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Climatic or geologic controls, such as tectonics or glacial drainage, might impose constraints on landscape self-organization resulting in spatial patterns of rivers and valleys which do not obey the typical self-similar relationships found in most landscapes. The goal of this study is to quantify how such geologic constraints express themselves on channel network topology, spatial heterogeneity of drainage patterns, and emergence of preferred scales of landscape dissection. We use as an example a basin located in the Upper Midwestern United States where successive glaciations over the past thousand years have led to a pronounced spatially anisotropic channel network structure which defeats most scaling laws of fluvial landscapes. This is contrasted with another river basin in the North-Central U.S. which has been organized under the absence of major geologic influences and follows a typical self-similar channel network organization. We show how the geologic constraints have imposed a competition for space which is captured in the slope–local drainage density probabilistic structure, in the failure of self-similarity in basin-wide river network topology, and in the length-area scaling relationship being not typical of fluvial landscapes. Via a two-dimensional wavelet analysis and synthesis, we demonstrate the occurrence of a gap in the power spectrum which corresponds to the presence of preferred scales of organization, and characterize them through multi-scale detrending. The developed methodologies can be useful in advancing our geomorphologic understanding of how external controls might manifest themselves in creating a landscape dissection that is outside the norm and how this dissection can be studied objectively for understanding cause and effect. [ABSTRACT FROM AUTHOR]

Glacial terrains are commonly recorded using a landsystem approach, which allows detailed documentation of the geomorphological evolution of the landscape. However, landsystem analysis of Quaternary subsurface stratigraphies in which landforms are not apparent or preserved is problematic, making delineation of the sedimentary architecture of a glaciated basin infill difficult. The purpose of this study is to delineate the sedimentary architecture of the Sólheimajökull (southern Iceland) glacial landsystem and to provide an architectural framework for allostratigraphy and modern analogue purposes. An integrated architectural–landsystem approach is applied here, which utilizes the principles from both architectural element analysis and landsystem analysis. A bounding surface hierarchy (fourth- to seventh-order surfaces) provides a framework within which the architecture is organized. Fieldwork was conducted at Sólheimajökull glacier in 2012 and 2013; and 22 different surface features (bounded by the fourth-order surfaces) were mapped, which were grouped into four different landsystem tracts (glaciofluvial, ice-contact, jökulhlaup, and colluvial slope; bounded by the sixth-order surfaces). Landsystem tracts were deconstructed into smaller architectural units (components; bounded by the fifth-order surfaces), which allowed the delineation of eight allostratigraphic units that record the evolution of the glacial landsystem from ~ 7000 YBP to A.D. 2013. The results of this study can provide insight to interpretation and delineation of the sedimentary architecture of other modern glacial landsystems and subsurface Quaternary deposits in North America and other formerly glaciated areas. [ABSTRACT FROM AUTHOR]

We investigate landscape evolution in a region of the Alps that has escaped glacial erosion during periodic glaciations of the last million years. The research is thus suited to investigate landscaping processes on a longer time scale at the eastern end of the Alps. Morphometric analysis reveals the presence of incised relict landscapes in several regions. In the Koralpe range topographic analysis is interpreted in terms of the relict landscape being present on both sides of the eastward tilted Koralpe block. This suggests that the relict landscape is younger than the tilting of the range, which is inferred to have taken place between 18 and 16Ma. In the Pohorje region, a relict landscape is developed across the contacts of a 19Ma pluton. We use apatite (U-Th)/He thermochronology to constrain the possible age of the Koralpe and Pohorje relict landscapes. The results indicate that the Pohorje massif had cooled below 70°C by about 15Ma suggesting that the relict landscape must be younger -- consistent with the interpretation of the Koralpe range. These results suggest that many relict landscapes of the eastern Alps may have formed after 15Ma in a period of tectonic quiescence and erosion. However, in both ranges channel profile projections show that about 387±105m uplift and incision occurred subsequently. This incision is likely to have occurred during the last 6-5Ma in response to the uplift of the whole region. It testifies to a renewed and ongoing uplift event that is earlier than the glaciation periods but might easily be confused with impact of glacial erosion elsewhere in the eastern Alps. [ABSTRACT FROM AUTHOR]

Modification of the landscape by glacial erosion reflects the dynamic interplay of climate through temperature, precipitation, and prevailing wind direction, and tectonics through rock uplift and exhumation rate, lithology, and range and fault geometry. We investigate these relationships in the northeast Pamir Mountains using mapping and dating of moraines and terraces to determine the glacial history. We analyze modern glacial morphology to determine glacier area, spacing, headwall relief, debris cover, and equilibrium line altitude (ELA) using the area x altitude balance ratio (AABR), toe-to-headwall altitude ratio (THAR) and toe-to-summit altitude method (TSAM) for 156 glaciers and compare this to lithologic, tectonic, and climatic data. We observe a pronounced asymmetry in glacial ELA, area, debris cover, and headwall relief that we interpret to reflect both structural and climatic control: glaciers on the downwind (eastern) side of the range are larger, more debris covered, have steeper headwalls, and tend to erode headward, truncating the smaller glaciers of the upwind, fault-controlled side of the range. We explain this by the transfer of moisture deep into the range as wind-blown or avalanched snow and by limitations imposed on glacial area on the upwind side of the range by the geometry of the Kongur extensional system (KES). The correspondence between rapid exhumation along the KES and maxima in glacier debris cover and headwall relief and minimums in all measures of ELA suggest that taller glacier headwalls develop in a response to more rapid exhumation rates. However, we find that glaciers in the Muji valley did not extend beyond the range front until at least 43ka, in contrast to extensive glaciation since 300ka in the south around the high peaks, a pattern which does not clearly reflect uplift rate. Instead, the difference in glacial history and the presence of large peaks (Muztagh Ata and Kongur Shan) with flanking glaciers likely reflects lithologic control (i.e., the location of crustal gneiss domes) and the formation of peaks that rise above the ELA and escape the glacial buzzsaw. [ABSTRACT FROM AUTHOR]

Abstract: Erosion by glacial and fluvial processes shapes mountain landscapes in a long-recognized and characteristic way. Upland valleys incised by fluvial processes typically have a V-shaped cross-section with uniform and moderately steep slopes, whereas glacial valleys tend to have a U-shaped profile with a changing slope gradient. We present a novel regional approach to automatically differentiate between fluvial and glacial mountain landscapes based on the relation of multi-scale curvature and drainage area. Sample catchments are delineated and multiple moving window sizes are used to calculate per-cell curvature over a variety of scales ranging from the vicinity of the flow path at the valley bottom to catchment sections fully including valley sides. Single-scale curvature can take similar values for glaciated and non-glaciated catchments but a comparison of multi-scale curvature leads to different results according to the typical cross-sectional shapes. To adapt these differences for automated classification of mountain landscapes into areas with V- and U-shaped valleys, curvature values are correlated with drainage area and a new and simple morphometric parameter, the Difference of Minimum Curvature (DMC), is developed. At three study sites in the western United States the DMC thresholds determined from catchment analysis are used to automatically identify 5×5km quadrats of glaciated and non-glaciated landscapes and the distinctions are validated by field-based geological and geomorphological maps. Our results demonstrate that DMC is a good predictor of glacial imprint, allowing automated delineation of glacially and fluvially incised mountain landscapes. [Copyright &y& Elsevier]

Abstract: Subglacial bedforms preserved in deglaciated landscapes record characteristics of past ice–sediment flow regimes, providing insight into subglacial processes and ice sheet dynamics. Individual forms vary considerably, but they can often be grouped into coherent fields, typically called flow-sets, that reflect discrete episodes of ice flow. Within these, bedform size–frequency distributions (predominantly height, width and length) are currently described by several statistics (e.g., mean, median, and standard deviation) that, arguably, do not best capture the defining characteristics of these populations. This paper seeks to create a better description based upon semi-log plots, which reveal that the frequency distributions of bedform dimensions (drumlin, mega-scale glacial lineation, and ribbed moraine) plot as straight lines above the mode (ϕ). This indicates, by definition, an exponential distribution, for which a simple and easily calculated, yet statistically rigorous, description is designed. Three descriptive parameters are proposed: gradient (λ; the exponent, characterising bedforms likely least affected by non-glacial factors), area-normalised y-intercept (β 0; quantifying spatial density), and the mode (ϕ). Below ϕ, small features are less prevalent due to i) measurement: data, sampling and mapping fidelity; ii) possible post-glacial degradation; or iii) genesis: not being created sub-glacially. This new description has the benefit of being insensitive to the impact of potentially unmapped or degraded smaller features and better captures properties relating to ice flow. Importantly, using λ, flow sets can now be more usefully compared with each other across all deglaciated regions and with the output of numerical ice sheet models. Applications may also exist for analogous fluvial and aeolian bedforms. Identifying the characteristic exponential and that it is typical of ‘emergent’ subglacial bedforms is a new and potentially powerful constraint on their genesis, perhaps indicating that ice–sediment interaction is fundamentally stochastic in nature. [Copyright &y& Elsevier]

Abstract: The processes of subglacial erosion depend not only on the sliding motion of glaciers over bedrock but also on the presence of meltwater and sediment in the subglacial environment. In particular, theoretical models for subglacial quarrying and abrasion, as well as hypothesized erosion thresholds associated with subglacial sediment transport, include both positive and negative effects of subglacial water and sediment on the rate of erosion. In order to incorporate the existing theoretical models for subglacial erosion by quarrying and abrasion in a long-term glacial landscape evolution model, we here present a coupled computational framework for simulating the simultaneous flow processes of ice, water, and sediment. We supplement a higher order ice sheet model with simple long-term models for glacial hydrology and subglacial sediment transport, as well as fluvial and hillslope-related erosion processes. An important strength of the modeling framework presented relates to the morphological detail of the landscapes produced, which facilitates direct comparison with existing landforms. This improves the connection between glacial landscape evolution models, geomorphological observations, and the existing knowledge of the physical processes that operate under glaciers. We demonstrate with model examples, how increased basal meltwater pressure and transport-limited subglacial erosion lead to both positive and negative feedbacks related to glacial erosion and the formation of overdeepenings. [Copyright &y& Elsevier]

Abstract: The Rwenzori Mountains are a high alpine mountain chain, about 40×80km in size, just north of the equator in the western branch of the East African Rift System in Africa. The central part of the mountain chain is located in Uganda, and the highest peak, the Margherita Peak with 5119m, lies on the border to the Democratic Republic of Congo. Topography is very pronounced, with steeply incised valleys and clear glacial landforms in the upper part of the mountain chain. The Rwenzori Mountains are an unusually high mountain chain located in the extensional setting of the East African Rift System, and the large elevation poses a challenging problem for geodynamists to explain. We have used the landscape evolution model ULTIMA THULE, which combines hillslope diffusion, fluvial erosion, and glacial abrasion and is driven by a climate driver, simulating the variations in temperature, precipitation, and relief over several glacial cycles. With a simulation time of 800ka, we test the hypothesis of climate–tectonic interactions on the uplift of the Rwenzori Mountains. Our results show that a moderate cooling of around 6° causes widespread glaciation of the high mountain regions as observed during the peak glacial phases, and that morphological processes degrading the landscape allow for a tectonic uplift rate of around 0.5mma−1. [Copyright &y& Elsevier]

Abstract: In southern South America, the maximum areal extent of ice during the Quaternary Period, the Greatest Patagonian Glaciation (GPG, [Mercer, J.H., 1983. Cenozoic glaciation in the southern hemisphere. Annual Reviews of Earth and Planetary Science 11, 99–132.]), occurred at 1.1 Ma and subsequent glaciations were overall less extensive. The GPG preceded global minimum temperatures and maximal volume of ice, which occurred in the last ~800 kyr, as recorded in the marine δ 18O record. Significant modification of the drainage morphology of the southern Andes from a non-glaciated to glaciated landscape occurred throughout the Quaternary Period. We infer a non-climatic relationship between glacial modification of the mountains and the decreasing extent of ice and we discuss processes of landscape development that could have caused the trend. Specifically, these include modification of valleys, such as development from a V- to a U-shape, and lowering of mass-accumulation areas. Such changes would strongly affect glacial dynamics, the mass balance profile and mass-flux during succeeding glaciations, especially for low-gradient outlet glaciers occupying low areas. Other areas around Earth (at least where ice has been warm-based) also may exhibit a non-random trend of decreasing extent of ice with time, ultimately because of glacial erosion in the Quaternary Period. [Copyright &y& Elsevier]

Abstract: The Central Karakoram, which includes K2 in Pakistan, is one of the most rapidly rising areas on Earth and exhibits complex topography and extreme relief. Impressive valley fills and glacial landforms are present throughout the valleys. The dynamics of landscape evolution of the region are currently not well understood. Consequently, the landforms were mapped and assessed in the Skardu, Shigar, and Braldu valleys, to elucidate the spatio-temporal scale dependencies of surface processes active in the region. These valleys were examined using geomorphic field methods, remote sensing, geomorphometry, and terrestrial cosmogenic nuclides (TCNs) surface exposure dating. The glaciers in this region have oscillated considerably throughout the Late Quaternary, and four glacial stages have been recognized including at least six glacial advances. Surface processes readjusted after glacier retreat, and ubiquitous mass movements and catastrophic landsliding transported material from steep slopes to valley bottoms, while glaciofluvial meltwater and glacier outburst floods redistributed sediment down valley. Glacier geochronology and late Holocene ages of the outburst flood deposits indicate that landscape evolution has been dominated by glaciation and paraglaciation during the late Quaternary. [Copyright &y& Elsevier]

Abstract: Mountain glaciers are sensitive probes of the local climate, and, thus, they present an opportunity and a challenge to interpret climates of the past and to predict future changes. Furthermore, glaciers can constitute hazards, including: glacier outburst floods; changes in the magnitude and timing of runoff in the mountains and adjacent regions; and, through worldwide loss of glacier ice, a global rise in sea level. To understand and ultimately to predict the dynamics and nature of climate and associated glacial and hydrological changes requires an integrated approach with communication and collaboration among glaciologists, glacial geologists, atmospheric scientists, geomorphologists, geochronologists, and tectonists. Current strategies of research are evolving towards integrating research on mountain glaciers to address key scientific, socio-economic and political issues. Given the rapid birth and growth of new technologies and tools with which to study glaciers and glacial landscapes, this community stands poised to address many of these challenges in the near future. The key challenges that must be met soon include: 1) determining the spatial–temporal pattern of fluctuations of mountain glaciers from the last glacial cycle through the present; 2) relating historical and past fluctuations in glaciers to variability in the primary features of ocean-atmospheric circulation; 3) identifying important but poorly understood processes controlling the motion and erosion of glaciers; 4) developing and expanding the application of numerical models of glaciers; 5) modeling the evolution of mountain landscapes in the face of repeated glaciation; 6) examining the climate and the balance of energy and mass at the surface of glaciers; 7) characterizing the role of intrinsic climate variability on glacier variations; and 8) predicting the distribution, sizes, and nature of glaciers in the future. While these ambitious goals are achievable and the research tools exist, success will require significant bridging between the existing research communities involved and ambitious integration of research on mountain glaciers. [Copyright &y& Elsevier]

Abstract: Relict surfaces contain information on past surface processes and long-term landscape evolution. A detailed investigation of relict non-glacial surfaces in a formerly glaciated mountain landscape of northern Sweden was completed, based on interpretation of colour infrared aerial photographs, analysis in a GIS, and fieldwork. Working backwards from landscape to process, surfaces were classified according to large- and small-scale morphologies that result from the operation of non-glacial processes, the degree of weathering, regolith characteristics, and the style of glacial modification. Surfaces were also compared in the GIS according to elevation, slope angle, and bedrock lithology. The study revealed five types of relict non-glacial surfaces but also two types of extensively weathered glacial surfaces that were transitional to relict non-glacial surfaces, illustrating spatially variable processes and rates of non-glacial and glacial landscape evolution. Rather than being static preglacial remnants, relict non-glacial surfaces are dynamic features that have continued to evolve during the Quaternary. The classification provides hypotheses for landscape evolution that can be field tested through, for example, terrestrial cosmogenic nuclide studies and geochemical analyses of fine matrix materials. The classification may be applicable to relict non-glacial surfaces in other formerly glaciated landscapes. [Copyright &y& Elsevier]

Abstract: The occurrence of tors within glaciated regions has been widely cited as evidence for the preservation of relic pre-Quaternary landscapes beneath protective covers of non-erosive dry-based ice. Here, we test for the preservation of pre-Quaternary landscapes with cosmogenic surface exposure dating of tors. Numerous granite tors are present on summit plateaus in the Cairngorm Mountains of Scotland where they were covered by local ice caps many times during the Pleistocene. Cosmogenic 10Be and 26Al data together with geomorphic relationships reveal that these landforms are more dynamic and younger than previously suspected. Many Cairngorm tors have been bulldozed and toppled along horizontal joints by ice motion, leaving event surfaces on tor remnants and erratics that can be dated with cosmogenic nuclides. As the surfaces have been subject to episodic burial by ice, an exposure model based upon ice and marine sediment core proxies for local glacial cover is necessary to interpret the cosmogenic nuclide data. Exposure ages and weathering characteristics of tors are closely correlated. Glacially modified tors and boulder erratics with slightly weathered surfaces have 10Be exposure ages of about 15 to 43 ka. Nuclide inheritance is present in many of these surfaces. Correction for inheritance indicates that the eastern Cairngorms were deglaciated at 15.6±0.9 ka. Glacially modified tors with moderate to advanced weathering features have 10Be exposure ages of 19 to 92 ka. These surfaces were only slightly modified during the last glacial cycle and gained much of their exposure during the interstadial of marine Oxygen Isotope Stage 5 or earlier. Tors lacking evidence of glacial modification and exhibiting advanced weathering have 10Be exposure ages between 52 and 297 ka. Nuclide concentrations in these surfaces are probably controlled by bedrock erosion rates instead of discrete glacial events. Maximum erosion rates estimated from 10Be range from 2.8 to 12.0 mm/ka, with an error weighted mean of 4.1±0.2 mm/ka. Three of these surfaces yield model exposure-plus-burial ages of 295−71 +84, 520−141 +178, and 626−85 +102 ka. A vertical cosmogenic nuclide profile across the oldest sampled tor indicates a long-term emergence rate of 31±2 mm/ka. These findings show that dry-based ice caps are capable of substantially eroding tors by entraining blocks previously detached by weathering processes. Bedrock surfaces and erratic boulders in such settings are likely to have nuclide inheritance and may yield erroneous (too old) exposure ages. While many Cairngorm tors have survived multiple glacial cycles, rates of regolith stripping and bedrock erosion are too high to permit the widespread preservation of pre-Quaternary rock surfaces. [Copyright &y& Elsevier]

The Garhwal Himalaya provides an excellent natural laboratory in which to examine landscape evolution in a monsoon-influenced high mountain environment. Geomorphic and sedimentological analysis and 10Be cosmogenic radionuclide (CRN) surface exposure dating of moraines, fans, and river and strath terraces in the Gori Ganga Valley of Nanda Devi, NE Garhwal, indicate that fans and river terraces developed rapidly by debris flow and flood processes during periods of deglaciation. These phases of high sediment transfer occurred at ∼1–2, ∼4–5, and ∼7–8 ka. Fan incision rates, subsequent to major times of resedimentation after each glacial advance, are between ∼19 and 57 mm/year. This contrasts with bedrock incision rates, based on mid-Holocene strath terraces, of ∼5 mm/year. These rates indicate that despite episodes of rapid denudation and resedimentation linked to glacial activity in this region, the background rates of denudation are similar to those for other regions of the Himalaya, averaging several millimeters per year. Furthermore, these data show the importance of climatic controls on landscape evolution and suggest a strong monsoonal control on the dynamics of earth surface processes in this region. [Copyright &y& Elsevier]

Quaternary valley fills and landforms in the Waqia valley of the Chinese Pamir were examined using geomorphic mapping, geomorphic and sedimentological analysis of landforms and sediments, and cosmogenic 10Be surface exposure dating. Six sets of moraines (M-1 to M-6) are identified and date to the penultimate or an older glacial cycle (M-1), penultimate glacial cycle (M-2), early last glacial and probably Marine Oxygen Isotope Stage (MIS) 4 (M-3), MIS 2 (M-4), Late Glacial (M-5), and early Holocene (M-6). Younger moraines are also present, but these were not examined in detail. Alluvial fans and outwash/river terraces are present throughout the valley. Four surfaces on alluvial fans and river terraces were dated to ~ 580 ka (T-1), ~ 120 ka (T-2), ~ 100 ka (T-3), and ~ 70 ka (T-4). Large landslide and lacustrine deposits are common within the valley fills and represent periods of major slope instability and possible damming of drainages. Glacial processes dominate the western side of the valley; landsliding is the leading process on its eastern side. Defining the nature and timing of landform formation in this valley highlights the punctuated nature of landform evolution in the Himalaya and Tibet and provides a framework for considering the abundant valley fill successions elsewhere in the orogen. [ABSTRACT FROM AUTHOR]

Here we investigate the influence of initial pre-glacial topography on spatial and temporal patterns of glacial erosion using numerical surface process modelling, including a higher order ice sheet model. First, we consider glacier dynamics when simulating glaciation in two real landscapes, representing plateau-type topography (southeast Australia) and characteristic steady-state fluvial topography (southern Taiwan). We find that the different initial landscape configurations result in distinctly different ice configurations and patterns of basal sliding. The sliding patterns are controlled by ice configuration and the resulting basal shear stresses and by the thermal properties at the base of the ice. We then investigate how these characteristic patterns of basal sliding control glacial erosion and long-term landscape evolution using synthetic representations of the two landscapes. The two landscape configurations result in markedly different spatial and temporal patterns of glacial erosion. However, the resulting landscapes may have similar morphology, irrespective of initial landscapes and glacial erosion patterns being significantly different. The numerical experiments also suggest that, in addition to basal temperature, basal shear stress is important in restricting long-term glacial erosion, which is relevant for the preservation of landforms during glaciations. Specifically, pre-glacial landforms may be eroded although they are initially protected by cold-based ice, when the ice configuration promotes significant basal shear stress (glacial erosion) at the edge of a plateau-like landscape. In contrast, pre-glacial landforms may be preserved irrespective of the ice being warm-based, when low gradients in the ice surface act to limit basal shear stress. [ABSTRACT FROM AUTHOR]