Glaciation Theory

Question 1

Inputs into Glacial systems

Answer 1

Kinetic Energy, Thermal Energy, Potential energy, Debris, Precipitation

Question 2

Throughputs in Glacial Systems

Answer 2

Ice, water and debris accumulations

Question 3

Outputs in Glacial Systems

Answer 3

Icebergs, Melt water, Water vapour and debris

Question 4

When is the glacier in equilibrium

Answer 4

When Inputs=Outputs/accumulation=Ablation

Question 5

How to find the mass balance

Answer 5

Difference between the amounts of accumulation and ablation

Question 6

Where is the equilibrium line

Answer 6

the point were accumulation=ablation

Question 7

Ways that the climate affects distribution and movement of glaciers

Answer 7

Temperature and amount of precipitation

Question 8

How does Precipitation effect movement and distribution of glaciers

Answer 8

It is the main input into glaciers and therefore a key element of the mass balance
Increased precipitation may lead to the glacier growing.
Vostok has extremely low amounts of precipitation (4mm per year)
High altitude locations generally have more eg Canadian Rockies (600mm per year)

Question 9

How does Temperature effect movement and distribution of glaciers

Answer 9

If temperatures rise above 1 degree snow will begin to melt and become an output from the glacier.
High altitude glaciers may experience large amounts of melting in the summer months.
Temperatures at high latitudes may never rise above zero, leading to the formation of ice sheets.
Melting can result in faster rates of flow due to lubrication of the base of the glacier.

Question 10

How can lithology effect rates of erosion in glaciers

Answer 10

Lithology is the physical composition of rocks and therefore how resistant they are to erosion. Lithology may also effect the likelyhood of dramatic glacial features being formed (weak lithology will not form sharp aretes). Clay and Limestone (carbonation) have a weak lithology, Basalt has a stronger lithology.

Question 11

How can structure effect rates of erosion in glaciers

Answer 11

Rocks with a weak structure are clearly more susceptible to erosion due to more cracks and bedding planes, leading to increased plucking by the glacier.

Question 12

How does Latitude effect the distribution and movement of glaciers

Answer 12

Locations at high latitudes most noticeably beyond 66.5o N/S, tend to have cold, dry climates with little seasonal variation in precipitation
This is because there is a greater distance of atmosphere for solar radiation to travel through and it is spread over a greater area, making the radiation less effective
Glaciated landscapes at such latitudes tend to develop under the influence of large, relatively stable ice sheets (Greenland and Antarctica)

Question 13

How does altitude effect the distribution and movement of glaciers

Answer 13

Locations at high altitudes tend to have higher precipitation inputs due to orographic rainfall, but more variable temperatures and hence more summer melting
The air pressure at high altitudes is lower and the air molecules have less kinetic energy as they do work when they expand at higher altitudes, meaning that glaciers can form even at the equator if the altitude is high enough
The Pastoruri glacier in Peru lies at an altitude of 5250 m and is just 10oN of the Equator. It is small glacier with a length of 4km

Question 14

How does relief influence glacier movement

Answer 14

The steeper the relief of the landscape, the greater the resultant force of gravity and the more energy a glacier will have to move downslope
Where air temperatures is close to zero, it can have a significant influence on the melting of snow and ice and the behaviour of glacier systems

Question 15

How does aspect influence glacier movement

Answer 15

Aspect has a large impact on microclimates
If the aspect of a slope faces away from the general direction of the sun, temperatures are likely to remain below zero for longer, as less solar energy is received, and so less melting occurs.
The mass balance of glaciers in such locations will, therefore, tend to be positive, causing them to advance.
This has an impact on shaping the landscape because glaciers with a positive mass balance are more likely to be larger, with greater erosive power

Question 16

Formation of glacial ice

Answer 16

Called Diagenisis, Glaciers form when temperatures are low enough for snow that falls in one year to remain frozen throughout the year. Fresh snow falls on top of the previous year’s snow (fresh snow consists of flakes with an open, feathery structure and a low density

Question 17

Constrained glaciers

Answer 17

Valley glaciers - tongues of ice confined within valleys in mountainous regions
Cirque glaciers - small glaciers that occupy a bowl shaped hollow at the head of a glacial valley

Question 18

Unconstrained glaciers

Answer 18

Piedmont glaciers - valley glaciers that have spilled out into lowland regions
Ice caps - glaciers that cover entire mountainous regions
Ice sheets - glaciers that can be over two miles thick and cover whole continents

Question 19

Features of warm based glaciers

Answer 19

High altitude locations
Steep relief
Basal temperatures at or above pressure melting point
Rapid rates of movement, typically 20-200m per year.
Not only will the rapid ice movements cause significant erosion and erosional landforms, but the ablation also produces lots of meltwater and so landforms of glaciofluvial origin are also common.

Question 20

Features of cold based glaciers

Answer 20

High latitude locations
Low relief
Basal temperatures below pressure melting point, thus frozen to the bedrock
Very slow rates of movement, only a few metres per year
Limited landscape impact due to a lack of erosion and deposition taking place

Question 21

Pressure Melting point

Answer 21

The pressure melting point is the temperature at which ice is on the verge of melting
At the surface this is at 0oC, but within an ice mass it will be fractionally lowered by increasing pressure
Ice at pressure melting point deforms more easily than ice below it.

Question 22

Types of glacial movement

Answer 22

Basal sliding, Internal deformation, substrate deformation

Question 23

Abrasion

Answer 23

Rock that has been plucked is carried along at the base of the glacier. This debris embedded in the base and sides of the glacier scoured the bedrock as the glacier moves over it, causing it to be worn away. Fine material will smooth the bedrock to a polished finish, while coarser debris will scratch the bedrock, leaving grooves known as striations or sometimes chips called chatter marks.

Question 24

Plucking

Answer 24

Plucking occurs as meltwater freezes in joints in the bedrock, enabling the glacier to pull out pieces of loose rock as it moves forward. Plucking is especially effective on the downstream side of well jointed protruding bedrock at the base of the glacier.
High pressure on the upstream side of a protrusion causes pressure melting
The meltwater flows into joints on the downstream side where pressure is lower and the water refreezes
As the glacier moves forward the rock is pulled away as it is held within the mass of the glacier.

Question 25

Factors that influence the rate of glacial erosion

Answer 25

Presence of Basal Debris
Debris size and shape
Relative hardness of basal debris and bedrock
Ice thickness
Basal water pressure
Sliding of basal ice

Question 26

Types of glacial transportation

Answer 26

supra glacial, en glacial, subglacial

Question 27

Frost shattering

Answer 27

rainwater enters cracks in the rocks on the valley sides during the day. As the temperature drops at night the water freezes and its volume increases by 9% which exerts pressure on the rock, creating cracks. During the day the ice thaws and meltwater can then penetrate deeper into the rock. As this process repeats the cracks widen and eventually pieces of rock break off to form scree which covers the slopes of glaciated valleys.

Question 28

Dilation

Answer 28

when overlying pressure on bedrock is removed, such as when a glacier begins to melt during deglaciation, the underlying rock expands (dilates) and fractures parallel to the surface. This weakens the rock and makes it more susceptible to future subglacial erosion or frost shattering.

Question 29

Carbonation

Answer 29

rainwater reacts with carbon dioxide in the atmosphere to produce weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate which is soluble. This process is reversible and precipitation of calcium creates stalagmites and stalactites.

Question 30

Hydrolysis

Answer 30

a chemical reaction between rock minerals and water that is slightly acidic. During the hydrolysis the metal cations are replaced by congruent dissolution, silicates combine with water producing secondary minerals such as clays, feldspar in granite reacts with hydrogen in water to produce kaolin (china clay).

Question 31

Slides

Answer 31

these may be linear, with movement along a straight line slip pane, such as a fault or a bedding plane between layers of rock, or rotational, with movement taking place along a curved slip plane (slumps). In glaciated landscape systems, slides may occur due to a steepening or undercutting of valley sides by erosion of the base of the slope, adding to the downslope forces. Slumps are common in weak rocks like clay, which also become heavier when wet, adding to down slope force.

Question 32

Rock fall

Answer 32

this occurs on slopes of 40° or more, especially if the surface is bare, when rocks may become detached from the slope by physical weathering processes. These then fall to the foot of the slope under gravity. Transport processes may then remove this material, or it may accumulate as a relatively straight, lower angled scree slope.

Question 33

Nivation

Answer 33

a glacial process that is thought to include a combination of freeze-thaw action, solifluction, transport by running water and, possibly, chemical weathering. Nivation may be responsible for the initial enlargement of hillside hollows and the incipient development of corries.

Question 34

Corries

Answer 34

Start in a sheltered, gently sloping hollow on the shady side of a mountain where snow accumulates and the process of nivation deepens the hollow further by a mixture of freeze-thaw action, chemical action and solifluction
Should this snow fail to melt in summer subsequent layers of snowfall will compress it into neve and ultimately ice - a corrie glacier is thus formed
The headwall is eroded predominantly by plucking and the floor by abrasion, deepening the corrie as the ice moves downhill under gravity
Weathering of exposed rock faces by frost shattering generates debris which falls onto the ice and down the headwall crevasse (bergschrund) providing material for abrasion by the glacier
Seasonal and daily melting allows water to flow down the bergschrund which by nivation causes disintegration of rocks at the bottom of the glacier.
Summer meltwater lubricates the base of the glacier.
As the volume of ice increases and pressure release sheeting takes place, blocks are plucked from well jointed rocks and the corrie is over deepened.
When the ice melts, an armchair shaped hollow with a steep-sided backwall remains. The hollow may be occupied by a small lake (tarn, llyn or corrie lake eg Red Tarn by Helvellyn)

Question 35

Aretes

Answer 35

An arete starts as a ridge between two adjacent hollows on a mountainside
The hollows are then deepened to form Corries and the sides of the ridge become steeper
The sides of the ridge lie above the ice so they are exposed to frost shattering and become sharper until they form a prominent ‘knife edge’
Examples of aretes include Striding edge above Red tarn.

Question 36

Pyramidal Peaks

Answer 36

angular, sharply pointed mountain peaks which results from the cirque erosion due to multiple glaciers diverging from a central point

They often start as high altitude ground (often a nunatak above the ice)
The steepening of corrie headwalls on all sides together with frost shattering and subsequent mass movement on the headwalls leaves a pyramid shaped peak at the center, surrounded by steep headwalls and aretes
Examples of pyramidal peaks include Mount Snowdon in North Wales and the Matterhorn in Zermatt.

Question 37

Glacial troughs

Answer 37

U-shaped valleys with flat floors and steep sides

They generally start with a pre glacial V shaped river valley
As the erosive power of the glacier deepens the base and sides of the valley a characteristic U shape is formed
A marked break of slope on the valley side generally indicates the depth of the glacier
This break in the slope is called a bench or shoulder
Post glaciation the river that originally formed the V shaped valley is relatively small compared to the size of the U shaped valley
This river is clearly not large enough to have eroded such a massive landform so it is called a misfit stream
An example of a misfit stream would be the River Duddon in the Lake district

Question 38

Roche Moutonnes

Answer 38

small bare outcrops of rock shaped by glacial erosion, with one side smooth and gently sloping and the other steep, rough, and irregular

Roche Moutonnees are formed when a lump of bedrock protrudes above the underlying rock
As the glacier moves over it, on the Stoss side (uphill) abrasion takes place, forming a smooth and polished surface and striations
Pressure builds up on the Stoss end, leading to pressure melting
The water flows downhill through joints and bedding planes to the Lee side of the Roche Moutonne where the pressure is lower so the water refreezes in the joints and bedding planes
Plucking then takes place, leaving the Lee side with it’s characteristic jagged and steep side

Question 39

Hanging Valley’s

Answer 39

a valley which is cut across by a deeper valley or cliff

Before glaciation tributary streams fed the main river channel
These rivers formed their own tributary valleys
However during glaciation the main valley would have been over deepened
After this glacier melts this tributary valley is left ‘hanging’ above the main trough, with its stream cascading as a waterfall above the edge
Examples of hanging valleys include the valley formed by the Corrie Glacier that formed Cwm Idwal.

Question 40

Truncated spurs

Answer 40

ridges that descend towards a valley floor or coastline from a higher elevation, ending in an inverted-V face

Before glaciation, truncated spurs were the interlocking spurs of the river valley
The glacier, being more powerful and less flexible than the river truncates them, leaving a line of steep cliffs
The southern slope of Blencathra in the Lake district, as well as the North side of the Nant Ffrancon Valley hold examples of truncated spurs

Question 41

Ribon Lake

Answer 41

a long and narrow, finger-shaped lake, usually found in a glacial trough
They require a glacial trough to be blocked at one end for example by a moraine, to create a natural dam that allows long thin lakes such as Windermere to form behind it
Many Ribbon lakes today such as the one that used to cover the base of the Nant Ffrancon Valley have been filled in by progressive sedimentation as weathered debris accumulates in the lake from surrounding slopes
Ribbon lakes normally formed on impermeable bedrock and the hollow that they are formed in may have been deepened due to weaker lithology in that area

Question 42

Striations

Answer 42

Rock that has been plucked is carried along at the base of the glacier, scouring the glacier. Coarser debris will scratch the bedrock, leaving the bedrock with grooves known as striations.

Question 43

Morraines

Answer 43

Ridges or humps of deposited load carried by the glacier. Divided into a number of types, recessional, terminal, lateral and medial.

Question 44

Drumlins details

Answer 44

They are streamlined hills of glacial till, usually around 50 m height and 500m long, formed under a fast moving ice sheet
They have a long axis indicating the direction of flow of the glacier, a steep upstream (stoss) end and a narrower tail facing downslope (lee slope).
They often occur in groups called swarms, for example in the vale of Eden, Cumbria, forming a ‘basket of eggs topography’

Question 45

Drumlins formation

Answer 45

One popular theory is that a large boulder core prevents till from passing over and thus causes sediment to gradually build up around the core, as a result of depositional processes
Another theory is that huge glacial floods scour out the drumlins and light sediment then builds up over them as the flood subsides leaving a drumlin, this would also help to explain why many drumlins are found in partially submerged areas such as Clew Bay, Ireland

Question 46

Till Sheets

Answer 46

Glacial till sheets are a uniform blanket of glacial deposits in a low lying area
They generally cover areas at the margins of former ice sheets
The bedrock surface during glaciation may have been highly eroded but it is concealed by a thick cover of till, sands and gravels deposited by the glacier
Glaciation often leads to confused surface geology as the deposited till may have been carried from hundreds of miles away
Tills are unsorted, unconsolidated and unstratified

Question 47

Logement till

Answer 47

Deposited by moving ice, the long axis is aligned with the direction of flow of the glacier.

Question 48

Ablation till

Answer 48

Deposited when the ice melts, no lining up of the long axis (rocky road).

Question 49

Kames

Answer 49

a hill composed of stratified and sorted gravel laid down by glacial meltwater

Question 50

Delta Kames

Answer 50

Some are formed by englacial streams emerging at the snout of the glacier. They lose energy at the base of the glacier and deposit their load. Others are the result of supraglacial streams depositing material on entering ice-marginal lakes, losing energy as they enter the static body of water.
Some also form as debris filled crebasses collapse during ice retreat
Example - Kames are widespread in East Lothian, Scotland

Question 51

Kame terraces

Answer 51

ridges of material running along the edge of the valley floor
Supraglacial streams on the edge of the glacier pick up and carry lateral moraine which is later deposited on the valley floor as the glacier retreats
The streams form due to the melting of ice warmed in contact with the valley sides as a result of friction and the heat-retaining properties of the valley-side slopes.
Example - Kingsdale valley of the Yorkshire Valley, a kame terrace 2km in length

Question 52

Eskers

Answer 52

long, sinuous ridge composed of stratified sand and gravel laid down by glacial meltwater
Material is deposited in subglacial tunnels as the supply of meltwater decreases at the end of the glacial period
Sub-glacial streams may carry huge amounts of debris under pressure in confined tunnels at the base of the glacier.
Some argue that deposition occurs when the pressure is released and meltwater emerges at the glacier snout.
As the glacier snout retreats, the point of deposition will gradually move backwards - a potential explanation for why some eskers are beaded.
However others argue that the beads are simply the result of the greater load carried by summer meltwater.
Example - the Trim esker near Dublin is one of a group of twelve in the area - it is 14.5km long and between 4 and 15m high.

Question 53

Outwash Plains

Answer 53

a flat expanse of sediment in the pro-glacial area
As meltwater streams gradually lose energy as they enter lowland areas beyond the ice front, they deposit their load
The largest material is deposited nearest the ice front and the finest further away. Outwash plains are typically drained by beaded streams. These are river channels subdivided by numerous islets and channels.
Debris-laden braided streams lose water at the end of the melting period and so carry less material. This material is deposited in the channel, causing it to divide.
Braiding begins with a mid-channel bar which grows downstream. Discharge decreases after a flood or a period of snow melt, causing the coarsest particles in the load to be deposited first.
As discharge continues to decrease, finer material is then added to the bar, increasing its size.
When exposed at times of low discharge, channel bars are stabilised by vegetations and become more permanent features
The river divides around the island and then re-joins.
Unvegetated bars lack stability and often move, form and reform with successive flood or high-discharge events.

Question 54

Kettle Holes

Answer 54

a hollow created when buried blocks of glacier ice melt out.
A kettle hole is formed by blocks of ice that are separated from the main glacier - perhaps the ice front stagnated or retreated or perhaps ice blocks were washed out from the glacier during a glacier flood or jökulhaup.
If conditions are right, the isolated blocks of ice then become partially or wholly buried in outwash.
When the ice blocks eventually melt they leave behind holes or depressions that fill with water to become kettle hole lakes.
In freshly deglaciated areas, such as along the south coast of Iceland, kettles form obvious small lakes in the outwash plains.
In Scotland, they may be preserved as isolated small lakes, or deep water-filled depressions in boggy areas that were once the low-lying outwash plains.
Many kettles have been infilled with sediments, especially peat, during the Holocene.

Question 55

How may Glaciofluvial land forms change over time

Answer 55

Advance and retreat of glaciers may change the landforms
In post glacial times landforms may be subject to colonisation
Temperatures increasing leads to more melting and therefore deposition of till
Temperatures increasing increases the growing season for vegetation

Question 56

Frost Heave

Answer 56

The upward dislocation of soil and rocks by the freezing and expansion of soil water. Frost push occurs when cold penetrates into the ground. Large stones become chilled more rapidly that the soil. Water below such stones freezes and expands, pushing up the stones. Frost pull can alter the orientation of a large stone causing it to stand upright. This occurs when ice creeps downwards from the surface. The growth of ice crystals on the upper

Question 57

Patterned Ground

Answer 57

There are 5 different forms of patterned ground - circles, nets, steps, stripes and polygons. Frost heave forces rocks and soil upwards to form circles which provide the basis for all the other patterns - the up doming of the ground causes larger stones to roll outwards under the effect of gravity, while finer sediment remains central and raised in the circle.

Question 58

Pingos details

Answer 58

Dome shaped hills that are commonly up to 500m in diameter and up to 50m in height. They are characterised by permafrost and a seasonally changing active layer. At the core of the pingo is an ice lens of varying size, and the surface layer is made of soil often topped with vegetation. The surface can also contain cracks as a result

Question 59

Closed system pingos formation

Answer 59

Typical in low lying areas where permanent and continuous permafrost can be found. Over winter, groundwater underneath Thermokarst lake sediments, within the Talik, can be trapped by ice from the lake’s surface as the lake freezes, and permafrost advances through the ground. This decrease in temperature causes this groundwater to freeze into an ice lens, which grows over time as water freezes to the ice lens due to the increase in hydrostatic pressure. This causes the sediment above to bulge upwards into the characteristic pingo shape.

Question 60

Open System Pingos formation

Answer 60

Occur in areas of discontinuous permafrost where there are interspersed areas of permafrost and talik. The active layer continually freezes and melts year on year above the permafrost layer and talik. Over winter, as the active layer freezes down, water can become trapped between the descending freezing plane of the active layer and the permafrost that surrounds it. This promotes the growth of an ice lens which pushes the land up above it as it expands. Water underneath the permafrost can move through the talik between the permafrost areas because of capillary action (the movement of water through the soil) and hydraulic pressure. This water migrates to the ice lens and freezes, swelling the ground above further.