Geophysical Research

Darrel A Swift

Department of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK At Haut Glacier d'Arolla, Switzerland (Fig. 3.1), suspended sediment transport during the 1998 melt season demonstrates the importance of subglacial drainage system morphology for basal sediment evacuation because it influences both the capacity of meltwater to transport basal sediment and the mechanisms by which sediment is accessed and entrained. Early in the melt season, surface runoff enters a...

Largescale erosional marks

Drumlin British Columbia

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...

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...

Deuterium excess in ice formed by water freezing

Deuterium Excess

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...

Glacial chemical weathering

Glacial 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...

The Lake Agassiz basin

Lake Agassiz Basin

During the first six millennia after the LGM, glacial meltwater and precipitation runoff west of the Michigan basin passed without interruption down the Mississippi River Valley, as the LIS margin retreated toward the northern limit of the Gulf of Mexico watershed. By 11.7ka (13,600cal.yr), the margin had retreated north of the continental divide, and had begun to impound water in proglacial lakes which drained south over the divide (Fig. 28.5a). Continued retreat of the ice margin expanded the...

Subglacial groundwater in past and modern environments

Sedimentary Basin

As ice sheets grow and expand over permeable rocks, groundwa-ter flow evolves from a subaerial, precipitation-fed system con- Figure 9.2 Modelled groundwater flow pattern under the margin of the Weichselian ice sheet at its maximum extent at the Main Stationary Line in Denmark (Bovbjerg). Large glaciotectonic folding was facilitated by high porewater pressure in the low-transmissivity bed, partly due to thin aquifers wedging out in the direction of groundwater flow. Note that the transition...

Glacier composition mechanics and dynamics

Department of the Environment and Heritage, Australian Antarctic Division, Channel Highway, Kingston, Tasmania, 7150, Australia The interrelations between the Earth's glaciers and global change (primarily climate change) are largely due to changes in the size and shape of the glaciers. The largest of these glaciers, by far, are the polar ice sheets of Antarctica and Greenland. Be that as it may, the temperate glaciers are important on time-scales

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...

Basic laws of groundwater flow through the subglacial sediment

Basic Groundwater Flow

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...

FDepartment of Geography University of Durham Science Site South Road Durham DH1 3LE UK

Since the concept of drumlin formation by glacifluvial processes was first proposed by Shaw (1983), a large number of papers have been published interpreting a wide range of subglacial landforms in North America as products of subglacial megafloods (e.g. Shaw & Kvill, 1984 Shaw et al., 1989, 2000 Shaw & Gilbert, 1990 Fisher & Shaw, 1992 Rains et al., 1993 Brennand et al., 1995 Sjogren & Rains, 1995 Shaw, 1996, 2002 Munro & Shaw, 1997 Beaney & Hicks, 2000 Beaney & Shaw, 2000...

Recent deuterium excess icecore studies

The Vostok ice-core has provided a great deal of information about environmental changes in the past 420,000yr (Petit et al., 1999). In a SD-S18O diagram, the ice samples are beautifully aligned on a regression straight line with a slope of 7.94. Vimeux et al. (1999, 2001) have interpreted Vostok deuterium excess variations as depending on fluctuations of the temperature of the oceanic moisture source only, by using a relationship between relative humidity of the air and sea-surface...

Lggecnrs Bp96 38402 Saint Martin dHeres Cedex France

The Russian station of Vostok was established in 1957 during the International Geophysical Year at the south geomagnetic pole by the Soviet Antarctic Expeditions. The site (78 28'S, 106 48'E) is 1500 km from the ocean, at an altitude of 3488 m a.s.l. with a continental climate and a mean annual temperature of -55 C. The station overlies the southern end of a giant subglacial lake, Lake Vostok. The total ice thickness is 3750 m, and the snow accumulation rate is only 2.2 cm water equivalent per...

The chicken or egg problem

The elegant glacier-centred hypothesis, regarded as a boon to the field of glaciology, was called into question, however, by the results of efforts to test two of its corollaries. If the hypothesis were correct, the IRD increases in both series should occur at the same time as, or slightly lead, the ocean-climate response, and synchronicity of discharges from different glaciers would be unlikely owing to the vagaries of internal glacier dynamics. Instead, it was found in some high-resolution...

Controls on North American runoff magnitude and routing

Laurentide Ice Sheet

Runoff from the melting Laurentide Ice Sheet (LIS) and precipitation, plus abrupt releases of stored water in proglacial lakes along the southern margin of the LIS, discharged at different times to the Gulf of Mexico, North Atlantic Ocean, western Arctic Ocean and finally to Hudson Bay. A primary control on the variability in runoff routing stems from the changing configuration of hydrological catchments and drainage basins during deglaciation, which developed by the combination of location of...

The landocean interface sensitivity of ocean thermohaline circulation to freshwater runoff

What Thermohaline Circulation

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...

Spatial variability

There has been a tendency to see glacial erosion as a uniform process that can be compared, for example, with fluvial erosion. One of the realizations from the use of remote sensing over the beds of former ice sheets is just how spatially variable glacial erosion is. There are now numerous accounts of surfaces, commonly marked by river valley networks, tors and blockfields, which have survived inundation by an ice sheet without significant modification, apparently as a result of cold-based...

Introduction

Laurentide Ice Sheet

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...

A brief history of changes in the concept of the LIS

By the 1890s a good deal of research had been carried out in the glaciated area of the USA and in southern Canada. State and Provincial Geological Surveys undertook much of this research. Of particular note were the long journeys (over several months) undertaken by Canadian geologists, often members of the Geological Survey of Canada. In retrospect the work of individuals such as Low, Tyrrell, Bell and others was amazing in its perception (Bell, 1884, 1898 Tyrell, 1898 Low, 1893 and see review...

Erosion by the LIS

In many ways our concept of glacial erosion is governed by data from present-day, often small, mountain glaciers (Hallet et al., 1996). Thus when considering glacial erosion these data usually are considered as more efficient per unit area than fluvial erosion. However, we need to consider present-day rates in the longer Quaternary context of the LIS. Thus a rate of 0.5mmyr-1 indicates the removal of 500 m of bedrock in 1 Myr or nearly 1500 m since the generally accepted date of Northern...

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...

Evidence of changes in icesheet geometry and abrupt changes in mass balance

If the LIS had been erosive at all points under its bed then the amount of information on past flow directions would be nonexistent. Far travelled glacial erratics (see above) would provide some information but these are not imprinted on the bed of the ice sheet, hence relative changes in flow regimes could not be ascertained. With the advent of LANDSAT and other highresolution imagery several research groups have developed procedures for mapping the relative ages of different flow directions...

Retreat of the LIS from the Last Glacial Maximum

The advent of radiocarbon dating rapidly resulted in compilations of data for the deglacial history of the LIS. This exercise was initiated in 1969 by the publication of two series of maps from different authors but with rather similar results (Bryson et al., 1969 Prest, 1969). These data were used in several publications dealing with LIS volume changes and patterns and causes of retreat (Paterson, 1972 Andrews, 1973). A major revision was undertaken in time for the INQUA meeting in Canada in...

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...

Palaeoice sheet volume and weathering zones of the Long Range Mountains

Felsenmeer Landform Manual Diagram

In eastern Canada, the extent of glaciation is not easily interpreted from a routine application of glacial geomorphology. This is Figure 89.1 Location of the two weathering zone type localities in western Newfoundland of Grant (1977) and the TCN sampling localities (numbers are last three digits of sample IDs in Table 89.1, erratic boulders in italics). Figure 89.1 Location of the two weathering zone type localities in western Newfoundland of Grant (1977) and the TCN sampling localities...

Surface ablation

Surface ablation is the removal of surface snow or ice from a site. It occurs through sublimation, melting and, on a local scale, wind-scouring. Surface melting is the dominant ablation mechanism for all global ice masses with the exception of the Antarctic Ice Sheet, where temperatures are too low to produce large-scale melting. Summertime surface melting occurs on all major Arctic and alpine icefields. Melting is limited in interior and northern regions of the Greenland Ice Sheet, but a...

Georg Kaser

Tropical Glaciology Group, Institute of Geography, Innrain 52, 6020 Innsbruck, Austria A glacier forms when the accumulation of ice exceeds its loss over a time span longer than a few years. The appropriate climatic conditions are driven by the general regional free atmosphere conditions but are also affected by the local topography (e.g. Oerlemans, 2001). A glacier's extent is determined not only by climate glacier-bed conditions also influence the glacier's geometry. Whereas in the highest...

The Great Lakes drainage basin

Rhizobitoxine Pathway

After 16.5 ka (19,700 cal. yr), the southern LIS margin receded into the basins of the southern Great Lakes (Erie Interstade) (Fig. 28.4a & b) (Barnett, 1992). For several hundred years the Ontario-Erie and Huron lobes of the LIS retreated enough to switch 0.038 Sv of drainage from the Gulf of Mexico to the North Atlantic Ocean via the Mohawk and Hudson valleys (Licciardi et al., 1999 Lewis et al., 1994) (Figs 28.2 & 28.4b, outlets C and D). (1 Sv 106m3 s-1, or about the present combined...

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,...

Institute for Marine and Atmospheric Research Utrecht Utrecht University PO Box 80005 3508 TA Utrecht The Netherlands

Over snow and ice, the surface mass balance determines whether the surface loses mass to or gains mass from the atmosphere. The mass balance is the sum of accumulation and ablation. In the case of dry snow surfaces, melt and runoff can be ignored, which means that ablation can take place only through sublimation and wind erosion. Surface sublimation represents the transport of water vapour directly from the snow surface into the atmosphere. Wind erosion occurs when winds are stronger than the...

School of Physical and Geographical Sciences Keele University Keele ST5 5BG UK

The study of glaciers has immense significance for understanding and predicting global environmental change. The planet's glaciers are major players in the unfolding drama of the changing environment, and provide a wealth of information about how climate and other components of the Earth system have changed in the past. Scientists from different fields have begun to come together in their common interest in glaciers and the Earth's changing environment, and to recognize the increasing...

Till on a rock bed

Jointed Bedrock

In cases when the rock is of low permeability compared with the till, the melt flux must be discharged through the till to the nearest low-pressure channel. Even tills in old, hard Shield areas, when in a non-dilatant state, tend to have hydraulic conductivities of the order of 10-6-10-8ms-1 (e.g. Engquist et al., 1978). For a basal melt rate of the order of 10-9ms-1, a till 1m thick with a conductivity of 10-7ms-1 would be able to discharge the winter melt towards a low pressure channel with a...

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...

Background the flow of modern ice sheets

Ice Sheet Dynamics

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...

Changes in glacier length and icethickness during the past 50 yr

Energy Profile For Acetylcholine

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...

Basal ice deformation

Above And Below Glacier

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...

William George Adam

School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK Many interpretations of glacial sediments to reconstruct the basal ice layers of former glaciers have focused upon melt-out tills and glacigenic sediment flows, relying on the preservation of diagnostic glacially derived structures (e.g. Lawson, 1979b Ham & Mickelson, 1994). This approach can be strengthened if the interpretation did not rely solely upon the preservation of diagnostic glacial...

Impacts of the seaice circulation

Except for areas of landfast ice near the coast, the Arctic ice pack is in near constant motion. The mean annual circulation has two major features, a clockwise motion in the Canada Basin known as the Beaufort Gyre, and a motion of ice from the Siberian coast, across the pole and through Fram Strait, known as the Transpolar Drift Stream (Fig. 23.3). Most of the ice that leaves the Arctic on an annual basis exits through the Fram Strait (between Spitzbergen and Greenland). This flux is primarily...

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...

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

Rogen Moraine

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...

Water source and drainage systems

Subglacial meltwater originates from a range of sources, mainly from melting of ice by geothermal heat trapped at the glacier sole and by the frictional heat caused by ice movement past the substratum. These two sources yield up to some 100 mmyr-1 of water. Close to the ice margin, in the area where englacial conduits extend to the bed, surface ablation water may reach the ice sole with recharge several orders of magnitude greater than the basal meltwater alone. It is difficult to estimate how...

Glacialisostatic adjustment and sealevel change around Greenland

Geophysics Gia Model

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...

Risk Involve In Glacimarine Environment

Since the early 1970s there has been a dramatic increase in the scope and sophistication of glacial sedimentology, to the extent that the discipline of today bears little resemblance to that of 30 yr ago. The intervening period has seen the introduction of a wide range of observational and analytical techniques which allow much more detailed characterization ofglacigenic sediments than was hitherto possible. Moreover, the same period has witnessed a deep shift in outlook among glacial...

An analysis of the AWSderived surface fluxes

For the year 2000, all components of the surface energy balance are calculated from the AWS data (Fig. 34.1). Daily mean incoming shortwave radiation shows a clear annual cycle. The day to day variation is due to clouds. In winter, reflected shortwave radiation almost equals incoming shortwave radiation owing to the high surface albedo, which drops in May when snow is starting to melt and ice appears at the surface. The mean annual albedo is 0.53. Incoming longwave radiation is generally less...

Continentalslope and oceanbasin morphology and sediments

The angle of the continental slope offshore of high-latitude shelves varies from 10 . The gradient of about 13,000km or 70 of Arctic continental margins was analysed by O'Grady & Syvitski (2002). They found that lower slope angles were associated with convergent modern and full-glacial ice flow and, by implication, with more rapid rates of sediment delivery (Dowdeswell & Siegert, 1999). Side-scan sonar and seismic-reflection surveys of Arctic and Antarctic continental slopes have shown that...

Results from Vostok

However, when interpreting palaeo-excess records there are even more ambiguities to consider than just evaporation conditions and their exact influence on the double isotopic composition. Currently Antarctic deep-ice drillings cover several glacial-interglacial cycles. The Vostok ice-core provides us with a deuterium excess record spanning now the past ca. 400,000yr (Vimeux et al., 1999, 2001, 2002). Fully interpreting this long-term record, Vimeux et al. (2002) came to an important...

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...

Interaction of the southern LIS and North Atlantic Ocean oscillations of the Mississippi Hudson valley routings

North Direction Schematic

Switches in runoff routing direction, early in deglaciation, between south to the Gulf of Mexico via the Mississippi River Figure 28.7 Schematic diagram of ocean-ice interaction and oscillatory switching of Mississippi runoff to and from Hudson River Valley (after Clark et al., 2001). See text for explanation. Figure 28.7 Schematic diagram of ocean-ice interaction and oscillatory switching of Mississippi runoff to and from Hudson River Valley (after Clark et al., 2001). See text for...

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...

List of contributors

Acu a Centro de Estudios Cient ficos, Valdivia, Chile. William George Adam School of Physical and Geographical Sciences, Keele University, Keele, Staffordshire ST5 5BG, UK. Richard B. Alley Department of Geosciences and Earth and Mineral Sciences EESI, The Pennsylvania State University, University Park, PA 16802, USA. Sridhar Anandakrishnan Department of Geosciences and Earth and Mineral Sciences EESI, The Pennsylvania State University, University Park, PA 16802, USA. Suzanne Prestrud...

Background to recent progress

The substantial progress that has been made in subsequent decades is well illustrated in the papers in this volume. One can recognize that progress has been stimulated by both technical developments that have increased the nature and areal coverage of data and the means to analyse them, as well as the emergence of the new theoretical structures of earth system science with its stress on interconnectedness. Remote sensing has opened up new horizons on a revolutionary scale. Whereas fieldworkers...

Environmental controls and glacier behaviour an overview

Glacier behaviour, and therefore the response of glaciers to environmental change, is fundamentally determined by an interdependent combination of climatic regime and the interaction of the glacier with its immediate geological and topographic environment. Climate controls glacier mass balance through its impact on rates, distributions and types of precipitation and ablation. This mass balance regime in turn is the fundamental ratecontrolling process for dynamics, because the rate of input and...

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...

H pgH dx ayox

Where the third term on the left-hand side represents basal traction and is often parameterized using a linear relation to slip velocity (MacAyeal, 1989). In both cases, similar expressions are used for the force balance in the y dimension and, in practice, the equations are solved by using Glen's flow law to substitute the relevant horizontal velocity components for the stress components. Models based around Equation (3) have relatively low computational demands because they are two...

British Antarctic Survey High Cross Madingley Rd Cambridge CB3 0ET UK

Estimating the bed topography and basal slipperiness indirectly through their effect on surface shape and surface velocity is an example of an inverse problem. If we put all available surface measurements into a vector y, denote the basal properties through x, and write the relationship between bed and surface as y f(x) where f is the forward model, the inverse problem is that of determining the conditional probability distribution function (PDF P(x y)) of a system state given the measurement...

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,...

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...

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...

LIAlike cycles in the Holocene

Holocene Bond Events

As the search for forcing mechanisms to explain glacial history on Holocene time-scales intensifies there is a need to ask are there Figure 21.7 Data from Iceland on Little Ice Age (LIA) time-scales. (A) Mann et al. (1999), (B) sea ice and S18O in B997-328, (C) Stykkisholmur winter and summer temperature trends, (D) Siglunes water column temperature and Stykkisholmur mean annual temperature (MAT). periodic LIA-like events within the Holocene (Bond et al., 1999, 2001), and are there recent...

British Geological Survey West Mains Road Edinburgh EH9 3LA UK

Since the advent of satellite imagery, geomorphologists have used remotely sensed images to gain a better understanding of large-scale landform assemblages. The main benefits of using satellite imagery are clear the large field of view and the range of display scales, both allowing a higher speed of coverage. Many features undetectable on aerial photographs at large scales become readily apparent on LANDSAT images when viewed at a scale of 1 100,000 or more. Unfortunately, few studies use both...

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...

Department of Geography University of Edinburgh Edinburgh EH8 9XP UK

Examining changes in past ice cover across Iceland is enlightening owing to the many feedbacks that are apparent between ice, atmosphere, ocean and the lithosphere. Unravelling this interaction presents a tough job but is important from three related perspectives 1 Iceland is influenced by an extreme maritime climate which yields ice-caps with large turnover and outlet glaciers that are both sensitive and responsive. Hence, changes in long-term North Atlantic circulation will have an immediate...

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...

Icefacies formation and types

Regelation

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...

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...

Rapid response to contemporary climate change

It can be argued that the majority of the Antarctic Ice Sheet may be uniquely insensitive to small changes in atmospheric climate change. This is because it is so large that the time-scale of the dynamic response is measured in 10 to hundreds of thousands of iecw 90 w 0 so'e we iecw 90 w 0 so'e we Figure 42.4 Long-term (> 30-yr) trends in mean annual temperature measured at meteorological stations around Antarctica. Note the absence of trend data from the sector 70 W to 170 E. (Reproduced...

Figure 651 Ice composition structure and deformation at the base of Suess Glacier in the Taylor Valley Antarctica

Boundinage Structure Photo

Fitzsimons, 1996 Fitzsimons et al., 1999 Lorrain et al., 1999 Sleewaegen et al., 2003). Holdsworth & Bull (1970) demonstrated that the effective bed of Meserve Glacier (basal temperature 18 C) occurred along the tops of boulders that protruded from the glacier bed into the basal ice. Holdsworth & Bull recorded a debris-rich amber basal ice layer up to 0.6 m thick and demonstrated that salts from the glacier substrate and or the amber ice extended up to 6 m above the glacier base. These...

Coldbased glaciation

Two major problems in ice-sheet reconstruction are how to interpret glaciated landscapes that show little or no direct evidence for glaciation and how to treat landscapes which contain old glacial landforms but little or no evidence for younger glacial events. It is now generally acknowledged that dry-bed conditions (ice sheet frozen to substrate) are the probable explanation for the inability of ice sheets to produce glacial lineations and for the preservation of older large- and small-scale...

Changing glaciers and their role in earth surface evolution187

37 Keynote introduction Changing glaciers and their role in earth surface evolution 188 David Sugden 38 Reconstruction of paleo-ice sheets inversion of their glacial geomorphological record 192 Johan Kleman, Clas H ttestrand, Arjen P. Stroeven, Krister N. Jansson, Hern n De Angelis and Ingmar Borgstr m 39 Reconstructing the pattern and style of deglaciation of Kola Peninsula, northeastern Fennoscandian Ice Sheet 199 Clas H ttestrand and Chris D. Clark 40 The Laurentide Ice Sheet a review of...

Glacier mass balance and the global glacier inventory GLIMS

The two methods discussed above for determining ice-sheet mass balance can be, and have been, used to determine the mass balance, not only of ice sheets, but also glaciers. Airborne laser altimetry was combined, for example, with cartographic maps, derived from aerial stereo photogrammetry from the 1950s, to estimate dh dt over a period as long as 40 yr for some 67 Alaskan glaciers (Arendt et al., 2002). The results suggested a mass wastage much higher than previous estimates, equivalent to...

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...

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...

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...

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...

Icefields and outlet glaciers in Patagonia

Two large ice-covered regions occur in Patagonia. The smaller one is called Hielo Patag nico Norte (Northern Patagonia Icefield NPI) and is about 100km in length and 50km wide, located around 47 S (Fig. 46.1). The larger one is called Hielo Patag nico Sur (Southern Patagonia Icefield SPI), which extends for about 350km from 48 20' to 51 30'S along 73 30'W (Fig. 46.2). The total surface areas of the NPI and the SPI were first estimated as 4400 km2 and 13,500km2 (Lliboutry, 1956), and were...

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,...

Ocean influences

A mean vertical profile of temperature and salinity over the Arctic Ocean reveals several features. There is a low salinity surface layer, with temperatures near the salinity-adjusted freezing point. Below this surface layer, extending to about 200-300 m depth, is a rapid increase in salinity. This is attended by an increase in temperature to maximum (and above-freezing) values at around 300-500m depth. Although temperature falls off at greater water depths, from about 400 m downward salinity...

Origin of precipitation moisture source temperature and deuterium excess in meteoric ice

Isotopic fractionation occurs at phase changes of water in the atmosphere. Two types of isotopic fractionations are involved. First, because the saturation vapour pressures of HDO and H218O water molecules are slightly lower than that of H216O, the condensed phase is enriched in heavy isotopes with respect to the vapour phase. During evaporation of sea water, the SD and S18O values of the vapour will be more negative than those of the liquid phase. This is an equilibrium fractionation....

Proglacial hydrology

The proglacial hydrology is relatively complex owing to several water inputs, an irregular topography and 200-300 m of per- Contours at 10 metre vertical Intervals (labelled at 50 metre vertical Intervals) 148 Heights In metres above sea level Figure 15.1 Map of the proglacial zone of Finsterwalderbreen, showing glacier terminus. (See www.blackwellpublishing.com knight for colour version.) mafrost. Main water inputs derive from snowmelt, rainfall and active layer melt. These accumulate in...

FEarth Science Program University of Calgary Calgary Alberta Canada

Hummock Figure

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...

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...

Relict landscapes

African Geophysical Images

The existence of well-preserved relict landscapes with early Weichselian eskers, frost shattered bedrock and the absence of erosional and depositional forms reflecting the flow of the late Weichselian ice sheet have been used by Kleman & H tterstrand (1999) to map areas where the late Weichselian ice sheet was frozen to its bed and where there was therefore no sliding and little or no erosion (Plate 2.1c see also Stroeven et al., this volume, Chapter 90). The fact that erosion can occur...

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...

Incorporation into models of icemass motion

Incorporation of basal motion explicitly into ice-sheet models generally is achieved by introducing a sliding term across those cells where basal temperature attains the pressure melting point according to Equation (9), using the local basal shear stress but Figure 67.5 Deformation profiles in glacier ice (a) above a basal zone of low traction corresponding to the location of a major melt-season basal channel and (b) above adjacent ice characterized by higher basal traction. (After Willis et...

Ploughmeter and dragometer

The ploughmeter (Fig. 76.4) is described in its current form in some detail by Fischer & Clarke (1994) who developed an earlier concept by Humphrey et al. (1993) for use at Trapridge Glacier. The core of the instrument is a ca. 1.5 m long and ca. 20 mm diameter steel rod, the lower end of which is machined into a conical tip for ease of insertion into the subglacial sediment. The rod is sheathed in a clear vinyl tube (internal diameter ca. 25 mm) beneath which strain gauges are bonded by...

Continentalshelf morphology and sediments

Bathymetry Glacier Debris Fanning

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...

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...

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...

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...

Groundwater flow dynamics under past ice sheets and preservation of old glacial groundwater

Numerical modelling shows that groundwater flow velocities and hydraulic heads in northwestern Europe, especially in the relatively shallow aquifers, were significantly higher under ice sheets than they are at present. For an area bordering the Baltic Sea in Germany, Piotrowski (1997b) estimated flow velocities in the upper aquifer under the last ice sheet as about 30 times higher than at present. Furthermore, a reversal of flow direction occurred. At present, the groundwater drains to the...

Coupled glacier and climate models

Glacier and ice sheet sensitivity experiments such as those described above highlight regions of the world that are most sensitive to expected changes in temperature or precipitation. More realistic, geographically and temporally explicit scenarios are required for quantitative forecasts of glacier and icefield response to climate change. Studies of this type require coupling of glacier and climate models, and have been carried out to assess the transient response of various ice masses to...

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...

Did all basal meltwater drain through the bed

Boulton & Dobbie (1993) suggested that areas in Holland, during the Saalian glaciation, had sufficient transmissivity to drain all meltwater from the ice sheet base. This inference was based on calculations with very low basal melting rates of 2-3mmyr-1, but claimed valid also in subsequent simulations with melting rates of 20mmyr-1 (Boulton et al., 1993). In a numerical model of groundwater flow under ice sheets of the last two glaciations along a transect from the ice divide in Scandinavia to...

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...

Ice dynamics

Besides being used for determining calving fluxes, velocities derived by SAR interferometry have been used to detect glacier surges (Joughin et al. 1996 Mohr et al., 1998), and to infer grounding-line positions and their migration. Rignot et al. (2001) report grounding-line retreat of most north and northeast Greenland floating glaciers between 1992 and 1996. The retreat rate varies from several hundred metres per year up to 1kmyr-1. Rignot et al. (2001) argue that the corresponding glacier...

Glacial debris release and moraine deposition

Exposure of debris-rich basal ice in many Canadian High Arctic subpolar glaciers during snout downwasting results in the formation of controlled moraine (Fig. 19.2). Preservation potential of these moraines is low, however, owing to sediment redistribution during melt-out. Hummocky till veneers interspersed with glacifluvial outwash occur on valley floors where piedmont glaciers have receded onto surrounding uplands, leaving buried glacier ice at lower elevations. Where debris accumulates by...

Glacier composition mechanics and dynamics283

56 Keynote introduction Glacier composition, mechanics and dynamics 284 T. H. Jacka 57 Manifestations of ice microphysical processes at the scale of whole ice sheets 290 K. M. Cuffey 58 Ice flow at low deviatoric stress Siple Dome, West Antarctica 300 Erin C. Pettit 59 Physical deformation modes of ice in glaciers and ice sheets 303 Paul Duval and Maurine Montagnat 60 Superplastic flow of ice relevant to glacier and ice-sheet mechanics 308 David L. Goldsby 61 Anisotropy and flow of ice 315 62...

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),...

Causes of variability of icefacies deformation rates

A range of laboratory studies have attempted to determine the effect of the physical presence of debris on ice rheology, by creating ice in the laboratory with embedded debris in carefully controlled conditions. These studies generally have found that the presence of debris decreases deformation rates, and that strain rates decrease with increasing debris-content (Fig. 63.4). For example, Hooke et al. (1972) found that the strain rate of ice decreased exponentially with the addition of debris...

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....