Jez Everest

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.

Late-Holocene and Younger Dryas glaciers in the northern Cairngorm Mountains, Scotland

We present 17 cosmogenic 10Be ages of glacial deposits in Coire an Lochain (Cairngorm Mountains), which demonstrate that glacial and nival deposits cover a longer timescale than previously recognised. Five ages provide the first evidence of a late-Holocene glacier in the British Isles. A previously unidentified moraine ridge was deposited after c. 2.8 kyr and defines a small slab-like glacier with an equilibrium line altitude (ELA) at c. 1047 m. The late-Holocene glacier was characterised by rapid firnification and a dominance of sliding, enabling the glacier to construct moraine ridges in a relatively short period. Isotopic inheritance means that the glacier may have existed as recently as the ‘Little Ice Age’ (LIA) of the 17th or 18th century ad, a view supported by glacier-climate modelling. Nine 10Be ages confirm a Younger Dryas Stadial (YDS) age for a cirque-floor boulder till, and date the glacier maximum to c. 12.3 kyr when the ELA was at c. 963 m altitude. Both glaciers existed because of enhanced accumulation from wind-blown snow, but the difference in ELA of only c. 84 m belies the YDS–LIA temperature difference of c. 7°C and emphasises the glacioclimatic contrast between the two periods. Three 10Be ages from till boulders originally deposited in the YDS yield ages <5.5 kyr and indicate snow-avalanche disturbance of older debris since the mid-Holocene, as climate deteriorated towards marginal glaciation.

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

Future evolution and uncertainty of river flow regime change in adeglaciating river basin

The flow regime of glacier-fed rivers are sensitive to climate change due to strong climate-cryosphere-hydrosphere interactions. Previous modelling studies have focussed on projecting changes in annual and seasonal flow magnitude, but neglect other changes in river flow regime that could also have socio-economic and environmental impacts. This study employs a more comprehensive, signature-based analysis of climate change impacts on the river flow regime for the deglaciating Virkisá river basin in southern Iceland. 25 metrics (signatures) are derived from 21st century projections of river flow time-series to 5 evaluate changes in different characteristics (magnitude, timing and variability) of river flow regime over sub-daily to decadal timescales. The projections are produced by a model chain that links numerical models of climate and glacio-hydrology. Five components of the model chain including the emission scenario, numerical climate model, downscaling procedure, snow/ice melt model and runoff-routing model are perturbed to propagate their uncertainties through to the river discharge projections. The signature-based analysis indicates that glacier-fed rivers will exhibit changes in the magnitude, timing and variability of 10 river flows over a range of timescales in response to climate change. For most signatures there is high confidence in the sign of change, but the magnitude of change is uncertain and varies substantially across the different signatures. A decomposition of the projection uncertainties using analysis of variance (ANOVA) shows that all five perturbed model chain components contribute to projection uncertainty, but their relative contributions vary across the signatures (characteristic and timescale) of river flow. Signature-based decompositions of projection uncertainty can be used to better design impact studies to provide 15 more robust projections.

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