Geomorphometry

Physiographic maps summarize and group the landforms of a territory into homogeneous areas in terms of kind and intensity of the main geomorphological process. These maps are often produced at semi-detailed scales, while examples at the regional scale are much less common. However, because the region is the main administrative level in Europe, physiographic maps can be very useful for land planning in many fields, such as ecological studies, risk maps, and soil mapping. This work presents a methodological example of a
regional physiographic map, compiled at a 1:250,000 scale, representing the whole Sicilian region, the largest of the Mediterranean islands. The physiographic units were classified
according to the geomorphological processes that were identified by stereo-interpretation of aerial photographs. In addition, information from other published maps, representing geomorphological landforms, eolian deposits, anthropic terraced slopes, and landslide were used to improve the accuracy and reliability of the map.

Topographic position index (TPI) is an algorithm increasingly used to measure topographic slope positions and to automate landform classifications. We applied TPI to a geoarchaeological research project in northwestern Belgium but its use led to erroneous landform classifications in this heterogeneous landscape. We asked whether deviation from mean elevation (DEV) was a better method for landform classification than TPI. We found that it enabled more accurate geomorphological assessment when using northwestern Belgium as a case study.

Digital elevation models (DEMs) built from repeated topographic surveys permit producing DEM of Difference (DoD) that enables assessment of elevation variations and estimation of volumetric changes through time. In the framework of sediment transport studies, DEM differencing enables quantitative and spatially-distributed representation of erosion and deposition within the analyzed time window, at both the channel reach and the catchment scale. In this study, two high-resolution Digital Terrain Models (DTMs) derived from airborne LiDAR data (2 m resolution) acquired in 2005 and 2011 were used to characterize the topographic variations caused by sediment erosion, transport and deposition in two adjacent mountain basins (Gadria and Strimm, Vinschgau-Venosta valley, Eastern Alps, Italy). These catchments were chosen for their contrasting morphology and because they feature different types and intensity of sediment transfer processes. A method based on fuzzy logic, which takes into account spatially variable DTMs uncertainty, was used to derive the DoD of the study area. Volumes of erosion and deposition calculated from the DoD were then compared with post-event field surveys to test the consistency of two independent estimates. Results show an overall agreement between the estimates, with differences due to the intrinsic approximations of the two approaches. The consistency of DoD with post-event estimates encourages the integration of these two methods, whose combined application may permit to overcome the intrinsic limitations of the two estimations. The comparison between 2005 and 2011 DTMs allowed to investigate the relationships between topographic changes and geomorphometric parameters expressing the role of topography on sediment erosion and deposition (i.e., slope and contributing area) and describing the morphology influenced by debris flows and fluvial processes (i.e., curvature). Erosion and deposition relations in the slope-area space display substantial differences between the Gadria and the Strimm basins. While in the former erosion and deposition clusters are reasonably well discriminated, in the latter, characterized by a complex stepped structure, we observe substantial overlapping. Erosion mostly occurred in areas that show persistency of concavity or transformation from convex and flat to concave surfaces, whereas deposi-tion prevailingly took place on convex morphologies. Less expected correspondences between curvature and to-pographic changes can be explained by the variable sediment transport processes, which are often characterized by alternation of erosion and deposition between different events and even during the same event.

Resumen: En países tropicales donde existen condiciones geodinámicas activas, tanto internas como externas, y el modelado del relieve está en constante modificación, los procesos de ladera son una de las amenazas naturales más recurrentes que causan pérdidas humanas y económicas todos los años. El área de estudio comprende una sección de 52 km 2 en las coordenadas geográficas extremas: 10,23° N y 10,18° S,-84,23° W y-84,14° E, la cual se localiza en la ladera noreste del volcán Poás en Costa Rica. El objetivo de este trabajo es mostrar un modelo morfométrico para determinar áreas susceptibles a procesos de ladera a partir del caso de estudio de la región más afectada por los des-lizamientos disparados durante el terremoto de Cinchona en 2009. Se desarrollaron siete mapas morfométricos que explican de manera indirecta la dinámica geomorfológica de este territorio. Se compararon los resultados del mapa de susceptibilidad a procesos de ladera con los movimientos en masa cosísmicos de 2009, lo que dio como resultado que un 98% de estos fenómenos coincidieran con las áreas de ocurrencia frecuente y máxima ocurrencia. Además, se utilizaron las superficies de ruptura de los procesos gravi-tacionales de 2009 para validar este modelo con un evento sísmico real, lo que dio un 78% de predicción. Por último, este modelo podría ser replicado en otras regiones tropicales como insumo de base para la toma de decisiones en la gestión del riesgo a desastres y el ordenamiento territorial.

Abstract: In tropical countries where both internal and external active geodynamic conditions exist and relief mo-deling is constantly changing, hillside processes are one of the most recurring natural hazards that cause human and economic losses each year. In Costa Rica, for example, these phenomena cause approximately 30% of the disasters that affect the country each year. The study area comprises a section of 52 km 2 in the extreme geographical coordinates: 10,23 ° N and 10,18 ° S;-84.23 ° W and-84.14 ° E; which is located on the northeast slope of the Poás volcano in Costa Rica and has the physical characteristics of rainfall above 2000 mm per year, intense tectonic dynamics associated with different tectonic faults and dense tropical vegetation. The objective of this work is to show a morphometric model to determine susceptible areas to hillslope processes, starting from the case study of the most affected region by the landslides triggered during the Cinchona Earthquake in 2009. The morphometry or geomorphometry is the quantitative analysis of the terrestrial surface; among its fundamental variables are altimetry or hypsometry, slope of the terrain and drainage density. The morphometric methods used are based on the approaches of Simonov (1985), Lugo (1988) and Zamorano (1990). Seven morphometric maps were developed that indirectly explain the geomorphological dynamics of this territory. Firstly, the cartography of dissection density, depth of dissection, relief energy and total erosion were performed. The density of the dissection calculates the concentration of river channels in a specific area, aiming to establish zones of greater or lesser concentration of river courses and therefore with greater river erosion. The depth of the dissection aims to measure the erosive capacity or activity of rivers vertically, as it analyzes the areas where river erosion has been more (or less) intense over time and provides an indirect relationship of the parameters that allow the dissection to increase, such as lithology, terrain inclination, precipitation and substrate weakness planes. The relief energy determines the maximum difference of the relative height in meters in a specific area and represents the potential energy that emerges from the relief. The total erosion determines zones with greater or less erosion of the recorded relief by means of the density of the curves of level in a determined area (by minimum spatial unit of analysis). All these parameters were analyzed from the three morphological regions that make up the study area (Poás volcanic complex, pyroclastic ramps and valley slopes), and then integrate these variables into the slope susceptibility map. Subsequently, the results of the map of susceptibility to hillside processes were compared with the coseismic mass movements of 2009, which resulted in that 98% of these phenomena coincided with the areas of frequent occurrence and maximum occurrence. In addition, the rupture surfaces of the gravitational processes of 2009 were used to validate this model with a real seismic event, giving 78% of prediction. It is possible to affirm that the model showed a very good performance to predict coseismic slope movements despite the fact that the model does not use any seismic parameters. It would then be expected that their verification with slope movements induced by extreme weather events would be equally acceptable. In view of the obtained results, it can be affirmed that the greatest virtue of the morphometric model is the use of easily obtained morphometric parameters from two fundamental variables: the hydrographic network and the elevation contours. It is for these reasons that the method can be applied in the territories of poor countries, by virtue of the provision of this base information. However, the limitation of the model is on the scale of the data sources and the size of the analysis cells that compose the grid of the study area. Finally, this model could be replicated in other regions or countries as a basic input for decision making in disaster risk management and land use planning.

The Multi-Scale Relief Model (MSRM) is a novel algorithm developed for the visual interpretation of landforms. This was tested within the Romagna plain, the south-eastern part of the Po Valley (Italy), to establish whether it was able to detect fluvial ridges within this alluvial landscape. Since the MSRM is not the only method to carry out morphometric analysis, it was compared with other techniques previously used in landscape archaeology, such as the Topographic Wetness Index (TWI), the Topographic Position Index (TPI), and the Deviation from mean Elevation (DEV). At the same time, the SRTM 1 Arc-Second Global was compared with a Local DEM based on ground control points. Subsequently, the result of the MSRM algorithm was tested through targeted desktop- and field-based research. This validation phase proved essential to test the accuracy of the DEM-derived products. Furthermore, it allowed us to verify the existence of the detected fluvial ridges, to propose a chronological range for some of them, and, finally, to collect new archaeological evidence.

The proper evaluation of soil resources, especially in mountainous areas, is very important for the suitable development of the local communities, which host traditional sustainable agriculture. Nonetheless, regarding the preservation of traditional sustainable agriculture and the introduction of a modern development plan to the area, an actualized and detailed distribution of soil cover is crucial. Soil legacy data is not always available at the right scale and spatial cover. To overcome such obstacles, the most suitable approach is the use of digital soil mapping for supplementing soil information. Sparse soil information is available for the Humor catchment, Eastern Carpathians, Romania, therefore we used a soil-landscape system  approach, which when coupled with a fuzzy logic-based assignment of soil to landscape system and a raster GIS representation model of the landscape environmental layers (SoLIM model), allow the continuous spatial modelling of the soil classes. The result was validated against available soil maps and soil profiles and it was shown to better represent spatial distribution of the soil cover, although further work is needed to better sample soils representing local conditions which because weren't predictable in the applied model, were included as punctual occurrences.