Climbing

Climbing Equipments

Shoes

http://en.wikipedia.org/wiki/Climbing_shoe

Harness

http://en.wikipedia.org/wiki/Climbing_harness

Carbiner

http://en.wikipedia.org/wiki/Carabiner

Climbing wall

http://en.wikipedia.org/wiki/Climbing_wall

SHORT & MEDIUM TERM GLACIER FLUCTUATION

Linkage between General Climate & Glacier snout behaviour



Factors controlling glacier response over time

Relaxation/ response time – time interval between change of input & the achievement of new equilibrium

Amplification factor – small change in mass balance initiate large change at the glacier terminus

Specific mass balance characteristics – damp down minor climatic oscillations

Steady state situation – glacier remain at zero for many years & glacier dimension remains constant

Glacier Morphology

Response to climate

Distance between snout & accumulation Area – contributes to fluctuations due to climate
Narrow valley glacier – more time to respond than ice cap

On Land – Glacier Responds by expanding/ withdrawing snout
Extension – more surface area exposed to ablation
Fjord – difficulty in achieving equilibrium, continue to advance until spread out & increase cross sectional area exposed to melting & calving

Mass Balance Changes
Minor oscillations – direct response to annual climate oscillations
Major advances/ retreats – indirect/ lagged, significant long term changes

Direct response – short term mass balance change
Negative mass balance – reflected in 1 season
Positive mass balance change – may not be reflected by several seasons
Climatically induced snout retreats – more rapidly than climatically induced snout advances



High Accumulation, Low Ablation – interrupts retreat
Glacier Activity – influences velocity of kinematic waves
Very active Glaciers (Western Side of New Zealand) – responds directly to climatic oscillations
Sluggish glaciers (eastern side) – greater time lag

Compute response tie of Glaciers (e.g. Berendon Glacier in British Columbia by Nye)

Glacier Length
Height of Glacier Surface above mean sea level
Slope of surface
Mass Balance data

Mathematical models – Assumes
- Climatic fluctuations are small
- Any effects caused by changes in the quantity of melt water at the base can be ignored
- Changes in the temperature of ice (and thus the relation of stress to strain rate) can be ignored

Glacier mass balance change – measureable
Predictable

Surge behaviour

Surge – snout advance
Have a cycle of activity
Not climatically induced

Prolonged storage of surplus mass – until critical stage of instability or threshold reached

Attainment of critical stage is predictable

Wavelength & amplitude of surge cycle – shorter for small valley glaciers

Variations over days & weeks – related to ablation rates & meltwater discharge

Short-lived advances interrupting overall period of retreat – rapid responses to minor climatic oscillations
Little ice Age – 1500 -1920

Alpine climatic fluctuations from
Records of vineyards
Fruit growing, settlement history
Cereal growing, ease of ocean travel aspect of individual dated settlement sites

Vegetation studies – pollen analysis, lichenometry, studies of changing tree-line altitude------information on climatic fluctuation

Archaelogical & pedological investigation – information on recent climatic fluctuations

Technique – radio – carbon dating

Indicator of severity of Icelandic climate – sea ice off Icelandic coasts

Radiometric dating, palynology, dendrochronology….lichnometric technique

Prediction of glacier Behaviour – numerical model experiments of Climap Project, NCAR project

Spatial Distribution of Glaciers

Current glacierization
Areal Extent of Glaciers

Flint: - Importance of knowledge of Glacier Volumns – appreciate the importance of glacierization

Glacier volume – by radio-echo sounding
Degree of Inundation of land surface by snow & ice
Degree of Glacierization – percentage of land surface covered at the end of Balance
Year,
Data Plotted on a grid instead of a map
Degree of relief by ice
- Morphological variable within a landscape system
- Index of the intensity or type of glacial or nival processes operating upon the bedrock base

Detailed movement of snow & ice thickness – radio echo sounding profile
Continuous data concerning ice surface altitude & form, ice thickness, sub-ice bedrock relief
Applied in Greenland, Arctic Canada & Antarctica

Factors influencing the current distribution of snow & ice
Precipitation
High Evaporation rate, low annual precipitation, negative net precipitation
High altitude west coast environment – extremely heavy precipitation
Glaciologically influence as precipitation in the form of rainfall – contributes little to glacier mass

Nivometric coefficient – index of snow effectiveness
- ratio of snowfall (in water equivalent) to total annual precipitation

Nivometric coefficient – > 1 low precipitation
less suitable for glacial growth suitable for prolonged glacial survival

Medium Nivometric coefficient – high precipitation
Marginal from point of view of glacierization

Nivometric coefficient < 1 – high precipitation

Temperature
Mean summer temperature
Relationship between regional temperature characteristics & glaciarization

Latitute
Ice cover zone
Frost rubble zone climatically contolled systems
Tundra Zone



Altitude
Independent parameter at regional & local scale. Fundamental control over climatic parameters & hence on glacier distribution
Altitudinal zonation of mountainous area
Glacial/ Nival
Sub nival
Alpine
Sub Alpine
Upto sea level in high laltitude
High altitude in low latitude

Relief
Surface relief
Breath of an individual summit determines whether or not a glacier can be supported
Glaciation level
Partsch – brucker method of defining this limit

Snow fence effect – jaggered mountain scenary in baffin island in trapping snow &
allowing cirque glacier to develop lower than normal altitudes
mass balance – position of snout
morphology of channel – precise location of channel

shape ratio: ratio of elevation to area – and over 600m
roughness index: geometric properties of surface
high dissected topography – inhibit glacierization

Aspect
Orientation of ground surface with respect to incoming solar radiation (local scale)
Little control at regional/ larger scales

Distance from nearest ocean
Independent variable – influencing
Regression analysis

Glacier Inertia
Ice caps & ice sheets – out of equilibrium with their climatic environment devoid of relationship between morphological parameters as altitude, aspect & relief













Regression graphs are used to pot relationships – eg . Between altitude of glaciations level for Norway & ocean distance – Chorlton & lister

Glacier Morphology

Ice dome - convex surface slope of ice dome

Thinner ice – steeper slope to flow
Thicker ice – lesser surface slope

On horizontal bed, h = -/2h.s
h. = 11m
s = horizontal distance from margin in metres

Ice sheet
















Valley glacier



Ice shelf















Dome of 10-50 km size
Precipitation increases with increasing altitude to summit
Dome of continental size
Increase of precipitation with altitude occurs only when near the periphery
Outlet glacier – peripheral zone of ice dome marked by radiating pattern of ice dome extending deyond dome margin within ice dome they occupies a depression & distinguished by a zone of rapidly moving ice bordered by crevasses ….ice stream

Longer glacier + gentler gradient
Greenland no mountain range, gentler gradient

Ice shelf
Models of developing principles of ice creep
Sheer cliff rising 30m above sea level
Flat surface

Accumulation
Flat upper surface
Land glaciers
Bottom freezing
Highest near the seaward edge & decreases inward

Ablation
Calving & bottom melting

Glaciers constrain by topography

Ice field
Level area of ice
Distinguished from the cap because no domelike shape
Difficult distinction between
Mountain icefield and non equilibrium ice cap
St. Elias Mountain Area, North America

Valley glaciers
Originates in icefield or cirque
Radiates from main massif, dendritic pattern simpler than rivers
Tributary glaciers joins main glacier

Hubbard glacier – 120km long
Usual size – 10-30km

Freed from constrained of valley forms piedmont lobes
Altitude high relative to size

Cirque glaciers
Accumulation from drifting snow, rigourous than larger adjacent glaciers
Plan shape of isolated cirque glacier favours strong convergent flow above EL & divergent flow below

Ice apron – thin masses of snow adhering to mountain sides
Ice fringes – bordering a coastline


Surface Ice Forms
Sastrugi – dunes of hard packed snow elongated in the direction of prevailing wind
Steeper Ice sheet Periphery

Crevasse
Surface feature related to glacier movement


Splaying crevasse


Chevron crevasse



Traverse crevasse




Life of crevasse is limited
Extensive crevassing – convex long profile
Foliation – banding in ice
Alternative layers of white bubbly ice & bluish ice

Glacier System

Input & Output

Mass Balance
Input/output relationships of ice firn, snow
Water equivalent (a amount of water instead of melted)

Accumulation
` Direct precipitation

Ablation
Surface melting
Basal & internal melting
Evaporation
Wind deflation
Calving

Mass Balance relationships

Season Spatial Variation Mass Balance Character
Autumn snow accumulation at Snow mass increasing
higher altitudes – ablation of Ice mass decreasing
ice continues at lower altitudes Total Mass constant

Winter Snow accumulates over whole Snow mass increasing
glacier, little ablation Ice mass Constant
Total mass increasing

Spring Snow Accumulating at Snow mass constant
higher altitudes. Ablation of Ice mass constant
winter snow at low altitudes total mass constant

Summer Little snow accumulation Snow mass decreasing
Except at high altitudes Ice mass decreasing
Ablation over much of glacier Total Mass Decreasing
(snow at higher altitude firn & ice
at lower altitude)

Difference between accumulation & ablution for a whole year – net balance

Balance year – interval between the time of minimum mass in one calendar year & time of minimum mass in the following year

Positive net balance – gain of ice & snow
Negative net balance – loss of ice & snow
Zero Net Balance- winter & summer balance are equal



Relationship to climate
Climate on ablation – melting
Adiative
Heat exchange with the air in contact with glacier

Efficacy of solar radiation on melting – albedo of glacier surface

Fresh snow – 0.6 – 0.9
Later season – 0.2 – 0.4

Heat exchange between air & glacier surface
Conduction of heat from air to ice (enhanced in windy conditions)
Condensation of water vapour on glacier surface results in release of latent heat

Rain =/= melting

Schytt – correlation between mass surface temperature & total ablation

Effect on glacier movement

Movement of glacier = F(input & output)

Characteristics
Input & output magnitude
Spatial distribution on a glacier

Energy input decreases – from maritime to continental climate
from temperate to high latitude

greater the amount of energy required - greater is mass loss in equilibrium line

distribution of total amounts of accumulation & ablation on a glacier also affects the discharge of ice

Glacier in humid area – more active than glaciers in dry area

Temperate - polar latitudes
Latitudinal decline in activity



Movement within a glacier

Continuous movement
Longitudinal dimension – maximum discharge at equilibrium line & decreases down glacier from it

Vertical velocity – accumulation zone, buries any stone above equilibrium line
Ablation zone, stone emerges due to ice melting

Nye: compressive flow – reduction in forward velocity
Extending flow – longitudinal stress more tensile than over burden pressure

Transverse direction
Channel slope – amount & nature of friction
Sheet flow – confined to any valley, base friction only
Stream flow – confined in rock valley

Channel – maximum flow at centre
Velocity reduction at margin

Velocity change with depth – not common

Periodic movements – f(long term, short term fluctuations of climate)
Research scope of glaciologists

Direct response
- Variations effect glaciers wholly
- Climatic detoriation, glaciers thickens (every part)
- Stable adjustment
- Thick or thin slightly in response to change
Until new equilibrium profile is reached


- Unstable adjustment
Initial change triggers charge which increases with time

Stable – extending flow
Unstable – comparing flow

Kinematic waves – means by which the effects of fluctuations is net mass balance are transmitted down the glacier
Bulge moves faster than ice on either side – amorainic rock would move ice faster than normal area

Surges – ice travels downglacier at speeds far above mormal
Consists of
- A wave of thickening ice subjected to compressive flow
- A zone of high velocity ice with intensely fracture ice behind the wave crest
- A zone of tension or extension where the ice is thinning

Slope graph following surge

Periodicity of surge

Causes
High velocity
Trigger mechanism

Variables affecting glacier movement
Independent variable – climate & nature of relief
Dependant variable – size & morphology of glacier

Independent variables
Geothermal environment
Permeability & geothermal heat eaffect glacier flow
Volumn & type of debris contained within glacier

Climate
High solid precipitation totals & high ablation values – rapid rate of flow
Initial high snow temperature, effect of warming by summer percolation of meltwater closer to mlting, creep processes are rapid
Warm ice flowing fast generates heat by deformation near base & by basal sliding
Regional relief & slope forms
Steepness of bedrock slope down affects velocity localised high velocity, icefall
Irregularities of bedrock floor
Whether glacier ice ends in land or calves in water

On land – snout thins/ thicks near snout, flow decreases near snout
On water – calving

Profile of glacier – its relationship to land

Dependant variables
Glacier morphology (Ahlaman)

GLACIER ENVIRONMENT: CONTROL

Kierman: controls of Glacial Environment

• Glacier Variables – ice temperature, glacier morphology, glacier consaint, glacier gradient, glacier movement & velocity, ice thickness, glacial processes
• Bedrock variables:- lithology, structure, orogenic & tectonic history, bedrock preparation, glacial sediment
• Topographic variables:- periglacial topography, contemporaneous topography, post glacial topography
• Temporal variables:- duration of glaciation, number of glacial stages

Source
Murray Gray: GeoDiversity Valuing & conserving Aboitic Nature

GLACIER ICE

Glacier Components

Ice Crystals

Air

Water

Rock Debris

ICE CYSTALS

Ice Crystal Characteristics

Weak & can easily be made to slip on planes parallel to basal plane

Water is a substance which is less dense when solid (ice)

International Association of Scientific Hydrology

- minimum 10 types of solid precipitation

Correlation between wind speed & snow Density

Wind speed = snow density

Rime Ice –

- formed when supercooled water droplets strike a cold solid object & freeze on impact

- whitish appearance because of entrapped air bubbles

- accumulates in cool, humid conditions on surface which are most exposed to wind, important in cool maritime glacial environment

Superimposed Ice

- formed when water comes in contact with cold glacer surface & freezes

- air temperature above or at freezing point

- ice source in polar continental areas like northern Canada & arctic Siberia

- water from rain or melting of previous wintrs snow cover

Transformation

Firn – snow which is survived a summer melt season & has begun the transformation to glacier ice

Density > 0.4 MG m-3

Temperature

Heat derived from

§ surface

§ base (geothermal heat Flux)

§ internal friction

Warm Ice Close to pressure melting point

Cold Ice Below pressure melting point

Pressure melting point- the temperature at which water freezes diminishes under additional pressure (@ 1 degree per 140 bars)

Cold Ice

Firn formed at temperature so low there is little or no surface melting in summer

Cold ice form is related to cooling of surface layers of a glacier by winter wind

Warm Ice

Formed whenever there is sufficient heat to rise the temperatures to pressure melting point

Basal Heat Sources raises temperature of basal ice

- Ice is thick

- Surface temperature is high

- Ice velocities are high

- Accumulation is high & moderate

Presence of Basal Ice at Pressure melting point

Water is present at the ice/rock interface

Ice movement Mechanisms

Time Lapse Photography – reality of glacier flow

Bucking of glacier ice (snot of storstrom glacier, droning Louise land Greenland)

Demonstration of glacier flow

Internal Deformation

Deforms in response to stresses setup within its ice mass by the force of gravity

Any point within the glacier subjected to uniaxial compressive stress as a result of overlying ice

- Hydrostatic pressure

- Shear stresses

Hydrostatic pressure – same in all directions related to weight of overlying ice

Shear Stress – related to weight of ice

Surface slope of glacier

t = p g h sin a

t = shear stress

p = density of ice

g = acceleration due to gravity

h = thickness of glacier

a = slope of upper surface

Creep

Deformation of ice in response to stress

Mutual displacement of ice crystals relative to each other

Glens flow law – applied to glaciers by Nye

E = A t^n

E = strain rate

A = constant f (Temperature)

T = effective shear stress

N = exponent with a mean value 3

Fracture

Ice creep cannot adjust sufficiently rapidly to the stresses within the ice & as a result the ice fractures & movement takes place along plane

Basal Sliding

Enhanced basal creep

Pressure melting

Slippage over a water layer

Enhanced basal creep

Glaciers flow over large obstacles

Boulder results in increased strain

Determines the direction of flow in ice

Pressure melting

Ice moves through series of bumps

Ice melts & freezes according to minor difference in pressure caused by obstacles

Regelation ice

Enhanced basal creep – efficient for large obstacles

Inefficient for small ones

Pressure melting – efficient for small obstacles

Slippage over a water layer

Role of other materials on glacier ice

Rock debris

Estimate 0.05% of total volumn of glacier ice varies to 8%

Sudden increase of glacier weight can increase flow rate of glacier locally

Air bubbles

Explodes with cracking sounds

Atmospheric debris

Dust & salts

Glaciers & Landscape

Glacial Studies – two dimensions

- Glacier Dynamics – Glaciology

- Glacier Form – Glacial Geomorphology

Glacier Systems

-systems approach

Input (Mass & Energy) Output (Mass & Energy)

Glacier

Water Vapour Water Ice Rock Detritus Heat

Precipitation Rock Detritus Gravity Solar Radiation Geothermal Heat

Two Subsystems –

- Accumulation

- Ablation

Equilibrium Line (Threshold)

Other Thresholds –

- Glacier Bedrock

- Glacier Atmosphere

Response time – glaciers experience a change of input

Lag before the response becomes discernible at snout

Glacier economics

Balance between rates of input, throughout output

Feedback mechanism

Negative feedback- effects of a change of input are damped down or eliminated

Positive feedback – change is exaggerated or propagated

Scale Awareness

Ideas of Tricart, 1965

Model examples (understanding schemes)

Ice Sheet or Ice Cap

Valley Glacier

Rate calculation of geomorphological process change

Rates of land surface change – focus of geomorphological research.

Problems faced

- In comprehend & compare different estimates and rates of change – reported in different forms or units

- Bias in examining areas with dynamic activity

- Scale, rate at one differential scale not be extrapolated at other spatial scale.

Glaciers & ice caps

Methods used for measuring glacial erosion

Present day glacialized region

- Use of artificial marks on rock surface later scraped by advancing ice

- Installation of plates to measure abrasion loss

- Measurement of the suspended, solutional & bedrock content of glacial meltwater streams and of the area of respective glacial basin

- The use of sediment cores from lake basins of known age which are fed by glacial meltwater

Pleistocene glaciation

- Reconstructions of periglacial or interglacial land surface

- Estimates of volume of glacial drift in a given region and its comparison with the area of the source region of that drift

Retreat of Valley Glaciers and Ice Sheets

Studies in the changes of snout positions from cartographic, photogrammetric & other data

Discovering the rates at which landscape change & the causes of these changes is a key current focus in geoscientific, environmental, ecological and archaeological research. The mechanisms are intricate involving many components – a complex of positive and negative feedback mechanisms

Erosive works achieved by glaciers

Climber geologist Bonney

- doubts about power of glacial process to achieve wholesale landform modification

- amount of materials transported by glacier as ground moraine exaggerated & much of it is swept as lateral torrents

- Appreciation of landscape based on travels

Gregory

- Opposed the idea of glaciers as effective erosive agents

- Studied nature & origin of fjords

Gardener & Jones

- Estimated the rates of denudation for raikot glacier in the Punjab Himalaya

- Achived by mapping and measuring the variable distribution & thickness of surface debris & sediment concentrations within the ice

- Calculated discharge values

Geographical Location

- Important control of the rate of erosion

- Characteristics that limit the power of glacial erosion – resistant litholigies, low relief frozen beds

- Enhance the power of glacial erosion – non resistant lithologies, proximity to former fast ice streams, thawed beds

Lithology – macroscopic physical characteristics of a rock

Erosion minimal under cold based ice at the centre of the cap because shear from ice flow is limited and ice is anchored to the underlying bedrock

Applachians – an area of active glacial erosion

O18 record from the ocean cores to deduce the duration of glaciation

West coastline of Norway – another area of active glacial erosion in Pleistocene

Application of a number of geological & geomorphological techniques

Sugden

Erosion style of an ice sheet closely related to basal thermal regime of the ice

Identified five zones

Sugden’s postulate = erosional style of ice sheet = F(basal thermal regime of ice)

Glacial abrasion

Moulded rock surfaces, grooves & striations together with large volumns of rock flours in the meltwater streams

Observation in european alps near chamonix & iceland by boulton

Attached rock & metal plates to bedrock beneath the Glacier D’Argentiere & breidamerkurjokull

Glacial Deposition

Rates of Glacial Movement

Movement types – move, advance retreat, build up wash away

Average rate: 3 – 300 m/a

Step icefalls: 1000 – 2000 m/a

Movement at lower velocities: internal deformation processes (e.g. in sluggish cold based glaciers)

High velocities – component added by basal sliding

Jakobshavan Isbrae outlet glacier in Greenland –

Flows at the rate of 7000 – 12000 m/a

Surging glaciers – periodic surges

Velocities 4000 – 7000 m/a (10 – 100 times faster than previous velocity)

Relationship between ablation & accumulation – rate of glacier flow

Glaciers with high impact of snowfall & relatively warn climate

More active than that of low snowfall & low temperatures

Retreat of valley glaciers & Ice sheets

Snout position studies obtained from cartographic, photogrammetric & other data

Glaciers provided some of the first unequivocal evidence of Quartarnary climatic change for their respond very readily changes in the rates of ablation & accumulation. Glaciers & ice caps have expanded & contracted with remarkable frequency during the multiple glacial & interglacial cycles of pleistocene

SOURCE:
The changing Earth - Rates of Geomorphological Processes, Andrew Goudie

SURGING GLACIAL SYSTEM

Landform-sediment assemblages of surging glacier margins in Iceland, Svalbard, USA and Canada

1982-83 surge of variegated glacier of Alaska

Thrust block & Push Moraines

Thrust block moraines – composite ridges & hill-hole pairs

Two ice-marginal settings

- Margins of surging glaciers
- Sub-polar glacier margin in permafrost region

Proglacial thrusting – rapid advance into proglacial sediments
(seasonally frozen, unfrozen & contain discontinuous permafrost)

Proglacially thrust unfrozen materials
Surge margins of Icelandic glacier Bruarjokull & Eyjabakkajokull

Thrust block Moraines – constructional feature produced by surging glacier, sufficient sediment available for glacitectonic thrusting, folding & stacking

Over ridden thrust block moraines

Ice moulded hills in the proglacial forelands of Bruarjokull & eyjabakkajokull – down ice of topographic depressions from which the hills were displaced by thrusting
Surface features – fluted/ Drumlinized
Internal structure – glacitectnized outwash or lake sediments, tops of which modified intoglacitectonite
Ice-moulded hills – overridden thrust block moraines
Thrust block moraine demarcates the former glacier margin during a surge
Prolonged period of modification by over-riding ice – thrust block moraines resemble cupola hills of Aber

Concertina Eskers

Sinuous Eskers and concertina plan-form eskers
(Knudsen) – Concertina eskers are produced by shortening of pre surge, sinuous eskers, deformed by extreme tectonic activity
Vertical thickening – concertina plan form

Crevasse – squeeze ridge

Bruarjokull & eyjabakkajokull, Iceland
Trapridge Glacier & donjek Glacier – in Yukon territory & from Svalbard
Tectonics experienced during surge – glacier is highly fractured & crevasses may extend to the glacier bed

Flutings

Forelands of many glaciers
Evidence of rapid advances over substantial distances foreland of Bruarjokull (regularly spaced parallel sided flutings)
Numerous boulders with short sediment prows/ flutes on their down-flow sides interpreted as ploughs/ incipent flutes produced by boulders embedded in glacier sole
Elongation of these flutes suggest, formed during a single flow event when basal water pressures & degree of ice-bed coupling remained shorter & much less uniform in long section
Flutings & crevasse squeezed ridges – aspect & subglacial geomorphology of surging glaciers

Thrusting/ squeezing.

Zone of thrusting in the snout, lifted from the bed thrusting in surging glaciers
Supraglacial sediments
Low relief hummock moraine comprising inter bedded sediment gravity flows & crudely bedded sediment sediments – small ridges, thrust intersected the bed

Hummocky moraine

Subsequent ice-stagnation of widespread & effective transportation of large volumns of material

Lowland surging glaciers – thrusting is dominant process in transporting large volumns of debris-rich stagnant ice preserved from a previous surge, producing thick sequences of debris rich & debris-covered ice in surging snout

Landform assemblage – Hummocky moraine
Kettle & kames Topography

Differential form of overridded thrust block moraine by extensive evidence of on going meltout of buried ice

Ice-cored outwash & glacilacustrine sediments

Variegated glacier surge – outbursts of supraglacial water

Landform model for surging glacier

Based on combination of observations from contemporary surging glacier margins & published literature
Geomorphic & sedimentological signature of surging

Geomorphology – 3 overlapping zones

· Outer Zone: of thrust block & push moraine
Weakly consolidated pre-surge sedimets
Structurally – major thrust block moraine restricted to topographic depression, large enough to collect sufficient sediment during the quiescent phases.
· Intermediate zone (zone B) – patchy hummocky moraine located on the down-glacier sides of topographic depression, dumped on ice proximal slopes of thrust block & push moraine.

SURGING GLACIER SYSTEM

Landform-sediment assemblages of surging glacier margins in Iceland, Svalbard, USA and Canada

1982 surge of Variegated Glacier of Alaska

Thrust Block and Push Moraine

Thrust Block moraines – composite ridges & hill hole pairs

Two ice-marginal settings

- Margins of surging glaciers

- Sub-polar glacier margins in permafrost terrain

Proglacial thrusting – rapid advance into proglacial sediments

(seasonally frozen, unfrozen or contain discontinuous permafrost)

Proglaciacially thrust unfrozen materal – surge margins of Icelandic Glacier (Bruarjokull & Eyjabakkajokull)

Thrust block moraines – constructional feature produced by surging glacier, sufficient sediment available for glacitectonic thrusting, folding and stacking

Over-ridden thrust block moraines

Ice-moulded hills in the proglacial forelands of bruarjokull and Eyjabakkajokul – downice of topographic depressions from which the hills were displaced by thrusting

Surface features – fluted/drumlinized

Internal structure – glacitectonized outwash or lake sediments, tops of which modified into glacitectonite

Ice-moulded hills – over-ridden thrust block moraines

Thrust block moraines demarcates the former glacier margin during a
surge

prolonged period of modification by over-riding ice – thrust block moraines resemble cupola hills of aber

Concertina Eskers

Sinuous eskers and concertina plan-form eskers

(Knudsen) – concertina eskers are produced by shortening of pre-surge sinuous eskers deformed by extreme tectonic activity & vertical thickening – concertina plan form

Crevasse-squeezed ridge

Bruarjokull & eyjabakkajokul, Iceland

Trapridge glacier & donjek Glacier – Yukon Territory & from Svalbard

Tectonics experienced during surge – glacier is highly fractured and crevasses may extend to the glacier bed

Flutings

- Forelands of many glaciers

- Evidence of rapid advances over substantial distances foreland of Bruarjokull (regularly spaced parallel-sided flutings)
- Numerous Boulders with short sediment prows/flutes on their downflow sides interpreted as ploughs/incipent flutes produced by boulders embedded in glacier ice
- Elongation of the flutes suggest, formed during a single flow event when the basal water pressures & degree of ice-bed coupling remained shorter & much less uniform in Section
- Flutings & crevasse squeezed ridges – aspect of subglacial geomorphology of surging glaciers

Thrusting & squeezing

Zone of thrusting in the snout, lifted from the bed, thrusting in surging glaciers, supraglacial sediment

Low-relief hummocky moraine comprising interbedded sediment gravity flows & crudely bedded stratified sediments

Small ridges, thrust intersected the bed

Hummocky moraine

Subsequent ice-stagnation of widespread & effective transportation of large volumns of material

Lowland surging glaciers – thrusting is dominant process in transporting large volumns of debris into englacial and supraglacial position

Successive surges – over-riding, overthrusting, incorporation of debris rich stagnant ice, preserved from a previous surge, producing thick sequences of debris rich & debris covered ice in surging snout

Landform assemblage

Hummocky moraine ridge

Kettle & kames topography

Differentiated from over-ridden thrust block moraine by extensive evidence of on-going meltout of buried ice

Ice cored outwash & glacilacustrine sediments

Variagated glacier surge – outbursts of supraglacial water

Landsystem model for surging glacier

Based on combination of observations from contemporary surging glacier margin & published literature

Geomorphic & sedimentological signature of glacier

Geomorphology – 3 overlapping zones

· Outer zone : of thrust block & push moraines weakly consolidated presurge sediments

Structurally – major thrust block moraine restricted to topographic depression large enough to collect sufficient sediment during the quiescent phases

· Intermediate Zone: patchy hummocky moraine located on the down-glacier sides of topographic depression, draped on ice proximal slopes of thrust block moraines & push moraines

Hummocky moraines – intensely glacitectonized fine grained stratified sediments & diamictions or poorly sorted gravels – products of thrusting, squeezing & bulldozing

· Inner Zone – subglacial deformation tills & low amplified flutings produced by sub-hole deformation during the surge

Crevasse-squeezed ridges, documenting the filling of basal crevasses, concertina eskers

Palimsets & outer surges (overridden moraines)

Proglacial outwash fans & streams (ice-cored collapsed outwash)

Ponded topographic depression on the foreland (collapsed lake

Plains)

GEOMORPHOLOGY ZONATION MAP OF EYJABAKKAJOKULL, ICELAND


CONCERTINA ESKER


CREVASE SQUEEZE RIDGE