Article

# Historical contingency in fluviokarst landscape evolution

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## Abstract

Lateral and vertical erosion at meander bends in the Kentucky River gorge area has created a series of strath terraces on the interior of incised meander bends. These represent a chronosequence of fluviokarst landscape evolution from the youngest valley side transition zone near the valley bottom to the oldest upland surface. This five-part chronosequence (not including the active river channel and floodplain) was analyzed in terms of the landforms that occur at each stage or surface. These include dolines, uvalas, karst valleys, pocket valleys, unincised channels, incised channels, and cliffs (smaller features such as swallets and shafts also occur). Landform coincidence analysis shows higher coincidence indices (CI) than would be expected based on an idealized chronosequence. CI values indicate genetic relationships (common causality) among some landforms and unexpected persistence of some features on older surfaces. The idealized and two observed chronosequences were also represented as graphs and analyzed using algebraic graph theory. The two field sites yielded graphs more complex and with less historical contingency than the idealized sequence. Indeed, some of the spectral graph measures for the field sites more closely approximate a purely hypothetical no-historical-contingency benchmark graph. The deviations of observations from the idealized expectations, and the high levels of graph complexity both point to potential transitions among landform types as being the dominant phenomenon, rather than canalization along a particular evolutionary pathway. As the base level of both the fluvial and karst landforms is lowered as the meanders expand, both fluvial and karst denudation are rejuvenated, and landform transitions remain active.

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... What is an appropriate measure of fitness in Earth surface systems (ESS)? A number of hypotheses have been proposed for optimal structures and configurations of, e.g., ecosystems, channel networks, topography, etc. Most, if not all, of these principles can be reduced to (or subsumed under) the idea of efficiency or resistance selection--more efficient and resistant forms and structures are more likely to persist and grow, or to occur repeatedly, than less efficient ones (see Jorgensen, 1997;Fath et al., 2001;Ulanowicz et al., 2006 on ecological systems; Huang and Nanson, 2000;Nanson and Huang, 2008;2018;Paik and Kumar, 2010;Phillips, 2010;2011;Smith, 2010;and Huang et al., 2014 on geomorphic systems;andOzawa et al., 2003 andKleidon et al., 2013 on geophysical phenomena more generally). To the extent that "fitter" (more efficient and/or resistant) geomorphic features and structures are subject to not just preferential preservation, but also enhancement (via positive feedbacks) and/or propagation, then algorithmic evolution models may apply to geomorphology, too--implying the possibility of geomorphic creativity. ...
... Thus creativity and innovation in biological evolution was accompanied by creativity and innovation in fluvial systems. However, selection for maximum efficiency structures and configurations has been shown to operate for a number of abiotic phenomena, including atmospheric fluid flows (Ozawa, et al., 2003); development of subsurface flow networks (Hunt, 2016), and evolution of stream channel networks, planforms, and cross-sections (Huang and Nanson, 2000;Nanson and Huang, 2008;2018;Kleidon et al., 2013;Paik and Kumar, 2010;Phillips, 2010;2011;Smith, 2010;Huang et al., 2014). ...
... Kentucky River case study Previous research (Phillips, 2018) examined a chronosequence of fluviokarst landscape development over ca 1.5 Ma in central Kentucky. That chronosequence is reexamined here with respect to evolution of dolines. ...
Article
In biological evolution, creativity occurs in the appearance of new entities by evolutionary dynamics. This is linked to mutations and genetic drift, which cannot occur in geophysical phenomena. Biota can exhibit evolutionary creativity that influences landforms, but how does creativity (defined here as the capacity for emergence of new entities that increase the adjustedness of the landscape to environmental conditions) occur in landforms and landscapes as entities independent of biota? Creativity in geomorphic evolution does not require any sort of goal functions or purposeful innovation‐‐just that geomorphic development is capable of producing novelties that may be better adapted (more efficient or durable) than predecessors. Independently of biota, evidence exists that landforms may develop to become more or less "fit" in terms of efficiency and/or durability. Thus emergence of novel features may lead to their persistence. Emergence of novel forms is illustrated for the case of karst sinkholes (dolines), which indicates increasing geomorphic diversity over Ma and Ga timescales. A case study of fluviokarst chronosequences in Kentucky demonstrates emergence and elimination of landforms as landscapes evolve. Some of these may represent generally (as opposed to locally) novel landforms. While this paper is more suggestive than demonstrative, results strongly suggest evolutionary creativity in geomorphology both tied to, and independent of, biological evolution. This occurs due to emergence of geomorphic entities that are subject to selection that tends to increase efficiency and durability.
... A direct empirical test of the implications of the model above would have to confirm (or not) the transition from rapid growth in initial stages of epikarst development to slow growth or steady-state later. This is not possible at the moment, though some chronosequences of fluviokarst landform development on the interior of Kentucky River meander bends (Phillips, 2018) might provide future opportunities if sufficient dating resolution could be obtained. However, a means of assessing the implications of the previous section can be developed, as described below. ...
... The Kentucky River has incised roughly 100 m since that time in the inner Bluegrass, carving the Kentucky River gorge. Phillips (2017Phillips ( , 2018 has shown how this incision has driven landform change on the uplands (as well as in the valleys). ...
... The Chenault includes rounded gravels of lithology not found in the local rock, and also sometimes sand, indicating a Kentucky River source. Phillips (2018) showed that some bends have a chronosequence of strath terraces on the erosional slip-off slopes of the bend interiors. Thus the presence of the deeper soils shows that they formed post-Kentucky River incision, and possibly from initially exposed bedrock. ...
Article
Tree roots have biogeomorphic engineering effects on epikarst weathering and soil deepening. This is investigated using a system model describing the interactions among biogeomorphic effects of roots, weathering, and soil-epikarst development. The model shows that the system is dynamically unstable when roots are limited by subsurface accommodation space and water availability, and weathering is moisture limited. Instability indicates relatively rapid, unstable growth of epikarst cavities and soil, driven by positive feedbacks. However, when belowground rooting space and moisture are no longer limiting, and weathering is reaction-limited, the system is dynamically stable, indicating steady state or slow growth of epikarst and soils. Results suggest an important role for biogeomorphic ecosystem engineering (BEE) by tree roots in soil and epikarst development, but that BEE is self-limiting. When moisture storage and supply for both plants and dissolution are adequate and sufficient root space is available, BEE effects become negligible. Supportive data and field observations from the Inner Bluegrass region of Kentucky indicate that BEE effects of trees can produce favorable conditions for tree growth, with these effects becoming negligible as soil thickness increases sufficiently.
... Another used geomorphic signatures to identify karst-to-fluvial and fluvial-to-karst transitions at the landform scale (Phillips, 2017). In a third study, a chronosequence based on fluvial strath terraces was used to examine historical contingency (Phillips, 2018a;Fig. 5.6). ...
... For the landform transitions, positive links were assigned where multiple examples of apparent transitions from one form to another were recognized in the field (Phillips, 2017a), where the "destination" landform did not precede the "origin" landform in the chronosequence (Phillips, 2018a), and where the basic principles of fluviokarst landform development support the transition (Phillips, 2015a(Phillips, , 2017a. Negative links were assigned where no evidence of a transition was observed, and principles suggest that a transition would be extremely unlikely, if not impossible. ...
Chapter
History matters. Global (independent of place and time) principles are necessary to explain landscape evolution, as are place factors (geographical and environmental context). But, by themselves, they are not sufficient. To explain landscape evolution—which by definition has important temporal dimensions—history must also be incorporated. Landscape evolution is historically contingent. This chapter outlines several different types of historical contingency, discusses multiple pathways and outcomes in landscape evolution, and evaluates why some imaginable pathways are rare and others common, and some trends are divergent and others convergent. Methods for evaluating path stability of historical trajectories are introduced and applied to several different Earth surface systems. The chapter concludes with a consideration of landscape evolution in the context of convergence, divergence, and equifinality.
... As dolinas são as formas de relevo mais comuns e representativas das paisagens cársticas, e estão relacionadas à maneira como se deu o processo de formação (morfogênese). Segundo Tavassos (2019, p. 78-81) 2016;BOČIĆ et al., 2015;JERIN;PHILLIPS, 2017;KOŠUTNIK, 2007;PHILLIPS, 2017PHILLIPS, , 2018PHILLIPS et al., 2004;TÎRLǍ et al., 2016). ...
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Abstract The vast occurence of Bambuí group carbonate rocks (Neoproterozoic), in Brazilian Central-West region, allows the realocation of great superficial rivers to the fragile underground ambient. In this sense, this work aims the identification of areas with the possibility of occurrence of sinkholes in Rio Corrente Basin, located in the northeast portion of Goiás state. These features are typical in karstic ambients, being responsible for the superficial hydrography capture to the subterranean area. Using the Geographic Information System (GIS), operating the softwares QGIS and SAGA GIS, attempts were made to the location of such areas from visual identification (considering criteria such as hydrography, altitude, contours and vegetation). From the application of these filters 170 polygons of were identified, representing areas of possibility of sinkholes occurrence, being necessary field work to validate them.
... It is considered that the stacking of the structural units leads to erosion and consequently, to the creation of juxtaposed basins to receive fluvial or marine sediments. Whipple and Tucker (1999), Gallen and Wegmann (2017) and Phillips (2018) incorporate rock uplift, U, into a fluvial erosion model to reach the steady state. To try to elucidate the nature of these structural units in northern Tunisia, we have used a digital terrain modeling (DTM) field to understand and model this dynamic in the context of complex tectonic disturbances, and for more or less constant climatic conditions. ...
Article
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Digital elevation modeling (DEM) was used to determine key morphological features such as hypsometry, slopes and topographic evolution in correlation with tectonic regimes and erosion mechanisms. This contribution discusses the tectonic model of northern Tunisia, which since 1977 has been described by geologists as an allochthonous unity domain of the Serravallian-Tortonian. This study presents new data from the erosion rate calculation following the establishment of these units and then proposes another view on regional tectonics. Therefore, the example used of Oued Sedjnene gives a rising rate of the order of 0.01 mm/year, almost equivalent to the results found in surrounding medeterranean belt (ex. Italy and Turkey). The structure and geomorphology of northern Tunisia is a result of folding of Cenozoic basin. However located tangential structure are related to transcurrent faults and not overthrust structure.
... In fluviokarst landscapes, the interpretation of river profiles is potentially impacted by other factors governing the evolution of channel networks, such as the relative influence of dissolution and mechanical processes on the erosion of the river bed, diversion of surface flow to the subsurface karst systems, and groundwater sapping (e.g., Dunne, 1980Dunne, , 1990Schorghofer et al., 2004;Anthony and Granger, 2007;Woodside et al., 2015;Francis et al., 2018). Furthermore, repeated transitions from a prevalence of dissolution processes to dominant fluvial erosion can result in hybrid or transitional landforms and complex patterns of erosion that render the interpretation of the fluviokarst landscape in terms of climate or uplift change problematic (Gallen and Wegmann, 2017;Phillips, 2017Phillips, , 2018. ...
Article
The evolution of fluviokarst landscapes results from the interplay of karst and fluvial processes, all driven by rock uplift or base level fall. The fluviokarst landscape of the Murge Plateau in the central Apulian Region (southeastern Italy) is characterized by narrow, steep-sided, V-shaped canyons, locally called ‘Gravine’, and deeply incised into the Plio-Pleistocene deposits of the Bradanic Trough and the underlying Apulian limestone bedrock. Previous studies propose alternative models of canyons development, however identifying a dominant morphogenetic process for the evolution of the ‘Gravine’ fluviokarst drainage basins remains an open question. The results of our regional morphometric analysis reveal a marked transition from the relict, low-relief landscape preserved in the Murge uplands to the steep channel reaches below prominent knickpoints showing evidence of a transient wave of river incision that is propagating inland. We observe anomalies of mean local relief and channel steepness, and the distribution of fluvial knickpoints consistent with a regional uplift affecting the Murge Plateau since Middle-Late Pleistocene. These findings demonstrate that the history of landscape evolution was dominated by fluvial processes. Using transformed river profile analysis we show that χ anomalies in the ‘Gravine’ trunk channels indicate drainage basin instability by drainage area capture. The convex-shape of the hypsometric curves and high hypsometric integrals confirm that the disequilibrium state of the 13 analyzed basins results from a combination of regional uplift and subsequent river network reorganization and plateau area captures. Based on our results, we propose a new model of landscape evolution for the ‘Gravine’ fluviokarst drainage basins.
... At the same time, these features and properties can influence future developmental trajectories. Within the systems approach, this property is identified as part of historical contingency, and is referenced frequently in the geosciences (Phillips, 2013(Phillips, , 2017. ...
Article
In the present paper we report on the only known example of a hummocky meadow in Poland. The area of the Hala Długa in the Gorce Mountains is a hotspot of complex geomorphic edge effects that have been widely studied in relation to human impacts and forest disturbances. Applying an interdisciplinary approach, we aimed to study the geomorphic activity in edge conditions between two contrasting ecosystems, a high-mountain meadow and a forest. Several methods were applied: geomorphic mapping, radiocarbon dating, soil analysis, geomorphometry, wood anatomy, and investigations of historical maps. These methods enabled us to reconstruct the history of the Hala Długa over the past ca 300 years, and to evaluate geomorphic activity and soil dynamics in this area. The treethrow pit-mound microtopography (hummocky meadow, Buckelwiese) of this area was formed under forest conditions, but due to long-term human impacts linked to sheep grazing and mowing, was preserved as a distinct topography for at least 100 years. While this topography was still clearly visible in the 1950s, when it was first reported, it is currently gradually disappearing under trees that have formed a belt around the study area. Soils of the study site were disturbed by tree uprooting, with many key features identified during the soil profile analysis: spots of coarse partly oriented sandstone fragments in pits, patches of organic matter in the metamorphic B horizon, and a large number of root remnants and pieces of charcoal in different parts of treethrow mounds and pits. We suggest a non-linear or even polygenetic soil evolution due to altered vegetation and disturbance regimes. The evaluation of wood remnants revealed that the majority of uprooted tree species were Picea abies (L.) H. Karst and Larix decidua Mill. We conclude that in the Gorce Mountains geomorphic edge effects can form hotspots of geomorphic activity driven by human impacts, natural disturbances, and the specific hydrological regime in the highest parts of the massif.
... Rather, they depend on a combination of fieldwork, soil survey data, and published research to develop a narrative of place formation. Field observations are based on work conducted for both site-specific and regional studies of differential landscape development on inner and outer bends of the Kentucky River gorge (Phillips, 2015), soil spatial complexity (Phillips, 2016a), fluviokarst landform transitions (Phillips, 2016a), and landform evolution on chronosequences associated with Kentucky River incision and lateral migration (Phillips, 2018a). Published soil surveys and related data utilized are shown in Table 2. ...
Article
Nine axioms for interpreting landscapes from a geoscience perspective are presented, and illustrated via a case study. The axioms are the self-evident portions of several key theoretical frameworks: multiple causality; the law–place–history triad; individualism; evolution space; selection principles; and place as historically contingent process. Reading of natural landscapes is approached from a perspective of place formation. Six of the axioms relate to processes or phenomena: (1) spatial structuring and differentiation processes occur due to fluxes of mass, energy, and information; (2) some structures and patterns associated with those fluxes are preferentially preserved and enhanced; (3) coalescence occurs as structuring and selection solidify portions of space into zones (places) that are internally defined or linked by mass or energy fluxes or other functional relationships, and/or characterized by distinctive internal similarity of traits; (4) landscapes have unique, individualistic aspects, but development is bounded by an evolution space defined by applicable laws and available energy, matter, and space resources; (5) mutual adjustments occur between process and form (pattern, structure), and among environmental archetypes, historical imprinting, and environmental transformations; and (6) place formation is canalized (constrained) between clock-resetting events. The other three axioms recognize that Earth surface systems are always changing or subject to change; that some place formation processes are reversible; and that all the relevant phenomena may manifest across a range of spatial and temporal scales. The axioms are applied to a study of soil landscape evolution in central Kentucky, USA.
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The Old Kentucky River system was a major contributor to the Teays River, draining southwestern Ohio and much of eastern Kentucky. The trunk river flowed northward from southeastern Kentucky throughout Frankfort and Carrollton, and then past Cincinnati and Dayton, joining the Teays River near Springfield, Ohio. North of the glacial boundary, which lies along the modern Ohio River, the course of the Old Kentucky River has been modified, and is today largely buried by drift. Although dissection is extensive to the south, there are many remnants of this entrenched and broadly meandering Teays-age valley system and of its sub-upland predecessors. These valleys contain areas of upward-fining, deeply weathered gravel, composed mainly of rounded quartz, chert, and silicified limestone pebbles derived from the headwaters of the system. Modern rivers have been entrenched 30 to 100 m below the Old Kentucky River valley and its main tributaries, the Old Licking and South Fork. The Old Kentucky River system was severed from the Teays when glaciation dammed its downstream reaches, forcing a reversal in flow direction between its junction with the Teays in west-central Ohio and Carrollton, Kentucky, and causing westward overflow into the Old Ohio River system. Piracy by the Old Ohio may also have contributed to the integration of the Old Kentucky and Old Ohio River basins. Ponded sediment is present in some of the now-abandoned valley remnants east of Cincinnati. As a result of glacial damming, the headwaters of the Teays River in southeastern Ohio and West Virginia overflowed westward across the Manchester divide into the Old Kentucky River drainage basin. All of these events led to establishment of the modern Ohio River system.
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Many landscapes are characterized by a mosaic of patches in various stages of succession. Whether successional paths dampen, track, or magnify extrinsic variation in initial conditions influences how much historical and site-specific detail is required to explain variation in patch composition. I investigated the patterns and importance of historical effects in a successional marine rocky intertidal community on the central coast of Oregon, USA Patches in the mid-intertidal mussel bed (M. californianus) were manually cleared in a way that mimicked natural disturbances. In four separate blocks (large patches ~9 m2), three sets of plots were initiated with their starting dates staggered by one year. Within each set of plots, I manipulated the presence/absence of two groups of early successional sessile species under each of three predator densities. This design allowed me to address the following general questions: (1) What are the separate and interactive effects of successional age, yearly variation, and initial conditions on the temporal changes observed after disturbance? (2) When do interactions between early species act to dampen or magnify natural variation between years or starting dates? Succession in mid-intertidal patches in the mussel bed displayed complex patterns of historical effects, which varied among species and between different stages of succession. Embedded in this potential complexity were some consistent and repeatable successional trends. Some potentially important canalizing, or 'noise-dampening' forces in this system included: (1) physiological and/or life history trade-offs between dispersal ability and competitive ability, (2) strong direct biotic interactions, which buffer environmental variability, and (3) compensatory ('buffering') responses of species within an important functional group. 'Noise-amplifying' forces included: (1) variable indirect effects of predators, (2) prey size escapes, and (3) predator saturation (or prey 'Swamp' escapes). Understanding the patterns and causes of consistency or contingency in succession will be critical for managing variability in landscapes that are increasingly dominated by anthropogenic disturbance regimes.
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Evidence is presented demonstrating that in areas of varied tectonic settings - shield, orogenic, platform - relief amplitude has increased over periods of 60-100 My. Slope steepening is characteristic of many of the areas discussed. Of the recognised models of landscape evolution Crickmay's model involving Unequal Activity is closest to that described here. But whereas Crickmay attributed areal inequalities in erosion to disparities between the erosive capacities of major streams and their tributaries draining divides, the present model is based largely in structure, and its control of shallow groundwaters, weathering and erosion, and in consequent reinforcement effects. This model involving increasing relief amplitude readily accommodates the very old palaeosurface remnants reported from various parts of the world. -Author
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In order to explore mechanisms of bedrock terrace formation, we have developed a numerical model that couples vertical river incision and meandering. Model results illustrate that flights of unpaired strath terraces can form purely from the internal dynamics of bedrock river meandering in vertically incising channels. Specifically, knickpoints that propagate upstream following meander cutoffs enhance vertical incision, whereas channel lengthening and corresponding slope reduction during meander growth suppresses vertical incision. Analysis of topography from the Smith River, Oregon, USA, suggests terrace formation by this mechanism. Our results introduce an alternative mechanism to climatic or tectonic forcing, namely inherent instability triggered by meander growth and cutoff, that explains both oscillations in rates of vertical bedrock incision and the formation of longitudinally traceable, unpaired bedrock terraces. In addition, our results point to simple topographic criteria for identifying internally generated fluvial bedrock terraces.
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Conference Paper
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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In order to contribute to the debate on the role of fluvial erosion in the shaping of karst, two nearby areas with different karstic landscapes were compared. Areas A and B are located relatively close to each other on the southern side of the Krk Island (Adriatic Sea, Croatia). Both areas are composed of similar limestone with a very high CaCO3 content.Area A is a typical doline or polygonal type (“classical”) of karst with numerous dolines (up to 57/km2) covered with terra rossa (red soil) and Mediterranean maquis shrubland. Dolines are located in zones which correspond to the strike of the main geological structures. Dry karstic valleys are visible only on gently inclined coastal slopes bordering the karstic plateau. In contrast, area B is typical of a bare karst landscape with a strong (palaeo)fluvial imprint. The dolines are absent, and the bedrock is only sporadically covered with terra rossa. Palaeogene marls have been observed in a few elongated depressions and in the coastal zone of area B. Along steep coastal slopes, valleys (up to 460 m/km2) are cut into the carbonates. The traces of episodic surface flows are visible in some of these valleys, in contrast to the valleys in area A. Remnants of a disrupted ancient fluvial network are clearly visible on the elevated karstic plateau in area B.Differences in the recent morphology are attributed mainly to varying thicknesses of the Palaeogene impermeable marly cover, and the intensity of tectonics in the two areas.
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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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Subsurface solutional pathways make limestone terrains sensitive to changes in soil properties that regulate flows to the epikarst. This study examines biogeomorphic factors responsible for changed water movements and erosion in fluviokarst slopes deforested 200 years ago along the Kentucky River, Kentucky. In this project, infiltration and water content data from forest and fescue grass soil profiles were analyzed within a detailed overview of system factors regulating hillslope hydrology. Results show that grass has growth and rooting characteristics that tend to create a larger volume of lateral water movement in upper soil layers than occurs under forests. This sets up the current emergent pattern of erosion in which water perches at grass slope bases and overwhelms pre-existing epikarst drainage. Tree roots are able to cause solution at multiple discrete points of entry into fractures and bedding planes, increasing storage capacity and releasing sediment over time. Grass roots do not enter bedrock, and their rooting depth limits diffuse vertical preferential flow in root channels to above one meter. In the areas dense clay soils, flow under grass is conducted sideways either through the regolith or at the bedrock surface. Rapid flow along rock faces in hillslope benches likely moves fines via subsurface routes from the hillslope shoulders, causing the exposure of flat outcrops under grass. Lower growing season evapotranspiration also promotes higher grass summer flow volumes. Gullying occurs at sensitive points where cutters pass from the uphill grassed area into the forest, or where flow across the bedrock surface crosses grass/forest boundaries oriented vertical to the slope. At these locations, loss of the protective grass root mat, coupled with instigation of tree root preferential flow in saturated soils, causes soil pipes to develop. Fluviokarst land management decisions should be based on site-specific slope, soil depth, and epkarst drainage conditions, since zones sensitive to erosion are formed by spatial and temporal conjunctions of a large number of lithologic, karst, soil, climate, and vegetation factors. This study shows that it is the composite of differing influences created by forest and grass that make forests critical for soil retention in high-energy limestone terrains.
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In the carbonate aquifers which underlie most karst terrains, groundwater flow is through a dendritic system of solution conduits. In such aquifers, termed shallow conduit-flow aquifers, the methods used to model granular and fracture aquifers are not generally applicable. Investigations were conducted in the Inner Bluegrass Karst Region of central Kentucky with the objective of developing methods of modeling shallow conduit-flow aquifers as well as obtaining quantitative information on a specific portion of the aquifer to assist in its management for water supply purposes.
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Geomorphic systems consist of coupled subsystems with traits of small-world networks (SWN), characterized by tightly connected clusters of components, with fewer connections between the clusters. Geomorphic systems based on scale hierarchies often exhibit a connected caveman small-world network (CCSWN) structure. SWNs are efficient for linking a large number of components with a relatively small number of links; but effects of CCSWN structure on synchronization and scale linkage have not been examined. Synchronization is analyzed via graph theory and applied to: (1) relationships among three levels of form–process interaction in stream channels; (2) hierarchical relationships of weathering systems at scales from weathering profiles to landscapes; and (3) interactions in fluviokarst systems at the scale of flow processes and of landscape evolution. Relationships among system components are represented as simple unweighted graphs. The largest eigenvalue of the adjacency matrix (spectral radius) reflects the critical coupling strength required to synchronize the system. The second-smallest eigenvalue of the Laplacian of the adjacency matrix (algebraic connectivity) is a measure of the synchronizability. In all examples both are much less than the maximum for networks of the same number of nodes. The sparseness of the networks is the major contributor to the low synchronization, but the specific pattern of connections (“wiring”) is also significant. Where CCSWN structures arise naturally, they help explain how geomorphic effects are transmitted between disparate scales in the absence of obvious scale linkage. Where CCSWNs are an option for representation of geomorphic systems in models and data structures, they will not improve scale linkage, despite the efficiency of SWNs in other respects. Methods developed here can be applied to evaluating alternative spatial data structures or mapping strategies which either increase synchronization, supporting a lumping or aggregation approach, or decrease synchronization, indicating disaggregation or splitting into scale hierarchies.
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The Earth's surface is the dynamic interface of climatic, biotic, and geologic systems and is often described as the Earth's critical zone. Structures and processes within this zone are highly complex and heterogeneous and therefore not yet completely understood, particularly with regard to their interactions. In contrast, parts of the critical zone still in their initial development stages are expected to be less complex and heterogeneous compared to mature systems. Therefore, research approaches concentrating on this crucial initial development period of ecosystems have been recently initiated. A central hypothesis is that the initial ecosystem development phase forms the later state of ecosystems. Similarly, the behavior of mature ecosystems can only be understood if knowledge about their evolution exists. The initial development stages of geo-ecosystems are characterized by highly dynamic abiotic and biotic processes. This results in the rapid formation and alteration of structures, which in turn constitute a new framework for new processes. To disentangle the structure-process interactions, interdisciplinary and integrative research approaches in the fields of geomorphology, ecology, biology, soil science, hydrology, and environmental modeling are required. We discuss ideas that emerged from the fourth Meeting of Young Researchers in Earth Sciences (MYRES IV) held at the Brandenburg University of Technology (BTU) Cottbus in 2010 (www.myres.org), which focused on the overarching question: what are the evolutionary constraints and pathways that govern development of spatiotemporal patterns in ecosystem process and structure? This paper presents a review of the most important aspects of initial ecosystem processes as key factors of landscape development.
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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
Verleysdonk, S., Krautblatter, M. and Dikau, R., 2011. Sensitivity and path dependence of mountain permafrost systems. Geografiska Annaler: Series A, Physical Geography, 93, 113–135. DOI: 10.1111/j.1468-0459.2011.00423.x This article is an attempt to transfer a classical geomorphological concept – the sensitivity concept by Brunsden and Thornes – onto mountain permafrost systems. Focus is put on the impulses applied on the system and its subsequent response. The system state, the ratio between sensitivity and resistivity, as well as all system components and the external impulses are understood to be variable in space and time. In order to address sensitivity and path dependence in mountain permafrost systems, not only the present system configuration but also their historical development and possible future attractors have to be analysed. Important elements are the system configuration, variable impulses and thresholds, processes and process rates and internal feedbacks. The Zugspitze in the Northern Calcareous Alps at the German/Austrian border is chosen as a test site for the applicability of the sensitivity concept on mountain permafrost systems due to the high quantity of research conducted there and the significant impact of climate change on the periglacial system. Further aspects include the consequences of the Eibsee Bergsturz event in 3700 bp in terms of path dependence and geomorphic response time. With this conceptual approach, we hope (1) to enhance the interlinkage between periglacial geomorphology and other sub-disciplines of geomorphology, (2) to contribute to the strengthening of the conceptual basis of periglacial geomorphology, and, therefore, (3) to strengthen the possibilities for holistic exchange within the cryospheric research community.
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
Landscapes subject to constant forcing tend to evolve toward equilibrium states in which individual landforms have similar characteristics. Yet, even in landscapes at or near equilibrium, there can be significant variability among individual landforms. Furthermore, sites subject to similar processes and conditions can have different mean landform characteristics. This variability is often ascribed to on-going transient evolution, or to heterogeneity in processes, material properties, forcing, or boundary conditions. Three surprising outcomes of landform evolution models suggest, however, that such variability could arise in equilibrium landscapes without any heterogeneity in the physical processes shaping the topography. First, homogeneous systems subjected to constant forcing can generate a heterogeneous distribution of equilibrium landforms. Second, even simple non-linear systems can have multiple stable equilibrium states. Third, evolving landscapes can exhibit path dependence and hysteresis. We show how these three mechanisms can produce variability in landforms that arises from the characteristics of the initial topographic surface rather than from heterogeneity in geomorphic processes. Numerical experiments on the formation of low-order fluvial valleys and transportational cyclic steps in erodible streambeds illustrate why it is important to consider the influence of initial conditions when comparing models with natural topography, estimating the uncertainty of model predictions, and studying how landscapes respond to disturbances. Copyright © 2011 John Wiley & Sons, Ltd.
Article
Jovan Cvijić was born in western Serbia and studied widely in the Dinaric Kras. His publication of Das Karstphänomen (1893) established that rock dissolution was the key process and that it created most types of dolines, “the diagnostic karst landforms”. The Dinaric Kras thus became the type area for dissolutional landforms and aquifers; Germanicised as “karst”, the regional name is now applied to modern and paleo-dissolutional phenomena worldwide. Cvijić related the complex behaviour of karstic aquifers to development of solutional conduit networks and linked it to a cycle of landform evolution. He is recognized as “the father of karst geomorphology”.
Article
The evolution and flow in a karst aquifer is studied with numerical simulations, based on the KARST model (Karst AquifeR Simulation Tool). The aquifer consists of a three-dimensional interconnected network of conduits representing fractures in the rock, and a porous rock matrix representing the finer fissured system in the rock. Flow through the aquifer can be driven by both diffuse recharge from precipitation and localised sinking streams, and the aquifer drains towards a large karst resurgence representing the base level. Superimposed onto the karst aquifer is a landscape, which can evolve with time by small-scale diffusive processes, large-scale river erosion, and karst denudation.Fractures in the aquifer are enlarged with time by chemical dissolution, enhancing the secondary porosity of the karst aquifer. The enlargement of fractures results in a dramatic increase of the aquifer conductivity over several orders of magnitude, and a change of flow patterns from an initially pore-controlled to a heterogeneous fracture-controlled aquifer. During the evolution, the water table is falling from an initially high position close to the land surface to a lower level coinciding with the actual base level.Two model scenarios are studied to elucidate the karst aquifer evolution in three dimensions. The evolution models are then complemented by event-type spring discharge modelling, which can be used as a predictive tool for karst spring discharge and contaminant transport.