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At least 1,153 records · Page 64Linked to original sources

USGS2018

Patterns, pace and processes of water-quality variability: Examples from a long-studied estuary

Environmental time series have rich information content that is invaluable for measuring and understanding changes over time and guiding policies to manage change. I extracted information from measurements of 10 water‐quality constituents in upper San Francisco Bay from 1975 to 2016, one of the longest observational records in a U.S. estuary. Changes were detected at every time scale captured by monthly sampling. Long‐term trends included increased ammonium (+53%), nitrate + nitrate (+50%), silicate (+14%), Secchi depth (+42%), and decreased chlorophyll a (Chl a ) (−74%) and suspended particulate matter (−45%). Changes at the decadal scale included abrupt shifts (Chl a , nitrate + nitrite) and oscillations between shorter trends of increase and decrease (Secchi depth, phosphate). Long‐term trends were not expressed equally across all seasons, and seasonal patterns of change varied across constituents. These examples illustrate key features of environmental variability at the land–sea interface: (1) water‐quality components change continually at time scales from months to decades; (2) patterns of seasonal, multiyear, and multidecadal change are complex and vary across constituents; (3) primary drivers of change are freshwater inflow, the master regulator of estuarine dynamics, and human activities such as river damming, water diversions, wastewater discharge, environmental policies, and species introductions; (4) extracting the full information content of time series requires multiple analyses, each revealing a different layer of insight into how changes develop over time; (5) water‐quality variability is nonstationary, so future changes cannot be forecast reliably; (6) repeated observation is an essential method of Earth system science with applications in the design and performance measures of environmental policies.

California↗

USGS2021

Identification of Global Priorities for New Mountain Protected and Conserved Areas

Mountain ecosystems are extremely diverse and fragile. They include astonishing biodiversity in terms of number of taxa and endemicity, and globally provide the most diverse range of ecosystem services. The world’s system of protected and conserved areas includes many outstanding areas within the earth’s mountainous landscape: about 19% of mountain areas are protected or conserved, globally. Furthermore, approximately 90% of the most-strongly-protected conservation estate occurs in mountains. Nevertheless, significant mountain areas are not adequately protected, and many mountain ranges are completely unprotected. Of over 6000 Key Biodiversity Areas (KBAs) in mountains worldwide, 40.4% are entirely unprotected. As the world conservation movement advocates to expand the global coverage of terrestrial protected areas over the next decade toward 30%, identifying priorities for new mountain protected and conserved areas will be most efficacious if it takes a strategic approach to ensure areas of highest value and most in need of protection are identified. This paper introduces an iterative six-step decision support tool for identifying and prioritizing candidate areas for conserving inadequately protected mountain ecosystems, species, and habitats. The tool begins with quantitative analyses of the adequacy of protection of mountain KBAs, world terrestrial ecosystems, biodiversity hotspots, and red-listed species. It then guides regional teams through qualitative assessments of other values to develop lists of priority areas to give heightened consideration for protection or conservation. The tool is framed on the notion that any of the more than 6000 mountain KBAs can be allocated into one of nine categories: four that identify inadequately protected areas prioritised for heightened consideration, two for which no further action is required unless circumstances change, and three not requiring further action due to being deemed adequately protected.

Final Report↗

USGS1989

Map showing late Quaternary faults and 1978-84 seismicity of the Los Angeles region, California

The Los Angeles region of California faces the greatest seismic risk of any part of the United States. The region is inhabited by more than 11 million people and is one of the Nation's key commercial and industrial centers. It lies astride a web of potentially active faults, including those segments of the San Andreas fault with the highest probability for generating a great earthquake during the next 30 years (Lindh, 1983; Sykes and Nishenko, 1984; Wesson and Wallace, 1985; U.S. Geological Survey, 1988). Moreover, many potentially active faults that can generate moderate-size, but damaging earthquakes lie within the metropolitan areas. Earthquakes along some of these faults—for example, a magnitude 6.5 event on the Newport-Inglewood zone—could produce losses exceeding those from a great earthquake on the more distant San Andreas fault (Evernden and Thomson, 1985). This map shows, at 1:250,000 scale, known or suspected late Quaternary faults of the Los Angeles region, the ages of their most recent surface movements, and the associated earthquake activity for a recent 7-year period (1978 through 1984). The geologic and seismologic character of these faults and their potential for generating damaging earthquakes recently were evaluated by Ziony and Yerkes (1985). The map is intended primarily to inform scientists, engineers, and planners of the distribution of those faults that may have a potential for generating damaging earthquakes and (or) displacements of the Earth's surface. The map data also should contribute to further investigations of the seismotectonic setting of the Los Angeles region. The mapped area extends from lat 33°15' N. to 34°45' N. and from long 116°45' W. to 120°00' W. This region encompasses parts of the Transverse Ranges (including the Santa Ynez, Santa Susana, Santa Monica, San Gabriel, and San Bernardino Mountains), the Los Angeles basin, part of the Mojave Desert, and segments of the Peninsular Ranges (including the Puente Hills, Santa Ana Mountains, and the northern San Jacinto Mountains). Offshore, it includes the eastern Santa Barbara Channel, several of the Channel Islands, the Santa Monica and San Pedro basins, Santa Catalina Island, and part of the Gulf of Santa Catalina. In addition to the Los Angeles metropolitan area, the cities of Santa Barbara, Ventura, Riverside, and San Bernardino are within the map area.

California↗

USGS1997

Isotopic and trace element compositions of upper mantle and lower crustal xenoliths, Cima volcanic field, California: Implications for evolution of the subcontinental lithospheric mantle

Ultramafic and mafic xenoliths from the Cima volcanic field, southern California, provide evidence of episodic modification of the upper mantle and underplating of the crust beneath a portion of the southern Basin and Range province. The upper mantle xenoliths include spinel peridotite and anhydrous and hydrous pyroxenite, some cut by igneous-textured pyroxenite-gabbro veins and dikes and some by veins of amphibole ?? plagioclase. Igneous-textured pyroxenites and gabbros like the dike rocks also occur abundantly as isolated xenoliths inferred to represent underplated crust. Mineral and whole rock trace element compositions among and within the different groups of xenoliths are highly variable, reflecting multiple processes that include magma-mantle wall rock reactions, episodic intrusion and it filtration of basaltic melts of varied sources into the mantle wall rock, and fractionation. Nd, Sr, and Pb isotopic compositions mostly of clinopyroxene and plagioclase mineral separates show distinct differences between mantle xenoliths (??Nd = -5.7 to +3.4; 87Sr/86Sr = 0.7051 - 0.7073; 206Pb/204Pb = 19.045 - 19.195) and the igneous-textured xenoliths (??Nd = +7.7 to +11.7; 87Sr/86Sr = 0.7027 - 0.7036 with one carbonate-affected outlier at 0.7054; and 206Pb/204Pb = 18.751 - 19.068), so that they cannot be related. The igneous-textured pyroxenites and gabbros are similar in their isotopic compositions to the host basaltic rocks, which have ??Nd of+5.1 to +9.3; 87Sr/86Sr of 0.7028 - 0.7050, and 206Pb/204Pb of 18.685 - 21.050. The igneous-textured pyroxenites and gabbros are therefore inferred to be related to the host rocks as earlier cogenetic intrusions in the mantle and in the lower crust. Two samples of peridotite, one modally metasomatized by amphibole and the other by plagioclase, have isotopic compositions intermediate between the igneous-textured xenoliths and the mantle rock, suggesting mixing, but also derivation of the metasomatizing magmas from two separate and distinct sources. Sm-Nd two-mineral "isochrons" yield apparent ages for petrographically identical rocks believed to be coeval ranging from -0 to 113 ?? 26 Ma, indicating the unreliability of dating these rocks with this method. Amphibole and plagioclase megacrysts are isotopically like the host basalts and probably originate by mechanical breakup of veins comagmatic with the host basaltic rocks. Unlike other Basin and Range localities, Cima Cr-diopside group isotopic compositions do not overlap with those of the host basalts. Copyright 1997 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2005

Spatial structures of stream and hillslope drainage networks following gully erosion after wildfire

The drainage networks of catchment areas burned by wildfire were analysed at several scales. The smallest scale (1-1000 m2) representative of hillslopes, and the small scale (1000 m2 to 1 km2), representative of small catchments, were characterized by the analysis of field measurements. The large scale (1-1000 km2), representative of perennial stream networks, was derived from a 30-m digital elevation model and analysed by computer analysis. Scaling laws used to describe large-scale drainage networks could be extrapolated to the small scale but could not describe the smallest scale of drainage structures observed in the hillslope region. The hillslope drainage network appears to have a second-order effect that reduces the number of order 1 and order 2 streams predicted by the large-scale channel structure. This network comprises two spatial patterns of rills with width-to-depth ratios typically less than 10. One pattern is parallel rills draining nearly planar hillslope surfaces, and the other pattern is three to six converging rills draining the critical source area uphill from an order 1 channel head. The magnitude of this critical area depends on infiltration, hillslope roughness and critical shear stress for erosion of sediment, all of which can be substantially altered by wildfire. Order 1 and 2 streams were found to constitute the interface region, which is altered by a disturbance, like wildfire, from subtle unchannelized drainages in unburned catchments to incised drainages. These drainages are characterized by gullies also with width-to-depth ratios typically less than 10 in burned catchments. The regions (hillslope, interface and chanel) had different drainage network structures to collect and transfer water and sediment. Copyright ?? 2005 John Wiley & Sons, Ltd.

Earth Surface Processes and Landforms↗

USGS1969

40Ar/36Ar analyses of historic lava flows

The ratio 40 Ar/ 36 Ar was measured for 26 subaerial historic lava flows. Approximately one-third of the samples had 40 Ar/ 36 Ar ratios either higher or lower than the atmospheric value of 295.5 at the 95% confidence level. Excess radiogenic 40 Ar in five flows ranged from about 1 × 10 −13 to 1.5 × 10 −12 mol/g. Possible excess 36 Ar in three flows was on the order of 10 −16 to 10 −15 mol/g. Upper 95% confidence limits for excess 40 Ar in samples with normal 40 Ar/ 36 Ar ratios are generally less than 3 × 10 −13 mol/g. The origin of the excess 36 Ar is unknown but it may be due either to the incorporation of primitive argon that has been stored in the mantle in very low potassium environments or to enrichment in 36 Ar as atmospheric argon diffuses into the rocks after they cool.

Earth and Planetary Science Letters↗

USGS1997

Effects of El Nino on streamflow, lake level, and landslide potential

One of the most important sources of year-to-year climate variation in the Southwest is the El Niño phenomenon of the tropical Pacific Ocean. El Niño is a natural but largely unpredictable condition that results from complex interplay among clouds and storms, regional winds, oceanic temperatures, and ocean currents along the equatorial Pacific. Under "normal" conditions, the tropical trade winds blow from east to west, Figure 1. Schematic diagram of normal and El Niño conditions in the Pacific Ocean. From NOAA El Niño website. ponding up warm water in the western Pacific. In the eastern Pacific, the trade winds pull up cold, deep, nutrient-rich waters along the equator from the Ecuadorian coast to the central Pacific. The warmth of the western Pacific results in a particularly vigorous hydrologic cycle there with towering cumulus clouds and tropical storms that "radiate" atmospheric waves and disturbances across vast regions of the globe. Heat and moisture lofted into the upper atmosphere by the clouds and storms are distributed by high-altitude winds across vast regions of the globe. During an El Niño, this situation is disrupted and the trade winds weaken, thus reducing the upwelling of cool waters in the eastern Pacific and allowing the pool of warm water in the west to drift eastward toward South America. As the central and eastern Pacific warms, atmospheric pressure gradients along the equator weaken, and the trade winds diminish even more. These changes in sea-level pressure of the atmosphere are characteristic of the strongest El Niño and were identified as the "Southern Oscillation" of the global atmosphere by Sir Gilbert Walker in the early decades of this century. A chicken-and-egg relation exists between the changes in ocean temperatures and changes in winds (and atmospheric pressure gradients); the two sets of changes reinforce and drive each other but neither is clearly or universally "the" initiator of El Niño. Ocean temperatures and surface winds interact to form the complex process, El Niño-Southern Oscillation (ENSO). The interactions can be set off by subtle changes in one or the other, by buffeting from other parts of the tropics, or from regions beyond the tropics. Such a complex interplay and its uncertain (and variable) origins are the primary limitations on our ability to predict El Niño. As the waters of the central and eastern Pacific warm, the powerful tropical Pacific storms begin to form farther east than usual (Fig. 1). As the distribution of storms spreads east along the equator, their influence on global weather systems also changes. Most notably, for our purposes, the jet stream over the North Pacific Ocean is invigorated and pulled farther south than normal, where it collects moisture and storms and carries them to the southwestern United States and northern Mexico. During an El Niño, the trade winds are too weak to cause upwelling of nutrient-rich waters off the coasts of Ecuador and Peru. Generations of South American fisherman thus have recognized these conditions by the disappearance of their standard catch, commonly during December and January, every three to seven years. Because of the near coincidence in timing between these conditions and Christmas, the fishing communities have called the phenomenon "El Niño", for the Christ child. The geologic record suggests that El Niño conditions have been a part of earth's climate for at least several thousand years. An El Niño event usually lasts for several seasons, and, along with its other effects, represents an interruption of the "normal" seasonal cycle of the tropical climate. After a few seasons, and usually during spring time (in the Northern Hemisphere), the seasonal cycle reasserts itself and the tropical ocean cools back to the normal east-to-west sea-surface temperature gradients. Sometimes the warm El Niño events give way to unusually cold sea-surface temperatures and unusually strong trade winds, a condition now called La Niña. On other occasions, La Niñas may begin on their own, without an immediately preceding El Niño. The effects of the El Niño and La Niña on global climate are, in part, mirror images of each other. For example, drought is a common occurrence in the southwestern United States during La Niña, in contrast to the wet years associated with El Niño.

Arizona, California, Nevada, New Mexico, Oregon, U↗

USGS2025

Iguanas rafted more than 8,000 km from North America to Fiji

Founder-event speciation can occur when one or more organisms colonize a distant, unoccupied area via long-distance dispersal, leading to the evolution of a new species lineage. Species radiations established by long-distance, and especially transoceanic, dispersal can cause substantial shifts in regional biodiversity. Here, we investigate the occurrence and timing of the greatest known long-distance oceanic dispersal event in the history of terrestrial vertebrates—the rafting of iguanas from North America to Fiji. Iguanas are large-bodied herbivores that are well-known overwater dispersers, including species that colonized the Caribbean and the Galápagos islands. However, the origin of Fijian iguanas had not been comprehensively tested. We estimated the phylogenetic relationships and evolutionary timescale of the iguanid lizard radiation using genome-wide exons and ultraconserved elements (UCEs). Those data indicate that the closest living relative of extant Fijian iguanas is the North American desert iguana and that the two taxa likely diverged during the late Paleogene near or after the onset of volcanism that produced the Fijian archipelago. Biogeographic models estimate North America as the most probable ancestral range of Fijian iguanas. Our analyses support the hypothesis that iguanas reached Fiji via an extraordinary oceanic dispersal event from western North America, and which spanned a fifth of the earth’s circumference (>8,000 km). Overwater rafting of iguanas from North America to Fiji strengthens the importance of founder-event speciation in the diversification of iguanids and elucidates the scope of long-distance dispersal across terrestrial vertebrates.

Proceedings of the National Academy of Sciences↗

USGS1969

Paleogene floras from the Gulf of Alaska

Numerous collections of fossil plants from the Gulf of Alaska region were obtained from rocks that are well dated by marine mollusks. The mollusks indicate that the oldest possible age for the lowest plant assemblage is middle Eocene (Domengine) and that the youngest possible age for the highest Paleogene plant assemblage is middle Oligocene (Lincoln). Paleobotanical correlations indicate that the lowest plant assemblage is of early late Eocene (early Ravenian) age and the highest plant assemblage is of early Oligocene (Kummerian) age. A new provincial stage--the Angoonian--is proposed, based on assemblages from rocks in southeastern Alaska. The Angoonian is thought to be of late Oligocene (early Blakeley) age. Only one stratigraphically isolated assemblage from the Gulf of Alaska region has been recognized as of Angoonian age. The biostratigraphy of the Gulf of Alaska region and of other regions in Alaska indicates that the Seldovian, Homerian, and Clamgulchian Stages are probably entirely of Neogene age. The early Ravenian assemblages represent Paratropical Rain forest (that is, similar to vegetation of a narrow region bordering the Tropical Rain forest) based on the physiognomic analysis of foliage; the most diverse families represented are Menispermaceae and Icacinaceae. These are accompanied by palms, Anonaceae, tjristicaceae, Dipterocarpaceae, Barringtoniaceae, and Myrtaceae. A minor element is represented by broad-leaved deciduous plants. The middle Ravenian was somewhat cooler, as indicated by foliar physiognomy, the fewer Tropical Rain forest elements, and the diversity of Lauraceae. The late Ravenian assemblage represents a broad-leaved deciduous forest indicating a temperate climate. The Kummerian assemblages were again dominated by Lauraceae, and the physiognomic characters of the foliage indicate that Subtropical forest was again represented. The existence of a broad-leaved evergreen forest in Alaska such as that of the early Ravenian indicates that extended periods of darkness could probably not have existed at that time. The Alaskan Paleogene floras, as well as those from other regions, indicate that the earth's axis of rotation may not have had as great an inclination in the past. Strong climatic fluctuations evidenced by foliar physiognomy of Tertiary floras is thought to have been the result of changes in the inclination of the earth's axis. The history of the development of the Arcto-Tertiary concept is reviewed, and the fundamental lack of evidence for this concept is shown. An alternative, more complex, concept is proposed for the development of the Mixed Mesophytic forest. Paleobotanical evidence indicates that tolerances of many genera have changed during the Tertiary. Many Mixed Mesophytic genera--particularly those that are today temperate outliers of basically tropical groups--may have had a wide distribution in the Paleogene Paratropical Rain and Subtropical forests and have entered the warm temperate forests only during the later Paleogene or Neogene. Some Mixed Mesophytic groups appear to be of later Neogene origin and have been significant members of the warm temperate forests since that time. Some Mixed Mesophytic genera apparently were members of the Paratropical Rain forest only in the earliest Paleogene and became adapted to warm temperate climates by the late Eocene or perhaps even earlier. The Mixed Mesophytic forest may have developed independently in Eurasia, western North America, and eastern North America.

Alaska↗

USGS2012

Evidence for a new geomagnetic reversal from lava flows in Idaho: Discussion of short polarity reversals in the Brunhes and late Matuyama polarity chrons

K-Ar ages and paleomagnetic data for basalt samples from a new core hole (site E) at the Idaho National Engineering Laboratory (INEL) indicate that the age of the reversed polarity event recorded in Snake River Plain lavas is older than 465±50 ka (1000 years before present) reported previously by Champion et al. (1981). Nine basalt flows, eight with normal polarity and one with reversed polarity, were recognized in the site E core hole. The flows above and below the reversed flow have ages of 491±80 ka and 580±93 ka, respectively. The inclination of the paleomagnetic field direction of the reversed flow at site E agrees with the inclination of reversed flows elsewhere at INEL which have an age of 565±14 ka. These reversed flows were previously thought to be correlative with the Emperor event. We suggest that this polarity event is an older event which we name the Big Lost Reversed Polarity Subchronozone and Subchron. A review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the Brunhes and two besides the Jaramillo in the late Matuyama. These 10 short subchrons begin to indicate the many short events that Cox (1968) hypothesized must exist if polarity interval lengths have a Poisson distribution. These events are true subchrons, not excursions, and may or may not have low associated paleointensities, although low field strengths might explain why the reversal process aborts. The mean sustained polarity interval length since late Matuyama Chron time is 90,000 years. The similarity of this number with the 10 5 -year period of the Earth's orbital eccentricity suggests anew that linkage between geomagnetic, paleoclimatic, and possible underlying Earth orbital parameters should be evaluated.

Journal of Geophysical Research Solid Earth↗

USGS1949

Populations and home range relationships of the box turtle, Terrapene carolina (Linnaeus)

A population study of Terrapene carolina (Linnaeus) was made at the Patuxent Research Refuge, Maryland, from 1944 to 1947. A thirty acre area in bottomland forest was selected for intensive study. Turtles were marked by filing notches in marginal scutes according to a code. Turtles make extensive use of brushy shelter during the day as well.as at night. Gully banks and woods openings are used for sunning. Nights are usually spent in a 'form,' constructed by the turtle in leaves, debris, or earth. A form may be used once or it may be used repeatedly by the same or different turtles. Weather conditions most favorable to turtle activity are high humidity, warm sunny days, and frequent rains. Periods of activity are alternated with periods of quiet, even in favorable weather. There is no evidence for territorialism. Ranges of turtles of all ages and both sexes overlap grossly. Turtles are frequently found near each other but no antagonistic behavior has been observed. Adult turtles occupy specific home ranges which they maintain from year to year. Turtles retained their ranges even though a flood that completely covered the study area. Maximum home range diameters were determined by measurements of the mapped ranges of individual turtles. There was no significant difference between sizes of male and female ranges: males 33O+ 26 feet, females 37O+29 feet. A trail-laying device was used in following travel routes for 456 turtle days. Normal movements within the home range are characterized by (1) turns, doublings, detours, and criss-crossing paths, (2) interspersion of fairly direct traverses of the home range, (3) frequently repeated travels over certain routes. Maximum limits of the home range are ordinarily reached within a few days or weeks, although some turtles cover only one portion of the range at a time. Some turtles have two home ranges. One of these turtles was followed with a trailer for 161 days in 1946 and 1947. Trips outside the home range are made by females for egg laying. Trips of unexplained nature are made by both males and females. Turtles from other areas are occasional transients through the study plot. Standardized census trips provided data for estimating the size of the population. Census data were taken after females had returned from egg laying. The samples were spaced at intervals of a week or more to allow free movement of turtles over their ranges and assure more nearly equal availability of all turtles. These standard samples were compared by a collection ratio. Assumptions involved in the use of this ratio are discussed. Correction factors were applied to make allowance for turtles whose ranges.were partly inside and partly outside the study area, and for transient turtles. A second estimate, on the basis of the entire season's collecting, gave closely comparable results. The population of the study area is estimated to be between four and five turtles per acre, with juveniles constituting less than ten per cent of the total.

Dissertation Abstracts International↗

USGS2007

ASTER-Derived 30-Meter-Resolution Digital Elevation Models of Afghanistan

INTRODUCTION The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is an imaging instrument aboard the Terra satellite, launched on December 19, 1999, as part of the National Aeronautics and Space Administration's (NASA) Earth Observing System (EOS). The ASTER sensor consists of three subsystems: the visible and near infrared (VNIR), the shortwave infrared (SWIR), and the thermal infrared (TIR), each with a different spatial resolution (VNIR, 15 meters; SWIR, 30 meters, TIR 90 meters). The VNIR system has the capability to generate along-track stereo images that can be used to create digital elevation models (DEMs) at 30-meter resolution. Currently, the only available DEM dataset for Afghanistan is the 90-meter-resolution Shuttle Radar Topography Mission (SRTM) data. This dataset is appropriate for macroscale DEM analysis and mapping. However, ASTER provides a low cost opportunity to generate higher resolution data. For this publication, study areas were identified around populated areas and areas where higher resolution elevation data were desired to assist in natural resource assessments. The higher resolution fidelity of these DEMs can also be used for other terrain analysis including landform classification and geologic structure analysis. For this publication, ASTER scenes were processed and mosaicked to generate 36 DEMs which were created and extracted using PCI Geomatics' OrthoEngine 3D Stereo software. The ASTER images were geographically registered to Landsat data with at least 15 accurate and well distributed ground control points with a root mean square error (RMSE) of less that one pixel (15 meters). An elevation value was then assigned to each ground control point by extracting the elevation from the 90-meter SRTM data. The 36 derived DEMs demonstrate that the software correlated on nearly flat surfaces and smooth slopes accurately. Larger errors occur in cloudy and snow-covered areas, lakes, areas with steep slopes, and southeastern-facing slopes. In these areas, holes, large pits, and spikes were generated by the software during the correlation process and the automatic interpolation method. To eliminate these problems, overlapping DEMs were generated and filtered using a progressive morphologic filter. The quadrangles used to delineate the DEMs in the publication were derived from the Afghan Geodesy and Cartography Head Office's (AGCHO) 1:100,000-scale maps series quadrangles. Each DEM was clipped and assigned a name according to the associated AGCHO quadrangle name. The geospatial data included in this publication are intended to be used with any GIS software packages including, but not limited to, ESRI's ArcGIS and ERDAS IMAGINE.

Data Series↗

USGS2010

Southern high latitude dune fields on Mars: Morphology, aeolian inactivity, and climate change

In a study area spanning the martian surface poleward of 50?? S., 1190 dune fields have been identified, mapped, and categorized based on dune field morphology. Dune fields in the study area span ??? 116400km2, leading to a global dune field coverage estimate of ???904000km2, far less than that found on Earth. Based on distinct morphological features, the dune fields were grouped into six different classes that vary in interpreted aeolian activity level from potentially active to relatively inactive and eroding. The six dune field classes occur in specific latitude zones, with a sequence of reduced activity and degradation progressing poleward. In particular, the first signs of stabilization appear at ???60?? S., which broadly corresponds to the edge of high concentrations of water-equivalent hydrogen content (observed by the Neutron Spectrometer) that have been interpreted as ground ice. This near-surface ground ice likely acts to reduce sand availability in the present climate state on Mars, stabilizing high latitude dunes and allowing erosional processes to change their morphology. As a result, climatic changes in the content of near-surface ground ice are likely to influence the level of dune activity. Spatial variation of dune field classes with longitude is significant, suggesting that local conditions play a major role in determining dune field activity level. Dune fields on the south polar layered terrain, for example, appear either potentially active or inactive, indicating that at least two generations of dune building have occurred on this surface. Many dune fields show signs of degradation mixed with crisp-brinked dunes, also suggesting that more than one generation of dune building has occurred since they originally formed. Dune fields superposed on early and late Amazonian surfaces provide potential upper age limits of ???100My on the south polar layered deposits and ???3Ga elsewhere at high latitudes. No craters are present on any identifiable dune fields, which can provide a lower age limit through crater counting: assuming all relatively stabilized dune fields represent a single noncontiguous surface of uniform age, their estimated crater retention age is <???10000years. An average-sized uncratered dune field (94km2) has a crater retention age <???8My. This apparent youth suggests that present-day climate conditions are responsible for the observed degradation and reduced level of aeolian activity. A lack of observed transport pathways and the absence of large dune fields in the largest basins (Hellas and Argyre Planitiae) are consistent with the previously proposed idea that dune sands are not typically transported far from their source regions on Mars. ?? 2009 Elsevier B.V.

Geomorphology↗

USGS1998

Large-area mapping of biodiversity

The age of discovery, description, and classification of biodiversity is entering a new phase. In responding to the conservation imperative, we can now supplement the essential work of systematics with spatially explicit information on species and assemblages of species. This is possible because of recent conceptual, technical, and organizational progress in generating synoptic views of the earth's surface and a great deal of its biological content, at multiple scales of thematic as well as geographic resolution. The development of extensive spatial data on species distributions and vegetation types provides us with a framework for: (a) assessing what we know and where we know it at meso-scales, and (b) stratifying the biological universe so that higher-resolution surveys can be more efficiently implemented, coveting, for example, geographic adequacy of specimen collections, population abundance, reproductive success, and genetic dynamics. The land areas involved are very large, and the questions, such as resolution, scale, classification, and accuracy, are complex. In this paper, we provide examples from the United States Gap Analysis Program on the advantages and limitations of mapping the occurrence of terrestrial vertebrate species and dominant land-cover types over large areas as joint ventures and in multi-organizational partnerships, and how these cooperative efforts can be designed to implement results from data development and analyses as on-the-ground actions. Clearly, new frameworks for thinking about biogeographic information as well as organizational cooperation are needed if we are to have any hope of documenting the full range of species occurrences and ecological processes in ways meaningful to their management. The Gap Analysis experience provides one model for achieving these new frameworks.

Conference Paper↗

USGS2006

Sedimentary deposits of the 26 December 2004 tsunami on the northwest coast of Aceh, Indonesia

The 2004 Sumatra-Andaman tsunami flooded coastal northern Sumatra to a depth of over 20 m, deposited a discontinuous sheet of sand up to 80 cm thick, and left mud up to 5 km inland. In most places the sand sheet is normally graded, and in some it contains complex internal stratigraphy. Structures within the sand sheet may record the passage of up to 3 individual waves. We studied the 2004 tsunami deposits in detail along a flow-parallel transect about 400 m long, 16 km southwest of Banda Aceh. Near the shore along this transect, the deposit is thin or absent. Between 50 and 400 m inland it ranges in thickness from 5 to 20 cm. The main trend in thickness is a tendency to thicken by filling low spots, most dramatically at pre-existing stream channels. Deposition generally attended inundation - along the transect, the tsunami deposited sand to within about 40 m of the inundation limit. Although the tsunami deposit contains primarily material indistinguishable from material found on the beach one month after the event, it also contains grain sizes and compositions unavailable on the current beach. Along the transect we studied, these grains become increasingly dominant both landward and upward in the deposit; possibly some landward source of sediment was exposed and exploited by the passage of the waves. The deposit also contains the unabraded shells of subtidal marine organisms, suggesting that at least part of the deposit came from offshore. Grain sizes within the deposit tend to fine upward and landward, although individual units within the deposit appear massive, or show reverse grading. Sorting becomes better landward, although the most landward sites generally become poorly sorted from the inclusion of soil clasts. These sites commonly show interlayering of sandy units and soil clast units. Deposits from the 2004 tsunami in Sumatra demonstrate the complex nature of the deposits of large tsunamis. Unlike the deposits of smaller tsunamis, internal stratigraphy is complex, and will require some effort to understand. The Sumatra deposits also show the contribution of multiple sediment sources, each of which has its own composition and grain size. Such complexity may allow more accurate modeling of flow depth and flow velocity for paleotsunamis, if an understanding of how tsunami hydraulics affect sedimentation can be established. Copyright ?? The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.

Earth, Planets and Space↗

USGS2023

The 2018 eruption of Kīlauea: Insights, puzzles, and opportunities for volcano science

The science of volcanology advances disproportionately during exceptionally large or well-observed eruptions. The 2018 eruption of Kīlauea Volcano (Hawai‘i) was its most impactful in centuries, involving an outpouring of more than one cubic kilometer of basalt, a magnitude 7 flank earthquake, and the volcano’s largest summit collapse since at least the nineteenth century. Eruptive activity was documented in detail, yielding new insights into large caldera-rift eruptions; the geometry of a shallow magma storage-transport system and its interaction with rift zone tectonics; mechanisms of basaltic tephra-producing explosions; caldera collapse mechanics; and the dynamics of fissure eruptions and high-volume lava flows. Insights are broadly applicable to a range of volcanic systems and should reduce risk from future eruptions. Multidisciplinary collaboration will be required to fully leverage the diversity of monitoring data to address many of the most important outstanding questions.

Hawai‘i↗

USGS1967

Geologic framework and petroleum potential of the Atlantic Coastal Plain and continental shelf, with a section on stratigraphy

The Atlantic Coastal Plain and Continental Shelf of North America is represented by a belt of Mesozoic and Cenozoic rocks, 150 to 300 miles wide and 2,400 miles long, extending from southern Florida to the Grand Banks of Newfoundland. This belt of Mesozoic and Cenozoic rocks encompasses an area of about 400,000 to 450,000 square miles, more than three-fourths of which is covered by the Atlantic Ocean. The volume of Mesozoic and Cenozoic rocks beneath the Atlantic Coastal Plain and Continental Shelf exceeds 450,000 cubic miles, perhaps by a considerable amount. More than one-half of this is seaward far enough to contain marine source rocks in sufficient proportion to attract exploration for oil. A larger fraction, perhaps three-quarters of the volume, may be of interest in exploration for gas. The Coastal Plain consists of land between the crystalline piedmont of the Appalachian System and mean low-tide from southern Florida to the tip of Long Island plus a few small offshore islands and the Cape Cod Peninsula. This is an area of more than 100,000 square miles. The Continental Shelf extends from mean law-tide to the break marking the beginning of the continental rise, which is somewhat less than 600 feet in depth at most places. It is a gently sloping platform, about 350,000 square miles in area, that widens from less than 3 miles off southern Florida to about 285 miles off Newfoundland. The Blake Plateau occupies an area of about 70,000 square miles between the 500 and 5,000-foot bottom contours from the Cape Hatteras vicinity to the northernmost bank of the Bahamas. It has a gentle slope with only minor irregularities and scattered patches of Recent sediments. Both gravity and magnetic anomalies along the Atlantic Coast reflect primarily compositional differences at considerable depths in the earth's crust, but are related to some extent to the structure and composition of the Coastal Plain sedimentary rocks and shallow basement. Four alternating belts of predominantly positive and predominantly negative Bouguer gravity anomalies extend diagonally across the region from southwest to northeast. These correspond roughly with the continental rise and slope, the Continental Shelf and Coastal Plain, the Appalachian Mountain System front, and the Piedmont Plateau-Blue Ridge-Appalachian Basin region.

Atlantic Coastal Plain↗

USGS2012

Lower-crustal xenoliths from Jurassic kimberlite diatremes, upper Michigan (USA): Evidence for Proterozoic orogenesis and plume magmatism in the lower crust of the southern Superior Province

Jurassic kimberlites in the southern Superior Province in northern Michigan contain a variety of possible lower-crustal xenoliths, including mafic garnet granulites, rare garnet-free granulites, amphibolites and eclogites. Whole-rock major-element data for the granulites suggest affinities with tholeiitic basalts. P–T estimates for granulites indicate peak temperatures of 690–730°C and pressures of 9–12 kbar, consistent with seismic estimates of crustal thickness in the region. The granulites can be divided into two groups based on trace-element characteristics. Group 1 granulites have trace-element signatures similar to average Archean lower crust; they are light rare earth element (LREE)-enriched, with high La/Nb ratios and positive Pb anomalies. Most plot to the left of the geochron on a 206 Pb/ €204 Pb vs 207 Pb/ €204 Pb diagram, and there was probably widespread incorporation of Proterozoic to Archean components into the magmatic protoliths of these rocks. Although the age of the Group 1 granulites is not well constrained, their protoliths appear to be have been emplaced during the Mesoproterozoic and to be older than those for Group 2 granulites. Group 2 granulites are also LREE-enriched, but have strong positive Nb and Ta anomalies and low La/Nb ratios, suggesting intraplate magmatic affinities. They have trace-element characteristics similar to those of some Mid-Continent Rift (Keweenawan) basalts. They yield a Sm–Nd whole-rock errorchron age of 1046 ± 140 Ma, similar to that of Mid-Continent Rift plume magmatism. These granulites have unusually radiogenic Pb isotope compositions that plot above the 207 Pb/ €204 Pb vs 206 Pb/ €204 Pb growth curve and to the right of the 4·55 Ga geochron, and closely resemble the Pb isotope array defined by Mid-Continent Rift basalts. These Pb isotope data indicate that ancient continental lower crust is not uniformly depleted in U (and Th) relative to Pb. One granulite xenolith, S69-5, contains quartz, and has a unique peraluminous composition. It has the lowest εNd and εHf values of the suite. Its isotopic compositions indicate that it is significantly older than the other granulites. Broken zircon cores encased by younger overgrowths suggest that this granulite includes a large component of pre-existing sedimentary rocks. Two distinct populations of zircons from S69-5 were dated by sensitive high-resolution ion microprobe. Abundant rounded zircons yield ages of 1104 ± 42 (2σ) Ma, which coincide with the Mid-Continent Rift flood basalt eruptions. Their morphology is similar to those found in lower-crustal rocks that have undergone granulite-facies metamorphism and thus they are considered to represent the age of Group 2 granulites. Also present are less abundant elongate zircon grains that yield a mean age of 1387 ± 32 (2σ) Ma. Their elongate shapes indicate growth from a melt or fluid, possibly associated with 1·3–1·5 Ga anorogenic granite magmatism exposed in the shallow crust to the south in Wisconsin, or related to an initial encroachment of the Keweenawan plume upon the lower crust. Older ages recognized in zircon cores are less well constrained but may be related to tectono-magmatic events in the southern Superior craton. Within the studied suite only S69-5 was recognized as a remnant of the Late Archean lower crust into which the Group 1 and 2 mafic granulite precursor basalts were intruded. Collectively, the data show that the lower crust beneath northern Michigan formed in Archean times and underwent a variety of tectono-magmatic processes throughout the Proterozoic, including orogenesis, partial melting and mafic magmatic underplating in response to upwelling mantle plumes.

Michigan↗