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At least 883 records · Page 49Linked to original sources

USGS1995

Hydrochemistry of aquifer systems and relation to regional flow patterns in Cretaceous and older rocks underlying Kansas, Nebraska, and parts of Arkansas, Colorado, Missouri, New Mexico, Oklahoma, South Dakota, Texas, and Wyoming

Aquifer systems in Cretaceous and older rocks of the Central Midwest are divided on the basis of hydrochemistry and ground-water flow patterns in the Plains subregion, the Western Interior Plains aquifer system contains sodium chloride type water with large concentrations of dissolved solids. Ion ratios suggest that the water was derived from seawater by concentration and by depletion of calcium and sulfate ions. In the overlying Western Interior Plains confining system, concentrations of depositional sea water and dissolution of extensive evaporite deposits have resulted in sodium chloride type water with large concentrations of dissolved solids and sodium. Overlying this confining system in the northwest part of the study area, the Great Plains aquifer system yields water that generally is less mineralized and more variable in water type than the underlying systems. Recharge of meteoric water, concentration of brackish water in which the rocks were deposited, and dissolution of underlying evaporite deposits have contributed to the observed water chemistry. The Great Plains confining system restricts the exchange of water between the underlying Great Plains aquifer system and the overlying unconfined aquifers. In the Ozark subregion, geological units equivalent to the Western Interior Plains aquifer system comprise the Ozark Plateaus aquifer system. Units of this aquifer system are exposed at the land surface, and fresh meteoric water moves rapidly through fractures and solution openings. Water chemistry in this system reflects primarily the dissolution of the predominately carbonate rocks.

Water-Resources Investigations Report↗

USGS1973

Hydrologic conditions in the Lakeland Ridge area of Polk County, Florida

The Lakeland ridge area of this investigation covers about 300 square miles in northwest Polk County in central Florida. The growth of industry, phosphate mining, and citrus production as well as population growth during the last two decades has resulted in an increase in ground-water pumpage from about 11 billion gallons in 1950 to 27 billion gallons in 1970.

Florida↗

USGS2014

Organic petrology of the Aptian-age section in the downdip Mississippi Interior Salt Basin, Mississippi, USA: Observations and preliminary implications for thermal maturation history

This study identifies a thermal maturity anomaly within the downdip Mississippi Interior Salt Basin (MISB) of southern Mississippi, USA, through examination of bitumen reflectance data from Aptian-age strata (Sligo Formation, Pine Island Shale, James Limestone, and Rodessa Formation). U.S. Geological Survey (USGS) reconnaissance investigations conducted in 2011–2012 examined Aptian-age thermal maturity trends across the onshore northern Gulf of Mexico region and indicated that the section in the downdip MISB is approaching the wet gas/condensate window (R o ~1.2%). A focused study in 2012–2013 used 6 whole core, one sidewall core, and 49 high-graded cutting samples (depth range of 13,000–16,500 ft [3962.4–5029.2 m] below surface) collected from 15 downdip MISB wells for mineralogy, fluid inclusion, organic geochemistry, and organic petrographic analysis. Based on native solid bitumen reflectance (R o generally > 0.8%; interpreted to be post-oil indigenous bitumens matured in situ), R o values increase regionally across the MISB from the southeast to the northwest. Thermal maturity in the eastern half of the basin (R o range 1.0 to 1.25%) appears to be related to present-day burial depth and shows a gradual increase with respect to depth. To the west, thermal maturity continues to increase even as the Aptian section shallows structurally on the Adams County High (R o range 1.4 to > 1.8%). After evaluating the possible thermal agents responsible for increasing maturity at shallower depths (i.e., igneous activity, proximity to salt, variations in regional heat flux, and uplift), we tentatively propose that either greater paleoheat flow or deeper burial coupled with uplift in the western part of the MISB could be responsible for the thermal maturity anomaly. Further research and additional data are needed to determine the cause(s) of the thermal anomaly.

International Journal of Coal Geology↗

USGS1980

Shorter contributions to stratigraphy and structural geology, 1979

PART A: A system of anticlines lies along the trend of the sinuous course of the Colorado River for a distance of 97 km in the central Grand Canyon. Similar anticlines occur in some perennially wet side canyons. The anticlines are most abundant and well developed along northeast-trending reaches of the main canyon where it is floored by the Cambrian Muav Limestone. Dips of the folded strata are as great as 60?, and the folding locally extends more than 250 m from the river. Low-angle thrust faults in the limbs of the anticlines parallel the river and have formed in response to folding of the comparatively brittle carbonate strata. High-angle reverse kink bands, along which rocks are displaced up toward the river, also parallel the anticlines and have develop2d in response to the upward bulging of the canyon floor. The river anticlines are an unloading phenomenon. They result from lateral squeezing toward the river of saturated shaly parts of the Muav Limestone and underlying Bright Angel Shale. The driving mechanism for the deformation is a stress gradient that results from a difference in lithostatic load between the heavily loaded rocks under the 650-m-high canyon walls and the unloaded canyon floor. Saturation appears to weaken the shaly rocks sufficiently to allow deformation to take place. River anticlines are not present in the eastern Grand Canyon, where the Cambrian rocks also occur at river level. Their absence is explained by a lack of shaly rocks that could flow when saturated. PART B: The current interest in contemporary tectonic processes in the Eastern United States is turning up abundant evidence of crustal movements in late geologic time. Topographic analysis of the highland areas from the southern Blue Ridge to the Adirondack Mountains indicates that most of the landforms owe their origin to erosion of rocks of different resistance rather than to tectonic processes. Most areas of high relief and high altitude have been formed on resistant rocks. The Cambrian and Ordovician belt, containing mostly shale and carbonate rock, on the other hand, forms an extensive lowland from Alabama to the Canadian border and girdles the Adirondack Mountains. Differences in altitude can be explained by the presence of resistant rocks outside the belt; these resistant rocks form local base levels on the streams that drain the belt. A few areas may have undergone local uplift at a higher rate than areas nearby--for example, the Piedmont region northwest of Chesapeake Bay. Most estimates of erosion rates, based on the load transported by streams and of uplift rates, based on removal during a known period of time, are of the same order of magnitude, averaging almost 4x 10^-2 millimeters per year. Rates of uplift, based on study of tilted Pleistocene beaches and repeated geodetic traverses, are at least an order of magnitude higher for comparable areas. Tectonic uplift of the highlands has been slow and involves mostly warping or tilting on a large scale. Erosion rates keep up with or exceed the rate of uplift and have been sufficient to mask evidence of faulting or other differential movements. The high rates of uplift that are inferred on tilted water planes in the glaciated regions or that are measured by differences in repeated geodetic traverses cannot have been sustained for long periods of time. PART C: The Hanson Creek Formation southwest of Eureka, Nev., in the Bellevue Peak Quadrangle is composed of three lithostratigraphic members: (1) a basal dark-gray dolomite, (2) a middle silty thin- to thick-bedded, locally nodular, dark-gray, light-yellow-mottled limestone topped by light-gray dolomite, and (3) an upper dark-gray dolomite, which is herein named the Combs Canyon Dolomite Member. Detailed geologic mapping and accompanying fossil collecting prove that the same lithostratigraphic and biostratigraphic sequence is present in the Mountain Boy Range and 11 km to the south near Wood Cone Peak. Minor differences in

Professional Paper↗

USGS1904

The geology and ore deposits of the Bisbee quadrangle, Arizona

The Bisbee quadrangle lies in Cochise County, in the southeastern part of Arizona, within what has been called in a previous paper the mountain region of the Territory. It is inclosed between meridians 109 ° 45' and 110 ° 00' and parallels 31° 30' and 31 ° 20', the latter being locally the Mexican boundary line. The area of the quadrangle is about 170 square miles, and includes the southeastern half of the Mule Mountains, one of the smaller of the isolated ranges so characteristic of the mountain region of Arizona. The Mule Mountains, while less markedly linear than the Dragoon, Huachuca, Chiricahua, and other neighboring ranges, have a general northwest-southeast trend. They may be considered as extending from the old mining town of Tombstone to the Mexican border, a distance of about 30 miles. On the northeast they are separated by the broad fiat floor of Sulphur Spring Valley form the Chiricahua Range, and on the southwest by the similar broad valley of the Rio San Pedro from the Huachuca Range (Pl. V, A).

Arizona↗

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↗

USGS2010

Surficial geology of the sea floor in Long Island Sound offshore of Plum Island, New York

The U.S. Geological Survey (USGS), the Connecticut Department of Environmental Protection, and the National Oceanic and Atmospheric Administration (NOAA) have been working cooperatively to interpret surficial sea-floor geology along the coast of the Northeastern United States. NOAA survey H11445 in eastern Long Island Sound, offshore of Plum Island, New York, covers an area of about 12 square kilometers. Multibeam bathymetry and sidescan-sonar imagery from the survey, as well as sediment and photographic data from 13 stations occupied during a USGS verification cruise are used to delineate sea-floor features and characterize the environment. Bathymetry gradually deepens offshore to over 100 meters in a depression in the northwest part of the study area and reaches 60 meters in Plum Gut, a channel between Plum Island and Orient Point. Sand waves are present on a shoal north of Plum Island and in several smaller areas around the basin. Sand-wave asymmetry indicates that counter-clockwise net sediment transport maintains the shoal. Sand is prevalent where there is low backscatter in the sidescan-sonar imagery. Gravel and boulder areas are submerged lag deposits produced from the Harbor Hill-Orient Point-Fishers Island moraine segment and are found adjacent to the shorelines and just north of Plum Island, where high backscatter is present in the sidescan-sonar imagery.

Open-File Report↗

USGS2010

Sea-floor geology and character offshore of Rocky Point, New York

Open-File Report↗

USGS1986

Geohydrology of the unsaturated zone at the burial site for low-level radioactive waste near Beatty, Nye County, Nevada

Low-level radioactive solid waste has been buried in trenches at a site near Beatty, Nevada, since 1962. In 1976, as part of a national program, the U.S. Geological Survey began a study of the geohydrology of the waste burial site to provide a basis for estimating the potential for radionuclide migration in the unsaturated zone beneath the waste burial trenches. Data collected include meteorological information for calibration of a long-term water budget analysis, soil moisture profiles, soil water potentials, and hydraulic properties of representative unsaturated sediment samples to a depth of about 10 m. The waste burial facility is in the northern Amargosa Desert about 170 km northwest of Las Vegas, NV. The region is arid; mean annual precipitation at Lathrop Wells, 30 km south of the site, is only 7.4 cm. The mean daily maximum temperature at Lathrop Wells in July, the hottest month, is 37 C. The site is underlain by poorly stratified deposits of gravelly or silty sand and sandy gravel, and thick beds of clayey sediments. The total thickness of valley fill deposits beneath the site is about 175 m; the unsaturated zone is about 85 m thick. Volumetric soil moisture to depths of 4 m ranges from 4% to 10%, but commonly is in the range from 6% to 8%. Soil water potential, measured to depths of 3 to 10 m, ranged from -10 to -70 bars. Unsaturated hydraulic conductivity computed from laboratory analyses of representative samples ranges from 10 to the -13th power to 10 to the -4th power cm/day. Evaporation studies over a 2-yr period were used to calibrate a numerical procedure for analyzing long-term precipitation data and estimating annual water budgets during the 15-yr period 1962-76. This analysis (1) demonstrated that a potential exists for deep percolation (> 2 m), despite high annual evaporation demands, and (2) provided predictions of the time of yr and the antecedent conditions which enhance the probability of deep percolation. Soil moisture profiles obtained monthly over an 18-mo period demonstrate that deep percolation does occur. Soil moisture conditions antecedent to an observed deep-percolation event, and the time of yr when the percolation occurred, support the interpretations based on long-term meteorological records. (Author's abstract)

Nevada↗

USGS1993

Application of borehole geophysics in defining the wellhead protection area for a fractured crystalline bedrock aquifer

Wellbore geophysical techniques were used to characterize fractures and flow in a bedrock aquifer at a site near Blackwater Brook in Dover, New Hampshire. The primary focus ofthis study was the development of a model to assist in evaluating the area surrounding a planned water supply well where contaminants introduced at the land surface might be induced to flow towards a pumping well. Well logs and geophysical surveys used in this study included lithologic logs based on examination of cuttings obtained during drilling; conventional caliper and natural gamma logs; video camera and acoustic televiewer surveys; highresolution vertical flow measurements under ambient conditions and during pumping; and borehole fluid conductivity logs obtained after the borehole fluid was replaced with deionized water. These surveys were used for several applications: 1) to define a conceptual model of aquifer structure to be used in groundwater exploration; 2) to estimate optimum locations for test and observation wells; and 3) to delineate a wellhead protection area (WHPA) for a planned water supply well. Integration of borehole data with surface geophysical and geological mapping data indicated that the study site lies along a northeast-trending intensely fractured contact zone between surface exposures of quartz monzonite and metasedimentary rocks. Four of five bedrock boreholes at the site were estimated to produce more than 150 gallons per minute (gpm) (568 L/min) of water during drilling. Aquifer testing and other investigations indicated that water flowed to the test well along fractures parallel to the northeast-trending contact zone and along other northeast and north-northwest-trending fractures. Statistical plots of fracture strikes showed frequency maxima in the same northeast and north-northwest directions, although additional maxima occurred in other directions. Flowmeter surveys and borehole fluid conductivity logging after fluid replacement were used to identify water-producing zones in the boreholes; fractures associated with inflow into boreholes showed a dominant northeast orientation. Borehole fluid conductivity logging after fluid replacement also gave profiles of such water-quality parameters as fluid electrical conductivity (FEC), pH, temperature, and oxidation-reduction potential, strengthening the interpretation of crossconnection of boreholes by certain fracture zones. The results of this study showed that the application of these borehole geophysical techniques at the Blackwater Brook site led to an improved understanding of such parameters as fracture location, attitude, flow direction and velocity, and water quality; all of which are important in the determination of a WHPA.

Log Analyst↗

USGS2021

Hydrogeologic framework, water levels, and selected contaminant concentrations at Valmont TCE Superfund Site, Luzerne County, Pennsylvania, 2020

The Valmont TCE Superfund Site, Luzerne County, Pennsylvania is underlain by fractured and folded sandstones and shales of the Pottsville and Mauch Chunk Formations, which form a fractured-rock aquifer recharged locally by precipitation. Industrial activities at the former Chromatex Plant resulted in trichloroethene (TCE) contamination of groundwater at and near the facility, which was identified in 1987 and led to listing as a Superfund site by the U.S. Environmental Protection Agency (EPA) in 1989. To address the problem of TCE concentrations in nearby residential wells that exceed the maximum contaminant level (MCL) of 5 micrograms per liter (μg/L), alternate water supplies were provided. A 2015 review of initial characterization and subsequent remediation by the EPA identified the need for an updated understanding of the complex hydrogeology and the conceptual site model. Additional contaminants present in groundwater at the site include some other volatile organic compounds (VOCs) and per- and polyfluoroalkyl substances (PFAS), predominantly consisting of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) present in concentrations that exceeded the EPA Health Advisory (HA) level of 5 nanograms per liter (ng/L) for combined PFOA and PFOS. In response to a request from the EPA in 2019, the U.S. Geological Survey (USGS) prepared cross sections and maps to provide more information about the hydrogeologic framework at and near the site and assist in improving the conceptual site model using water level and contaminant data collected by the EPA in 2020. The cross sections present lithologic correlations from available geophysical logs collected in wells from 2002 to 2014; they show alternating intervals of relatively elevated and reduced natural gamma activity that correspond to changes in lithology, with water-bearing zones and well screens commonly located at lithologic contacts, sometimes near thin coal seams. Water-bearing zones commonly are associated with fractures at or near lithologic contacts but also may be associated with fractures at or near apparent faulting. Recent (March 2020) water-level data shown on cross sections and maps indicate large downward vertical gradients and apparent radial gradients laterally to the northeast, northwest, and southwest that generally following topography. Recent (February to March 2020) data for TCE groundwater concentration shown on cross sections and maps indicate the highest TCE concentrations (greater than 3,000 μg/L and as much as 75,000 μg/L) and combined PFOA and PFOS concentrations (greater than 1,000 ng/L and up to at least 2,350 ng/L) are from shallow (less than 60 feet [ft] below land surface [bls]) and intermediate depth (60 to 100 ft bls) wells near the center of the former Chromatex Plant. TCE and PFAS (as combined PFOA and PFOS) contamination is present at greater depths, as much as 304 ft bls, as evidenced by samples collected from one well (a reconstructed former production well) near the plant, that contained concentrations of about 240 μg/L and 508 ng/L, respectively. The 2020 data also indicate that TCE and PFAS concentrations which exceed drinking-water MCL or HA levels are present in groundwater depths of less than 200 ft in an area that extends predominantly in a northeast direction from the former Chromatex Plant, and is apparently influenced by hydraulic gradients, lithology, and geologic structure.

Pennsylvania↗

USGS2017

Geology along the Blue Ridge Parkway in Virginia

Detailed geologic mapping and new SHRIMP (sensitive high-resolution ion microprobe) U-Pb zircon, Ar/Ar, Lu-Hf, 14 C, luminescence (optically stimulated), thermochronology (fission-track), and palynology reveal the complex Mesoproterozoic to Quaternary geology along the ~350 km length of the Blue Ridge Parkway in Virginia. Traversing the boundary of the central and southern Appalachians, rocks along the parkway showcase the transition from the para-autochthonous Blue Ridge anticlinorium of northern and central Virginia to the allochthonous eastern Blue Ridge in southern Virginia. From mile post (MP) 0 near Waynesboro, Virginia, to ~MP 124 at Roanoke, the parkway crosses the unconformable to faulted boundary between Mesoproterozoic basement in the core of the Blue Ridge anticlinorium and Neoproterozoic to Cambrian metasedimentary and metavolcanic cover rocks on the western limb of the structure. Mesoproterozoic basement rocks comprise two groups based on SHRIMP U-Pb zircon geochronology: Group I rocks (1.2-1.14 Ga) are strongly foliated orthogneisses, and Group II rocks (1.08-1.00 Ga) are granitoids that mostly lack obvious Mesoproterozoic deformational features. Neoproterozoic to Cambrian cover rocks on the west limb of the anticlinorium include the Swift Run and Catoctin Formations, and constituent formations of the Chilhowee Group. These rocks unconformably overlie basement, or abut basement along steep reverse faults. Rocks of the Chilhowee Group are juxtaposed against Cambrian rocks of the Valley and Ridge province along southeast- and northwest-dipping, high-angle reverse faults. South of the James River (MP 64), Chilhowee Group and basement rocks occupy the hanging wall of the nearly flat-lying Blue Ridge thrust fault and associated splays. South of the Red Valley high-strain zone (MP 144.5), the parkway crosses into the wholly allochthonous eastern Blue Ridge, comprising metasedimentary and meta-igneous rocks assigned to the Wills Ridge, Ashe, and Alligator Back Formations. These rocks are bound by numerous faults, including the Rock Castle Creek fault that separates Ashe Formation rocks from Alligator Back Formation rocks in the core of the Ararat River synclinorium. The lack of unequivocal paleontologic or geochronologic ages for any of these rock sequences, combined with fundamental and conflicting differences in tectonogenetic models, compound the problem of regional correlation with Blue Ridge cover rocks to the north. The geologic transition from the central to southern Appalachians is also marked by a profound change in landscape and surficial deposits. In central Virginia, the Blue Ridge consists of narrow ridges that are held up by resistant but contrasting basement and cover lithologies. These ridges have shed eroded material from their crests to the base of the mountain fronts in the form of talus slopes, debris flows, and alluvial-colluvial fans for perhaps 10 m.y. South of Roanoke, however, ridges transition into a broad hilly plateau, flanked on the east by the Blue Ridge escarpment and the eastern Continental Divide. Here, deposits of rounded pebbles, cobbles, and boulders preserve remnants of ancestral west-flowing drainage systems. Both bedrock and surficial geologic processes provide an array of economic deposits along the length of the Blue Ridge Parkway corridor in Virginia, including base and precious metals and industrial minerals. However, common stone was the most important commodity for creating the Blue Ridge Parkway, which yielded building stone for overlooks and tunnels, or crushed stone for road base and pavement.

Virginia↗

USGS1960

Occurrence of strontium in natural water

The regions where the stable strontium content of surface waters is relatively low (less than 0.50 ppm) include the Pacific Northwest, Northeastern United States, and the Central Lowlands, Particularly the Lower Mississippi basin and the Western Gulf Coast area. Moderate concentrations of strontium (0.50 to 1.5 ppm) are found in streams of Southeastern United States, most of the Great Plains Region, the Western Mountain and Plateau Regions, and California. Relatively high concentrations of strontium occur in the surface waters of an area that includes Northern and Western Texas and Southern New Mexico and Arizona. Exceptions to the above distribution are due to local geologic conditions.

Circular↗

USGS1986

Geologic map of the South Jackson Mountains Wilderness Study Area, Humboldt County, Nevada

The Federal Land Policy and Management Act (Public Law 94-579, October 21, 1976) requires the U.S. Geological Survey and the U.S. Bureau of Mines to conduct mineral surveys on certain areas to determine their mineral values, if any, that may be present. Results must be made available to the public and be submitted to the President and the Congress. This report presents the results of a mineral survey of the South Jackson Mountains (NV-020-603) Wilderness Study Area, Humboldt County, Nevada. The South Jackson Mountains Wilderness Study Area is in south-central Humboldt County, approximately 50 miles northwest of Winnemucca, Nevada. The boundaries originally specified for the wilderness study area encompassed an area of 60,211 acres. The draft Environmental Impact Statement issued in 1983 by the U.S. Bureau of Land Management (BLM) identified 20,094 acres within the wilderness study area as potentially suitable for inclusion into the National Wilderness Preservation System. Subsequent (August 27, 1984) deletions by the BLM have resulted in the present study area of approximately 10,300 acres. The boundaries of the study area are approximated by the range crestline to the east and the 4,400-ft contour along the west side of the range from King Lear Peak north to the divide between Hobo and Christiorsson Canyons.

Nevada↗

USGS1996

Ground-water flow patterns and water budget of a bottomland forested wetland, Black Swamp, eastern Arkansas

The U.S. Geological Survey, working in cooperation with the U.S. Army Corps of Engineers, Waterways Experiment Station, collected surface-water and ground-water data from 119 wells and 13 staff gages from September 1989 to September 1992 to describe ground-water flow patterns and water budget in the Black Swamp, a bottomland forested wetland in eastern Arkansas. The study area was between two streamflow gaging stations located about 30.5 river miles apart on the Cache River. Ground-water flow was from northwest to southeast with some diversion toward the Cache River. Hydraulic connection between the surface water and the alluvial aquifer is indicated by nearly equal changes in surface-water and ground-water levels near the Cache River. Diurnal fluctuations of hydraulic head ranged from more than 0 to 0.38 feet and were caused by evapotranspiration. Changes in hydraulic head of the alluvial aquifer beneath the wetland lagged behind stage fluctuations and created the potential for changes in ground-water movement. Differences between surface-water levels in the wetland and stage of the Cache River created a frequently occurring local ground-water flow condition in which surface water in the wetland seeped into the upper part of the alluvial aquifer and then seeped into the Cache River. When the Cache River flooded the wetland, ground water consistently seeped to the surface during falling surface-water stage and surface water seeped into the ground during rising surface-water stage. Ground-water flow was a minor component of the water budget, accounting for less than 1 percent of both inflow and outflow. Surface-water drainage from the study area through diversion canals was not accounted for in the water budget and may be the reason for a surplus of water in the budget. Even though ground-water flow volume is small compared to other water budget components, ground-water seepage to the wetland surface may still be vital to some wetland functions.

Water-Resources Investigations Report↗

USGS1997

Geohydrology and Numerical Simulation of the Ground-Water Flow System of Molokai, Hawaii

A two-dimensional, steady-state, areal ground-water flow model was developed for the island of Molokai, Hawaii, to enhance the understanding of (1) the conceptual framework of the ground-water flow system, (2) the distribution of aquifer hydraulic properties, and (3) the regional effects of ground-water withdrawals on water levels and coastal discharge. The model uses the finite-element code AQUIFEM-SALT, which simulates flow of fresh ground water in systems that may have a freshwater lens floating on denser underlying saltwater. Model results are in agreement with the general conceptual model of the flow system on Molokai, where ground water flows from the interior, high-recharge areas to the coast. The model-calculated ground-water divide separating flow to the northern and southern coasts lies to either the north or the south of the topographic divide but is generally not coincident with the topographic divide. On the basis of model results, the following horizontal hydraulic conductivities were estimated: (1) 1,000 feet per day for the dike-free volcanic rocks of East and West Molokai, (2) 100 feet per day for the marginal dike zone of the East Molokai Volcano, (3) 2 feet per day for the West Molokai dike complex, (4) 0.02 feet per day for the East Molokai dike complex, and (5) 500 feet per day for the Kalaupapa Volcanics. Three simulations to determine the effects of proposed ground-water withdrawals on water levels and coastal discharge, relative to model-calculated water levels and coastal discharge for 1992-96 withdrawal rates, show that the effects are widespread. For a withdrawal rate of 0.337 million gallons per day from a proposed well about 4 miles southeast of Kualapuu and 3 miles north of Kamiloloa, the model-calculated drawdown of 0.01 foot or more extends 4 miles southeast and 6 miles northwest from the well. For a withdrawal rate of 1.326 million gallons per day from the same well, the model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 9 miles northwest from the well. In a third scenario, the withdrawal rate from an existing well near Kualapuu was increased by 0.826 million gallons per day. The model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 8 miles northwest from the well. In all scenarios, coastal discharge is reduced by an amount equal to the additional withdrawal. Additional data needed to improve the understanding of the ground-water flow system on Molokai include: (1) a wider spatial distribution and longer temporal distribution of water-levels, (2) independent estimates of hydraulic conductivity, (3) improved recharge estimates, (4) information about the vertical distribution of salinity in ground water, (5) streamflow data at additional sites, and (6) improved information about the subsurface geology.

Water-Resources Investigations Report↗

USGS2022

Lateral moraines, ice-dammed lakes, and meltwater-carved channels in the Pelham, Shutesbury, Leverett area of west-central Massachusetts: A record of Connecticut Valley ice lobe retreat

Temporary ice-dammed glacial lakes formed high in the landscape in several westward sloping valleys on the east side of the Connecticut Valley lowland during late Wisconsinan deglaciation. These lakes were impounded by a lengthy lobe of ice that extended farther south in the lowland than at upland retreatal ice-margin positions (fig. 1). The formation, lowering, and drainage of these ice-dammed lakes successively preceded the extension of glacial Lake Hitchcock northward in the Deerfield Basin as the ice lobe retreated to the north of the Holyoke Range. Detailed surficial geologic mapping of the Shutesbury Quadrangle (Stone, J.R., 1978), along with regional compilation for the Surficial Materials Map of Massachusetts (Stone, J.R. and others, 2018), and ongoing compilation of the Quaternary Geologic Map of Massachusetts has established the extent of these lake deposits and locations of their meltwater- carved spillways. However, recently obtained Lidar-derived high-resolution digital elevation model (DEM) images provide new evidence for mapping of previously unrecognized features not visible on traditional 1:24,000-scale, 10-ft contour interval topographic maps. The newly mapped features have less than 10 ft (3 m) of relief and are believed to be successive lateral moraines left behind by the west-northwesterly retreating Connecticut Valley ice lobe. On the Fieldtrip, we will examine deltaic deposits of ice-dammed glacial lakes in the valleys of Amethyst Brook in the town of Pelham and Roaring Brook in Shutesbury and Leverett, as well as their associated meltwater-carved spillways and feeding meltwater channels. Physical aspects of the low ridges interpreted as lateral moraines will be examined on the ground. Much of the landscape in Pelham, Shutesbury, and Leverett is forested, much is classified as open space, and there are many trails.

Massachusetts↗

USGS2015

Aftershocks illuminate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

Virginia↗