Systems and Processes in Glaciers and Glacial Landscapes

Question 1

What are the inputs in a glacial system?

Answer 1

Direct snowfall
Blown snow
Avalanches/rock falls

Question 2

What is the snow line?

Answer 2

During the summer the glacier retreats, during the winter the glacier advance. Shorter summers allow less time for snow to melt. This leads to permanent snow cover in upland areas, the lower edge of which, is the snow line. As mean annual temperatures drop, the snow line moves down the slope.

Question 3

What is the zone of accumulation?

Answer 3

The upper part of the glacier where inputs exceed outputs and mass is gained.

Question 4

What is the zone of ablation?

Answer 4

The lower part of the glacier where outputs exceed inputs and mass is gained.

Question 5

What is the equilibrium line?

Answer 5

The boundary between ablation and accumulation where net gain and loss are balanced.

Question 6

What are the characteristics of temperate/warm based glaciers?

Answer 6

More mobile - more meltwater, meaning more likely to erode, transport and deposit
The surface is thin and subject to seasonal temperature fluctuations - melts rapidly at around 0 degrees Celsius
Pressure melting point occurs - where the glacier is near melting point because of warmer atmospheric temperatures and the weight of the ice above.

Question 7

What are the characteristics of polar/cold based glaciers?

Answer 7

Very old
Very little meltwater - geothermal and atmospheric heat isn’t enough to reach melting point
Moves very slowly - often frozen to their beds, most movement is from internal flow
Less erosion, transportation and deposition.

Question 8

What is weathering?

Answer 8

The breakdown/decay of rock though mechanical, biological or chemical processes.

Question 9

What are frost-action/threeze-thaw cycles?

Answer 9

Water enters cracks during day, then at night the water freezes in the cracks. This expands and makes the cracks bigger through repeating the cycle.

Question 10

What is nivation?

Answer 10

Processes that happen under patches of snow in hollows. Freeze-thaw and chemical weathering causes underlying rock to disintegrate. When the snow melts in the spring the ,material is flushed-out and moved downslope through solifluction and meltwater. Repeated seasons of this causes nivation hollows - the start of a corrie.

Question 11

What is internal deformation?

Answer 11

When ice is frozen to the bed and added pressure builds up within the glacier. This allows the ice to behave with plasticity and flow, and ice crystals inside move past each other.

Question 12

What is rotational flow?

Answer 12

When a glacier in a corrie pivots and rotates, this with increased pressure leads to greater erosion and over deepening of the corrie floor.

Question 13

What is compressional flow?

Answer 13

Occurs when there is a reduction in the gradient of the valley floor, leading to deceleration and more accumulation of mass. This increases ice erosion.

Question 14

What is extensional flow?

Answer 14

Occurs when there is an increase in the gradient of the valley floor, leading to acceleration and an ablation of ice. This decreases ice erosion.

Question 15

What is basal sliding?

Answer 15

When a glacier moves over bedrock friction and pressure allows more melting - meltwater acts as a lubricant and ice flows more rapidly.

Question 16

What are surges?

Answer 16

When glaciers move forward very suddenly due to an excessive build up of meltwater - can move as much as 250-300 m in one day

Question 17

What is abrasion?

Answer 17

Happens when the material the glacier is carrying rubs at the valley floor/sides.
Coarser, harder debris leaves striations.
Finer debris polishes and smooths rock.
The debris involved is usually worn down into rock flour.

Question 18

What is sub-glacial debris?

Answer 18

Material found at the base of a glacier

Question 19

What is en-glacial debris?

Answer 19

Buried within the ice

Question 20

What is supra-glacial debris?

Answer 20

Carried on top of the glacier

Question 21

What is till?

Answer 21

Material deposited directly by ice.
An unsorted mixture of rocks, clay and sand that was mainly transported supra-glacial and en-glacial.
Till reflects the character of the rocks over which the glacier has passed.

Question 22

What are corries?

Answer 22

Armchair shaped rock hollows with steep back walls and over deepened basins, with a rock lip.
Often contains a small lake - a tarn
Found on north, north-east, and east facing slopes where lower levels of insulation allowed increased accumulation of snow.
Dimensions of the corries depends on the topography of the area and the size of the glacier that formed them.

Question 23

What is an arete?

Answer 23

When two corries are back to back or alongside each other, if enlarged over many glaciations, a narrow steep-sided ridge between the two hollows is formed.

Question 24

What is a pyramidal peak?

Answer 24

When more than two corries develop on a mountain the remaining central mass will survive as a pyramidal peak
Which appears sharp because of frost shattering
e.g. The Matterhorn in the Alps bordering Switzerland

Question 25

What are glacial troughs?

Answer 25

Glaciers straighten, widen and deepen V shaped valleys into a U shaped valley.
Ice + Meltwater + Sub-glacial debris = glacial trough
Contains rock basins filled with ribbon lakes
Contains fjords
Contains hanging valleys
Contains truncated spurs
Contains roches moutonnees

Question 26

What are fjords?

Answer 26

Over deepening past the present sea level leads to the formation of fjords when sea levels rose after ice ages

Question 27

What are hanging valleys?

Answer 27

On the side of the main valley
Either pre-glacial tributary river valleys that were not glaciatied
Or smaller tributary glacial valleys - with small glaciers, resulting in less erosion than the main valley
Higher than the main valley when the ice retreated

Question 28

What are truncated spurs?

Answer 28

Areas of land projecting from the river-valley side that have been removed by the glacier

Question 29

What are rouches moutonnees?

Answer 29

Small mounds of resistant rock on the valley floor that aren’t completely removed by the glacier.
Have an up/stoss slope (which is smooth from abrasion) and a down/lee slope (which is jagged from plucking)

Question 30

What is lodgement till?

Answer 30

Sub-glacial material that was deposited by an actively moving glacier - e.g. a Drumlin

Question 31

What is ablation till?

Answer 31

Produced at the snout when the ice melts - e.g Terminal, push and recessional moraine

Question 32

What are drumlins?

Answer 32

Smooth egg shaped small hills
Have a steeper upstream end and gently sloping downstream end
Elongated in the direction of ice advance
Formed from unsorted till with little internal structure

Question 33

How are drumlins formed?

Answer 33

Ice becomes overloaded with debris and capacity to carry is reached. Deposition occurs at the base of the ice and this material is shaped by further glacier advance.

Question 34

What are terminal moraines?

Answer 34

Formed at the snout when the glacier has reached its furthest extent downstream

Question 35

What are recessional moraines?

Answer 35

As the glacier retreats, moraine form along the length of the valley showing points where retreat paused

Question 36

What are push moraines?

Answer 36

When a glacier advances previously deposited moraine is moved forward into a mound

Question 37

What are till plains?

Answer 37

Wide areas of flat relief created by a till sheet.
Hidden by a thick covering of glacial till, sands and gravel.
Material is compacted giving poor drainage - bogs lakes and slow moving meandering streams

Question 38

Explain the theoretical stages in the diversion of the river Severn.

Answer 38

Pre-Glacial - flowed northwards into the irish sea
The last ice age - Ice blocked the river Severn from the north and the water from the blocked river formed a huge pro-glacial lake - Lake Lapworth. The lake eventually overflowed the watershed to join the original Lower Severn, cutting through a solid rock area and creating a gorge at Ironbridge
Deglaciation - As ice retreated to the north the route north was still blocked with deposits and the Ironbridge gorge was cut deep so the river severn now flows from wales to the Bristol Channel

Question 39

Explain pro-glacial lakes and overflow channels

Answer 39

When rivers get blocked during glaciation and form lakes.

Then when lake overflows it creates overflow channels

Question 40

What are eskers?

Answer 40

Long ridges of material running in the direction of ice advance - often stratisfied/layered
Made by sub-glacial streams

Question 41

What are kames?

Answer 41

Mounds of fluvio-glacial material left when meltwater flows into a lake and dams the front of the glacial snout by recessional moraine deposits. When ice retreats further the delta kame collapses.

Question 42

What are outwash planes?

Answer 42

In front of a glacier snout, deposited by meltwater streams.
Material brought by the glacier, picked up, sorted and then dropped.
Coarsest material travels shortest distance and fine material is deposited far
Layered vertically to show the seasonal flow of meltwater streams