The potential of small unmanned aircraft systems and structure-from-motion for topographic surveys: a test of emerging integrated approaches at Cwm Idwal, North Wales

Novel topographic survey methods that integrate both structure-from-motion (SfM) photogrammetry and small unmanned aircraft systems (sUAS) are a rapidly evolving investigative technique. Due to the diverse range of survey configurations available and the infancy of these new methods, further research is required. Here, the accuracy, precision and potential applications of this approach are investigated. A total of 543 images of the Cwm Idwal moraine–mound complex were captured from a light (b5 kg) semi-autonomous multi-rotor unmanned aircraft system using a consumer-grade 18 MP compact digital camera. The imageswere used to produce a DSM(digital surfacemodel) of themoraines. The DSMis in good agreement with 7761 total station survey points providing a total verticalRMSE value of 0.517mand verticalRMSE values as lowas 0.200mfor less densely vegetated areas of the DSM. High-precision topographic data can be acquired rapidly using this technique with the resulting DSMs and orthorectified aerial imagery at sub-decimetre resolutions. Positional errors on the total station dataset, vegetation and steep terrain are identified as the causes of vertical disagreement. Whilst this aerial survey approach is advocated for use in a range of geomorphological settings, care must be taken to ensure that adequate ground control is applied to give a high degree of accuracy

Internal structure and significance of ice-marginal moraine in the Kebnekaise Mountains, northern Sweden

Despite a long history of glaciological research, the mode of formation and palaeoenvironmental significance of moraine systems in the Kebnekaise Mountains, Sweden has remained uncertain. These landforms offer the potential to elucidate glacier response prior to the period of direct monitoring and provide an insight into the ice-marginal processes operating at polythermal valley glaciers. This study sets out to test existing interpretations of Scandinavian ice-marginal moraines which invoke ice stagnation, pushing, stacking/dumping, and push-deformation as important moraine forming processes. Moraines at Isfallsglaciären were investigated using ground-penetrating radar to document the internal structural characteristics of the landform assemblage. Radar surveys revealed a range of substrate composition and reflectors, indicating a debris-ice interface and bounding surfaces within the moraine. The moraine is demonstrated to contain both ice-rich and debris-rich zones, reflecting a complex depositional history and a polygenetic origin. As a consequence of glacier overriding, the morphology of these landforms provides a misleading indicator of glacial history. Traditional geochronological methods are unlikely to be effective on this type of landform as the fresh surface may post-date the formation of the landform following reoccupation of the moraine rampart by the glacier. This research highlights that the interpretation of geochronological datasets from similar moraine systems should be undertaken with caution

Origin and significance of dispersed facies basal ice: Svínafellsjökull, Iceland

Dispersed facies basal ice – massive (i.e. structureless) ice with dispersed debris aggregates – is present at the margins of many glaciers and, as a product of internal glacial processes, has the potential to provide important information about the mechanisms of glacier flow and the nature of the subglacial environment. The origin of dispersed facies is poorly understood, with several hypotheses having been advanced for its formation, and there is disagreement as to whether it is largely a sedimentary or a tectonic feature. We test these established hypotheses at the temperate glacier Svínafellsjökull, Iceland, and find that none fully account for dispersed facies characteristics at this location. Instead, dispersed facies physical, sedimentological and stable-isotope (δ18O, δD) characteristics favour a predominantly tectonic origin that we suggest comprises the regelation and strain-induced metamorphism of debris-rich basal ice that has been entrained into an englacial position by tectonic processes operating at the base of an icefall. Further thickening of the resultant dispersed facies may also occur tectonically as a result of ice flow against the reverse bed slope of a terminal overdeepening. Lack of efficient subglacial drainage in the region of the overdeepening may limit basal melting and thus favour basal ice preservation, including the preservation of dispersed facies. Despite the relatively low sediment content of dispersed facies (∼1.6% by volume), its thickness (up to 25 m) and ubiquity at Svínafellsjökull results in a significant contribution to annual sediment discharge (1635–3270 m3 a−1) that is ∼6.5 times that contributed by debris-rich stratified facies basal ice

Origin, evolution and dynamic context of a Neoglacial lateral-frontal moraine at Austre Lovenbreen, Svalbard

Moraines marking the Neoglacial limits in Svalbard are commonly ice cored. Investigating the nature of this relict ice is important because it can aid our understanding of former glacier dynamics. This paper examines the composition of the lateral-frontal moraine associated with the Neoglacial limit at Austre Lovénbreen and assesses the likely geomorphological evolution. The moraine was investigated using ground-penetrating radar (GPR), with context being provided by structural mapping of the glacier based on an oblique aerial image from 1936 and vertical aerial imagery from 2003. Multiple up-glacier dipping reflectors and syncline structures are found in the GPR surveys. The reflectors are most clearly defined in lateral positions, where the moraine is substantially composed of ice. The frontal area of the moraine is dominantly composed of debris. The core of the lateral part of the moraine is likely to consist of stacked sequences of basal ice that have been deformed by strong longitudinal compression. The long term preservation potential of the ice-dominated lateral moraine is negligible, whereas the preservation of the debris-dominated frontal moraine is high. A glacier surface bulge, identified on the 1936 aerial imagery, provides evidence that Austre Lovénbreen has previously displayed surge activity, although it is highly unlikely to do so in the near future in its current state. This research shows the value of relict buried ice that is preserved in landforms to aiding our understanding of former glacier characteristics. © 2013 Elsevier B.V. All rights reserved

Origin and significance of dispersed facies basal ice: Svínafellsjökull, Iceland

Dispersed facies basal ice (massive ice with dispersed debris aggregates) outcrops at the margins of many ice masses and is important to glaciologists because of the information it provides about the nature of subglacial conditions and processes in the deep interior of glaciers and ice sheets. There has been little agreement, however, about how it forms with possible mechanisms including regelation and water flow through the intercrystalline vein network, strain-induced metamorphism of firnified glacier ice, shearing of basal debris-rich ice, freeze-on of subglacial water, and incorporation of surface debris into glacier ice. We test these established hypotheses at the temperate glacier Svínafellsjökull, southeast Iceland, and show that none fully account for dispersed facies characteristics here. From analysis of physical, sedimentological and stable isotope ( 18O and D) characteristics we suggest that dispersed facies forms from a combination of regelation and strain-induced metamorphism of debris-laden ice originally entrained by tectonic processes at the base of an icefall. We suggest that a terminal overdeepening may serve to further thicken dispersed facies as the glacier flows against a prominent reverse bedslope. There may also be a lack of subglacial drainage across the overdeepening which further allows dispersed facies to survive in thicknesses up to 20m despite the temperate location. Our results demonstrate that, despite its low sediment content ( 1.6%), the thick layer of dispersed facies contributes a higher annual sediment flux than other more debris-rich basal ice types. Hence dispersed facies and the processes that create it should not be overlooked in assessments of glacial sediment budgets

Terminal zone glacial sediment transfer at a temperate overdeepened glacier system

Continuity of sediment transfer through glacial systems is essential to maintain subglacial bedrock erosion, yet transfer at temperate glaciers with overdeepened beds, where subglacial fluvial sediment transport should be greatly limited by adverse slopes, remains poorly understood. Complex multiple transfer processes in temperate overdeepened systems has been indicated by the presence of large frontal moraine systems, supraglacial debris of mixed transport origin, thick basal ice sequences, and englacial thrusts and eskers. At Svinafellsjokull, thrusts comprising decimetre-thick debris-rich bands of stratified facies ice of basal origin, with a coarser size distribution and higher clast content than that observed in basal ice layers, contribute substantially to the transfer of subglacial material in the terminal zone. Entrainment and transfer of material occurs by simple shear along the upper surface of bands and by straininduced deformation of stratified and firnified glacier ice below. Thrust material includes rounded and well-rounded clasts that are also striated, indicating that fluvial bedload is deposited as subglacial channels approach the overdeepening and then entrained along thrusts. Substantial transfer also occurs within basal ice, with facies type and debris content dependent on the hydrological connectedness of the adverse slope. A process model of transfer at glaciers with terminal overdeepenings is proposed, in which the geometry of the overdeepening influences spatial patterns of ice deformation, hydrology, and basal ice formation. We conclude that the significance of thrusting in maintaining sediment transfer continuity has likely been overlooked by glacier sediment budgets and glacial landscape evolution studies

Comment on : "A test of the englacial thrusting hypothesis of 'hummocky' moraine formation"

Comment on : "A test of the englacial thrusting hypothesis of 'hummocky' moraine formation