Glaciation Flashcards
how much more frequent is nuisance flooding today than 50 ya?
300-500%
how many people live in areas below the projected tideline by 2050
150 million people
how much has the sea level risen since 1850
21-24cm
since when has the ocean been warming rapidly causing thermal expansion?
1980s/90s
where is much of the ice loss occurring?
fringes of the antarctic ice sheet-> up to 10m a year
what are ice shelves
ice connected to the ground sheet but extending over the ocean (floating)
- thinner and more likely to melt
effect of ice shelves on the flow of the overall glacier
slow the flow and therefore ice loss
compare the east and west antarctic ice sheets
east antarctic ice sheet contains more ice but may be more stable than the west antarctic ice sheet which is mostly on land below sea level
last time temperatures were similar to today, what level were the seas?
6-9m higher
when was the last time CO2 was as high as present?
the Pliocene-> sea levels at least 6m higher
what occurred to sea levels about 20,000 yrs ago?
global warming event after ice age, meltwater pulse 1A caused 15m change in levels over a few 100 yrs
what sea do the antarctic ice sheets flow into?
Ross Sea
in what way can warming actually lead to ice sheet build up>
more snow
5 ways that glaciers impact humans
- meltwater= source of freshwater
- changes to ecosystems due to glacial changes
- driver of local tourism
- power from meltwater
- glacier floods= hazards
what is a glacier
a piece of ice that persists year on year and is massive enough to deform under its own weight
what is an ice sheet
over 50,000 km2, any changes in underlying topography dont impact ice flow
what is an ice cap
less than 50,000 km2, still not impacted by underlying topography
what is an ice stream
channel of relatively fast flowing ice-> flow from middle to edges
what are calved pieces of ice also known as
ice bergs
what is the constraining factor on alpine glaciers
topography
3 essential factors to form a glacier
land surface, persistent cold temperatures, precipitation
what is glacial mass balance
how the mass of the glacier changes over time
what occurs in the accumulation zone
snow falls and persists at the top of the glacier
equilibrium line
usually corresponds with the freezing level
in which zone does the glacier melt
ablation zone
what occurs when the equilibrium line goes up
the glacier decreases
what happens when the equilibrium line goes down
the glacier increases
supraglacial water
on top of the glacier
englacial water
through the glacier
moulins
near vertical shafts that allow supraglacial water to enter the glacier
subglacial water
water below the glacier
N-channels versus R-channels
N-channels-> cut down into the channel
R-channels-> cut up into the (warmer) ice
how can we measure or detect subglacial drainage systems
radar
what is the effect of water at the base of the glacier
increases flow
why do cracks form on the surface of glaciers
less pressure on top than below
regelation
freezing point decreases due to pressure when approaching an obstacle. water flows around obstacle and refreezes on downslope side
what is the process by which glaciers move under their own weight
ice deformation
surging glaciers
meltwater builds up in subglacial reservoirs before overflowing, causing a rapid increase in sliding
what occurs to clasts when entrained and carried by glacier over time
they go from angular to smoothed
why is less work done on the landscape in v cold polar regions
ice only moves by internal deformation
what do glacial troughs and hanging valleys mark
where glacier tributaries once joined the main glacier
stoss and lee features
subglacial features caused by regelation
debris cracked off during refreezing
forms gentle slope up and steep cracked slope down
rouche moutonées
small stoss and lees
eskers
r-channels fill with sediment over time and are left behind when glacier melts
how can eskers climb hills?
high pressure forces water upwards
where are drumlins common
areas which had warm fast flowing ice
flutes
like stoss and lee forms but the cavity side gets filled with sediment
what is left behind by pro-glacial lakes
glacial flour, builds up in layers
what is surface-exposure dating?
atoms from deep space hit the surface of rocks and make a reaction that expels some subatomic particles- measure how many were removed…
(shows when the rock was deposited by the glacier)
in a warmer climate, is there a higher or lower proportion of 18O than a cooler climate?
higher
what other gas matches quite closely with ice core proxy data
methane
where does most mass come to ice sheets from
smaller, faster flowing ice streams or outlet glaciers
nivometric component
percentage of precip falling as snow in an area
give 5 controlling factors on distribution of ice and snow
latitude, altitude, relief, aspect, continentality
snowline
where fresh snow still lies- retreats up glacier by late summer
firn
wetted/compacted snow over a year old
2 zones of the accumulation zone
dry-snow zone: no melt
wet-snow zone: entire snowpack is saturated by end of summer
superimposed ice
water that refreezes at the base of the glacier
how does snow transform to ice when water is present
melting, percolation and refreezing-> fast changes
how does snow turn to ice when no water
slow process, packing and settling, changes to ice crystal size and shape from sublimation and deformation
warm ice
at pressure melting point and contains water
cold ice
at temps below pressure melting point, doesnt contain liquid water
what does the thermal regime of the glacier control
the water system and range of processes that can occur at the bed of the glacier
3 types of thermal regime
temperate glacier, cold glacier, polythermal glacier
4 main morphologies of subglacial water systems
- thin sheet flow
- network of channels
- linked cavities
- braided system of canals
what can cause R channels to close up
ice creep
at what time of year are water pressures highest in r channels
spring, melting
where do linked cavities form
downstream of bedrock bumps
is water in a large canal at higher or lower pressure than a smaller canal
higher
where are canals likely to occur
where low-slope glaciers overlie soft sediment
how many glaciers mapped under the Antarctic ice sheet
over 400
3 mechanisms of glacier flow
internal deformation, sliding, bed deformation
what two factors cause drag at the bed
bed roughness (form drag) and rock to rock friction (frictional drag)
enhanced creep
increased compressive stress upstream side of obstacle, most effective for larger obstacles
Glens flow law
creep rate proportional to the 3rd power of the stress
how fast are fast flowing glaciers
100-1000m a yr
glacial crushing
direct fracturing of the bedrock due to weight of ice
5 ways glacial crushing might occur
stress concentration due to stones in basal ice, pre existing weaknesses in bedrock, repeated cycles of loading and unloading, freeze-thaw, pressure release due to large amounts of rock removal
product of glacial crushign
large, angular rocks
outcome of chemical erosion due to meltwater
decomposition of minerals to ionic constituents
3 factors that control erosion rates
changes in basal temp, glacier velocity, bedrock properties
how much on average do valley glaciers erode each year
1mm
how are the sediments resulting from glacial deposition classified
by the process of their deposition
till
sediment deposited from a glacier
lodgement till
frictional resistance between clast in transport at the base exceeds the drag imposed by the ice- grain by grain plastering
deformation till
pre-existing subglacial materials folded, sheared and partially homogenised by movement above of debris rich ice
meltout till
ice surrounding sediment melts
flow till
continuous supply of water in summer, poor draining, common sediment flows, particle sorting
crag and tail features
features of erosion: resistant rock left standing proud of surface, smaller cavities form behind more resistant rock
chatter marks
formed when ice moves over the bed with stick-slip motions
push moraines
glacier pushes sediment up to form a ridge
dump moraines
ridges formed transverse to the flow from material delivered to the margin of the glacier by ice flow
lateral moraines
parallel to sides of glaciers from dumped and frost-shattered matter
hummocky moraines
irregular mounds of material from meltout of supraglacial or englacial matter
de Greer moraines
linear ridges of sediment, transverse to the flow where a retreating ice mass borders on a glacial lake
crevasse-fill ridges
glacier with deep crevasses sinks into soft water saturated sediments
kettle holes
depressions from melting stagnant ice
kames
mound of sediment forme when a hole in a melting stagnant ice mass becomes filled with sediment
