Geomorphological expression of glacial erosion or lack thereof

The years following World War II saw earth scientists exploring a wide range of glacier environments from Antarctica to mountain glaciers and ice caps lying at the Equator. This geographical coverage combined with recruitment into the new field of 'glaciol-ogy' of physicists and mathematicians led to the development of models of temperature conditions at the bed of glaciers and the large ice sheets. Sugden (1977, 1978) wrote two seminal papers that first developed an estimate for the...

Other dating methods

Another approach to the dating of ice cores is the use of radioactive decay methods, but their usefulness is limited by factors such as the half-life, the low concentration of trace substances and gases in the ice as well as complexities concerning sampling and time resolution. The reader is referred to the literature, for example, the review paper by Stauffer et al. (1989). Such methods can, however, serve as a rough verification of the model or seasonal chronologies, or can be used where...

Subglacial water

Whether fast ice streaming is accommodated by hard-bed sliding or till deformation, at the most basic level it is enabled by the presence of subglacial water at pressures close to the overburden pressure (e.g. Engelhardt & Kamb, 1997 Engelhardt et al., 1990b Kamb, 1991, 2001). Theoretical calculations of basal melting freezing rates indicate that, at least in the Siple Coast region, basal melting predominates inland, particularly beneath ice-stream tributaries, where it takes place at rates...

Basal ice deformation

Examination of deformation processes at the base of glaciers is beset by numerous problems, which include limited accessibility, structural complexity and spatial variability in physical properties and temporal variability of deformation processes. Access to subglacial locations is a significant problem because deformation of basal ice and subglacial sediment takes place at the ice- substrate interface beneath a substantial thickness of ice, which makes direct observation of deformation...

Basal processes

The important fact that shear margins support a significant fraction of ice stream gravitational driving stress is caused ultimately by excess basal lubrication of ice streams, which leads to the situation in which td < tb or even td < < tb. (Raymond, 2000 Tulaczyk et al., 2000a,b Kamb, 2001). Early models of ice-stream mechanics focused on application of the hard-bed sliding theory assuming that the basal lubrication is due to ice-bed separation by a subglacial water film layer (e.g....

Polar Science Center Applied Physics Laboratory University of Washington Seattle USA

The Northeast Greenland Ice Stream (NEGIS) provides a good illustration of the utility of interferometric synthetic aperture radar (InSAR) for studying ice dynamics and ice-sheet mass balance. This 700-km-long ice stream was discovered only in the mid-1990s when its presence was detected through the analysis of features visible in SAR imagery (Fahnestock et al., 1993). Soon after velocity on a central portion of this ice stream was mapped using InSAR (Kwok & Fahnestock, 1996). This was...

Glacierclimate relationships Little Ice Age LIA scale

'The term Little Ice Age relates to the behaviour of the glaciers not directly to climate' (Grove, 2001, p. 76 after Luckman). What was once a well accepted, if poorly understood, interval of Earth history is now in debate, as is its companion, the Medieval Warm Period (MWP) (Bradley & Jones, 1993 Hughes & Diaz, 1994 Broecker, 2001). Instrumental data for climatic variables do not exist prior to the 17th century, therefore the atmospheric and ocean climates (Figs 21.1 & 21.2) have to...

Chris D Clark Sarah L Greenwood and David J A Evansf

*Department of Geography, University of Sheffield, Sheffield S10 2TN, UK fDepartment of Geography, Durham University, South Road, Durham DH1 3LE, UK Reconstructing the extent, flow geometry and topography of former ice sheets has recently become more than an academic exercise because of the increasing perception of the importance of the cryosphere in climate change in the earth-ocean-atmosphere system. Of particular note is the discovery that punctuated delivery of freshwater from ice sheets...

Viscous behaviour of ice at low stresses application to polar ice sheets

For conditions prevailing in ice sheets (equivalent stress lower than 0.2MPa), the stress exponent is slightly lower than 2, a value close to that found in isolated single crystals (Fig. 59.1). This result is supported by densification measurements of bubbly ice at Vostok (Lipenkov etal., 1997). The high difference in strain rate between crystals oriented for basal slip and isotropic ice (Fig. 59.1) cannot be explained by a geometric effect related to the random orientation of grains. As at...

Centre for Polar Observation and Modelling School of Geographical Sciences University of Bristol Bristol BS8 1SS UK

In this case study we will illustrate the range of models available to study terrestrial ice masses by concentrating on the study of the ice streams of Antarctica. Ice streams are the focus of a great deal of contemporary research because they discharge the majority (more than 90 ) of the ice leaving Antarctica, and their dynamics are therefore likely to affect the volume of ice stored in the ice sheet and, hence, global sea levels. Ice-flow models can best be classified according to the...

Deuterium excess in ice formed by water freezing

Heavy isotopic water molecules are preferentially incorporated into the growing ice so that the solid is enriched in deuterium and oxygen 18 compared to the water. Equilibrium fractionation always occurs at the ice-water interface but the observed fractionation between ice and bulk water can be lower, depending on the isotopic concentration in the water at the interface. Souchez & Jouzel (1984) have demonstrated that, by partial freezing of an open or a closed system, samples of ice plot in...

Glaciers and their coupling with hydraulic and sedimentary processes2

2 Keynote introduction Glaciers and their coupling with hydraulic and sedimentary processes 3 Geoffrey S. Boulton 3 Haut Glacier d'Arolla, Switzerland hydrological controls on basal sediment evacuation and glacial erosion 23 Darrel A. Swift 4 A glimpse at meltwater effects associated with continental ice sheets 25 John Shaw 5 The erosional origin of hummocky terrain, Alberta, Canada 33 Mandy J. Munro-Stasiuk and Darren Sjogren 6 Tunnel channel character and evolution in central southern Ontario...

Philippe Huybrechts

Alfred-Wegener-Institut f r Polar- und Meeresforschung, Postfach 120161, D-27515 Bremerhaven, Germany and Departement Geografie, Vrije Universiteit Br ssel, Pleinlaan 2, B-1050 Br ssel, Belgium Ice sheets respond dynamically to changes in boundary conditions, such as climate variations, basal thermal conditions, and isostatic adjustments of the underlying bedrock. These cause the ice sheets to evolve towards a new equilibrium. Long response time-scales of up to 104 years are involved,...

Landsystems as modern analogues

The landsystems approach is given more credibility and applicability wherever landscape evolution can be monitored, thereby providing modern analogues for the interpretation of ancient glaciated terrain (e.g. Price, 1969 Gustavson & Boothroyd, 1987 Kruger, 1994 Dyke & Savelle, 2000 Kjsr & Kr ger, 2001 Evans & Twigg, 2002). This type of research on modern glaciers has led to the identification of landform-sediment suites indicative of specific styles of glaciation (e.g. plateau...

The last glacial cycle abrupt glaciological responses to climate

Research on marine cores from the 1970s onward have shown that the isotopic changes in foraminiferal S18O have variations that match those predicted from calculations of the variations in the Earth's orbit (Hays et al., 1976). In particular, peaks in spectral analysis with periodicities of ca. 22, 41 and 100 kyr match variations in obliquity, precession and eccentricity, and it was widely argued that changes in solar insolation, at high northern latitudes, forced changes in the global ice-sheet...

Upscaling from local to global scale

The simplest way to upscale a glaciological characteristic from the local to global scale is to assume that the global value is equal to the average of the available measurements (local values by definition). This seems unsatisfactory for the temperature sensitivity of glaciers because we know that the sensitivity varies greatly between glaciers (see Fig. 83.2), with lower sensitivities in the Arctic (Canada and Svalbard) and in the former Soviet Union and Asia and higher sensitivities in North...

Glacier mass balance

Glacier mass balance, b, is a measure of the net accumulation minus ablation of snow and ice, b a - m. The most common convention is to consider net annual mass balance, where a represents the total annual snow ice accumulation and m is the total annual snow ice loss through ablation. Sources of accumulation are primarily meteoric, although 'internal accumulation' occurs through the refreezing of surface meltwater that percolates into the snow or firn. Internal accumulation represents an...

Y Im ksw

Tunnel valleys Moraine ridges Meltwater channels Lateral meltwater channels Loch Lomond readvance limit Loch Lomond readvance (inferred) Shelf-edge fans Esker Lithological limit relevant to erratic dispersal Inferred erratic path Erratic limit Drumlin Limit of glacigenic deposits Trimline Indicator erratic source area Moraines Glaciolacastrine deposits Ice-dammed lake at its lower stand Ice-dammed lakes Figure 50.4 The BRITICE compilation of a 'Glacial map of Britain', which includes moraines,...

Department of Earth and Ocean Sciences University of British Columbia 6339 Stores Road Vancouver BC V6T 1Z4 Canada

This case study briefly turns the spotlight upon a topic with a broader significance that may prove to belie its perhaps modest appearance differences in the winter groundwater responses of glacierized and glacier-free watersheds to climatic warming. Glacial runoff could be altered significantly by projected anthropogenic climate warming, and observed long-term trends in surface water resources under historical warming conditions can be dramatically different between glacierized and nival...

Department of Earth and Atmospheric Sciences University of Alberta Edmonton Alberta Canada T6G 2E3

This chapter covers some of the aspects of the subglacial landscape attributed to meltwater activities beneath the mid-latitude, Pleistocene ice sheets. A preliminary discussion deals with the sedimentary evidence for the presence of meltwater beneath their central parts. This is an essential step without such evidence refuting the notion of cold-based ice-sheet centres, it would be Figure 4.1 Form analogy. The aerial photograph (a) shows asymmetrical, parabolic drumlins. These bedforms are...

Deuterium excess in ice formed at the grounding line

Figure 35.3 Double-diffusion freezing at the grounding line in Terra Nova Bay. (a) Sketch of the suggested mechanism. (b) SD-S18O diagram of the ice samples. Black circles, ice samples open circles, initial water samples computed from S values of ice samples and equilibrium fractionation coefficients. The straight line represents the best-fit line for the waters. Insert shows a diagram for glacier ice samples in the area. (Reproduced by permission of International Glaciological Society from...

Recent trend of climate change in southern South America

When glacier variations in Patagonia are discussed from a climatic point of view, meteorological data at Puerto Aisen and Punta Arenas are often cited, from which we cannot identify any significant trends in air temperature and annual precipitation (Warren & Sugden, 1993). Although these stations provide relatively long, continuous records from around Patagonian glaciers, they are located far from glaciers, the former station being about 150 km to the north of the northern margin of the NPI...

Does GBSlimited flow occur within glaciers and ice sheets

To provide an overview of the relevance of GBS-limited creep for glacier and ice sheet mechanics, a deformation mechanism map for ice, drawn on axes of grain size and stress, is shown in Fig. 60.3 for T 268 K. The GBS-limited creep regime and the dislocation creep regime are separated by the solid boundary, along which both mechanisms contribute equally to the strain rate. Within each creep regime, strain-rate contours are calculated using the appropriate flow law for that creep regime. As...

Robert T Meehan

86 Athlumney Castle, Navan, County Meath, Ireland As with all glacial processes, the processes of ice advance and retreat operate at a variety of scales that associated with the general growth of an ice sheet over thousands of years and thousands of kilometres, or shunts of the ice margin of a few centimetres on a single day. The measurement of past regional-scale ice advances is achieved by mapping 'first order' glacial geological features (e.g. drumlins and ribbed moraines), which identify...

Department of Geography University of Edinburgh Edinburgh EH8 9XP UK

This case study is concerned with the application of a three-dimensional ice flow model to Haut Glacier d'Arolla, a small temperate glacier in the Swiss Alps. The study illustrates both the potential and certain limitations of using high-resolution, three-dimensional flow modelling constrained by observations to aid our understanding of alpine glacier systems. In particular, the combination of flow modelling with detailed field measurements at Haut Glacier d'Arolla provides a powerful tool to...

A generalized hypothesis for ice sheet flow

At the shallowest depths within an ice sheet (at tens-of-metres depths), where effective stresses are < 0.0001 MPa, deformation likely proceeds via diffusion creep (Goldsby & Kohlstedt, 2001). Diffusion creep in this shallow ice is consistent with the lack of c-axis fabrics near the surfaces of the ice sheets, although finite strains may be too small in this region to yield significant fabrics even if creep proceeded via a c-axis-fabric-producing mechanism. With increasing depth (stress),...

PreB0lling chronology

The seasonal stratigraphy could in principle have been measured in situ as long as a(z) was at least a few millimetres thick, but in practice this was not possible as the measurements became too time consuming as a(z) approached 1cm hence only selected sequences of the deeper ice strata were measured with a seasonal resolution. The GRIP continuous seasonal stratigraphy therefore ends around 60kyrBP. For older layers the sequential analysis can be used to establish a chronology, but the accuracy...

Fortyeight

Quantifying the significance of recent glacier recession in the Cordillera Blanca, Per a case study of hydrological impact and climatic control Department of Geography, The Ohio State University, Columbus, OH 43210, USA The Peruvian Cordillera Blanca is the most extensively glacierized mountain range in the tropics, and an important location to study the practical impact and climatic control of ongoing glacier volume loss. Draining most of the glacierized area in the Cordillera Blanca, the R o...

Instrument deployment in the glacier substrate

Deployment of instrumentation into subglacial sediment suffers from the uncertainty about the precise position of the instrument with respect to the ice-bed interface, not least because of its expected complexity. Subglacial sediment may squeeze upward into the bottom of boreholes. In this case, instruments, although inserted in sediment, are potentially installed within the body of the glacier. From our experience, this possibility can in most cases be ruled out because the shear-deformation...

Byrd station example

To illustrate this generalized description of ice-sheet flow, a comparison is made between data from studies on the Byrd Station borehole in Antarctica with the deformation mechanism map for ice. In Fig. 60.5, the measured grain size versus depth profile (Gow etal., 1968) and estimated shear stress versus depth profiles (Frost & Ashby, 1982) for the Byrd Station drill site are plotted. Following Frost & Ashby (1982), shear stresses T were estimated from T pgh sin (a), where p is ice...

The enigmatic 1470yr cycle

Any effort to explain ocean-ice interactions during the last glaciation must take into account the puzzling and widespread ca. 1470-yr cyclicity found in glacial records from ice cores and in marine and terrestrial sediments in both hemispheres (see Alley et al., 2001). In records of S18O from Greenland ice, the cycle appears as a sharp peak in spectral energy that suggests a truly periodic process with a period of about 1470yr (Mayewski et al., 1997 Grootes & Stuiver, 1997). Recently,...

Mike J Smith Paul Dunlopf and Chris D Clark

*School of Earth Sciences and Geography, Kingston University, Penrhyn Road, Kingston-upon-Thames, Surrey KT1 2EE, UK fSchool of Environmental Sciences, University of Ulster, Coleraine, BT52 ISA, Northern Ireland, UK Department of Geography, University of Sheffield, Winter Street, Sheffield S10 2TN, UK Figure 75.1 Summary map of glacial bedforms for Ireland, incorporating drumlins and ribbed (rogen) moraine including extensive ribbed moraine fields reported by Clark & Meehan (2001). Note the...

The problem of the basal boundary

The nature of the coupling at the basal boundary is one of the major unresolved problems of glaciology. Ice, with a rheology defined by Glen's law (where the strain rate E ktn, where k is a temperature dependent constant, t is shear stress and n has a value of between 3 and 4), can be regarded as a perfectly plastic solid with a yield strength of about 100 kPa. If the ice-bed interface is a strong interface, the average shear stress (given by pgh sin a where pi is the density of ice, g the...

Basic laws of groundwater flow through the subglacial sediment

If a glacier or an ice sheet rests on a permeable bed, be it rock or soft sediment, a part of the subglacial meltwater will enter the bed and be evacuated as groundwater flow, governed by the same physical rules as groundwater flow in confined aquifers outside the glaciated areas. The major differences, however, are that (i) the flow is driven by hydraulic gradient imposed by ice overburden, and (ii) some groundwater may be advected within the sediment if it deforms in response to glacier...

Icefacies formation and types

As indicated above, the characteristics of glacier ice are known to vary significantly through individual glaciers in ways that affect the value of flow parameter A in Equation (2), and hence the response of the ice to applied stress. The most systematic occurrence of significantly different ice within glaciers occurs in the basal zone, because the interaction of the glacier with the bed can lead to the development of layers near the bed of distinctive regelation ice, and to metamorphism of...

FEarth Science Program University of Calgary Calgary Alberta Canada

Hummocky terrain is comprised of tracts of hummocks and depressions of various sizes and shapes that occur in formerly glaciated areas. Traditionally, this terrain is known as 'hummocky moraine', and is believed to represent deposition via letdown at, or near, the ice margins during ablation. Hummocks therefore have been used to delineate recessional stages of glaciation in many regions. For example, the four prominent north-south trending hummocky complexes (Fig. 5.1) in Alberta, Canada, are...

Response of the polar ice sheets to future climatic warming

80.4.3.1 Response during the 21st century Three-dimensional ice-sheet modelling studies all indicate that on time-scales less than a century the direct effects of changes in the surface mass-balance dominate the response. This means that the response is largely static, and thus that the ice flow on this time-scale does not react much to changes in surface mass balance. Greenland studies by Van de Wal & Oerlemans (1997) and Huybrechts & de Wolde (1999) found that ice-dynamics counteract...

The Global Land Ice Measurements from Space GLIMS project

*Department of Geography, University of Zurich *For the GLIMS consortium. Figure 85.1 Tasman glacier, New Zealand. Depicted terrain section is about 25 X 25 km. The ASTER satellite image was taken on 29 April 2000. North is to the top. Imaging is within the project Global Land Ice Measurements from Space (GLIMS) project. (Satellite data courtesy of NASA GSFC METI ERSDAC JAROS, and US Japan ASTER science team processed by A. Kaab, University of Zurich.) The ASTER satellite sensor carries cameras...

Chris R Stokes and Chris D Clarkf

*Landscape and Landform Research Group, Department of Geography, The University of Reading, Reading RG6 6AB, UK fDepartment of Geography, The University of Sheffield, Sheffield S10 2TN, UK Ice streams not only exert a profound influence on ice-sheet mass balance and stability but they can also influence the ocean-climate system through profligate iceberg discharge and subsequent melting. In recent years, palaeo-ice stream imprints have been identified with a greater degree of confidence than...

Glacialisostatic adjustment and sealevel change around Greenland

Present-day sea-level change around Greenland is dominated by glacial-isostatic adjustment (GIA), which is the Earth's viscoelas-tic response to surface-load changes associated with the redistribution of continental ice and ocean water. The most prominent changes occurred after the Last Glacial Maximum (LGM, ca. 21kyr BP), which involved the melting of ice equivalent to ca. 130m of water when distributed evenly over the present-day ocean surface (Lambeck et al., 2000). We consider separately...

Background the flow of modern ice sheets

The dynamics of modern ice sheets, and the nature of their spatial and temporal variability in flow, are important to our understanding of the high-latitude marine sedimentary record. This is because the flux of ice, and any associated meltwater and sediment load delivered to the adjacent ocean, will vary significantly depending on the ice-flow regime. The large-scale form and flow of contemporary ice sheets and large ice caps have been examined using a variety of satellite and airborne...

Krista M McKinzey

Institute of Geography, School of GeoSciences, The University of Edinburgh Drummond Street, Edinburgh EH8 9XP Scotland, UK The Franz Josef Glacier (FJG) descends from the western peaks of the Southern Alps of New Zealand (Fig. 54.1A). It is one of the world's lowest lying mid-latitude glaciers and as of March 2001 terminated at 275ma.s.l. This maritime valley glacier has a terminus response time of 5-20yr (Oerlemans, 1997), which implies that it responds rapidly to perturbations in temperature,...

Clas Httestrand and Chris D Clarkf

*Department of Physical Geography and Quaternary Geology, Stockholm University, Stockholm, Sweden fDepartment of Geography, The University of Sheffield, Sheffield S10 2TN, UK The last deglaciation of the Fennoscandian Ice Sheet is fairly well constrained, particularly around the southern and eastern margin. The deglaciation of the northeastern sector of the ice sheet, including the Kola Peninsula, is much less well understood. The area is of particular interest for ice-sheet reconstructions,...

Continentalshelf morphology and sediments

High-latitude continental shelves range from a few tens to several hundred kilometres in width. The shelves of both the Arctic and Antarctic are typically made up of relatively deep cross-shelf troughs and intervening shallower banks. The Norwegian shelf provides a Northern Hemisphere example (Plate 30.1), as does the Ross Sea in Antarctica (e.g. Anderson, 1999 Shipp et al., 1999 Ottesen et al., 2002). Many troughs are linked to relatively narrow deep-water fjords which dissect the mountainous...

Introduction

For most individuals the Laurentide Ice Sheet (LIS) refers to Antarctic-size ice sheets that extended from the general area of the Great Lakes in the USA northward to the Canadian Arctic coast, and westward from the uplands and fjords of Baffin Island and Labrador to the foot of the Rocky Mountains (Fig. 40.1). However, the late V. Prest insisted that the term was applicable only to the ice sheet during the last glaciation. In this section I will adopt the more general usage for an ice sheet...

Largescale erosional marks

Large-scale erosional marks in bedrock might be loosely delimited as those with lengths > 10 m. There are three main kinds streamlined bedrock hills (Sawagaki & Hirakawa, 1997), crescentic scours and rock drumlins (Kor et al., 1991), and furrows (Kor et al., 1991). These large-scale forms all carry superimposed smaller forms. Figure 4.5 Erosional drumlins and horseshoe vortices. Drumlins near Prince George, British Columbia (a) are clearly defined by hairpin scours related to horseshoe...

Basal sliding

Weertman (1957, 1964) considered basal sliding in terms of two discrete processes enhanced deformation and regelation. Local stress fields are established within basal ice as it passes over a rough bed. Locally enhanced stoss-face stresses induce enhanced local basal drag (tb), forcing the ice to deform around bedrock hummocks particularly rapidly. As velocity scales with strain rate times distance, the larger the hummock of a given shape the greater the ice deformation rate Ud, yielding (for a...

Chemical composition of glacial runoff

The chemical composition of glacial runoff from ice sheets, ice caps and glaciers around the world is shown in Table 14.1 (after Brown, 2002 Tranter, 2003), which also includes the composition of global mean river water for comparative purposes. Sea salt is a variable component of glacial runoff, and the dominant non-sea- Figure 14.1 Scatterplot of crustal calcium flux and calcium concentration versus discharge at Manitsoq Glacier, southwest Greenland. Table 14.2 Specific runoff and cationic...

Casassa A Riveraf and M Schwikowski

*Centro de Estudios Cient ficos, Valdivia, Chile fDepartment of Geography, University of Chile, Santiago, Chile ffiaul Scherrer Institut, Labor f r Radio- und Umweltchemie, Switzerland Southern South America (SSA), i.e. south of 30 S, comprises an estimated glacier area of ca. 27,500km2 (Fig. 47.1), which represents ca. 89 of all Andean glaciers. The glaciers in the region show a generalized retreat and thinning (Naruse, this volume, Chapter 46). In spite of their importance in water resources...

Glacial chemical weathering

The principal reactions that comminuted bedrock undergo in glaciated terrain are summarized below. We assume that the bedrock is primarily composed of silicates and aluminosilicates. Glacial comminution crushes bedrock and exposes the trace reactive components within crystal aggregates more rapidly than would be the case in temperate and tropical soils, where new minerals are ultimately accessed via solubilization of aluminosilicate lattices. Hence, glaciers are effective at promoting the...

FGeological Survey of Canada 601 Booth Street Ottawa Ontario K1A 0E8 Canada

Valleys that truncate subglacial bedforms, contain eskers and follow upslope paths are the geomorphological expression of large subglacial channels tunnel channels or valleys that efficiently evacuated meltwater from beneath past ice sheets. In recent years there has been considerable debate as to the mechanism by which such large meltwater channels formed (e.g. 0 Cofaigh, 1996). Such debate is important as interpretations have a direct bearing on reconstructions of Late Wisconsinan ice-sheet...

Scope and goals

The concept that glaciers and ice sheets have different responses to ocean and atmospheric climate, depending on a specific time-scale, is an appropriate but not the only way to organize this chapter. On the decadal to century scales, such as the Little Ice Age (LIA), then the changes in glacier extent are largely a function of changes in glacier mass balance, which in turn are linked with changes in ocean and atmosphere climates (Fig. 21.2). On the 104-105yr scale (the Milankovitch or orbital...

The landocean interface sensitivity of ocean thermohaline circulation to freshwater runoff

Surface ocean currents bring relatively warm water to northern latitudes of the Atlantic Ocean from equatorial and temperate regions where it has gained heat (Broecker, 1987, 1997 Clark et al., 2002b Rahmstorf, 2002). As the surface water cools in Figure 28.8 Schematic diagrams of oscillations of Lake Agassiz area, level and outflow routings as a result of ice retreat, climatic feed-backs and differential rebound. In these diagrams, the external forcing of relatively high summer insolation...

Esker distributions and tunnel valleys

Plate 2.3 shows the distribution of eskers on the Fennoscandian Shield. Although eskers occur beyond the Shield, they are infrequent. A similar situation applies on and around the Laurentide Shield in North America. It is not entirely clear whether eskers are simply not so well preserved in the fringing soft-sediment areas, whether subglacial tunnel flow eroded deep channels into the substratum rather than being contained in R-tunnels, or whether eskers are largely replaced by tunnel valleys,...

Martyn S Stoker David Long Joseph Bulat and Stephen Davisonf

*British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, Scotland, UK fDepartment of Geology and Geophysics, University of Edinburgh, Grant Institute, West Mains Road, Edinburgh, EH9 3JW, Scotland, UK During the past decade, insights into the history and extent of the former British Ice Sheet (BIS) off northwest Britain have been revealed by the integration of geomorphological information from geophysical data with stratigraphical and lithological data from sea-bed...

Cavityfill drumlins

The nature of the flows that formed drumlins in the form of infilled cavities (Fig. 4.3) can be determined only by deduction based on shape and composition of the drumlins themselves. The initial work in this regard was on the so-called Livingstone Lake drumlin field, northern Saskatchewan (Figs 4.1 & 4.2 Shaw, 1983 Shaw & Kvill, 1984). In the first instance, the drumlins in this field, when inverted, were seen to be identical in form to sets of ero-sional marks in areas of bedrock...

Massbalance measurements

Ahlmann (1948) first developed mass-balance concepts in a series of pioneering measurements in Nordic countries. The longest continuous measurements were started in 1946 on Storglaciaren in northern Sweden (Schytt, 1962) and similar measurements started in the 1940s and 1950s on other glaciers in Norway, the Alps, western North America, and on numerous glaciers in the former USSR. The number of glaciers studied and their geographical coverage expanded rapidly in the 1960s under the impetus of...

Ice streams

Areas dominated by sheet flow, e.g. the southwestern shield-area parts of the Keewatin and Quebec domes, display 'classic' glacial landscapes comprising abundant glacial lineations, eskers aligned to lineations, ribbed moraine and a scarcity of sharp lateral contrasts in lineation length and development. Older ice-flow directions may be manifested by overridden large 'ghost' drumlins or older cross-cut striae. Landscapes that probably are sites of former ice-stream webs or networks show...

An unfrozen unlithified sediment bedglaciological implications

A large proportion of the beds that directly underlay the soles of mid-latitude ice sheets of the last glacial period were composed of thick unlithified sediment sequences rather than rock. Soft beds have been the subject of much research in the past 25 yr since their significance was first recognized. They have proved to be phenomenologically rich, and as a consequence are still a very active source of research and debate. It is thus important to register what is known, what has been...

Distribution of glaciers in South America

A number of glaciers exist in the Andes, extending from the Equator to 55 S on the western side of South America. They are in the forms of small hanging or cirque glaciers, valley glaciers, ice caps and vast ice fields. In terms of glacier area, about 65 of the total is made up by two separate icefields in Patagonia (45 -53 S), with the rest located mostly at high altitudes in the Andes from 10 N to 45 S (Williams & Ferrigno, 1998), and in Tierra del Fuego and other small islands in southern...

Continuum damage model

Continuum damage mechanics describes the deterioration of material due to a progressive increase of damage (damage means Figure 62.2 Simulation of crevasse formations in the west face hanging glacier of the Eiger, Switzerland. According to Pralong et al. (2003), the damage is assumed to be isotropic. The crevasses appear in the model as concentration of damage. The dark grey colour represents ice without microcracks (D 0). Light grey corresponds to broken ice (D 1), i.e., ice with a very high...

Fabric and flow

The effects of anisotropy on deformation are complex. One way to represent fabric is through a cone angle, where the cone angle goes from a 0 for all crystals aligned, to a 90 for isotropic ice. In general, stronger anisotropy (smaller cone angle) makes the ice softer in shear parallel to the basal planes, and stiffer in compression normal to the basal planes (think of a deck of cards), as shown in Fig. 61.2. It has been a common practice to account for the effects of anisotropy with scalar...

Enhancement factor in the LGM ice

Analyses of the deformation behaviour of polar ice clearly show that ice deposited during the Last Glacial Maximum (LGM) deforms more readily than Holocene ice (cf. reviews of Budd & Jacka, 1989 Paterson, 1991). The enhanced flow is believed to be due to the high concentration of solid impurities (Dahl-Jensen, 1985 Fisher & Koerner, 1986 Dahl-Jensen & Gundestrup, 1987). Data on the concentration of solid impurities in Holocene and LGM ice in the Antarctic and Greenland ice sheets are...

Changes in glacier length and icethickness during the past 50 yr

Changes in frontal positions and surface areas of outlet glaciers during the past 50yr were clarified by analysing satellite data (Landsat, Spot, and others), aerial photographs and topographic maps with field survey data (Aniya et al., 1992, 1997). Variations Figure 46.1 The Northern Patagonia Icefield (NPI) and its outlet glaciers (Aniya, 1988 Naruse et al., 1995). Reproduced by permission of the International Glaciological Society. Figure 46.1 The Northern Patagonia Icefield (NPI) and its...

Phosphorus in the snowpack

Dissolved forms of P are present in snowpacks of the Arctic this paper , the European Alps Tockner et al., 2002 , and the Himalayas Mayewski et al., 1984 Table 17.1 . Mayewski et al.'s 1984 study of a firn ice core suggests that P adsorption onto wind blown Fe-oxide particles might be a major precursor to P deposition at high-altitude continental sites. Otherwise, winter Table 17.1 Published phosphorus data for glacier basins. Average concentrations are given as gPL-1 for snow and runoff, and...