Contrasting origins of Cenozoic silicic volcanic rocks from the western Cordillera of the United States

Two fundamentally different types of silicic volcanic rocks formed during the Cenozoic of the western Cordillera of the United States. Large volumes of dacite and rhyolite, mostly ignimbrites, erupted in the Oligocene in what is now the Great Basin and contrast with rhyolites erupted along the Snake River Plain during the Late Cenozoic. The Great Basin dacites and rhyolites are generally calc-alkaline, magnesian, oxidized, wet, cool (<850°C), Sr-and Al-rich, and Fe-poor. These silicic rocks are interpreted to have been derived from mafic parent magmas generated by dehydration of oceanic lithosphere and melting in the mantle wedge above a subduction zone. Plagioclase fractionation was minimized by the high water fugacity and oxide precipitation was enhanced by high oxygen fugacity. This resulted in the formation of Si-, Al-, and Sr-rich differentiates with low Fe/Mg ratios, relatively low temperatures, and declining densities. Magma mixing, large proportions of crustal assimilation, and polybaric crystal fractionation were all important processes in generating this Oligocene suite. In contrast, most of the rhyolites of the Snake River Plain are alkaline to calc-alkaline, ferroan, reduced, dry, hot (830–1,050°C), Sr-and Al-poor, and Nb-and Fe-rich. They are part of a distinctly bimodal sequence with tholeiitic basalt. These characteristics were largely imposed by their derivation from parental basalt (with low fH₂O and low fO₂) which formed by partial melting in or above a mantle plume. The differences in intensive parameters caused early precipitation of plagioclase and retarded crystallization of Fe–Ti oxides. Fractionation led to higher density magmas and mid-crustal entrapment. Renewed intrusion of mafic magma caused partial melting of the intrusive complex. Varying degrees of partial melting, fractionation, and minor assimilation of older crust led to the array of rhyolite compositions. Only very small volumes of distinctive rhyolite were derived by fractional crystallization of Fe-rich intermediate magmas like those of the Craters of the Moon-Cedar Butte trend. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Market transfers of water for environmental protection in the western United States

Buying and leasing water rights for environmental protection is becoming an important method for protecting river and stream flows in the western United States. The region has experienced an increasing number of market transfers of water to protect water quality and fish and wildlife habitat. From 1990 to 1997, more than US$37 million was spent to lease 2 million acre-feet of water and US$23.8 was spent to purchase 132,000 acre-feet of water for environmental protection. State and federal agencies are responsible for most of these market transfers, but there is increasing activity on the part of private organizations to acquire water for instream needs. This paper examines recent developments of instream flow marketing in the western United States. The paper reviews recent transfers and acquisitions programs and discusses the growing entrepreneurial efforts by private organizations to acquire water rights for instream use. Market information including price and quantity of water traded was collected from market participants. The average purchase and lease prices for the region are US$397 and US$30 per acre-foot, respectively.     

Evapotranspiration response to multiyear dry periods in the semiarid western United States

Analysis of measured evapotranspiration shows that subsurface plant‐accessible water storage (PAWS) can sustain evapotranspiration through multiyear dry periods. Measurements at 25 flux tower sites in the semiarid western United States, distributed across five land cover types, show both resistance and vulnerability to multiyear dry periods. Average (±standard deviation) evapotranspiration ranged from 660 ± 230 mm yr^?1 (October–September) in evergreen needleleaf forests to 310 ± 200 mm yr^?1 in grasslands and shrublands. More than 52% of the annual evapotranspiration in Mediterranean climates is supported on average by seasonal drawdown of subsurface PAWS, versus 29% in monsoon‐influenced climates. Snowmelt replenishes dry‐season PAWS by as much as 20% at sites with significant seasonal snow accumulation but was insignificant at most sites. Evapotranspiration exceeded precipitation in more than half of the observation years at sites below 35°N. Annual evapotranspiration at non‐energy‐limited sites increased with precipitation, reaching a mean wet‐year evapotranspiration of 833 mm for evergreen needleleaf forests, 861 mm for mixed forests, 558 mm for woody savannas, 367 mm for grasslands, and 254 mm for shrublands. Thirteen sites experienced at least one multiyear dry period, when mean precipitation was more than one standard deviation below the historical mean. All vegetation types except evergreen needleleaf forests responded to multiyear dry periods by lowering evapotranspiration and/or significant year‐over‐year depletion of subsurface PAWS. Sites maintained wet‐year evapotranspiration rates for 8–33 months before attenuation, with a corresponding net PAWS drawdown of as much as 334 mm. Net drawdown at many sites continued until the dry period ended, resulting in an overall cumulative withdrawal of as much as 558 mm. Evergreen needleleaf forests maintained high evapotranspiration during multiyear dry periods with no apparent PAWS drawdown; these forests currently avoid drought but may prove vulnerable to longer and warmer dry periods that reduce snowpack storage and accelerate evapotranspiration.     

The response of natural river channels to urbanization: Two case studies from southeast England

The hypothesis that natural channels become enlarged as a result of an increase in flood flows following urbanization was tested in two areas of southeast England. In the West Sussex Study, a regression equation was used to calculate the expected cross-sectional area of channels draining rural areas. The channel enlargement ratio, which is the actual cross-sectional area of channels draining urbanized catchments divided by the predicted cross-sectional area of the stream if its basin was rural, was then calculated for 27 urbanized catchments. The relationship between the channel enlargement ratio and the percentage of the catchment paved revealed that a 10% paving of a basin should increase channel size downstream by 1.7 times but the variance explained by the equation was not as high as that found in an American study. The second study involved a comparison of the cross-sectional morphology of the Canon's Brook, Harlow, Essex in 1956 and 1970. The 1956 survey was undertaken when little building had taken place in the catchment whilst in 1970 about 18% of the basin was paved. Although various measures of central tendency indicated an increase in channel size during the period, this conclusion was not confirmed by a difference of means test suited to paired observations. A possible explanation for this finding is that there is a lag time between increases in flood flows and channel enlargement. Some validity can therefore be given to the view that urbanization leads to the enlargement of natural channels but further work using these and other methods is needed.     

The impact of beaver dams on the morphology of a river in the eastern United States with implications for river restoration

Restoration projects in the United States typically have among the stated goals those of increasing channel stability and sediment storage within the reach. Increased interest in ecologically based restoration techniques has led to the consideration of introducing beavers to degraded channels with the hope that the construction of beaver dams will aggrade the channel. Most research on beaver dam modification to channels has focused on the long‐term effects of beavers on the landscape with data primarily from rivers in the western United States. This study illustrated that a role exists for beavers in the restoration of fine‐grained, low gradient channels. A channel on the Atlantic Coastal Plain was analyzed before, during, and after beaver dams were constructed to evaluate the lasting impact of the beaver on channel morphology. The channel was actively evolving in a former reservoir area upstream of a dam break. Colonization by the beaver focused the flow into the channel, allowed for deposition along the channel banks, and reduced the channel width such that when the beaver dams were destroyed in a flood, there was no channel migration and net sediment storage in the reach had increased. However, the majority of the deposition occurred at the channel banks, narrowing the channel width, while the channel incised between sequential beaver dams. The study indicated that where channels are unstable laterally and bank erosion is a concern, the introduction of beavers can be a useful restoration tool. However, because of the likelihood of increased channel bed erosion in a reach with multiple beaver dams, they may not be the best solution where aggradation of an incised channel bed is the desired result. Copyright © 2014 John Wiley & Sons, Ltd.     

Short‐term variability in isotopic composition of precipitation: A case study from the Midwestern United States

Oxygen and deuterium isotopes in precipitation were analysed to define local isotopic trends in Iowa, US. The area is far inland from an oceanic source and the observed averages of δ¹⁸O and δ D are ? 6·43‰ and ? 41·35‰ for Ames, ? 7·53‰ and ? 51·33‰ for Cedar Falls, and ? 6·01‰ and ? 38·19‰ for Iowa City, respectively. Although these data generally follow global trends, they are different when compared to a semi‐arid mid‐continental location in North Platt, Nebraska. The local meteoric water lines of Iowa are δ D = 7·68 δ¹⁸O + 8·0 for Ames, δ D = 7·62 δ¹⁸O + 6·07 for Cedar Falls, and δ D = 7·78 δ¹⁸O + 8·61 for Iowa City. The current Iowa study compares well with a study conducted in Ames, Iowa, 10 years earlier. The differences between Iowa and Nebraska studies are attributed to a variable climate across the northern Great Plains ranging from sub‐humid in the east to semi‐arid in the west. Iowa being further east in the region is more strongly influenced by a moist sub‐humid to humid climate fed by the tropical air stream from the Gulf of Mexico. The average d‐excess values are 10·06‰ for Ames, 8·92‰ for Cedar Falls and 9·92‰ for Iowa City. Eighty seven percent of the samples are within the global d‐excess range of 0‰ and 20‰. The results are similar to previous studies, including those by National Atmospheric Deposition Programs and International Atomic Energy Agency. It appears that the impact of recycled water or secondary evaporation on δ¹⁸O values of area precipitation is minimal. Copyright © 2008 John Wiley & Sons, Ltd.     

Nitrogen and phosphorus dynamics during runoff events over a transition from grassland to shrubland in the south‐western United States

During the last 150 years, land degradation across the semi‐arid grasslands of the south‐western United States has been associated with an increase in runoff and erosion. Concurrent with this increase in runoff and erosion is a loss of nitrogen (N) and phosphorus (P), which are plant‐essential nutrients. This study investigates the runoff‐driven redistribution and loss of dissolved and particulate‐bound N and P that occurs during natural runoff events over a trajectory of degradation, from grassland to degraded shrubland, in central New Mexico. Runoff‐driven nutrient dynamics were monitored at four stages over a transition from grassland to shrubland, for naturally occurring rainfall events over 10 × 30 m bounded runoff plots. Results show that particulate‐bound forms of N and P are responsible for most of N and P lost from the plots due to erosion occurring during runoff events. Results suggest that for high‐magnitude rainfall events, the output of N and P from the plots may greatly exceed the amount input into the plots, particularly over shrub‐dominated plots where erosion rates are higher. As these results only become apparent when monitoring these processes over larger hillslope plots, it is important to recognize that processes of nutrient cycling related to the islands of fertility hypothesis may have previously been overstated when observed only at smaller spatial scales. Thus, the progressive degradation of semi‐arid grassland ecosystems across the south‐western United States and other semi‐arid ecosystems worldwide has the potential to affect N and P cycling significantly through an increase in nutrient redistribution and loss in runoff. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of winter atmospheric circulation on temporal and spatial variability in annual streamflow in the western United States

Abstract

Winter mean 700-hectoPascal (hPa) height anomalies, representing the average atmospheric circulation during the snow season, are compared with annual streamflow measured at 140 streamgauges in the western United States. Correlation and anomaly pattern analyses are used to identify relationships between winter mean atmospheric circulation and temporal and spatial variability in annual streamflow. Results indicate that variability in winter mean 700-Hpa height anomalies accounts for a statistically significant portion of the temporal variability in annual streamflow in the western United States. In general, above-average annual streamflow is associated with negative winter mean 700-Hpa height anomalies over the eastern North Pacific Ocean and/or the western United States. The anomalies produce an anomalous flow of moist air from the eastern North Pacific Ocean into the western United States that increases winter precipitation and snowpack accumulations, and subsequently streamflow. Winter mean 700-hPa height anomalies also account for statistically significant differences in spatial distributions of annual streamflow. As part of this study, winter mean atmospheric circulation patterns for the 40 years analysed were classified into five winter mean 700-hPa height anomaly patterns. These patterns are related to statistically significant and physically meaningful differences in spatial distributions of annual streamflow.     

Post‐fire bedload sediment delivery across spatial scales in the interior western United States

Post‐fire sediment yields can be up to three orders of magnitude greater than sediment yields in unburned forests. Much of the research on post‐fire erosion rates has been at small scales (100 m² or less), and post‐fire sediment delivery rates across spatial scales have not been quantified in detail. We developed relationships for post‐fire bedload sediment delivery rates for spatial scales up to 117 ha using sediment yield data from six published studies and two recently established study sites. Sediment yields and sediment delivery ratios (SDRs; sediment delivered at the catchment scale divided by the sediment delivered from a plot nested within the catchment) were related to site factors including rainfall characteristics, area, length, and ground cover. Unit‐area sediment yields significantly decreased with increasing area in five of the six sites. The annual SDRs ranged from 0.0089 to 1.15 and these were more closely related to the ratio of the plot lengths than the ratio of plot areas. The developed statistical relationships will help quantify post‐fire sediment delivery rates across spatial scales in the interior western United States and develop process‐based scaling relationships. Published in 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Upper-mantle structure in the central United States from P- and S-wave spectra

The upper-mantle structure down to about 220 km in the central United States has been inferred from long-period P- and S-wave spectra of deep earthquakes recorded at three WWSSN stations, by using the re-formulated transfer ratio method. This method has been experimentally shown to be a very powerful means for elucidating the fine configuration of the low-velocity zone. The strong advantage of this method is its ability to determine separately the extent of the velocity decrease and the depth to the bottom of this zone, which is more uncertain by the other methods.From the Interior Plain to the Gulf of Mexico the low-velocity zone shifts to a shallower depth while increasing its thickness and decreasing its velocities. This zone is made up of an approx. 50 km thick layer ranging in depth from about 150 to 200 km under the Interior Plain, an approx. 75 km thick layer from about 120 to 195 km under the Gulf Coastal Plain, and an approx. 80 km thick layer from about 95 to 175 km under the continental shelf of the Gulf of Mexico, all nearly along 89°N longitude. The decrease in S-wave velocity at the top of this zone is about 0.30, 0.45, and 0.70 km/sec under each of the above areas, although the last value may be somewhat an overestimate. Both boundaries of this zone are sharp, the transition occurring over at most ca. 10 km. In this region the existence of the high-velocity lid zone is possible.     

A review of rock mechanics studies in the United States pertinent to earthquake prediction

Premonitory phenomena such as dilatancy, creep, acoustic emission, and changes in seismic velocity and attenuation, electrical resistivity, magnetic moment, and gas emission, which occur before fracture of initially intact rock and before stick-slip on faults or between finely ground surfaces of rock, have been reviewed and discussed in relation to earthquake prediction. This review is restricted to the results of laboratory experiments that have been carried out in the United States of America.     

Vadose Zone Monitoring: Experiences and Trends in the United States

The vadose zone is the portion of the geologic profile above a perennial aquifer. Inclusion of mandatory vadose zone monitoring techniques as an approach to aquifer protect ion was first proposed under the Resource Conservation and Recovery Act in the United States in 1978 and has since received increasing acceptance at federal and stale levels. The goals of a vadose zone characterization and monitoring effort are to establish background conditions, identify contaminant transport pathways, identify the extent and degree of existing contamination, establish the basis for monitoring network design, measure the parameters needed in a risk assessment, and provide detection of contaminant migration toward ground water resources. The benefits of vadose zone monitoring include early warning of contaminant migration, potential reduction of ground water monitoring efforts, reduction of contaminant spreading and volume, and reduced time and cost of remediation once a contaminant release occurs. Vadose zone characterization and monitoring techniques should be considered as critical hydrologic tools in the prevention of ground water resource degradation.     

Groundwater Governance in the United States: Common Priorities and Challenges

Groundwater is a critical component of the water supply for agriculture, urban areas, industry, and ecosystems, but managing it is a challenge because groundwater is difficult to map, quantify, and evaluate. Until recently, study and assessment of governance of this water resource has been largely neglected. A survey was developed to query state agency officials about the extent and scope of groundwater use, groundwater laws and regulations, and groundwater tools and strategies. Survey responses revealed key findings: states' legal frameworks for groundwater differ widely in recognizing the hydrologic connection between surface water and groundwater, the needs of groundwater‐dependent ecosystems, and the protection of groundwater quality; states reported a range in capacity to enforce groundwater responsibilities; and states have also experienced substantial changes in groundwater governance in the past few decades. Overall, groundwater governance across the United States is fragmented. States nevertheless identified three common priorities for groundwater governance: water quality and contamination, conflicts between users, and declining groundwater levels. This survey represents an initial step in a broader, continuing effort to characterize groundwater governance practices in the United States.     

美国最近三代地震区划图中的断裂震源模型

活断层与古地震定量数据在美国近三代地震区划图中的应用基本上体现了各阶段活断层研究的最新成果,其中断裂震源模型起到了桥梁的作用,并不断得到完善。在1996年地震区划图中引入了特征地震模型与截断的G—R模型,用以表述断层的震级一频度分布关系。在2002年地震区划图中更明确地处理了参数的不确定性,并引入逻辑树概念,同时在特征地震模型中试用了多段破裂模型。在2008年地震区划图中引用了更为广泛的逻辑树来描述地震构造几何形态、地震震级和复发周期的不确定性,其中特征地震模型包括：单段破裂和多段破裂的特征地震模型,以及给定震级的浮动地震模型（或不固定分段模型）。这些经验值得在我国第五代地震区划图的编制工作中借鉴。     

Monitoring active volcanoes and mitigating volcanic hazards: the case for including simple approaches

Simple approaches to problems brought about eruptions and their ensuing hazardous effects should be advocated and used by volcanologists while awaiting more sophisticated remedies. The expedients we advocate have all or many of the following attributes: only locally available materials are required; no extensive training of operators or installation is necessary; they are affordable and do not require foreign aid or exports; they are often labor intensive and are sustainable without outside assistance. Where appropriate, the involvement of local residents is advocated. Examples of simple expedients which can be used in forecasting or mitigating the effects of crises emphasize the relative ease and the less elaborate requirements with which simple approaches can be activated. Emphasis is on visual observations often by untrained observers, simple meteorogical measurements, observations of water level in lakes, temperature and chemistry of springs and fumaroles, new springs and collapse areas and observations of volcanic plumes. Simple methods are suggested which can be applied to mitigating damage from mudflows, nuées ardentes, tephra falls and gas discharge. A review in hindsight at Ruiz includes the use of both chemical indicators and simple mudflow alarms. Simple expedients are sufficiently effective that any expert volcanologist called to aid in a crisis must include them in the package of advice offered. Simple approaches are a critical and logical complement to highly technical solutions to hazardous situations.     

Linking transit times to catchment sensitivity to atmospheric deposition of acidity and nitrogen in mountains of the western United States

Transit times are hypothesized to influence catchment sensitivity to atmospheric deposition of acidity and nitrogen (N) because they help determine the amount of time available for infiltrating precipitation to interact with catchment soil and biota. Transit time metrics, including fraction of young water (F_yw) and mean transit time (MTT), were calculated for 11 headwater catchments in mountains of the western United States based on differences in the amplitude of the seasonal signal of δ¹⁸O in streamflow and precipitation. Results were statistically compared with catchment characteristics to elucidate controlling mechanisms. Transit times also were compared with stream solute concentrations to test the hypothesis that transit times are a primary influence on weathering rates and biological assimilation of atmospherically deposited N. Results indicate that transit times in the study catchments are strongly related to soil, vegetation, and topographic characteristics, with barren terrain (bare rock and talus) and steep slopes linked to high F_yw and short MTT, whereas forest soil (hydrogroup B) was linked to low F_yw and greater MTT. Concentrations of silicate weathering products (Na⁺ and Si) were negatively related to F_yw and barren terrain, and positively related to MTT and forest soil, supporting the concept that weathering fluxes and buffering capacity tend to be low in alpine areas due to short transit times. Nitrate concentrations were positively related to N deposition, catchment slope, and barren terrain, and negatively related to forest, indicating that hydrologic and/or biogeochemical processes associated with steep slopes limit uptake of atmospherically deposited N by biota. Interannual and seasonal variability in transit times and source water contributions in the study catchments was substantial, reflecting the influence of strong temporal variations in snowmelt inputs in high‐elevation catchments of the western United States. Results from this study confirm that short transit times in these areas are a key reason they are highly sensitive to atmospheric pollution and climate change.     

Review: The International Sediment Initiative case studies of sediment problems in river basins and their management

Management of sediment in river basins and waterways has been an important issue for water managers throughout history. The changing nature of sediment issues has meant that water managers today face many complex technical and environmental challenges in relation to sediment management. UNESCO's International Hydrological Programme(IHP) launched the International Sediment Initiative(ISI) in 2002.ISI aims to further advance sustainable sediment management on a global scale. This is achieved through the delivery of a decision support framework for sediment management that provides guidance on legislative and institutional solutions, applicable across a range of socio-economic and physiographic settings in the context of global change. ISI mobilizes international experience on sediment problems and their management through the compilation of a series of case studies representative of a broad range of physiographic and socio-economic conditions, which are made available as guidance for policy makers dealing with water and river basin management. Case studies prepared to date include the basins of the Nile, Mississippi, Rhine, Volga, Yellow, and Haihe and Liaohe rivers. Available in full from the ISI website,these detailed case studies are briefly introduced in this review articles.     

Influence of topographic,geomorphic, and hydrologic variables on beaver dam height and persistence in the intermountain western United States

Stream ecosystems can be dramatically altered by dam-building activities of North American beaver (Castor canadensis). The extent to which beavers’ ecosystem engineering alters riverscapes is driven by the density, longevity, and size (i.e. height and length) of the dams constructed. In comparison to the relative ubiquity of beaver dams on the landscape, there is a scarcity of data describing dam heights. We collected data describing dam height and dam condition (i.e. damaged or intact) of 500 beaver dams via rapid field survey, differentiating between primary and secondary dams and associating each dam with a beaver dam complex. With these data, we examined the influence of beaver dam type (primary/secondary), drainage area, streamflow, stream power, valley bottom width, and HUC12 watershed on beaver dam height with linear regression and the probability that a beaver dam was damaged with logistic regression. On average, primary dams were 0.46 m taller than secondary dams; 15% of observed dams were primary and 85% secondary. Dam type accounted for 21% of dam height variation (p <0.0001). Slope (p = 0.0107), discharge (p = 0.0029), and drainage area (p = 0.0399) also affected dam height, but each accounted for less than 3% of dam height variation. The average number of dams in a dam complex was 6.1 (SD ± 4.5) and ranged from 1 to 21. The watershed a beaver dam was located in accounted for the most variability (17.8%) in the probability that a beaver dam was damaged, which was greater than the variability explained by any multiple logistic regression model. These results indicate that temporally dynamic variables are important influencers of dam longevity and that beaver dam ecology is a primary factor influencing beaver dam height. © 2020 John Wiley & Sons, Ltd.