Surficial Features Research Articles

Arsenic concentrations in dust emissions from wind erosion and off-road vehicles in the Nellis Dunes Recreational Area, Nevada, USA

Field and laboratory experiments were performed in the Nellis Dunes Recreational Area near Las Vegas, NV, USA to evaluate arsenic concentrations associated with dust emissions from wind erosion and offroad vehicles. Soil samples were collected from 17 types of desert surfaces and five unpaved parking lot locations for analyses. The surface units are based on surficial characteristics that affect dust emissions. Arsenic concentrations were also measured in dust emitted from each surface unit using a Portable In Situ Wind Erosion Laboratory (PI-SWERL). Emissions were measured from ORV trails and undisturbed terrain. Concentrations of As in the soil and parking lot samples ranged from 3.49 to 83.02 l gg 1

Controls on the geomorphic expression and evolution of gryphons, pools, and caldera features at hydrothermal seeps in the Salton Sea Geothermal Field, southern California

In the Salton Sea Geothermal Field in southern California, expulsion of gas, sediment and water creates unique geomorphic features similar to those seen on the surface of dormant mud volcanoes. These include pools of water or highly fluid mud named “mud pots” and 0.5 to 2.5m-tall gryphons. The features vary in size, shape, and type of eruptive activity and change form over time. To evaluate controls on the surface morphology and evolution of these features we used repeated differential GPS surveys, observations of eruptive activity, and measurements of erupted mud properties to document the physical characteristics and changes in the system over a 28-month period.We find that the morphology of the gryphons is primarily a function of the mud expulsion style. Taller (1.5m to 2.4m) gryphons form where narrower vents (5cm to 15cm diameter) expel mud to the surface in discrete Strombolian-type eruptions caused by individual gas bubbles pushing mud up through the gryphon conduit and exploding at the surface. Smaller (0.6m to 1.5m) gryphons form where wider vents allow a greater amount of gas to pass through, which creates 0.25 to 1m diameter mud craters that bubble continuously, often from multiple points within the crater. Although viscous mud is required to create these positive topographic features, variations in erupted mud temperature (30°C to 68.5°C), density (1.44g/cm3 to 1.59g/cm3), and water content (36% to 44%) between different gryphons did not correlate with gryphon size. All the active gryphons experienced periods of growth and erosion over the study period due to changes in the degree of activity or small variations in the vent locations within the gryphons, but the net change in height distributions over time was negligible.Pools directly adjacent to gryphon clusters are surficial features whose water level depends on seasonal rainfall and temperature. Isolated pools are also present and do not show similar response to seasonal changes, suggesting that these pools are connected to the local groundwater system. Although changes in vent morphology and activity do occur, the new data demonstrate that the system is steady-state in terms of the height distribution of the gryphons, and the location of the main seeps. Most of the gryphons occur in clusters that are surrounded by caldera-like depressions that range from 10 to 25m in diameter. Mud expelled from the gryphons is largely contained within the caldera depressions, and we infer that subsidence of the calderas accounts for the lack of large-scale build-up of material in the surrounding area. This study provides the first examination of the processes controlling the morphology of these features and the results may help to understand the dynamics and temporal evolution of gryphons, which are found in both hydrothermal systems and on dormant mud volcanoes.

Combining surface mapping and process data to assess, predict, and manage dust emissions from natural and disturbed land surfaces

The impact of dust emission on air quality is a significant health and environmental concern. Accurately determining the source (natural versus anthropogenic) and load of dust is an important component of any mitigation effort. We develop an approach to assess dust emission potential based on study of Nellis Dunes Recreation Area, a popular off-road vehicle area close to Las Vegas, Nevada. A mapping approach to assess dust emission potential is presented, which may serve as a template to assess other areas for this hazard. A 1:10,000 map delineating units based upon surficial characteristics affecting dust emission (e.g., soil texture, rock cover, surface crusts, and vegetation) was created. Seventeen surface units are grouped into four major classes (sand, silt and clay, rock covered, and active drainages). A >500 km network of trackways was digitized into a geographic information system (GIS) to determine the distribution of tracks across surface types to assess the density of disturbance. Wind-erosion measurements and off-road experiments using different vehicles (four-wheeler, motorcycle, and dune buggy) were performed on the various surface types to assess the amount of dust generated. Dust emission risk maps for Nellis Dunes Recreation Area are presented for two types of processes: off-road vehicular (ORV) activity and wind erosion. Highest dust emissions for ORV activity occur on map units composed of silt and clay, and on desert pavements. These areas can also produce large amounts of dust through natural wind erosion when disturbed. In contrast, the sandy units produce high emissions through natural wind erosion, and therefore limiting ORV use in those areas provides no benefit to air quality.

The influence of stream channels on distributions of Larrea tridentata and Ambrosia dumosa in the Mojave Desert, CA, USA: patterns, mechanisms and effects of stream redistribution

AbstractDrainage channels are among the most conspicuous surficial features of deserts, but little quantitative analysis of their influence on plant distributions is available. We analysed the effects of desert stream channels (‘washes’) on Larrea tridentata and Ambrosia dumosa density and cover on an alluvial piedmont in the Mojave Desert, based on a spatial analysis of transect data encompassing a total length of 2775 m surveyed in 5 cm increments. Significant deviations from average transect properties were identified by bootstrapping. Predictably, shrub cover and density were much reduced inside washes, and elevated above average levels adjacent to washes. Average Larrea and Ambrosia cover and density peaked 1·2–1·6 m and 0·5–1·0 m from wash edges, respectively. We compared wash effects in runon‐depleted (−R) sections, where washes had been cut off from runon and were presumably inactive, with those in runon‐supplemented (+R) sections downslope from railroad culverts to help identify mechanisms responsible for the facilitative effect of washes on adjacent shrubs. Shrub cover and density near washes peaked in both + R and − R sections, suggesting that improved water infiltration and storage alone can cause a facilitative effect on adjacent shrubs. However, washes of < 2 m width in + R sections had larger than average effects on peak cover, suggesting that plants also benefit from occasional resource supplementation. The data suggest that channel networks significantly contribute to structuring plant communities in the Mojave Desert and their disruption has notable effects on geomorphic and ecological processes far beyond the original disturbance sites. Copyright © 2010 John Wiley & Sons, Ltd.

Introduction to the thematic issue: “From Geosites to Geomorphosites: how to decode the landscape? Geodynamic processes, surficial features and landforms, past and present environments”

Engineering geomorphology (levees and canals, banks calibration, rectification of river beds, drainage, irrigation...) and process geomorphology (mechanical and/or chemical erosion) and their general effects on landforms development (levelling of mountains, alluvial fans, deltas...), were briefly discussed from antiquity (Ellenberger, 1988) but did not really emerge before the Renaissance period, for example in the context of land use planning in the Po Valley (Baulig, 1950). These general co...

Structural mapping under cover with airborne EM

The drive to explore under cover necessitates methods of geological or geochemical mapping that can ?see through? the masking cover rocks. Magnetic data are routinely collected for this type of structural mapping in various terranes. In Mali, magnetic data have been of very limited use to Resolute Mining?s mineral exploration programs - magnetically featureless cover rocks hide almost all structural expression in the basement. Airborne EM has proven invaluable in tracing lithological contacts, subtle stratigraphic horizons, and intrusive bodies through conductive weathering up to 100m deep. Helicopter time domain systems with high transmitter moments penetrate deep enough to escape contamination by surficial conductivity features such as drainage patterns. The results under basin cover in Mali are particularly impressive in their ability to provide a clean picture of basement geological structure.

A photographic and acoustic transect across two deep-water seafloor mounds, Mississippi Canyon, northern Gulf of Mexico

In the northern Gulf of Mexico, a series of seafloor mounds lie along the floor of the Mississippi Canyon in Atwater Valley lease blocks 13 and 14. The mounds, one of which was drilled by the Chevron Joint Industry Project on Methane Hydrates in 2005, are interpreted to be vent-related features that may contain significant accumulations of gas hydrate adjacent to gas and fluid migration pathways. The mounds are located ∼150 km south of Louisiana at ∼1300 m water depth. New side-scan sonar data, multibeam bathymetry, and near-bottom photography along a 4 km northwest–southeast transect crossing two of the mounds (labeled D and F) reveal the mounds' detailed morphology and surficial characteristics. Mound D, ∼250 m in diameter and 7–10 m in height, has exposures of authigenic carbonates and appears to result from a seafloor vent of slow-to-moderate flux. Mound F, which is ∼400 m in diameter and 10–15 m high, is covered on its southwest flank by extruded mud flows, a characteristic associated with moderate-to-rapid flux. Chemosynthetic communities visible on the bottom photographs are restricted to bacterial mats on both mounds and mussels at Mound D. No indications of surficial gas hydrates are evident on the bottom photographs.

Surface Variability of Alluvial Fans Generated by Disparate Processes, Eastern Death Valley, CA*

This study explores the surface variability of alluvial fans from digital elevations model (DEM) derivatives generated from 1-m planimetric resolution airborne laser swath mapping data. Channel and interfluve dimensions of debris flow (DF) fans and fans generated from predominantly fluvial flows and some older debris flows (mixed flow [MF]) are extracted with the aid of a planimetric curvature classification. Significant differences are identified between the fan surface topography of DF and MF fans. MF fans tend to have smaller channel and interfluve widths, have smaller elevation differences between the crest of the interfluve and channel, and are more dissected than DF fans. The morphometric differences between the two fan classes can be explained by differences in the primary processes that develop the surficial features, but also the preponderance for secondary erosional processes acting on the MF fans.

Observations from the Basin and Range Province (western United States) pertinent to the interpretation of regional detachment faults

Abstract This paper summarizes the results of completed and ongoing research in three areas of the Basin and Range Province of the western United States that casts doubt on the interpretation of specific regional detachment faults and the large extensional strains with which such faults are commonly associated. Given that these examples were influential in the development of ideas about low-angle normal faults, and particularly in making the case for frictional slip at dips of appreciably less than the 30° lock-up angle for μ ≈ 0.6 (where μ is the coefficient of friction), we advocate a critical re-examination of interpreted detachments elsewhere in the Basin and Range Province and in other extensional and passive margin settings. The Sevier Desert ‘detachment’ of west-central Utah is reinterpreted as a Palaeogene unconformity that has been traced to depth west of the northern Sevier Desert basin along an unrelated seismic reflection (most probably a splay of the Cretaceous-age Pavant thrust). The absence of evidence in well cuttings and cores for either brittle deformation (above) or ductile deformation (below) is inconsistent with the existence of a fault with as much as 40 km of displacement. The Pavant thrust and the structurally higher Canyon Range thrust are erosionally truncated at the western margin of the southern Sevier Desert basin, and are not offset by the ‘detachment’ in the manner assumed by those inferring large extension across the basin. The Mormon Peak detachment of SE Nevada is reinterpreted as a series of slide blocks on the basis of detachment characteristics and spatially variable kinematic indicators that are more closely aligned with the modern dip direction than the inferred regional extension direction. A particularly distinctive feature of the detachment is a basal layer of up to several tens of centimetres of polymictic conglomerate that was demonstrably involved in the deformation, with clastic dykes of the same material extending for several metres into overlying rocks in a manner remarkably similar to that observed at rapidly emplaced slide blocks. The Castle Cliff detachment in the nearby Beaver Dam Mountains of SW Utah is similarly regarded as a surficial feature, as originally interpreted, and consistent with its conspicuous absence in seismic reflection profiles from the adjacent sedimentary basin. The middle Miocene Eagle Mountain Formation of eastern California, interpreted on the basis of facies evidence and distinctive clast provenance to have been moved tectonically more than 80 km ESE from a location close to the Jurassic-age Hunter Mountain batholith of the Cottonwood Mountains, is reinterpreted as having accumulated in a fluvial–lacustrine rather than alluvial fan–lacustrine setting, with no bearing on either the amount or direction of tectonic transport. The conglomeratic rocks upon which the provenance argument was based are pervasively channelized, with erosional relief of less than 1 m to as much as 15 m, fining-upwards successions at the same scale and abundant trough cross-stratification – all characteristic features of fluvial sedimentation and not of alluvial fans. The interpretation of the Eagle Mountain Formation as having been deposited within a few kilometres of the Hunter Mountain batholith, which depends strongly on assumptions about the dimensions of alluvial fans, is therefore not required. The result is important because the Eagle Mountain offset has been viewed as representing the strongest evidence for extreme extension in this part of California, and for the existence of detachment faults of regional dimensions.

Geomorphic and sedimentologic evidence for the separation of Lake Superior from Lake Michigan and Huron

A common break was recognized in four Lake Superior strandplain sequences using geomorphic and sedimentologic characteristics. Strandplains were divided into lakeward and landward sets of beach ridges using aerial photo- graphs and topographic surveys to identify similar surficial features and core data to identify similar subsurface features. Cross-strandplain, elevation- trend changes from a lowering towards the lake in the landward set of beach ridges to a rise or reduction of slope towards the lake in the lakeward set of beach ridges indicates that the break is associated with an outlet change for Lake Supe- rior. Correlation of this break between study sites and age model results for the strandplain sequences suggest that the outlet change occurred sometime after about 2,400 calendar years ago

Surficial features associated with ponded water on playas of the arid southwestern United States: Indicators for delineating regulated areas under the Clean Water Act

Desert playas can be unambiguously identified in a geological context. However, identifying those portions of desert playas that are defined as either three-parameter wetlands or Waters of the United States (WoUS) in the Clean Water Act (CWA), and thus under the jurisdiction of Federal agencies charged with enforcing the CWA, is sometimes problematic. Although the WoUS definition specifically includes playas, the guidance for playa delineation is not as highly developed as that for wetlands. Delineating WoUS on desert playas involves determining the Ordinary High Water Mark. Field experience has demonstrated that the indicators for Ordinary High Water on desert playas have not been fully identified nor have they been associated with ponding that represents the limits of Ordinary High Water. This report discusses the distribution of indicators above, below, and at the Ordinary High Water Mark. Fifteen playa features are identified for possible delineation use and are rated for reliability and their relationship to the Ordinary High Water position.

Macropolygon morphology, development, and classification on North Panamint and Eureka playas, Death Valley National Park CA

Panamint and Eureka playas, both located within Death Valley National Park, exhibit a host of surficial features including fissures, pits, mounds, and plant-covered ridges, representing topographic highs and lows that vary up to 2 m of relief from the playa surface. Aerial photographs reveal that these linear strands often converge to form polygons, ranging in length from several meters to nearly a kilometer. These features stand out in generally dark contrast to the brighter intervening expanse of flat, plant-free, desiccated mud of the typical playa surface. Ground-truth mapping of playa features with differential GPS (Global Positioning System) was conducted in 1999 (North Panamint Valley) and 2002 (Eureka Valley). High-resolution digital maps reveal that both playas possess macropolygons of similar scale and geometry, and that fissures may be categorized into one of two genetic groups: (1) shore-parallel or playa-interior desiccation and shrinkage; and (2) tectonic-induced cracks. Early investigations of these features in Eureka Valley concluded that their origin may have been related to agricultural activity by paleo-Indian communities. Although human artifacts are abundant at each locale, there is no evidence to support the inference that surface features reported on Eureka Playa are anthropogenic in origin. Our assumptions into the genesis of polygons on playas is based on our fortuitous experience of witnessing a fissure in the process of formation on Panamint Playa after a flash flood (May 1999); our observations revealed a paradox that saturation of the upper playa crusts contributes to the establishment of some desiccation features. Follow-up visits to the same feature over 2 yrs' time are a foundation for insight into the evolution and possible longevity of these features.

Preservation of Arctic landscapes overridden by cold-based ice sheets

For nearly 40 years, a massive, well-preserved glaciomarine delta more than 54,000 years old and ancillary landforms have formed the cornerstone of models positing limited ice-sheet extent in Arctic Canada during the late Wisconsinan. We present exposure ages for large boulders on the delta surface, which coupled with preservation of relict landforms demonstrate that the region was covered by minimally erosive, cold-based ice during the late Wisconsinan. Our data suggest that surficial features commonly used to define the pattern of late Wisconsinan ice movement cannot be used on their own to constrain late Wisconsinan ice-sheet margins in Arctic regions.

Surface expression of buried geologic features in Kansas

Abstract Now they knew that she was a real princess [geologist] because she had felt [mapped] the pea [structure] right through the twenty mattresses [two thousand feet of sediment] and the twenty … beds [limestones]. Nobody but a real princess [geologist] could be as sensitive as that. Apologies to Hans Christian Andersen, The Princess and the Pea, 1835. Topographic features, under certain circumstances, may reveal information about what is hidden beneath. By studying the configuration of the surface, information can be gained as to what might be below, and visa versa the configuration of subsurface features can give insight as to what may be expected on the surface. Thus, surficial topographic features may be indicators of buried folds, faults, igneous intrusives, and other subsurface geologic features. The Big Springs (Shawnee/Douglas counties) and Beagle (Miami County) anomalies in eastern Kansas are given as examples.

Thermal inertia mapping over the Brahmaputra basin, India using NOAA-AVHRR data and its possible geological applications

Thermal inertia is a volume property and shows the resistance power of the material against changes in its temperature. The thermal inertia of a surficial feature of interest cannot be directly measured. Hence, a proper modelling is required for its estimation. The objective of the project is to develop a technique to generate thermal inertia images using available National Oceanic and Atmospheric Administration (NOAA) satellite data to detect thermal anomalies and oilfield signature over a known producing basin. The Brahmaputra valley in Upper Assam is selected for this study. NOAA-Advanced Very High Resolution Radiometer (AVHRR) thermal data were converted to temperature, based on the look-up table (LUT) given in the NOAA-AVHRR CD and by using split-window atmospheric attenuation correction models. The thermal inertia imagery is constructed with the help of the albedo imagery generated from the daytime and with the knowledge of the surface temperature change between the daytime and night-time data. The thermal inertia values are computed for all pixels common to both daytime and night-time and the thermal inertia imagery generated for the study area. The thermal inertia of a surface cannot be measured directly; so another model is also used to estimate apparent thermal inertia (ATI). The images from both the models have shown similar results. The geological map when draped over the ATI image shows good correlation of gross lithology and thermal inertia. The metamorphics/basement and the sediments are well differentiated by their tonal and textural characters. The Mikir massif shows conspicuously brighter signature than the featureless darker signatures of the surrounding valley. Within the valley, the river water exhibits bright tone, whereas the present-day sandbars within the river exhibit darker tone than the alluvial plains of the valley. This is in agreement with the available published data. Major thrusts can be mapped as bright linear tone, and their geometry coincides well with those mapped in the field. Exposed cross faults can also be mapped in Arunachal foothills and faults in Mikir massif. The isoneotectonic map when draped over the ATI image shows that the identified isoneotectonic units can be well differentiated in the image on the basis of tonal characters. The prominent lineaments mapped in Mikir massif can be traced in the valley part also. The producing and dry structures in the valley show very few signatures on the thermal inertia images, possibly due to poor spectral and spatial resolution of the NOAA data. It is planned to use the developed technique to generate thermal inertia maps using higher spatial and spectral resolution satellite data (e.g. Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER)), which may provide better oilfield signatures.

Processes and Consequences of Deep Subduction

Oceanic lithosphere subduction is the phenomenon responsible for some of the most spectacular and powerful expressions of the ceaseless motion of the Earth's tectonic plates. Subduction is manifested at the Earth's surface by a global system of oceanic trenches, the deep abyssal scars in the ocean floor that extend over tens of thousands of kilometers and cut up to 4 km deep into the planet's surface. Subduction zones are also associated with regional gravity anomalies, island arc formation, and a large portion of the world's earthquakes and volcanoes, including the deepest and most energetic earthquakes, which have been observed at depths of 660—700 km.In addition to these dramatic surficial features, the process of subduction affects mineral physics, geochemistry, petrology structural geology, and rock mechanics. The conditions associated with subduction provide a unique natural laboratory in which the entrainment of water and sediment with anomalously cold slabs of subducted oceanic lithosphere creates a dynamic and volatile environment as plates sink and encounter hot ambient mantle, mineralogical phase boundaries, and rheological transitions. Part of the difficulty in unravelling the complexity of these systems lies in understanding the feedback that occurs between phenomena operating at macroscopic and microscopic scales. For example, phase transformation rates affect buoyancy, and therefore subduction rates. This affects the regional thermal structure and thereby the phase transformations. Slab rheology and morphology may similarly be affected by mineral transformations and their kinetics.

Constraining continental structure by integrating Os isotopic ages of lithospheric mantle with geophysical and crustal data: An example from southeastern Australia

Rocks exposed at the Earth's surface provide an incomplete record of the varied and complex processes that have acted to form and modify the continents. The continental lithospheric mantle (CLM), sampled as xenoliths carried in explosive volcanics, is an alternative reservoir of age information that has only recently begun to be tapped. Data from southeastern Australia, a technically complex region, illustrate that the CLM can record important aspects of continental evolution that are not indicated by the exposed crustal rocks. Re‐Os isotopic data and the resultant model ages for 15 spinel peridotite xenoliths from five localities in southeastern Australia show that parts of the CLM are ∼ 1960 Myr old, some 1400 Myrs older than the oldest crust exposed immediately in the sampled region. As the five sampled localities are east of the presumed eastern edge of the Precambrian interior of Australia, the preservation of Proterozoic ages in the lithosphere indicates that the supposed Precambrian edge of the Australian continent (the Tasman Line) is a surficial feature rather than a lithospheric scale boundary. This conclusion is consistent with recent Skippy seismic tomography models for Australia. The mantle xenolith age distribution also suggests a significant age change from Proterozoic to dominantly Phanerozoic, which appears coincident with the surface expression of the boundary between two major fold belts (Lachlan and Delamerian) and with a deep lithospheric boundary previously proposed on the basis of differences in Sr and Pb isotopic systematics of southeast Australian basalts.

Tepees and other Surficial Deformation Features of Cretaceous Rocks in Central and West Texas, Resulting from Sub-Recent Calichification

Tepees and other Surficial Deformation Features of Cretaceous Rocks in Central and West Texas, Resulting from Sub-Recent Calichification

The Lake Lahontan highstand: age, surficial characteristics, soil development, and regional shoreline correlation

The Lake Lahontan basin has been the site of numerous pluvial lakes during the Pleistocene. We address the question of whether or not the highest remnant shoreline features around the perimeter of the lake were produced during the most recent Sehoo highstand (∼13 ka), the penultimate Eetza highstand (∼140–280 ka), or both. To do so, we document surficial characteristics, morphologic preservation, and soil development on multiple Sehoo beach barriers in the Jessup embayment to define the range in characteristics displayed by latest Pleistocene beach features. Sehoo barriers generally exhibit original constructional morphology that has been little modified by erosion. Soils developed on Sehoo barriers are generally thin and weakly developed and are strongly influenced by the introduction of eolian fines into the predominately clast-supported coarse beach gravels. Similar observations from 13 other highstand barriers and from seven older-than-latest Pleistocene paleosols located around the basin form the basis for a regional comparison. Based on similar characteristics, including the degree of morphologic preservation and weak soil development, we conclude that the widespread and nearly continuous high shoreline around the perimeter of Lake Lahontan dates from the most recent major lake cycle in all areas except in the Walker Lake subbasin. In the Walker Lake subbasin, isolated early to middle Pleistocene lacustrine outcrops and landforms are elevated as much as 70 m above the late Pleistocene limit, but are differentiated by their degraded form and lack of continuity around the subbasin. Similar unambiguous landforms were not observed elsewhere and at similar elevations in the northern subbasins of Lake Lahontan.

Geographic information systems for selection of CRP tracts to meet different management goals after contract expiration

AbstractLand use decisions, following expiration of Conservation Reserve Program (CRP) contracts, can be aided by Geographical Information System (GIS) analysis. We utilized a GIS to overlay maps of CRP tracts including wetlands, a surficial aquifer, lakes, rivers and other landscape features in a small watershed in eastern South Dakota. Attribute data including the percentage of highly erodible land, soil type, vegetation, and land capability class were also integrated with the maps. Lake County, South Dakota was used to test the GIS selection model. Criteria were developed for the selection of tracts suitable for various management goals including: protection of surface and groundwater resources, wildlife enhancement, and row-crop or grassland agriculture. The maximum percentage of tract hectares selected for each goal was 17 for groundwater protection, 22 for surface water protection, 18 for wildlife enhancement, 30 for rowcrop production, and 38 for pasture or rangeland. All CRP tracts were selected at least once. The GIS provides a mechanism for selecting CRP tracts to meet several management goals.