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At least 631 records · Page 35Linked to original sources

USGS2021

A multidisciplinary investigation into the eruptive style, processes, and duration of a Cascades back-arc tholeiitic basalt: A case study of the Brushy Butte flow field, northern California, United States

The Cascades back-arc in northern California is dominated by monogenetic tholeiitic basalts that erupted throughout the Pleistocene. Elucidating their eruptive history and processes is important for understanding potential future eruptions here. We focus on the well-exposed monogenetic volcano that emplaced the Brushy Butte flow field, which constructed a ∼150 m tall edifice, has flow lobes up to >10 km long, and in total covers ∼150 km 2 with an eruptive volume of 3.5 km 3 . We use a multidisciplinary approach of field mapping, petrography, geochemistry, paleomagnetism, geochronology, and lidar imagery to unravel the eruptive history and processes that emplaced this flow field. Tholeiitic basalts in northern California have diverse surface morphology and vegetation cover but similar petrographic appearances, which makes them hard to distinguish in the field. Geochemistry and paleomagnetism offer an independent means of distinguishing tholeiitic basalts. Brushy Butte flow field lavas are similar in major-oxide and trace-element abundances but differ from adjacent tholeiitic basalts. This is also apparent in remanent magnetic directions. Additionally, paleomagnetism indicates that the flow field was emplaced during a geologically brief time interval (10–20 years), which 36 Cl cosmogenic dating puts at 35.7 ± 1.7 ka. Lidar imagery shows that these flows erupted from at least 28 vents encompassing multiple scoria cones, spatter cones, and craters. Flows can be grouped into four pulses using stratigraphic position and volume. Pulse 1 is the most voluminous, comprising eight eruptions and ∼2.3 km 3 . Each subsequent pulse started rapidly but decayed quickly, and each successive pulse erupted less lava (i.e., 2.3 km 3 for pulse 1, 0.6 km 3 for pulse 2, 0.3 km 3 for pulse 3, and 0.2 km 3 for pulse 4). Many of these flows host well-established lava channels and levees (with channel breakouts) that lead to lava fans, with some flows hosting lava ponds. Similar flow features from tholeiitic eruptions elsewhere demonstrate that these morphologies generally occur over weeks, months, or longer (e.g., Puʻu ʻŌʻō eruption at K–llauea, Hawaiʻi). This multidisciplinary study shows the range of eruptive styles and durations of a Cascades back-arc eruption and illustrates how potential future tholeiitic eruptive activity in the western United States might progress.

California↗

USGS2023

Modeling the effects of interior headland restoration on estuarine sediment transport processes in a marine-dominant estuary

The effects of interior headland restoration on estuarine sediment transport processes were assessed through process-based numerical modeling. Three proposed interior headland restoration scenarios in the Grand Bay estuary (Mississippi/Alabama) were modeled using Delft3D to understand impacts on suspended sediment concentrations, bed level morphology, and sediment fluxes under present-day conditions and a sea level rise (SLR) of 0.5 m, representing a high projection of SLR by the year 2050. Model results showed localized differences in bed levels near the restored features after a year of simulated morphologic change. The restored headland features acted as a sediment source to the immediate surroundings while also providing some non-significant sheltering effect of backshore shoals and marsh shorelines. Sediment fluxes were sensitive to wind directions and the presence of the restored headlands. However, regardless of wind direction, mean sea level, or restoration action, the greatest sediment fluxes were always export fluxes from the estuary, which were further increased with increased sea level. Suspended sediment concentrations were highly influenced by SLR in a non-linear manner. Sediment concentrations both increased and decreased depending on depth under SLR. Furthermore, SLR allowed for the suspension and deposition of sediments on the marsh platform. Overall, the influence of SLR was more impactful to changing sediment dynamics than the influence of the restoration features.

Alabama↗

USGS2022

A geomorphic-process-based cellular automata model of colluvial wedge morphology and stratigraphy

The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. To explore theoretical colluvial wedge evolution, we develop a cellular automata model driven by the production and disturbance (e.g., bioturbative reworking) of mobile regolith and fault-scarp collapse. We consider both 90 and 60 ∘ dipping faults and allow the colluvial wedges to develop over 2000 model years. By tracking sediment transport time, velocity, and provenance, we classify cells into analogs for the debris and wash sedimentary facies commonly described in paleoseismic studies. High values of mobile regolith production and disturbance rates produce relatively larger and more wash-facies-dominated wedges, whereas lower values produced relatively smaller, debris-facies-dominated wedges. Higher lateral collapse rates lead to more debris facies relative to wash facies. Many of the modeled colluvial wedges fully developed within 2000 model years after the earthquake, with many being much faster when process rates are high. Finally, for scenarios with the same amount of vertical displacement, differently sized colluvial wedges developed depending on the rates of geomorphic processes and fault dip. A change in these variables, say by environmental change such as precipitation rates, could theoretically result in different colluvial wedge facies assemblages for the same characteristic earthquake rupture scenario. Finally, the stochastic nature of collapse events, when coupled with high disturbance, illustrates that multiple phases of colluvial deposition are theoretically possible for a single earthquake event.

Earth Surface Dynamics↗

USGS1997

Geochemical processes controlling uranium mobility in mine drainages

Comprehensive models of ore genesis incorporate metal sources, transport and concentration mechanisms, and preservation mechanisms. Analogous concepts apply to the problem of metal migration from mines, mine wastes, and mine tailings, including: the concentrations, mineralogical occurrence, and availability of metals in mineral deposits, host rocks, mine wastes, and tailings (the source); the mechanisms for metal mobilization and transport during weathering; the mechanisms for metal fixation and the permanence of the fixation. Similarly, undisturbed mineral deposits or alteration zones that are exposed at the Earth's surface may be natural sources from which metals can be solubilized during weathering. Uranium (U), a naturally-occurring radioactive element, may be present in mineral deposits in sufficient concentrations that in itself constitutes ore. It may also be present in ores of other metals at concentrations that exceed average crustal abundances. Any uranium that is not completely removed from these ores in the mining and milling process may be available for mobilization into ground or surface waters via the weathering and oxidation of solid tailings or mine waste piles. This chapter discusses the relative importance of various geochemical processes that control uranium mobility via weathering in both mined and unmined mineralized environments. The data presented in this paper focus on mined areas because the great extent of historic mining in the field areas examined for this study preclude extensive consideration of undisturbed areas.

Book chapter↗

USGS2015

Getting ocean acidification on decision makers' to-do lists: dissecting the process through case studies

Much of the detailed, incremental knowledge being generated by current scientific research on ocean acidification (OA) does not directly address the needs of decision makers, who are asking broad questions such as: Where will OA harm marine resources next? When will this happen? Who will be affected? And how much will it cost? In this review, we use a series of mainly US-based case studies to explore the needs of local to international-scale groups that are making decisions to address OA concerns. Decisions concerning OA have been made most naturally and easily when information needs were clearly defined and closely aligned with science outputs and initiatives. For decisions requiring more complex information, the process slows dramatically. Decision making about OA is greatly aided (1) when a mixture of specialists participates, including scientists, resource users and managers, and policy and law makers; (2) when goals can be clearly agreed upon at the beginning of the process; (3) when mixed groups of specialists plan and create translational documents explaining the likely outcomes of policy decisions on ecosystems and natural resources; (4) when regional work on OA fits into an existing set of priorities concerning climate or water quality; and (5) when decision making can be reviewed and enhanced.

Oceanography↗

USGS2007

Evaluation of marsh development processes at Fire Island National Seashore: Recent and historic perspectives

Purpose and significance of the study: Salt marshes are dynamic environments, increasing in vertical elevation and migrating, often landward, as sea level rises. With sea level rise greater than marsh elevation increase, marshes can be submerged, marsh soils become waterlogged, and plant growth becomes stressed, often resulting in conversion of vegetation-dominated marsh to mudflat or open water habitat. Given that the rate of sea level rise is expected to accelerate over the next century and that some marshes in the northeast are becoming submerged (e.g., Jamaica Bay, NY), it is important to understand the processes that control marsh development. More specifically, the objectives of this project were to quantify vertical marsh elevation change in relation to recent rates of sea-level rise and to investigate factors or processes that are most influential in controlling the development and maintenance of Fire Island salt marshes.

Report↗

USGS2003

Storms as agents of wetland elevation change: their impact on surface and subsurface sediment processes

Direct measures of the impact of major storms on wetland sediment elevation are rare. Recently developed techniques have enabled simultaneous, quantitative observations of surface and subsurface processes affecting sediment elevation. An analysis of ten wetland sites revealed the following patterns of sediment elevation change after storm passage: (1) elevation change equivalent to sediment accretion or erosion, (2) elevation loss in spite of sediment deposition, or in excess of erosion, and (3) elevation gain greater than the amount of sediment accretion. These observations suggest that storms influence sediment elevation not only by sediment deposition and erosion but also through subsurface processes of sediment compaction, root growth and decomposition, and water flux. Wetlands receiving a substantial deposit of sediment did not always realize an equivalent elevation gain. Some realized a net loss in elevation as a result of sediment compaction apparently caused by the weight of the sediment deposit or the tidal surge waters, or both. Sediment elevation collapsed in two mangrove forests with highly organic substrate when the storm killed the forest. In two marshes, elevation gain exceeded deposition apparently through increased sediment water storage or plant root growth via nutrient enrichment from storm sediment deposits. The elevation responses were either temporary or permanent on an ecological time scale (> 8 years). In one organic marsh substrate, compaction was followed by expansion, only to be compacted again by another storm. Thus the elevation response of coastal wetlands to major storms varied depending on local substrate conditions and degree of storm impact.

Book chapter↗

USGS2011

Connecting pattern and process in greater sage-grouse populations and sagebrush landscapes

Abstract. Spatial patterns influence the processes that maintain Greater Sage-Grouse (Centrocercus urophasianus) populations and sagebrush (Artemisia spp.) landscapes on which they depend. We used connectivity analyses to: (1) delineate the dominant pattern of sagebrush landscapes; (2) identify regions of the current range-wide distribution of Greater Sage-Grouse important for conservation; (3) estimate distance thresholds that potentially isolate populations; and (4) understand how landscape pattern, environmental disturbance, or location within the spatial network influenced lek persistence during a population decline. Long-term viability of sagebrush, assessed from its dominance in relatively unfragmented landscapes, likely is greatest in south-central Oregon and northwest Nevada; the Owyhee region of southeast Oregon, southwest Idaho, and northern Nevada; southwest Wyoming; and south-central Wyoming. The most important leks (breeding locations) for maintaining connectivity, characterized by higher counts of sage-grouse and connections with other leks, were within the core regions of the sage-grouse range. Sage-grouse populations presently have the highest levels of connectivity in the Wyoming Basin and lowest in the Columbia Basin Sage-Grouse management zones (SMZs). Leks separated by distances 13-18 km could be isolated due to decreased probability of dispersals from neighboring leks. The range-wide distribution of sage-grouse was clustered into 209 separate components (units in which leks were interconnected within but not among) when dispersal was limited to distances 18 km. The most important components for maintaining connectivity were distributed across the central and eastern regions of the range-wide distribution. Connectivity among sage-grouse populations was lost during population declines from 1965-1979 to 1998-2007, most dramatically in the Columbia Basin SMZ. Leks that persisted during this period were larger in size, were more highly connected, and had lower levels of broad-scale fire and human disturbance. Protecting core regions and maintaining connectivity with more isolated sage-grouse populations may help reverse or stabilize the processes of range contraction and isolation that have resulted in long-term population declines.

Book chapter↗

USGS1986

Processing techniques for digital sonar images from GLORIA.

Image processing techniques have been developed to handle data from one of the newest members of the remote sensing family of digital imaging systems. This paper discusses software to process data collected by the GLORIA (Geological Long Range Inclined Asdic) sonar imaging system, designed and built by the Institute of Oceanographic Sciences (IOS) in England, to correct for both geometric and radiometric distortions that exist in the original 'raw' data. Preprocessing algorithms that are GLORIA-specific include corrections for slant-range geometry, water column offset, aspect ratio distortion, changes in the ship's velocity, speckle noise, and shading problems caused by the power drop-off which occurs as a function of range.-from Author

Photogrammetric Engineering and Remote Sensing↗

USGS1986

USE OF SPACE TECHNOLOGY IN FEDERALLY FUNDED LAND PROCESSES RESEARCH IN THE UNITED STATES.

A review of the use of space technology in federally funded earth science research in the US was carried out in 1985 by the President's Office of Science and Technology Policy. Five departments and three independent agencies, representing the primary earth science research agencies in the Federal government, participated in the review. The review by the subcommittee indicated that, while there is considerable overlap in the legislated missions of the earth science agencies, most of the space-related land processes research is complementary. Summaries are provided of the current and projected uses of space technology in land processes activities within the eight Federal organizations.

Conference Paper↗

USGS1987

US GEOLOGICAL SURVEY'S NATIONAL SYSTEM FOR PROCESSING AND DISTRIBUTION OF NEAR REAL-TIME HYDROLOGICAL DATA.

The US Geological Survey is utilizing a national network of more than 1000 satellite data-collection stations, four satellite-relay direct-readout ground stations, and more than 50 computers linked together in a private telecommunications network to acquire, process, and distribute hydrological data in near real-time. The four Survey offices operating a satellite direct-readout ground station provide near real-time hydrological data to computers located in other Survey offices through the Survey's Distributed Information System. The computerized distribution system permits automated data processing and distribution to be carried out in a timely manner under the control and operation of the Survey office responsible for the data-collection stations and for the dissemination of hydrological information to the water-data users.

Conference Paper↗

USGS1994

Hydraulics and sediment transport processes in a pool-riffle rocky mountain stream

Sediment transport processes related to varying channel-bed morphology were investigated from April to November, 1993 along a 1 km pool-riffle and step-pool reach of North Saint Vrain Creek, a small mountain stream in the Northern Colorado Rocky Mountains. Three hundred sixteen 16-256 mm tracer particles placed in two separate pool-riffle-pool sequences, forty-three direct bedload measurements at three separate cross-sections in discharges ranging between 0.27-8.8 m3/s, and indirect velocity measurements at thirteen cross-sections in 23 discharges ranging between 0.23-9.2 m3/s are used to assess sediment sorting patterns and sediment transport capacity variations. An investigation of secondary flow features and wave patterns provides preliminary evidence of turbulent controls on sediment entrainment and transport, and was used to develop a conceptual model of bedload transport and channel-bed maintenance on North Saint Vrain Creek. Recirculating eddy systems provide a means to constrict flow in pools, leading to modeled velocity-reversals at high flows. Tracer particle depositional evidence also indicates higher sediment transport capacities in pools versus riffles at high flow. Modeled hydraulic conditions and depositional evidence of tracers indicates that high-flow recirculating-eddy-influenced velocity-reversals and associated turbulence may provide the primary pool maintenance processes in this channel.

Conference Paper↗

USGS1994

Rates and processes of bluff recession along the Lake Michigan shoreline in Illinois

Examined bluffs along 30 km of the Lake Michigan shoreline from Wilmette to Waukegan, Illinois, to measure amounts and variation in retreat rates and to determine what factors control rates and processes of retreat. The predominant bluff-retreat process is shallow- to intermediate-depth translational landsliding triggered by heavy rainfall and wave erosion at the base of the bluff; rotational slumping and shallow creep and earth flow also are common. Using historical maps and airphotos, we measured amounts of bluff-top retreat at 300 locations. For two time periods, 1872-1937 and 1937-1987, rates of retreat vary from 10 to 75 cm/yr between discrete segments of bluffs (defined by lithology) and between time periods for a given bluff segment. The average retreat rates for the entire area, however, do not vary significantly between the two time periods and are approximately 20-25 cm/yr. Longterm average and short-term extreme lake levels and precipitation also do not vary significantly between the two periods, and thus local temporal variations in retreat rate cannot be attributed to these factors. Shore protection built to date may have altered the spatial distribution of retreat rates in the area but has had little overall effect on the average regional retreat rates. -from Authors

Journal of Great Lakes Research↗

USGS1994

Strong-motion data processing

Processing of strong-motion earthquake accelerograms is now carried out routinely on a world-wide basis. Two international workshops have given participants the opportunity to assess their capabilities. Data from the larger instrumentation networks are disseminated widely. The US Geological Survey's strong-motion network consists largely of film recorders, due to their long reliable life and the relatively slow addition of digital recorders. The USGS processing of film records contains steps which have become necessary in dealing with the triggered nature of these records.

Conference Paper↗

USGS1997

Bathymetric comparisons adjacent to the Louisiana barrier islands: Processes of large-scale change

This paper summarizes the results of a comparative bathymetric study encompassing 150 km of the Louisiana barrier-island coast. Bathymetric data surrounding the islands and extending to 12 m water depth were processed from three survey periods: the 1880s, the 1930s, and the 1980s. Digital comparisons between surveys show large-scale, coherent patterns of sea-floor erosion and accretion related to the rapid erosion and disintegration of the islands. Analysis of the sea-floor data reveals two primary processes driving this change: massive longshore transport, in the littoral zone and at shoreface depths; and increased sediment storage in ebb-tidal deltas. Relative sea-level rise, although extraordinarily high in the study area, is shown to be an indirect factor in causing the area's rapid shoreline retreat rates.

Louisiana↗

USGS2003

Wildfire-related debris-flow generation through episodic progressive sediment-bulking processes, western USA

Debris-flow initiation processes on hillslopes recently burned by wildfire differ from those generally recognized on unburned, vegetated hillslopes. These differences result from fire-induced changes in the hydrologic response to rainfall events. In this study, detailed field and aerial photographic mapping, observations, and measurements of debris-flow events from three sites in the western U.S. are used to describe and evaluate the process of episodic progressive sediment bulking of storm runoff that leads to the generation of post-wildfire debris flows. Our data demonstrate the effects of material credibility, sediment availability on hillslopes and in channels, the degree of channel confinement, the formation of continuous channel incision, and the upslope contributing area and its gradient on the generation of flows and the magnitude of the response are demonstrated. ?? 2003 Millpress.

Conference Paper↗

USGS2006

Deep Europe today: Geophysical synthesis of the upper mantle structure and lithospheric processes over 3.5 Ga

We present a summary of geophysical models of the subcrustal lithosphere of Europe. This includes the results from seismic (reflection and refraction profiles, P- and S-wave tomography, mantle anisotropy), gravity, thermal, electromagnetic, elastic and petrological studies of the lithospheric mantle. We discuss major tectonic processes as reflected in the lithospheric structure of Europe, from Precambrian terrane accretion and subduction to Phanerozoic rifting, volcanism, subduction and continent-continent collision. The differences in the lithospheric structure of Precambrian and Phanerozoic Europe, as illustrated by a comparative analysis of different geophysical data, are shown to have both a compositional and a thermal origin. We propose an integrated model of physical properties of the European subcrustal lithosphere, with emphasis on the depth intervals around 150 and 250 km. At these depths, seismic velocity models, constrained by body-and surface-wave continent-scale tomography, are compared with mantle temperatures and mantle gravity anomalies. This comparison provides a framework for discussion of the physical or chemical origin of the major lithospheric anomalies and their relation to large-scale tectonic processes, which have formed the present lithosphere of Europe. ?? The Geological Society of London 2006.

Geological Society Memoir↗

USGS1973

Ground control requirements for precision processing of ERTS images

With the successful flight of the ERTS-1 satellite, orbital height images are available for precision processing into products such as 1:1,000,000-scale photomaps and enlargements up to 1:250,000 scale. In order to maintain positional error below 100 meters, control points for the precision processing must be carefully selected, clearly definitive on photos in both X and Y. Coordinates of selected control points measured on existing ½ and 15-minute standard maps provide sufficient accuracy for any space imaging system thus far defined. This procedure references the points to accepted horizontal and vertical datums. Maps as small as 1:250,000 scale can be used as source material for coordinates, but to maintain the desired accuracy, maps of 1:100,000 and larger scale should be used when available.

Book↗