Readings

Question 1

Benn and Lehmkuhl 2000

Answer 1

Mass balance characteristics of glaciers in high-mountain environments complicate the relationship between ELAs and precipitation/air T
- avalanches/debris cover/topographic effects

ELA = position where over one year accumulation exactly balanced by ablation

Former ELAs = powerful method of quantifying palaeoclimates if e.g. other evidence is lacking

Question 2

Maisch 1995

Answer 2

Knowledge of glacier ELAs = palaeoclimatic data = predict future glacier response to climatic change

Question 3

Braithwaite 2002

Answer 3

Study of glacier mass balance 1946-1995 for 246 glaciers

Western Europe, North America and USSR

Biased towards wetter conditions

Direct stakes/snowpits method - recognised integration with geodetic/remote sensing would be more useful

Glaciers mainly gain mass (accumulation) as snow and mostly lose mass (ablation) by melting and iceberg calving

Local importance of glaciers to societies e.g. HEP or irrigation, or hazards

Question 4

Hock 2005

Answer 4

Modelling ice/snow melt important for issues e.g. water resource management, avalanche forecasting, glacier dynamics, hydrology/hydrochemistry, climate change

Modelling of turbulent fluxes and spatial/temporal variability in albedo = major uncertainties

Typical characteristics of glacier runoff = melt-induced diurnal cyclicality and concentration of annual flow during melt season

High temporal resolution essential for predicting peak flows in glacierised/snow-covered basins
High spatial resolution needed to account for large spatial heterogeneity w.r.t. ice/snow melt due to topography

Energy balance melt models more properly describe physical processes at glacier surface than temperature-index methods but require much more data

Further research to focus on links between different energy fluxes and synoptic weather pattern, and investigate potential for operational use in melt forecasting

Question 5

Jacob et al 2012

Answer 5

Glaciers/ice caps = important contributors to global mean SLR

Monthly GRACE method from Jan 2003-Dec 2010 for inversion of mass change over all ice-covered regions larger than 100km2

Results:

• GIC excluding Greenland and Antarctica peripheral glaciers and ice caps contributed 0.41+/-0.08mm/yr
• with G/A = 1.06+/-0.19mm/yr

Total agreed with independent estimates within error bars

Question 6

Nakawo and Young 1982

Answer 6

Ablation under a debris layer could be estimated from meteorological variables if surface T data (estimation of thermal resistance) of layer is available

Generally good method but surface roughness (large at stagnant areas near glacier terminus) should be noted with care

Question 7

Fountain and Walder 1998

Answer 7

Understanding water movement through glacier is fundamental to e.g. glacier dynamics/glacier-induced floods/runoff predictions

Firn temporarily stores water and smooths out variations in supply rate (accumulation zone)

In ablation zone, flux of water depends directly on rate of surface melt/rainfall = varies greatly

Describes water flow in a “nonarborescent network”, poorly connected to a well-connected aborescent channel network

Stored water may be released abruptly and catastrophically in the form of outburst floods

Episodic surging of some glaciers due to temporal changes in subglacial hydrology

Near-surface, englacial and subglacial water flow are coupled

Hydrological system components = snow, firn, surface streams; crevasses, moulins and other englacial passages; and basal channels, cavities and till

Question 8

Gulley and Benn 2009

Answer 8

Mapped 8.25km of passage in 27 distinct englacial conduits in temperate, polythermal, cold-based and debris-covered glaciers between 2005 and 2009 using speleological techniques

In all cases = single unbranching conduit

Morphologies intimately linked to orientation of glacier’s principal stresses or presence of pre-existing lines of high hydraulic conductivity

Shreve-type englacial drainage systems do not exist - englacial conduits can only penetrate through thick ice to recharge the bed where supra glacial bodies intersect/advect through zones of acceleration

Question 9

Nienow et al 1998

Answer 9

Used dye tracing techniques for glacier-wide changes in englacial/subglacial system of Haut Glacier d’Arolla 1990-1991

Removal of snow (high albedo and water storage) increases runoff into moulins

System of major, hydraulically efficient channels expands up glacier (retreating snowline), replacing inefficient distributed drainage system over course of season

Three factors control evolution of subglacial drainage over summer melt season (1) weather conditions (2) pattern of snowline retreat (3) distribution of moulins and crevasses

Uncrevassed glaciers with a surface layer permanently below melting point, surface melt may never reach glacier bed

Question 10

Sorg et al 2012

Answer 10

Focus in the Tien Shan, Central Asia
Regions with little summer precipitation = glaciers important role in streamflow regimes

At first shrinking glaciers supply increased glacial runoff but ultimately will result in decrease

= ecological problems and political instability

Question 11

Nienow et al 2015

Answer 11

Greenland Ice Sheet (GIS)

Ice motion across land-terminating region in west gIS slower in 2007-2014 compared with 1985-1994 despite 50% increase in meltwater production

i.e. these sectors of the ice sheet are more resilient to the dynamic impacts on enhanced meltwater production than previously though

Question 12

Zwally et al 2002

Answer 12

Greenland Ice Sheet

Glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface

Floating glacier tongues and Antarctic ice shelves respond quickly. in contrast to the flow of grounded ice

Question 13

Alley et al 1986

Answer 13

WAIS

• radar sounding = wet bed
• most ice-stream velocity arises at bed
• deformation within the till is the primary mechanism by which the ice stream moves

Question 14

Bamber et al 2000

Answer 14

90% of AIS is drained through ice-streams

Question 15

Engelhardt and Kamb (1998)

Answer 15

Stake method used to measure basal sliding in Ice Stream B, WAIS

Basal sliding rate is 83% of total motion
- may include contribution from shear deformation of till

Mechanism of rapid ice stream motion concentrated at/near top of till rather than spread throughout thickness of till layer

Question 16

Harrison and Post (2003)

Answer 16

Till deformation processes dominate glacier motion in quiescence

Climate and weather affect surge initiation, termination and magnitude

Non-random geographic distribution of surge-type glaciers but poorly understood - would be useful for constraints on mechanism of surging

Distributed systems exist seasonally under parts of Variegated Glacier during quiescent phase and discrete system below surge front during surge

Hypothesis for winter initiation of surges = presence of englacial water trapped late in melt season

Question 17

Kamb et al 1985

Answer 17

Surging-type glaciers speed up for relatively short time to flow rates as much as a hundred times the normal rate then drops back to normal flow state

1982-1983 Variegated Glacier surge caused by build up of high water pressure in basal passageway system

Question 18

Sevestre and Benn 2015

Answer 18

Highest densities of surge-type glaciers occur within an optimal climatic envelope with T and precipitation thresholds
= intermediate conditions

Two superclusters:
1) Arctic Ring

2) High Mountain Asia

Question 19

Stokes et al 2007

Answer 19

Sticky spots = localised patches of basal friction

4 primary causes of stickiness
1) bedrock bumps

2) till-free areas
3) areas of ‘strong’ (well-drained) till
4) freeze-on of subglacial meltwater

Act together or in isolation

Question 20

Alley et al 2005

Answer 20

Future SL rise related to continuing build up of atmospheric GHG concentrations

Freshwater fluxes from GIS and AIS may affect oceanic circulation, contributing to climate change

Heavy concentration of population live along coastlines = substantial societal and economic impacts

• coastal erosion
• increased susceptibility to storm surges
• groundwater contamination by salt intrusion

EAIS actually likely to grow (increased accumulation if warmings don’t exceed 5’C

Warming has increased mass loss from coastal areas more than it has increased mass gain from snowfall in cold central regions

Question 21

Benn et al 2007a

Answer 21

Calving rates increase dramatically in response to increases in velocity +/ retreat of the glacier margin

Calving and related dynamic processes poorly represented in current ice sheet models

1st order control = strain rate determining location and depth of surface crevasses

Large icebergs have a cooling effect on oceans through latent and sensible heat exchanges

Question 22

Joughin and Alley 2011

Answer 22

Much of the grounded ice in W Antartica lies on a bed that deepens inland and extents well below SL = thinning could ultimately float much of the ice sheet’s interior

Mass loss for WAIS ranges from 100 to 200Gt/yr, dominated from draining of Amundsen Sea sector

Collapse of the marine ice sheet in West Antarctica would raise SL by more than 3m over the course of several centuries or less

Question 23

Paolo and Padman 2015

Answer 23

West Antarctic losses increased by 70% in the last decade and earlier volume gain by EAIS ceased

In the Amundsen and Bellingshausen regions some ice shelves have lost up to 18% of their thickness in less than two decades

Question 24

Shepherd et al 2001

Answer 24

The (grounded) Pine Island Glacier transports 69 km3 of ice each year from ~10% of WAIS
Retreat may accelerate ice discharge from WAIS interior

Question 25

Nick et al 2009

Answer 25

Numerical ice-flow model for Helheim Glacier, one of Greenland’s largest outlet glaciers
Ice acceleration, thinning and retreat begins at calving terminus then propagates upstream through dynamic coupling along glacier - likely caused by basal lubrication through surface melt propagating to glacier bed

Tidewater outlet glaciers adjust extremely rapidly to changing boundary conditions at the calving terminus

Question 26

Pattyn 2018

Answer 26

Shallow Ice Approximation = ice deformation is due to shearing close to bed

MISI is based on observation that since ice flux increases with ice thickness, the location of a grounding line on a bed sloping inwards is unstable

Increase in computational efficiency enabling high spatial resolution modelling, high resolution datasets of bedrock topography and surface velocity, longer time series on ice sheet changes and the improved initialisation of ice sheet models = move towards robust predictions on decadal time scales, hindcastidg and potentially reanalysis

Question 27

Boulton 1974

Answer 27

Focus on three important subglacial erosional processes:

1) abrasion of bed by debris embedded in glacier sole
2) crushing of subglacial bedrock due to pressure fluctuation produced by glacier flow over bedrock hummock
3) removal by plucking by above

Question 28

Glasser and Bennett 2004

Answer 28

Glacial erosion involves removal and transport of bedrock and/or sediment by glacial quarrying, glacial abrasion and glacial meltwater

All landforms of glacial erosion provide evidence for the release of subglacial meltwater and the existence of warm-based ice

Landforms dominated by glacial abrasion are created when there is no ice-bed separation

Exposure dating techniques including cosmogenic isotope dating of bedrock surface = important for increasing understand of age/chronological significance of landforms

Question 29

Gordon 1981

Answer 29

Topographic form of areal scouring relates closely to bedrock structure (strike/dip of bedding planes, layering, joins, structural weaknesses)

Asymmetric roche moutonnée-type forms generally exist in sympathy of bedrock structure regardless of ice movement direction

Question 30

Schweizer and Iken 1992

Answer 30

Basal ice is debris-laden so friction exists between the substratum and rock particles embedded in the basal ice

Question 31

Briner et al 2003

Answer 31

Relative weathering of landscape surfaces has often been used to define the former location of landscape surfaces - highly weathered landscapes took a long time to form and thus must have escaped RECENT glaciation

BUT presence of pseudo-erratics on high-elevation weathered surfaces (Arctic Canada) = non erosive ice covered these

Question 32

Jamieson et al 2008

Answer 32

Ice sheet model (GLIMMER) with erosion component, modelling evolution of landscapes under ice sheets over long time scales in hypothetical conditions

Results: bed morphology exerts a greater influence under low basal slip conditions because ice cannot respond readily to thermal instabilities

Question 33

Bradwell et al 2008

Answer 33

Role of ice streams in landscape evolution

Ullapool area NW Scotland shows large-scale megagrooves and streamlined bedrock forms in a well-defined ~20km wide zone interpreted as signature of fast-flowing tributary that once fed a palaeo-ice stream

Elongation ratios <5:1 and >5:1 represent transition from potentially cold-based slow flow to warm-based fast flow

Rapid spatial bedroom evolution reflects an increase in subglacial erosive power that may be diagnostic of paleo-ice sheet thermal boundaries (i.e. cold to warm based)

Question 34

Evans et al 2006

Answer 34

Reference for definitions of glacitectonite, subglacial traction till, melt-out till

Deformation, flow, sliding, lodgement and ploughing co-exist at the base of temperate glacier ice and act to mobilise, transport and deposit sediment

Till/till sequences may contain a superimposed signature of former transportation/deposition at the ice-bed interface

Glacitectonite = rock/sediment deformed by subglacial shearing/deformation but retains some of structural characteristics of parent material

Subglacial traction till = sediment deposited by a glacier sole either sliding over +/ deforming its bed, with sediment directly released from ice by pressure melting +/liberated from substrate then disaggregated and completely/largely homogenised by shearing

Melt-out till = sediment released by melting of stagnant/slowly moving debris-rich glacier ice and directly deposited without subsequent transport or deformation

Question 35

Ò Cofaigh and Dowdeswell 2001

Answer 35

Laminated glacimarine sediments form by e.g. suspension settling from turbid overflow plumes, turbidity current deposition and contour current activity

Subglacial deformation of pre-existing sediments may also produce laminated deposits in the forms of glacitectonite/deformation till
= discrimination important for reconstruction

Question 36

Boulton 1996a

Answer 36

Flux of glacially transported sediment is related to ice flux = inner zone of ice sheet predominantly one of erosion and outer zone of deposition

Extensive subglacial aquifers drain the glacier bed and inhibit deformation processes = reduce rates of erosion/deposition

Fine-grained sediments on glacier bed are eroded/transported more readily = contribute preferentially to till

Question 37

Clark (2010)

Answer 37

Subglacial bedforms are emergent phenomena arising from self-organisation in the coupled flow of ice, sediment and water; patterning of bedforms due to naturally arising flow instability

Subglacial bedforms have recently been discovered beneath the Antarctic Ice Sheet

Rogen moraines should be called Subglacial Ribs because they are not actually moraines

Drumlins form by coupled interaction between ice flow and flow of soft underlying substrate (instability theory)

Scepticism of instability theory: combat by thinking about smoothing surface of dry sand on a beach - ripples will appear = analogous

Note: instability theory cannot make prediction of internal structures and sediment properties, it is a simple conceptual model with potential

Question 38

Stokes et al 2013

Answer 38

Pro instability theory; first paper to assess if compatibility with sediments found within drumlins

Results: one would expect a diverse range of constituents depending on:

1) inheritance of sediments that pre-date drumlin formation
2) duration/variability of ice flow
3) balance between erosion and deposition at the ice-bed interface

So IS compatible

Question 39

Benn 1989

Answer 39

Focus in N Scotland during LLS

Moraine asymmetry correlated with distribution of free faces in valleys

Within valley asymmetry of moraines is interpreted as one aspect of long-term asymmetric landscape evolution

Question 40

Evans 2009

Answer 40

Controlled moraines = supra glacial debris concentrations that become hummocky moraine upon deicing and possess clear linearity due to inheritance of former pattern of debris-rich folia in parent ice

Question 41

Gorrell and Shaw 1991

Answer 41

Sediment in an esker in Lanark, Ontario, Canada

Mainly coarse grained, varies from boulders with fine-sand matrix (max discharge) to diamicton (low discharge)

Small scale fining upwards sequence in fans and beads indicates deposition by large no. of flow events

Fan and bead environments are areas of ice-bed decoupling, at least during high flow conditions

Question 42

Carlson et al 2005

Answer 42

Kettle Moraine in Wisconsin = single, ~3km wide hummocky ridge for ~90% of its 200km extent with double ridge at beginning - due to extensive underlying ice with thin debris cover between supraglacial fluvial deposits at the time of deposition

Sedimentary architecture of glacial landforms helps to explain genesis and provide better understanding of the pale-glaciology of ice sheets

Question 43

Livingstone et al 2010

Answer 43

Brampton kame belt in Cumbria = one of largest glaciofluvial complexes within the UK (over 44km2)

Demonstrates development of complex glacier karst and process of topographic inversion:

• kettle holes
• eskers
• flat-topped hills (ice-walled lake plains)

Represents major depositional episode during advanced stages of recession of Late Devensian BIIS in Solway Lowlands = critical for constructing deglaciation style

Question 44

Evans and Twigg 2002

Answer 44

Active temperate landsystem in Bredamerkurjökull and Fjallsjökull, Iceland

1) areas of extensive, low amplitude marginal dump, push and squeeze moraines often recording annual recession of active ice
2) incised and terraced glacifluvial forms e.g. recessional ice-contact fans and hochsandur fans/eskers/pitted outwash
3) subglacial landforms assemblages; flutes/drumlins/overridden push moraines between ice marginal glacifluvial depo-centres

Lack of supraglacial sediment in active temperate glaciers precludes the widespread development of chaotic hummocky moraine

Subtle surge signatures present = illustrates danger of employing landform-sediment associations from restricted study areas for entire glaciated terrain

Question 45

Evans et al 2016

Answer 45

Snaefelljokull volcano-centred ice cap landsystem, W Iceland

Rapidly thinning and receding from its historical Little Ice Age maximum limit

Profound effects on generation of freshwater for surrounding communities

Provides landsystem signature for independent volcano-centred ice caps

• outer zone of ice-cored moraine
• in front = locally developed set of proglacially thrust pumice deposits
• ice-cored moraine passes proximally into bouldery drift and push moraine
• then large area of flutings/glacially abraded rock (indicative of temperate basal ice conditions)

This landsystem is an exemplar relevant specifically to Icelandic landscape but also more widely relevant to glaciered volcanic terrains globally

Question 46

Carr et al 2013

Answer 46

Marine-terminating outlet glaciers can undergo dramatic dynamic change at annual timescales

3 primary climatic/oceanic controls on outlet glacier dynamics;

1) air T
2) ocean T
3) sea-ice concentrations

Uncertainties on controls on outlet glacier dynamics:

• spatial variation in relative importance of each factor
• contribution of glacier-specific factors to glacier dynamics
• limitations in accurate modelling

There is a danger in extrapolating rates of mass loss from a small sample of study glaciers

Arctic warming expected 4-7’C by 2100

Greenland Ie Sheet contributed 0.46mm/a to SL rise between 2000 and 2008

Marine-terminating outlet glacier = channel of fast-moving ice that drains an ice cap or ice sheet and terminates in the ocean at either a floating or grounded margin (Benn and Evans 2010)

Reverse bed slopes pose instability

Meltwater-enhanced basal sliding contributes to marine-terminating outlet glacier velocities at seasonal scales but capacity of subglacial hydrological system to evolve limits effect on inter annual behaviour