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Topographic Relief (topographic + relief)
Selected AbstractsInvestigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicityEARTH SURFACE PROCESSES AND LANDFORMS, Issue 12 2006Rob Westaway Abstract Many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over Quaternary timescales. On the basis of the rheological knowledge gained, it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust. This view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation. It is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity, and by instances of seasonal seismicity that correlates with seasonal climate. Human interference in the environment can affect surface loading: for instance, deforestation for agriculture or urban development can cause increased erosion rates; global warming is expected to cause increased storminess (and thus increased erosion rates) and/or global sea-level rise. The possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment. Copyright © 2006 John Wiley & Sons, Ltd. [source] Contribution of deep-seated bedrock landslides to erosion of a glaciated basin in southern AlaskaEARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2005Ann M. Arsenault Abstract Landslides represent a key component of catchment-scale denudation, though their relative contribution to the erosion of glaciated basins is not well known. Bedrock landslide contribution was investigated on the surface of one of eleven glaciers on a glaciated ridge in the Chugach-St Elias Range of southern Alaska, where the debris from four major landslides is easily distinguished from moraines and other supraglacial material. A series of aerial and satellite photos from 1972 to 2000 and field observations in 2001 and 2002 indicate that three of four landslides have fallen onto the surface of the glacier since about 1978. The landslides, which originated from the steeply dipping (60,70°) bedrock walls, were deposited onto the glacier in the ablation zone and are currently being transported downstream supraglacially. Individual glacial valleys with topographic relief of ,400 m are cut into high-grade metamorphic rock characterized by a steep north-dipping foliation and fractured by numerous large joints. Measurements of landslide area and average thickness obtained from high-resolution survey data indicate a total landslide volume of ,2·3 × 105 m3. This volume suggests a basin-averaged erosion rate from landslides of 0·48 mm a,1. An overall basin-scale erosion rate of 0·7 to 1·7 mm a,1 can be inferred, but depends on the percentage of the total-basin sediment yield contributed by supraglacial sources. A mean rockwall retreat rate of 6·7 mm a,1 is calculated and is considerably higher than published rates, which range from 0·04 to 4·0 mm a,1. Controls on landslide generation include seismicity, freeze,thaw processes, topography, rock strength, and debuttressing. It is likely all of these factors contribute to failure, although the primary controls for the landslides in this study are thought to be rock strength and topography. The absence of landslides on ten of the eleven glaciers on this ridge is attributed to landslide magnitude,frequency relationships and short temporal scale of this study. Large-volume bedrock landslides (>100 000 m3) may have low frequency, occurring less than once in a 55-year time frame. Copyright © 2005 John Wiley & Sons, Ltd. [source] Interpretation of observed fluid potential patterns in a deep sedimentary basin under tectonic compression: Hungarian Great Plain, Pannonian BasinGEOFLUIDS (ELECTRONIC), Issue 1 2001J. Tóth Abstract The , 40 000 km2 Hungarian Great Plain portion of the Pannonian Basin consists of a basin fill of 100 m to more than 7000 m thick semi- to unconsolidated marine, deltaic, lacustrine and fluviatile clastic sediments of Neogene age, resting on a strongly tectonized Pre-Neogene basement of horst-and-graben topography of a relief in excess of 5000 m. The basement is built of a great variety of brittle rocks, including flysch, carbonates and metamorphics. The relatively continuous Endr,d Aquitard, with a permeability of less than 1 md (10,15 m2) and a depth varying between 500 and 5000 m, divides the basin's rock framework into upper and lower sequences of highly permeable rock units, whose permeabilities range from a few tens to several thousands of millidarcy. Subsurface fluid potential and flow fields were inferred from 16 192 water level and pore pressure measurements using three methods of representation: pressure,elevation profiles; hydraulic head maps; and hydraulic cross-sections. Pressure,elevation profiles were constructed for eight areas. Typically, they start from the surface with a straight-line segment of a hydrostatic gradient (,st = 9.8067 MPa km,1) and extend to depths of 1400,2500 m. At high surface elevations, the gradient is slightly smaller than hydrostatic, while at low elevations it is slightly greater. At greater depths, both the pressures and their vertical gradients are uniformly superhydrostatic. The transition to the overpressured depths may be gradual, with a gradient of ,dyn = 10,15 MPa km,1 over a vertical distance of 400,1000 m, or abrupt, with a pressure jump of up to 10 MPa km,1 over less than 100 m and a gradient of ,dyn > 20 MPa km,1. According to the hydraulic head maps for 13 100,500 m thick horizontal slices of the rock framework, the fluid potential in the near-surface domains declines with depth beneath positive topographic features, but it increases beneath depressions. The approximate boundary between these hydraulically contrasting regions is the 100 m elevation contour line in the Duna,Tisza interfluve, and the 100,110 m contours in the Nyírség uplands. Below depths of ,,600 m, islets of superhydrostatic heads develop which grow in number, areal extent and height as the depth increases; hydraulic heads may exceed 3000 m locally. A hydraulic head ,escarpment' appears gradually in the elevation range of ,,1000 to ,,2800 m along an arcuate line which tracks a major regional fault zone striking NE,SW: heads drop stepwise by several hundred metres, at places 2000 m, from its north and west sides to the south and east. The escarpment forms a ,fluid potential bank' between a ,fluid potential highland' (500,2500 m) to the north and west, and a ,fluid potential basin' (100,500 m) to the south and east. A ,potential island' rises 1000 m high above this basin further south. According to four vertical hydraulic sections, groundwater flow is controlled by the topography in the upper 200,1700 m of the basin; the driving force is orientated downwards beneath the highlands and upwards beneath the lowlands. However, it is directed uniformly upwards at greater depths. The transition between the two regimes may be gradual or abrupt, as indicated by wide or dense spacing of the hydraulic head contours, respectively. Pressure ,plumes' or ,ridges' may protrude to shallow depths along faults originating in the basement. The basement horsts appear to be overpressured relative to the intervening grabens. The principal thesis of this paper is that the two main driving forces of fluid flow in the basin are gravitation, due to elevation differences of the topographic relief, and tectonic compression. The flow field is unconfined in the gravitational regime, whereas it is confined in the compressional regime. The nature and geometry of the fluid potential field between the two regimes are controlled by the sedimentary and structural features of the rock units in that domain, characterized by highly permeable and localized sedimentary windows, conductive faults and fracture zones. The transition between the two potential fields can be gradual or abrupt in the vertical, and island-like or ridge-like in plan view. The depth of the boundary zone can vary between 400 and 2000 m. Recharge to the gravitational regime is inferred to occur from infiltrating precipitation water, whereas that to the confined regime is from pore volume reduction due to the basement's tectonic compression. [source] Geomorphic characteristics of the Minjiang drainage basin (eastern Tibetan Plateau) and its tectonic implications: New insights from a digital elevation model studyISLAND ARC, Issue 2 2006Hui-Ping Zhang Abstract The Minshan Mountain and adjacent region are the major continental escarpments along the eastern Tibetan Plateau. The Minjiang drainage basin is located within the plateau margin adjacent to the Sichuan Basin. Based on the analysis of the digital elevation model (DEM) acquired by the Shuttle Radar Topography Mission (SRTM), we know that the Minjiang drainage basin has distinct geomorphic characteristics. The regular increasing of local topographic relief from north to south is a result of the Quaternary sediment deposition within the plateau and the holistic uplift of the eastern margin of the Tibetan Plateau versus the Sichuan Basin. Results from DEM-determined Minjiang drainage sub-basins and channel profiles show that the tributaries on the opposite sides are asymmetric. Lower perimeter and area of drainage sub-basins, total channel length and bifurcation ratio within eastern flank along the Minjiang mainstream are the result of the Quaternary differential uplift of the Minshan Mountain region. Shorter stream lengths and lower bifurcation ratio might be the indications of the undergrowth and newborn features of these eastern streams, which are also representative for the eastern uplift of the Minshan Mountain. [source] Debris flow and slide deposits at the top of the Internal Liguride ophiolitic sequence, Northern Apennines, Italy: A record of frontal tectonic erosion in a fossil accretionary wedgeISLAND ARC, Issue 1 2001Michele Marroni Abstract In the Northern Apennines, the Internal Liguride units are characterized by an ophiolite sequence that represents the stratigraphic base of a late Jurassic,early Paleocene sedimentary cover. The Bocco Shale represents the youngest deposit recognized in the sedimentary cover of the ophiolite and can be subdivided into two different groups of deep sea sediments. The first group is represented by slide, debris flow and high density turbidity current-derived deposits, whereas the second group consists of thin-bedded turbidites. Facies analysis and provenance studies indicate, for the former group, small and scarcely evoluted flows that rework an oceanic lithosphere and its sedimentary cover. We interpret the Bocco Shale as an ancient example of a deposit related to the frontal tectonic erosion of the accretionary wedge slope. The frontal tectonic erosion resulted in a large removal of materials, from the accretionary wedge front, that was reworked as debris flows and slide deposits sedimented on the lower plate above the trench deposits. The frontal tectonic erosion was probably connected with subduction of oceanic crust characterized by positive topographic relief. This interpretation can be also applied for the origin of analogous deposits of Western Alps and Corsica. [source] Patterns of woody plant species richness in the Iberian Peninsula: environmental range and spatial scaleJOURNAL OF BIOGEOGRAPHY, Issue 10 2008Ole R. Vetaas Abstract Aim, Climate-based models often explain most of the variation in species richness along broad-scale geographical gradients. We aim to: (1) test predictions of woody plant species richness on a regional spatial extent deduced from macro-scale models based on water,energy dynamics; (2) test if the length of the climate gradients will determine whether the relationship with woody species richness is monotonic or unimodal; and (3) evaluate the explanatory power of a previously proposed ,water,energy' model and regional models at two grain sizes. Location, The Iberian Peninsula. Methods, We estimated woody plant species richness on grid maps with c. 2500 and 22,500 km2 cell size, using geocoded data for the individual species. Generalized additive models were used to explore the relationships between richness and climatic, topographical and substrate variables. Ordinary least squares regression was used to compare regional and more general water,energy models in relation to grain size. Variation partitioning by partial regression was applied to find how much of the variation in richness was related to spatial variables, explanatory variables and the overlap between these two. Results, Water,energy dynamics generate important underlying gradients that determine the woody species richness even over a short spatial extent. The relationships between richness and the energy variables were linear to curvilinear, whereas those with precipitation were nonlinear and non-monotonic. Only a small fraction of the spatially structured variation in woody species richness cannot be accounted for by the fitted variables related to climate, substrate and topography. The regional models accounted for higher variation in species richness than the water,energy models, although the water,energy model including topography performed well at the larger grain size. Elevation range was the most important predictor at all scales, probably because it corrects for ,climatic error' due to the unrealistic assumption that mean climate values are evenly distributed in the large grid cells. Minimum monthly potential evapotranspiration was the best climatic predictor at the larger grain size, but actual evapotranspiration was best at the smaller grain size. Energy variables were more important than precipitation individually. Precipitation was not a significant variable at the larger grain size when examined on its own, but was highly significant when an interaction term between itself and substrate was included in the model. Main conclusions, The significance of range in elevation is probably because it corresponds to several aspects that may influence species diversity, such as climatic variability within grid cells, enhanced surface area, and location for refugia. The relative explanatory power of energy and water variables was high, and was influenced by the length of the climate gradient, substrate and grain size of the analysis. Energy appeared to have more influence than precipitation, but water availability is also determined by energy, substrate and topographic relief. [source] EVALUATION OF LIGHT DETECTION AND RANGING (LIDAR) FOR MEASURING RIVER CORRIDOR TOPOGRAPHY,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2002Zachary H. Bowen ABSTRACT: LIDAR is relatively new in the commercial market for remote sensing of topography and it is difficult to find objective reporting on the accuracy of LIDAR measurements in an applied context. Accuracy specifications for LIDAR data in published evaluations range from 1 to 2 m root mean square error (RMSEx,y) and 15 to 20 cm RMSEz. Most of these estimates are based on measurements over relatively flat, homogeneous terrain. This study evaluated the accuracy of one LIDAR data set over a range of terrain types in a western river corridor. Elevation errors based on measurements over all terrain types were larger (RMSEz equals 43 cm) than values typically reported. This result is largely attributable to horizontal positioning limitations (1 to 2 m RMSEx,y) in areas with variable terrain and large topographic relief. Cross-sectional profiles indicated algorithms that were effective for removing vegetation in relatively flat terrain were less effective near the active channel where dense vegetation was found in a narrow band along a low terrace. LIDAR provides relatively accurate data at densities (50,000 to 100,000 points per km2) not feasible with other survey technologies. Other options for projects requiring higher accuracy include low-altitude aerial photography and intensive ground surveying. [source] | ||||||||||