References Flashcards
(125 cards)
1
Q
ELA = where over one year accumulation of snow = ablation
A
Benn and Lehmkuhl 2000
2
Q
Former ELAs = powerful method of quantifying palaeoclimates if e.g. other evidence is lacking
A
Benn and Lehmkuhl 2000
3
Q
Knowledge of glacier ELAs = palaeoclimatic data = predict future glacier response to climatic change
A
Maisch 1995
4
Q
Mass balance characteristics of glaciers in high-mountain environments complicate the relationship between ELAs and precipitation/air T
- avalanches/debris cover/topographic effects
A
Benn and Lehmkuhl 2000
5
Q
Study of glacier mass balance 1946-1995 for 246 glaciers
Western Europe, North America and USSR
Biased towards wetter conditions
A
Braithwaite 2002
6
Q
Direct stakes/snowpits method - recognised integration with geodetic/remote sensing would be more useful
A
Braithwaite 2002
7
Q
Glaciers mainly gain mass (accumulation) as snow and mostly lose mass (ablation) by melting and iceberg calving
A
Braithwaite 2002
8
Q
Local importance of glaciers to societies e.g. HEP or irrigation, or hazards
A
Braithwaite 2002
9
Q
Modelling ice/snow melt important for issues e.g. water resource management, avalanche forecasting, glacier dynamics, hydrology/hydrochemistry, climate change
A
Hock 2005
10
Q
Modelling of turbulent fluxes and spatial/temporal variability in albedo = major uncertainties
A
Hock 2005
11
Q
Typical characteristics of glacier runoff = melt-induced diurnal cyclicality and concentration of annual flow during melt season
A
Hock 2005
12
Q
Modelling: 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
A
Hock 2005
13
Q
Energy balance melt models more properly describe physical processes at glacier surface than temperature-index methods but require much more data
A
Hock 2005
14
Q
Further research needed in modelling to focus on links between different energy fluxes and synoptic weather pattern, and investigate potential for operational use in melt forecasting
A
Hock 2005
15
Q
Glaciers/ice caps = important contributors to global mean SLR
A
Jacob et a 2012
16
Q
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
A
Jacob et al 2012
17
Q
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
A
Nakawo and Young 1982
18
Q
Understanding water movement through glacier is fundamental to e.g. glacier dynamics/glacier-induced floods/runoff predictions
A
Fountain and Walder 1998
19
Q
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
A
Fountain and Walder 1998
20
Q
Describes water flow in a “nonarborescent network”, poorly connected to a well-connected aborescent channel network
A
Fountain and Walder 1998
21
Q
Stored water may be released abruptly and catastrophically in the form of outburst floods
A
Fountain and Walder 1998
22
Q
Episodic surging of some glaciers due to temporal changes in subglacial hydrology
A
Fountain and Walder 1998
23
Q
Near-surface, englacial and subglacial water flow are coupled
A
Fountain and Walder 1998
24
Q
Hydrological system components = snow, firn, surface streams; crevasses, moulins and other englacial passages; and basal channels, cavities and till
A
Fountain and Walder 1998
25
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
Gulley and Benn 2009
26
Used dye tracing techniques for glacier-wide changes in englacial/subglacial system of Haut Glacier d'Arolla 1990-1991
Nienow et al 1998
27
Removal of snow (high albedo and water storage) increases runoff into moulins
Nienow et al 1998
28
Removal of snow (high albedo and water storage) increases runoff into moulins
Nienow et al 1998
29
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
Nienow et al 1998
30
Uncrevassed glaciers with a surface layer permanently below melting point, surface melt may never reach glacier bed
Nienow et al 1998
31
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
Sorg et al 2012
32
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
Nienow et al 2015
33
Glacial sliding is enhanced by rapid migration of surface meltwater to the ice-bedrock interface
Zwally et al 2002
34
Floating glacier tongues and Antarctic ice shelves respond quickly. in contrast to the flow of grounded ice
Zwally et al 2002
35
GIS grounded above SL and generally believed to respond gradually to climate warming
Zwally et al 2002
36
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
Alley et al 1986
37
90% of AIS is drained through ice-streams
Bamber et al 2000
38
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
Engelhardt and Kamb 1998
39
Mechanism of rapid ice stream motion concentrated at/near top of till rather than spread throughout thickness of till layer
Engelhardt and Kamb 1998
40
Climate and weather affect surge initiation, termination and magnitude
Harrison and Post 2003
41
Till deformation processes dominate glacier motion in quiescence
Harrison and Post 2003
42
Non-random geographic distribution of surge-type glaciers but poorly understood - would be useful for constraints on mechanism of surging
Harrison and Post 2003
43
Distributed systems exist seasonally under parts of Variegated Glacier during quiescent phase and discrete system below surge front during surge
Harrison and Post 2003
44
Hypothesis for winter initiation of surges = presence of englacial water trapped late in melt season
Harrison and Post 2003
45
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
Kamb et al 1985
46
1982-1983 Variegated Glacier surge caused by build up of high water pressure in basal passageway system
Kamb et al 1985
47
Highest densities of surge-type glaciers occur within an optimal climatic envelope with T and precipitation thresholds
= intermediate conditions
Sevestre and Benn 2015
48
Two superclusters of surging-type glaciers:
1) Arctic Ring
2) High Mountain Asia
Sevestre and Benn 2015
49
Sticky spots = localised patches of basal friction
Stokes et al 2007
50
4 primary causes of sticky spots
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
Stokes et al 2007
51
Future SL rise related to continuing build up of atmospheric GHG concentrations
Alley et al 2005
52
Freshwater fluxes from GIS and AIS may affect oceanic circulation, contributing to climate change
Alley et al 2005
53
Heavy concentration of population live along coastlines = substantial societal and economic impacts
- coastal erosion
- increased susceptibility to storm surges
- groundwater contamination by salt intrusion
Alley et al 2005
54
EAIS actually likely to grow (increased accumulation if warmings don't exceed 5'C
Alley et al 2005
55
Warming has increased mass loss from coastal areas more than it has increased mass gain from snowfall in cold central regions
Alley et al 2005
56
Calving rates increase dramatically in response to increases in velocity +/ retreat of the glacier margin
Benn et al 2007a
57
Calving and related dynamic processes poorly represented in current ice sheet models
Benn et al 2007a
58
1st order control on calving = strain rate determining location and depth of surface crevasses
Benn et al 2007a
59
Large icebergs have a cooling effect on oceans through latent and sensible heat exchanges
Benn et al 2007a
60
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
Joughin and Alley 2011
61
Mass loss for WAIS ranges from 100 to 200Gt/yr, dominated from draining of Amundsen Sea sector
Joughin and Alley 2011
62
Collapse of the marine ice sheet in West Antarctica would raise SL by more than 3m over the course of several centuries or less
Joughin and Alley 2011
63
West Antarctic losses increased by 70% in the last decade and earlier volume gain by EAIS ceasedP
Paolo and Padman 2015
64
Antarctica: In the Amundsen and Bellingshausen regions some ice shelves have lost up to 18% of their thickness in less than two decades
Paolo and Padman 2015
65
The (grounded) Pine Island Glacier transports 69 km3 of ice each year from ~10% of WAIS
Retreat may accelerate ice discharge from WAIS interior
Shepherd et al 2001
66
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
Nick et al 2009
67
Tidewater outlet glaciers adjust extremely rapidly to changing boundary conditions at the calving terminus
Nick et a 2009
68
Shallow Ice Approximation = ice deformation is due to shearing close to bed
Pattyn 2018
69
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
Pattyn 2018
70
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
Pattyn 2018
71
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
Boulton 1974
72
Glacial erosion involves removal and transport of bedrock and/or sediment by glacial quarrying, glacial abrasion and glacial meltwater
Glasser and Bennett 2004
73
All landforms of glacial erosion provide evidence for the release of subglacial meltwater and the existence of warm-based ice
Glasser and Bennett 2004
74
Landforms dominated by glacial abrasion are created when there is no ice-bed separation
Glasser and Bennett 2004
75
Exposure dating techniques including cosmogenic isotope dating of bedrock surface = important for increasing understand of age/chronological significance of landforms
Glasser and Bennett 2004
76
Topographic form of areal scouring relates closely to bedrock structure (strike/dip of bedding planes, layering, joins, structural weaknesses)
Gordon 1981
77
Asymmetric roche moutonnée-type forms generally exist in sympathy of bedrock structure regardless of ice movement direction
Gordon 1981
78
Basal ice is debris-laden so friction exists between the substratum and rock particles embedded in the basal ice
Schweizer and Iken 1992
79
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
Briner et al 2003
80
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
Jamieson et al 2008
81
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
Bradwell et al 2008
82
Elongation ratios <5:1 and >5:1 represent transition from potentially cold-based slow flow to warm-based fast flow
Bradwell et al 2008
83
Rapid spatial bedform evolution reflects an increase in subglacial erosive power that may be diagnostic of paleo-ice sheet thermal boundaries (i.e. cold to warm based)
Bradwell et al 2008
84
Reference for definitions of glacitectonite, subglacial traction till, melt-out till
Evans et al 2006
85
Deformation, flow, sliding, lodgement and ploughing co-exist at the base of temperate glacier ice and act to mobilise, transport and deposit sediment
Evans et al 2006
86
Till/till sequences may contain a superimposed signature of former transportation/deposition at the ice-bed interface
Evans et al 2006
87
Glacitectonite = rock/sediment deformed by subglacial shearing/deformation but retains some of structural characteristics of parent material
Evans et al 2006
88
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
Evans et al 2006
89
Melt-out till = sediment released by melting of stagnant/slowly moving debris-rich glacier ice and directly deposited without subsequent transport or deformation
Evans et al 2006
90
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
O Cofaigh and Dowdeswell 2001
91
Flux of glacially transported sediment is related to ice flux = inner zone of ice sheet predominantly one of erosion and outer zone of deposition
Boulton 1996a
92
Extensive subglacial aquifers drain the glacier bed and inhibit deformation processes = reduce rates of erosion/deposition
Boulton 1996a
93
Fine-grained sediments on glacier bed are eroded/transported more readily = contribute preferentially to till
Boulton 1996a
94
Subglacial bedrooms 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
Clark 2010
95
Subglacial bedforms have recently been discovered beneath the Antarctic Ice Sheet
Clark 2010
| King et al 2007
96
Rogen moraines should be called Subglacial Ribs because they are not actually moraines
Clark 2010
97
Drumlins form by coupled interaction between ice flow and flow of soft underlying substrate (instability theory)
Clark 2010
98
Scepticism of instability theory: combat by thinking about smoothing surface of dry sand on a beach - ripples will appear = analogous
Clark 2010
99
Note: instability theory cannot make prediction of internal structures and sediment properties, it is a simple conceptual model with potential
Clark 2010
100
Pro instability theory; first paper to assess if compatibility with sediments found within drumlins
Stokes et al 2013
101
Results: one would expect a diverse range of constituents in drumlins 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
= instability theory is compatible
Stokes et al 2013
102
Moraine asymmetry correlated with distribution of free faces in valleys
Benn 1989
103
Within valley asymmetry of moraines is interpreted as one aspect of long-term asymmetric landscape evolution
Benn 1989
104
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
Evans 2009
105
Sediment in an esker in Lanark, Ontario, Canada
Mainly coarse grained, varies from boulders with fine-sand matrix (max discharge) to diamicton (low discharge)
Gorrell and Shaw 1991
106
Small scale fining upwards sequence in fans and beads (eskers) indicates deposition by large no. of flow events
Gorrell and Shaw 1991
107
Fan and bead environments are areas of ice-bed decoupling, at least during high flow conditions (eskers)
Gorrell and Shaw 1991
108
Sedimentary architecture of glacial landforms helps to explain genesis and provide better understanding of the pale-glaciology of ice sheets
Carlson et al 2005
109
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
Carlson et al 2005
110
Brampton kame belt in Cumbria = one of largest glaciofluvial complexes within the UK (over 44km2)
Livingstone et al 2010
111
Represents major depositional episode during advanced stages of recession of Late Devensian BIIS in Solway Lowlands = critical for reconstructing deglaciation style
Livingstone et al 2010
112
Lack of supraglacial sediment in active temperate glaciers precludes the widespread development of chaotic hummocky moraine
Evans and Twigg 2002
113
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
Evans and Twigg 2002
114
Active temperate landsystem in Bredamerkurjökull and Fjallsjökull, Iceland
Subtle surge signatures present = illustrates danger of employing landform-sediment associations from restricted study areas for entire glaciated terrain
Evans and Twigg 2002
115
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
Evans et al 2016
116
Snaefelljokull volcano-centred ice cap landsystem, W Iceland
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
Evans et al 2016
117
Marine-terminating outlet glaciers can undergo dramatic dynamic change at annual timescales
Carr et al 2013
118
3 primary climatic/oceanic controls on outlet glacier dynamics;
1) air T
2) ocean T
3) sea-ice concentrations
Carr et al 2013
119
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
Carr et al 2013
120
There is a danger in extrapolating rates of mass loss from a small sample of study glaciers
Carr et al 2013
121
Arctic warming expected 4-7'C by 2100
Carr et al 2013
122
Greenland Ie Sheet contributed 0.46mm/a to SL rise between 2000 and 2008
Carr et al 2013; van den Broeke et al 2009
123
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)
Carr et al 2013
124
Reverse bed slopes pose instability
Carr et al 2013
125
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
Carr et al 2013
