Rock avalanches in high mountains

A thesis submitted for the degree of Doctor of Philosophy of the University of LutonRock avalanches are a high magnitude, low frequency catastrophic mass movement involving the failure of over 1 x 106 m3 of mountainside. Rock avalanches are considered a major hazard of the high mountains due to the excessive run-out often associated with them. To date the mechanism that allows for such excessive travel distance is unproven although several dozen possibilities have been proposed. Rock-avalanche deposits exhibit characteristic features such as sharp lateral margins, confinement to local topography, super-elevation on valley sides, intensely fragmented interiors and preserved stratigraphy relative to the source. However, there are few detailed studies of the internal sedimentology of rock-avalanche deposits. Such studies are a vital piece of evidence in the search for the mechanisms of motion as rock avalanches are rarely witnessed. This thesis examines the detailed sedimentology of five rock avalanche deposits of varied lithology and morphology. A novel methodology is developed to sample deposits for their grainsize distributions (GSD). The GSD's prove similar for deposits, with significant variation due to preserved lithological banding in the interior. This finding refutes the commonly held view that rock-avalanche deposits are simply inversely graded. Instead, a facies model is developed of a coarse Carapace facies forming the surface and near surface that overlies a highly fragmented Body facies that is in turn underlain by the Basal facies that is free to interact with the substrate. The sedimentology of the Body facies is considered in fine detail and is shown to be fractal in nature, that is, self-similar at all scales of observation. A predictive sedimentological plot is presented that allows generation of the grain-size distribution and descriptive statistics from a simple estimation of weight percent gravel at a rock avalanche exposure. The morphology of rock-avalanche deposits are examined and a classification presented of 'spread' 'two-phase' and 'stalled'. The hazard and features of each morphology is described in relation to the observed deposits

Sedimentological characterization of Antarctic moraines using UAVs and Structure-from-Motion photogrammetry

In glacial environments particle-size analysis of moraines provides insights into clast origin, transport history, depositional mechanism and processes of reworking. Traditional methods for grain-size classification are labour-intensive, physically intrusive and are limited to patch-scale (1m2) observation. We develop emerging, high-resolution ground- and unmanned aerial vehicle-based ‘Structure-from-Motion’ (UAV-SfM) photogrammetry to recover grain-size information across an moraine surface in the Heritage Range, Antarctica. SfM data products were benchmarked against equivalent datasets acquired using terrestrial laser scanning, and were found to be accurate to within 1.7 and 50mm for patch- and site-scale modelling, respectively. Grain-size distributions were obtained through digital grain classification, or ‘photo-sieving’, of patch-scale SfM orthoimagery. Photo-sieved distributions were accurate to <2mm compared to control distributions derived from dry sieving. A relationship between patch-scale median grain size and the standard deviation of local surface elevations was applied to a site-scale UAV-SfM model to facilitate upscaling and the production of a spatially continuous map of the median grain size across a 0.3 km2 area of moraine. This highly automated workflow for site scale sedimentological characterization eliminates much of the subjectivity associated with traditional methods and forms a sound basis for subsequent glaciological process interpretation and analysis

Corrigendum to “The million-year evolution of the glacial trimline in the southernmost Ellsworth Mountains, Antarctica” [Earth and Planetary Science Letters 469 (2017) 42–52]

No abstract available

Blue-ice moraines formation in the Heritage Range, West Antarctica: implications for ice sheet history and climate reconstruction

Blue ice is found in areas of Antarctica where katabatic winds, focussed by steep surface slopes or by topography around nunataks, cause enhanced surface ablation. This process draws up deeper, older ice to the ice sheet surface, often bringing with it englacial sediment. Prevailing theories for dynamically stable moraine surfaces in East Antarctica suggest that: (i) it is this material, once concentrated, that forms blue-ice moraines (BIM), (ii) that the moraine formation can be dated using cosmogenic isotope approaches, and that, (iii) since we expect an increase in exposure age moving away from the ice margin towards bedrock, dating across the moraine can be used to constrain ice-sheet history. To test this lateral accretion model for BIM formation we visited Patriot, Marble and Independence Hills in the southern Heritage Range, West Antarctica. Detailed field surveys of surface form, sediment and moraine dynamics were combined with geophysical surveys of the englacial structure of the moraines and cosmogenic nuclide analysis of surface clasts. Results suggest sediment is supplied mainly by basal entrainment, supplemented by debris-covered valley glaciers transferring material onto the ice sheet surface, direct deposition from rock-fall and slope processes from nunataks. We find that once sediment coalesces in BIM, significant reworking occurs through differential ablation, slope and periglacial processes. We bring these processes together in a conceptual model, concluding that many BIM in West Antarctica are dynamic and, whilst they persist through glacial cycles, they do not always neatly record ice sheet retreat patterns since linear distance from the ice margin does not always relate to increased clast exposure age. Understanding the dynamic processes involved in moraine formation is critical to the effective interpretation of the typically large scatter of cosmogenic nuclide exposure ages, opening a deep window into the million-year history of the West Antarctic Ice Sheet

Drift-dependent changes in iceberg size-frequency distributions

Although the size-frequency distributions of icebergs can provide insight into how they disintegrate, our understanding of this process is incomplete. Fundamentally, there is a discrepancy between iceberg power-law size-frequency distributions observed at glacial calving fronts and lognormal size-frequency distributions observed globally within open waters that remains unexplained. Here we use passive seismic monitoring to examine mechanisms of iceberg disintegration as a function of drift. Our results indicate that the shift in the size-frequency distribution of iceberg sizes observed is a product of fracture-driven iceberg disintegration and dimensional reductions through melting. We suggest that changes in the characteristic size-frequency scaling of icebergs can be explained by the emergence of a dominant set of driving processes of iceberg degradation towards the open ocean. Consequently, the size-frequency distribution required to model iceberg distributions accurately must vary according to distance from the calving front

Airborne radar evidence for tributary flow switching in Institute Ice Stream, West Antarctica: implications for ice sheet configuration and dynamics

Despite the importance of ice streaming to the evaluation of West Antarctic Ice Sheet (WAIS) stability we know little about mid- to long-term dynamic changes within the Institute Ice Stream (IIS) catchment. Here, we use airborne radio-echo sounding to investigate the subglacial topography, internal stratigraphy and Holocene flow regime of the upper IIS catchment near the Ellsworth Mountains. Internal layer buckling within three discrete, topographically-confined tributaries, through Ellsworth, Independence and Horseshoe Valley troughs provides evidence for former enhanced ice-sheet flow. We suggest that enhanced ice flow through Independence and Ellsworth troughs, during the mid- to late-Holocene was the source of ice streaming over the region now occupied by the slow-flowing Bungenstock Ice Rise. Although buckled layers also exist within the slow-flowing ice of Horseshoe Valley Trough, a thicker sequence of surface-conformable layers in the upper ice column suggests slowdown more than ~4000 years ago, so we do not attribute enhanced flow switch-off here, to the late-Holocene ice flow reorganization. Intensely buckled englacial layers within Horseshoe Valley and Independence troughs cannot be accounted for under present day flow speeds. The dynamic nature of ice flow in IIS and its tributaries suggests that recent ice-stream switching and mass changes in the Siple Coast and Amundsen Sea Sectors are not unique to these sectors and that they may have been regular during the Holocene and may characterize the decline of the WAIS

Radar‐detected englacial debris in the West Antarctic Ice Sheet

Structural glaci‐geological processes can entrain basal sediment into ice, leading to its transportation and deposition downstream. Sediments potentially rich in essential nutrients, like silica and iron, can thus be transferred from continental sources to the ocean, where deposition could enhance marine primary productivity. However, a lack of data has limited our knowledge of sediment entrainment, transfer and distribution in Antarctica, until now. We use ice‐penetrating radar to examine englacial sediments in the Weddell Sea sector of the West Antarctic Ice Sheet. Radargrams reveal englacial reflectors on the lee side of nunataks and subglacial highlands, where Mie scattering analysis of the reflectors suggests particle sizes consistent with surface moraine sediments. We hypothesize that these sediments aare entrained at the thermal boundary between cold and warm‐based ice. Conservative estimates of >130 x109 kg of englacial sediment in Horseshoe Valley alone suggest that the ice sheet has significant entrainment potential unappreciated previously

The association between foot-care self efficacy beliefs and actual foot-care behaviour in people with peripheral neuropathy: a cross-sectional study

<p>Abstract</p> <p>Background</p> <p>People with diabetes and peripheral neuropathy often do not implement the foot-care behavioural strategies that are suggested by many health professionals. The concept of self-efficacy has been shown to be an effective predictor of behaviour in many areas of health. This study investigated the relationships between foot-care self-efficacy beliefs, self-reported foot-care behaviour and history of diabetes-related foot pathology in people with diabetes and loss of protective sensation in their feet.</p> <p>Methods</p> <p>Ninety-six participants were included in this cross-sectional study undertaken in a regional city of Australia. All participants had diabetes and clinically diagnosed loss of protective sensation in their feet. The participants completed a self-report pen-paper questionnaire regarding foot-care self efficacy beliefs (the "Foot Care Confidence Scale") and two aspects of actual foot-care behaviour-preventative behaviour and potentially damaging behaviour. Pearson correlation coefficients were then calculated to determine the association between foot-care self-efficacy beliefs and actual reported foot-care behaviour. Multiple analysis of variance was undertaken to compare mean self-efficacy and behaviour subscale scores for those with a history of foot pathology, and those that did not.</p> <p>Results</p> <p>A small positive correlation (r = 0.2, p = 0.05) was found between self-efficacy beliefs and preventative behaviour. There was no association between self-efficacy beliefs and potentially damaging behaviour. There was no difference in self-efficacy beliefs in people that had a history of foot pathology compared to those that did not.</p> <p>Conclusion</p> <p>There is little association between foot-care self-efficacy beliefs and actual foot-care behaviour. The usefulness of measuring foot-care self-efficacy beliefs to assess actual self foot-care behaviour using currently available instruments is limited in people with diabetes and loss of protective sensation.</p