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At least 523 records · Page 29Linked to original sources
USGS2010

Oscillating load-induced acoustic emission in laboratory experiment

Spatial and temporal patterns of acoustic emission (AE) were studied. A pre-fractured cylinder of granite was loaded in a triaxial machine at 160 MPa confining pressure until stick-slip events occurred. The experiments were conducted at a constant strain rate of 10 −7 s −1 that was modulated by small-amplitude sinusoidal oscillations with periods of 175 and 570 seconds. Amplitude of the oscillations was a few percent of the total load and was intended to simulate periodic loading observed in nature (e.g., earth tides or other sources). An ultrasonic acquisition system with 13 piezosensors recorded acoustic emissions that were generated during deformation of the sample. We observed a correlation between AE response and sinusoidal loading. The effect was more pronounced for higher frequency of the modulating force. A time-space spectral analysis for a “point” process was used to investigate details of the periodic AE components. The main result of the study was the correlation of oscillations of acoustic activity synchronized with the applied oscillating load. The intensity of the correlated AE activity was most pronounced in the “aftershock” sequences that followed large-amplitude AE events. We suggest that this is due to the higher strain-sensitivity of the failure area when the sample is in a transient, unstable mode. We also found that the synchronization of AE activity with the oscillating external load nearly disappeared in the period immediately after the stick-slip events and gradually recovered with further loading.

Book chapter↗
USGS1976

The Viking landing sites: Selection and certification

During the past several years the Viking project developed plans to use Viking orbiter instruments and Earth-based radar to certify the suitability of the landing sites selected as the safest and most scientifically rewarding using Mariner 9 data. During June and July 1976, the Earth-based radar and orbital spacecraft observations of some of the prime and backup sites were completed. The results of these combined observations indicated that the Viking 1 prime landing area in the Chryse region of Mars is geologically varied and possibly more hazardous than expected, and was not certifiable as a site for the Viking 1 landing. Consequently, the site certification effort had to be drastically modified and lengthened to search for a site that might be safe enough to attempt to land. The selected site considered at 47.5°W, 22.4°N represented a compromise between desirable characteristics observed with visual images and those inferred from Earth-based radar. It lies in the Chryse region about 900 kilometers northwest of the original site. Viking 1 landed successfully at this site on 20 July 1976.

Science↗
USGS2014

Spectroscopy from Space

This chapter reviews detection of materials on solid and liquid (lakes and ocean) surfaces in the solar system using ultraviolet to infrared spectroscopy from space, or near space (high altitude aircraft on the Earth), or in the case of remote objects, earth-based and earth-orbiting telescopes. Point spectrometers and imaging spectrometers have been probing the surfaces of our solar system for decades. Spacecraft carrying imaging spectrometers are currently in orbit around Mercury, Venus, Earth, Mars, and Saturn, and systems have recently visited Jupiter, comets, asteroids, and one spectrometer-carrying spacecraft is on its way to Pluto. Together these systems are providing a wealth of data that will enable a better understanding of the composition of condensed matter bodies in the solar system. Minerals, ices, liquids, and other materials have been detected and mapped on the Earth and all planets and/or their satellites where the surface can be observed from space, with the exception of Venus whose thick atmosphere limits surface observation. Basaltic minerals (e.g., pyroxene and olivine) have been detected with spectroscopy on the Earth, Moon, Mars and some asteroids. The greatest mineralogic diversity seen from space is observed on the Earth and Mars. The Earth, with oceans, active tectonic and hydrologic cycles, and biological processes, displays the greatest material diversity including the detection of amorphous and crystalline inorganic materials, organic compounds, water and water ice. Water ice is a very common mineral throughout the Solar System and has been unambiguously detected or inferred in every planet and/or their moon(s) where good spectroscopic data has been obtained. In addition to water ice, other molecular solids have been observed in the solar system using spectroscopic methods. Solid carbon dioxide is found on all systems beyond the Earth except Pluto, although CO 2 sometimes appears to be trapped in other solids rather than as an ice on some objects. The largest deposits of carbon dioxide ice are found on Mars. Sulfur dioxide ice is found in the Jupiter system. Nitrogen and methane ices are common beyond the Uranian system. Saturn’s moon Titan probably has the most complex active extra-terrestrial surface chemistry involving organic compounds. Some of the observed or inferred compounds include ices of benzene (C 6 H 6 ), cyanoacetylene (HC 3 N), toluene (C 7 H 8 ), cyanogen (C 2 N 2 ), acetonitrile (CH 3 CN), water (H 2 O), carbon dioxide (CO 2 ), and ammonia (NH 3 ). Confirming compounds on Titan is hampered by its thick smoggy atmosphere, where in relative terms the atmospheric interferences that hamper surface characterization lie between that of Venus and Earth. In this chapter we exclude discussion of the planets Jupiter, Saturn, Uranus, and Neptune because their thick atmospheres preclude observing the surface, even if surfaces exist. However, we do discuss spectroscopic observations on a number of the extra-terrestrial satellite bodies. Ammonia was predicted on many icy moons but is notably absent among the definitively detected ices with possible exceptions on Charon and possible trace amounts on some of the Saturnian satellites. Comets, storehouses of many compounds that could exist as ices in their nuclei, have only had small amounts of water ice definitively detected on their surfaces from spectroscopy. Only two asteroids have had a direct detection of surface water ice, although its presence can be inferred in others.

Reviews in Mineralogy and Geochemistry↗
USGS2012

Galileo observations of Post-Imbrium lunar craters during the first Earth-Moon flyby

Copernican‐age craters are among the most conspicuous features seen on the far side and western limb of the Moon in the Galileo multispectral images acquired in December 1990. Among the new morphologic observations of far‐side craters are bright rays, continuous ejecta deposits, and dark rings associated with probable impact‐melt veneers. These observations suggest that the mapped age assignments of several large far‐side craters (Ohm, Robertson, and possibly Lowell and Lenz) need revision. New crater size‐frequency measurements on Lunar Orbiter images suggest the following age reassignments: Hausen (170 km diameter), Pythagoras (120 km), and Bullialdus (61 km) from Eratosthenian to Upper Imbrian, and Carpenter (60 km) and Harpalus (39 km) from Copernican to Eratosthenian. Colors and albedos of craters (away from impact‐melt veneers) are correlated with their geologic emplacement ages as determined from counts of superposed craters; these age‐color relations are used to estimate the emplacement age (time since impact event) for other Copernican‐age craters. These age‐color relations indicate a probable Copernican age for 27 far‐side or western limb craters larger than 10 km diameter that were not previously mapped as Copernican. The apparent deficiency of Copernican craters on the far side compared with the near side in published geologic maps is not present in our data. Age‐color trends differ between mare and highland regions and between the interiors and continuous ejecta of the craters. Similar trends are established for color and albedo versus soil‐maturity indices for the returned lunar samples, with distinct trends for mare and highland soils. However, the mare versus highland offsets are reversed in the two comparisons. These relations can be explained by variations in regolith thicknesses and rates of mixing with relatively fresh, crystalline ejecta. Therefore, the soil‐maturity trends represent longer geologic time periods in regions with thinner regoliths, such as the maria.

Journal of Geophysical Research E: Planets↗
USGS2021

Synoptic analysis of a decade of daily measurements of SO2 emission in the troposphere from volcanoes of the global ground-based Network for Observation of Volcanic and Atmospheric Change

Volcanic plumes are common and far-reaching manifestations of volcanic activity during and between eruptions. Observations of the rate of emission and composition of volcanic plumes are essential to recognize and, in some cases, predict the state of volcanic activity. Measurements of the size and location of the plumes are important to assess the impact of the emission from sporadic or localized events to persistent or widespread processes of climatic and environmental importance. These observations provide information on volatile budgets on Earth, chemical evolution of magmas, and atmospheric circulation and dynamics. Space-based observations during the last decades have given us a global view of Earth's volcanic emission, particularly of sulfur dioxide ( SO 2 ). Although none of the satellite missions were intended to be used for measurement of volcanic gas emission, specially adapted algorithms have produced time-averaged global emission budgets. These have confirmed that tropospheric plumes, produced from persistent degassing of weak sources, dominate the total emission of volcanic SO 2 . Although space-based observations have provided this global insight into some aspects of Earth's volcanism, it still has important limitations. The magnitude and short-term variability of lower-atmosphere emissions, historically less accessible from space, remain largely uncertain. Operational monitoring of volcanic plumes, at scales relevant for adequate surveillance, has been facilitated through the use of ground-based scanning differential optical absorption spectrometer (ScanDOAS) instruments since the beginning of this century, largely due to the coordinated effort of the Network for Observation of Volcanic and Atmospheric Change (NOVAC). In this study, we present a compilation of results of homogenized post-analysis of measurements of SO 2 flux and plume parameters obtained during the period March 2005 to January 2017 of 32 volcanoes in NOVAC. This inventory opens a window into the short-term emission patterns of a diverse set of volcanoes in terms of magma composition, geographical location, magnitude of emission, and style of eruptive activity. We find that passive volcanic degassing is by no means a stationary process in time and that large sub-daily variability is observed in the flux of volcanic gases, which has implications for emission budgets produced using short-term, sporadic observations. The use of a standard evaluation method allows for intercomparison between different volcanoes and between ground- and space-based measurements of the same volcanoes. The emission of several weakly degassing volcanoes, undetected by satellites, is presented for the first time. We also compare our results with those reported in the literature, providing ranges of variability in emission not accessible in the past. The open-access data repository introduced in this article will enable further exploitation of this unique dataset, with a focus on volcanological research, risk assessment, satellite-sensor validation, and improved quantification of the prevalent tropospheric component of global volcanic emission.

Earth System Science Data↗
USGS2019

User needs for future Landsat missions

Landsat satellites have been operating since 1972, providing the longest continuous observation record of the Earth’s land surface. Over the past half century, the Landsat user community has grown exponentially, encompassing more diverse and evolving scientific research and operational uses. Understanding current and future user needs is crucial to informing the design of Landsat missions beyond Landsat 9. The U.S. Geological Survey (USGS) initiated a user needs collection process to document needs from U.S. Federal civil subject matter experts who rely on moderate-resolution land imaging data across a diverse range of scientific research and application domains. In total, 379 moderate-resolution land imaging user needs were collected through structured interviews. The findings indicate that, at present, users need continuity in Landsat capabilities with free and open data access. Improvements to future Landsat systems should include 10 m spatial resolution and at least weekly cloud-free observation frequency. Spectral enhancements should include the addition of red edge bands, and multiple, narrower visible, near infrared, shortwave infrared, and thermal infrared bands. Ideally, a variety of applications need continuous, full-spectrum coverage in 10 nm-wide bands spanning the visible to shortwave infrared (VSWIR) region (400–2500 nm) and 5 to 8 multispectral thermal infrared bands. Non-Federal (state, local, commercial, academic, and international) sources found similar results, but a more comprehensive comparison across these communities through a broader survey may provide additional insights. USGS-collected moderate-resolution land imaging user needs are an input to the Landsat 10 Architecture Study to develop and assess feasible Landsat 10 mission architectures.

Remote Sensing of Environment↗
USGS2004

Numerical simulations of large earthquakes: Dynamic rupture propagation on heterogeneous faults

Our current conceptions of earthquake rupture dynamics, especially for large earthquakes, require knowledge of the geometry of the faults involved in the rupture, the material properties of the rocks surrounding the faults, the initial state of stress on the faults, and a constitutive formulation that determines when the faults can slip. In numerical simulations each of these factors appears to play a significant role in rupture propagation, at the kilometer length scale. Observational evidence of the earth indicates that at least the first three of the elements, geometry, material, and stress, can vary over many scale dimensions. Future research on earthquake rupture dynamics needs to consider at which length scales these features are significant in affecting rupture propagation. ?? Birkha??user Verlag, Basel, 2004.

Pure and Applied Geophysics↗
USGS2010

Geochemistry of southern Pagan Island lavas, Mariana arc: The role of subduction zone processes

New major and trace element abundances, and Pb, Sr, and Nd isotopic ratios of Quaternary lavas from two adjacent volcanoes (South Pagan and the Central Volcanic Region, or CVR) located on Pagan Island allow us to investigate the mantle source (i.e., slab components) and melting dynamics within the Mariana intra-oceanic arc. Geologic mapping reveals a pre-caldera (780-9.4ka) and post-caldera (<9.4ka) eruptive stage for South Pagan, whereas the eruptive history of the older CVR is poorly constrained. Crystal fractionation and magma mixing were important crustal processes for lavas from both volcanoes. Geochemical and isotopic variations indicate that South Pagan and CVR lavas, and lavas from the northern volcano on the island, Mt. Pagan, originated from compositionally distinct parental magmas due to variations in slab contributions (sediment and aqueous fluid) to the mantle wedge and the extent of mantle partial melting. A mixing model based on Pb and Nd isotopic ratios suggests that the average amount of sediment in the source of CVR (~2.1%) and South Pagan (~1.8%) lavas is slightly higher than Mt. Pagan (~1.4%) lavas. These estimates span the range of sediment-poor Guguan (~1.3%) and sediment-rich Agrigan (~2.0%) lavas for the Mariana arc. Melt modeling demonstrates that the saucer-shaped normalized rare earth element (REE) patterns observed in Pagan lavas can arise from partial melting of a mixed source of depleted mantle and enriched sediment, and do not require amphibole interaction or fractionation to depress the middle REE abundances of the lavas. The modeled degree of mantle partial melting for Agrigan (2-5%), Pagan (3-7%), and Guguan (9-15%) lavas correlates with indicators of fluid addition (e.g., Ba/Th). This relationship suggests that the fluid flux to the mantle wedge is the dominant control on the extent of partial melting beneath Mariana arc volcanoes. A decrease in the amount of fluid addition (lower Ba/Th) and extent of melting (higher Sm/Yb), and an increase in the sediment contribution (higher Th/Nb, La/Sm, and Pb isotopic ratios) from Mt. Pagan to South Pagan could reflect systematic cross-arc or irregular along-arc melting variations. These observations indicate that the length scale of compositional heterogeneity in the mantle wedge beneath Mariana arc volcanoes is small (~10km).

Contributions to Mineralogy and Petrology↗
USGS2019

Topographic changes during the 2018 Kīlauea eruption from Single-pass Airborne InSAR

The 2018 eruption of Kīlauea volcano, Hawai‘i, was its most effusive in over 200 years. We apply the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN‐A) interferometric synthetic aperture radar (InSAR) instrument to measure topographic change associated with the eruption. The GLISTIN‐A radar flew in response to the eruption, acquiring observations of Kīlauea on seven days between May 18 and September 15, 2018. Topography differences were computed relative to GLISTIN‐A observations in 2017. Bare‐earth topography and off‐shore bathymetry were used to correct for vegetation and creation of new coastal land within the Lower East Rift Zone (LERZ) lava flow field. We estimate that the LERZ subaerial flows total bulk volume is 0.593 ± 0.011 km 3 and that the summit collapse volume is ‐0.836 ± 0.002 km 3 . Within the temporal sampling and uncertainty from submarine flow volumes, we find that both the LERZ and caldera volume changes were approximately linear.

Hawaii↗
USGS2019

Overcoming barriers to progress in seismic monitoring and characterization of debris flows and lahars

Debris flows generate seismic signals that contain valuable information about events as they unfold. Though seismic waves have been used for along-channel debris-flow and lahar monitoring systems for decades, it has proven difficult to move beyond detection to more quantitative characterizations of flow parameters and event size. This is for two primary reasons: (1) our limited understanding of how the radiated wavefield relates to debris flow characteristics and dynamics, and (2) difficulties quantifying the effects of heterogeneous shallow earth structure on the observed wavefield. The latter issue, essentially our inability to sufficiently separate seismic path effects from source information, is a barrier to improving our understanding of the first issue. We review the progress that has been made toward establishing the theory, models and methods required to use seismic observations to make quantitative measurements of flows and summarize the practical, social, and scientific barriers to progress. We discuss some specific ongoing efforts to overcome some of these barriers, with a focus on how we are using large-scale seismic experiments at the U.S. Geological Survey debris-flow flume to develop methods for directly measuring path effects and to develop and validate theoretical debris flow seismicity models.

Conference Paper↗
USGS1977

Geologic map of the Eridania Quadrangle of Mars

The Eridania quadrangle is located within the densely cratered terrain of the southern hemisphere of Mars, east of the large circular Hellas Basin. The areas contain three distinct physiographic provinces that div ide the quadrangle into latitud in al belts. The northern part of the quadrangle is dominated by cratered upland plateau, the central part by plains, the southern part by a mottled surface of rugged topography and a high density of craters subdued by erosion. In general, the oldest geologic unit occurs in the upland terrain, the youngest in the central lowlands. Large contrast in albedo were observed on Mars from Earth long before Mariner spaceflight missions. The most conspic uous of these features within the quadrangle are areas of low albedo in the north and in the south that corresponds to the two main belts of high-relief terrain. The intervening region of high albedo corresponds to the central plains belt, also an area of recurrent seasonal frost. The southern polar cap extends to about 50 ˚ S lat and includes all of the southern belt of high relief.

IMAP↗
USGS1969

(RLC-14) Geologic map of the Alphonsus region of the moon

This 1:250,000- scale geologic map is one of a series prepared largely from photographs transmitted by Ranger IX (reproduced in a report by Jet Propulsion Lab., 1966). It depicts the geology of the crater Alphonsus (in which Ranger IX impacted) and environs. The primary objective of the mapping was to apply extant lunar mapping techniques used on relatively small scale telescopic photographs to the larger scale Ranger photographs, in preparation for extensive analysis of Lunar Orbiter photography in support of the Apollo program. An additional objective was to shed more light on the formation of Alphonsus and its associated features. The map outlines rock units that are inferred from surface features and characteristics, such as topography and albedo. Each rock unit is assigned an age and arranged in the explanation so that the youngest unit are at the top and the oldest at the bottom. The age classification is based on the early work of Shoemaker and Hackman (1962), and subsequent revisions reported by McCauley (1967) and Wilhelms (1966). Geology of the region has been mapped at a scale of 1:1,000,000 on the basis of Earth-based photographs and observations (Howard and Masursky , 1968). A more detailed, 1;50,000-scale map of part of the Alphonsus floor was prepared by McCauley (1969), who used Ranger IX photographs as his source of geologic information.

IMAP↗
USGS1996

Use of SAR data to study active volcanoes in Alaska

Synthetic Aperture Radar (SAR) data of the Westdahl, Veniaminof, and Novarupta volcanoes in the Aleutian Arc of Alaska were analysed to investigate recent surface volcanic processes. These studies support ongoing monitoring and research by the Alaska Volcano Observatory (AVO) in the North Pacific Ocean Region. Landforms and possible crustal deformation before, during, or after eruptions were detected and analysed using data from the European Remote Sensing Satellites (ERS), the Japanese Earth Resources Satellite (JERS) and the US Seasat platforms. Field observations collected by scientists from the AVO were used to verify the results from the analysis of SAR data.

Earth Observation Quarterly↗
USGS2006

Documentation of a spreadsheet for time-series analysis and drawdown estimation

Drawdowns during aquifer tests can be obscured by barometric pressure changes, earth tides, regional pumping, and recharge events in the water-level record. These stresses can create water-level fluctuations that should be removed from observed water levels prior to estimating drawdowns. Simple models have been developed for estimating unpumped water levels during aquifer tests that are referred to as synthetic water levels. These models sum multiple time series such as barometric pressure, tidal potential, and background water levels to simulate non-pumping water levels. The amplitude and phase of each time series are adjusted so that synthetic water levels match measured water levels during periods unaffected by an aquifer test. Differences between synthetic and measured water levels are minimized with a sum-of-squares objective function. Root-mean-square errors during fitting and prediction periods were compared multiple times at four geographically diverse sites. Prediction error equaled fitting error when fitting periods were greater than or equal to four times prediction periods. The proposed drawdown estimation approach has been implemented in a spreadsheet application. Measured time series are independent so that collection frequencies can differ and sampling times can be asynchronous. Time series can be viewed selectively and magnified easily. Fitting and prediction periods can be defined graphically or entered directly. Synthetic water levels for each observation well are created with earth tides, measured time series, moving averages of time series, and differences between measured and moving averages of time series. Selected series and fitting parameters for synthetic water levels are stored and drawdowns are estimated for prediction periods. Drawdowns can be viewed independently and adjusted visually if an anomaly skews initial drawdowns away from 0. The number of observations in a drawdown time series can be reduced by averaging across user-defined periods. Raw or reduced drawdown estimates can be copied from the spreadsheet application or written to tab-delimited ASCII files.

Scientific Investigations Report↗
USGS2009

Review: Progress in rotational ground-motion observations from explosions and local earthquakes in Taiwan

Rotational motions generated by large earthquakes in the far field have been successfully measured, and observations agree well with the classical elasticity theory. However, recent rotational measurements in the near field of earthquakes in Japan and in Taiwan indicate that rotational ground motions are 10 to 100 times larger than expected from the classical elasticity theory. The near-field strong-motion records of the 1999 M w 7.6 Chi-Chi, Taiwan, earthquake suggest that the ground motions along the 100 km rupture are complex. Some rather arbitrary baseline corrections are necessary in order to obtain reasonable displacement values from double integration of the acceleration data. Because rotational motions can contaminate acceleration observations due to the induced perturbation of the Earth’s gravitational field, we started a modest program to observe rotational ground motions in Taiwan. Three papers have reported the rotational observations in Taiwan: (1) at the HGSD station ( Liu et al. , 2009 ), (2) at the N3 site from two TAiwan Integrated GEodynamics Research (TAIGER) explosions ( Lin et al. , 2009 ), and (3) at the Taiwan campus of the National Chung-Cheng University (NCCU) ( Wu et al. , 2009 ). In addition, Langston et al. (2009) reported the results of analyzing the TAIGER explosion data. As noted by several authors before, we found a linear relationship between peak rotational rate (PRR in mrad/sec) and peak ground acceleration (PGA in m/sec 2 ) from local earthquakes in Taiwan, PRR=0.002+1.301 PGA, with a correlation coefficient of 0.988.

Bulletin of the Seismological Society of America↗
USGS2010

The effect of error in theoretical Earth tide on calibration of borehole strainmeters

Since the installation of borehole strainmeters into the ground locally distorts the strain in the rock, these strainmeters require calibration from a known source which typically is the Earth tide. Consequently, the accuracy of the observed strain changes from borehole strainmeters depends upon the calibration derived from modeling the Earth tide. Previous work from the mid-1970s, which is replicated here, demonstrate that the theoretical tide can differ by 30% from the tide observed at surface-mounted, long-baseline strainmeters. In spite of possible inaccurate tidal models, many of the 74 borehole strainmeters installed since 2005 can be “calibrated”. However, inaccurate tidal models affect the amplitude and phase of observed transient strain changes which needs to be considered along with the precision of the data from the inherent drift of these borehole instruments. In particular, the error from inaccurate tidal model dominates the error budget in the observation of impulsive, sub-daily, strain-transients.

Geophysical Research Letters↗
USGS1994

Fractionation of families of major, minor, and trace metals across the melt-vapor interface in volcanic exhalations

Chemical families of metals fractionate systematically as they pass from a silicate melt across the interface with the vapor phase and on into a cooled volcanic plume. We measured three groups of metals in a small suite of samples collected on filters from the plumes of Kilauea (Hawaii, USA), Etna (Sicily), and Merapi (Java) volcanoes. These were the major, minor, and trace metals of the alkali and alkaline earth families (K, Rb, Cs, Ca, Sr, Ba), a group of ordinarily rare metals (Cd, Cu, In, Pb, Tl) that are related by their chalcophile affinities, and the radon daughter nuclides 210Po, 210Bi, and 210Pb. The measurements show the range and some details of systematic melt-vapor fractionation within and between these groups of metals. In the plumes of all three volcanoes, the alkali metals are much more abundant than the alkaline earth metals. In the Kilauea plume, the alkali metals are at least six times more abundant than the alkaline earth metals, relative to abundances in the melt; at Etna, the factor is at least 300. Fractionations within each family are, commonly, also distinctive; in the Kilauea plume, in addition to the whole alkaline earth family being depleted, the heaviest metals of the family (Sr, Ba) are progressively more depleted than the light metal Ca. In plumes of fumaroles at Merapi, K/Cs ratios were approximately three orders of magnitude smaller than found in other earth materials. This may represent the largest observed enrichment of the "light ion lithophile" (LIL) metals. Changes in metal ratios were seen through the time of eruption in the plumes of Kilauea and Etna. This may reflect degree of degassing of volatiles, with which metals complex, from the magma bodies. At Kilauea, the changes in fractionation were seen over about three years; fractionation within the alkaline earth family increased, and that between the two families decreased, over that time. All of the ordinarily rare chalcophile metals measured are extremely abundant in volcanic plumes, and Cd and Tl are enriched relative to the others. Indium is much more abundant in the plume of the hotspot volcano Kilauea than in the Etna plume (probably non-hotspot in character). It may be a useful indicator of the tapping of deep mantle zones, or could aid in the interpretation of reports of Pt group metals in exhalations from hot spot volcanoes. Indium in old glacial ice strata could help assess magnitude and variability of exhalations from hotspot volcanoes in past time. Strong melt-vapor fractionation of the alkali and alkaline earth metals may only be observed in plumes during quiescent degassing of volcanoes; when large amounts of ash or spatter (undifferentiated lava) enter the plume, its alkali and alkaline earth metal composition may approach that of the melt. Ratios among the chalcophile metals may not be much changed by addition of ash, because their concentrations in melt are so small, and masses of them in any plume may remain dominated by transfer across the melt-vapor interface. Radon daughter nuclides give information about state of volcanic activity at time of sampling. The precisely known origins, ultratrace detectability, decay systematics, and wide variations in volatility of these species provide information about residence times, degassing and travel histories, and identities of melt bodies in volcanic systems. ?? 1994.

Geochimica et Cosmochimica Acta↗
USGS2025

Climate change and future water availability in the United States

The steady rise in global temperature as a result of human activity is causing changes in Earth’s water cycle. The balance of water stored within and moving between vapor, liquid, and frozen states in the water cycle is shifting, with consequences for water availability that include increases in drought, fire weather, flooding, and heavy precipitation, as well as cryosphere decline and sea-level rise. In this chapter of the U.S. Geological Survey Integrated Water Availability Assessment—2010–20, we provide an overview of climate-change observations and projections from Earth-system model simulations that relate to future water availability, from global and national climate assessments and from the published literature. Effects of climate change on primary water-cycle components are discussed in context of how global-scale hydroclimate drivers influence regional processes within the United States. Understanding the major climate drivers impacting the water cycle is crucial to predicting future changes in water availability and developing adaptation strategies to ensure human and ecosystem water supplies. First, we provide background information on the water cycle, the climate-model ensemble simulations developed to produce projections based on warming scenarios, and attribution and certainty levels. Tipping points, self-reinforcing feedbacks, cascading effects, and compound extremes are introduced. The framework of climatic impact drivers (CIDs) outlined in the Intergovernmental Panel on Climate Change Sixth Assessment Report (IPCC AR6) is used to show primary drivers of physical change to the water cycle and to understand and predict changes in future water availability. Specific climate-change related observations and projections are discussed for water cycle components of precipitation, evapotranspiration, soil moisture, streamflow, lakes and wetlands, ice and snow, and groundwater, as well as their implications for future water availability for humans and ecosystems. The chapter concludes with a synthesis discussion of three examples of complex regional-scale hydroclimate processes that influence water availability for populations in the United States, including (1) mountain and coastal precipitation, (2) aridification and drought, and (3) the influence of forest-cover change on terrestrial water-vapor recycling.

Professional Paper↗