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At least 109 records · Page 6Linked to original sources
USGS2014

Quantitative study of tectonic geomorphology along Haiyuan fault based on airborne LiDAR

High-precision and high-resolution topography are the fundamental data for active fault research. Light detection and ranging (LiDAR) presents a new approach to build detailed digital elevation models effectively. We take the Haiyuan fault in Gansu Province as an example of how LiDAR data may be used to improve the study of active faults and the risk assessment of related hazards. In the eastern segment of the Haiyuan fault, the Shaomayin site has been comprehensively investigated in previous research because of its exemplary tectonic topographic features. Based on unprecedented LiDAR data, the horizontal and vertical coseismic offsets at the Shaomayin site are described. The measured horizontal value is about 8.6 m, and the vertical value is about 0.8 m. Using prior dating ages sampled from the same location, we estimate the horizontal slip rate as 4.0 ± 1.0 mm/a with high confidence and define that the lower bound of the vertical slip rate is 0.4 ± 0.1 mm/a since the Holocene. LiDAR data can repeat the measurements of field work on quantifying offsets of tectonic landform features quite well. The offset landforms are visualized on an office computer workstation easily, and specialized software may be used to obtain displacement quantitatively. By combining precious chronological results, the fundamental link between fault activity and large earthquakes is better recognized, as well as the potential risk for future earthquake hazards.

Gansu↗
USGS1989

The geomorphology of the Mississippi River chenier plain

The chenier plain of the Mississippi River is a shore-parallel zone of alternating transgressive clastic ridges separated by progradational mudflats. The term chenier is derived from the cajun term chene for oak, the tree species that colonizes the crests of the higher ridges. The Mississippi River chenier plain stretches 200 km from Sabine Pass, Texas, to Southwest Point, Louisiana and ranges between 20 and 30 km wide, with elevations of 2–6 m. The timing and the process of formation could be re-evaluated in the light of new chronostratigraphic findings in the Mississippi River delta plain. The stratigraphic relationship between the Teche and Lafourche delta complexes and Ship Shoal offshore indicates that these delta complexes belong to different delta plains that developed at different sealevels. It appears that the Teche delta complex is associated with the late Holocene delta plain which developed 7000 to 3000 yrs B.P. when sealevel stood 5–6 m lower than present. A regional transgression occurred between approximately 3000 BP and 2500 yrs B.P., leading to the transgressive submergence of the late Holocene delta plain, producing the regional Teche shoreline. The timing of this transgression conforms to the age of the most landward ridge in the chenier plain, the Little Chenier-Little Pecan Island trend, which dates at about 2500 yrs B.P. This ridge trend was originally interpreted as representing the Teche delta complex switching event with the landward Holocene/Pleistocene contact representing the high stand shoreline. The implication of this new interpretation is that the Little Chenier-Little Pecan Island trend represents the high stand shoreline, a continuation of the Teche shoreline separating the late Holocene and Recent delta plains, and that the Holocene/Pleistocene contact represents the leading edge of the marshes transgressing onto the Prairie Terrace. Significant mudflat progradation seems to require a westerly position of the Mississippi River, but the numerous different forms and ages of cheniers do not correspond well to the timing of major delta complex switching. Progradation of the chenier plain appears to be associated with building of the Recent delta plain and not the Teche complex of the late Holocene delta plain. The occurrence of individual ridges appears to be primarily tied to delta lobe switching within the Lafourche complex and variations in sediment supply from local rivers. The recent development of the Atchafalaya delta complex to the west is the closest position of an active distributary to the chenier plain since sealevel stabilization; a new episode of rapid mudflat progradation is thus taking place.

Marine Geology↗
USGS2021

Does geomorphology determine vulnerability of mangrove coasts to sea-level rise?

The greatest climate-based threat to coastlines worldwide is sea-level rise. We tested the hypothesis that tropical coasts fringed by mangroves and receiving high inputs of terrigenous sediment are less vulnerable to sea-level rise than biogenic systems dependent upon peat formation for vertical land development. An analysis of published data spanning a range of geomorphic settings showed that mineral accretion was a poor predictor of vulnerability to rising sea level. We additionally compared two oceanic island systems representing two extremes along this sediment gradient to further examine controls on elevation dynamics in minerogenic versus biogenic mangrove systems. Minerogenic systems characterized by intermediate to high rates of mineral sedimentation (Pacific high islands in Micronesia) were not better buffered against sea-level rise because of high subsidence rates. Peat-forming systems (Caribbean low islands in Belize) kept pace with relative sea-level rise (combined ocean and land movements) because of subsurface expansion driven by root matter accumulation. The data were not consistent with the paradigm that tropical coastlines characterized by peat-forming mangroves are generally more vulnerable to sea-level rise compared to minerogenic systems; however, they are not necessarily equally sensitive to the same external and internal forces controlling soil elevations. Our findings demonstrate that reliance on surface accretion data alone can lead to an inaccurate evaluation of coastal vulnerability and why all surface and subsurface land movements must be considered in relation to local sea-level trends to assess risk of submergence. Recognition of such differences is essential to proper management of tropical coastlines to ensure their resilience in the face of future sea-level rise.

Book chapter↗
USGS2011

Regional geomorphology and history of Titan's Xanadu province

Titan’s enigmatic Xanadu province has been seen in some detail with instruments from the Cassini spacecraft. The region contains some of the most rugged, mountainous terrain on Titan, with relief over 2000 m. Xanadu contains evolved and integrated river channels, impact craters , and dry basins filled with smooth, radar-dark material, perhaps sediments from past lake beds . Arcuate and aligned mountain chains give evidence of compressional tectonism, yet the overall elevation of Xanadu is puzzlingly low compared to surrounding sand seas. Lineations associated with mountain fronts and valley floors give evidence of extension that probably contributed to this regional lowering. Several locations on Xanadu’s western and southern margins contain flow-like features that may be cryovolcanic in origin, perhaps ascended from lithospheric faults related to regional downdropping late in its history. Radiometry and scatterometry observations are consistent with a water–ice or water–ammonia–ice composition to its exposed, eroded, fractured bedrock; both microwave and visible to near-infrared (v-nIR) data indicate a thin overcoating of organics, likely derived from the atmosphere. We suggest Xanadu is one of the oldest terrains on Titan and that its origin and evolution have been controlled and shaped by compressional and then extensional tectonism in the icy crust and ongoing erosion by methane rainfall.

Icarus↗
USGS2021

Azorella compacta's long-term growth rate, longevity, and potential for dating geomorphological and archaeological features in the arid southern Peruvian Andes

We determine the long-term growth rate and longevity of an Azorella compacta growing on Misti volcano, near Arequipa, Peru to investigate the species' capacity as a geochronological resource. Using 14 C dating on stem pieces sequestered within the plant's cushion, which grows larger through time, we obtain ages of 15 ± 15 14 C yrs BP and 165 ± 15 14 C yrs BP at depths of 15 cm and 29 cm below the cushion's living surface, respectively. Applying a mixed calibration curve with a Bayesian growth model yields calendar age ranges of 1948–1958 CE and 1802–1935 CE for our 14 C dates, respectively. Such ages provide sufficiently precise constraints for investigations requiring dating during the last few hundred years when individual 14 C dates yield imprecise calendar age ranges. We infer a long-term growth rate of 1.3–3.5 mm yr −1 , corroborating published maximum short-term growth rates. Extrapolating our growth model to the A. compacta 's core suggests that it began growing as early as 1462–1830 CE. At such age it lived through myriad important geological and historical events, including regional earthquakes, volcanic unrest at Misti, decades to centuries of the Little Ice Age, and a broad transect of Peruvian history possibly beginning during the Inca Empire. A. compacta may provide another important geochronological resource in the arid Central Andes that can be applied to date volcanological, glacial, mass-movement, and archaeological features, especially where dendrochronology and lichenometry are not possible.

Peruvian Andes↗
USGS2009

Geomorphology, stability and mobility of the Currituck slide

Over the last 100,000??years, the U.S. Atlantic continental margin has experienced various types of mass movements some of which are believed to have taken place at times of low sea level. At one of these times of low sea level a significant trigger caused a major submarine mass movement off the coast of Virginia: the Currituck slide which is believed to have taken place between 24 and 50??ka ago. This slide removed a total volume of about 165??km 3 from this section of the continental slope. The departure zone still shows a very clean surface that dips at 4?? and is only covered by a thin veneer of postglacial sediment. Multibeam bathymetric and seismic survey data suggest that this slide took place along three failures surfaces. The morphology of the source area suggests that the sediments were already at least normally consolidated at the time of failure. The slide debris covers an area as much as 55??km wide that extends 180??km from the estimated toe of the original slope. The back analysis of slide initiation indicates that very high pore pressure, a strong earthquake, or both had to be generated to trigger slides on such a low failure plane angle. The shape of the failure plane, the fact that the surface is almost clear of any debris, and the mobility analysis, all support the argument that the slides took place nearly simultaneously. Potential causes for the generation of high pore pressures could be seepage forces from coastal aquifers, delta construction and related pore pressure generation due to the local sediment loading, gas hydrates, and earthquakes. This slide, and its origin, is a spectacular example of the potential threat that submarine mass movements can pose to the US Atlantic coast and underline the need to further assess the potential for the generation of such large slides, like the Grand Banks 1927 landslide of similar volume. ?? 2008 Elsevier B.V.

Marine Geology↗
USGS2007

Topography and geomorphology of the Huygens landing site on Titan

The Descent Imager/Spectral Radiometer (DISR) aboard the Huygens Probe took several hundred visible-light images with its three cameras on approach to the surface of Titan. Several sets of stereo image pairs were collected during the descent. The digital terrain models constructed from those images show rugged topography, in places approaching the angle of repose, adjacent to flatter darker plains. Brighter regions north of the landing site display two styles of drainage patterns: (1) bright highlands with rough topography and deeply incised branching dendritic drainage networks (up to fourth order) with dark-floored valleys that are suggestive of erosion by methane rainfall and (2) short, stubby low-order drainages that follow linear fault patterns forming canyon-like features suggestive of methane spring-sapping. The topographic data show that the bright highland terrains are extremely rugged; slopes of order of 30° appear common. These systems drain into adjacent relatively flat, dark lowland terrains. A stereo model for part of the dark plains region to the east of the landing site suggests surface scour across this plain flowing from west to east leaving ∼100-m-high bright ridges. Tectonic patterns are evident in (1) controlling the rectilinear, low-order, stubby drainages and (2) the “coastline” at the highland–lowland boundary with numerous straight and angular margins. In addition to flow from the highlands drainages, the lowland area shows evidence for more prolific flow parallel to the highland–lowland boundary leaving bright outliers resembling terrestrial sandbars. This implies major west to east floods across the plains where the probe landed with flow parallel to the highland–lowland boundary; the primary source of these flows is evidently not the dendritic channels in the bright highlands to the north.

Planetary and Space Science↗
USGS2001

Geomorphologic evidence for liquid water

Besides Earth, Mars is the only planet with a record of resurfacing processes and environmental circumstances that indicate the past operation of a hydrologic cycle. However the present-day conditions on Mars are far apart of supporting liquid water on the surface. Although the large-scale morphology of the Martian channels and valleys show remarkable similarities with fluid-eroded features on Earth, there are major differences in their size, small-scale morphology, inner channel structure and source regions indicating that the erosion on Mars has its own characteristic genesis and evolution. The different landforms related to fluvial, glacial and periglacial activities, their relations with volcanism, and the chronology of water-related processes, are presented.

Conference Paper↗
USGS1999

General geology and geomorphology of the Mars Pathfinder landing site

The Mars Pathfinder (MPF) spacecraft landed on relatively young (late Hesperian-early Amazonian; 3.1-0.7 Ga) plains in Chryse Planitia near the mouth of Ares Vallis. Images returned from the spacecraft reveal a complex landscape of ridges and troughs, large hills and crater rims, rocks and boulders of various sizes and shapes, and surficial deposits, indicating a complex, multistage geologic history of the landing site. After the deposition of one or more bedrock units, depositional and erosional fluvial processes shaped much of the present landscape. Multiple erosional events are inferred on the basis of observations of numerous channels, different orientations of many streamlined tails from their associated knobs and hills, and superposition of lineations and streamlines. Medium- and small-scale features, interpreted to be related to late-stage drainage of floodwaters, are recognized in several areas at the landing site. Streamlined knobs and hills seen in Viking orbiter images support this inference, as they seem to be complex forms, partly erosional and partly depositional, and may also indicate a series of scouring and depositional events that, in some cases, further eroded or partially buried these landforms. Although features such as these are cited as evidence for catastrophic flooding at Ares Vallis, some of these features may also be ascribed to alternative primary or secondary depositional processes, such as glacial or mass-wasting processes. Close inspection of the landing site reveals rocks that are interpreted to be volcanic in origin and others that may be conglomeratic. If such sedimentary rocks are confirmed, fluvial processes have had a greater significance on Mars than previously thought. For the last several hundred million to few billion years, eolian processes have been dominant. Dunes and dune-like features, ventifacts, and deflation and exhumation features around several rocks probably are the most recent landforms. The relatively pristine nature of the overall landscape at the MPF site suggests weathering and erosion processes on Mars are exceptionally slow.

Journal of Geophysical Research E: Planets↗
USGS2005

Nitrogen transport and transformations in a coastal plain watershed: Influence of geomorphology on flow paths and residence times

Nitrogen transport and groundwater‐surface water interactions were examined in a coastal plain watershed in the southeastern United States. Groundwater age dates, calculated using chlorofluorocarbon and tritium concentrations, along with concentrations of nitrogen species and other redox‐active constituents, were used to evaluate the fate and transport of nitrate. Nitrate is stable only in recently recharged (<10 years) water found in the upper few meters of saturated thickness in the upland portion of a surficial aquifer. Groundwater with a residence time between 10 and 30 years typically has low nitrate and elevated excess N 2 concentrations, indications that denitrification has reduced nitrate concentrations. Groundwater older than 30 years also has low nitrate concentrations but contains little or no excess N 2 , suggesting that this water did not contain elevated concentrations of nitrate along its flow path. Nitrate transport to streams varies between first‐ and third‐order streams. Hydrologic, lithologic, and chemical data suggest that the surficial aquifer is the dominant source of flow and nitrate to a first‐order stream. Iron‐reducing conditions occur in groundwater samples from the bed and banks of the first‐order stream, suggesting that direct groundwater discharge is denitrified prior to entering the stream. However, nitrogen from the surficial aquifer is transported directly to the stream via a tile drain that bypasses these reduced zones. In the alluvial valley of a third‐order stream the erosion of a confining layer creates a much thicker unconfined alluvial aquifer with larger zones of nitrate stability. Age dating and chemical information (SiO 2 , Na/K ratios) suggest that water in the alluvial aquifer is derived from short flow paths through the riparian zone and/or from adjacent streams during high‐discharge periods.

Water Resources Research↗
USGS2019

Environmental and geomorphological changes on the eastern North American Continental Shelf across the Paleocene-Eocene Boundary

Foraminiferal evidence from two sites in southern Maryland, eastern United States, reveals a series of rapid ecological changes on the continental shelf during the onset of the Paleocene-Eocene Thermal Maximum (PETM). Benthic and planktic foraminifer assemblages from the South Dover Bridge (SDB) and Mattawoman Creek-Billingsley Road (MCBR) cores in the central Salisbury Embayment record changing latest Paleocene and earliest Eocene ecological conditions that began prior to the carbon isotope excursion (CIE) that marks the beginning of the PETM. The foraminiferal response reflects increases in productivity first in bottom water and then in the mixed layer, a minor dissolution event, and rising sea-surface temperatures in the latest Paleocene. Relative sea level changes, a sudden change in sedimentary regime, a decrease in bottom water oxygenation, and a downward expansion of the mixed layer occurred across the PETM onset. In the earliest Eocene, foraminiferal assemblages document a gradual shallowing of the thermocline and/or cooling of the surface layer. While SDB assemblages support a rise in sea level across the PETM onset, MCBR assemblages record a drop in sea level interpreted as delta progradation. Transitional carbon isotope values characterizing the nature of the CIE are recorded in these delta sediments. We present an initial bathymetric reconstruction of the Salisbury Embayment showing the physical effects of the CIE onset on shelf morphology and highlight the importance of understanding coastal zone processes when examining shelf sediments.

Delaware, Maryland, New Jersey, Pennsylvania, Virg↗
USGS2023

River geomorphology affects biogeochemical responses to hydrologic events in a large river ecosystem

Shifts in the frequency and intensity of high discharge events due to climate change may have important consequences for the hydrology and biogeochemistry of rivers. However, our understanding of event-scale biogeochemical dynamics in large rivers lags that of small streams. To fill this gap, we used high-frequency sensor data collected during four consecutive summers from a main channel and backwater site of the Upper Mississippi River. We identified high discharge events and calculated event concentration-discharge responses for both physical-chemical (nitrate, turbidity, and fluorescent dissolved organic matter) and biological (chlorophyll-a and cyanobacteria) constituents using metrics of hysteresis and slope. We found a range of responses across events, particularly for nitrate. Although fluorescent dissolved organic matter (FDOM) and turbidity exhibited more consistent responses across events, contrasting hysteresis metrics indicated that FDOM was flushed to the river from more distant sources than turbidity. Biological responses (chlorophyll a and cyanobacteria) differed more between sites than physical and chemical constituents. Lastly, we found that the event characteristics best explaining concentration responses differed between sites, with event magnitude more frequently related to responses in the main channel, and antecedent wetness conditions associated with response variation in the backwater. Our results indicate that event responses in large rivers are distinct across the diverse habitats and biogeochemical components of a large floodplain river, which has implications for local and downstream ecosystems as the climate shifts.

Minnesota, Wisconsin↗
USGS2020

Geomorphological evidence for a dry dust avalanche origin of slope streaks on Mars

Mars has several different types of slope feature that resemble aqueous flows. However, the current cold, dry conditions are inimical to liquid water, resulting in uncertainty about its role in modern surface processes. Dark slope streaks were among the first distinctive young slope features to be identified on Mars and the first with activity seen in orbital images. They form markings on steep slopes that can persist for decades, and the role of water in their formation remains a matter of debate. Here I analyse the geomorphic features of new slope streaks using high-resolution orbital images. Comparison of images before and after streak formation reveal how this process affects the surface and provides information about the cause. These observations demonstrate that slope streaks erode and deposit material in some instances. They also reveal that streaks can jump slopes and may be erosive very near their termini. These observations support a formation model where dark slope streaks form as ground-hugging, low-density avalanches of dry surface dust. Such streaks need not be treated as Special Regions for planetary protection.

Nature Geoscience↗
USGS2025

Modeling lamprey distribution using flow, geomorphology, and elevation in a terminal lake system

Objective Lampreys are an ecologically important group of fishes. Several species are imperiled and lack key distribution and habitat data. The terminal Goose Lake Basin, U.S.A. is home to two such species, the Goose Lake Lamprey, Entosphenus sp. (formally undescribed), and the Pit-Klamath Brook Lamprey, E. lethophagus . Species distribution models (SDMs) are useful for identifying key habitats; however, SDMs are subject to accuracy impairments caused by scale mismatches and spatial autocorrelation—both exacerbated by the hierarchical structure of dendritic stream networks. Our goal was to relate lamprey presence–absence to ecological drivers and predict the distribution of lampreys across the Goose Lake Basin. Methods Using a dataset pooling approach, we integrated count and presence–absence data from five surveys and relevant habitat variables from publicly available, geospatial datasets to build logistic regression models. To account for potential mismatches of scale, we compared three sample grains for slope and sinuosity (i.e., stream segment lengths: 250, 500, and 1,000 m), and two scales of elevation (site and watershed). We accounted for spatial autocorrelation by incorporating network-based and Euclidean spatial dependencies using a spatial stream network (SSN) modeling approach. Using the best-fit spatial and non-spatial models, we predicted basin-wide lamprey distribution. Result Flow, sinuosity at our largest sample grain (1,000 m), and watershed-scale elevation were positively associated with lamprey presence, whereas slope was negatively associated. The non-spatial model predicted lamprey presence among sinuous, low-gradient streams, whereas the spatial model, which identified Euclidean and flow-connected spatial relationships, predicted contiguous patches with a high probability of occurrence near areas with previously observed presences. Conclusions Our study revealed ecological relationships and produced an accurate basinwide SDM. Prediction and inference improved after accounting for spatial relationships across multiple scales. Developing accurate and efficient modeling strategies that incorporate the hierarchical structure inherent to stream ecosystems aids in the management and conservation of native fishes such as lampreys.

Transactions of the American Fisheries Society↗