A Level Geography - Glaciers
WB glacier - basal temp
Basal temperatures at or above pressure melting point
CB glacier - basal temp
Basal temperatures below pressure melting point so movement is limited
How does aspect affect a glaciated landscape?
If a slope faces away from the sun, temperatures remain below zero for longer so less solar energy is received and more melting occurs
WB glacier - surface melting
In summer, rises above 0C allowing some surface melting
WB glacier - erosion
Landforms of erosion Greater erosive power
CB glacier - erosion
Less erosive power
CB glacier - surface melting
Limited summer melting
How does latitude affect a glaciated landscape?
Locations at high latitudes tend to have cold, dry climates with little seasonal variation in precipitation At lower latitudes, places with high altitudes are characterised by dynamic valley glaciers
How does altitude affect a glaciated landscape?
Lower latitudes and higher altitudes create dynamic valley glaciers Temperature decreases with altitude at a rate of approximately 0.6C/100m
WB Glacier - meltwater
Meltwater percolates through glacier and acts as a lubricant for movement
CB glacier - movement
Move slower, often only a few m/yr
Corrie/ Cirque/ Cwms Glacier
Named after the bowl-like hollows they occupy Found on high mountain sides and tend to be wide rather than long
CB Glacier - meltwater
Often frozen to bedrock
WB glacier - movement
Rapid rates of movement (20-200m/yr)
How does relief affect a glaciated landscape?
The steeper the landscape, the greater the resultant force of gravity and the more energy a glacier will have to move downslope
Basal Sliding
Warm based glaciers may move by basal sliding Glacier can slip/slide on a layer of meltwater- lubricant Movement causes friction, enhancing melting Most effective on steep slopes
Surging
rapid movement occurs due to large levels of inputs or large amounts of meltwayer a short-lived phase of accelerated flow glacier surface can become broken up into a maze of crevasses
Serac
(from the french) a tower of unstable ice that forms between crevasses, commonly in ice falls or other regions of accelerated glacier flow
process of deposition
- glaciers deposite their load when their capacity is reduced. This usually occurs due to ablation during periods of retreat or de-glaciation - material can also be deposited during avalanche or when the glacier is overloaded with debris
Process of - Freeze-thaw weathering/rock shattering
- ice occupies nearly 10% more space than water -water enters the cracks and freezes over night, expands and causes pressure -crack widen -process repeats -rocks break off
when does Extending and compressing flow occur?
- occurs when there is a change in gradient
Extending flow
- steep- velocity increases- extentional - ice becomes thinner as it is streached
How does climate affect a glaciated landscape?
-Wind - aerolean processes =erosion, transportation and deposition -Precipitation - provides inputs - Temp. - Above 0C, ice starts to melt and adds to outputs.
diagenesis process
1. Fresh snow falls 2. Snow that survives one summer is called firn 3. With further compaction by subsequent years of snow fall, it becomes glacier ice
What percentage of the worlds land areas do glaciers occupy?
10%
Crevasse
A deep crack or fissure in the ice of a glacier.
Firn
A dense, icy pack of old snow
valley glacier
A long, narrow glacier that forms when snow and ice build up in a mountain valley
How does basal sliding effect the rate of erosion?
Abrasion increases with basal sliding
Soft Bed Subglacial Movement
As soft sediment below the glacier deforms, it moves the ice sheet with it
Sub-glacial moraine
At base of glacier
Process of carbonation
CO2 dissolved in water forms a weak carbonic acid Reacts with calcium carbonate (limestone) -> calcium bicarbonate which then dissolves
process of hydrolysis
Chemical reaction between rock minerals and water. Silicates combine with water producing secondary minerals
How does temperature effect the rate of erosion?
Cold based = decreased erosion
Scree
Debris on side on glacier
Drift
Deposits made by glaciers which include both till and outwash
Diagenesis
Each new fall of snow compresses and compacts the layer beneath, causing air to be expelled and converting low density snow into higher density ice
process of oxidation
Eg. Iron becomes soluble in very acidic conditions and the original structure is destroyed. Often attacks iron rich cements binding sand grains in sandstone
How does velocity effect the rate of erosion?
Faster = increased erosion
Glacial surge/advance
Glaciers may take many years to react to changes in accumulation or ablation but where snowfall is exceptionally heavy the glacier may react quickly and surge forward
rock flour
Ground-up rock produced by the grinding effect of a glacier.
Internal Deformation (creep)
Ice becomes plastic. The crystals orientate themselves in the direction of movement.
How does basal water temperature effect the rate of erosion?
If water at the base is under pressure the glacier can be buoyed up meaning less pressure and erosion
Englacial moraine
In glacier
How does supply of rock fragments effect the rate of erosion?
Increased fractured rock = increased erosion
How does ice thickness effect the rate of erosion?
Increased ice thickness= increased nasal contact pressure= increased abrasion
How does resistance o bedrock relative to debris effect the rate of erosion?
Increased rates when debris is harder than bedrock
striations
Long parallel scars in rocks carved by rock fragments being dragged across them by a glacier (erosional)
Why may slides occur?
May occur due to steepening or undercutting of valley sides by erosion at the base of the slope, adding to the downslope forces
Rotational slides
Movement along a curved slip plane common in weather rocks that become heavier when wetlands
Linear slides
Movement along a straight slip plane as a fault of bedding between layers of rocks
Process of rockfall
On slopes of 40*+ especially if the surface is bare, rocks may become detached from the slope by physical weather in processes.
Supra-glacial moraine
On top of glacier
ablation zone
Outputs exceed inputs
process of solution
Some salts are soluble in water, others are only soluble in very acidic water
Glacial Budget/net balance
The NET balance of accumulation and ablation. It compares the the amount of snow accumulation on the ice sheet and the amount of meltwater leaving the ice sheet. it is measured on a monthly basis.
Equilibrium (firn) line
The dividing line between the two zones
Accumulation
The net gain in an ice mass
plucking
The process by which a glacier picks up rocks as it flows over the land
till
The sediments deposited directly by a glacier
How does debris amount, resistance , size and shape effect the rate of erosion?
These are the tools to erode - intermediate amounts = increased erosion
Hydration
Water molecules + rock minerals -> new minerals of a larger volume. Causes surface flaking in many rocks
Dilitation
Weight of overlying ice reduces, underlying rock expands and fractures
Steady State
When amounts of accumulation and ablation are equal over the course of a year As a result, the snout of the glacier will remain stationary, but the mass of ice will still be passing through
Ice Cap
a covering of ice over a large area, especially on the polar region of a planet. under 50000km2
Macro-scale
a kilometre or greater in size e.g. cirque/corrie
Ice Shelf
a massive extension of glacial ice over the sea, often protruding hundreds of miles
Meso-scale
a metre to a kilometre e.g. roche moutonnee
ice sheet
a very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation center(s). over 50000km2
abrasion
angular material carried by the glacer rubs away at valley floor and sides
Enhanced basal creep
basal ice deforms around irregularities onn bedrock
Moraine
debris on/in glacier
medial moraine
deposit of sediment formed when the lateral moraines of two glaciers meet
Nivation
erosion of the ground beneath and at the sides of a snow bank, mainly as a result of alternate freezing and thawing.
Piedmont Glacier
glacier that reaches a valley floor and spreads out in a bowl shape
WB glacier - altitude / latitude
high altitude
CB glacier - altitude / latitude
high latitude
strong lithology means?
highly resistant due to dense interlocking crystals
structure of rocks?
jointing / cracks = increased permeability
How does geology affect a glaciated landscape?
lithology and structure
weak lithology means?
little resistance to erosion as bonds between particles are weak
CB Glacier - relief
low
What are glaciers?
masses of ice (and debris) compressed over many years which are continually changing
Outwash/ glacio-fluvial material
material deposited by meltwater from a glacier
Micro-scale
metres or less e.g. striations
lateral moraine
moraine that forms along the side of a glacier
Glacier Speed
o Extremely variable o Fastest up to 50m and 400m per year o Flow rates of 1000m a year or more in large ice streams in Antarctica and outlet glaciers in Greenland
why is there an ablation zone?
o Less snowfall o Temperatures are higher
Where is the Ablation Zone?
o Lower altitudes o Towards the snout of a glacier
Why is there an accumulation zone
o More precipitation at higher altitudes (the orographic effect), mainly snow o New snow is highly reflective, so it absorbs less heat and melts more slowly o Strong winds at higher altitudes blow snow into hollows and basins where it can accumulate o Temperatures are low, so sublimation (solid to vapour) is low and meltwater is likely to refreeze
Lithology
physical and chemical characteristics of rock
Relegation slip
pressure melting in up-glacier side of obstacle induces melting. Meltwater flows over obstacle and re-freezes on down-glacier side as relegation ice
compressing flow
reduced gradient- velocity falls - ice catches up with ice in front, compression occurs, ice thickens
Sublimation
solid to gas
WB Glacier - relief
steep
Ablation
the process of wastage of snow or ice, especially by melting
Niche Glacier
very small glacier that occupies gullies and hollows on north-facing slopes (northern hemisphere); may develop into cirque glacier if conditions are favorable.
Accumulation zone of a glacier
where inputs exceed outputs
WB Glacier - pressure melting
yes
Corrie / Cirque Characteristics
• Confined to an armchair or bowl shaped depression - steep back wall, overdeepened basin, rock lip • High altitude • Sheltered location, most favourable for snow accumulation • Can become source of glacier ice • Northern hemisphere, NE facing (shaded and sheltered from westerly winds)