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At least 73 records · Page 4Linked to original sources
USGS2017

Radiometric characterization of Landsat Collection 1 products

Landsat data in the U.S. Geological Survey (USGS) archive are being reprocessed to generate a tiered collection of consistently geolocated and radiometrically calibrated products that are suitable for time series analyses. With the implementation of the collection management, no major updates will be made to calibration of the Landsat sensors within a collection. Only calibration parameters needed to maintain the established calibration trends without an effect on derived environmental records will be regularly updated, while all other changes will be deferred to a new collection. This first collection, Collection 1, incorporates various radiometric calibration updates to all Landsat sensors including absolute and relative gains for Landsat 8 Operational Land Imager (OLI), stray light correction for Landsat 8 Thermal Infrared Sensor (TIRS), absolute gains for Landsat 4 and 5 Thematic Mappers (TM), recalibration of Landsat 1-5 Multispectral Scanners (MSS) to ensure radiometric consistency among different formats of archived MSS data, and a transfer of Landsat 8 OLI reflectance based calibration to all previous Landsat sensors. While all OLI/TIRS, ETM+ and majority of TM data have already been reprocessed to Collection 1, a completion of MSS and remaining TM data reprocessing is expected by the end of this year. It is important to note that, although still available for download from the USGS web pages, the products generated using the Pre-Collection processing do not benefit from the latest radiometric calibration updates. In this paper, we are assessing radiometry of solar reflective bands in Landsat Collection 1 products through analysis of trends in on-board calibrator and pseudo invariant site (PICS) responses.

Conference Paper↗
USGS1988

Thematic mapping from satellite imagery

This report, produced between 1984 and 1987 in a bilingual edition (English and French), provides a wealth of information on a wide variety of cartographic applications which are being developed to make effective use of new data that is now being collected by Earth observation satellites. At a time when natural resource development and environmental problems have to be taken into account in their entirety, satellites provide an exceptional means of evaluating, synthesizing and creating geographic information. The production of new images, such as the Landsat Thematic Mapper, the SPOT High Resolution Visible Sensor and the adoption meteorological images such as AVHRR sensors on NOAA satellites, which have been extended to thematic domains such as agriculture and glaciology, have led to many new developments as well as problems for the cartographer. These problems are numerous and varied and recur frequently depending on the images and themes being processed e.g. how to select the graphic specification of maps and legends and account for classification accuracy; how to introduce the minimum of topographical data into an image in order to supply users with an adequate geographic reference; when using a physical terrain image, on which, by definition there are no `blanks' and where no details have been eliminated, how to overcome conceptual difficulties e.g. the side by side placing of different semiological information; the interpretation levels left to reader; achieving a balance between objectivity and readability. Obviously the cartographers role is of prime importance in solving these problems. In order to illustrate the way in which this information is presented, the report provides samples from 33 thematic applications taken from 13 different categories, including agriculture, town planning and water resources. Each application is provided with a descriptive note both in English and French indicating the objective, method and results obtained. This volume provides an important record of current developments in thematic mapping from satellite imagery and should be essential reference for all cartographers.

Book↗
USGS2023

Comparison of ventifact orientations and recent wind direction indicators on the floor of Jezero crater, Mars

Wind-abraded rocks and aeolian bedforms have been observed at the Mars 2020 Perseverance landing site, providing evidence for recent and older wind directions. This study reports orientations of aeolian features measured in Perseverance images to infer formative wind directions. It compares these measurements with orbital observations, climate model predictions, and wind data acquired by the Mars Environmental Dynamics Analyzer. Three-dimensional orientations of flute textures on rocks, regolith wind tails extending from behind obstacles, and other aeolian features were measured using Digital Terrain Models (DTMs) derived from Mastcam-Z and navigation camera (Navcam) stereo images. Orientations of rock flutes measured in images acquired through Sol (martian day) 400 yielded a mean azimuth of 94° ± 7° (wind from the west). However, similar measurements of regolith wind tails indicate that recent sand-driving winds have been blowing from the east-southeast, nearly the opposite direction (mean azimuth = 285° ± 15°). Atmospheric modeling generally predicts net annual sand transport from the east-southeast at present, consistent with Perseverance regolith wind tail and orbital observations. The orientation of ventifact flutes thus suggests that they were formed under a different climate regime. Differences in orientations of recent and paleo-wind indicators have been noted at other Mars landing sites and may result from major orbital/axial changes that can cause significant changes in atmospheric circulation. Orientation differences between modern and older wind direction indicators at Jezero are useful clues to the climate history of the region.

JGR Planets↗
USGS2005

SEGY to ASCII Conversion and Plotting Program 2.0

INTRODUCTION SEGY has long been a standard format for storing seismic data and header information. Almost every seismic processing package can read and write seismic data in SEGY format. In the data processing world, however, ASCII format is the 'universal' standard format. Very few general-purpose plotting or computation programs will accept data in SEGY format. The software presented in this report, referred to as SEGY to ASCII (SAC), converts seismic data written in SEGY format (Barry et al., 1975) to an ASCII data file, and then creates a postscript file of the seismic data using a general plotting package (GMT, Wessel and Smith, 1995). The resulting postscript file may be plotted by any standard postscript plotting program. There are two versions of SAC: one version for plotting a SEGY file that contains a single gather, such as a stacked CDP or migrated section, and a second version for plotting multiple gathers from a SEGY file containing more than one gather, such as a collection of shot gathers. Note that if a SEGY file has multiple gathers, then each gather must have the same number of traces per gather, and each trace must have the same sample interval and number of samples per trace. SAC will read several common standards of SEGY data, including SEGY files with sample values written in either IBM or IEEE floating-point format. In addition, utility programs are present to convert non-standard Seismic Unix (.sux) SEGY files and PASSCAL (.rsy) SEGY files to standard SEGY files. SAC allows complete user control over all plotting parameters including label size and font, tick mark intervals, trace scaling, and the inclusion of a title and descriptive text. SAC shell scripts create a postscript image of the seismic data in vector rather than bitmap format, using GMT's pswiggle command. Although this can produce a very large postscript file, the image quality is generally superior to that of a bitmap image, and commercial programs such as Adobe Illustrator? can manipulate the image more efficiently.

Open-File Report↗
USGS2005

The orphan tsunami of 1700—Japanese clues to a parent earthquake in North America

Summary A puzzling tsunami entered Japanese history in January 1700. Samurai, merchants, and villagers wrote of minor flooding and damage. Some noted that no parent earthquake had been felt; they were wondering what had set off the waves. They had no way knowing that the tsunami had been spawned during an earthquake along the coast of northwestern North America. This orphan tsunami would not be linked to its parent earthquake until the middle 1990s, through an extraordinary series of discoveries in both North America and Japan. The Orphan Tsunami of 1700 , now in its second edition, tells this scientific detective story through its North American and Japanese clues. The discoveries underpin many of today’s precautions against earthquakes and tsunamis in the Cascadia region of northwestern North America. The Japanese tsunami of March 2011 called attention to those hazards as a mirror image of the transpacific waves of January 1700.

Professional Paper↗
USGS2004

Preliminary report on using imaging spectroscopy to map ultramafic rocks, serpentinites, and tremolite-actinolite-bearing rocks in California

Airborne Visible/InfraRed Imaging Spectrometer (AVIRIS) data were collected in approximately 3- kilometer-wide swaths over selected areas in El Dorado and Plumas Counties that contain serpentinite and ultramafic rocks as part of an experiment to determine if potentially asbestos-bearing rocks could be identified spectrally. M ineral maps created from the AVIRIS data were used successfully to delineate exposures of serpentine and tremolite-actinolite/talc in areas with up to 70 percent vegetation cover in some cases. In other cases, the density of vegetation is so high that it prevented spectral identification by AVIRIS of minerals in those areas, thus there may be more serpentine and tremolite-actinolite/talc present than is shown on the mineral maps. It also is important to note that not all tremolite-actinolite is fibrous, and just because tremolite-actinolite was mapped, does not necessarily mean it is tremolite- or actinolite-asbestos. Finally, it is difficult to spectrally distinguish tremolite-actinolite from talc using AVIRIS. Serpentine has been detected outside of known serpentinite outcrop areas, mostly as aggregate that covers dirt roads. Four flight lines of AVIRIS data were analyzed over areas selected to show trends in degree of surface exposure as a function of elevation and vegetation cover. Field checking has verified the accuracy of the mineral maps at 25 accessible locations. Eleven additional flight lines remain to be analyzed and field checked pending future funding. AVIRIS mineral mapping has shown promise as a complement to field mapping but cannot replace it. Because AVIRIS is a remote-sensing technology, the presence of serpentine or tremolite-actinolite would have to be verified in the field by direct observation and by appropriate sampling and laboratory analysis, if needed. At this time, no conclusions regarding the presence or absence of asbestos minerals in the identified areas are possible from the AVIRIS data alone. Identification of asbestos minerals in the identified areas would require appropriate sampling and laboratory analysis of the materials in those areas.

California↗
USGS2005

Geologic map of the northern plains of Mars

The northern plains of Mars cover nearly a third of the planet and constitute the planet's broadest region of lowlands. Apparently formed early in Mars' history, the northern lowlands served as a repository both for sediments shed from the adjacent ancient highlands and for volcanic flows and deposits from sources within and near the lowlands. Geomorphic evidence for extensive tectonic deformation and reworking of surface materials through release of volatiles occurs throughout the northern plains. In the polar region, Planum Boreum contains evidence for the accumulation of ice and dust, and surrounding dune fields suggest widespread aeolian transport and erosion. The most recent regional- and global-scale maps describing the geology of the northern plains are largely based on Viking Orbiter image data (Dial, 1984; Witbeck and Underwood, 1984; Scott and Tanaka, 1986; Greeley and Guest, 1987; Tanaka and Scott, 1987; Tanaka and others, 1992a; Rotto and Tanaka, 1995; Crumpler and others, 2001; McGill, 2002). These maps reveal highland, plains, volcanic, and polar units based on morphologic character, albedo, and relative ages using local stratigraphic relations and crater counts. This geologic map of the northern plains is the first published map that covers a significant part of Mars using topography and image data from both the Mars Global Surveyor and Mars Odyssey missions. The new data provide a fresh perspective on the geology of the region that reveals many previously unrecognizable units, features, and temporal relations. In addition, we adapted and instituted terrestrial mapping methods and stratigraphic conventions that we think result in a clearer and more objective map. We focus on mapping with the intent of reconstructing the history of geologic activity within the northern plains, including deposition, volcanism, erosion, tectonism, impact cratering, and other processes with the aid of comprehensive crater-density determinations. Mapped areas include all plains regions within the northern hemisphere of Mars, as well as an approximately 300-km-wide strip of cratered highland and volcanic regions, which border the plains. Note that not all of the contiguous northern plains are mapped, because some minor parts of Elysium and Amazonis Planitiae lie south of the equator.

Scientific Investigations Map↗
USGS1995

[Book review] The Eastern Screech Owl: Life History, Ecology and Behavior in the Suburbs and Countryside, by Frederick Gehlback

Review of: Eastern Screech Owl: Life History, Ecology, and Behavior in the Suburbs and Countryside. Frederick R. Gehlbach. Issue 16; Issue 2008 of W. L. Moody Jr. Natural History Series. Texas A&M University Press; 1st edition (November 1994). ISBN: 0890966095. For ornithologists and ecologists alike, Fred Gehlbach's book promises to hold both interest and information value as a comprehensive study of the eastern screech owl (Otus asio hasbroucki). Gehlbach was intrigued with screech owls as a boy and encouraged as an undergraduate by William Hamilton, who underscored that in-depth studies of familiar backyard species can be as fascinating as those in exotic sites. Correspondence with another owl-aficionado, the late H. N. Southern, inspired the author's long-term study of screech owls in a woodland landscape in central Texas and led him to provide nest boxes to enhance his access and sample size. This book is based on observations over a 25-year period-beginning in 1967, with intensive study during an 11-year period (1976-1987) in Texas south of Waco, where Gehlbach teaches at Baylor University. The study represents observations on 659 screech owls, covering several generations of birds and entire lives of many individuals. Gehlbach compares screech owl nesting behavior in a rural versus suburban setting and includes chapters on food supplies and predation tactics; egg-laying, incubation, and parental behavior; vocalizations; and population structure and flux. He discusses why screech owls are widespread across the eastern half of North America and why they succeed among people in suburban environments, where they adapt as easily to mailboxes and porch columns as to natural tree cavities. The book mixes two approaches: on the one hand the dense style of a technical book in which the professional biologist can find information on many aspects of screech owl behavior, life history, and population, including tables, figures, summary statistics, results of statistical comparisons, and experimental tests of hypotheses. On the other hand, each chapter begins with and includes vivid visual images, personal experiences, and thoughtful reflections to draw in the general reader, bridging the interesting topic to the technical details and making the information accessible to a wider audience. The reader is impressed with Dr. Gehlbach's love of his subject, his devotion to long-term study, and his care in presenting the work to his fellow ornithologists, ecologists, and all those interested in wildlife and conservation. It will be a useful reference because of its wealth of information on all aspects of screech owl life history. It is well documented and, in addition to its 10 chapters, includes 10 appendices with information on types of food supplies, bird species that mob screech owls, a daily chronology of nestling development, and a selection of edited field notes to provide background for each chapter. The book is thoroughly referenced and indexed. The Eastern Screech Owl will be read with interest by those with an interest in long-term, in-depth studies and those who love charming stories about remarkable birds with strong personalities and interesting behavior.

Wildlife Review↗
USGS2010

Streamflow of 2009--Water year summary

The maps and graph in this summary describe streamflow conditions for water-year 2009 (October 1, 2008 to September 30, 2009) in the context of the 80-year period 1930-2009, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's National Streamflow Information Program. The period 1930-2009 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. Each of the maps and graphs can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2026

Small-volume tephra deposits of the May 1924 explosions from Halemaʻumaʻu, Kīlauea volcano, and their origin

More than 50 explosive eruptions occurred from Halemaʻumaʻu at Kīlauea volcano over 17 days from May 11 to 27, 1924. Ballistics weighing as much as 14,000 kg were ejected and most landed within 2 km of the vent. Fine ash made up a major component of the tephra and was dispersed tens of kilometers downwind. Draining of the Halemaʻumaʻu lava lake occurred in late February 1924, with the crater floor eventually subsiding by a further ∼70 m (to ∼180 m below the crater rim) by the time the first explosions took place during the night of May 10–11. The largest explosions occurred on May 17–18 and smaller explosions continued until May 27, at which point Halemaʻumaʻu had more than doubled in width and depth. The explosions generated plumes reaching up to ∼10 km high with ballistics ejected up to 2 km from the crater. Almost 100 years later, we investigate and characterize the preserved tephra deposits within ∼3 km of the 1924 crater rim. Grain size and shape analyses were performed on 202 samples collected from 34 tephra profiles using dynamic image analysis, with a subset of layers from nine tephra profiles used for componentry (200 grains per layer in the 0.5–1 mm size fraction). Additionally, we characterize the average diameters (using the five largest clasts) at 216 locations and measure the average diameters of 2291 ballistics (largest per ∼100 m 2 area). Physical descriptions from fieldwork and grain size distributions were used to subdivide the tephra layers into five lithofacies: coarse homogeneous, fine homogenous, red ash, accretionary lapilli-bearing, and finely laminated. Grain size versus shape data show a range of values that demonstrate most grains are dense, smooth, and equant, in alignment with lithic clasts dominating the tephra componentry. The fine grained and accretionary lapilli-bearing nature of some of these lithofacies confirms that water influenced the style of the explosions. However, we also note juvenile clasts within many of the tephra layers, indicating that many of the layers were formed during phreatomagmatic explosions (sensu stricto), despite the eruptive mechanism being dominantly phreatic. Juvenile clasts are more abundant higher in the tephra profiles, suggesting that juvenile magma was more involved later in the explosive sequence. Thermal and hydrologic modeling indicate that groundwater inflow into a short-lived, small-diameter volcanic conduit (10-m to 120-m-diameter used for modeling) during the 78–85 days preceding the first explosion provides a physically plausible mechanism for this eruptive sequence.

Hawaii↗
USGS2011

Streamflow of 2010--Water year summary

The maps and graph in this summary describe streamflow conditions for water-year 2010 (October 1, 2009 to September 30, 2010) in the context of the 81-year period 1930-2010, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2010 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2012

Streamflow of 2011 - Water year summary

The maps and graph in this summary describe streamflow conditions for water year 2011 (October 1, 2010, to September 30, 2011) in the context of the 82-year period from 1930 through 2011, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program (http://water.usgs.gov/nsip/). The period 1930-2010 was used because, prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. Each of the maps and graphs can be expanded to a larger view by clicking on the image. In all of the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2016

Streamflow of 2015—Water year national summary

Introduction The maps and graphs in this summary describe national streamflow conditions for water year 2015 (October 1, 2014, to September 30, 2015) in the context of the 86-year period 1930–2015, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey’s (USGS) National Streamflow Information Program http://water.usgs.gov/nsip ). The period 1930–2015 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term “runoff,” which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a specified time period was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. Each of the maps and graphs can be expanded to a larger view by clicking on the image. In all of the graphics, a rank of 1 indicates the highest flow of all years analyzed. Rankings of streamflow are grouped into much-below normal, below normal, normal, above normal, and much-above normal, based on percentiles of flow (greater than 90 percent, 76–90 percent, 25–75 percent, 10–24 percent, and less than 10 percent, respectively) ( http://waterwatch.usgs.gov/?id=ww_current ). Some data used to produce maps and graphs are provisional and subject to change.

Fact Sheet↗
USGS2026

Identifying overwintering habitat of silver and bighead carp in the lower Mississippi River: Implications for harvesting and population reduction

A total of 41 sites along a 58 mi reach of the Lower Mississippi River (LMR) were surveyed during winter 2022 for invasive carp aggregation.* Sites consisting of scallops closest to the dike-vegetated bank interface with deeper, slow-moving water and consistent access back to the main channel were preferred. Carp avoided strong currents, and there was no trend in depth selection other than avoiding shallow (less than 20 ft) water. In January 2023, recreation-grade sonar (e.g., side-scan and down-imaging) surveys were conducted in the same reach of the LMR to demonstrate the technology and evaluate carp population size at sites with high abundances based on previous surveys. Fish density was estimated to be 32 fish/10,000 yd 3 (95% confidence interval [CI; 31–34]) using down-imaging software, which is the first estimate of assumed bigheaded carp density in the LMR. Additional fish collections are needed to confirm species composition and size abundance provided by sonar technology. Resurveying sites with high carp abundance over a range of river stages would be necessary to fully characterize habitat conditions, evaluate influence of river stage on occupancy duration, and continue to evaluate species composition and mass removal techniques as a management option in the Lower Mississippi River.

Louisiana, Mississippi↗
USGS2004

Map showing geology, oil and gas fields, and geologic provinces of the Caribbean Region

This CD-ROM compilation contains a map and associated spatial data showing surface geology, faults, oil and gas field centerpoints, and geologic provinces of the Caribbean region, draped over a shaded relief image of topography and bathymetry. The map is provided in the Environmental Systems Research Institute, Inc. (ESRI) ArcMap and ArcReader GIS formats, as well as in Adobe Acrobat Portable Document Format (PDF). On this CD-ROM, ESRI ArcReader and Adobe Acrobat Reader software provide a way to view and interact with the maps. The organization and user-friendly navigation of this CD-ROM ensure easy access to its maps and data by using the links on the right side of each page. A link to the USGS World Energy Project website is also provided to access the latest information, updates, and interactive maps, as they relate to this and other world energy products. In addition, system requirements, permission, and contact information can be found in the readme section of this product. Navigation of this product can be fully utilized with most web browsers (Internet Explorer 6.0/Netscape Navigator 7.1 or later recommended). Note: an Internet connection is necessary to view USGS website links, World Energy website, and the Caribbean Internet Map Service.

Open-File Report↗
USGS1982

A regional assessment of potential environmental hazards to and limitations on petroleum development of the Southeastern United States Atlantic continental shelf, slope, and rise, offshore North Carolina

More than 11,000 km of high-resolution seismic-reflection data, 325 km of mid-range sidescan-sonar data, and 500 km of long-range sidescan-sonar data were examined and used to construct an environmental geology map of the Continental Shelf, Slope, and Rise for the area of the U.S. Atlantic margin between lats. 32?N. and 37?N. Hardgrounds and two faults described in previous literature also are shown on the map. On the Continental Shelf, at least two faults, the Helena Banks fault and the White Oak lineament, appear to be tectonic in origin. However, a lack of historical seismicity associated with these faults indicates that they are probably not active at the present time. Hardgrounds are widely scattered but are most abundant in Onslow Bay. Although paleostream channels are common nearshore, they do not appear to be common on the central and outer shelf except off Albemarle Sound where extensive Pleistocene, Pliocene, and late Miocene channels extend across the shelf. Mobile bottom sediments are confined mainly to the shoals off Cape Romain, Cape Fear, Cape Lookout, and Cape Hatteras. Elsewhere the sand cover is thin, and older more indurated rocks are present in subcrop. No slope-instability features were noted on the Florida-Hatteras slope off North Carolina. The lack of features indicates that this slope is relatively stable. Evidence for scour by strong currents is ubiquitous on the northern Blake Plateau although deep-water reefs are sparse. The outer edge of the plateau is dominated by a major growth fault and numerous splay and antithetic faults. These faults are the product of salt tectonism in the Carolina trough and thus are not associated with seismicity. Displacements observed near the sea floor and breached diapirs offshore indicate that the main fault is still moving. Associated with the faults are collapse features that are interpreted to be caused by karst solution and cavernous porosity in Eocene and Oligocene limestones at depth. Major slumps have taken place in two large areas of the Continental Slope. Seismic-reflection profiles of the southern area, centered on the lower slope at 1at. 33?N., long. 76?W., show a 80-m-hlgh scarp in which bedding has been truncated. Rotational slump faults are present in this area on the middle and upper slope. Sidescan images show that large blocks have slid downslope from the scarp face, furrowing the bottom. High-resolution (3.5-kHz) records show that the rotational slump faults upslope are active. The association of these slumps and the scarps with salt diapirs suggests subsidence accompanying salt tectonism as the cause. Seismic-reflection records over the northern area, at about fat. 36?20'N., long. 74?40'W., show two steep scarps, each about 225 m high on the upper and middle-slope. These slump scars and an absence of Pleistocene sediments indicate that large blocks of the slope have been removed by slumping. The slope north of fat. 35?N. is highly dissected by canyons. Mid-range sidescan-sonar records suggest that the canyons are the product of mass wasting and have probably formed largely by slumping. Sediments in a wide zone on the upper rise are highly disturbed and faulted owing to salt tectonism. Twenty-six salt diapirs are mapped, as is a zone of disturbed bottom related to salt tectonism. An area of frozen bottom (clathrate) under which shallow free gas is trapped underlies the outer Blake Plateau, the slope, and the upper rise. Although the hazards of drilling into or through clathrates have not been tested, the release of gas from beneath this frozen layer may prove to be a primary hazard to exploration.

Open-File Report↗
USGS2007

Streamflow of 2006 -- Water Year Summary

The maps and graphs appearing in this summary describe streamflow conditions for water-year 2006 (October 1, 2005 to September 30, 2006) in the context of the 77-year period 1930-2006, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2006 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term 'runoff,' which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. The runoff value for a geographic area is computed as the median runoff value for all streamgages in that geographic area. For example, the runoff value for a state is the median for all streamgages in that state, and the median for the Nation is the median value for all streamgages in the Nation. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2008

Streamflow of 2007--Water year summary

The maps and graphs appearing in this summary describe streamflow conditions for water-year 2007 (October 1, 2006 to September 30, 2007) in the context of the 78-year period 1930-2007, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2007 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. The runoff value for a geographic area is computed as the median runoff value for all streamgages in that geographic area. For example, the runoff value for a State is the median for all streamgages in that State, and the median for the Nation is the median value for all streamgages in the Nation. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗