Andrew Finlayson

Fracturing, block faulting, and moulin development associated with progressive collapse and retreat of a maritime glacier: Falljökull, SE Iceland

Since 2007, Falljokull in southeast Iceland has been undergoing passive downwasting, providing an ideal opportunity to study a range deformation structures developed in response to ice-marginal collapse and retreat. An integrated terrestrial lidar, Ground Penetrating Radar, and glaciological structural study of the clean, debris-free ice at the margin of Falljokull has allowed a detailed model of the surface and subsurface 3D structure to be developed. Collapse of the glacier margin takes the form of a multiple rotational failure controlled by large-scale, down-ice dipping normal faults. As the fault-bound blocks of ice are displaced downslope, they rotate leading to localized compression and the formation of down-faulted graben-like structures. Moulins present within the marginal zone of Falljokull are closely associated with the zones of relatively more intense brittle deformation which crosscut the glacier. A model is proposed where the moulins have formed in response to the progressive collapse of englacial drainage channels located along down-ice dipping normal faults. The preferential development of the moulins and englacial drainage channels along the normal faults weakens the ice along these structures, promoting or even accelerating further collapse of the ice margin. The complex pattern of surface lowering within the marginal zone of Falljokull has also been shown to be directly related to movement on the main faults controlling the collapse of the ice margin. This evidence suggests that structurally controlled collapse may, in some instances, have a profound effect on glacier surface lowering and geodetic mass balance measurements.

THE LAST GLACIATION OF SHETLAND, NORTH ATLANTIC

Abstract. Evidence relating to the extent, dynamics, and relative chronology of the last glaciation of the Shetland Islands, North Atlantic, is presented here, in an attempt to better illuminate some of the controversies that still surround the glacial history of the archipelago. We appraise previous interpretations and compare these earlier results with new evidence gleaned from the interpretation of a high resolution digital terrain model and from field reconnaissance. By employing a landsystems approach, we identify and describe three quite different assemblages of landscape features across the main islands of Mainland, Yell and Unst. Using the spatial interrelationship of these landsystems, an assessment of their constituent elements, and comparisons with similar features in other glaciated environments, we propose a simple model for the last glaciation of Shetland. During an early glacial phase, a coalescent British and Scandinavian ice sheet flowed approximately east to west across Shetland. The terrestrial land‐forms created by this ice sheet in the north of Shetland suggest that it had corridors of relatively fast‐flowing ice that were partially directed by bed topography, and that subsequent deglaciation was interrupted by at least one major stillstand. Evidence in the south of Shetland indicates the growth of a local ice cap of restricted extent that fed numerous radial outlet glaciers during, or after, ice‐sheet deglaciation. Whilst the absolute age of these three landsystems remains uncertain, these new geo‐morphological and palaeoglaciological insights reconcile many of the ideas of earlier workers, and allow wider speculation regarding the dynamics of the former British ice sheet.

Structural evolution triggers a dynamic reduction in active glacier length during rapid retreat: Evidence from Falljökull, SE Iceland

Over the past two decades Icelands glaciers have been undergoing a phase of accelerated retreat set against a backdrop of warmer summers and milder winters. This paper demonstrates how the dynamics of a steep outlet glacier in maritime SE Iceland have changed as it adjusts to recent significant changes in mass balance. Geomorphological evidence from Falljokull, a high-mass turnover temperate glacier, clearly shows that between 1990 and 2004 the ice front was undergoing active retreat resulting in seasonal oscillations of its margin. However, in 2004–2006 this glacier crossed an important dynamic threshold and effectively reduced its active length by abandoning its lower reaches to passive retreat processes. A combination of ice surface structural measurements with radar, lidar, and differential Global Navigation Satellite Systems data are used to show that the upper active section of Falljokull is still flowing forward but has become detached from and is being thrust over its stagnant lower section. The reduction in the active length of Falljokull over the last several years has allowed it to rapidly reequilibrate to regional snowline rise in SE Iceland over the past two decades. It is possible that other steep, mountain glaciers around the world may respond in a similar way to significant changes in their mass balance, rapidly adjusting their active length in response to recent atmospheric warming.

Concentrated, ‘pulsed’ axial glacier flow: structural glaciological evidence from Kvíárjökull in SE Iceland

A detailed structural glaciological study carried out on Kviarjokull in SE Iceland reveals that recent flow within this maritime glacier is concentrated within a narrow corridor located along its central axis. This active corridor is responsible for feeding ice from the accumulation zone on the south-eastern side of Oraefajokull to the lower reaches of the glacier and resulted in a c. 200 m advance during the winter of 2013–2014 and the formation of a push-moraine. The corridor comprises a series of lobes linked by a laterally continuous zone of highly fractured ice characterised by prominent flow-parallel crevasses, separated by shear zones. The lobes form highly crevassed topographic highs on the glacier surface and occur immediately down-ice of marked constrictions caused by prominent bedrock outcrops located on the northern side of the glacier. Close to the frontal margin of Kviarjokull, the southern side of the glacier is relatively smooth and pock-marked by a number of large moulins. The boundary between this slow moving ice and the active corridor is marked by a number of ice flow-parallel strike-slip faults and a prominent dextral shear zone which resulted in the clockwise rotation and dissection of an ice-cored esker exposed on the glacier surface. It is suggested that this concentrated style of glacier flow identified within Kviarjokull has affinities with the individual flow units which operate within pulsing or surging glaciers

Digital surface models and the landscape: interaction between bedrock and glacial geology in the Ullapool area

Synopsis The front cover image for this volume is a hill-shaded digital surface model (DSM) of the Ullapool area, created using NEXTMap Britain elevation data from Intermap Technologies. This is a classic area for bedrock geology, transected by the Moine Thrust Zone, and in recent years it has also been studied in detail for its glacial history. Perhaps equally important, this is one of Scotlands most iconic landscapes. The geology of the area comprises a number of distinct sequences, each of which has a characteristic landscape expression as illustrated by the DSM. This paper considers the influence of the bedrock geology on the glacial geomorphology, and shows that the interplay of the two has led to the development of the different landscape elements of this spectacular area. Surprisingly, it is not always the major geological features – such as the Moine Thrust – that have the strongest topographic expression.

Morphology and Significance of Transverse Ridges (De Geer Moraines) Adjacent to the Moray Firth, NE Scotland

Abstract High-resolution NEXTMap digital surface models and aerial photographs are used to map suites of transverse ridges at Tarbat Ness and to the west of Elgin, along the margins of the Moray Firth in northeast Scotland. Based on their morphology, configuration and location, interpret these landforms as De Geer moraines which formed at or near former grounding line positions of the Moray Firth palaeo-ice stream. The Tarbat Ness De Geer moraines almost certainly formed at a marine margin. Reaching altitudes of 55 m above present OD, these landforms may provide one of the highest geomorphological indicators for former relative sea level in mainland Britain. Evidence from surrounding landforms and sediments suggest that the ridges formed between c. 15 000–18 000 cal yrs BP, indicating that a significant fall in relative sea level may have taken place prior to an ice margin re-advance in the Moray Firth, known as the Ardersier Oscillation.

Deep urban groundwater vulnerability in India revealed through the use of emerging organic contaminants and residence time tracers

Demand for groundwater in urban centres across Asia continues to rise with ever deeper wells being drilled to avoid shallow contamination. The vulnerability of deep alluvial aquifers to contaminant migration is assessed in the ancient city of Varanasi, India, using a novel combination of emerging organic contaminants (EOCs) and groundwater residence time tracers (CFC and SF6). Both shallow and intermediate depth private sources (<100 m) and deep (>100 m) municipal groundwater supplies were found to be contaminated with a range of EOCs including pharmaceuticals (e.g. sulfamethoxazole, 77% detection frequency, range <0.0001-0.034 μg L-1), perfluoroalkyl substances (e.g. PFOS, range <0.0001-0.033 μg L-1) as well as a number of pesticides (e.g. phenoxyacetic acid, range <0.02-0.21 μg L-1). The profile of EOCs found in groundwater mirror those found in surface waters, albeit at lower concentrations, and reflect common waste water sources with attenuation in the subsurface. Mean groundwater residence times were found to be comparable between some deep groundwater and shallow groundwater sources with residence times ranging from >70 to 30 years. Local variations in aquifer geology influence the extent of modern recharge at depth. Both tracers provide compelling evidence of significant inputs of younger groundwater to depth >100 m within the aquifer system.

Deglacial landform assemblage records fast ice-flow and retreat, Inner Hebrides, Scotland

High-resolution bathymetric data have been central to recent advances in the understanding of past dynamics of the former British–Irish Ice Sheet (BIIS). As approximately two-thirds of the former BIIS was probably marine-based during the Last Glacial Maximum (LGM) ( c. 29–23 ka), geomorphic observations of the seabed are required increasingly to understand the extent, pattern and timing of past glaciation. Until recently, glacial reconstructions for the Inner Hebrides, offshore of western Scotland, have been based primarily on terrestrial observations. Previous workers have proposed generalized reconstructions in which the Inner Hebrides are located within a significant former ice-sheet flow pathway that drained the western Scottish sector of the BIIS, feeding the Barra Fan during the LGM and earlier glaciations (Fig. 1). Results from numerical ice-sheet modelling suggest that former ice-flow velocities within the region were on the order of hundreds to thousands of metres per year, but yield further insight by demonstrating how dynamic binge/purge cycles may have affected ice-sheet mass balance over time (Hubbard et al. 2009). Following the LGM, ice-sheet retreat through the area is estimated to have been in the order of 20 m per year (Clark et al. 2012). Here we present swath-bathymetric data from the Inner Hebrides that provide in situ constraints on ice-sheet flow and subsequent retreat dynamics from within this important sector of the BIIS. Fig. 1. Swath-bathymetric images. ( a ) Inner Hebrides, Scotland (acquired with both multibeam (e.g. Kongsberg EM3002D) and interferometric systems for the Maritime and Coastguard Agencys UK Civil Hydrography Programme

Subglacial drumlins and englacial fractures at the surge-type glacier, Múlajökull, Iceland: SUBGLACIAL DRUMLIMS AND ENGLACIAL FRACTURES

1 The interaction between drumlins and overriding glacier ice is not well studied, 2 largely due to the difficulty of identifying and accessing suitable active subglacial en3 vironments. The surge-type glacier Múlajökull, in central Iceland, overlies a known 4 field of actively forming drumlins and therefore provides a rare opportunity to inves5 tigate the englacial structures that have developed in association with ice flow over 6 the subglacial drumlins. In this study detailed ground penetrating radar surveys are 7 combined with field observations to identify clear sets of up-glacier and down-glacier 8 dipping fractures at Múlajökull’s margin. These are interpreted as conjugate shear 9 planes or Pand R-type Reidel shears that developed and filled with saturated sedi10 ment derived from the glacier bed, during a previous surge. The fracture sets exhibit 11 focused spatial distributions that are influenced by the subglacial topography. In 12 particular, down-glacier dipping fractures are strongly focused over drumlin stoss 13 slopes. These fractures, although well developed at depth, were mostly unable to 14

Fracturing, block-faulting and moulin development associated with progressive collapse and retreat of a polar maritime glacier: Virkisjokul-Falljokull, SE Iceland

Since 2007, Falljokull in southeast Iceland has been undergoing passive downwasting, providing an ideal opportunity to study a range deformation structures developed in response to ice-marginal collapse and retreat. An integrated terrestrial lidar, Ground Penetrating Radar, and glaciological structural study of the clean, debris-free ice at the margin of Falljokull has allowed a detailed model of the surface and subsurface 3D structure to be developed. Collapse of the glacier margin takes the form of a multiple rotational failure controlled by large-scale, down-ice dipping normal faults. As the fault-bound blocks of ice are displaced downslope, they rotate leading to localized compression and the formation of down-faulted graben-like structures. Moulins present within the marginal zone of Falljokull are closely associated with the zones of relatively more intense brittle deformation which crosscut the glacier. A model is proposed where the moulins have formed in response to the progressive collapse of englacial drainage channels located along down-ice dipping normal faults. The preferential development of the moulins and englacial drainage channels along the normal faults weakens the ice along these structures, promoting or even accelerating further collapse of the ice margin. The complex pattern of surface lowering within the marginal zone of Falljokull has also been shown to be directly related to movement on the main faults controlling the collapse of the ice margin. This evidence suggests that structurally controlled collapse may, in some instances, have a profound effect on glacier surface lowering and geodetic mass balance measurements.