Glaciated Landscapes Flashcards
1
Q
What is a glacier?
A
A land based ice mass that is thick enough to flow under its own weight.
2
Q
What is a a glaciated landscape?
A
Parts of the surface that have been shaped, at least by the action of glaciers.
3
Q
Characteristics of a valley glacier
A
- follow the course of the existing river valley.
- may be outlet glaciers from ice sheets.
- confined by valley sides.
- between 10-30km long.
4
Q
Characteristics of an ice sheet
A
- large accumulations of ice.
- 69% of the worlds ice.
- there are only two: Antarctica and Greenland.
- extend for more than 50000km2.
5
Q
Present day distribution of glaciers
A
- glaciers cover 10% of the earths surface.
- mainly in north and south poles.
6
Q
Past day distributions of glaciers
A
- glaciers reach as far south as 43 degrees north latitude.
- ice as far south as northers USA states.
- 30% of earths surface was glaciated 18000 years ago.
7
Q
Ice age definition
A
An extended period of time where the earth experienced a cycle of very cold phases interspaced with warmer phases.
8
Q
Glacial definition
A
A very cold phase where global temperatures dropped by approximately 5 degrees resulting in the spread of ice.
9
Q
Interglacial definition
A
Warm phase where temperatures increased to present level or above.
10
Q
Ablation zone
A
at lower altitudes where ablation>accumulation
11
Q
Accumulation zone
A
at higher altitudes where accumulation>ablation
12
Q
Equilibrium line
A
Separates the two zones and is where annual accumulation = annual ablation.
13
Q
The glacier mass balance
A
- the difference between the amount of snow and ice accumulation an the amount of ablation occurring in a glacier over a 1 year period.
Winter: positive glacial budget, glacier gets larger.
Summer: negative glacier budget, glacier gets smaller.
14
Q
Inputs into a glacial system
A
- snow
- glacial ice
- avalanches
- kinetic energy
- thermal energy
- GPE
15
Q
Processes of a glacial system
A
- accumulation
- ablation
- glacial movement
- diagenesis
- erosion
- weathering
16
Q
Outputs of a glacial system
A
- meltwater
- moraine
- deposition
- evaporation
- sublimation
17
Q
Types of energy in a glacial system
A
- gravitational potential
- thermal
- kinetic
18
Q
gravitational potential energy
A
the higher and the heavier the glacier, the more energy is stored.
19
Q
kinetic energy
A
the heavier the thing is and the faster it moves the more kinetic energy it has.
20
Q
thermal energy
A
the energy that comes from the movement of atoms and molecules in a substance.
21
Q
Formation of glacial ice
A
- fresh snowfall is low density because fresh snow consists of an open, feathery structure and low density of 0.05g/cm3.
- snow which as survived throughout the year is called neve or firn.
- each layer of snow causes air to be expelled and density to increase because of pressure melting and compaction.
- with depth and over time, glacial ice forms.
22
Q
Warm based glaciers
A
- high altitude areas
- areas of steep relief
- water is present through ice mass and acts as a lubricant allowing ice to move freely.
- heat generated by the pressure of ice creating meltwater which percolates into the bedrock.
- they have velocities of 20-200m per year but can reach speeds up to 1000m per year.
23
Q
Cold based glaciers
A
- found at high latitudes.
- low relief areas.
- ice remains frozen at the base.
- very little erosion occurs.
- may only advance a few metres in a year.
24
Q
Pressure melting point
A
temperature at which ice is on the verge of melting.
25
types of basal sliding
- slippage
- regelation
- substrate deformation
26
Slippage
- if the basal temp is at or above PMP, a thin film of meltwater exists between the ice and the valley floor so friction is reduced.
- meltwater can also come through the surface through moulins or crevasses on the surface of the glacier.
27
Regelation
- when the base of the ice meets a rock outcrop on the valley floor ice may flow around it.
- on the upvalley side of the obstruction, ice has higher pressure and will create higher temperatures.
- this causes the ice to deform and spread around the obstruction like a plastic.
- increased pressure causes ice to melt.
- this water might relocate and go down cracks in the rock or ice and refreeze where there is lower pressure.
28
Substrate deformation
- when meltwater is present beneath the ice it will seep into any sediment below the glacier.
- if the sediment becomes saturated, it acts as a lubricant and the ice will slide upon it.
- if the substrate is solid, it will not deform.
29
Types of internal deformation
- intergranular slip
- laminar flow
30
Intergranular slip
- overlying weight of ice can result in the individual ice crystals changing shape due to compaction.
- ice crystals become flattened and so slide over each other.
- this enables the ice to deform and flow like putty.
31
Laminar flow
- the steeper the slope, the faster the motion of gravity.
- it does not require the ice to melt and refreeze.
- the greater depth of ice can cause more deformation to occur as there is greater mass and more pressure.
- it doesnt usually occur in the upper layers of the glacier which tend to remain rigid.
- the movement of these layers is due to the movement of the ice below.
32
Extending flow
When ice moves over a steep slope it it unable to deform quickly enough so it fractures forming crevasses. the leading ice pulls away from the ice behind it.
33
Compressing flow
as the ice thickens and the flowing ice pushes over the slower moving leading ice. this causes the ice to thicken an therefore erosion can be at its highest.
34
dynamic equilibrium
a state of balance between continually changing processes.
35
what are geomorphic processes?
natural mechanisms of weathering, mass movement, transportation, erosion and deposition which all influence the glaciated landscape system.
36
3 categories of weathering
physical - the breakdown of rock by physical processes that produce smaller fragments of the same rock.
chemical - the decay of rock as a result of chemical weathering, which involves chemical reactions between the elements of the weather and some minerals within the rock.
biological - may consist of physical actions such as growth of plant roots or chemical processes.
37
examples of physical weathering
- freeze thaw - when water enters cracks/ joints and expands nearly 10% when it freezes. this exerts pressure on the rock causing it to split or pieces to break off. the more frequent the fluctuations of temperate around zero, the more effective the process will be,
- frost shattering - at extremely low temperatures water trapped in rock pores freezes and expands. this creates stress which disintegrates the dock into small pieces.
38
examples of chemical weathering
- pressure release - when the weight of the overlying ice in a glacier is lost due to melting, the underlying rock expands and fractures parallel to the surface.
- carbonation - rainwater combines with dissolved carbon dioxide from the atmosphere to produce a weak carbonic acid, this reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate which is soluble.
39
examples of biological weathering
- organic acids - these are produced during decomposition of plant and animal litter and cause soil water to become more acidic and react with some minerals in a process called chelation. this can occur when organisms such as lichens on rocks produce acids.
- tree roots - tree roots grow into cracks or joints in rocks and exert outward pressure. also, when a tree topples, their roots can also exert leverage on rock and soil bringing them to the surface and exposing them to further weathering.
40
main processes of mass movement
- slides
- slumps
- rockfalls
41
slides
an entire mass of material moves downwards along a straight line slip plane until it impacts at the bottom of a slope.
42
slumps
when material slips down a curved slip line with rotational movement, leaving a series of back tilted steps or terraces.
43
rockfalls
on a steep slope (over 70 degrees), bare rock can become detached from the slope by physical weathering forming scree.
44
45
surpa glacial debris
carried on the surface of the glacier, come from weathering and mass movement.
46
englacial debris
carried within the glacier, comes from surface debris which has fallen down a crevasse or sunken into the glacier from pressure melting or buried by snowfall.
47
subglacial debris
transported at the base of the debris, comes mainly from plucking and abrasion.
48
glacial till
material deposited directly by the ice.
49
glacio fluvial material
deposited by meltwater
50
characteristics of glacial till
- unsorted
- no orientation
- not stratified
51
corrie:
definition
example
size
- a corrie is a circular, steep sided rocky hollow high up on a mountainside.
- red tarn, lake district
- 100m wide, 300m high backwall
52
formation of corries in early stages of glaciation
- nivation of a small hollow on a north facing hillside.
- snow collects in the hollow and accumulates over successive years.
- snow patch encourages nivation and hollow is enlarged allowing more snow to accumulate.
- eventually snow is compresses into glacial ice by diagenesis.
- due to gravity the ice starts to move downhill as a glacier.
53
formation of corries during glaciation
- FTW affects backwall, weakening rock and causing supraglacial debris to form.
- ice acquires a rotational movement under its own weight.
- weakened rock is plucked from the backwall making it steep.
- extending flow occurs as glacier moves downhill causing a bergschrund crevasse to form between slope and glacier.
- meltwater runs down crevasse and freezes causing FTW.
- as glacier moves, it plucks shattered lumps further steepening backwall.
- as rock is eroded from backwall, pressure release causes joins to open and widen enabling erosion.
- debris from FTW falls down crevasse and embeds in the ice.
- subglacial debris abrades and deepens the floor of the corrie.
- rotational slip means there is more pressure from ice at the backwall.
- compressing flow due to lower gradient causes the ice to be thicker at this point.
- base of the backwall is eroded the most and this results in a deep armchair shaped hollow with steep backwall and sides.
- once hollow has deepened, thinner ice is unable to erode rapidly creating a higher corrie lip, this lip may consist of moraine deposited by ice.
54
how has flows of energy shaped a corrie?
- height and weight of glacier determines GPE.
- this determines the PMP as thermal energy is generated at the base.
- presence of meltwater enables glacial movement via basal sliding.
- more meltwater = more kinetic energy = more erosion from abrasion = deeper hollow.
55
how have flows of materials shaped a corrie?
- FTW takes place on the backwall = makes backwall steeper and creates subglacial debris.
- as glacier moves under its own weight = subglacial debris is moved under the glacier = abrasion = hollow is deepened and widened.
- as glacier flows out of corrie = subglacial debris will be deposited building up the height of the lip.
- FTW and rockfall modify the gradient of the backwall.
56
arete
definition:
example:
size:
- a knife edged ridge which forms between 2 corries.
- striding edge, lake district, between red tarn and nethermost cove
- 200- 300m high
57
pyramidal peaks
definition:
example:
size:
- isolated pyramid shaped point caused by the backwards erosion of three or more corries into the same mountain sides.
- matterhorn, switzerland
- 4478m above sea level
58
how have flows of materials shape aretes and pyramidal peaks?
- FTW takes place on the backwall of each corrie = subglacial debris. this falls down the bergschrund crevasse to create subglacial debris. rocks on each backwall are also weakened by FTW.
- as glacier moves under it own weight = rock are weakened by FTW and plucked out of each backwall = steepens backwalls = narrows the land between the backwalls = subglacial material is moved under = abrasion = hollow becomes wider and deeper.
- FTW and rockfall sharpen aretes and create scree slopes and rocky summit of pyramidal peaks is maintained.
59
how do flows of energy shape aretes and pyramidal peaks?
- height and weight determines GPE.
- KE is generated as the glacier begins to flow under its own weight and erosion via erosion and plucking.
- inputs of thermal energy from the sun causes meltwater to run down the bergschrund crevasse = it freezes and cracks the backwall causing FTW.
- as glacier gains kinetic energy and flows downhill and both corries are steepened by plucking.
- FTW continues as the meltwater freezes and thaws.
- loosened rock has GPE due to steepness of backwall .
60
glacial trough
definition:
example:
size:
- valley glaciers widen, straighten and deepen preglacial valleys. they are therefore steep but rarely vertical and have a deep valley with a flat floor.
- patterdale glacial trough, lake district
- length - up to 50km wide, width - 0.5 - 3km wide
61
features associated with glacial troughs
- truncated spurs
- rock basins and rock bars
- ribbon lakes
- hanging valleys
- misfit stream
62
how do flows of energy shape a glacial trough?
- height and mass dictate GPE. mass generates thermal energy as PMP is reached and moves due to basal sliding = glacier gains kinetic energy = rates of plucking and abrasion increase = valley gets wider and creates truncated spurs.
- tributary glaciers add mass increasing GPE and KE = main glacier erodes more deeply and tributary is left as a hanging valley = uneven valley floor = rock basins.
- GPE is larger as ice thickens and KE increases = more erosion which over deepen the rock basin.
- when temps rise, thermal energy melts ice and rock basins fill with water to create ribbon lakes.
63
how have flows of material shaped a glacial trough?
- FTW above glacier ends in scree = rockfall and outputs debris from the glacier.
- plucked debris from the valley sides and floor.
- basal sliding moves the debris, subglacial debris causes abrasion = deepens and widens glacial trough.
- rock basin may be dammed by terminal moraine which is formed from deposition of debris at the snout of the glacier.
- FTW, scree and rockfall can continue to modify the valley slopes.
64
roche moutonnee
definition:
example:
size:
- resistant rock eroded by glacial ice moving over it, so it has become shaped.
- norfolk island, ullswater
- 1-5m high, 5-20cm long
65
how have flows of energy influenced the formation of a roche moutonee?
- at stoss end: thermal energy created by pressure as ice meets mass of resistant rock. PMP is reached and ice gains kinetic energy as it flows around the obstacle via regelation. as ice moves, subglacial debris causes abrasion, polishing the rock and creating a gentle slope with striations.
- on lee slope: pressure is reduced as ice flows over landform. thermal energy is lost and water refreezes. plucking occurs as the ice advances creating a steep, jagged slope.
66
characteristics of glacial till
- angular
- unsorted
- not orientated
- not stratified
67
end moraines
- terminal moraine (at the end of a glacial trough)
- recessional moraine (runs to end just above the terminal moraine but in the same shape as the terminal moraine)
- lateral moraine (down the sides parallel to each other of the valley)
68
formation of terminal moraine
- forms at snout of glacier when it is stationary (accumulation = ablation) for a period of time and a ridge of deposited material can form at the snout = marks the extent of the glacier.
- ice is continually melting at snout and as it melts, it dumps a mixture of supra glacial and englacial debris = mirrors the shape of the snout in a crescent shape.
- melting ice is continually replaced by new flows like a conveyor belt and this continues to deposit.
- subglacial debris and valley floor deposits are bulldozed by the snout. ice supports deposits making them more likely to collapse.
69
formation of lateral moraines
- material comes from further up valley. material loosened by FTW on valley sides, rolls down the valley side by mass movement and material is also abraded and plucked by glacier adds to this mound on top of the glacier.
- debris carried at side of glacier on top of the glacier at the valley sides as the glacier moves.
- in warmer conditions, as the glacier retreats , the till is deposited on the valley floor.
70
formation of recessional moraine
- forms during an episode of retreat when the glacier has a a negative mass balance. a temporary stand still creates ridges of till between the snout and terminal moraine.
- there may be a series of recessional moraines that the glacier creates as it retreats.
