SEARCH · Search USGS

Results for “Developments in Earth Surface Processes”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources

USGS2021

Sediment-ecological connectivity in a large river network

Sediment eroded from the headwaters of a large basin strongly influences channels and ecosystems far downstream, but the connection is often difficult to trace. Disturbance-dependent riparian trees are thought to rely primarily on floods for formation of the sand bars necessary for seedling establishment, but pulses of sediment should also promote formation of such features. In order to expand understanding of the role of sediment connectivity in governing ecological processes, here we explore the hypothesis that cottonwood forest along the Green and Yampa Rivers in Utah and Colorado are dominated by trees established a century ago during a period of extensive channel migration caused by significant headwater erosion. Analysis of historical documents and aerial photographs suggests that three key tributaries of the Yampa River underwent significant historical erosion from roughly 1880 to 1940. Average width and depth of tributaries with defined arroyos increased two to six times from historical surveys, resulting in the export of ~30 million metric tons of sediment, sizably increasing the sediment load and channel migration rate of the Yampa and Green Rivers. Establishment of major portions of several downstream cottonwood forests occurred during this period of historical erosion, increased sediment loads, and heightened channel migration rates, and the area of forest dating to that time is much greater than can be explained by high flows alone. Viewed collectively, our findings suggest tributary erosion played a vital role in successful downstream forest establishment, a link we contend is best illustrated through a sediment-ecological connectivity framework. Broadly, this framework facilitates consideration of linkages between morphological and ecological processes at the watershed-scale. Development and utilization of a watershed-scale sediment-ecological connectivity perspective highlights the value of sediment as a critical ecological resource to be managed jointly with flow to ensure the maintenance of vital riverine ecosystems.

Colorado, Utah↗

USGS2007

Climate Change Research at USGS Center for Earth Resources Observation and Science (EROS)

Research and development projects at EROS apply unique resources to support the USGS mission of developing understanding, monitoring, and modeling of climate variability and change and their human, physical, and biological impacts. Remote sensing resources, both new and archived, form the core of our ability to determine changes in the state or condition of the Earth’s surface and its dynamic landscape and ecosystem processes. This rich resource provides powerful biophysical information for local to global areas. Archival data form the basis for assessing human and climate impacts on the land surface, trends of land use, and an understanding of climate and management impacts. Biophysical information from satellite data is assimilated into quantitative models that allow all disciplines of the USGS to understand impacts on ecosystem processes. Major processes and problems we address include: carbon fluxes, hydrological processes, albedo changes and regional climates, mangroves and wetland protection of coastal environments, natural and manmade hazards (e.g., fire and drought), ecosystem change and succession, land use and land cover change, and more. The integration of remote sensing, modeling, and multidisciplinary approaches fosters international scientific leadership across all disciplines for the USGS.

Fact Sheet↗

USGS2025

Hyperspectral imaging of river bathymetry using an ensemble of regression trees

Remote sensing has emerged as an effective tool for characterizing river systems, and machine learning (ML) techniques could make this approach even more powerful. To explore this possibility, we developed an ML-based workflow for hyperspectral imaging of river bathymetry using an ensemble of regression trees (HIRBERT). This approach involves using paired observations of depth and reflectance to select wavelength bands as predictors and then train a depth retrieval model; applying the model to the image yields a spatially continuous bathymetric map. We used data from five rivers with diverse morphologies and optical characteristics to assess whether HIRBERT can (1) provide more accurate depth estimates than a band ratio-based algorithm and (2) extend the range of depths detectable via remote sensing. Relative to single band combinations identified via optimal band ratio analysis (OBRA), regression tree ensembles improved depth retrieval performance, with observed versus predicted (OP) regression R 2 values increasing for all five sites. Similarly, HIRBERT provided more reliable depth estimates than OBRA over the full range of depths present along each river. These results suggest that by incorporating additional spectral information from multiple wavelength bands, ML could enhance bathymetric mapping across a range of river environments. In addition, we show how graphical tools can facilitate interpretation of ML-based depth retrieval models and yield insight regarding relationships between depth and reflectance. The HIRBERT workflow is packaged in free, standalone software developed to support applications in river research and management. Although ML can enhance remote sensing of river bathymetry, the limitations of this approach must also be acknowledged: Field measurements of water depth are required to train a depth retrieval model and the resulting model should only be applied to the image from which the training data were derived. The inherently image-specific nature of this approach implies that developing generalized regression tree ensembles that could be applied at larger scales would require additional research.

California, Idaho, Nebraska, Oregon, Wyoming↗

USGS2025

Pediment formation and subsequent erosion in Gale crater: Clues to the climate history of Mars

Evidence of paleo-rivers, fans, deltas, lakes, and channel networks across Mars has prompted much debate about what climate conditions would permit the formation of these surface water derived features. Pediments, gently sloping erosional surfaces of low relief developed in bedrock, have also been identified on Mars. On Earth, these erosional landforms, often thought to be created by overland flow and shallow channelized runoff, are typically capped by fluvial sediments, and thus in exceptionally arid regions, pediments are interpreted to record past wet periods. Here we document the Greenheugh pediment in Gale crater, exploiting the observational capability of the Curiosity rover. The absence of a fluvial cap suggests that the pediment was likely cut by wind erosion, not fluvial processes. The pediment was then buried by an aeolian deposit (Stimson sandstone) that mantled the lower footslopes of Aeolis Mons (informally known as Mt. Sharp). This burial terminated active wind erosion, preserving the pediment surface (as an angular unconformity). Groundwater was present prior-to, during, and shortly after Stimson deposition, perhaps contributing to lithification and certainly to early diagenesis. Post lithification, wind erosion first cut canyons in the northern most footslopes (north of Vera Rubin ridge). Unlithified gravels were deposited in these canyons, likely due to runoff from Mt. Sharp. Boulder-rich fluvial and debris flow deposits built a > 70 m thick sequence (Gediz Vallis ridge) on the southern Greenheugh pediment. Continued wind erosion left elevated patches of gravel on the northern footslopes, and exposure age dating shows that erosion essentially ceased before 1 Ga (but possibly much earlier). Erosion to the south led to emergence of Vera Rubin ridge, retreat of the Greenheugh pediment, and the formation of Glen Torridon valley. Hence, this footslope environment of Mt. Sharp records climate-driven periods of wind erosion, aeolian deposition (and groundwater activity), surface runoff and sediment deposition, followed by further significant wind erosion that declined to present very slow rates. This likely occurred during the late Hesperian and possibly into the Amazonian.

Icarus↗

USGS2010

Mg isotope constraints on soil pore-fluid chemistry: Evidence from Santa Cruz, California

Mg isotope ratios ( 26 Mg/ 24 Mg) are reported in soil pore-fluids, rain and seawater, grass and smectite from a 90 kyr old soil, developed on an uplifted marine terrace from Santa Cruz, California. Rain water has an invariant 26 Mg/ 24 Mg ratio (expressed as δ26 Mg> δ26 Mg ) at −0.79 ± 0.05‰, identical to seawater δ26 Mg> δ26 Mg . Detrital smectite (from the base of the soil profile, and therefore unweathered) has a δ26Mg"> δ26Mg value of 0.11‰, potentially enriched in 26 Mg by up to 0.3‰ compared to the bulk silicate Earth Mg isotope composition (although within the range of all terrestrial silicates). The soil pore-waters show a continuous profile with depth for δ26 Mg> δ26 Mg , ranging from −0.99‰ near the surface to −0.43‰ at the base of the profile. Shallow pore-waters (<1 m) have δ26 Mg> δ26 Mg values that are similar to, or slightly lower than the rain waters. This implies that the degree of biological cycling of Mg in the pore-waters is relatively small and is quantified as <32%, calculated using the average Mg isotope enrichment factor between grass and rain ( δ26 Mggrass- δ26 Mgrain> δ26 Mggrass- δ26 Mgrain ) of 0.21‰. The deep pore-waters (1–15 m deep) have δ26 Mg> δ26 Mg values that are intermediate between the smectite and rain, ranging from −0.76‰ to −0.43‰, and show a similar trend with depth compared to Sr isotope ratios. The similarity between Sr and Mg isotope ratios confirms that the Mg in the pore-waters can be explained by a mixture between rain and smectite derived Mg, despite the fact that Mg and Sr concentrations may be buffered by the exchangeable reservoir. However, whilst Sr isotope ratios in the pore-waters span almost the complete range between mineral and rain inputs, Mg isotopes compositions are much closer to the rain inputs. If Mg and Sr isotope ratios are controlled uniquely by a mixture, the data can be used to estimate the mineral weathering inputs to the pore-waters, by correcting for the rain inputs. This isotopic correction is compared to the commonly used chloride correction for precipitation inputs. A consistent interpretation is only possible if Mg isotope ratios are fractionated either by the precipitation of a secondary Mg bearing phase, not detected by conventional methods, or selective leaching of 24 Mg from smectite. There is therefore dual control on the Mg isotopic composition of the pore-waters, mixing of two inputs with distinct isotopic compositions, modified by fractionation. The data provide (1) further evidence for Mg isotope fractionation at the surface of the Earth and (2) the first field evidence of Mg isotope fractionation during uptake by natural plants. The coherent behaviour of Mg isotope ratios in soil environments is encouraging for the development of Mg isotope ratios as a quantitative tracer of both weathering inputs of Mg to waters, and the physicochemical processes that cycle Mg, a major cation linked to the carbon cycle, during continental weathering.

California↗

USGS2017

Manganese

Manganese is an essential element for modern industrial societies. Its principal use is in steelmaking, where it serves as a purifying agent in iron-ore refining and as an alloy that converts iron into steel. Although the amount of manganese consumed to make a ton of steel is small, ranging from 6 to 9 kilograms, it is an irreplaceable component in the production of this fundamental material. The United States has been totally reliant on imports of manganese for many decades and will continue to be so for at least the near future. There are no domestic reserves, and although some large low-grade resources are known, they are far inferior to manganese ores readily available on the international market. World reserves of manganese are about 630 million metric tons, and annual global consumption is about 16 million metric tons. Current reserves are adequate to meet global demand for several decades. Global resources in traditional land-based deposits, including both reserves and rocks sufficiently enriched in manganese to be ores in the future, are much larger, at about 17 billion metric tons. Manganese resources in seabed deposits of ferromanganese nodules and crusts are larger than those on land and have not been fully quantified. No production from seabed deposits has yet been done, but current research and development activities are substantial and may bring parts of these seabed resources into production in the future. The advent of economically successful seabed mining could substantially alter the current scenario of manganese supply by providing a large new source of manganese in addition to traditional land-based deposits. From a purely geologic perspective, there is no global shortage of proven ores and potential new ores that could be developed from the vast tonnage of identified resources. Reserves and resources are very unevenly distributed, however. The Kalahari manganese district in South Africa contains 70 percent of the world’s identified resources and about 25 percent of its reserves. South Africa, Brazil, and Ukraine together accounted for nearly 65 percent of reserves in 2013. The combination of total import reliance for manganese, the mineral commodity’s essential uses in our industrialized society, and the potential for supply disruptions because of the limited sources of the ore makes manganese among the most critical minerals for the United States. Manganese is the 12th most abundant element in Earth’s crust. Its concentration varies among common types of rocks, mostly in the range of from 0.1 to 0.2 percent. The highest quality manganese ores contain from 40 to 45 percent manganese. The formation of these ores requires specialized geologic conditions that concentrate manganese at several hundred times its average crustal abundance. The dominant processes in forming the world’s principal deposits take place in the oceans. As a result, most important manganese deposits occur in ancient marine sedimentary rocks that are now exposed on continents as a result of subsequent tectonic uplift and erosion. In many cases, other processes have further enriched these manganiferous sedimentary rocks to form some of today’s highest grade ores. Modern seabed resources of ferromanganese nodules cover vast areas of the present ocean floor and are still forming by complex interactions of marine microorganisms, manganese dissolved in seawater, and chemical processes on the seabed. Manganese is ubiquitous in soil, water, and air. It occurs most often in solid form but can become soluble under acidic conditions. Manganese mining, like any activity that disturbs large areas of Earth’s surface, has the potential to produce increases in manganese concentrations that could be harmful to humans or the environment if not properly controlled. Although manganese is an essential nutrient for humans and most other organisms, overexposure can lead to neurotoxicity in humans. Workers at manganese mining and processing facilities have the greatest potential to inhale manganese-rich dust. Without proper protective equipment, these workers may develop a permanent neurological disorder known as manganism. Each manganese mine is unique and presents its own suite of potential hazards and preventative measures. Likewise, various nations have their own sets of standards to ensure safe mining, isolation of mine waste, treatment of mine waters, and mine closure and restoration. Interest in mining trace metals contained in ferromanganese nodules and crusts on the seabed has increased rapidly in the past decade. Prime areas for future research include overcoming the technological challenges presented by mining as deep as 6,500 meters below sea level and understanding and mitigating the potential impacts of seabed mining on marine ecosystems.

Professional Paper↗

USGS2018

On the development of a magnetic susceptibility‐based tracer for aeolian sediment transport research

Aeolian processes — the erosion, transport, and deposition of sediment by wind — play important geomorphological and ecological roles in drylands. These processes are known to impact the spatial patterns of soil, nutrients, plant‐available water, and vegetation in many dryland ecosystems. Tracers, such as rare earth elements and stable isotopes have been successfully used to quantify the transport and redistribution of sediment by aeolian processes in these ecosystems. However, many of the existing tracer techniques are labor‐intensive and cost‐prohibitive, and hence simpler alternative approaches are needed to track aeolian redistribution of sediments. To address this methodological gap, we test the applicability of a novel metal tracer‐based methodology for estimating post‐fire aeolian sediment redistribution, using spatio‐temporal measurements of low‐field magnetic susceptibility (MS). We applied magnetic metal tracers on soil microsites beneath shrub vegetation in recently burned and control treatments in a heterogeneous landscape in the Chihuahuan desert (New Mexico, USA). Our results indicate a spatially homogeneous distribution of the magnetic tracers on the landscape after post‐burn wind erosion events. MS decreased after wind erosion events on the burned shrub microsites, indicating that these areas functioned as sediment sources following the wildfire, whereas they are known to be sediment sinks in the undisturbed (e.g., not recently burned) ecosystem. This experiment represents the first step toward the development of a cost‐effective and non‐destructive tracer‐based approach to estimate the transport and redistribution of sediment by aeolian processes.

Earth Surface Processes and Landforms↗

USGS2011

The interactions between vegetation and erosion: new directions for research at the interface of ecology and geomorphology

Vegetation and processes of erosion and deposition are interactive. An objective of this paper is to review selected studies that emphasize the interdependencies. The reviews suggest new directions for research uniting ecology and geomorphology – the sub‐discipline of biogeomorphology. The research, which recently has become vigorous, includes the sources, movement, and fates of fluvial loads of sediment, organic carbon, nutrients, contaminants, and woody debris to low‐energy storage sites; the function of biota in causing soil evolution, stability, and sequestration of carbon; the development of new methods to characterize watersheds based on edaphic conditions; and the refinement of current empirical and conceptual models and dendrochronological techniques to measure landscape change. These well acknowledged topics and others less well anticipated ensure that biogeomorphology will remain vibrant.

Earth Surface Processes and Landforms↗

USGS1999

Temporal and spatial variability in thalweg profiles of a gravel-bed river

This study used successive longitudinal thalweg profiles in gravel-bed rivers to monitor changes in bed topography following floods and associated large sediment inputs. Variations in channel bed elevations, distributions of residual water depths, percentage of channel length occupied by riffles, and a spatial autocorrelation coefficient (Moran's I ) were used to quantify changes in morphological diversity and spatial structure in Redwood Creek basin, northwestern California. Bed topography in Redwood Creek and its major tributaries consists primarily of a series of pools and riffles. The size, frequency and spatial distribution of the pools and riffles have changed significantly during the past 20 years. Following large floods and high sediment input in Redwood Creek and its tributaries in 1975, variation in channel bed elevations was low and the percentage of the channel length occupied by riffles was high. Over the next 20 years, variation in bed elevations increased while the length of channel occupied by riffles decreased. An index [(standard deviation of residual water depth/bankfull depth) × 100] was developed to compare variations in bed elevation over a range of stream sizes, with a higher index being indicative of greater morphological diversity. Spatial autocorrelation in the bed elevation data was apparent at both fine and coarse scales in many of the thalweg profiles and the observed spatial pattern of bed elevations was found to be related to the dominant channel material and the time since disturbance. River reaches in which forced pools dominated, and in which large woody debris and bed particles could not be easily mobilized, exhibited a random distribution of bed elevations. In contrast, in reaches where alternate bars dominated, and both wood and gravel were readily transported, regularly spaced bed topography developed at a spacing that increased with time since disturbance. This pattern of regularly spaced bed features was reversed following a 12-year flood when bed elevations became more randomly arranged.

Earth Surface Processes and Landforms↗

USGS1983

Subsidence from underground mining; environmental analysis and planning considerations

Subsidence, a universal process that occurs in response to the voids created by extracting solids or liquids from beneath the Earth's surface, is controlled by many factors including mining methods, depth of extraction, thickness of deposit, and topography, as well as the in situ properties of the rock mass above the deposit. The impacts of subsidence are potentially severe in terms of damage to surface utility lines and structures, changes in surface-water and ground-water conditions, and effects on vegetation and animals. Although subsidence cannot be eliminated, it can be reduced or controlled in areas where deformation of the ground surface would produce dangerous or costly effects. Subsidence prediction is highly developed in Europe where there are comparatively uniform mining conditions and a long history of field measurements. Much of this mining has been carried out beneath crowded urban and industrial areas where accurate predictions have facilitated use of the surface and reduced undesirable impacts. Concerted efforts to understand subsidence processes in the United States are recent. Empirical methods of subsidence analysis and prediction based on local conditions seem better suited to the current state of knowledge of the varied geologic and topographic conditions in domestic coal mining regions than do theoretical/mathematical approaches. In order to develop broadly applicable subsidence prediction methods and models for the United States, more information is needed on magnitude and timing of ground movements and geologic properties.

Circular↗

USGS2023

SaTSeaD: Satellite Triangulated Sea Depth open-source bathymetry module for NASA Ames Stereo Pipeline

We developed the first-ever bathymetric module for the NASA Ames Stereo Pipeline (ASP) open-source topographic software called Satellite Triangulated Sea Depth, or SaTSeaD, to derive nearshore bathymetry from stereo imagery. Correct bathymetry measurements depend on water surface elevation, and whereas previous methods considered the water surface horizontal, our bathymetric module accounts for the curvature of the Earth in the imagery. The process is semiautomatic, reliable, and repeatable, independent of any external bathymetry data eliminating user bias in selecting bathymetry calibration points, and it can generate a fully integrated and seamless topo-bathymetry digital elevation model (TBDEM) in the same coordinate system, comparable with the band-ratio method irrespective of the regression method used for the band-ratio algorithm. The ASP output can be improved by applying a camera bundle adjustment to minimize reprojection errors and by alignment to a more accurate topographic (above water) surface without any bathymetric input since the derived TBDEM is a rigid surface. These procedures can decrease bathymetry root mean square errors from 30 to 80 percent, depending on environmental conditions, the quality of satellite imagery, and the spectral band used (e.g., blue, green, or panchromatic).

Remote Sensing↗

USGS2006

The Piedmont landscape of Maryland: a new look at an old problem.

Both equilibrium and episodic erosion features can be recognized in the modern landscape. An equilibrium condition is suggested by adjustment of first and second order streams to rock structure and lithology, entrenchment of some streams against gneiss domes, altitudinal zonation of rock types around gneiss domes, correlation of lithology with overburden thickness on uplands, etc. The long-term episodic character of erosion is suggested by clastic wedges on the adjacent Coastal Plain, an upland of low relief that truncates non-carbonate rocks of different lithologies, isovolumetric chemical weathering of alumino-silicate rocks, clastic deposition in marble valleys, and weathering profile truncation by modern drainage. The upland surface preserved in the eastern Piedmont developed by the Late Cretaceous. In the interval from the Late Cretaceous to the Late Miocene, low input of terrigenous sediments to the Coastal Plain, dominance of marine sedimentation, and spotty evidence of saprolite formation on crystalline rocks, suggest that the Maryland Piedmont was an area of low relief undergoing intense weathering. Incised valleys were formed during a cycle of erosion probably initiated in the Late Miocene and extensive colluvial sediments were deposited on hillslopes by periglacial processes during the Pleistocene.-after Authors

Earth Surface Processes and Landforms↗

USGS2020

Wildfire and landscape change

Wildfire is a worldwide phenomenon that is expected to increase in extent and severity in the future, due to fuel accumulations, shifting land management practices, and climate change. It immediately affects the landscape by removing vegetation, depositing ash, influencing water-repellent soil formation, and physically weathering boulders and bedrock. These changes typically lead to increased erosion through sheetwash, rilling, dry ravel, and increased mass movement in the form of floods, debris flow, rockfall, and landslides. These process changes bring about landform changes as hillslopes are lowered and stream channels aggrade or incise at increased rates. Furthermore, development of alluvial fans, debris fans, and talus cones are enhanced. The window of disturbance to the landscape caused by wildfire is typically on the order of 3–4 years, with some effects persisting up to 30 years.

Book chapter↗

USGS2019

Induced biological soil crust controls on wind erodibility and dust (PM10) emissions

Inducing biological soil crust (biocrust) development is an appealing approach for dust mitigation in drylands due to the resistance biocrusts can provide against erosion. Using a portable device, we evaluated dust emissions from surfaces either inoculated with biocrust, amended with a plant‐based soil stabilizer, or both at varying wind friction velocities. Four months after application, emissions from all treatments were either indistinguishable from or greater than controls, despite evidence of biocrust establishment. All treatments had greater surface roughness and showed more evidence of entrapment of windblown sediment than controls, factors which may have been partially responsible for elevated emissions. There was a synergistic effect of inoculation and stabilizer addition, resulting in a nearly two‐fold reduction in estimated emissions compared to either treatment alone. Stepwise regression analysis indicated that variables associated with surface crust strength (aggregate stability, penetration resistance) were negatively associated with emissions and variables associated with sediment supply (sand content, loose sediment cover) were positively associated with emissions. With more time to develop, the soil‐trapping activity and surface integrity of biocrust inoculum and soil stabilizer mixtures is expected to increase with the accumulation of surface biomass and enhancement of roughness through freeze–thaw cycles.

Utah↗

USGS2008

Derivation of ground surface and vegetation in a coastal Florida wetland with airborne laser technology

The geomorphology and vegetation of marsh-dominated coastal lowlands were mapped from airborne laser data points collected on the Gulf Coast of Florida near Cedar Key. Surface models were developed using low- and high-point filters to separate ground-surface and vegetation-canopy intercepts. In a non-automated process, the landscape was partitioned into functional landscape units to manage the modeling of key landscape features in discrete processing steps. The final digital ground surface-elevation model offers a faithful representation of topographic relief beneath canopies of tidal marsh and coastal forest. Bare-earth models approximate field-surveyed heights by + 0.17 m in the open marsh and + 0.22 m under thick marsh or forest canopy. The laser-derived digital surface models effectively delineate surface features of relatively inaccessible coastal habitats with a geographic coverage and vertical detail previously unavailable. Coastal topographic details include tidal-creek tributaries, levees, modest topographic undulations in the intertidal zone, karst features, silviculture, and relict sand dunes under coastal-forest canopy. A combination of laser-derived ground-surface and canopy-height models and intensity values provided additional mapping capabilities to differentiate between tidal-marsh zones and forest types such as mesic flatwood, hydric hammock, and oak scrub. Additional derived products include fine-scale shoreline and topographic profiles. The derived products demonstrate the capability to identify areas of concern to resource managers and unique components of the coastal system from laser altimetry. Because the very nature of a wetland system presents difficulties for access and data collection, airborne coverage from remote sensors has become an accepted alternative for monitoring wetland regions. Data acquisition with airborne laser represents a viable option for mapping coastal topography and for evaluating habitats and coastal change on marsh-dominated coasts. Such datasets can be instrumental in effective coastal-resource management.

Florida↗

USGS1972

Preliminary photointerpretation map of landslide and other surficial deposits of the Mount Hamilton quadrangle and parts of the Mount Boardman and San Jose quadrangles, Alameda and Santa Clara Counties, California

The nine San Francisco Bay region counties lie within a geologically active, young, and dynamic part of the central and northern Coast Ranges of California. Significant movements of the earth's crust are occurring here at the present time, posing numerous problems to urbanization, including some of special concern. Geological processes such as fault movements, earthquakes, land subsidence, landsliding, slow downslope movement of bedrock and surficial materials, coastal and stream erosion, flooding, and sedimentation are all potentially hazardous. Because of these factors, an understanding of the operation of physical processes in the bay region is desirable for harmonious, efficient, and safe land-use planning, particularly now, with greatly expanded pressures for urban growth. This map presents preliminary information about one aspect of the physical environment necessary to sound land-use planning--the nature and distribution of surficial deposits. Because surficial deposits are common and well developed in much of the bay region, it is useful to know how and why they have formed, as well as what properties they possess. When maps like this are used in combination with other types of environmental information, such as data on soils, bedrock geology, slopes, vegetation, climatic variation, seismic response, and hydrology, it should be easier to arrive at sound decisions regarding the physical aspects of land use. The U.S. Geological Survey is studying many of these factors in the bay region and hopes to provide the community with much of the required information as part of its San Francisco Bay Region Study in cooperation with the Department of Housing and Urban Development. The representation of surficial deposits on this map reflects the way in which a geologist, working exclusively with aerial photographs, interpreted the origin of various elements of the present landscape. The deposits shown here have not been examined in the field. However, by viewing overlapping vertical aerial photographs through a stereoscope, the geologist sees a three-dimensional relief model of the ground surface and can study and interpret the origins of landforms with considerable ease. In fact, for mapping surficial deposits, particularly in reconnaissance-type studies, photointerpretation has advantages over both ground observations and laboratory studies of surficial materials. Of course, better information can be provided when all aspects of the study are integrated. These preliminary photointerpretation maps are only the first stage in a detailed study of surficial deposits in the bay region, but they should provide land-use planners with immediately useful information about the regional distribution of landslide and other surficial deposits. This map indicates the dominant surficial processes that have probably been operative by showing the distribution of different types of surficial deposits. Processes such as weathering, erosion, sedimentation, and the slow as well as rapid downslope movement of earth materials have constantly reshaped the land surface in the past and will continue to in the future, although at varying rates. The processes are interrelated to varying degrees. For example, crustal uplift of the Coast Ranges will lead to increased erosion and downcutting by streams that in turn generally results in increased deposition of sediments in river valleys, lakes, and shoreline areas. Older flood planes and river deposits may be eroded, leaving elevated terrace deposits. In addition, downcutting by streams may cause adjacent slopes to become unstable, thereby increasing the possibility of slope failures. Man's activities can alter natural physical processes in many ways. Simple acts such as overwatering a lawn or placing a septic tank drainfield in ground that is marginally stable may weaken the bedrock and surficial materials enough to induce landsliding. Relatively stable areas may be made unstable as a result of construction activities that involve cutting or oversteepening of natural slopes. Engineers, builders, conservationists, and others concerned with land use must evaluate the potential effects of all types of development, and maps that show the nature and distribution of surficial deposits should provide much of the basic information they need. This map, then, shows the cumulative effects of various processes that have yielded surficial deposits up to the time the photographs used for photointerpretation were taken. It does not indicate directly areas where processes will be most active, nor does it show the rate at which they will operate. However, knowledge of the history of geologic events is a key to understanding and predicting the evolution of an area, even where man's activities significantly change the character of the land. Almost all new landslides, for example, occur in areas with a history of landslide activity.

California↗

USGS1998

Evolution of cutoffs across meander necks in Powder River, Montana, USA

Over a period of several decades, gullies have been observed in various stages of forming, growing and completing the cutoff of meander necks in Powder River. During one episode of overbank flow, water flowing over the down-stream bank of the neck forms a headctu. The headcut migrates up-valley, forming a gully in its wake, until it has traversed the entire neck, cutting off the meander. The river then follows the course of the gully, which is subsequently enlarged as the river develops its new channel. The complete process usually requires several episodes of high water: in only one of the five cases described herein was a meander cutoff initiated and completed during a single large flood.

Earth Surface Processes and Landforms↗

USGS2005

Evolution of melt-vapor surface tension in silicic volcanic systems: Experiments with hydrous melts

We evaluate the melt‐vapor surface tension (σ) of natural, water‐saturated dacite melt at 200 MPa, 950–1055°C, and 4.8–5.7 wt % H 2 O. We experimentally determine the critical supersaturation pressure for bubble nucleation as a function of dissolved water and then solve for σ at those conditions using classical nucleation theory. The solutions obtained give dacite melt‐vapor surface tensions that vary inversely with dissolved water from 0.042 (±0.003) J m −2 at 5.7 wt % H 2 O to 0.060 (±0.007) J m −2 at 5.2 wt % H 2 O to 0.073 (±0.003) J m −2 at 4.8 wt % H 2 O. Combining our dacite results with data from published hydrous haplogranite and high‐silica rhyolite experiments reveals that melt‐vapor surface tension also varies inversely with the concentration of mafic melt components (e.g., CaO, FeO total , MgO). We develop a thermodynamic context for these observations in which melt‐vapor surface tension is represented by a balance of work terms controlled by melt structure. Overall, our results suggest that cooling, crystallization, and vapor exsolution cause systematic changes in σ that should be considered in dynamic modeling of magmatic processes.

Journal of Geophysical Research B: Solid Earth↗