glacier Flashcards
what are fluvioglacial landforms
those that are created by the work of meltwater streams in front of an often retreating glacier
created largely through deposition but also by erosion
how does meltwater change glacial sediments
glacial deposits tend to be unstratified (have no layers)
meltwater changes the glacial sediment or till be sorting them by size, stratifying them into layers and rounding the sediments
how does discharge and sediment load of meltwater streams vary
in summer discharges will be very high as meltwater arrives from many meltwater streams
in winter meltwater discharge may even stop as temperature may never rise above the pressure melting point
also varies on a daily basis, greatest discharges coinciding with highest daily temperatures
where are contemporary fluvioglacial landscapes found
warm based glacial systems (for example in alpine regions)
in areas that tend to have meltwater (ones that have activity at lower elevations like valleys or outwash planes
under what conditions will a glacier deposit materials
exceeding the carrying capacity - when the vector can no longer carry the material e.g. melting
losing energy: shrinking ~(not advancing) and change in relief (flat ground loses spread)
what are erratics
glacier-transported rock fragment that differs from the local bedrock. Erratics may be embedded in till or occur on the ground surface and may range in size from pebbles to huge boulders weighing thousands of tonnes
what is till
unsorted material deposited directly by ice (boulder clay)
what is lodgement till
material lodged on the valley e.g. subglacial debris
what is ablation till
combination of englacial and supraglacial debris, dropped in situ as the glacier begins to melt
what is an outwash plain
Outwash plains are formed in front of a glacier and are where material is deposited over a wide area
the till levels out the landscape creating a characteristically flat topography
what are moraines
a general term for unstratified and unsorted deposits of sediment that form through the direct action of, or contact with, glacier ice
define a corrie
a deep hollow in a mountain side left behind by a glacier - characterised by a steep back wall and over deepened base
define arête
a knife edge ridge separating two or more corries
e.g. striding edge, lake district
define pyramidal peak
sharp summit and steep sides between 3 or more corries that have continuously eroded backwards
what is a roche moutonnée
a mass of resistant rock which has a smooth, rounded up (stoss) slope facing against the direction of the ice flow and a steep, jagged face on the far (lee) side
define glacial trough
also known as a u shaped valley
high, steep sided walls wis a flat, wide base
formed due to glaciers eroding the whole SA of valley much faster than the valley river
define misfit stream
rivers in a glacial trough that did not erode to form the valley
define hanging valley
remnants of river tributary valleys
smaller valleys that sit high on the sides of glacial troughs
define truncated spur
former interlocking spurs that have been sawn off (truncated) by the glacier
end in an abrupt steep edge
define ribbon lake
long and narrow lake found in a glacial trough
formation begins when a glacier moves over an area containing alternate sections of hard and soft rocks
soft rock is less resistant and erodes faster than hard rock, creating a rock basin, the hard rock acts as a dam where rain water accumulates
define weathering
the breakdown of rock or parent material by external processes in situ
what is physical/mechanical weathering
disintegration of rock without a chemical change
e.g. freeze thaw/exfoliation
often results in piles of angular rock fragments known as scree that can be found at the foot of a mountain
what is chemical weathering
the decomposition of rocks caused by a chemical reaction with it e.g. acidic rainwater can react with and dissolve certain rocks and minerals
what is biological weathering
involves the actions of flora and fauna e.g. plant roots expanding cracks in the rocks
define mechanical weathering
creating a fragmented or angular landscape with loose material called scree
what is freeze thaw/frost shattering
A crack in a rock can fill with water which then freezes as the temperature drops. As the ice expands, it pushes the crack apart, making it larger
requires temperature fluctuation below and above freezing
what is carbonation
the mixing of water with carbon dioxide to make carbonic acid
what is nivation
an umbrella term used to cover a range of processes associated with patches of snow that result in the formation of hollows
the collection of seasonal snow in hollows which encourage frost weathering beneath them
describe the process of nivation
Snow and ice build-up on sheltered/shaded sloped areas. These patches often remain through the summer months. Compact névé snow can develop when snow melts and refreezes. Firn ice can develop over time in these shallow depressions, and when movement occurs, the ice can pluck small bits of loosened rock from the back surface of the area.
Freeze-thaw cycles around the edges and below the snow patch cause frost shattering.
When thawing occurs, the smaller pieces of frost shattered rock are moved down the slope by meltwater, solifluction and gelifluction.
As a result of these processes, nivation hollows are formed, over time these can develop into corries.
where are nivation processes most active
at the edges of snow patches because the exposed rock with low albedo absorbing more energy
define abrasion
when rock fragments frozen to the glacier base smooth and sandpaper the bedrock as the glacier moves over it
define plucking
as a glacier moves meltwater gets into cracks and freeze
this rips or plucks out rock fragments from bedrock
plucking can also occur on the headwall of a corrie, where the glacier is attached to the mountain
define dynamic equilibrium
All natural systems are in this state state
it means changing balance
for glaciers, as inputs are constantly changing due to climate, the system needs to adjust to the changes in order to reach a new state of balance
glacial budget
The balance between inputs and outputs
the glacial budget is constantly changing
the amount of ice in the glacier
what is accumulation
inputs > outputs so glacier grows in size
what is ablation
outputs > inputs so glacier will retreat and reduce in size
what is a mass balance
accumulation - ablation
positive balance
accumulation > ablation
negative balance
ablation > accumulation
what is net balance
annual mass balance of a glacier over a year
a negative balance means the glacier snout is reterating
a positive balance means that the glacier snout is advancing
balance is a steady state or equilibrium
describe the temporal variation in glacial budget
winter - positive balance = acculmulation = snout advance
greater precipitation input
reduced melting due to lower temperatures
summer - negative balance = ablation = snout retreat
reduced precipitation input
increased melting, sublimation and calving due to raised temps
moving faster, more energy, higher rates of erosion
describe the spatial variation in glacial budget
ice caps/sheets: accumulation zone is in the centre
ablation zone is in the periphery
valley glaciers:
accumulation zone - high altitudes
ablation zone - snout
what is humus
processed organic matter
dead organic matter that has been broken down
what is regolith
inorganic material and weathered down material (rocks)
often helps with drainage
what is biota
living plants and animals in soil
what are adiabatic temperature changes
changing temp without adding or subtracting heat. result of compressing air or allowing allowing to expand
what is the difference between isostatic and eustatic changes
Isostatic change is a local rise or fall in land levels. Eustatic change involves a rise or fall in water levels caused by a difference in the volume of water
define a periglacial landscape
a landscape that undergoes seasonal freezing and thawing, typically on the fringes of past and present glaciated regions
how does base temperature determine glacial movement
Warm based glaciers have a higher temperature at base than the pressure melting point this means that water that would’ve previously been frozen exists as liquid
this leads to an increase in melt water which lubricates the base reducing friction and causes increased basal sliding
a buildup of this meltwater can cause a surge (300m in a day)
warmer temperatures also result in enhanced basal creep which is when an object in the path of the glacier causes increased pressure resulting in a higher PMP and therefore more meltwater
In cold-based glaciers there is a lower temperature PMP so they do not experience as much basil sliding
they move through internal defamation which is when the weight of the ice causes the ice crystals to stretch resulting in the downward motion of the glacier
in some cold temperatures ice could freeze and attach to bedrock meaning subglacial internal deformation is the only force of movement
cold temperature glaciers move much slower than warm temperatures
what is the difference between ice creep and basal creep
Ice creep is when ice crystals slide past each other advancing the ice surface
enhanced basal creep is the increased pressure from an obstacle in the path of the glacier leading to a low-pressure melting point and more meltwater
ice creep happens everywhere whereas basal creep happens sub glacially
where within the glacier is basal creep fastest
Ice cream happens fastest at the top/surface and the middle away from sides because there is the least friction with the sides and bedrock
how does ice overcome obstacles
Through enhanced basal creep and basal slippage enhanced basal creep is caused by an obstacle which causes pressure whereras basal slippage is caused by increased pressure from ice and lower PMP so it travels more rapidly
what is the difference between extending and compressing flow
extending flow is when a steeper gradient causes ice to move faster so the ice mass stretches becoming thinner
compressional flow is where the gradient is less steep so the ice mass slows, backs up and crevasses close
when will a surge occur
when excessive meltwater builds up at base and the glacier moves 300m in a day
when and where does basal slippage occur
in temperate glaciers
more frequent in summer
how does bedrock permeability affect glacier speed
movement is faster over impermeable surfaces rather than permeable. This is because impermeable surfaces don’t allow meltwater to escape and it stays at the base of the glacier. This decreases friction which allows the glacier to advance at faster rates
what are the different kinds of permafrost
Continuous permafrost covers the largest areas with temperatures below -5°C
Discontinuous permafrost occurs over smaller areas with temperatures between -5°C and -1.5°C
Sporadic permafrost covers the smallest areas where temperatures are between -1.5°C and 0°C
Permafrost can be classified as continuous (>90% of land area underlain by permafrost), discontinuous (90%-50%), sporadic (50%-10%)
what is solifluction
the progressive movement of a mass down a slope caused by freeze-thaw activity
define erosion
The wearing away and removal of rock by external agent
define regelation
Regelation is the phenomenon of ice melting under pressure and refreezing when the pressure is reduced
What are the names of the mechanical and chemical processes of subglacial melt water erosion
mechanical is fluvial abrasion
Chemical is corrosion Corrosion is the process of slowly eating up metals by gas and water vapours present in the atmosphere due to the formation of certain compounds like oxide, sulphides, carbonate, etc
define pressure release
aka dilation
When the overlying mass is removed by weathering, the confining pressure decreases, allowing the rock to expand
what is a rock step
outcrop or platform that is caused by a difference in type of rock hard/soft
