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... As a result of the various foci in complexity science a large variety of different approaches and techniques exist to investigate complex systems. Perhaps due to the origin of most concepts in other disciplines, a broad and critical discussion on the different concepts and assumptions of complex systems in geomorphology has not yet concluded (Phillips, 2015). As a result, specific complex systems approaches are sometimes still combined with contradicting conventional concepts in geomorphology (e.g. ...
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Complexity has long been recognized and is increasingly becoming mainstream in geomorphology. However, the relative novelty of various concepts and techniques associated to it means that ambiguity continues to surround complexity. In this commentary, we present and discuss a variety of recent contributions that have the potential to help clarify issues and advance the use of complexity in geomorphology. This article is protected by copyright. All rights reserved.
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Much geomorphological enquiry has been devoted to the understanding of landscapes via the construction of models based on the relationships between process and form. This paper examines the philosophical, theoretical and practical problems involved in bridging the gap between studies of geomorphological processes and explanations of landscape development. It argues that process geomorphology is essentially reductionist and discusses the practical and logical limitations of such an approach to science. It suggests that landscapes are emergent phenomena and, by drawing from the philosophical and practical lessons derived from the physics of non-linear systems, demonstrates that they are not amenable to reductionist explanations.
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Base-level lowering plays an important role in cave passage development and morphology. Cave conduits are commonly formed at depth below the water table, and subhorizontal conduits can form at depths of more than 100 m below the water table. Subsequent base-level lowering is responsible for evolution from a deep phreatic to a shallow phreatic to a vadose, water table setting. Most caves do not evolve to a vadose passage stretching from sink to spring because the flow is captured by undercaptures: passages at a lower elevation and below the water table. Undercaptures provide much of the complexity seen in cave maps. Distributary springs and bypass passages can also be formed during short-term rises in base level that also produce wall notches.
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Traditional conceptual models of landscape evolution view topography as an outcome of endogenic forces (uplift) working against exogenic forces of denudation. The energy considerations of these concepts have focused on the conver-sion of the potential energy of landscape relief to kinetic energy. The concept of the biosphere as a planetary membrane for capturing and converting solar energy, coupled with the critical geomorphic role of biota, call for a consideration of biotic contribu-tions to geomorphic work. A review of estimates of global rates of kinetic energy of denudation and uplift, and net primary production (NPP) indicates that the energy density of NPP is, on average, three to seven orders of magnitude greater than the others. If even a tiny fraction of NPP is geologically significant, then the biological subsidy to the energy of landscape evolution must be considered on a par with that of geophysical and geochemical phenomena. A case study in eastern Kentucky shows that even if only 0.1 percent of NPP is geomorphically significant, it still far exceeds the energy inputs from uplift and conversion of potential to kinetic energy by denudation. This is unlikely to be unique, though the relative importance of biological and geophysical processes must obviously vary with climate, tectonic setting, and other factors. Results indicate that, particularly where biological activity is significant, geomorphic work performed by biota may be greater than that associated with endogenic processes and with die kinetic energy of denudation.
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The karstic canyon of Lower Ardèche is located in the Middle Rhône valley, which is directly tributary to the Mediterranean Sea. The Rhône River is emblematic of the Messinian Salinity Crisis (MSC) impact on landscape morphology. Along the edge of the Saint-Remèze Plateau, the Rhône valley displays four benchmark levels generated by the MSC: the Pre-evaporitic abandonment surface (1), the Messinian erosional surface (2), the Marine/non-marine surface of the Pliocene ria (3) and the Pliocene abandonment surface (4).
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In this research, karstification in Menteşe Region of southwest of Turkey has been studied by GIS and remote sensing applications. Macro karstic features (doline, uvala, tectono-karstic depression and fluvio-karstic valley) of the area extending from Lake Bafa to Gökova Bay have been mapped with digitized geology and topography maps and satellite image. Micro and macro karstification have developed in dolomitic and cherty limestones belonging to Dogger-Createcous, Campanian-Maestrihtien, Senonian, Jurassic-Createcous, Middle Triassic-Liassic, Permian and terrestrial limestones of Pliocene. Dislocation lines (fault-lineament) in the direction of northwest-southeast and northeast-southwest extracted from geology maps and satellite image are important agents in evaluation of macro karstic forms. Relief generation cycles at three levels have been defined according to the TIN surface (Triangulated Irregular Network) and geomorphology map of Turkey. Based on this application, it is possible to say that changing climatic and tectonic conditions from Miocene to Pliocene have affected to the course of karstification. Slope and elevation maps extracted from DEM have been compared with macro karstic features in GIS environment. Macro karst features have mostly developed between 0–40° and in areas where slope is greater than 40° a clear macro karst hasn't become. Tectono-karstic depressions and uvalas have formed between 0–1,000 m, doline type karstic depressions have developed between 1,000–1,500 m and an evident macro karst form hasn't become at elevations higher than 1,500 m. Shaded relief image of the area originated from DEM has designated that the area has a rough relief being created by neotectonic movements. This uneven area dissected by rivers is a suitable environment for karstic process. According to the agents functioning on karstification, it has been described that Menteşe Region has a "structure-erosion-corrosion karst" type. German Das Menteşe Gebiet, das sich vom Bafa See bis zur Gökova Bucht erstreckt, wurde mit digitalisierten topographischen und geologischen Karten und Satellitendaten analysiert. Große Karstformen (Dolinen, Uvalas, tektonisch bedingte Karsthohlformen und Trockentäler) sowie Kleinformen sind in dolomitischen und feuersteinhaltigen Kalken (Perm–Pliozän) entwickelt. Tektonische NE-SE und NE-SW verlaufende Linien, die aus geologischen Karten und Satellitenbildern ermittelt wurden, haben einen großen Einfluss auf die Formenentwicklung. In Anlehnung an das TIN Netz (Triangulated Irregular Network) und die geomorphologische Karte der Türkei wurden drei Reliefgenerationszyklen bestimmt. Diese Grundlagen erlauben die Aussage, dass die Veränderungen der klimatischen und tektonischen Bedingungen vom Miozän zum Pliozän den Verlauf der Verkarstung beeinflusst haben. Aus dem digitalen Geländemodell entwickelte Hang- und Höhenkarten zeigten im Vergleich mit den Karstformen, dass sich die Makrokarstformen überwiegend in Gebieten mit Hangneigungen zwischen 0–40° entwickelten, während klare Makrokarstformen bei Hangneigungen über 40° fehlten. Tektonisch bedingte Karsthohlformen und Uvalas bestimmen den Formenschatz der Höhenlage zwischen 0 und 1,000 m, von 1,000 bis 1,500 m Höhe sind Dolinen dominant und oberhalb 1,500 m fehlen augenscheinlich große Karstformen. Schattierte Darstellungen aus dem digitalen Geländemodell zeigen ein schroffes Relief, das auf die neotektonischen Bewegungen zurückgeht. Das durch Flüsse gegliederte Menteşe Gebiet bietet günstige Faktoren für Verkarstungsvorgänge und wird nach den die Verkarstung bestimmenden Elementen als ein von Struktur, Erosion und Korrosion geprägter Karsttyp eingestuft. French Dans cette recherche, karstification dans Menteşe Région de sud-ouest de Turquie a été étudiée par les applications de GIS et télédétection. Les caractéristiques de karstic de macro (doline, uvala, la dépression de tectono-karstic et la vallée de fluvio-karstic) du domaine s'étendant de Bafa de Lac à la Baie de Gökova a été fait la carte d'avec la géologie digitalisée et les cartes de topographie et l'image de satellite. Micro et karstification de macro a développé dans les calcaire de dolomitic et cherty étant au Dogger-Createcous, le Campanian-Maestrihtien, Senonian, le Jurassique-Createcous, le Triassic-Liassic de Milieu, Permian et les calcaire terrestres de Pliocene. Les lignes de luxation (le défaut-trait) dans la direction de nord-ouest-sud-est et de nord-est-sud-ouest extrait des cartes de géologie et de l'image de satellite sont des agents importants dans l'évaluation de formes de karstic de macro. Les cycles de génération de soulagement à trois niveaux ont été définis selon la surface d'ETAIN (Triangulated le Réseau Irrégulier) et la carte de géomorphologie de Turquie. Basé sur cette application, c'est possible de dire que cela changeant climatique et les conditions de tectonic de Miocene à Pliocene ont affecté au cours de karstification. Les cartes de pente et élévation extraites de DEM comparé aux caractéristiques de karstic de macro dans l'environnement de GIS. Les caractéristiques de karst de macro ont développé surtout entre 0–40° et dans les domaines où la pente est plus grande que 40° un macro karst hasn clair't est devenu. Les dépressions de Tectono-karstic et uvalas ont formé entre 0–1.000 m, les dépressions de karstic de type de doline ont développé entre 1.000–1.500 m et un hasn de forme de karst de macro évident't est devenu aux élévations plus hautes que 1.500 m. L'image ombragée de soulagement du domaine provenu de DEM a désigné que le domaine a un soulagement rude étant créé par les mouvements de neotectonic. Ce domaine inégal disséqué par les rivières est un environnement convenable pour le procédé de karstic. Selon les agents fonctionnant sur karstification, il a été décrit que Menteşe Région a un «structure-erosion-corrosion karst» le type.
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Assertions of a ‘naughty world’ (Kennedy, 1979) point to the importance of place-based knowledge in informing landscape interpretations and management applications. Building upon conceptual and theoretical insights into the geomorphic character, behaviour and evolution of rivers, this paper outlines an approach to the practice of fluvial geomorphology: ‘reading the landscape’. This scaffolded framework of field-based interpretations explicitly recognizes the contingent nature of biophysical interactions within any given landscape. A bottom-up, constructivist approach is applied to identify landforms, assess their morphodynamics, and interpret the interaction and evolution of these features at reach and catchment scales. Reading the landscape is framed as an open-ended and generic set of questions that inform process-form interpretations of river landscapes. Rather than relying unduly on conceptual or theoretical representations of landscapes that suggest how the world ‘should’ ideally look and behave, appropriately contextualized, place-based understandings can be used to detect where local differences matter, thereby addressing concerns for the transferability of insights between locations and the representativeness of sample or reference sites. The approach provides a basis for scientifically informed management efforts that respect and work with the inherent diversity and dynamics of any given river system.
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The Cousance karst (located between the valleys of the Saulx and Marne) has been studied to determine the temporal records of river incision in the eastern Paris Basin, around the ANDRA experimental nuclear waste repository. Two generations of karst are recognized. The first is a palaeophreatic karst indicative of an old base level, now uplifted +75 m above the underground streams. It is underlain and drained by a second generation of karst with active sinks, which records the vertical evolution following the entrenchment of the River Marne. Ten U/Th dates of speleothems from shafts in the karst show that there were discontinuous growth episodes, mainly during isotopic stages 3 and 5 (between 102.4 ± 1.2 and 49.4 ± 0.4 ka bp) but also during isotopic stage 2 at 16.3 ± 0.1 and 20.9 ± 0.3 ka bp. These dates provide an absolute age limit for the start of vertical development of the karst, at the latest during isotope stage 5c.
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Many theories, old and new, of landscape and earth-surface system development involve concepts of self-organization. There are at least eleven distinct definitions of self-organization in the literature that are relevant to landscapes. Some have profoundly different implications with respect to the nature and trajectories of landscape evolution and earth-surface system behavior, including whether evolution is convergent or divergent, whether entropy or energy dissipation is maximized or minimized, the role of chaos, and the mechanisms by which self-organized patterns are generated. Despite these differences, most self-organization concepts can be broadly aggregated into two categories: those concerned with the evolution of order and regularity in the aggregate or ensemble properties of the landscape, and those concerned with the differentiation of landscapes into more diverse spatial units. This paper presents a theory of spatially divergent self-organization related to the latter, showing that autogenic differentiation is directly linked to dynamical instability and chaos. The determination of the self-organization properties of a landscape should be a starting point rather than a goal of geographic explanation. The extent to which field-testable hypotheses are generated, or explanations provided based on process mechanics or landscape history, will ultimately determine the utility of self-organization concepts and methods in physical geography.
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Environmental Change explores the nature, causes, rates and directions of environmental change throughout earth history. Huggett introduces the interdependent parts of the natural environment - cosmic, ecological, geological - and the dynamic nature of the environmental system. Integrating a wealth of examples and illustrations from around the world, the book examines evidence and causes of change in life, climate (air and water), soils, sediments and landforms, and the impacts of human-environment interaction.
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This chapter focuses upon the ‘sediment bucket’ in the Lane diagram (sediment calibre and volume). Processes of sediment entrainment, transport and deposition are discussed in the context of the Hjulström diagram. The influence of grain-by-grain interactions on the channel bed (i.e. packing arrangements), bedform generation in sand- and gravel-bed rivers, partial and equal mobility, supply- and transport-limited rivers and the role of material cohesiveness in fine-grained (silt-clay) channels is discussed, followed by an outline of the controls upon depositional processes in river systems. Prior to outlining key principles in the development of a practical approach to river sediment analysis, scales of depositional features in river systems and contrasting sedimentary sequences in bedload, mixed-load and suspended-load depositional environments are briefly summarised, and key considerations in efforts to interpret sediment sequences when reading the landscape are outlined.
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The twenty largest perennial springs of Kentucky were identified and ranked over a ten-year period. Since most large springs are not shown on topographic or geologic maps, ranked springs were primarily located from previous hydrogeologic surveys, field reconnaissance, and literature review. Spring flows were ranked by minimum annual discharge, which ranged from 0.15-0.68 m 3/s. These springs are classified as 3rd Magnitude, based on the Meinzer (1923) discharge scale. Unit base flow (the ratio of minimum discharge to basin area) revealed diverse hydrogeologic yield of the karst spring group, ranging from 0.22-12.27 L/s/km 2, suggesting significant unattributed losses and gains. Most large springs are derived from classic fluviokarst basins draining well-developed karst of Mississippian-age limestones. However, one-third result from short stream or meander cutoffs of less than 5 km, which are not necessarily related to well-developed karst terrane. An index of karst basin development can be obtained by the ratio of subsurface flow length to total basin length.
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This textbook provides a modern, quantitative and process-oriented approach to equip students with the tools to understand geomorphology. Insight into the interpretation of landscapes is developed from basic principles and simple models, and by stepping through the equations that capture the essence of the mechanics and chemistry of landscapes. Boxed worked examples and real-world applications bring the subject to life for students, allowing them to apply the theory to their own experience. The book covers cutting edge topics, including the revolutionary cosmogenic nuclide dating methods and modeling, highlights links to other Earth sciences through up-to-date summaries of current research, and illustrates the importance of geomorphology in understanding environmental changes. Setting up problems as a conservation of mass, ice, soil, or heat, this book arms students with tools to fully explore processes, understand landscapes, and to participate in this rapidly evolving field.
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The primary goal of this project is to develop a relative chronology of events in the geologic history of the Kentucky River, and to consider the geologic controls on those events. This study utilized published geologic and topographic data, as well as field observations and extensive compilation and comparison of digital data, to examine the fluvial record preserved in the Kentucky River valley in central Kentucky. Numerous fluvial features including abandoned paleovalleys, fluvial terraces and deposits, bedrock benches, and relict spillways between adjacent river valleys were identified during the course of the study. The morphology of the modern valley coincides with bedrock lithology and can be used to describe the distribution and preservation of modern and ancient fluvial deposits and features in the study area. Bedrock lithology is the dominant control on valley morphology and on the distribution and preservation of fluvial deposits and features in the study area. Some stream trends are inherited from the late Paleozoic drainage of the Alleghanian orogeny. More recent inheritance of valley morphology has resulted from the erosion of the river from one lithology down into another lithology with differing erosional susceptibility, thus superposing the meander patterns of the overlying valley style onto the underlying lithology. One major drainage reorganization related to a pre-Illinoisan glacial advance disrupted the northward flow of the Old Kentucky River toward the Teays River system and led to organization of the early Ohio River. This greatly reduced the distance to baselevel, and led to abrupt incision and a change in erosional style for the Kentucky River. The successful projection of valley morphologies on the basis of bedrock stratigraphy, the history of erosion suggested by fission track data and the results of this study, as well as soil thickness and development, all argue against the existence of a midto late-Tertiary, low-relief, regional erosional surface. This study instead hypothesizes that the apparent accordance of ridge-top elevations in the study area is a reflection of a fluvially downwasted late Paleozoic depositional surface.
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Article
Nickpoint recession in the Buchan karst, southeastern Australia, has resulted in the formation of an underground meander cut-off system in the Murrindal River valley. Three nickpoints have been stranded in the surface channel abandoned by the subterranean piracy, and these can be correlated with river terraces and epiphreatic cave passages in the nearby Buchan River valley. The presence of palaeomagnetically reversed sediments in the youngest cave passage in the Buchan valley implies that the topographically lowest nickpoint in the Murrindal valley is more than 730 ka old, and the other nickpoints are probably several million years old. The nickpoints are occasionally active during floods, but the diversion of most surface flow underground has slowed down their retreat to the extent that they have been effectively stationary for several million years. Underground nickpoint migration has been by both incision within major phreatic conduits and their abandonment for lower-level passages. The nickpoints are all present in the upstream part of the cave system, but have not migrated past the sink in the river channel, despite the long period of time available for this to happen. The sink is characterized by collapsed limestone blocks; these filter out the coarse bedload from the river channel. As a result, erosion within the cave passages is dominantly solutional and therefore slower than in the surface channel, where it is mostly mechanical. In addition, to transmit a drop in base level the cave system requires the removal of a larger volume of rock than for the surface migration of a nickpoint, because any roof collapse material in the subsurface system must be removed. These factors have slowed the migration of the base-level changes through the subsurface system, and may be a general feature in caves that have diffuse sinks as their main inputs.
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Previous experimental, field, and modeling studies of confluence dynamics have focused mainly on junctions formed by straight channels. In contrast, natural rivers often meander and tributaries can enter meandering rivers on the outside of bends to form a junction planform known as a confluent meander bend. In this study, field measurements of three-dimensional velocity components and bed topography at a confluent meander bend reveal a complex hydrodynamic environment that responds to changes in momentum-flux ratio, while channel morphology remains relatively stable. Flow from the tributary deflects high-velocity flow and helical motion in the curving main river toward the inside of the bend, inducing bed scour and inhibiting point-bar development. The high junction angle forces the tributary flow to abruptly realign to the orientation of the downstream channel, initiating a counter-rotating helical cell over the outer portion of the bend. Two surface-convergent helical cells persist through the downstream channel, where the combined flows accelerate as the channel cross-sectional area is constricted by a bar along the downstream junction corner, precluding flow separation. Long-term stability of its planform suggests that this confluent meander bend represents a quasi-stable channel configuration. Overall, patterns of flow and channel morphology are quite different from typical patterns in most meander bends, but are generally consistent with a conceptual model of confluent meander bends derived from previous laboratory experiments and numerical modeling.
Article
Many geomorphic system states and behaviors often interpreted as tendencies toward establishment and maintenance of steady-state equilibrium are actually emergent outcomes of two simple principles: gradient selection and threshold-mediated modulation. The principle of gradient selection is simply that geomorphic features associated with gradient-driven flows persist and grow relative to other features and pathways. The principle of threshold-mediated modulation reflects the inherent limits on system development along any particular pathway. Thresholds not only define a restricted state space for any given geomorphic system, but may also result in oscillatory behavior around an intermediate condition that resembles fluctuations around a steady-state equilibrium. Together, these principles often produce outcomes that mimic steady-state equilibria. Examples are given involving several aspects of fluvial systems (channel profiles, alluvial channel changes, and drainage density), hillslope gradients, and barchan dunes. Steady-states indeed occur in Earth surface systems, and are a useful simplification in some models. However, the assumption that such states are somehow normative, or the only natural condition, is incorrect, and can lead to problems in geomorphic interpretations, environmental restoration and management, and conceptions of how Earth systems work.
Article
This investigation attempts to analyze the spatial patterns of karst depression elongation and orientation relative to structural trends in a part of south central Kentucky. Depression elongation is defined by the ratio of the long axis of the depression to its short axis. Depression orientation is measured by the azimuth of the long axis in relation to the azimuth of an associated line of structural fracture. From these data the percentage of structurally aligned depressions was determined. The percentage of structurally aligned depressions was found to be highest where the following conditions prevailed: 1) in areas where limestones were characterized by low insoluble residue contents; 2) in areas where hydraulic gradients were high, as indicated by the existence of high karst relief ratios; 3) in areas where a high proportion of the surface runoff was concentrated in the subterranean drainage systems; and 4) in areas, which were located near the mouth of the subterranean drainage system. (Location in the subterranean drainage system was estimated by the mean distance to the drainage system mouth.) The percentage of structurally aligned depressions tended to decrease as the insoluble residue contents in the limestones increased, the karst relief ratios decreased, the percent area drained by subterranean streams decreased, and the mean distance from the drainage system mouth increased. Depression elongation ratios were highest in areas characterized by the following conditions: 1) low limestone insoluble residue contents; 2) high karst relief ratios, indicating high hydraulic gradients; 3) the presence of dense limestones; 4) proximity to the drainage system mouth; and 5) a high proportion of structurally aligned depressions (in this region this tended to be the most important factor influencing depression elongation). Depression elongation ratios decreased where any combination of the five previously described conditions did not occur in the optimum state. Regression analysis accounted for fifty-seven percent of the spatial variation of the distribution of structurally aligned depressions and eighty-eight percent of the variation of elongation ratios.
Article
An analysis of 40 winding streams and valleys reveals that a higher proportion of large tributaries than small ones occurs on the concave (out) side of bends. The principal reason for this is that large tributaries experience greater difficulty than small ones forming in the limited amount of space on the convex (in) side of bends. The proportions of small and large tributaries on the concave side of bends are determined largely by the spatial requirements of tributaries, valley sinuosity, mean valley bend length, and mean rate of bend migration. In addition, the proportion of large tributaries on the concave side of bends is affected by junction angle adjustments that deflect a main stream toward a large tributary, thereby creating a bend with the large tributary on its concave side. These adjustments increase the proportion of large tributaries on the concave side of bends, especially along low-sinuosity headwater streams.
Article
The exponent of the mainstream length-drainage area relationship is interpreted as a fractal quantity, superseding the previous allometric interpretation. The fractal interpretation is based on the assumption that cartographic generalization is applied evenly to all map scales. Twenty-three drainage basins of the Eaton River (Quebec, Canada) were delineated from topographic maps at three different scales (1:20,000, 1:50,000, and 1:125,000). The exponent of the length-area relation is much lower (0.546) at the largest scale than at the smallest scales (0.65), and its value corresponds to that obtained from a Richardson analysis of 10 interior stream segments. At the 1:20,000 map scale, the exponent is entirely fractal. The larger exponent values obtained at the smallest scales exceed the fractal value and incorporate an allometric component. This component is not functional, however, and it merely reflects the generalization process of cartographic abstraction of stream heads as scale is reduced. The fractal dimension of streams should not be inferred from the exponent of the length-area relation because its value is likely to be scale-dependent.
Article
Examines some of the formal relations between landform parameters themselves, or between them and supposed governing processes in terms of the information required in geomorphological theories and the constraints imposed by sound mechanical theories. It is principally concerned with empirical proportional relations and the sections include: allometric analysis; the form of alluvial fans; functionally; determined allometry: total stream length and drainage area; allometry as a test of formal assumptions; hydromorphological equations; dimensional analysis and similitude. -Keith Clayton
Article
The sequential arrangement of tributaries along trunk channels of 45 basins display complex patterns that cannot be fully explained either by assuming that a single process dominated tributary organization or that streams are topologically random. The arrangement of tributaries can be considered as representing a response to geometrical and spatial requirements imposed by other basin attributes, the effects of which are not equally influential along the entire length of a channel. However, because these factors are usually considered stable or normal properties of dentritic streams, it may be assumed that the observed tributary arrangement represents a normal characteristic of such networks. -from Author
Article
The 1920s-1930s debates over the origin of the 'Channeled Scabland' landscape of eastern Washington, northwestern USA, focused on the cataclysmic flooding hypothesis of J Harlen Bretz. During the summer of 1922, Bretz began leading field parties of advanced University of Chicago students into the region. In his first paper, published in the Bulletin of the Geological Society of America, Bretz took special care not to mention cataclysmic origins. However, in a subsequent paper in the Journal of Geology, to the editorial board of which he had recently been added, Bretz formally described his hypothesis that an immense late Pleistocene flood, which he named the 'Spokane Flood', had derived from the margins of the nearby Cordilleran Ice Sheet. This cataclysm neatly accounted for numerous interrelated aspects of the Channeled Scabland landscape and nearby regions. Nevertheless, the geological community largely resisted Bretz's hypothesis for decades, despite his enthusiastic and eloquent defence thereof. Resolution of the controversy came gradually, initially through the recognition by J. T. Pardee of a plausible source for the flooding: ice-dammed Pleistocene glacial Lake Missoula in northern Idaho and western Montana. Eventually, by the 1960s, the field evidence for cataclysmic flooding became overwhelming, and physical processes were found to be completely consistent with that evidence. The controversy is of philosophical interest in regard to its documentation of the attitudes of geologists toward hypotheses, which illustrate aspects of geological reasoning that are distinctive in degree from those of other sciences.
Article
London Bridge spans Burra Creek in the Southern Tablelands. It was formed by the development of an underground cut‐off through a limestone lens in the waist of a meander spur and controlled by the strike of the limestone and dip and unloading joints. The meander loop is occupied by a tributary alluvial fan, which may have been a dynamic factor in forming the cut‐off, not simply a consequence of it. Abandoned caves along the strike at higher level represent earlier cut‐offs. Descending profiles in these caves were caused by a rejuvenation head, held at the meander by resistant greywacke. London Bridge combines scientific interest and natural beauty to such a degree that it should be preserved as a geologic monument.
Article
Central Kentucky is characterized by a mixture of karst and fluvial features, typically manifested as mosaic of karst-rich/channel-poor (KRCP) and channel-rich/karst-poor (CRKP) environments. At the regional scale the location and distribution of KRCP and CRKP areas are not always systematically related to structural, lithological, topographic, or other controls. This study examines the relationship of KRCP and CRKP zones along the Kentucky River gorge area, where rapid incision in the last 1·5 million years has lowered local base levels and modified slopes on the edge of the inner bluegrass plateau. At the scale of detailed field mapping on foot within a 4 km2 area, the development of karst and fluvial features is controlled by highly localized structural and topographic constraints, and can be related to slope changes associated with retreat of the Kentucky River gorge escarpment. A conceptual model of karst/fluvial transitions is presented, which suggests that minor, localized variations are sufficient to trigger a karst–fluvial or fluvial–karst switch when critical slope thresholds are crossed. Copyright © 2004 John Wiley & Sons, Ltd.
Article
Hypotheses in geomorphology may be conventional or unconventional. It is argued that outrageous hypotheses produced by conventional thinkers with a streak of unconventionality occasionally shift paradigms and are invaluable alternatives to conventional hypotheses, which tend merely to shore up seemingly safe and secure ruling paradigms.
Article
A partly confined river is one along which the contemporary channel abuts the valley margin along 10–90% of its length. They occur along sections of longitudinal profiles that are transitional from fully bedrock confined to fully alluvial rivers. At this position in the landscape, there is sufficient accommodation space for discontinuous floodplain pockets to form. Segregation of the river's load and dissipation of flow energy result in sediments being stored outside the channel. Bedrock- and planform-controlled variants of these rivers, and associated floodplains, are differentiated. Terraces, fans, and piedmont zones act as secondary confining features on channel planform and floodplain formation in these valleys. The influence of these antecedent features on contemporary river character and behaviour in partly confined valleys of the upper Hunter catchment, New South Wales, Australia is appraised. The balance of formative and reworking processes, and associated capacity for geomorphic adjustment, is influenced by the site-specific configuration of antecedent controls at any floodplain pocket. Downstream patterns of these river types are analysed along all major tributaries of the upper Hunter catchment to highlight the extent of antecedent control on contemporary river forms and processes in this landscape setting.
Article
The long and complex depositional and tectonic history of the Appalachians has produced a substrate of folded and faulted sandstones, shales, and carbonate rocks (leaving aside the metamorphic and igneous core). The Appalachian fluviokarst is an evolving landscape developed on the carbonate rocks. The erosion of surface streams competes with dissolutional processes in the carbonate rocks, and both compete with tectonic uplift of the eastern margin of the North American plate. The Appalachians have undergone erosion since the Jurassic and 5 to 15 km of sediment have been removed. Many karst landscapes have come and gone during this time period. The earliest cosmogenic-isotope dates place the oldest Appalachian caves in the early Pliocene. Various interpretations and back-calculations extend the recognizable topography to the mid to late Miocene. Much of the present-day karst landscape was created during the Pleistocene. There have been many measurements and estimates of the rate of denudation of karst surfaces by dissolution of the carbonate bedrock and many estimates of the rate of downcutting of surface streams. Curiously, both of these estimates give similar values (in the range of 30 mm ka 21), in spite of the differences in the erosional processes. These rates are somewhat higher than present-day rates of tectonic uplift, leaving the contemporary landscape the result of a balance between competing processes. Introduction of tectonic forces into the interpretation of karst landscapes requires consideration of the long-term uplift rates. In the Davisian point of view, uplift was episodic, with short periods of rapid uplift followed by long static periods that allowed the development of peneplains. In the Hackian point of view, uplift has occurred at a more or less constant rate, so that present topography is mainly the result of differential erosion rates. Attempts to back-calculate the development of karst landscapes requires a conceptual model somewhere between these rather extreme points of view.
Article
Since the publication of Dynamic Basis of Geomorphology by Arthur Stahler (1952)61. Strahler , A. N. 1952. Dynamic basis of geomorphology. Geological Society of America Bulletin, 63: 923–37. [CrossRef], [Web of Science ®]View all references geomorphology has become dominated by the process approach to inquiry. This approach treats geomorphological processes and process-form interactions as manifestations of mechanical stresses and strains acting on earth materials. Little attention has been given to the philosophical underpinnings of this approach, which correspond to the doctrine of mechanistic materialism. Concerns about limitations of the process approach have been raised recently, including its inherent reductionism; difficulty in dealing with complex, large-scale geomorphic phenomena; and lack of a historical focus. This article presents an alternative perspective on the dynamic basis of geomorphology grounded in process philosophy. The central theme of process philosophy is that processes are ontologically and epistemologically more primary than substantive material objects. A major implication of process philosophy is that mechanistic concepts, while epistemically valuable, represent abstractions that lack ontological depth. Evidence both from contemporary science and from human experience suggests that the notions of matter as unchanging substance and of dynamic change as matter in motion under mechanistic influences are flawed ontologically. Instead, this evidence indicates that the nature of reality, including geomorphological phenomena, is fundamentally processual. By casting aside the constraints of mechanistic materialism, a process perspective grounded in process philosophy embraces the entire spectrum of research in contemporary geomorphology and has the potential to open new avenues of thought and inquiry, perhaps in ways that may also lead to enhanced connections between human and physical geography.
Article
Geomorphic enquiry ranges from interpretations of landscape evolution framed within geological sciences to contemporary process-form analyses that build upon engineering applications. Geographic discourse blends these perspectives, emphasizing spatio-temporal relationships across a range of scales. Following a brief historical overview, this article highlights how emerging themes in geomorphic enquiry emphasize nonlinear, emergent aspects of geomorphic systems. Such understandings extend beyond traditional conceptualizations of landscapes that were based upon notions of deterministic stability and predictability. The unique configuration and temporal sequence of drivers, disturbances and responses of each landscape, along with the historical imprint, result in system-specific behavioural and evolutionary traits wherein landscape forms and processes are contingent upon a multitude of factors. This place-based perspective of landscapes is an inherently geographical approach to enquiry. Such geomorphic thinking provides a coherent template for a range of environmental management applications, especially in interdisciplinary fields such as landscape ecology and landscape engineering.
Article
During the last two decades or so, studies on the applications of the concepts of nonlinear dynamics and chaos to hydrologic systems and processes have been on the rise. Earlier studies on this topic focused mainly on the investigation and prediction of chaos in rainfall and river flow, and further advances were made during the subsequent years through applications of the concepts to other problems (e.g. data disaggregation, missing data estimation, and reconstruction of system equations) and other processes (e.g. rainfall-runoff and sediment transport). The outcomes of these studies are certainly encouraging, especially considering the exploratory stage of the concepts in hydrologic sciences. This paper discusses some of the latest developments on the applications of these concepts to hydrologic systems and the challenges that lie ahead on the way to further progress. As for their applications, studies in the important areas of scaling, groundwater contamination, parameter estimation and optimization, and catchment classification are reviewed and the inroads made thus far are reported. In regards to the challenges that lie ahead, particular focus is given to improving our understanding of these largely less-understood concepts and also finding ways to integrate these concepts with the others. With the recognition that none of the existing one-sided ‘extreme-view’ modeling approaches is capable of solving the hydrologic problems that we are faced with, the need for finding a balanced ‘middle-ground’ approach that can integrate different methods is stressed. To this end, the viability of bringing together the stochastic concepts and the deterministic concepts as a starting point is also highlighted.