Michael J. Hambrey

Structure and changing dynamics of a polythermal valley glacier on a centennial timescale: Midre Lovénbreen, Svalbard

Hambrey, Michael, Murray, T., Glasser, N.F., Hubbard, A., (2005) Structure and changing dynamics of a polythermal valley glacier on a centennial timescale: Midre Lovenbreen, Svalbard, Journal of Geophysical Research 110 pp. 1-19 RAE2008

The Pagodroma Group - a Cenozoic record of the East Antarctic ice sheet in the northern Prince Charles Mountains

The northern Prince Charles Mountains overlook the western side of the 700 km long Lambert Glacier–Amery Ice Shelf drainage system. Within these mountains, at Amery Oasis (70°50′S, 68°00′E) and Fisher Massif (71°31′S, 67°40′E), the Cenozoic glaciomarine Pagodroma Group consists of four uplifted Miocene and Pliocene–early Pleistocene formations here named the Mount Johnston, Fisher Bench, Battye Glacier and Bardin Bluffs formations. These are composed of massive and stratified diamicts, boulder gravels and minor laminated sandstones, siltstones and mudstones. Each formation rests on either Precambrian metamorphic rocks, or on Permo-Triassic fluvial strata. The unconformity surfaces are parts of the walls and floors of palaeofjords. The Miocene Fisher Bench Formation exceeds 350 m in thickness at Fisher Massif, where the yet older Miocene (or Oligocene) Mount Johnston Formation overlies basement rocks at up to 1400 m above sea level. Individual formations contain either Miocene diatoms, or else Pliocene–early Pleistocene diatom-foram assemblages. The diamicts are interpreted as fjordal ice-proximal or ice-contact sediments, deposited seawards of tidewater glacier fronts located some 250 to 300 km inland of the present ocean margin. Each formation records an ice recession following a glacial expansion.

The Origin and Significance of Debris‐charged Ridges at the Surface of Storglaciären, Northern Sweden

Abstract Storglaciären is a 3.2 km long polythermal valley glacier in northern Sweden. Since 1994 a number of small (1–2 m high) transverse debris‐charged ridges have emerged at the ice surface in the terminal zone of the glacier. This paper presents the results of a combined structural glaciological, isotopic, sedimentological and ground‐penetrating radar (GPR) study of the terminal area of the glacier with the aim of understanding the evolution of these debris‐charged ridges, features which are typical of many polythermal glaciers. The ridges originate from steeply dipping (50–70°) curvilinear fractures on the glacier surface. Here, the fractures contain bands of sediment‐rich ice between 0.2 and 0.4 m thick composed of sandy gravel and diamicton, interpreted as glaciofluvial and basal glacial material, respectively. Structural mapping of the glacier from aerial photography demonstrates that the curvilinear fractures cannot be traced up‐glacier into pre‐existing structures visible at the glacier surface such as crevasses or crevasse traces. These curvilinear fractures are therefore interpreted as new features formed near the glacier snout. Ice adjacent to these fractures shows complex folding, partly defined by variations in ice facies, and partly by disseminated sediment. The isotopic composition (δ18O) of both coarse‐clear and coarse‐bubbly glacier ice facies is similar to the isotopic composition of the interstitial ice in debris layers that forms the debris‐charged ridges, implying that none of these facies have undergone any significant isotopic fractionation by the incomplete freezing of available water. The GPR survey shows strong internal reflections within the ice beneath the debris‐charged ridges, interpreted as debris layers within the glacier. Overall, the morphology and distribution of the fractures indicate an origin by compressional glaciotectonics near the snout, either at the thermal boundary, where active temperate glacier ice is being thrust over cold stagnant ice near the snout, or as a result of large‐scale recumbent folding in the glacier. Further work is required to elucidate the precise role of each of these mechanisms in elevating the basal glacial and glaciofluvial material to the ice surface.

Proglacial Sediment—Landform Associations of a Polythermal Glacier: Storglaciären, Northern Sweden

Abstract Mapping and laboratory analysis of the sediment—landform associations in the proglacial area of polythermal Storglaciären, Tarfala, northern Sweden, reveal six distinct lithofacies. Sandy gravel, silty gravel, massive sand and silty sand are interpreted as glaciofluvial in origin. A variable, pervasively deformed to massive clast‐rich sandy diamicton is interpreted as the product of an actively deforming subglacial till layer. Massive block gravels, comprising two distinctive moraine ridges, reflect supraglacial sedimentation and ice‐marginal and subglacial reworking of heterogeneous proglacial sediments during the Little Ice Age and an earlier more extensive advance. Visual estimation of the relative abundance of these lithofacies suggests that the sandy gravel lithofacies is of the most volumetric importance, followed by the diamicton and block gravels. Sedimentological analysis suggests that the role of a deforming basal till layer has been the dominant factor controlling glacier flow throughout the Little Ice Age, punctuated by shorter (warmer and wetter climatic) periods where high water pressures may have played a more important role. These results contribute to the database that facilitates discrimination of past glacier thermal regimes and dynamics in areas that are no longer glacierized, as well as older glaciations in the geological record.

Development of Landform and Sediment Assemblages at Maritime High-Arctic Glaciers

Detailed studies of sedimentary processes and landform development at modern glaciers are an essential pre-requisite for the interpretation of Quaternary glacial sediments and landforms. Recent work on polythermal glaciers in Svalbard has provided new insight concerning the processes responsible for glacial sediment/landform assemblages. Although the landforms associated with Svalbard glaciers are not in themselves unique, the particular assemblages and proportions of sedimentary facies differ markedly from those in temperate and cold glacier systems. The main conclusion is that deformation within glacier ice, as debris is entrained and subsequently transported, is the primary control on the nature of landform/sediment assemblages in the proglacial areas of Svalbard valley glaciers. The most important landform-creating modes of debris entrainment are: n n(1) n nIncorporation of angular rockfall material within the stratified sequence of snow, firn and superimposed ice, followed by folding with flow-parallel axes; the resulting medial moraines are preserved in the proglacial area as linear debris trains; n n n n n(2) n nEntrainment of debris at the bed to form a several metre-thick basal ice layer, which is released as a sheet of basal till; n n n n n(3) n nIncorporation of basal debris within longitudinal foliation, resulting in landforms referred to as foliation-parallel ridges; n n n n n(4) n nThrusting, whereby basal and subglacial sediments are uplifted towards the glacier surface, and ultimately released as individual mounds within a large end-moraine complex (often referred to as ‘hummocky moraine’); n n n n n(5) n nSubglacial upright folding with transverse axes and faulting also producing large end-moraine complexes; n n n n n(6) n nReworking of thrust-or fold-derived glaciofluvial material to produce longitudinal debris ridges in the ice, although their translation into landforms is poor.

The global cryosphere: past, present and future . Roger Barry & Thian Yew Gan, Cambridge University Press, Cambridge, 2011, ISBN 978-0-521-15685-1. 472 pp. £42.50

The term cryosphere, according to this excellent new volume, is derived from the Greek word kryos for icy cold, which collectively describes the frozen parts of the Earth’s surface, including sea ice, lake ice, river ice, snow cover, glaciers, ice sheets, and frozen ground. This volume is a major contribution to our understanding of the cryosphere, by combining the authors’ first-hand knowledge of the issues and presenting a synthesis of a vast range of published literature. The publishers claim that this is the first textbook to address all components of the cryosphere, by providing a concise, but comprehensive summary of cryospheric processes for upper-level undergraduates and graduates in environmental science, geography, geology, glaciology, hydrology, water-resource engineering and ocean sciences. They claim also to provide a superb up-to-date summary of cryospheric processes for researchers from a range of sciences. To evaluate these claims, this review outlines the key components of the book, and considers how well the book has been assembled. First, it is worth noting the credentials of the authors. Roger Barry was formerly Director of the World Data Centre for Glaciology and Professor of Geography at the University of Colorado at Boulder. He is a leading authority on climate change, Arctic and mountain environments, and snow and ice processes. He is the recipient of several awards and medals, including the Founder’s Medal of the Royal Geographical Society. T.Y. Gan is a Professor at the University of Alberta with interests in snow hydrology and climate change impacts. These authors are thus well placed to summarize the state-of-the-art, now that it has become widely recognized that the cryosphere represents a critical and sensitive component of the Earth System, especially in the context of global warming. The book has four parts, subdivided into eleven chapters. The first two parts cover the terrestrial and marine cryosphere. Focussing on historical background, characteristics, distribution, physical processes, numerical modelling and cross-linkages the treatment is wide-ranging, with a chapter for each of these cryosphere components. These chapters are full of fascinating facts; I was particularly impressed with the brief historical treatments of each topic. There are, however, some notable gaps, and the claim to ‘address all components of the cryosphere’ is an exaggeration. For example, in the Glaciers and Ice Caps chapter, I found it surprising that there was little mention of glacial erosional and depositional processes, surely a key aspect of interpreting past cryospheric processes? Similarly, several aspects of the attributes of glaciers, such as glacier flow, are treated in a superficial and unbalanced fashion but the authors do refer to some of the key texts that address related topics more rigorously. Part III deals with the past history and future of the cryosphere. Given the volume of research on past glacial history, no single book, let alone the one short chapter here, can do justice to this topic, and I did not see reference to many of the key monographs and textbooks dealing with Quaternary and older glaciations. Readers of this chapter will not get a particularly balanced view of our understanding of past cryospheric changes. In contrast, the paired chapter on recent and future changes in the cryosphere is much more valuable, combining recent observations with predictions of global impacts based on IPCC scenarios. Indeed, it is worth summarizing what these recent changes have been (Chapter 10.3). To quote:

delta D-delta O-18 relationships on a polythermal valley glacier: Midtre Lovenbreen, Svalbard

Glasser, N. F., Hambrey, M. J. (2002). delta D-delta O-18 relationships on a polythermal valley glacier: Midtre Lovenbreen, Svalbard. Polar Research, 21 (1), 123-131.