Physical geomorphometry for elementary land surface segmentation and digital geomorphological mapping

By interpretations related to energy, elementary land surface segmentation can be treated as a physical problem. Many pieces of such a view found in the literature can be combined into a synthetic comprehensive physical approach. The segmentation has to be preceded by defining the character and size of searched units to result from the segmentation. A high-resolution digital elevation model (DEM) is the key input for this task; it should be generalized to the resolution best expressing information about the searched units. Elementary land surface units can be characterized by various parts of potential gravitational energy associated with a set of basic geomorphometric variables. Elevation above sea level (z) represents Global Geomorphic Energy (GGE). Regional and Local Geomorphic Energy (RGE and LGE) are parts of GGE, represented respectively by relative elevation above the local base level (zrel) and local relief (elevation differential in a moving window Δz). Derivation (change) of elevation defines the slope inclination (S), determining the local Potential Energy of Surface (PES) applicable to mass flow. Normal slope line (profile) curvature (kn)s and normal contour (tangential) curvature (kn)c express change in the PES value (ΔPES(kn )s, ΔPES(kn )c), responsible for acceleration/deceleration and convergence/ divergence of flow. Mean curvature (kmean) determines the Potential Energy of Surface applicable to Diffusion (PESD). Energetic interpretation of basic geomorphometric variables enables their direct comparison and systematic evaluation. Consequently, the homogeneity of basic geomorphometric variables defines a hierarchy of states of local geomorphic equilibria: static equilibrium, steady state, and non-steady state dynamic equilibrium. They are local attractors of landform development reflected in the geomorphometric tendency to symmetry (horizontality, various types of linearity, and curvature isotropy, together expressed by gravity concordance). Nonequilibrium and transitional states can be characterized by the PES excess (PESe) determined by difference curvature (kd), by gravity discordant change of the PES characterized by twisting curvature (τg)c, and by Integral Potential Energy of Surface Curvature (IPESC) expressed by Casorati curvature (kC) (general curvedness). Excluding zrel and Δz, all these energy-related geomorphometric variables are local point-based. Local area-based and regional variables such as Glock’s Available Relief, Melton Ruggedness Number, Stream Power Index, Openness, Topographic Position Index, Topographic Wetness Index, and Index of Connectivity also have energetic interpretations although their definition is more complex. Therefore we suggest exclusive use of the local point-based variables in designs of elementary land surface segmentation. The segmentation should take notice of natural interconnections, the hierarchy of geomorphometric variables, elements of Local Geomorphic Energy, and (dis)equilibria states, so that elementary segments are clearly interpretable geomorphologically. This is exemplified by Geographic Object-Based Image Analysis (GEOBIA) segmentation of Sandberg, a territory on the boundary of the Carpathians and Vienna Basin with a complex geomorphic history and marked morphodynamics. Compared with expert-driven field geomorphological mapping, the automatic physically-based segmentation resulted in a more specific delineation and composition of landforms. Physical-geomorphometric characteristics of the elementary forms enabled the formulation of their system and subsequent improvement of the expert-based qualitative genetic analysis, with interpretation leading to a deeper understanding of the development and recent dynamics of the landscape

Sulfuric acid speleogenesis and surface landform evolution along the Vienna Basin Transfer Fault : Plavecký Karst, Slovakia

Hypogene caves in the Plavecký hradný vrch Hill (Western Slovakia, Central Europe) were formed by waters ascending along faults in fractured Triassic carbonates related to the horst-graben structure at the contact of the Malé Karpaty Mountains and the NE part of the Vienna Basin. The Plavecká jaskyňa and Pec caves mostly contain horizontal passages and chambers with flat corrosion bedrock floors, fissure discharge feeders, wall water-table notches, replacement pockets, as well as a few other speleogens associated with sulfuric acid speleogenesis. The low-temperature sulfuric acid development phases of the Plavecká Jaskyňa are also indicated by the presence of sulfate minerals (i.e., gypsum and jarosite).Subaerial calcite popcorn rims were precipitated from water condensation at the edges of feeding fissures that were still active as thermal vents when the water table dropped. Hydrogen sulfide involved in the sulfuric acid speleogenesis was likely derived from anhydrites and/or hydrocarbon reservoirs with sulfate-saline connate waters in the fill of the adjacent Vienna Basin. It ascended to the surface along deep-rooted sub-vertical fault zones at the contact of the Vienna Basin with neighboring mountains. Three cave levels at 295 to 283 m asl in the Pec Cave, and five levels at 225 to 214 m asl in the Plavecká jaskyňa corresponded to phases of stable local erosional base levels in the bordering part of the Vienna Basin, most likely during periods of strongly decelerated and/or interrupted subsidence. Cave levels separated by vertical differences of only a few meters may also be related to the Pleistocene climatic cycles. The subhorizontal parts of the Pec Cave are probably of late Early Pleistocene age (˃0.99–1.07 Ma?). The two highest levels of the Plavecká jaskyňa developed during the early Middle Pleistocene (˃600 ka). Fine-grained sediments in the passage at 225 m asl with normal magnetic polarity contain jarosite. The middle level of the Plavecká jaskyňa at 220 m asl was formed in the mid-Middle Pleistocene, while the lower and lowermost levels formed in the late Middle Pleistocene (˃270 ka). The water table in the lowermost cave level probably dropped after the tectonic reactivation of the Podmalokarpatská zníženina Depression just in the front of a marginal horst structure of the Malé Karpaty Mountains

Modelling the geomorphic history of the Tribeč Mts. and the Pohronský Inovec Mts. (Western Carpathians) with the CHILD model

Numerical models were developed in order to provide a suitable computational framework for exploring research questions related to long-term landscape evolution. We used the Channel-Hillslope Integrated Landscape Development (CHILD) model to prove three hypotheses concerning the processes contributing to the neotectonic landscape evolution of the Tribeč Mts. and the Pohronský Inovec Mts. (Western Carpathians): (1) simultaneous planation and uplift; (2) temporally and spatially varying uplift; (3) exhumation of a part of the area from below Neogene sediments. Given the size of the area, its lithological variability and the insufficient knowledge of the palaeogeographical settings, using a detachment-limited model to express river incision into bedrock as well as water (rill) erosion on hillslopes proved the best solution. Results of the simulations were compared with real topography through hypsographic curves and the distribution of remnants of planation surfaces. The real surface corresponds best to a combination of the hypotheses (2) and (3), with more intensive Quaternary tectonic uplift of the Pohronský Inovec Mts. and the adjacent Rázdiel part of the Tribeč Mts., and exhumation of a mature palaeosurface from below Miocene sediments in the east of the Tribeč Mts

Assessing the natural hazard of gully erosion through a geoecological information system (GEIS) :a case study from the Western Carpathians

The development of gullies represents a specific type of fluvial erosion that is triggered when surface runoff becomes concentrated during extreme rainfall events. This study investigates a part of the Povazske Valley and Strazovske Mountains in Slovakia to assess the potential susceptibility and gully erosion hazard using a Geoecological Information System (GeIS). The landscape of the area was studied through primary field research and the analysis of secondary materials. The GeIS was then constructed in order to undertake specific multidimensional statistical methods. These were used to assess the potential susceptibly and gully erosion hazard. Those areas with the greatest potential susceptibility occur in Butkovska Furrow and the Podmaninska Hills whilst those with the least potential susceptibility occur in Butkovske Klippes and the Trencianska Upland. The greatest gully erosion hazard was identified on arable land in the Podmaninska Hills and on the river terraces in the Ilavska Basin. It is clear that the majority of the permanent gullies within the study area are controlled by the course of existing anthropogenic linear features such as unpaved field and forest roads and balks in arable land.15216

Exposure to human influence – a geographical field approximating intensity of human influence on landscape structure

<p>A new spatial variable for the land use and land cover change modelling is introduced, approximating the intensity of human influence on the landscape. The ‘exposure’ simulates the dilution of human activity from settlements (source points with information about population size or other human activity quantification) to landscape, based on the accessibility. Exposure to a settlement is directly proportional to its population size and inversely proportional to the cost distance from the settlement. Cost distance uses the sine of the slope angle as a cost raster to simulate a barrier effect of the terrain. Overall exposure to human influence summates exposure to all individual settlements in a region. The resultant raster field created for Slovakia achieves observable resemblance to the actual intensity of land use derived from Corine Land Cover map. The ArcGIS tool developed for the exposure calculation is supplemented.</p

Influence of neotectonics on land surface evolution in the upper part of the Blue Nile Basin (Ethiopia): findings from a DEM

The morphometric analysis of lineaments, valleys and signs of erosion taken from a digital elevation model (DEM) made it possible to not only confirm most of the conclusions of the morphotectonic development of the Blue Nile Basin from the previously published results of structural, petrological, tectonic and geochronological analyses, but also to expand our knowledge by applying several new hypotheses. The relative age of the morpholineaments of particular directions was estimated from the character of topographic profiles. Faults, lineaments and valleys are predominantly oriented in a direction compatible to the published concepts of the tectonic development of the area. Overall, the most abundant NE-SW and NNE-SSW lines reflect a change of extension from a NW-SE to WNW-ESE direction during the Pliocene, in relation to the creation and development of the Main Ethiopian Rift (MER). This is confirmed by a more developed character of the valleys and less pronounced erosion activity of the NE-SW oriented valleys contrary to the deeper narrower NNE-SSW valleys characterised by downward and headward erosion in the second direction. The most pronounced morphological manifestations of the E-W extension of the MER and western Afar during the Quaternary are confined to the borders of the MER. The directions of the Pre-Neogene rift structures to the NW-SE and WNW-ESE are compatible with the oldest elements of the current landscape and with the relict fragments of the valley network on the SE boundary of the upper Blue Nile Basin, which could have been drained across current shoulders of the MER to the S and E before the Late Miocene

Exposition to human influence - ArcGIS toolbox and raster for Slovakia

"Exposition to human influence" is a new spatial variable for the land use and land cover change modelling, approximating the intensity of human influence on the landscape. The “exposition” simulates the dilution of human activity from settlements (source points with information about population size or other human activity quantification) to landscape, based on the accessibility. Exposition to a settlement is directly proportional to its population size and inversely proportional to the cost distance from this settlement. Cost distance uses sine of the slope angle as a cost raster to simulate a barrier effect of the terrain. Overall exposition to human influence sums all expositions to individual settlements in a region. Resulting raster field created for Slovakia achieves an observable resemblance to the actual intensity of land use, derived from Corine Land Cover map. The ArcGIS tool developed for the exposition computation is supplemented