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W8L1 Glacial Processes Flashcards

1
Q

strongest erosional agent

A

ice

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2
Q

ice sheets and glaciers are

A

large masses of recrystallised ice

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3
Q

ice sheets and glaciers persist

A

all year round

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4
Q

ice sheets and glaciers move

A

byinternal dynamics

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5
Q

ice sheets and glaciers form

A

at high latitudes or high altitufe
cold local climate
persistemt snowfall
no summer melt

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6
Q

ice preserves

A

environmental conditions

precipitation (rain from atmosphere) so icesheets can measure atmsopheric change

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7
Q

glacial ice forms

A

Year on year, snow accumulates in a north-facing sheltered hollow (cirque) -
with increasing overburden pressure, the ice undergoes diagenesis and metamorphoses
compacts
recrystallises
grains grow with time
pore space reduces
ice eventually flows out of the cirque

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8
Q

Glacier Dynamic accumulation zone

A 
Accumulation Zone
higher latitude or altitude
sublimation
little/no summer melt
ice moves by internal pressure to - ablation zone
need pressure!
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9
Q

Glacier ABlation zone

A

lower latitude or altitude
ancient ice slowly exhumed
melting and iceberg calving

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10
Q

glacier sublimation

A

sublimation. the transition of a substance from the solid phase directly to the vapor phase, or vice versa, without passing through an intermediate liquid phase.

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11
Q

ice sheet albedo

A

large ice area changes albedo effect

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12
Q

ice sheet force

A

mass is the motive force

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13
Q

ice sheet flow

A

will flowuphill if overburden pressure in maintained

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14
Q

ice sheet viscosity

A

extreme viscosit of ice means powerful erosive force and effiicient transport agent

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15
Q

ice sheet sediment

A

glaciers & ice sheets create, transport & deposit huge quantities of sediment

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16
Q

Periglacial features are

A

this is whats perserved thru rock, find things around the iceand what can be reconstructed

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17
Q

ice dynamics reaction to pressure

A

Differential pressure produces different behaviour in the ice profile
in the upper 50 m, pressure & brittle strength are relatively low
cracks & crevasses
sediment falling on to ice surface is incorporated & transported
below 50 m, pressure is high & ductile strength is low
deformation & flow

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18
Q

Wet vs . dry dynamics

A

temperate wet vs polar dry

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19
Q

temperate glaciers

A

Temperate wet-based glaciers –

ice slips over a meltwater/sediment slurry

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20
Q

polar glaciers

A

frozen to substrate

flow by internal ductile deformation

21
Q

erosional flow is

A

flow is from the accumulation zone to the ablation zone
individual ice crystals follow a curved trajectory
regardless of melting in the ablation zone or stalled flow at the ice front, th ice body flows as long as accumulation is sustained

22
Q

scouring erosion . and incorporation ofbedrock

A

occurs under the accumulation zone
as pressure slackens, melting occurs & sediments are released
melting beneath the ice leads to sediment dumping – lodgement till
sediment, carried on and in the ice, is dumped at ice front – terminal moraine
meltwater streams emerging from ice front carry sediment away to the outwash plain

23
Q

direction of flow

A

flows from accumulartion to deposition

24
Q

doiminant deposited mineral

25
Sediment weathering and transport moraines
Freeze-thaw shattering supplies clasts to the surface of mountain glaciers physical weathering - angular clasts - no change in mineralogy slower ice flow at valley sides melting and sediment concentration side moraines central moraines result from the confluence of two or more valley glaciers
26
clast and bedrock weathering
lasts incorporated through crevasses transported & weathered reduction of grainsize & unstable minerals clasts at the glacier base abrade the bedrock striations parallel to flow upstream of obstruction flow slows ice freezes to bedrock downstream of obstruction flow restarts clasts plucked from surface best indicator of ice (geologcial past) : striations parallel to flow
27
Erosional force
100s of vertical metres of rock are removed by glacial erosion 1000s of cubic kilometres obstacles will be eroded by clasts in the ice and form valleeys or rivers
28
Sediment Transport surface load
no change in grainsize or mineralogy
29
sediment internal load
decrease of grainsize and unstable minerals
30
clasts in contact with bedrock
extremely high weathering
31
sediment transport
rock flour clasts dumped when pressure slackens terminal moraines lodgement till
32
Till and Tillite
All sizes of clast dumped beneath, beside and in front of the ice unsorted unstratified compositionally & texturally immature gravity flow: debris flow bcs nothing to distinguish direct indicator: scratch marks indiredct indicator: would be context, other glacial features around
33
Glacial erratics
pushed/dragged/carried by the ice in some cases for kilometres thought to be transported by swift-moving ice streams, then ice melted and rocks left behind usually identified by anomalous rock type protects bedrock from weathering processes
34
Glacial outwash
moves / shifts around extremely large volume of material
35
glacial outwash stream
Typical braided stream & forms outwash plain stream full of sediment (rolling bedload & suspended load) high capacity/ low competence
36
bars and channels
rapid formation, filling, abandonment and reformation
37
glacial outwash sediment
highly weathered clasts highly rounded clays, quartz sands, pebbles and cvobbles compositionally and texturally mature cross-bedded, sorted and deposited by seasonal braided streams pebbles/cobbles are imbricated river conglomerates, coarse marine gravels, glacial outwash sediments
38
proglacial lakes
iceberg calving dropstones (ice-rafted debris) a tell-tale sign of glaciation two distinct seasons in proglacial lakes (frozen & meltwater) deposition of varves
39
ice sheet at sea level
ice shelves extend from the land when ice sheet is grounded on the shelf
40
ice sheets debris bcs of glaciation
the amount of ice-rafted debris in marine sediments is commensurate to intensity of glaciation
41
glacial ice clast size
can transport any clast . size ions to cliff sized boulders
42
glacial ice forms at
forms at high latitudes and altitudes | over 100s/1000s of years, snow transformed to ice by overburden pressure flows under its own weight
43
glaciers flow
from accumulation zone (high pressure) to ablation zone (low pressure)
44
glaciers in high altitudes
in high-altitudes frost-shattering supplies clasts to the ice surface
45
glaciers accumulation zone
under the accumulation zone, plucking & abrasion erode the bedrock and incorporate clasts into the ice
46
glacial sediment
sediment carried on and in the ice and is dumped where pressure slackens - unsorted, unstratified, mixed mineralogy till
47
glacial ice front
at the ice front meltwater streams deposit sorted, stratified clays, quartz silts, sands & gravels lowland glaciers can terminate in proglacial lakes
48
varves
winter/summer contrast produces laminated sediment – ‘varves’
49
ice shelves
ice at sea level is grounded on the shelf – ‘ice shelves’ | cebergs transport ice-rafted debris into the ocean

Surface Processes (14 decks)

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