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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 739 records · Page 41Linked to original sources
USGS2000

Quality assurance and analysis of water levels in wells on Pahute Mesa and vicinity, Nevada Test Site, Nye County, Nevada

Periodic and continual water-level data from 1963 to 1998 were compiled and quality assured for 65 observation wells on Pahute Mesa and vicinity, Nye County, Nevada. As part of the quality assurance of all water levels, ancillary data pertinent to computing hydraulic heads in wells were compiled and analyzed. Quality-assured water levels that were not necessarily in error but which did not represent static heads in the regional aquifer system, or required some other qualification, were flagged. Water levels flagged include those recovering from recent pumping or well construction, water levels affected by nuclear tests, and measurements affected by borehole deviations. A cursory examination of about 30 wells with available water-level and down-hole temperature data indicate that water levels in most wells on Pahute Mesa would not be significantly affected by temperature if corrected to 95 degrees Fahrenheit. Wells with large corrections (greater than 10 feet) are those with long water columns (greater than 1,500 feet of water above the assumed point of inflow) in combination with mean water-column temperatures exceeding 105 degrees Fahrenheit. Water-level fluctuations in wells on Pahute Mesa are caused by several factors including infiltration of precipitation, barometric pressure, Earth tides, ground-water pumpage, and seismic events caused by tectonic activity and underground nuclear testing. No observed water-level fluctuations were attributed to a naturally occurring earthquake. The magnitude and duration of changes in water levels caused by nuclear tests are affected by the test size and the distance from a well to the test. Identifying water levels that might be affected by past nuclear tests is difficult because pre-testing water-level data are sparse. Hydrologically significant trends were found in 13 of 25 wells with multiple years of water-level record. The largest change in water levels (1,029 feet in 25 years) occurred in well U-19v PS 1D as a result of the Almendro nuclear test. Likely explanations for trends in most of the wells are either changes in precipitation patterns that affect recharge rates to the ground-water system, pumping effects from water-supply well U-20 WW, or a combination of these two factors.

Nevada↗
USGS2012

Sea-level history during the Last Interglacial complex on San Nicolas Island, California: implications for glacial isostatic adjustment processes, paleozoogeography and tectonics

San Nicolas Island, California has one of the best records of fossiliferous Quaternary marine terraces in North America, with at least fourteen terraces rising to an elevation of ~270 m above present-day sea level. In our studies of the lowest terraces, we identified platforms at 38-36 m (terrace 2a), 33-28 m (terrace 2b), and 13-8 m (terrace 1). Uranium-series dating of solitary corals from these terraces yields three clusters of ages: ~120 ka on terrace 2a (marine isotope stage [MIS] 5.5), ~120 and ~100 ka on terrace 2b (MIS 5.5 and 5.3), and ~80 ka (MIS 5.1) on terrace 1. We conclude that corals on terrace 2b that date to ~120 ka were reworked from a formerly broader terrace 2a during the ~100 ka sea stand. Fossil faunas differ on the three terraces. Isolated fragments of terrace 2a have a fauna similar to that of modern waters surrounding San Nicolas Island. A mix of extralimital southern and extralimital northern species is found on terrace 2b, and extralimital northern species are on terrace 1. On terrace 2b, with its mixed faunas, extralimital southern species, indicating warmer than present waters, are interpreted to be from the ~120 ka high sea stand, reworked from terrace 2a. The extralimital northern species on terrace 2b, indicating cooler than present waters, are interpreted to be from the ~100 ka sea stand. The abundant extralimital northern species on terrace 1 indicate cooler than present waters at ~80 ka. Using the highest elevations of the ~120 ka platform of terrace 2a, and assuming a paleo-sea level of +6 m based on previous studies, San Nicolas Island has experienced late Quaternary uplift rates of ~0.25-0.27 m/ka. These uplift rates, along with shoreline angle elevations and ages of terrace 2b (~100 ka) and terrace 1 (~80 ka) yield relative (local) paleo-sea level elevations of +2 to +6 m for the ~100 ka sea stand and -11 to -12 m for the ~80 ka sea stand. These estimates are significantly higher than those reported for the ~100 ka and ~80 ka sea stands on New Guinea and Barbados. Numerical models of the glacial isostatic adjustment (GIA) process presented here demonstrate that these differences in the high stands are expected, given the variable geographic distances between the sites and the former Laurentide and Cordilleran ice sheets. Moreover, the numerical results show that the absolute and differential elevations of the observed high stands provide a potentially important constraint on ice volumes during this time interval and on Earth structure.

California↗
USGS2000

The use of earthquake rate changes as a stress meter at Kilauea volcano

Stress changes in the Earth's crust are generally estimated from model calculations that use near-surface deformation as an observational constraint. But the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues. Although this possibility has considerable appeal, because seismicity data are routinely collected and have good spatial and temporal resolution, the method has not yet proven successful, owing to the nonlinearity of earthquake rate changes with respect to both stress and time. Here, however, we present two methods for inverting earthquake rate data to infer stress changes, using a formulation for the stress- and time-dependence of earthquake rates. Application of these methods at Kilauea volcano, in Hawaii, yields good agreement with independent estimates, indicating that earthquake rates can provide a practical remote-sensing stress meter.

Nature↗
USGS2004

Pancam multispectral imaging results from the Spirit Rover at Gusev crater

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.

Science↗
USGS1998

Geochemical evidence for a comet shower in the late Eocene

Analyses of pelagic limestones indicate that the flux of extraterrestrial helium-3 to Earth was increased for a 2.5-million year (My) period in the late Eocene. The enhancement began ~1 My before and ended ~1.5 My after the major impact events that produced the large Popigai and Chesapeake Bay craters ~36 million years ago. The correlation between increased concentrations of helium-3, a tracer of fine-grained interplanetary dust, and large impacts indicates that the abundance of Earth-crossing objects and dustiness in the inner solar system were simultaneously but only briefly enhanced. These observations provide evidence for a comet shower triggered by an impulsive perturbation of the Oort cloud.

Science↗
USGS1992

Diagenetic formation of bedded chert: Evidence from chemistry of the chert-shale couplet

Theories concerning the formation of bedded chert traditionally have emphasized either depositional or diagenetic processes. Major and rare earth element data from Franciscan assemblage (Mesozoic) and Claremont Formation (Miocene) bedded chert sequences, along with physical observations such as the presence of rare and highly corroded radiolarians in shale interbeds, are most consistent with a dominantly diagenetic origin of chert-shale couplets and are incompatible with many depositional theories. Chemical distributions between Franciscan and Claremont bedded chert=shale closely match chemical fractionations recorded by Monterey Formation and Deep Sea Drilling Project-sampled cherts formed by diagenetic SiO 2 dissolution, transport, and reprecipitation, suggesting that diagenetic migration of SiO 2 from proto-shale to proto-chert is also largely responsible for chert-shale couplets. Identical Ce anomalies (Ce/Ce*) found in immediately adjacent chert-shale layers indicate that turbidites or other transport mechanisms are not responsible for the alternating beds. Neither the chemistry of the chert-shale couplet nor the overall stratigraphy of the sequences is consistent with couplet formation being caused by productivity fluctuations. Chemical mass balance calculations reconstructing the total bulk sediment composition suggest that modern siliceous sequences do not contain enough labile biogenic SiO 2 to form entire stratigraphies of bedded chert.

Geology↗
USGS1994

Some observations of landslides triggered by the 29 April 1991 Racha earthquake, Republic of Georgia

On 29 April 1991 an M s 7.0 earthquake occurred in the Racha region of the Great Caucasus Mountains in north-central Republic of Georgia. The earthquake occurred on a thrust fault striking roughly east-west and dipping about 20° to 45° northward; focal depth was 17 ± 2 km. We observed no surface fault rupture, but the earthquake caused extensive structural damage to the many unreinforced stone buildings in the area, and at least 114 people were killed. Many landslides were triggered in a 2500-km 2 epicentral area, and they caused much of the structural damage and at least half the fatalities. We observed the following six types of landslides (in order of decreasing abundance): rock falls, debris slides, slumps, earth slides, rock block slides, and rock avalanches. The types of landslides triggered by the earthquake are controlled primarily by lithology and geologic structure. Enigmatic landslide processes associated with this earthquake include (1) delays of several days between earthquake shaking and significant landslide movement, probably caused by changes in groundwater conditions; (2) small co-seismic displacement of landslides active at the time of the earthquake, a possible result of viscoplastic damping of the seismic shaking; and (3) somewhat unusual failure geometries related to local topography and geologic structure.

Bulletin of the Seismological Society of America↗
USGS1974

Apollo 11 voice transcript pertaining to the geology of the landing site

On July 20, 1969, America's Eagle touched down in southwestern Mare Tranquillitatis beginning man's firsthand exploration of the moon. This document is an edited record of the conversations between astronauts Neil Armstrong and Edwin "Buzz" Aldrin, Jr., at Tranquility Base, and Bruce McCandless at Mission Control in Houston during the approximately 22 hours spent on the lunar surface. It includes additional commentary during their return to Earth. It is a condensation hopefully of all the verbal data having geological significance. All discussions and observations documenting the lunar landscape, its geologic characteristics, the rocks and soils collected, and the photographic record are retained along with supplementary remarks essential to the continuity of events during the mission. We have deleted the words of mechanical housekeeping and engineering data, attempting not to lose the personal and philosophical aspects of this intensely human experience. The sources of this verbal transcript are the complete audio tapes recorded during the mission and the Technical Air-to-Ground Voice Transcription published by NASA. The voice record is listed chronologically given in days, hours, minutes, and seconds. These are the Ground Elapsed Times (GET) after launch from Kennedy Space Center which was 9:32 a.m. EDT on July 16, 1969. Figure 1 shows the vicinity of the landing site that was described, sampled, and photographed by the Apollo 11 crewmen.

Final Report↗
USGS2024

Empirical ground-motion basin response in the California Great Valley, Reno, Nevada, and Portland, Oregon

We assess how well the Next-Generation Attenuation-West 2 (NGA-West2) ground-motion models (GMMs), which are used in the US Geological Survey’s (USGS) National Seismic Hazard Model (NSHM) for crustal faults in the western United States, predict the observed basin response in the Great Valley of California, the Reno basin in Nevada, and Portland and Tualatin basins in Oregon. These GMMs rely on site parameters such as the time-averaged shear-wave velocity ( V S ) in the upper 30 m of Earth’s crust ( V S30 ) and depths to 1.0 and 2.5 km/s shear-wave isosurfaces ( Z 1.0 and Z 2.5 ) to capture basin effects and were developed using observations and simulations primarily from the Los Angeles region in southern California. Using ground-motion records from mostly small-to-moderate earthquakes and mixed-effects regression analysis, we find that the GMMs perform well with our local basin-depth models for the California Great Valley. With our local basin-depth models for Reno, the GMMs do not perform as well for this relatively shallow basin and exhibit little sensitivity to the basin parameters used in the NGA-West2 GMMs. We also find good performance for the local Z 1.0 model across the Portland region, whereas the local Z 2.5 model provides little predictive power except at sites in the deepest part of the Tualatin basin. Additional work could improve the performance of the site and basin terms in the NGA-West2 GMMs for regions with geologic structure different than the deep basins in southern California and the Great Valley. In addition, we find significant discrepancies among the GMMs in how the uncertainty in the ground motion varies with basin depth and pseudospectral period. Our results can help guide seismic hazard analyses on whether to include these local basin-depth models.

Earthquake Spectra↗
USGS2015

Multiscale geophysical imaging of the critical zone

Details of Earth's shallow subsurface—a key component of the critical zone (CZ)—are largely obscured because making direct observations with sufficient density to capture natural characteristic spatial variability in physical properties is difficult. Yet this inaccessible region of the CZ is fundamental to processes that support ecosystems, society, and the environment. Geophysical methods provide a means for remotely examining CZ form and function over length scales that span centimeters to kilometers. Here we present a review highlighting the application of geophysical methods to CZ science research questions. In particular, we consider the application of geophysical methods to map the geometry of structural features such as regolith thickness, lithological boundaries, permafrost extent, snow thickness, or shallow root zones. Combined with knowledge of structure, we discuss how geophysical observations are used to understand CZ processes. Fluxes between snow, surface water, and groundwater affect weathering, groundwater resources, and chemical and nutrient exports to rivers. The exchange of gas between soil and the atmosphere have been studied using geophysical methods in wetland areas. Indirect geophysical methods are a natural and necessary complement to direct observations obtained by drilling or field mapping. Direct measurements should be used to calibrate geophysical estimates, which can then be used to extrapolate interpretations over larger areas or to monitor changing processes over time. Advances in geophysical instrumentation and computational approaches for integrating different types of data have great potential to fill gaps in our understanding of the shallow subsurface portion of the CZ and should be integrated where possible in future CZ research.

Reviews of Geophysics↗
USGS2013

U–Pb, Rb–Sr, and U-series isotope geochemistry of rocks and fracture minerals from the Chalk River Laboratories site, Grenville Province, Ontario, Canada

As part of the Geologic Waste Management Facility feasibility study, Atomic Energy of Canada Ltd. (AECL) is evaluating the suitability of the Chalk River Laboratories (CRL) site in Ontario, situated in crystalline rock of the southwestern Grenville Province, for the possible development of an underground repository for low- and intermediate-level nuclear waste. This paper presents petrographic and trace element analyses, U–Pb zircon dating results, and Rb–Sr, U–Pb and U-series isotopic analyses of gneissic drill core samples from the deep CRG-series characterization boreholes at the CRL site. The main rock types intersected in the boreholes include hornblende–biotite (±pyroxene) gneisses of granitic to granodioritic composition, leucocratic granitic gneisses with sparse mafic minerals, and garnet-bearing gneisses with variable amounts of biotite and/or hornblende. The trace element data for whole-rock samples plot in the fields of within-plate, syn-collision, and volcanic arc-type granites in discrimination diagrams used for the tectonic interpretation of granitic rocks. Zircons separated from biotite gneiss and metagranite samples yielded SHRIMP-RG U–Pb ages of 1472 ± 14 (2 σ ) and 1045 ± 6 Ma, respectively, in very good agreement with widespread Early Mesoproterozoic plutonic ages and Ottawan orogeny ages in the Central Gneiss Belt. The Rb–Sr, U–Pb, and Pb–Pb whole-rock errorchron apparent ages of most of the CRL gneiss samples are consistent with zircon U–Pb age and do not indicate substantial large-scale preferential element mobility during superimposed metamorphic and water/rock interaction processes. This may confirm the integrity of the rock mass, which is a positive attribute for a potential nuclear waste repository. Most 234 U/ 238 U activity ratios (AR) in whole rock samples are within errors of the secular equilibrium value of one, indicating that the rocks have not experienced any appreciable U loss or gain within the past 1 Ma. However, 234 U/ 238 U AR in fracture mineral samples collected down to borehole lengths of about 740 m deviate from the secular equilibrium value and 234 U/ 238 U model ages calculated for fracture mineral samples showing excess 234 U range from 593 to 1415 ka, thus providing evidence of fracture flow in the associated bedrock during the past 1.5 Ma. Rare earth element patterns are variable in fracture-filling calcites and Fe oxides/hydroxides but are similar to those observed in associated whole-rock samples. The observed Ce anomalies are very small ( Ce N / Ce N ∗ ≈ 1 "> CeN/CeN∗≈1 ), do not vary with depth, and, therefore, do not contain evidence that the studied fracture minerals precipitated from oxidizing waters at the conceptual depth of a repository.

Ontario↗
USGS2019

Stormquakes

Seismic signals from ocean-solid Earth interactions are ubiquitously recorded on our planet. However, these wavefields are typically incoherent in most frequency bands limiting their utilization for understanding ocean dynamics or solid Earth properties. In contrast, we find that during large storms such as hurricanes and Nor’easters the interaction of long-period ocean waves with shallow seafloor features located near the edge of continental shelfs, known as ocean banks, excites coherent transcontinental Rayleigh wave packets in the 20 to 50 s period band. These “stormquakes” migrate coincident with the storms, but are spatiotemporally focused seismic point sources with equivalent earthquake magnitudes that can be greater than 3.5. Stormquakes thus provide new coherent sources to investigate Earth structure in locations that typically lack both seismic instrumentation and earthquakes. Moreover, they provide a new geophysical observable with high spatial and temporal resolution with which to investigate ocean wave dynamics during large storms.

Geophysical Research Letters↗
USGS2006

Comment on “222Rn Premonitory signals for earthquakes?”

Radon and other terrestrial gases in groundwater and soil air have been studied in recent years in seismically active areas, especially in China, Japan, the former Soviet Union, and the United States, in search of changes that may be useful for earthquake prediction. Concentrations of radon, helim, hydrogen, mercury vapor, carbon dioxide, and several other gases have been found to be high along active faults. Faults may thus be paths of least resistance along which terrestrial gases generated or stored in the Earth can escape into the atmosphere. Gas-concentration changes with durations of hours to months have been observed before and after earthquakes at relatively few favorably situated sites, and their patterns have not always been repeated. Some of these sites are located as far as several hundred kilometers away from earthquake epicenters. These “sensitive” sites are generally situated along active faults, whether the seismogenic ones or not, especially at their intersections or bends, or at other structurally weak zones, possibly because of concentration of tectonic strain and abundance of pore fluids at such places (see review papers by King , 1986, 1990). Due to this selectivity and for two other important reasons, studies of terrestrial gases for earthquake prediction have not been viewed favorably by most geophysicists, especially those in the United States.

Eos Science News↗
USGS2017

A land data assimilation system for sub-Saharan Africa food and water security applications

Seasonal agricultural drought monitoring systems, which rely on satellite remote sensing and land surface models (LSMs), are important for disaster risk reduction and famine early warning. These systems require the best available weather inputs, as well as a long-term historical record to contextualize current observations. This article introduces the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (FLDAS), a custom instance of the NASA Land Information System (LIS) framework. The FLDAS is routinely used to produce multi-model and multi-forcing estimates of hydro-climate states and fluxes over semi-arid, food insecure regions of Africa. These modeled data and derived products, like soil moisture percentiles and water availability, were designed and are currently used to complement FEWS NET’s operational remotely sensed rainfall, evapotranspiration, and vegetation observations. The 30+ years of monthly outputs from the FLDAS simulations are publicly available from the NASA Goddard Earth Science Data and Information Services Center (GES DISC) and recommended for use in hydroclimate studies, early warning applications, and by agro-meteorological scientists in Eastern, Southern, and Western Africa.

Scientific Data↗
USGS2024

Polar paleoenvironmental perspectives on modern climate change

In today’s rapidly changing climate, society needs a better understanding of climate impacts on sea level, ice sheets and glaciers, sea ice, ocean circulation, ecosystems, biodiversity, and other aspects of planet Earth. Paleoenvironmental records provide a unique and invaluable source of insight into these complex issues, and place recent observations into a broader historical context. This essay discusses why paleoclimate reconstructions from polar regions provide critical information to help anticipate possible future climate impacts. By highlighting some key research examples, this essay explains the value of expanding proxy-based research in Arctic/Antarctic regions, and makes a case for paying greater attention to the lessons already distilled from it.

PLOS Climate↗
USGS2026

High-resolution transboundary vegetation community maps of the Sonoran and Mojave Desert ecoregion to support critical landscape conservation planning and habitat management needs

We produced a 30-m resolution binational land cover map of Bird Conservation Region 33 (BCR 33) for the U.S. North American Bird Conservation Initiative. The region covers large portions of the Sonoran and Mojave Deserts. The map can support the U.S. Fish and Wildlife Service (FWS) Migratory Bird Program’s recovery planning efforts and constitutes the first known binational land cover dataset spanning sections of the United States–Mexico border and using a consistent classification system for both countries. The mapped region includes 152 distinct land cover classes, covering a total area of 38,421,453 ha (148,345 mi 2 ), of which 13,148,345 ha (52,706 mi 2 ) are located in Mexico and 24,770,640 ha (95,639 mi 2 ) in the United States. We primarily used Landsat 8 (OLI) imagery, supplemented by limited ground surveys from two field campaigns, drone-based aerial data, and existing vegetation classification frameworks from both countries. The classification applied a data-fusion approach integrating 30-m Landsat 8 imagery, decadal phenology metrics from vegetation indices, and a random forest model trained mainly with datasets from a comprehensive national mapping project from the U.S. Geological Survey (USGS) GAP Analysis Project (GAP) and federal wildland fire agencies’ Landscape Fire and Resource Management Planning Tools (LANDFIRE) (GAP/LANDFIRE) [United States side] and the National Institute of Statistics and Geography (INEGI) [Mexico side] as well as land cover maps and opportunistic open-access and field observations. Mapping of the full BCR 33 region was carried out in two phases: 1) Phase I, the prototype map, covered a smaller portion of the transboundary area and identified 31 land cover classes, and 2) Phase II, the full BCR 33 map (refer to Figure 1), which resulted in 152 land cover classes. Using a Random Forest classifier, we achieved an overall prediction accuracy of 92% for the Phase I map and 87% for the Phase II full region map. This slight decrease can be attributed to working on a larger, more complex area with a greater number of land cover classes. No formal validation was conducted, aside from using a subset of the collected field observations and training data to assess model performance during and after training. The training sites were further verified using Google Earth (Google, 2026) imagery. Two undergraduate students who worked for over a year visually inspected imagery and open access public images to confirm each training site during model training using in-house developed, online, visual tools. A portion of this field training data was reserved for model validation, and the corresponding results are to be presented in later sections. The project developed an end-to-end, medium- and fine-resolution remote sensing–based data fusion mapping approach. This effort produced a map (Nagler et al., 2025) and the online tools to support a dynamic, live, online map for visualizing the transboundary vegetation communities in BCR 33. The toolset is currently hosted by the University of Arizona (UofA) Vegetation Index and Phenology (VIP) Lab to support FWS partners (https://vip.arizona.edu/viplab_data_explorer?LCM_BCR33). The online map is designed to allow rapid updates using new training, validation, or correction data, making it dynamic and maintainable. The approach we took established a framework for rapid updating and correction of land cover maps, as the model can be quickly retrained with new field observations, updated training data, or other sources. This enables dynamic mapping and change detection of the region’s vegetation. This framework is an advance in data fusion and crowdsourced mapping of complex, vulnerable regions, providing support to regional stakeholders and the wider user community. This transboundary map can inform the protection, conservation, and restoration of vegetation, habitat, and ecosystems, particularly for threatened and endangered species across the two nations using consistent and harmonized binational mapping systems. Beyond supporting land management decisions and stakeholders in the transboundary desert ecoregions, this BCR 33 mapping effort establishes a foundation for future rapid, low-cost, cross-border land cover mapping that can benefit and advance ecosystem management.

Arizona, Baja California, California, Nevada, Sina↗
USGS1981

Rare-earth element geochemistry of the island-arc volcanic rocks of Rabaul and Talasea, New Britain

The island-arc volcanic rocks of Rabaul and Talasea, New Britain, range in composition from basalt through rhyolite. Rare-earth elements have been determined by mass-spectrometric isotope dilution in 16 samples. Chondrite-normalized rare-earth element patterns are distinct for each volcanic center, but all are relatively flat (Ce/Yb E.F. = 1.1 to 3.0). Within each center, rare-earth element concentrations increase from basalt to dacite, and Eu anomalies become progressively more negative from basalt to dacite (Eu/Eu* = 1.0 to 0.8). Lavas inferred to contain cumulate phenocrysts show positive Eu anomalies (Eu/Eu* of up to 1.2). The observed variations are consistent with fractional crystallization of basalt or basaltic andesite by removal or accumulation of the observed phenocrysts, including olivine, plagioclase, pyroxene, and opaque minerals. Quantitative trace-element models for Talasea lavas indicate precipitation of 50 wt percent of phenocrysts from basalt to produce andesite and an additional 22 wt percent to produce dacite. A total-equilibrium model provides the best approximation to observed concentrations, implying that the process took place at a depth sufficient to allow slow cooling of the magma as precipitation proceeded. The “least fractionated” basalts and basaltic andesites are similar in rare-earth element pattern to those of corresponding type suites in other oceanic-island arcs, implying a widespread uniformity of source and process in the production of each magma type.

Geological Society of America Bulletin↗