades. Treeline has moved upslope and alpine tundra communities have had some species increase and others decrease. The response for both, however, has been inconsistent if taken as a whole. Problematic factors for this response are outlined for both: abiotic and biotic interactions partially decouple the plant communities from climate. Differences across spatial and temporal scales complicate interpretation. Partial decoupling leads to nonlinear responses and difficulties for prediction and for planning mitigation.

Progress in Physical Geography: Earth and Environm↗
USGS2021

Linking modern pollen accumulation rates to biomass: Quantitative vegetation reconstruction in the western Klamath Mountains, NW California, USA

Quantitative reconstructions of vegetation abundance from sediment-derived pollen systems provide unique insights into past ecological conditions. Recently, the use of pollen accumulation rates (PAR, grains cm −2 year −1 ) has shown promise as a bioproxy for plant abundance. However, successfully reconstructing region-specific vegetation dynamics using PAR requires that accurate assessments of pollen deposition processes be quantitatively linked to spatially-explicit measures of plant abundance. Our study addressed these methodological challenges. Modern PAR and vegetation data were obtained from seven lakes in the western Klamath Mountains, California. To determine how to best calibrate our PAR-biomass model, we first calculated the spatial area of vegetation where vegetation composition and patterning is recorded by changes in the pollen signal using two metrics. These metrics were an assemblage-level relevant source area of pollen (aRSAP) derived from extended R-value analysis ( sensu Sugita, 1993) and a taxon-specific relevant source area of pollen (tRSAP) derived from PAR regression ( sensu Jackson, 1990). To the best of our knowledge, aRSAP and tRSAP have not been directly compared. We found that the tRSAP estimated a smaller area for some taxa (e.g. a circular area with a 225 m radius for Pinus ) than the aRSAP (a circular area with a 625 m radius). We fit linear models to relate PAR values from modern lake sediments with empirical, distance-weighted estimates of aboveground live biomass (AGL dw ) for both the aRSAP and tRSAP distances. In both cases, we found that the PARs of major tree taxa – Pseudotsuga, Pinus, Notholithocarpus , and TCT (Taxodiaceae, Cupressaceae, and Taxaceae families) – were statistically significant and reasonably precise estimators of contemporary AGL dw . However, predictions weighted by the distance defined by aRSAP tended to be more precise. The relative root-mean squared error for the aRSAP biomass estimates was 9% compared to 12% for tRSAP. Our results demonstrate that calibrated PAR-biomass relationships provide a robust method to infer changes in past plant biomass.

California, Oregon↗
USGS2018

Tracking magmatic processes through Zr/Hf ratios in rocks and Hf and Ti zoning in zircons: An example from the Spirit Mountain batholith, Nevada

Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near-chondritic Zr/Hf ratios of ???35-40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15-30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/ Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons themselves provide a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/ Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (TTiZ) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, document repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ???30-40 for cumulates and 18-30 for high-SiO2 granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and TTiZ (>100??C) for individual zircons. Such variations are consistent with field relations and ion-probe zircon geochronology that indicate a >1 million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO2 zone. ?? 2006 The Mineralogical Society.

Mineralogical Magazine↗
USGS2018

Uranoan thorite in lithophysal rhyolite - Topaz Mountain, Utah, U.S.A.

Uranoan thorite crystals have been found occurring as a sparse constituent in lithophysae in 6.1 to 6.8 Ma alkali rhyolite flows at Thomas Mountain, Utah, USA. The crystals are associated with sandidine, quartz, topaz, hematite, magnetite, and calcite; they are leek to dark grass green, transparent, well-formed, euhedral prisms, showing development of forms {100}, {101}, and {111}. The mineral is both optically isotropic, with a refractive index of 1.86(1), and X-ray amorphous, indicating its metamict state. Electron microprobe analysis yields: SiO 2 17.3, ThO 2 56.8, UO 2 25.4, total 99.5%, and a structural formula of (Th 0.72 U 0.31 ) Σ1.03 Si 0.97 O 4 . This appears to be the first reported occurrence of thorite in volcanic rocks of rhyolitic composition, and may account for part or all of the Th reported in alkali rhyolites and so-called ‘topaz-rhyolites’ of the western USA.

Utah↗