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Question 1

Ice Ages:

Answer 1

Begin as a result of global climatic changes.
• During the Quaternary period, which began just over 2 million years ago, the ice began to spread from the polar ice caps. At its greatest extent the ice covered nearly a third of the Earth’s surface and only 18,000 years ago it covered the UK from the Bristol Channel across Norfolk.

Question 2

Climatic Influences:
Reasons for climatic fluctuations are thought to include:

Answer 2

• Changes in the Earth’s position in space, its orbit and tilt.
• Variations in sunspot activity changing the amount of solar radiation received.
• Changes in amount of volcanic dust affecting the amount of radiation trapped by the atmosphere.
• Trapping of carbon dioxide by the oceans reducing the total amount in the atmosphere and thus cooling the planet.
• Variations in ocean currents.

Question 3

Glaciers as Systems:

Answer 3

• Glaciers are masses of ice which are continually changing and may be seen as an open system with inputs which add to the mass, and outputs which decrease the mass.
• Near the source, inputs generally exceed outputs and this is known as the zone of accumulation. This is due to:
  High altitudes have more precipitation (the orographic effect), mainly in the form of snow.
  New snow is highly reflective, absorbing less heat and therefore melting less.
• Stronger winds at higher altitudes cause snow to be blown into hollows and basins to that it accumulates.
• As temperature is low, sublimation and other losses are low, and meltwater is likely to refreeze.
• The zone of ablation is found at lower altitudes where inputs exceed outputs.

Question 4

firn (or equilibrium) line.

Answer 4

• The dividing line between the two zones is called the firn (or equilibrium) line. Gravity moves ice continually down to this line.

Question 5

glacial budget or net balance.

Answer 5

• The difference between total accumulation and total ablation for the whole of the glacier over one year

• This is calculated for the balance year which runs from autumn to autumn which is when summer ablation will have reduced the total ice mass to a minimum. There is a positive winter and negative summer balance.
• When the amounts of accumulation and ablation are equal, the glacier is in a steady state.

Question 6

Glacier Ice Formation:

Answer 6

• The climate deteriorates over a period of years.
• More precipitation falls as snow in winter.
• Shorter, less intense summers lead to a reduced degree of snow melting.
• If climate continues to deteriorate, snow will remain all year.
• This will form a permanent snowline.
• As the climate deteriorates further, the snowline moves downhill.

Question 7

Conversion of Snow to Ice:

Answer 7

• Snow falls as flakes - open feathery structures - trapping air as they accumulate (alimentation).
• Continued accumulation leads to compression of the upper layers of the snow.
• Lower layers turn to nevé or firn - compressed snow but not ice.
• Nevé is now denser and soon turns to ice pellets.
• Further compaction causes the grains of firn to re-crystallise and it turns bluish.
• It takes roughly 25-40 years to form solid glacial ice in temperate latitudes

Question 8

What Factors Influence Distribution of Ice Cover?

Answer 8

Latitude:

Altitude:

Relief:

Aspect:

Question 9

Latitude:

Answer 9

• At higher latitudes, much less of the sun’s rays hit the ground.
• This means that much less solar energy is received per unit area near the poles than nearer the equator. Due to this, average temperatures are much lower.

Question 10

Altitude:

Answer 10

• Annual temperatures are lower at higher elevation.
• This is because, as the altitude increases, lower atmospheric pressure causes air to expand its volume, lose energy and decrease in temperature.
• everyomne 100m upwards, temp decreases by 1 degree - environmental lapse rate
  An example of equatorial ice is Kilimanjaro in Kenya.

Question 11

Relief:

Answer 11

In steep, high relief areas and mountains, it is less likely that glaciers can build up as there is less low-angle ground to hold snow and allow accumulation.

Question 12

Aspect:

Answer 12

• North-facing slopes are shadier in the Northern Hemisphere due to there being less insolation.
  They are therefore more conductive to snow accumulation.
• The warm south-westerly prevailing wind is also a factor and will have less effect on north or north-east facing slopes.
• The snow-bearing winds tend to blow in from the north and will therefore hit north facing slopes.

Question 13

Glacial Surges:

Answer 13

• Where snowfall is exceptionally heavy or there is much rainfall, the glacier may react quickly and surge forward
• Flow rates of over 1000m a year or more are seen in large ice streams in Antarctica and outlet glaciers in Greenland.

Question 14

Glacier Size and Shape:

Answer 14

Niche Glaciers

Corrie Glaciers

Valley Glaciers

Piedmont Glaciers

Ice Caps

Question 15

Niche Glaciers

Answer 15

are small patches of glacier found on upland slopes. Most prevalent on north-facing slopes in the northern hemisphere and have no effect on topography.

Question 16

Corrie Glaciers

Answer 16

are small ice masses on mountain slopes which gradually erode armchair shaped hollows. If they develop too large for the hollow, they spill over the lip to feed a valley glacier.

Question 17

Valley Glaciers

Answer 17

are larger masses of ice that flow from icefields or a corrie and usually follow preglacial river valleys, developing steep sides as they erode their course.

Question 18

Piedmont Glaciers

Answer 18

are large lobes of ice formed when the glaciers spread out. They may merge on reaching lowland areas and escape the confines of their valleys.

Question 19

Ice Caps

Answer 19

are huge, flattened, dome-shaped masses of ice that develop on high plateaus. When over 50000km squared in area they are known as ice sheets.

Question 20

Cold-based (polar) glaciers

Answer 20

occur in polar latitudes where the temperature of the snowfall is far below freezing and the glacier remains at well below freezing point. Ice remains frozen to the bedrock and as a result there is very little ice movement and thus limited erosion.

Question 21

Warm-based (temperate) glaciers

Answer 21

include most glaciers outside of Antarctica and the northern Greenland ice caps. Water is present throughout the ice mass and acts as a lubricant. This allows for much greater movement.

Question 22

Types of Ice Movement:

Answer 22

Internal Flow or Internal Deformation:

Basal Slippage:

Extensional and Compressional Flow:

Rotational Flow:

Question 23

Internal Flow or Internal Deformation:

Answer 23

• This is the movement within the glacier ice resulting from the stresses applied by the force of gravity.
• Where ice crystals orientate themselves in the direction of the glacier’s overall movement, they may slide past each other.
• Such movements often result in the formation of crevasses within and at the surface of the ice.

Question 24

Basal Slippage:

Answer 24

• This is the sliding effect of a glacier over the bedrock by either regelation slip or creep.
• Regelation slip operates most effectively with smaller obstacles while creep is the process that mainly overcomes larger protuberances.
• On the upglacier side of an obstacle, the increasing pressure in the lower ice causes pressure melting locally. The meltwater permits slippage of the ice over the obstacle but then refreezes in the lower-pressure conditions on the downglacier side of the obstacle.
• The thin layer of ice where this happens is called the regelation layer.
• Creep may occur where there is little or no regelation slip. It refers to the plastic deformation that occurs within the ice when its course is impeded by larger obstacles. Larger obstacles greatly increase the stress in the ice and cause it to become more plastic in behaviour so that it creeps or flows around the obstacle.

Question 25

Extensional and Compressional Flow:

Answer 25

• Velocity steadily increases in the accumulation zone as the firn line approaches, as downvalley ice is consistently pulling away from upvalley ice. Such a condition is called extensional flow.
• Below the line, velocities fall as the ice from the upper valley is continually pushing against downvalley ice. This is compressional flow.
• Sudden breaks in velocity such as at icefalls give rise to extreme extending flow and large transverse and longitudinal crevasses are generated, creating a landscape of sharp-crested angular blocks called seracs.

Question 26

Rotational Flow:

Answer 26

• This movement is characteristic of corries where the ice slides down into an armchair-shaped hollow about a central point of rotation.

Question 27

Influences on Rate of Movement:

Answer 27

• Snow and ice masses do not generally move downslope until the thickness exceeds 60m.
• Steep glaciers flow faster than gently graded ones and thus are usually thinner.
• Movement is faster over an impermeable surface compared with a permeable surface in temperate zones as basal meltwater is retained, which aids slippage.
• The amount of precipitation and ablation are significant factors.
• The greatest velocity is usually at the firn line, as velocity is directly related to thickness.
• The centre of the glacier, which the ice is thickest, moves more rapidly than the margins, where friction plays a considerable role in reducing speed.