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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 1,621 records · Page 90Linked to original sources
USGS1977

A reconnaissance investigation of a large meromictic lake in southeastern Alaska

Redoubt Lake is one of the largest documented meromictic lakes in North America. The chemocline extends in depth from 80 to 100 m (meters) and the steepest gradient is between 98 and 100 m. The monimolimnion is anoxic, contains hydrogen sulflde, and has a salinity about two-thirds that of seawater. Turnover appears to introduce additional sodium chloride from the chemocline to the mixolimnion, but diffusion is probably the dominant mixing mechanism. Vertical profiles show a dichothermic temperature curve. A minimum temperature of 3°C in the chemocline is unexplained, but higher temperatures in the monimolimnion may be a result of solar radiation. At the lower limit of the chemocline there is a sharp decrease in pH, which could be due to bacterial action. Redoubt Lake is probably a relict fiord. The data presented herein support the hypothesis that the lake was gradually isolated from the sea by uplift. While seawater was entering the lake, it probably mixed with the freshwater in the mixolimnion and therefore the monimolimnion is less saline than seawater. Geologic and geophysical evidence support the speculation that significant amounts of saltwater inflow probably ceased about 650-800 years before the present.

Alaska↗
USGS2015

The U.S. Geological Survey Geologic Collections Management System (GCMS)—A master catalog and collections management plan for U.S. Geological Survey geologic samples and sample collections

**Updated guidance is available in USGS Instructional Memorandum CSS 2019-01 .** Abstract The U.S. Geological Survey (USGS) is widely recognized in the earth science community as possessing extensive collections of earth materials collected by research personnel over the course of its history. In 2006, a Geologic Collections Inventory was conducted within the USGS Geology Discipline to determine the extent and nature of its sample collections, and in 2008, a working group was convened by the USGS National Geologic and Geophysical Data Preservation Program to examine ways in which these collections could be coordinated, cataloged, and made available to researchers both inside and outside the USGS. The charge to this working group was to evaluate the proposition of creating a Geologic Collections Management System (GCMS), a centralized database that would (1) identify all existing USGS geologic collections, regardless of size, (2) create a virtual link among the collections, and (3) provide a way for scientists and other researchers to obtain access to the samples and data in which they are interested. Additionally, the group was instructed to develop criteria for evaluating current collections and to establish an operating plan and set of standard practices for handling, identifying, and managing future sample collections. Policies and procedures promoted by the GCMS would be based on extant best practices established by the National Science Foundation and the Smithsonian Institution. The resulting report—USGS Circular 1410, “The U.S. Geological Survey Geologic Collections Management System (GCMS): A Master Catalog and Collections Management Plan for U.S. Geological Survey Geologic Samples and Sample Collections”—has been developed for sample repositories to be a guide to establishing common practices in the collection, retention, and disposal of geologic research materials throughout the USGS. While constructing this report, the GCMS’s potential customers and their needs were considered. Two critical definitions have been clarified: a repository is a facility for the long-term management of geologic collections, and a collection is a set of specimens that have been brought together on the basis of some common characteristic. Required sample metadata for newly collected samples, as well as for older collections, were also stipulated and are listed and explained in this report. Several basic policies are also recommended by the GCMS in order to standardize operations among the physical repositories where collections are currently housed. The GCMS Collection Management Plan provides a set of protocols and templates for the management of scientific collections, including access, storage, transfer, and disposal of physical geologic samples and data. This plan is flexible to allow each repository to adapt the practices best suited to its collections. The general consideration for implementation of the GCMS is that all active USGS geologic sample repositories will form the core of GCMS and that participating science centers will develop procedures based on proposed GCMS methodologies. The GCMS is a collective resource for the entire USGS community and the users who discover the geologic materials kept in these repositories and seek to access them.

Circular↗
USGS2007

Kinematic GPS solutions for aircraft trajectories: Identifying and minimizing systematic height errors associated with atmospheric propagation delays

When kinematic GPS processing software is used to estimate the trajectory of an aircraft, unless the delays imposed on the GPS signals by the atmosphere are either estimated or calibrated via external observations, then vertical height errors of decimeters can occur. This problem is clearly manifested when the aircraft is positioned against multiple base stations in areas of pronounced topography because the aircraft height solutions obtained using different base stations will tend to be mutually offset, or biased, in proportion to the elevation differences between the base stations. When performing kinematic surveys in areas with significant topography it should be standard procedure to use multiple base stations, and to separate them vertically to the maximum extent possible, since it will then be much easier to detect mis-modeling of the atmosphere. Copyright 2007 by the American Geophysical Union.

Geophysical Research Letters↗
USGS1998

Geology, geochemistry, geophysics, mineral occurrences, and mineral resource assessment for the Commonwealth of Puerto Rico

The Commonwealth of Puerto Rico has been investigated over a very long period of time by earth scientists from many disciplines and with diverse objectives in the studies. This publication attempts to apply much of the geologic, geochemical, geophysical, and mineral occurrence information to a single objective focused on producing a mineral resource assessment for the Commonwealth of Puerto Rico. However, the value of this publication lies not within the results of the mineral resource assessment nor within the interactive PDF files which can be viewed on the screen, but within the geologic, geochemical, geophysical, and mineral occurrence digital map coverages and databases which can be used for their own unique applications. The mineral resource assessment of Puerto Rico represents compilation of several decades of mineral investigations and studies. These investigations have been the joint efforts of the U.S. Geological Survey, the Puerto Rico Department of Natural Resources, and the University of Puerto Rico. This report contains not only the mineral-resource assessment, but also much of the scientific evidence upon which the assessment was based.

Puerto Rico↗
USGS1981

Geophysical reconnaissance of Lemmon Valley, Washoe County, Nevada

Rapid growth in the Lemmon Valley area, Nevada, during recent years has put increasing importance on knowledge of stored ground water for the valley. Data that would fill voids left by previous studies are depth to bedrock and depth to good-quality water beneath the two playas in the valley. Depths to bedrock calculated from a gravity survey in Lemmon Valley indicate that the western part of Lemmon Valley is considerably deeper than the eastern part. Maximum depth in the western part is about 2 ,600 feet below land surface. This depression approximately underlies the Silver Lake playa. A smaller, shallower depression with a maximum depth of about 1,500 feet below land surface exists about 2.5 miles north of the playa. The eastern area is considerably shallower. The maximum calculated depth to bedrock is about 1,000 feet below land surface, but the depth throughout most the eastern area is only about 400 feet below land surface. An electrical resistivity survey in Lemmon Valley consisting of 10 Schlumberger soundings was conducted around the playas. The maximum depth of poor-quality water (characterized by a resistivity less than 20 ohm-meters) differed considerably from place to place. Maximum depths of poor-quality water beneath the playa east of Stead varied from about 120 feet to almost 570 feet below land surface. At the Silver Lake playa, the maximum depths varied from about 40 feet in the west to 490 feet in the east. (USGS)

Open-File Report↗
USGS2012

Integrated characterization of the geologic framework of a contaminated site in West Trenton, New Jersey

Fractured sedimentary bedrock and groundwater at the former Naval Air Warfare Center in West Trenton, New Jersey (United States of America) are contaminated with chlorinated solvents. Predicting contaminant migration or removing the contaminants requires an understanding of the geology. Consequently, the geologic framework near the site was characterized with four different methods having different spatial scales: geologic field mapping, analyses of bedrock drill core, analyses of soil and regolith, and S-wave refraction surveys. A fault zone is in the southeast corner of the site and separates two distinct sedimentary formations; the fault zone dips (steeply) southeasterly, strikes northeasterly, and extends at least 550 m along its strike direction. Drill core from the fault zone is extensively brecciated and includes evidence of tectonic contraction. Approximately 300 m east of this fault zone is another fault zone, which offsets the contact between the two sedimentary formations. The S-wave refraction surveys identified both fault zones beneath soil and regolith and thereby provided constraints on their lateral extent and location.

New Jersey↗
USGS1959

The petroleum potential of the emerged and submerged Atlantic coastal plain of the United States

Increasing geological and geophysical information about the Atlantic continental shelf of the United States is changing the basis for judging the area's petroleum potential. No nation can afford to overlook an area that overlies 175,000 cubic miles (730,000 km 3 ) of possibly petroliferous sediments (including the emerged coastal plain), though the first barrel of oil is yet to be produced. Seismic and magnetic surveys indicate that the basement is deeper and more irregular than previously supposed and that a basement ridge may separate the shelf sediments into two major elongate basins parallel to the shelf edge, thus forming possible entrapping structures and possibly restricted depositional basins. Lower Paleozoic clastic rocks found in the subsurface of Georgia and Florida, and which may occur elsewhere in downfaulted basins, could be source beds and reservoir rocks for oil and gas over wide areas. Lower Cretaceous, Upper Jurassic( ?), and Triassic sedimentary rocks recognized in some wells must wedge out updip, and numerous unconformities probably occur. The marine sediments were presumably deposited in or close to shelf areas that possibly contain reefs and are partially bordered by known granite washes; thus both source and reservoir rocks are probably present. It can be expected that petroleum will eventually be discovered beneath the continental shelf and perhaps the emerged coastal plain, but it will not be discovered (economic factors aside) until geologists have projected paleogeographic settings into the sediments beneath the shelf from the data obtained through onshore and submarine geology, drilling, and geophysics.

Conference Paper↗
USGS2011

Time-domain electromagnetic soundings collected in Dawson County, Nebraska, 2007-09

Between April 2007 and November 2009, the U.S. Geological Survey, in cooperation with the Central Platte Natural Resources District, collected time-domain electro-magnetic (TDEM) soundings at 14 locations in Dawson County, Nebraska. The TDEM soundings provide information pertaining to the hydrogeology at each of 23 sites at the 14 locations; 30 TDEM surface geophysical soundings were collected at the 14 locations to develop smooth and layered-earth resistivity models of the subsurface at each site. The soundings yield estimates of subsurface electrical resistivity; variations in subsurface electrical resistivity can be correlated with hydrogeologic and stratigraphic units. Results from each sounding were used to calculate resistivity to depths of approximately 90-130 meters (depending on loop size) below the land surface. Geonics Protem 47 and 57 systems, as well as the Alpha Geoscience TerraTEM, were used to collect the TDEM soundings (voltage data from which resistivity is calculated). For each sounding, voltage data were averaged and evaluated statistically before inversion (inverse modeling). Inverse modeling is the process of creating an estimate of the true distribution of subsurface resistivity from the mea-sured apparent resistivity obtained from TDEM soundings. Smooth and layered-earth models were generated for each sounding. A smooth model is a vertical delineation of calculated apparent resistivity that represents a non-unique estimate of the true resistivity. Ridge regression (Interpex Limited, 1996) was used by the inversion software in a series of iterations to create a smooth model consisting of 24-30 layers for each sounding site. Layered-earth models were then generated based on results of smooth modeling. The layered-earth models are simplified (generally 1 to 6 layers) to represent geologic units with depth. Throughout the area, the layered-earth models range from 2 to 4 layers, depending on observed inflections in the raw data and smooth model inversions. The TDEM data collected were considered good results on the basis of root mean square errors calculated after inversion modeling, comparisons with borehole geophysical logging, and repeatability.

Nebraska↗
USGS1980

Map showing a deep-tow geophysical study of the north end of the San Clemente Fault, California Borderland

A deep-tow geophysical study of a small ridge along the north end of the San Clemente fault, informally termed Kimki Ridge by Arne Junger and J.G. Vedder (unpub. data, 1979), was conducted in April 1976 using the R/V Melville of the Scripps Institution of Oceanography. The purpose of the survey was to search for evidence of active faulting along the north-ward extension of the San Clemente fault, a major structural feature in the California Borderland (fig. 1).

California↗
USGS1990

Continuous seismic reflection profiling of hydrogeologic features beneath New River, Camp Lejeune, North Carolina

A medium-power, wide-frequency seismic system was used to collect more than 100 miles of continuous seismic reflection profiling data over a 4- day period along a 24-mile segment of the New River estuary and Intracoastal Waterway. The seismic reflection data were evaluated to determine the continuity of aquifer sediments and correlation with existing borehole geophysical well-log data at the Base. Results indicate that the Castle Hayne aquifer, the major source of freshwater for the military base and surrounding area, and deeper aquifers are continuous beds that gently dip to the southeast. However, immediately above the Castle Hayne aquifer, the survey showed that sediment beds are thin and discontinuous. This not only allows rainfall to more easily percolate and recharge the aquifer, but also makes the Castle Hayne more vulnerable to contamination.

North Carolina↗
USGS1998

An application of well data in oil and gas assessment-arctic national wildlife refuge

A current assessment of oil and gas resources in the Arctic National Wildlife Refuge (ANWR) 1002 Area by the U.S. Geological Survey relies upon seismic data, geological mapping of exposures south and west of the assessment area, and exploratory wells. Information obtained from wells up to 50 km west and north of ANWR is presented. It is emphasized that the synthesis of well data with other geological and geophysical data provides a quantitative foundation for resource estimates of ANWR.

Conference Paper↗
USGS2014

Report of committee on glaciers, April 1939

The Committee on Glaciers at present is constituted as follows: Harry Fielding Reid—Professor‐Emeritus of Geology, Johns Hopkins University (former member of the International Glacier Commission), 608 Cathedral Street, Baltimore, Maryland William H. Hobbs—Professor‐Emeritus of Geology, University of Michigan (until recently Vice‐ President of the International Glacier Commission, at present associate member), Ann Arbor, Michigan J. E. Church—Professor of Classics, University of Nevada (President of the International Commission of Snow, and Chairman of the Committee on Snow of the Section of Hydrology, American Geophysical Union), Reno, Nevada Colonel Lawrence Martin—Chief of the Division of Maps, Library of Congress, Washington, D. C. Wm. Osgood Field, Jr.—Explorer, 18 West Twelfth Street, New York, N.Y. Earl A. Trager—Chief of the Naturalist Division, National Park Service, Washington, D. C. Glenn L. Parker—District Engineer, Water Resources Branch, United States Geological Survey, 406 Federal Building, Tacoma, Washington Oliver Kehrlein—Chairman, Committee on Glacier Studies, Sierra Club, 1050 Mills Tower, San Francisco, California Kenneth N. Phillips—Associate Hydraulic Engineer, Water Resources Branch, United States Geological Survey, Chairman, Research Committee of the Mazamas, 606 Post‐Office Building, Portland, Oregon William S. Cooper—Professor of Botany, University of Minnesota, Minneapolis, Minnesota Gerald FitzGerald, Senior Topographic Engineer, Alaska Branch, United States Geological Survey, Washington, D.C. Laurence M. Gould, Professor of Geology, Carleton College, Northfield, Minnesota François E. Matthes, Chairman , Senior Geologist, Section of Glacial Geology, United States Geological Survey (titular member of the International Glacier Commission), Washington, D.C. In 1938, as in previous years, the Committee devoted its energies primarily to the collecting of data on the variations in length and volume of American glaciers, it being felt that the maintenance of a continuous record of these variations is of prime importance, not only to hydrology and glaciology, but, as has become increasingly evident recently, also to climatology, geomorphology, geography, ecology, history, and archaeology. As the time available for the work of the Committee is limited and does not permit covering the entire field of glaciology, it seems best to devote it before all else to this line of research which yields results of value to so many different sciences. Besides, the gathering of data on glacier‐oscillations is not a one‐man job that can be taken up or dropped at convenience from time to time, but is an organized and far‐flung enterprise whose success depends upon the faithful cooperation of many volunteer workers located in different parts of the country. Such an enterprise, once launched, must be kept running or it will disintegrate and the precious enthusiasm of the field‐workers will be lost.

Eos, Transactions, American Geophysical Union↗
USGS2011

Survey explores active tectonics in northeastern Caribbean

There is renewed interest in studying the active and complex northeastern Caribbean plate boundary to better understand subduction zone processes and for earthquake and tsunami hazard assessments [e.g., ten Brink and Lin , 2004; ten Brink et al ., 2004; Grindlay et al ., 2005]. To study the active tectonics of this plate boundary, the GEOPRICO-DO (Geological, Puerto Rico-Dominican) marine geophysical cruise, carried out between 28 March and 17 April 2005 (Figure 1), studied the active tectonics of this plate boundary. Initial findings from the cruise have revealed a large underwater landslide, and active faults on the seafloor (Figures 2a and 2c). These findings indicate that the islands within this region face a high risk from tsunami hazards, and that local governments should be alerted in order to develop and coordinate possible mitigation strategies.

Eos, Transactions, American Geophysical Union↗
USGS2014

The channel‐storage method of determining effluent seepage

Some years ago the senior author, in collaboration with Norah Dowell Stearns, undertook to make a monthly inventory of the water‐supply of the Pomperaug River Basin, in Connecticut, from a study of data obtained by A. J. Ellis from 1913 to 1916. For this purpose approximate determinations or estimates were made of the ground‐water runoff, that is, of the part of the daily discharge of the river that consisted of water derived from the zone of saturation by effluent seepage. The determinations or estimates were essentially based on the assumption that after a week of fair weather the storm‐water was all discharged and that until the next rain the runoff was essentially all ground‐water (U.S. Geol, Surv. Water‐Supply Paper 597, pp. 107–116 and pi. 19, 1929). In the discussion of the methods and results of this investigation, the following statement was made (Water‐Supply Paper 597, pp. 145–146): “In this investigation the estimates of ground‐water runoff were based on the discharge of the Pomperaug at Bennetts Bridge—that is, on the discharge during the periods between rains, when there was virtually no direct runoff left in the stream‐system. Much better results could be obtained by basing the estimates on periods beginning as soon after rains as all of the direct runoff has reached the streams. With this method the ground‐water runoff during any particular day would be the total runoff minus the decrease in stream‐storage. The decrease in stream‐storage could be estimated by maintaining gages at several points on the trunk‐stream and on selected tributaries and making surveys of the stream‐system showing the approximate water‐areas of different parts of the system at different gage‐heights.”

Eos, Transactions, American Geophysical Union↗
USGS2008

Magnetic monitoring of earth and space

For centuries, navigators of the world’s oceans have been familiar with an effect of Earth’s magnetic field: It imparts a directional preference to the needle of a compass. Although in some settings magnetic orientation remains important, the modern science of geomagnetismhas emerged from its romantic nautical origins and developed into a subject of great depth and diversity. The geomagnetic field is used to explore the dynamics of Earth’s interior and its surrounding space environment, and geomagnetic data are used for geophysical mapping, mineral exploration, risk mitigation, and other practical applications. A global distribution of ground-based magnetic observatories supports those pursuits by providing accurate records of the magnetic-field direction and intensity at fixed locations and over long periods of time. Magnetic observatories were first established in the early 19th century in response to the influence of Alexander von Humboldt and Carl Friedrich Gauss. Since then, magnetic measurement has advanced significantly, progressing from simple visual readings of magnetic survey instruments to include automatic photographic measurement and modern electronic acquisition. To satisfy the needs of the scientific community, observatories are being upgraded to collect data that meet ever more stringent standards, to achieve higher acquisition frequencies, and to disseminate data in real time. To appreciate why data from magnetic observatories can be used for so many purposes, one needs only to recall that the geomagnetic field is a continuum, connecting the different parts of Earth to each other and to nearby space. Beneath our feet and above our heads, electric currents generate magnetic fields that contribute to the totality of the geomagnetic field measured at an observatory on Earth’s surface. The many physical processes that operate in each geophysical domain give rise to a complicated field that exhibits a wide variety of time-dependent behavior. In this article I review the status of the global community of magnetic observatories, show how Earth and space can be monitored for purposes of scientific understanding and practical application, and highlight the role played by magnetic observatories in the history of geomagnetism research.

Physics Today↗
USGS1968

Seismic survey in the region of recent earthquake activity near Denver, Colorado

A seismic -reflection survey was carried out near Denver , Colorado , for the U. S. Geological Survey , to determine if structures exist in the 12,000-ft sedimentary section or in the Precambrian basement that might explain the recent earthquake activity . No major faults were revealed in the sedimentary section. Reflections from a steeply dipping horizon believed to be in the basement complex may be indicative of faulting; however, the magnitude cannot be ascertained, as reflection events cannot be correlated at these depths. The results of the survey suggest the possibility of monitoring and studying subsurface structural conditions and related parameters in regions of seismic activity and/or suspected zones of tectonic instability.

Colorado↗
USGS2006

Effects of spatially variable resolution on field-scale estimates of tracer concentration from electrical inversions using Archie's law

Two important mechanisms affect our ability to estimate solute concentrations quantitatively from the inversion of field-scale electrical resistivity tomography (ERT) data: (1) the spatially variable physical processes that govern the flow of current as well as the variation of physical properties in space and (2) the overparameterization of inverse models, which requires the imposition of a smoothing constraint (regularization) to facilitate convergence of the inverse solution. Based on analyses of field and synthetic data, we find that the ability of ERT to recover the 3D shape and magnitudes of a migrating conductive target is spatially variable. Additionally, the application of Archie's law to tomograms from field ERT data produced solute concentrations that are consistently less than 10% of point measurements collected in the field and estimated from transport modeling. Estimates of concentration from ERT using Archie's law only fit measured solute concentrations if the apparent formation factor is varied with space and time and allowed to take on unreasonably high values. Our analysis suggests that the inability to find a single petrophysical relation in space and time between concentration and electrical resistivity is largely an effect of two properties of ERT surveys: (1) decreased sensitivity of ERT to detect the target plume with increasing distance from the electrodes and (2) the smoothing imprint of regularization used in inversion.

Geophysics↗
USGS1983

Petroleum and mineral resources of Antarctica

No known petroleum or mineral resources occur in Antarctica. The data on these subjects have been collected, mainly since the IGY (International Geophysical Year), 1957-58, as a part of other research carried out by geologists and geophysicists from a number of countries. Specific resource-related studies have not been made. Wright and Williams (1974) summarized what was known of Antarctic mineral resources a decade ago. The U.S. Geological Survey has been actively pursuing various investigations in Antarctica since 194 7. In the course of this work and that of our colleagues elsewhere in the United States and in other countries, much information relevant to petroleum and mineral resources has been obtained. Since 1976, modern state-of-the-art multichannel seismic reflection and aeromagnetic surveys by several countries over the continental margin of Antarctica have indicated thick sedimentary basins. However, no offshore drilling beneath the continental shelf has taken place since the DSDP (Deep Sea Drilling Project) holes in the Ross Sea in 1973. Geologic field investigations begun at the turn of the twentieth century have been intensified in the past two decades; most rock outcrops have been visited and samples collected. Technology to exploit resources, particularly in the Arctic, has been developing at a rapid rate, and much of it could be applied to Antarctica. As a result of the petroleum price increases of the past decade, the attention of a number of countries has turned to Antarctica, but under the policy of "voluntary restraint" adopted by the Antarctic Treaty nations, no active petroleum or mineral exploration is taking place. The Antarctic treaty countries are in the process of negotiating an Antarctic mineral resources regime that is anticipated to be completed within the next several years. Therefore it seemed timely to us to readdress the question of petroleum and mineral resources. These reports review and summarize the available information. The first report summarizes the information relevant to petroleum resources. Although uneconomic at present, petroleum is generally considered more likely to be exploited (if supergiant fields were ever found) in the next few decades than hard minerals. The second report reviews the reported occurrences of minerals in Antarctica and discusses their significance. The final report discusses the Dufek layered mafic intrusion, second only to the Bushveld Complex in size in the world; the Dufek intrusion might be considered as a potential target for mineral exploration.

Circular↗