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Research about conterminous United States

Source-linked reports with geographic coverage including conterminous United States.

At least 127 records · Page 7Linked to original sources
USGS1997

Climate change and the detection of trends in annual runoff

This study examines the statistical likelihood of detecting a trend in annual runoff given an assumed change in mean annual runoff, the underlying year-to-year variability in runoff, and serial correlation of annual runoff. Means, standard deviations, and lag-1 serial correlations of annual runoff were computed for 585 stream gages in the conterminous United States, and these statistics were used to compute the probability of detecting a prescribed trend in annual runoff. Assuming a linear 20% change in mean annual runoff over a 100 yr period and a significance level of 95%, the average probability of detecting a significant trend was 28% among the 585 stream gages. The largest probability of detecting a trend was in the northwestern U.S., the Great Lakes region, the northeastern U.S., the Appalachian Mountains, and parts of the northern Rocky Mountains. The smallest probability of trend detection was in the central and southwestern U.S., and in Florida. Low probabilities of trend detection were associated with low ratios of mean annual runoff to the standard deviation of annual runoff and with high lag-1 serial correlation in the data.

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USGS1996

Data base for a national mineral-resource assessment of undiscovered deposits of gold, silver, copper, lead, and zinc in the conterminous United States

For this assessment, the conterminous United States was divided into 12 regions Adirondack Mountains, Central and Southern Rocky Mountains, Colorado Plateau, East Central, Great Basin, Great Plains, Lake Superior, Northern Appalachians, Northern Rocky Mountains, Pacific Coast, Southern Appalachians, and Southern Basin and Range. The assessment, which was conducted by regional assessment teams of scientists from the USGS, was based on the concepts of permissive tracts and deposit models. Permissive tracts are discrete areas of the United States for which estimates of numbers of undiscovered deposits of a particular deposit type were made. A permissive tract is defined by its geographic boundaries such that the probability of deposits of the type delineated occurring outside the boundary is neglible. Deposit models, which are based on a compilation of worldwide literature and on observation, are sets of data in a convenient form that describe a group of deposits which have similar characteristics and that contain information on the common geologic attributes of the deposits and the environments in which they are found. Within each region, the assessment teams delineated permissive tracts for those deposit models that were judged to be appropriate and, when the amount of information warranted, estimated the number of undiscovered deposits. A total of 46 deposit models were used to assess 236 separate permissive tracts. Estimates of undiscovered deposits were limited to a depth of 1 km beneath the surface of the Earth. The estimates of the number of undiscovered deposits of gold, silver, copper, lead, and zinc were expressed in the form of a probability distribution. Commonly, the number of undiscovered deposits was estimated at the 90th, 50th, and 10th percentiles. A Monte Carlo simulation computer program was used to combine the probability distribution of the number of undiscovered deposits with the grade and tonnage data sets associated with each deposit model to obtain the probability distribution for undiscovered metal.

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USGS1989

Isostatic residual gravity and crustal geology of the United States

A new isostatic residual gravity map of the conterminous United States presents continent-wide gravity data in a form that can be readily used, with geologic information and other geophysical data, in studies of the composition and structure of the continental crust. This map was produced from the gridded gravity data on which the recently released Gravity Anomaly Map of the United States is based. About 1 million onland and 0.8 million offshore gravity observations interpolated to a 4- by 4-km grid serve as the basis for both maps. The Airy-Heiskanen model of isostatic compensation of topography applied to topographic and bathymetric data averaged over 5- by 5-min compartments was used to remove, to first order, the large, long-wavelength Bouguer gravity anomalies caused by deep density distributions that support topographic loads. The parameters used in the Airy-Heiskanen model were topographic density, 2.67 g/cm 3 ; sea-level crustal thickness, 30 km; and density contrast across the base of the model crust, 0.35 g/cm 3 . Many of the conspicuous short-wavelength anomalies (widths less than several hundred kilometers) on the isostatic residual gravity map correlate with mapped or near-surface geologic features, and primarily reflect shallow-density distributions rather than any departures from isostatic equilibrium. In general, gravity highs occur over (1) mafic igneous bodies emplaced in rift or magmatic arc settings or as isolated intrusions controlled by structures; (2) accreted slices of mafic oceanic, island-arc, or transitional crust; and (3) uplifted crystalline basement. Gravity lows are found over (1) thick bodies of felsic intrusive or extrusive rocks; (2) sedimentary deposits in extensional, convergent, or transform settings; and (3) depressed crystalline basement. Anomalies with widths as much as 1,000 km or more also appear to reflect crustal properties in many cases—several broad gravity highs are associated with crust having a high average seismic wave velocity, and comparable broad gravity lows occur over areas of low average seismic velocity. Alternative ways of viewing the isostatic residual gravity data provide additional information about density distributions in the crust. The first-vertical derivative map accentuates gravity anomalies over shallow, abrupt density changes at the expense of those resulting from deeper or more gradual density transitions. The maximum horizontal gradient map contains information about the locations of pronounced density boundaries. Two-dimensional spectral analysis of the gravity data provides a quantitative means for identifying dominant fabrics in the gravity field and for distinguishing various terranes from each other. Neither Bouguer nor isostatic residual gravity anomalies are particularly well suited for practical modeling of deep structure in conjunction with deep seismic information. However, a scheme in which the entire Earth outside the area of interest is approximated by laterally homogeneous layers and isostatically compensated topography, and in which the area of interest is modeled using the seismic constraints applied in a two-and-one-half-dimensional geometry, holds promise for exploiting useful features of both the Bouguer and isostatic residual gravity anomalies.

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USGS1988

Natural aggregates of the conterminous United States

Crushed stone and sand and gravel are the two main sources of natural aggregates. These materials are commonly used construction materials and frequently can be interchanged with one another. They are widely used throughout the United States, with every State except two producing crushed stone. Together they amount to about half the mining volume in the United States. Approximately 96 percent of sand and gravel and 77 percent of the crushed stone produced in the United States are used in the construction industry. Natural aggregates are widely distributed throughout the United States in a variety of geologic environments. Sand and gravel deposits commonly are the results of the weathering of bedrock and subsequent transportation and deposition of the material by water or ice (glaciers). As such, they commonly occur as river or stream deposits or in glaciated areas as glaciofluvial and other deposits. Crushed stone aggregates are derived from a wide variety of parent bedrock materials. Limestone and other carbonates account for approximately three quarters of the rocks used for crushed stone, with granite and other igneous rocks making up the bulk of the remainder. Limestone deposits are widespread throughout the Central and Eastern United States and are scattered in the West. Granites are widely distributed in the Eastern and Western United States, with few exposures in the Midwest. Igneous rocks (excluding granites) are largely concentrated in the Western United States and in a few isolated localities in the East. Even though natural aggregates are widely distributed throughout the United States, they are not universally available for consumptive use. Some areas are devoid of sand and gravel, and potential sources of crushed stone may be covered with sufficient unconsolidated material to make surface mining impractical. In some areas many aggregates do not meet the physical property requirements for certain uses, or they may contain mineral constituents that react adversely when used as concrete aggregate. In areas where suitable natural aggregate is not available or accessible, it may become necessary to improve the quality of existing aggregate, to import aggregate from outside the area, or to substitute artificial aggregate for natural aggregate. In most cases, all of these alternatives add substantially to the cost of the final product. Even though an area may be blessed with an abundance of aggregate suitable for the intended purpose, existing land uses, zoning, or regulations may preclude commercial exploitation of the aggregate. This report also discusses the aggregate industry in general terms, including exploration, mining, and processing, as well as aggregate production rates. Proper long-range planning based on an understanding of the aggregate industry can help assure adequate supplies of aggregate.

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USGS1987

Hydraulics and basin morphometry of the largest flash floods in the conterminous United States

The maximum rainfall-runoff floods measured by indirect methods in small basins (0.39-370 km 2 ) in the conterminous United States are examined. This analysis identified twelve floods that were the largest ever measured. These floods all occurred in semiarid to arid areas. For eleven of the twelve largest rainfall-runoff floods measured in small basins by the slope-area method, values of hydraulic depth; hydraulic radius; width-depth ratio; n value; mean velocity; velocity-head coefficient; Froude number; water-surface, energy, and channel slopes; shear stress; and unit stream power are tabulated. Estimated composite n values weighted by subsection conveyance range from 0.028 to 0.048 with a mean of 0.038. Mean velocities ranged from 3.47 to 9.97 m s −1 . Froude numbers ranged from 0.81 to 2.49, with 9 of 12 floods having values greater than 1.00. Water-surface, energy, and channel slopes vary considerably for each flood. Energy slope always was less than water-surface slope by values of 1–104%. Channel slope was greater than energy slope in eight floods. Shear stresses ranged between 61 and 855 N m −2 , and unit stream power from 212 to 8131 w m −1 . Floods in these small basins produced shear stresses and unit stream powers several hundred times greater than floods in large rivers. Floods on other small streams, with smaller unit discharges, produced greater shear stresses and stream powers. This indicates that the force of a flood is controlled by the depth-slope product, not absolute discharge. In the twelve watersheds studied, basin relief ranged from 165 to 1280 m, elongation ratios ranged from 0.55 to 0.80, the number of first-order streams (basin magnitude) ranged from 10 to 4297, drainage density ranged from 4.1 to 10.9 km km −2 , basin slope ranged from 0.0043 to 0.2486, relief ratio ranged from 0.0097 to 0.34, ruggedness number ranged from 0.69 to 7.17, and first-order channel frequency ranged from 5.1 to 38.6 km −2 . Elongation ratios were larger, and drainage density and first-order channel frequency lower, than other small flash-flood prone basins in the United States. These twelve basins have neither the most favorable morphometric characteristics which contribute to flash-flood peaks, nor did the storms causing these flash floods have the greatest short-duration intensities. Maximum flood peaks originate from an optimal combination of basin morphology and physiography, and storm intensity.

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USGS1982

Landslide overview map of the conterminous United States

The accompanying landslide overview map of the conterminous United States is one of a series of National Environmental Overview Maps that summarize geologic, hydrogeologic, and topographic data essential to the assessment of national environmental problems. The map delineates areas where large numbers of landslides exist and areas which are susceptible to landsliding. It was prepared by evaluating the geologic map of the United States and classifying the geologic units according to high, medium, or low landslide incidence (number) and high, medium, or low susceptibility to landsliding. Rock types, structures, topography, precipitation, landslide type, and landslide incidence are mentioned for each physical subdivision of the United States. The differences in slope stability between the Colorado Plateau, the Appalachian Highlands, the Coast Ranges of California, and the Southern Rocky Mountains are compared in detail, to illustrate the influence of various natural factors on the types of landsliding that occur in regions having different physical conditions. These four mountainous regions are among the most landslide-prone areas in the United States. The Colorado Plateau is a deformed platform where interbedded sedimentary rocks of varied lithologic properties have been gently warped and deeply eroded. The rocks are extensively fractured. Regional fracture systems, joints associated with individual geologic structures, and joints parallel to topographic surfaces, such as cliff faces, greatly influence slope stability. Detached blocks at the edges of mesas, as well as columns, arched recesses, and many natural arches on the Colorado Plateau, were formed wholly or in part by mass movement. In the Appalachian Highlands, earth flows, debris flows, and debris avalanches predominate in weathered bedrock and colluvium. Damaging debris avalanches result when persistent steady rainfall is followed by a sudden heavy downpour. Landsliding in unweathered bedrock is controlled locally by joint systems similar to those on the Colorado Plateau. In some places, outward gravitational movement of valley walls due to stress release has formed anticlines and caused thrusting in the center of valleys. In the Coast Ranges of California, slopes are steep, and rocks are varied and extensively deformed. One of the most slide-prone terrains of the Coast Ranges is the tectonic melange of the Franciscan assemblage, on which huge masses of debris are moving slowly downslope. In southern California, debris flows generated by soil slips are particularly damaging. Similar flows are common in poorly consolidated Tertiary rocks of the central part of the State. Like the debris avalanches of the Appalachian Highlands, the flows form during intense rainfall after previous steady rain. The Southern Rocky Mountains are complex in rock type and climate, so that the landslides there are also complex. Slides range from rock-falls at one extreme to slumps and debris flows at the other. They include ?sackungen,? which are distinguished by ridgetop grabens associated with uphill-facing scarps on ridge sides, both features of gravitational origin. Extensive regional joint patterns have not been recognized, and shallow soil slips are only a minor hazard.

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USGS1973

Structure of the crust in the conterminous United States

On the basis of the newest interpretations of all sufficiently long seismic profiles, a contour map of the Mohorovičić discontinuity for the conterminous United States is compiled. Differences from earlier interpretations are discussed.

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USGS1971

A new stratification of mourning dove call-count routes

The mourning dove ( Zenaidura macroura ) call-count survey is a nationwide audio-census of breeding mourning doves. Recent analyses of the call-count routes have utilized a stratification based upon physiographic regions of the United States. An analysis of 5 years of call-count data, based upon stratification using potential natural vegetation, has demonstrated that this uew stratification results in strata with greater homogeneity than the physiographic strata, provides lower error variance, and hence generates greatet precision in the analysis without an increase in call-count routes. Error variance was reduced approximately 30 percent for the contiguous United States. This indicates that future analysis based upon the new stratification will result in an increased ability to detect significant year-to-year changes.

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USGS1971

Eggshell thickness in mourning dove populations

Eggs ( n = 452) of the mourning dove ( Zenaidura macroura ) were collected from 9 states in 1969 and 11 states in 1970, and shell thickness was compared with that of eggs ( n = 97) collected from 24 states during the years 1861 to 1935. Mean shell thickness did not differ significantly in the test groups.

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