Geomorphic Terrain Research Articles

Morphological evidence for the extension of the Zabargad Transform Fault Zone to the Saudi Arabian Red Sea margin

The fault locations and orientation of the Zabargad Transform Fault Zone, also called the Zabargad Fracture Zone (ZFZ), have previously only been delineated by satellite-based geophysical data, causing intense debate over the last few decades. Newly recognized geomorphological features identified in bathymetric and LiDAR data from the NE Red Sea margin present the first ground evidence for the northern extent of the ZFZ. The features are aligned over 84 km, starting from the Mabahiss Deep, near the spreading axis, and continuing to the shallow Saudi Arabian shelf along the northern termination of the Al Wajh carbonate platform. Analysis of the seafloor morphology reveals three geomorphic terrains: (1) a deeply incised canyon feeding into the Mabahiss Deep, which is characterized by dozens of amphitheatre-shaped scarps; (2) a 22 km wide head-scarp that follows the edge of the Al Wajh platform; and (3) multiple fault scars and graben-like structures on the shallow shelf. We interpret these morphological features as deformation indicators associated with the deformation processes in the ZFZ and postulate that they represent the northern end of the ZFZ. In addition, the fault zone delineates the NW margin of the Al Wajh carbonate platform and most likely continues to shape it. This paper gives new insights into the interaction between fracture zones and continental margins and their role in the morphogenesis of the seafloor.

A Probabilistic Framework to Model Distributions of VS30

ABSTRACT The time-averaged shear-wave velocity in the upper 30 m depth from the ground surface, or VS30, is often used as a predictor to describe local site effects in ground-motion models. Although VS30 is typically determined from in situ measurements, it is not always feasible to obtain such measurements due to project restrictions or site accessibility. This motivates the development and use of proxy-based VS30 predictions that leverage more readily available secondary information such as surface geology, topographic slope, or geomorphic terrain classes to estimate the mean VS30 and associated uncertainty. Traditionally, empirical distributions of VS30 have been observed to have long right tails, leading to high levels of associated uncertainty. In this study, we present a physical framework that is grounded in fundamental principles of geostatistics and probability to explain the uncertainty and skewness associated with VS30 measurements. Specifically, by invoking Lyapunov’s central limit theorem, we hypothesize that the distribution of VS30 can be theoretically approximated by a reciprocal–normal distribution. We show that a non-normal and skewed distribution of VS30 is to be expected and is not a sign of measurement error or sampling bias, although sampling bias can exaggerate such skewness. Our framework also enables us to propose the mode as a characteristic value of VS30 measurements, as opposed to the mean or median, which can overestimate the most probable value.

Геоморфологическое районирование на основе цифровых моделей рельефа (по данным SRTM для Верхнего Поднепровья)

The methodology was proposed for the distinguishing of geomorphological areas on the map of the surface slopes, created from SRTM by visualization tools. Such areas are considered as parts of the image that differ in the ratios of different slopes and their relative position in space (“textureˮ). The scheme of geomorphological zoning of the Upper Dnieper basin (left bank) was built. Forty geomorphological regions with an average area of about 2.25 km 2 were allocated. It was shown that the main internal differences of the topography in the region is consistent with the regional geomorphological zonation schemes based on traditional cartographic materials. Identified differences relate to the allocation of geomorphological areas of alluvial and glacio-fluvial plains corresponding to the wide sections of river valleys. Topographic differentiation was caused by neotectonic movements, geological structure, paleogeographic peculiarities of the Quaternary period. Information was provided about the differences of geomorphic terrain regions that are not available directly from SRTM data, in particular on the distribution of density of the river network.

Assessment of Soil Erosion in Siruvani Watersheds based on USLE and Hypsometric Curve Methods

Soil erosion poses a serious threat over the maintenance activities of a reservoir and its watershed. This study has been taken us to assess the extent of soil erosion in the watersheds of the Siruvani Reservoir located in the district of Kerala. Two methods namely, Universal Soil Loss equation (USLE) and Hypsometric curve methods are adapted in this study. Hypsometry of watersheds (area-elevation analysis) has generally been used to reveal the stages of geomorphic development (stabilized, mature and young). The watersheds of Siruvani Reservoir were delineated from the generated Digital Elevation Model (DEM) using Geographic Information System (GIS). Various set of data like land use map, rainfall and soil map have been used for this analysis to generate five factors namely finally, the soil erosion risk map was created to identify the regions which are susceptible to erosion. Hypsometric analysis deals with measurement of the interrelationships between basin area and altitude of basin which has been used to understand the influence of various factors such as climate, geology and tectonic changes. GIS provides advanced tools to obtain hypsometric information and also helps to estimate the associated parameters of landforms. The entire study area has been sub-divided into 5 watersheds for hypsometric analysis and their area ranges from 1.77 to 6.94 km2. The hypsometric curve of the whole the watersheds reflects the mature geomorphic terrain whereas hypsometric integral indicates that the drainage basin has already eroded per cent of land masses. These findings would emphasize the importance of soil and water conservation measures to be taken up in the Siruvani watersheds for controlling further erosion, reducing the sediment outflows and conserve water

Assessment of Soil Erosion in Siruvani Watersheds Based on USLE and Hypsometric Curve Methods

Soil erosion poses a serious threat over the maintenance activities of a reservoir and its watershed. This study has been taken us to assess the extent of soil erosion in the watersheds of the Siruvani Reservoir located in the district of Kerala. Two methods namely, Universal Soil Loss equation (USLE) and Hypsometric curve methods are adapted in this study. Hypsometry of watersheds (area-elevation analysis) has generally been used to reveal the stages of geomorphic development (stabilized, mature and young). The watersheds of Siruvani Reservoir were delineated from the generated Digital Elevation Model (DEM) using Geographic Information System (GIS). Various set of data like land use map, rainfall and soil map have been used for this analysis to generate five factors namely finally, the soil erosion risk map was created to identify the regions which are susceptible to erosion. Hypsometric analysis deals with measurement of the interrelationships between basin area and altitude of basin which has been used to understand the influence of various factors such as climate, geology and tectonic changes. GIS provides advanced tools to obtain hypsometric information and also helps to estimate the associated parameters of landforms. The entire study area has been sub-divided into 5 watersheds for hypsometric analysis and their area ranges from 1.77 to 6.94 km2. The hypsometric curve of the whole the watersheds reflects the mature geomorphic terrain whereas hypsometric integral indicates that the drainage basin has already eroded per cent of land masses. These findings would emphasize the importance of soil and water conservation measures to be taken up in the Siruvani watersheds for controlling further erosion, reducing the sediment outflows and conserve water.

Limitations Posed by Free DEMs in Watershed Studies: The Case of River Tanaro in Italy

Topography is a critical element in the hydrological response of a drainage basin and its availability in the form of Digital Elevation Models (DEM) has advanced the modelling of hydrological and hydraulic processes. However, progress experienced in these fields may stall, as intrinsic characteristics of free DEMs may limit new findings, while at the same time new releases of free, high-accuracy, global digital terrain models are still uncertain. In this paper, the limiting nature of free DEMs is dissected in the context of hydrogeomorphology. Nine sets of terrain data are analysed: the SRTM GL1 and GL3, HydroSHEDS, TINITALY, ASTER GDEM, EU DEM, VFP, ALOS AW3D30, MERIT and the TDX. In specific, the influence of three parameters are investigated, i.e., spatial resolution, hydrological reconditioning and vertical accuracy, on four relevant geomorphic terrain descriptors, namely the upslope contributing area, the local slope, the elevation difference and the flow path distance to the nearest stream, H and D, respectively. The Tanaro river basin in Italy is chosen as the study region and the newly released LiDAR for the Italian territory is used as benchmark to reassess vertical accuracies. In addition, the EU-Hydro photo-interpreted river network is used to compare DEM-based river networks. Most DEMs approximate well the frequency curve of elevations of the LiDAR, but this is not necessarily reflected in the representation of geomorphic features. For example, DEMs with finer spatial resolution present larger contributing areas; differences in the slope can reach 10%; between 5 m and 12 m H, none of the considered DEMs can faithfully represent the LiDAR; D presents significant variability between DEMs; and river network extraction can be problematic in flatter terrain. It is also found that the lowest mean absolute error (MAE) is given by the MERIT, 2.85 m, while the lowest root mean square error (RMSE) is given by the SRTM GL3, 4.83 m. Practical implications of choosing a DEM over another may be expected, as the limitations of any particular DEM in faithfully reproducing critical geomorphic terrain features may hinder our ability to find satisfactory answers to some pressing problems.

Variation in Soil Respiration across Soil and Vegetation Types in an Alpine Valley.

Background and AimsSoils of mountain regions and their associated plant communities are highly diverse over short spatial scales due to the heterogeneity of geological substrates and highly dynamic geomorphic processes. The consequences of this heterogeneity for biogeochemical transfers, however, remain poorly documented. The objective of this study was to quantify the variability of soil-surface carbon dioxide efflux, known as soil respiration (Rs), across soil and vegetation types in an Alpine valley. To this aim, we measured Rs rates during the peak and late growing season (July-October) in 48 plots located in pastoral areas of a small valley of the Swiss Alps.FindingsFour herbaceous vegetation types were identified, three corresponding to different stages of primary succession (Petasition paradoxi in pioneer conditions, Seslerion in more advanced stages and Poion alpinae replacing the climactic forests), as well as one (Rumicion alpinae) corresponding to eutrophic grasslands in intensively grazed areas. Soils were developed on calcareous alluvial and colluvial fan deposits and were classified into six types including three Fluvisols grades and three Cambisols grades. Plant and soil types had a high level of co-occurrence. The strongest predictor of Rs was soil temperature, yet we detected additional explanatory power of sampling month, showing that temporal variation was not entirely reducible to variations in temperature. Vegetation and soil types were also major determinants of Rs. During the warmest month (August), Rs rates varied by over a factor three between soil and vegetation types, ranging from 2.5 μmol m-2 s-1 in pioneer environments (Petasition on Very Young Fluvisols) to 8.5 μmol m-2 s-1 in differentiated soils supporting nitrophilous species (Rumicion on Calcaric Cambisols).ConclusionsOverall, this study provides quantitative estimates of spatial and temporal variability in Rs in the mountain environment, and demonstrates that estimations of soil carbon efflux at the watershed scale in complex geomorphic terrain have to account for soil and vegetation heterogeneity.

A Multiple Natural Hazards Assessment Model Based on Geomorphic Terrain Units

A Multiple Natural Hazards Assessment (MNHA) procedural model was developed to provide stakeholders (e.g., community planners and decision makers) with a clear methodology that examines the landscape as a probabilistic-based composite measure of the natural hazards at a terrain mapping unit scale. The model consists of four phases: (1) data collection; (2) individual natural hazard assessment (INHA); (3) Geomorphic Terrain Unit (GTU) development; and (4) composite MNHA classification. The model was tested in a case study across southern Davis County, Utah. Six hazards were integrated within a GIS model, producing a nonweighted probabilistic-based multi-hazard classification across GTUs. Examination of the results by stakeholders showed great potential for the model. During the evaluation workshop, stakeholders concurred that normalizing the class values using a simple frequency-based scale makes it easier to discern the differences in composite hazardousness across the community. The model is easily expanded to include objective or subjective weighting factors.

Modeling the natural degradation of earthworks

AbstractStratigraphic, topographic, and ground‐penetrating radar data obtained from a ca. 1800‐year‐old embankment and adjacent ditch at the Hopewell Mound Group (Chillicothe, Ohio) are used to validate the archaeological application of a simple finite‐differences diffusion model employed frequently to assess geomorphic change in natural landscapes. Although diffusion models have been used to describe the topographic degradation of landforms in a variety of geomorphic terrains, the approach has not been applied to ancient earthworks in an archaeological context. The results of this study indicate that a variety of initial earthwork forms can result in the sinusoidal profile apparent on the current landscape. Using the model results to interpret the field data, we suggest that the initial embankment form was steeper and the adjacent ditch was deeper. As a result of natural degradation processes, the earthwork widened and flattened over time. These results have broad implications for any study aimed at: (1) assessing the function of original earthwork forms, (2) determining the formation processes of complicated stratigraphies or artifact assemblages, (3) estimating the time and labor investment required for construction, or (4) identifying the socio‐political structures necessary to build earthworks. © 2005 Wiley Periodicals, Inc.

A remote-sensing method of mapping soils and surficial lags from a deeply weathered arid region, near Cobar, NSW, Australia

The work reported here describes the use of hyperspectral imagery for discriminating and mapping the mineralogy of surface materials at a semi-arid site in New South Wales, Australia. Hyperspectral imagery for the Mrangelli test site near Cobar was acquired by the HyMap instrument, a 126-channel, high spectral and spatial resolution airborne scanner. Ground investigations demonstrate that HyMap is able to acquire spectra of 5 m pixels that have a similar spectral resolution to spectra acquired with a field spectrometer. Unmixing of endmembers from calibrated HyMap imagery allowed outcrops of maghemite-rich pisoid lags, lithic lags, ferrolithic lags, metasediments and soils to be discriminated and mapped. The pisoid lag is shown by field and image spectra to be a mixture of hematite/maghemite Fe oxides and kaolinite. Lithic lags show features that resemble mixtures of hematite and illite. Class maps derived from the visible and near-infrared (VISNIR) part of the spectrum delineate terrain elements distinguished by their Fe mineralogy and content. Class maps derived from the shortwave infrared part (SWIR) of the spectrum delineate terrain elements distinguished by their clay mineralogy, content and crystallinity. Unique combinations of VISNIR- and SWIR-derived terrain elements define geomorphic terrains common within the region. It is proposed that maps of lag distribution and the accompanying terrains derived from HyMap imagery could be used to differentiate in-situ from transported materials and therefore aid in the planning of sample locations for soil and lag geochemistry exploration programmes.

Source of lunette dune sediments: a geomorphic terrain analysis approach in Etosha National Park, Namibia

Zusammenfasssung: Zur Herkunft von Lunettediinen-Sedimenten im Etoscha-Nationalpark, Namibia Vorkommen von so genannten Lunette-Dunen am leeseitigen Rand von Pfannen in Nord-Namibia haben zu einer Diskus sion iiber ihre Genese in Verbindung mit der Entstehung der zugehorigen flachen Becken gefuhrt. Das Sediment der Lunette Diinen ist iiberwiegend grober als das der Pfannen, von denen das Sediment angeblich stammen soil, was gegen eine Aus wehung von der Pfannenoberflache spricht. Im Fall der Etoschapfanne ergibt sich ein weiterer Widerspruch aus der Tatsache, dass die Diinen am Nordwest- und Westrand der Pfanne liegen, die vorherrschenden heutigen Winde jedoch aus Nordost wehen. Erganzende Daten wurden gemeinsam mit hochauflosenden Satellitenbilddaten in eine geomorphologische Relief analyse eingebunden. Alle Befunde weisen darauf hin, dass das Ekuma-Delta am Nordwestrand der Pfanne und nicht der Pfannenboden selbst die Quelle der Sedimente ist. Vermudich stammen auch an anderen Pfanne die groberen Leeseiten sedimente aus fluvialem Eintrag und sind nicht, wie haufig angenommen, das korrelate Sediment einer durch Deflation entstandenen Pfanne. Summary: The presence of so-called lunette dunes in the lee of pans in northern Namibia sprouted a discussion on the formation of the shallow basins related to them. These lunette dunes are made up of larger particles than those found in the pans, from which the sediments are thought to have originated. At Etosha Pan, this contradiction is compounded by the fact that the dunes are found on the northwestern and western side of the pan, whilst the prevailing dominant wind, believed to have played a formative role in their development, blows from the northeast. Ancillary data, in concert with high-resolution, multi-date satellite imagery were examined through the prism of geomorphic terrain analysis. The resultant indicators unequivocally point to the Ekuma delta, on the northwestern rim of the pan, in direct opposition to the pan floor proper, as the source of these dune sediments. It is therefore probable that coarser sediments found on the lee side of similar pans can be similarly explained as originating from former inlet deposition and not from wind excavation in the process of pan initiation as popularly held.

Crater size-shape profiles for the moon and mercury: Terrain effects and interplanetary comparisons

New crater size-shape data were compiled for 221 fresh lunar craters and 152 youthful mercurian craters. Terraces and central peaks develop initially in fresh craters on the Moon in the 0–10 km diameter interval. Above a diameter of 65 km all craters are terraced and have central peaks. Swirl floor texture is most common in craters in the size range 20–30 km, but it occurs less frequently as terraces become a dominant feature of crater interiors. For the Moon there is a correlation between crater shape and geomorphic terrain type. For example, craters on the maria are more complex in terms of central peak and terrace detail at any given crater diameter than are craters in the highlands. These crater data suggest that there are significant differences in substrate and/or target properties between maria and highlands. Size-shape profiles for Mercury show that central peak and terrace onset is in the 10–20 km diameter interval; all craters are terraced at 65 km, and all have central peaks at 45 km. The crater data for Mercury show no clear cut terrain correlation. Comparison of lunar and mercurian data indicates that both central peaks and terraces are more abundant in craters in the diameter range 5–75 km on Mercury. Differences in crater shape between Mercury and the Moon may be due to differences in planetary gravitational acceleration (gMercury=2.3gMoon). Also differences between Mercury and the Moon in target and substrate and in modal impact velocity may contribute to affect crater shape.