High-relief Landscapes Research Articles

Configuration of the Scandinavian Ice Sheet in southwestern Norway during the Younger Dryas

The extent of the Scandinavian Ice Sheet in southwestern Norway is precisely located during the well-characterized Younger Dryas re-advance. However, the thickness of the ice sheet is less well constrained inland from the terminal position. Some exceptions include lateral moraines traced inland and up to 1000 m a.s.l. along Hardangerfjorden. Here, we apply 10Be dating in two areas: (1) bedrock and boulders in the high-relief landscapes near the Younger Dryas margin around the Bergen urban area, and (2) boulders from an upland 1600 m a.s.l. much farther (120 km) inland. We find that coastal summits ranging from ~400 to ~680 m a.s.l. and located only ~10–15 km up-flow from the ice margin, were covered by the Scandinavian Ice Sheet during the Younger Dryas. The scatter in the 10Be age population of 22 boulder samples is best explained by isotopic inheritance owing to inefficient subglacial erosion during the foregoing glaciation. Most of the 11 bedrock samples also exhibit inheritance, pointing to the source of inheritance in boulders and implying inefficient subglacial erosion during the last glaciation even in valley-bottoms near Bergen. Regional glacial striae compilations suggest that ice flow during maximum Younger Dryas ice-sheet configurations was for the most part cross-valley, with potentially low basal slip rates. Five new 10Be ages from the inland site help to constrain ice height far inland. We combine these new results with prior information to generate a cross profile of the Younger Dryas ice sheet in southern Norway.

Drought, megafires and flood - climate extreme impacts on catchment-scale river water quality on Australia's east coast

Increased frequency and intensity of drought, wildfires and flooding due to climate change has major implications for river water quality, yet there are limited high-temporal resolution data capturing the combined transient impacts of these extreme events at large catchment scales. We present flow-stratified water quality data from a large coastal catchment (Macleay River, Australia) spanning severe drought and extensive fires followed by flooding. We examine concentrations (C), discharge (Q) and flux of suspended sediment, major ions, dissolved organic carbon (DOC) and key nutrients (NO3 and PO4), with a focus on the critical first-flush period after the fires. Highly elevated suspended sediment (∼5500 mg L−1; >100x median pre-fire levels) during the initial post-fire period reflected enhanced erosion from fire-impacted, high-relief landscapes, with peak monthly suspended sediment loads of ∼1.1–3.7 t ha−1. The greatest sensitivity to erosion was during initial flow events following fire, highlighting the compounding effect of sequential extreme events on sediment transport. Maximum solute concentrations typically occurred during the first hydrograph peak post-fire with significantly (P = 0.01) elevated major ions following the order of K>Ca>SO4>HCO3≈Mg>Cl>Na, broadly reflecting the composition of ash materials. Distorted CQ relationships for major ions, DOC and nutrients indicated mobilisation behaviour and enhanced surface runoff during initial hydrograph peaks post-fire, with mean concentrations and CQ relationships progressively shifting to those approximating pre-fire within ∼3–12 months. Elevated DOC (∼7x; P = 0.01) displays distinct changes in fluorescence excitation-emission matrix spectral characteristics, attributable to both fire and drought. Both NO3N (160 μM) and PO4 (7.5 μM) were significantly elevated after the fires (∼15–22x; P = 0.01), with maximum monthly loads of 0.82 and 0.14 kg ha−1 respectively. Fast biogeochemical cycling of dissolved inorganic nitrogen (DIN) species occurred during initial flow events following fire, with NH4N initially dominant (>80% of DIN) and exceeding ecosystem guideline threshold values (>100 μM NH4N), followed by rapid (∼1 week) nitrification. The extreme dynamism and transience of water quality parameters highlights the critical importance of high-frequency sampling to adequately capture the compound impacts drought, fires and floods on aquatic systems.

Linking exhumation, paleo-relief, and rift formation to magmatic processes in the western Snake River Plain, Idaho, using apatite (U-Th)/He thermochronology

Abstract The western Snake River Plain (WSRP) in southwest Idaho has been characterized as an intracontinental rift basin but differs markedly in topography and style from other Cordilleran extensional structures and structurally from the down-warped lava plain of the eastern Snake River Plain. To investigate mechanisms driving extension and topographic evolution, we sampled granitoid bedrock from Cretaceous and Eocene-aged plutons from the mountainous flanks of the WSRP to detail their exhumation history with apatite (U-Th)/He (AHe) thermochronometry. AHe cooling dates from seventeen samples range from 7.9 ± 1.4 Ma to 55 ± 10 Ma. Most cooling dates from Cretaceous plutons adjacent to the WSRP are Eocene, while Eocene intrusions from within the Middle Fork Boise River canyon ~35 km NE of the WSRP yield Miocene cooling dates. The AHe dates provide evidence of exhumation of the Idaho batholith during the Eocene, supporting a high relief landscape at that time, followed by decreasing relief. The Miocene AHe dates show rapid cooling along the Middle Fork Boise River that we take to indicate focused river incision due to base level fall in the WSRP. Eocene AHe dates limit magnitudes of exhumation and extension on the flanks of the WSRP during Miocene rift formation. This suggests extension was accommodated by magmatic intrusions and intrabasin faults rather than basin-bounding faults. We favor a model where WSRP extension was related to Columbia River Flood Basalt eruption and enhanced by later eruption of the Bruneau-Jarbidge and Twin Falls volcanic fields, explaining the apparent difference with other Cordilleran extensional structures.

Direct Georeferencing UAV-SfM in High-Relief Topography: Accuracy Assessment and Alternative Ground Control Strategies along Steep Inaccessible Rock Slopes

Steep rock slopes present key opportunities and challenges within Earth science applications. Due to partial or complete inaccessibility, high-precision surveys of these high-relief landscapes remain a challenge. Direct georeferencing (DG) of unoccupied aerial vehicles (UAVs) with advanced onboard GNSS receivers presents opportunities to generate high-resolution 3D datasets without ground-based access to the study area. However, recent research has revealed large vertical errors using DG that may prove problematic in near-vertical terrain. To address these concerns, we examined more than 75 photogrammetric UAV-datasets with various imaging angles (nadir, oblique, and combinations) and ground control scenarios, including DG, along a steep slope exposure. Results demonstrate that mean errors in DG scenarios are up to 0.12 m higher than datasets using integrated georeferencing with well-distributed GCPs. Inclusion of GCPs greatly reduced mean error values but had limited influence on precision (<0.01 m) for any given imaging strategy. Use of multiple image angles resulted in the highest precisions, regardless of georeferencing strategy. These findings have implications for applications requiring the highest precision and accuracy (e.g., geotechnical engineering, hazard mitigation and mapping, and geomorphic change detection), which should consider using ground control whenever possible. However, for applications less concerned with absolute accuracy, our results show that DG datasets provide strong internal consistency and relative accuracy that may be suitable for high precision measurements within a model, without use of ground control.

The invasive amphipod Gammarus tigrinus Sexton, 1939 conquering the north of Europe using a new pathway: the first recordings from Norway

The invasive amphipod Gammarus tigrinus has during the last decades spread to large parts of Northern Europe, mainly using pathways eastwards from The British Isles to Continental Europe and further northeast into the Baltic Sea. From the coastline it has to some extent spread further inland, especially in topographically low-relief landscapes with highly polluted rivers. This account reports another geographical direction of dispersal, towards north into Southern Norway. In coastal brackish-water regions G. tigrinus may displace other gammarids. Large parts of Norway consist of high-relief landscapes close to many estuaries, so the further spread into this country is doubtful. However, if the taxon can avoid the initial barriers using vectors and spread into new watercourses above such barriers and thrive in this new ambient water chemistry, it may have large negative influence on the other benthic fauna. But Norwegian lakes and rivers are most probably too electrolyte-poor to support this species. However, in estuaries and other brackish waters along the coast, at least in the southern part of Norway, the species will thrive. Gammarus tigrinus is the only known intermediate host for the native American acanthocephalan parasite Paratenuisentis ambiguus, which has the American eel as its main host. This parasite also infects the European eel, and this poses an additional threat to the already endangered eel in Norwegian rivers where G. tigrinus has been recorded.

Hyper-resolution ensemble-based snow reanalysis in mountain regions using clustering

Abstract. Spatial variability in high-relief landscapes is immense, and grid-based models cannot be run at spatial resolutions to explicitly represent important physical processes. This hampers the assessment of the current and future evolution of important issues such as water availability or mass movement hazards. Here, we present a new processing chain that couples an efficient sub-grid method with a downscaling tool and a data assimilation method with the purpose of improving numerical simulation of surface processes at multiple spatial and temporal scales in ungauged basins. The novelty of the approach is that while we add 1–2 orders of magnitude of computational cost due to ensemble simulations, we save 4–5 orders of magnitude over explicitly simulating a high-resolution grid. This approach makes data assimilation at large spatio-temporal scales feasible. In addition, this approach utilizes only freely available global datasets and is therefore able to run globally. We demonstrate marked improvements in estimating snow height and snow water equivalent at various scales using this approach that assimilates retrievals from a MODIS snow cover product. We propose that this as a suitable method for a wide variety of operational and research applications where surface models need to be run at large scales with sparse to non-existent ground observations and with the flexibility to assimilate diverse variables retrieved by Earth observation missions.

Enhancing UAV–SfM 3D Model Accuracy in High-Relief Landscapes by Incorporating Oblique Images

Complex landscapes with high topographic relief and intricate geometry present challenges for complete and accurate mapping of both lateral (x, y) and vertical (z) detail without deformation. Although small uninhabited/unmanned aerial vehicles (UAVs) paired with structure-from-motion (SfM) image processing has recently emerged as a popular solution for a range of mapping applications, common image acquisition and processing strategies can result in surface deformation along steep slopes within complex terrain. Incorporation of oblique (off-nadir) images into the UAV–SfM workflow has been shown to reduce systematic errors within resulting models, but there has been no consensus or documentation substantiating use of particular imaging angles. To address these limitations, we examined UAV–SfM models produced from image sets collected with various imaging angles (0–35°) within a high-relief ‘badland’ landscape and compared resulting surfaces with a reference dataset from a terrestrial laser scanner (TLS). More than 150 UAV–SfM scenarios were quantitatively evaluated to assess the effects of camera tilt angle, overlap, and imaging configuration on the precision and accuracy of the reconstructed terrain. Results indicate that imaging angle has a profound impact on accuracy and precision for data acquisition with a single camera angle in topographically complex scenes. Results also confirm previous findings that supplementing nadir image blocks with oblique images in the UAV–SfM workflow consistently improves spatial accuracy and precision and reduces data gaps and systematic errors in the final point cloud. Subtle differences among various oblique camera angles and imaging patterns suggest that higher overlap and higher oblique camera angles (20–35°) increased precision and accuracy by nearly 50% relative to nadir-only image blocks. We conclude by presenting four recommendations for incorporating oblique images and adapting flight parameters to enhance 3D mapping applications with UAV–SfM in high-relief terrain.

Detrital zircon provenance record of middle Cenozoic landscape evolution in the southern Rockies, USA

The high-elevation, high-relief landscape of the southern Rocky Mountains (Rockies), USA, reflects interactions between tectonics, paleoclimate, and surface processes. The southern Rockies experienced several episodes of uplift, extension, and major climate changes during the Cenozoic, but the landscape and river drainage evolution remain poorly constrained. Here we apply detrital zircon UPb geochronology to Eocene-Miocene strata in south-central Colorado to constrain the depositional ages and sediment provenance. A total of 1284 concordant UPb ages were determined and are grouped into 75–11 Ma, 1500–1300 Ma, and 1800–1500 Ma populations. Intense late Eocene-Oligocene regional volcanism provided abundant air fall zircons into the latest Eocene-Oligocene sedimentary systems where maximum depositional ages can be used to closely proximate depositional ages and improve the chronostratigraphy. The new data are integrated with interpretation of sedimentary environments, and the detrital zircon signatures of potential source terranes and age-equivalent strata in other nearby basins to interpret landscape and paleodrainage evolution. Specifically, the new provenance data show that (1) after the main phase of the Laramide deformation, the Wet Mountains, but not the Sangre de Cristo Range, was the dominant local topographic feature, and a southward-flowing river connected the Wet Mountain Valley with the Huerfano and Raton Basins to the south; (2) during the Eocene-early Oligocene, aggradation of the Wet Mountain Valley and the Huerfano Basin formed a low-relief surface, and subsequent river erosion changed the drainage pattern eastward and likely formed the modern lower Arkansas River valley; and (3) during the Miocene, dissection of the low-relief surface by the opening of the Rio Grande Rift formed the upper Arkansas River valley, and the upper valley was connected with the lower valley to establish the modern drainage pattern of the Arkansas River in the southern Rockies.

STREAMS DO WORK: MEASURING THE WORK OF LOW-ORDER STREAMS ON THE LANDSCAPE USING POINT CLOUDS

Abstract. The mutable nature of low-order streams makes regular updating of surface water maps necessary for accurate representation. Low-order streams make up roughly half the streams in the conterminous United States by length, and small inaccuracies in stream head location can result in significant error in stream reach, order, and density. Reliable maps of stream features are vital for hydrologic modeling, ecosystem research, and boundary monitoring. High resolution digital elevation models derived from lidar data have shown promise in low order stream modeling yet forested high relief landscapes and low relief agricultural areas remain challenging. Here we present early results from research analyzing lidar point clouds to identify features and patterns that may be used in low-order stream identification and classification in challenging geographic conditions. This work has identified characteristics derived from point clouds that correlate with the presence of streams and stream heads and show promise for mapping small streams. In low topographic relief agricultural areas, cross sections collected at regular intervals along drainage channels extracted as 3D lines show a significant jump in value and variance of profile curvature standard deviation at stream heads. In high relief areas, observations show potential for stream mapping by identifying trends in riparian zone structure. Lidar return point density from riparian vegetation under 30 feet tall dips in the vicinity of intermittent stream heads. Also seen is an increase in point density above 60 feet downstream of stream heads. The trends found here likely reflect a change in vegetation structure relative to the presence of streams.

Large landslides lie low: Excess topography in the Himalaya-Karakoram ranges

Mass wasting is an important process for denuding hillslopes and lowering ridge crests in active mountain belts such as the Himalaya-Karakoram ranges (HKR). Such a high-relief landscape is likely to be at its mechanical threshold, maintained by competing rapid rock uplift, river incision, and pervasive slope failure. We introduce excess topography, Z E , for quantifying potentially unstable rock-mass volumes inclined at angles greater than a specified threshold angle. We find that Z E peaks along major fluvial and glacial inner gorges, which is also where the majority of 492 large (>0.1 km 2 ) rock-slope failures occur in the Himalaya9s largest cluster of documented Pleistocene to Holocene bedrock landslides. Our data reveal that bedrock landslides in the HKR chiefly detached from near or below the median elevation, whereas glaciers and rock glaciers occupy higher-elevation bands almost exclusively. Less than 10% of the area of the HKR is upslope of glaciers, such that possible censoring of evidence of large bedrock landslides above the permanent snow line barely affects this finding. Bedrock landslides appear to preferentially undermine topographic relief in response to fluvial and glacial incision along inner gorges, unless more frequent and smaller undetected failures, or rigorous (peri-)glacial erosion, compensate for this role at higher elevation. Either way, the distinct patterns of excess topography and large bedrock landsliding in the HKR juxtapose two stacked domains of landslide and (peri-)glacial erosion that may respond to different time scales of perturbation. Our findings call for more detailed analysis of vertical erosional domains and their geomorphic coupling in active mountain belts.

Mapping asbestos-cement roofing with hyperspectral remote sensing over a large mountain region of the Italian Western Alps.

The World Health Organization estimates that 100 thousand people in the world die every year from asbestos-related cancers and more than 300 thousand European citizens are expected to die from asbestos-related mesothelioma by 2030. Both the European and the Italian legislations have banned the manufacture, importation, processing and distribution in commerce of asbestos-containing products and have recommended action plans for the safe removal of asbestos from public and private buildings. This paper describes the quantitative mapping of asbestos-cement covers over a large mountainous region of Italian Western Alps using the Multispectral Infrared and Visible Imaging Spectrometer sensor. A very large data set made up of 61 airborne transect strips covering 3263 km2 were processed to support the identification of buildings with asbestos-cement roofing, promoted by the Valle d'Aosta Autonomous Region with the support of the Regional Environmental Protection Agency. Results showed an overall mapping accuracy of 80%, in terms of asbestos-cement surface detected. The influence of topography on the classification's accuracy suggested that even in high relief landscapes, the spatial resolution of data is the major source of errors and the smaller asbestos-cement covers were not detected or misclassified.

Denudation and flexural isostatic response of the Colorado Plateau and southern Rocky Mountains region since 10 Ma

Over the past 10 Ma, the high-relief landscapes of the Colorado Plateau–southern Rocky Mountains region have been shaped by erosional processes. Incision rates have increased in the southern Rocky Mountains, the Colorado River system has been superimposed across buried Laramide structures as it was integrated from the Rocky Mountains to the Gulf of California, the modern Grand Canyon formed, and there has been widespread denudation of the Canyonlands region of the Colorado Plateau. We examine the spatial and temporal distribution of erosion and its associated isostatic rebound since 10 Ma. Erosion estimates come from apatite fission track (AFT) and apatite (U-Th)/He (AHe) thermochronometric studies at 14 sites across the region, including recent AHe data with ages younger than 12 Ma, and from ca. 10 Ma 40 Ar/ 39 Ar dated basalt paleosurfaces at 55 locations on the perimeter of the Colorado Plateau and in the southern Rocky Mountains. Estimated eroded thickness is added to modern topography above numerous control points to reconstruct a 10 Ma paleosurface across the region (referenced to modern elevations); this also yields an eroded thickness volume. Erosion has been spatially variable since 10 Ma: we find widespread denudation with as much as 2 km of incision along rivers in the Canyonlands region of Utah, 1–1.5 km of incision along rivers exiting the Rocky Mountains onto the eastern piedmont since 6 Ma, ∼1 km removed across the high peaks of the southern Rocky Mountains since 10 Ma, and little net erosion in the Basin and Range. Post–10 Ma flexural isostatic response to the eroded volume is calculated using known variable elastic thickness. This rebound caused much of the Colorado Plateau region to undergo more than 800 m of rock uplift, exceeding 1 km in local areas in the Canyonlands and southwestern Colorado. The Lees Ferry and Glen Canyon areas have been isostatically uplifted >500 m relative to the eastern Grand Canyon and the Tavaputs Plateau has been isostatically uplifted 400 m relative to Browns Park. This differential rock uplift driven by erosional isostasy has created or accentuated many of the features of the modern landscape. This component of rock uplift is “removed” by adding the eroded thickness onto modern topography, then subtracting the calculated rebound. The resulting (pre-erosion and pre-rebound) map provides a model of the 10 Ma landscape, neglecting any tectonic uplift contribution to regional elevations. This model suggests the presence of internal drainages on the Colorado Plateau, that the elevation of the Green River Basin and the Tavaputs Plateau were subequivalent, allowing the Green River to flow southward, and shows high topography in the Rocky Mountains that mimicked modern topography, but with potentially lower relief. Future refinements of both the timing and magnitude of differential erosion and rebound models provide an avenue for improved models for Cenozoic landscape evolution of the region. This paper is an advance over previous studies that focused just on the Colorado Plateau. Here we evaluate isostatic response to erosion in an extended region that includes parts of the Basin and Range, Colorado Plateau, southern Rocky Mountains, and eastern piedmont of the Rocky Mountains. We find that erosion of the southern Rocky Mountains and eastern piedmont is comparable to that of the Colorado Plateau and that the flexural isostatic rebounds of all these regions are coupled and cannot be considered in isolation. Furthermore, we focus on the 10 Ma time frame, rather than the 30 or 70 Ma period of previous researchers, as the key time frame during which the modern landscape rapidly evolved. In addition, the use of AFT and AHe thermochronometric constraints on thicknesses and ages of now-eroded sediments has solved key problems that hampered previous erosion studies. Data and analyses of regional post–10 Ma differential erosion and its resulting differential isostatic rebound provide essential constraints for any viable models for landscape evolution in this classic region.

Miocene exhumation of the Pamir revealed by detrital geothermochronology of Tajik rivers

The Pamir mountains are the western continuation of the Tibetan‐Himalayan system, the largest and highest orogenic system on Earth. Detrital geothermochronology applied to modern river sands from the western Pamir of Tajikistan records the history of sediment source crystallization, cooling, and exhumation. This provides important information on the timing of tectonic processes, relief formation, and erosion during orogenesis. U‐Pb geochronology of detrital zircons and40Ar/39Ar thermochronology of white micas from five rivers draining distinct tectonic terranes in the western Pamir document Paleozoic through Cenozoic crystallization ages and a Miocene (13–21 Ma) cooling signal. Detrital zircon U‐Pb ages show Proterozoic through Cenozoic ages and affinity with Asian rocks in Tibet. The detrital40Ar/39Ar data set documents deep and regional exhumation of the Pamir mountains >30 Myr after Indo‐Asia collision, which is best explained with widespread erosion of metamorphic domes. This exhumation signal coincides with deposition of over 6 km of conglomerates in the adjacent foreland, documenting high subsidence, sedimentation, and regional exhumation in the region. Our data are consistent with a high relief landscape and orogen‐wide exhumation at ∼13–21 Ma and correlate with the timing of exhumation of the Pamir gneiss domes. This exhumation is younger in the Pamir than that observed in neighboring Tibet and is consistent with higher magnitude Cenozoic deformation and shortening in this part of the orogenic system.

Testing Predictions of Stream Landscape Theory for Fish Assemblages in Highly Fragmented Watersheds

Predictions of stream landscape theory were tested with common agency fishery data in watersheds heavily fragmented by dams and barriers; large stream fragments support higher species diversity, more abundant populations, and a greater range of fish sizes. Study watersheds discharge to the Hudson River in New York USA, drain rocky and high relief landscapes, and have numerous mill dams and stream barriers. Stream fragments with fish collections ranged from 0.3 km to 119 km in contiguous length. Larger stream fragments had more diverse fish communities but not higher fish densities nor a wider range of fish sizes. However, almost all large stream fragments were supporting reproduction and rearing of the dominant stream species (brown trout Salmo trutta, brook trout Salvelinus fontinalis) while small fragments had no evidence of providing this fish community support. Therefore, consistent with the fundamental basis of stream landscape theory, large stream networks provide support for more species and more secure populations. The study supports the concept that diverse fish communities and secure populations benefit from access to a wide range of stream habitats.

Livestock grazing and vegetative filter strip buffer effects on runoff sediment, nitrate, and phosphorus losses

Livestock grazing in the Midwestern United States can result in significant levels of runoff sediment and nutrient losses to surface water resources. Some of these contaminants can increase stream eutrophication and are suspected of contributing to hypoxic conditions in the Gulf of Mexico. This research quantified effects of livestock grazing management practices and vegetative filter strip buffers on runoff depth and mass losses of total solids, nitrate-nitrogen (NO₃-N), and ortho-phosphorus (PO₄-P) under natural hydrologic conditions. Runoff data were collected from 12 rainfall events during 2001 to 2003 at an Iowa State University research farm in central Iowa, United States. Three vegetative buffers (paddock area:vegetative buffer area ratios of 1:0.2, 1:0.1, and 1:0 no buffer [control]) and three grazing management practices (continuous, rotational, and no grazing [control]) comprised nine treatment combinations (vegetative buffer ratio/grazing management practice) replicated in three 1.35 ha (3.34 ac) plot areas. The total 4.05 ha (10.02 ac) study area also included nine 0.4 ha (1.0 ac) paddocks and 27 vegetative buffer runoff collection units distributed in a randomized complete block design. The study site was established on uneven terrain with a maximum of 15% slopes and consisted of approximately 100% cool-season smooth bromegrass. Average paddock and vegetative buffer plant tiller densities estimated during the 2003 project season were approximately 62 million and 93 million tillers ha⁻¹ (153 million and 230 million tillers ac⁻¹), respectively. Runoff sample collection pipe leakage discovered and corrected during 2001 possibly reduced runoff depth and affected runoff contaminant mass losses data values. Consequently, 2001 runoff analysis results were limited to treatment comparisons within the 2001 season and were not compared with 2002 and 2003 data. Analysis results from 2001 showed no significant differences in average losses of runoff, total solids, NO₃-N, and PO₄-P among the nine vegetative buffer/grazing practice treatment combinations. Results from 2002 indicated significantly higher losses of runoff and total solids from 1:0 no buffer/rotational grazing and 1:0 no buffer/continuous grazing treatment combination plots, respectively, compared among other 2002 season treatment combinations. The 2003 results showed significantly higher runoff and total solids losses from 1:0 no buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and from 1:0.1 vegetative buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and with respective 2002 treatment combinations. However, the 2003 results indicated effective vegetative buffer performance with significantly lower runoff, total solids, and NO₃-N losses from the larger 1:0.2 buffer area compared among the smaller 1:0.1 buffer area and 1:0 no buffer treatment combinations. The 2003 results also indicated a highly significant increase in losses of NO₃-N from 1:0.1 buffer/no grazing treatment combination plots compared among other 2003 season treatment combinations and with respective 2002 treatment combinations. Overall results from this study suggest a shift from significantly higher 2002 season plot losses of continuous and rotational grazing treatment combinations to significantly higher 2003 season losses of no grazing treatment combinations. We speculate this shift to significantly higher runoff and contaminant losses from no grazing treatment combination plots during 2003 reflects the variability inherent to a complex and dynamic soil-water environment of livestock grazing areas. However, we also hypothesize the environmental conditions that largely consisted of a dense perennial cool-season grass type, high-relief landscape, and relatively high total rainfall depth may not necessarily include livestock grazing activities.

Holocene slope processes and landforms in the northern Faroe Islands

ABSTRACTThe exposed nature of the northern Faroe Islands high relief landscape enabled widespread Holocene slope process activity and deposition of related landforms, which seem largely controlled by extreme meteorological conditions. Three different slope landforms – the large colluvial Glyvurs fan, the lower Marknastiggjur mountainside debris-flow deposits in the town of Klaksvik, and the mountain top aeolian sediment cover on Eidiskollur – were investigated by a combination of geomorphological, stratigraphic, sedimentological, chronological and modern process studies.Sporadic Holocene snow-avalanche and debris-flow activity were documented, with sedimentation starting significantly before 8000 cal yr BP in the Glyvurs fan, which still sporadically experiences activity. The largest amounts of Holocene slope sedimentation seem to occur in colluvial fans, such as the Glyvurs fan, which are located below large dyke canyons, called gjogvs. The lower Marknastiggjur mountainside consists of mainly debris-flow deposits, which started before 7800 cal yr BP. A relatively small amount of precipitation, but with high precipitation intensity after a dry summer, triggered modern small-scale debris-flows in the northern islands, also at the Marknastiggjur mountainside, early in Autumn 2000. Extensive continuous mountaintop aeolian sedimentation from cliff weathering started around 6900 cal yr BP on the Eidiskollur peninsula.No direct influence of settlement on slope process activity was found at the different investigated slope landforms in the northern Faroe Islands.

Hillslope Evolution by Bedrock Landslides

Bedrock landsliding is a dominant geomorphic process in a number of high-relief landscapes, yet is neglected in landscape evolution models. A physical model of sliding in beans is presented, in which incremental lowering of one wall simulates baselevel fall and generates slides. Frequent small slides produce irregular hillslopes, on which steep toes and head scarps persist until being cleared by infrequent large slides. These steep segments are observed on hillslopes in high-relief landscapes and have been interpreted as evidence for increases in tectonic or climatic process rates. In certain cases, they may instead reflect normal hillslope evolution by landsliding.