Small-scale Landforms Research Articles

Patterns, processes and models - an analytical review of current ambiguous interpretations of the evidence for pre-Pleistocene glaciations

Models (paradigms) and former interpretations have often been presupposed when conducting field research. In the 19th century diamictites were for the first time interpreted to have originated from ancient glaciations. These interpretations have to a large part prevailed in the geological community, although there has been much progress in the areas of sedimentology, glaciology and physical geography. The present work is an effort to find criteria which most clearly discriminate between geological features produced by different processes, mainly glaciation and mass flow, the latter predominantly sediment gravity flows. Geological features which have been interpreted to have formed by glaciation throughout pre-Pleistocene Earth history are compared to similar-appearing geological features formed by mass flow and tectonics, so as to uncover variations in the appearance between features resulting from these different processes. The starting point for this comparison is documentation of the appearance of Quaternary products of erosion and deposition, in order to discern the origin of older formations. It is shown that the appearance and origin of pavements, dropstones, valleys, small-scale landforms, surface microtextures and most other geological features may in some cases be equivocal, but in others the details are indicative of the process which generated the feature. Detailed geological field data which have been compiled by geologists from outcrops of pre-Pleistocene strata, more often than is considered in most papers, commonly point to a mass flow origin, mainly a sediment gravity flow origin, rather than a glaciogenic origin. A process of multiple working hypotheses or interpretations is therefore advocated, based mainly on a comparison of the appearance of features formed by different geological processes documented from different research disciplines. Instead of starting with current interpretations or models, this multiple working hypothesis or methodology helps to avoid confirmation bias and jumping to conclusions.

When Individual Geosites Matter Less—Challenges to Communicate Landscape Evolution of a Complex Morphostructure (Orlické–Bystrzyckie Mountains Block, Czechia/Poland, Central Europe)

This paper explores problems associated with explanation of geoheritage at the landscape scale and argues that focus on individual geosites that show rock outcrops or small-scale landforms may not be sufficient to tell the story. The area of Orlické–Bystrzyckie Mountains Block in Central Europe lacks spectacular landforms or large rock outcrops, and yet has a most interesting geological history that involved Mesozoic planation, Cretaceous marine transgression and the origin of sedimentary cover, Cenozoic differential uplift and the origin of tectonic topography, resultant fluvial incision and Quaternary periglaciation. Individual geosites documented in the area fail to show this complexity and give an incomplete picture. Therefore, viewpoint geosites, allowing for in situ interpretation of regional landscapes, have a role to play and they collectively illustrate the effects of the main stages of geological and geomorphological evolution. In addition, the potential of simple visualization technologies is investigated, as these 3D visualizations may enhance ground views, putting things into even broader perspective.

Simulation, modeling and authoring of glaciers

Glaciers are some of the most visually arresting and scenic elements of cold regions and high mountain landscapes. Although snow-covered terrains have previously received attention in computer graphics, simulating the temporal evolution of glaciers as well as modeling their wide range of features has never been addressed. In this paper, we combine a Shallow Ice Approximation simulation with a procedural amplification process to author high-resolution realistic glaciers. Our multiresolution method allows the interactive simulation of the formation and the evolution of glaciers over hundreds of years. The user can easily modify the environment variables, such as the average temperature or precipitation rate, to control the glacier growth, or directly use brushes to sculpt the ice or bedrock with interactive feedback. Mesoscale and smallscale landforms that are not captured by the glacier simulation, such as crevasses, moraines, seracs, ogives, or icefalls are synthesized using procedural rules inspired by observations in glaciology and according to the physical parameters derived from the simulation. Our method lends itself to seamless integration into production pipelines to decorate reliefs with glaciers and realistic ice features.

Competitive dominance mediates the effects of topography on plant richness in a mountain grassland

Small-scale landforms influence plant species richness, but their mechanisms and effects in semi-natural dry grasslands have been poorly investigated. In this study we compared vascular plant richness, species composition, plant traits, soil properties and biomass nutrient content of convex (hillocks) and concave (hollows) karst landforms in a mountain pasture of the Central Apennines (Italy), at a small spatial scale (1 m2 plots). We found hillocks had significantly higher species richness than hollows. On hillocks, smaller Specific Leaf Area and Lateral Width, together with greater allocation of resources to Below-Ground Organs, indicated lower water availability, whereas hollows had deeper (thus moister), more acidic and more fertile soils, with aboveground plant biomass displaying higher nutrient levels. Partial correlation and regression tree models suggested that fine-scale richness patterns were not directly determined by abiotic properties, but were rather the result of competition levels associated with the cover of Agrostis capillaris (=A. tenuis) – a calcifuge and drought-sensitive grass able to achieve dominance only in hollows. The higher functional convergence exhibited by hollows suggests that A. capillaris is a strong competitor both above- and below-ground, mediating the effects of topography by imposing a biotic filter. On hillocks, competition is released by lower levels of available soil water in summer and higher soil pH, resulting in higher species richness and a more functionally divergent assemblage.

Grid-based mapping: A method for rapidly determining the spatial distributions of small features over very large areas

The increased volume, spatial resolution, and areal coverage of high-resolution images of Mars over the past 15 years have led to an increased quantity and variety of small-scale landform identifications. Though many such landforms are too small to represent individually on regional-scale maps, determining their presence or absence across large areas helps form the observational basis for developing hypotheses on the geological nature and environmental history of a study area. The combination of improved spatial resolution and near-continuous coverage significantly increases the time required to analyse the data. This becomes problematic when attempting regional or global-scale studies of metre and decametre-scale landforms. Here, we describe an approach for mapping small features (from decimetre to kilometre scale) across large areas, formulated for a project to study the northern plains of Mars, and provide context on how this method was developed and how it can be implemented.Rather than “mapping” with points and polygons, grid-based mapping uses a “tick box” approach to efficiently record the locations of specific landforms (we use an example suite of glacial landforms; including viscous flow features, the latitude dependant mantle and polygonised ground). A grid of squares (e.g. 20km by 20km) is created over the mapping area. Then the basemap data are systematically examined, grid-square by grid-square at full resolution, in order to identify the landforms while recording the presence or absence of selected landforms in each grid-square to determine spatial distributions. The result is a series of grids recording the distribution of all the mapped landforms across the study area. In some ways, these are equivalent to raster images, as they show a continuous distribution-field of the various landforms across a defined (rectangular, in most cases) area. When overlain on context maps, these form a coarse, digital landform map.We find that grid-based mapping provides an efficient solution to the problems of mapping small landforms over large areas, by providing a consistent and standardised approach to spatial data collection. The simplicity of the grid-based mapping approach makes it extremely scalable and workable for group efforts, requiring minimal user experience and producing consistent and repeatable results. The discrete nature of the datasets, simplicity of approach, and divisibility of tasks, open up the possibility for citizen science in which crowdsourcing large grid-based mapping areas could be applied.

Small-scale lunar graben: Distribution, dimensions, and formation processes

The Lunar Reconnaissance Orbiter Camera (LROC) is the first instrument to provide widespread coverage with a range of incidence angles at the resolution required to detect small-scale landforms. A sample (n=238) of globally distributed, small-scale graben average 26m wide and 179m long. When dividing the population into those located within mare and highland regions, we observe that graben located within mare tend to be narrower, shorter, and more irregularly spaced than those in highland terrane. For graben associated with contractional landforms, those in mare are smaller in width and length than those in highlands; the same is true for graben independent of contractional landforms. Assuming a simple geometry, widths of mare graben associated with scarps or ridges are used to estimate the minimum depth range to a mechanical discontinuity (e.g., base of the regolith) resulting in values of ∼4–48m. These values are similar to the ranges estimated for regolith thickness from previous workers using Apollo 14 seismic data (3.9–8.5m), crater counting techniques (8–33m), crater morphology techniques (2.5–9m), and crater blockiness (8–31m). Widths of highland graben yield minimum depths of faulting of 209–296m. While this range agrees well with models for regolith production (an older surface will have thicker regolith), this estimate likely does not represent the thickness of a mechanical unit due to the fragmented nature of the highland crust (it does not provide a defining boundary between bedrock and regolith). Spacing of mare graben not associated with contractional landforms is used to estimate maximum local mare unit thickness for two graben groups: 190m for Posidonius and 296m for Vitello. Maximum graben ages range from late Eratosthenian to early Copernican based on superposed and crosscut crater ages with a group of graben deforming ejecta from Copernicus crater. Data presented here provide further evidence of a globally distributed, young, small-scale graben population that has formed as a result of localized extension either from flexural bending or dilation due to contractional faulting or volcanic uplift, indicating a significant level of recent geologic activity.

Delineation of small-scale landforms relative to flood inundation in the western Red River delta, northern Vietnam using remotely sensed data

Flood susceptibility mapping using geomorphologic approaches is effective for delineating flood extent and various degrees of potential flood-affected areas. This approach is useful where the channel system and floodplain morphology change dynamically and in regions where detailed digital elevation models are not available. The first important step in flood zonation using this approach is detailed geomorphologic mapping, also called landform classification. This study aims to describe landform classification using the rule-based method of Ho et al. (Int J Geoinform 8(4):27–38, 2012) adapted to local characteristics in the western plain of the Red River delta, northern Vietnam. The original classification scheme is generally based on the moist condition classification, local land-surface parameters, and relative position indices derived from multi-temporal Landsat data and a shuttle radar topographic mission digital elevation model (SRTM DEM). This study uses average elevations and the standard deviation of elevations as local land-surface parameters rather than local relief, which was used in the study by Ho et al. (Int J Geoinform 8(4):27–38, 2012). Multi-temporal land cover classification was performed using an integrated method to effectively correct the SRTM DEM. The overall classification is consistent with manual mapping by visual comparison. The quantitative comparison between landform units and past flood-affected areas demonstrates a precise boundary delineation of landform objects using this method. The high agreement between the boundaries of landform units and flood-inundated areas suggests the applicability of this method taking advantage of readily available remotely sensed datasets in alluvial floodplains.

A new karren feature: hummocky karren

Karren are small-scale landforms on karst surfaces and many types have been described so far. Here we present an apparently new feature which was found on the Hochschwab karst massive in the Northern Calcareous Alps of Austria. So far only few outcrops each having less than 1 m² within a very restricted area have been found. Morphometric analysis reveals that the karren consist of a randomly distributed, dispersed assemblage of small hummocks and depressions in between. The mean distance between neighbouring hummocks is 4 to 5 cm and the mean height is 0.85 cm. Longitudinal sections are gently sinuous. The occurrences are delimited by thin soil cover with grassy vegetation. The karst features continue below that vegetation cover. Therefore, it is clear that the karren have formed subcutaneously. Corroded fissures where water could infiltrate into the epikarst are absent. The bedrock lithology is Middle Triassic limestone of the Wetterstein Formation in lagoonal facies. Geological structures do not govern the feature. The surface is not a bedding plane and small joints and fractures do not govern the arrangement of the hummocks. Thin section analysis regarding rock texture and dolomite components show that there is no compositional difference between hummocks and depressions. Geochemical analyses show that the limestone is very pure with a very low content of Magnesia. Slightly higher Magnesia contents at the hummock surfaces are significant. The data obtained so far only indicate that some dissolution mechanism but not any rock property governs the irregular array. As there exist no descriptions of comparable features in literature, the name “hummocky karren” is suggested for that type of karren landform.

Evidence of Recent Thrust Faulting on the Moon Revealed by the Lunar Reconnaissance Orbiter Camera

Lunar Reconnaissance Orbiter Camera images reveal previously undetected lobate thrust-fault scarps and associated meter-scale secondary tectonic landforms that include narrow extensional troughs or graben, splay faults, and multiple low-relief terraces. Lobate scarps are among the youngest landforms on the Moon, based on their generally crisp appearance, lack of superposed large-diameter impact craters, and the existence of crosscut small-diameter impact craters. Identification of previously known scarps was limited to high-resolution Apollo Panoramic Camera images confined to the equatorial zone. Fourteen lobate scarps were identified, seven of which are at latitudes greater than +/-60 degrees, indicating that the thrust faults are globally distributed. This detection, coupled with the very young apparent age of the faults, suggests global late-stage contraction of the Moon.

Determination of the tridimensional shape of canopy gaps using two hemispherical photographs

The goal of this paper is to develop an approach to measuring tridimensional shape of canopy gap (TSCG), which is one of the most important factors affecting the understory light environment. TSCG may be expressed as a series of measurements: the gap size, the gap shape, and the canopy height in each azimuthal direction. The proposed method is based on two vertically separated hemispherical photographs of the canopy gap, and is thus named the two hemispherical photographs (THP) method. The small displacements between corresponding physical features on the two photographs can be used to measure the TSCG through a series of geometric equations based on the polar projection of the fisheye lens. In order to test the accuracy of this method, gap sizes were also measured by several ground-based methods, and the mean canopy height was measured by LaserAce hypsometer in a case study. The effects of two factors (the camera location and height difference between two photos) on the THP measures (the gap size, gap shape and mean canopy height) were also evaluated. Our results indicate that the THP measures of the gap size and mean canopy height have strong positive correlation and no significant difference with their corresponding alternatives. THP thus has a good accuracy. Moreover, ANOVA results show that all THP measures are not significantly affected not only by the height difference, but also by the location of the camera when the image is processed at 10° intervals in this sample. In addition, the THP measures of the gap size and gap shape are not influenced by the rugged canopy gap and the small-scale landform. In conclusion, THP is a rapid, simple, objective and accurate approach to the determination of TSCG.

Geology, Soils, and Geomorphology of the Walnut Gulch Experimental Watershed, Tombstone, Arizona

Abstract The surface geology of the Walnut Gulch Experimental Watershed (WGEW), Tombstone, Arizona, is dominated by fan deposits, but in southern and southeastern parts of WGEW a complex history of tectonism has resulted in igneous-intrusive and volcanic rocks, and highly disturbed Paleozoic and Mesozoic rocks in the Tombstone Hills. Soils, which are dominantly sand and gravel loams that vary from deep and well drained to thin and immature, are reflective of the rocks on which they formed. Large landforms are mostly dissected pediments and erosion surfaces, and hills of the volcanic and carbonate rocks. Episodic faulting that began in Precambrian time has resulted in complex geologic and geomorphic conditions that remain poorly understood owing to Basin and Range structural and depositional processes. Small-scale landforms of the watershed are individual hills, undissected remnants of alluvial fans (fan terraces), basin floors, alluvial fans, and recent alluvial sediment of stream channels, flood plains, ...

Bedrock slope evolution in saltrock terrain

Saltrock is a highly soluble terrain-forming material and, over short periods of time under predominantly solutional erosion processes, shows readily measurable change. It provides an analogue for landform evolution on less rapidly soluble materials such as limestone and gypsum. Saltrock erosion in a Mediterranean environment is observed with erosion pins on both solid outcrop and rockfall debris. Erosion of the salt terrains is very closely related to rainfall events. Surface lowering rates of up to 20 mm per 100 mm rainfall are observed, representing an annualised rate of ca 100 mm a−1 (= 10 m per century or 100 m per millennium). Clear relationships, which are described by bivariate polynomial equations, exist between slope angle and erosion rate. Slope evolution is then modelled with these equations, to reveal good correspondence with the small-scale landforms present at the field sites.

A comparison of methods used to estimate the height of sand dunes on Mars

The collection of morphometric data on small-scale landforms from other planetary bodies is difficult. We assess four methods that can be used to estimate the height of aeolian dunes on Mars. These are (1) stereography, (2) slip face length, (3) profiling photoclinometry, and (4) Mars Orbiter Laser Altimeter (MOLA). Results show that there is good agreement among the methods when conditions are ideal. However, limitations inherent to each method inhibited their accurate application to all sites. Collectively, these techniques provide data on a range of morphometric parameters, some of which were not previously available for dunes on Mars. They include dune height, width, length, surface area, volume, and longitudinal and transverse profiles. The utilization of these methods will facilitate a more accurate analysis of aeolian dunes on Mars and enable comparison with dunes on other planetary surfaces.

Analysis of glaciers and geomorphology on Svalbard using multitemporal ERS-1 SAR images

The all-weather capability makes synthetic aperture radar (SAR) interesting with respect to glaciological studies in remote Arctic areas. The aim of this project was to investigate how the European Remote Sensing Satellite (ERS) SAR backscatter from certain glaciological and geomorphological structures varied with time and find out at which time of the year a SAR acquisition will give the best result when observing certain features. Five ERS-1 SAR images, one from the winter and four from the summer, were acquired over the northwestern part of Svalbard, Norway. Ground measurements and observations were made at the same time as one of the summer SAR acquisitions. The ground data as well as meteorological recordings were used to analyze the SAR backscatter changes in the multitemporal data set. A zonation on the glaciers representing snow, firn/superimposed ice, and glacier ice was detected in the winter image only. The equilibrium line could also be derived from this SAR image. Information on drainage patterns, distribution of wet and dry snow areas, and the occurrence of crevasses was derived from the summer images. Changes in snow cover distribution was identified in the summer images. The form and position of ice-cored moraines, fossil beach ridges, and river channels were identified in all images. Early summer images showed the highest potential for identification of landforms. Small-scale landforms, such as patterned ground and tundra polygons, could not be identified.

Some Observations on Boulder-Cored Frost Boils

resulting from vertical frost heaving of individual boulders. They were observed in various stages of development on two glacier forelands in Jotunheimen, southern Norway. In their final stage the features comprise a boulder core partially exposed at the surface but retaining a sediment/vegetation capping. Surrounding the boulder is a shallow trough or moat beneath which is a distinct concentration of stones and gravel. Separating this aureole of clastic material from the sides of the boulder is a gap up to 5 cm wide. It is concluded that the 'frost puir mechanism of frost heave is most likely to bring large boulders to the surface. During winter freezing a boulder acts as a heat sink, leading to radial advance of the freezing plane into the surrounding till. Once the boulder has stabilized, the resulting lateral frost sorting concentrates coarser elements of the till diamicton around the embedded portion of the boulder. The formation of boulder-cored frost boils on till surfaces exposed by post-AD 1750 glacier retreat indicates the rapidity of their development and demonstrates the advantages of glacier forelands for the study of periglacial processes and landforms. BOULDER-CORED MOUNDS up to about 1.5m in diameter, and in various stages of development, were observed at sites near the glaciers Boverbreen and Storbreen, Jotunheimen mountains, southern Norway (Fig. 1). These small-scale landforms were found in poorly-drained tills deposited within the 'Little Ice Age' limits of the glaciers. Frost heaving of individual boulders towards the surface is considered to be the main process responsible for their formation. Although up-heaved boulders that have disturbed or partly emerged from the ground surface have been reported in the literature (Dionne, 1966; Washburn, 1969; Price, 1970), little attention has been given to developmental sequences. We describe here a complete sequence, including previously unrecorded forms characteristic of the later stages. Inferences are made concerning the vertical and horizontal frost sorting processes involved in their formation, the significance of which are discussed in the broader context of frost heave, with particular reference to the so-called 'frost push' and 'frost pulL mechanisms. Nature of the sites At Boverbreen, boulder-cored frost boils are associated with a complex 'Little Ice Age' end moraine system (Fig. 1, inset A). The site is immediately adjacent to a lake, dammed by the moraines, which maintains a high moisture content and a high water table in the till. The lake level lies within 0.5m of the ground surface at this site. At Storbreen the boils occur between the two outermost 'Little Ice Age' end moraines, at the foot of the proximal slope of the outermost moraine (Fig. 1, inset B). This site, crossed by ephemeral streams, is characterized by pools of standing water in wet weather. The site at Storbreen was deglaciated after ice retreat from the glacier limit of about AD 1750 (Matthews, 1974, 1977). It is probable that the Boverbreen site

Structural geomorphology of a fast-spreading rise crest: The East Pacific Rise near 3�25?S

A deeply-towed instrument package was used in a detailed survey of the crest of the East Pacific Rise (EPR) near 3°25′S, where the Pacific and Nazca plates are separating at 152 mm/yr. A single 90 km-long traverse of the rise crest extends near-bottom observations onto the rise flanks. A ridge at the spreading axis is defined by its steep regional slopes, probably caused by rapid crustal contraction as the spreading magma chamber freezes, rather than by outward-facing fault scarps. It can be divided into a marginal horst-and-graben zone with low (<50 m), symmetric fault blocks, and a 2 km-wide elongate axial shield volcano that is unfaulted except for a narrow crestal rift zone. This has a summit graben (10–35 m deep) probably formed by caldera collapse, and narrow pillow basalt walls built over vent fissures. Small, low (<50 m) volcanic peaks occur on the shield volcano and the horst-and-graben zone, and some may have been built away from the spreading axis. Major plate-building lava flows issue from the crestal rift zone and flow an average of 500 m down the sides of the volcano. The marginal horst-and-graben zone results from tensional faulting of a thin crust of lava, and evolves by progressive shearing on inclined fault planes. Crustal extension continues at least as far as 20 km from the axis, and the large, long fault blocks formed in thicker crust beyond the subaxial magma chamber develop into abyssal hills. Pelagic sedimentation, at a maximum rate of 22 m/106 years, gradually infills open fissures and smooths the small-scale roughness of the fault blocks. Off-axis volcanism has also resulted in smoother crust, and built seamounts. Comparison of the EPR at 3°25′S with the Famous Rift and Galapagos Rift reveals a similarity in the processes and small-scale landforms at fast, medium and slow-spreading ridges. There are significant differences in the medium-scale landforms, probably because plate-boundary volcanic and tectonic processes act on crust of very different strength, thickness, and age.