Glaciers Revision Notes

Components of glacial systems, Energy and sediment flows through glacial systems
    → Open system - can be added to

Annual glacier mass balance

    → the annual mass balance is the difference between accumulation and ablation over     one year

    → accumulation zone = top of glacier where there is least melting, meaning there is a     positive mass balance

    → the lower section (snout) = ablation zone, negative mass balance

    → glaciers can lose mass through:

• evaporation

• sublimation

• meltwater

• calving

• avalanche

• winds 

The effect of climate on the distribution and movement of glaciers

    → Higher temperatures correlate with a faster surface velocity, as higher         temperatures mean more meltwater at the bottom of the glacier to lubricate its         movement. higher temperatures inside the ice also allow more internal         deformation

The effect of geology on rates of glacial erosion

    → weak rock types have little resistance to erosion, weathering and mm as there are         weaker bonds between particles (e.g. clay)

    → strong rock types have dense interlocking crystals so very resistant (e.g. basalt)

    → some rocks are soluble in weak acids, allowing chemical weathering (e.g. chalk)

The effect of latitude and altitudes on the distribution and movement of glaciers

    → high latitudes tend to have colder and drier climates with little seasonal variation,         leading to ice being more likely to remain for multiple seasons and therefore         eventually condense (e.g. greenland, antarctica). this is usually where cold based         glaciers form

    → high altitudes are closer to the sky, and therefore more likely to find precipitation         falling as snow instead of rain. this means there can be glaciers closer to the                  equator (e.g. the andes), due to high altitudes. this is usually where warm based         glaciers form

The effect of relief and aspect on glacier movement

    → as a glacier flows over steep slopes it cannot deform quickly enough, so stretches     and fractures forming crevasses (extending flow)

    → as the gradient of slope decreases, the ice thickens and the crevasses close due to     compression (compressing flow)

    → the steeper the relief the faster a glacier moves, evidenced by increasing crevasses     on steep relief glaciers

    → aspect (the direction the glacier faces) can impact the mass balance. if aspect is     facing away from sun, there is more accumulation, and if it faces sun there is more     ablation

Formation of glacier ice

    → glacier ice forms from low density snow fall. over time these layers of snow     compress to form layers of firn (snow that lasts through the year). This is then     pressurised, removing air from the glacier, and causing the glacier to become more     dense (glacial ice reaches densities of 0.9g/cm). This causes the glacier to look blue,     as there is a lack of oxygen. This is called diagenesis.

Types of glacier

    → constrained - smaller glaciers, limited by terrain (e.g. valley walls). valley glaciers     and corrie glaciers are constrained. tend to be smaller. often form u-shaped valleys.

    → unconstrained -larger glaciers which are able to erode surrounding landscape. ice     sheets and ice caps are unconstrained. create smoother landscapes like drumlins.

Temperature regime

    → warm based glaciers form at high altitudes, but low latitudes (e.g. alps, rockies).     the relief is steep. the basal temperature must be above pressure melting point,     causing the glacier to move relatively rapidly (20-200m a year)

    → cold based glaciers form at high latitudes (e.g. antarctica, greenland), but not     necessarily high altitudes. the relief is low. the basal temperatures are below pmp     causing no meltwater, leading to the glacier becoming frozen to the bedrock. this     causes the glacier to move extremely slowly

Glacier movement

    → gravity - causes glaciers to move down

    → gradient - steeper the slope, faster movement of ice

    → thickness of ice - influences pmp, which influences how glacier moves, and internal     deformation

    → internal ice temperature - allows for different areas of ice to move at different     speeds

    → mass balance - a positive mass balance allows advance at the snout

Glacial processes

    → erosion - plucking, meltwater seeps into rocks, freezes and rocks attach to glacier,         as glacier flows, rocks pulled off, most effective at base of glacier. abrasion - glacier         moves across surfaces, and debris in glacier wear away at rocks.

    → transportation - rockfall, avalanches, debri flows, aeolian deposits (wind), ``              eruptions,plucking, abrasion

    → deposition - lodgement till, material deposited by advancing ice, pressure melts         around objects. ablation till, material deposited by melting ice from stagnant or         retreating ice, rocks are angular and a mix of sizes. 

Weathering processes

    → physical - freeze thaw, water enters cracks, expanding by 10% when frozen. frost         shattering - water trapped in pores freezes and expands.

    → chemical - chemical reaction between water and minerals in rocks, usually                increasing in warmer temperatures.

Mass movement and nivation

    → slides (straight line or rotational) and rock fall

    → nivation - combination of freeze thaw action, transport, and chemical weathering,     causing initial enlargement of corries. 

Erosional landforms

    → corries - glacier erodes hollows through plucking and abrasion, and rotational     abrasion through rotational movement of glacier.

    → aretes - two glaciers form in neighboring hollows, and as erosion continues on     each side, the rock between the corries becomes steeper and narrower (throigh     freeze thaw weathering)

    → pyramidal peaks - aretes developed, and when three or more aretes converge,     they isolate into a central point

    → glacial troughs - during cold periods, glaciers form in a v shaped valley, and     reshape the valley into a u-shape through plucking and abrasion

    → roche motonnee - obstacle at base of glacier, glacier flows over. as the meltwater     melts and refreezes (regelation) it freezes into cracks on the jagged lee side, and as     glacier moves, it plucks. very smooth side (stoss) faces glacier), very jagged side (lee)

    → striations - scratches on roche motonnee, due to abrasion, as stones are dragged     over roche by the glacier

Depositional landforms

    → moraines - terminal moraine, a ridge of till at the end of a glacier, highlighting     where the end of the glacier is. lateral moraine, ridge running along edges of a glacial     valley. recessional moraine, series of ridges running transversely across glacial     troughs, parallel to each other and the terminal moraine.

    → erratics - movement and deposition of one type of rock, to an area where the rock     does not usually exist

    → drumlins - steep, stoss side is upstream, lee tail side is shallow. hypothesis 1: large     rock in centre, glaciers with lots of sediment coalesses around obstacle, creating     stream lined shaped by creation of tail behind obstacle. hypothesis 2: subglacial     sediment deformation, under the glacier, sediemtn is moulded.

    → till sheets - large expanses of thick, unsorted til, deposited by an ice sheet, as it     retreats.