A-Level Geography: Glaciation Keywords

Internal deformation

A 'creep' method found generally in cold-based glaciers where the ice crystals orientate themselves in the direction of movement. This allows ice crystals to slide past one another.

Benchmark glacier

A glacier chosen to be monitored annually for ablation and accumulation

Rock glacier

A glacier covered by a layer of scree/talus or a mass of rock and debris mixed with ice; forms a glacier like landform

U shaped valley

A hanging valley where tributaries must drop down into the glaciated valley floor, produced by erosion and the chopping of mountains due to glaciation

Loch Lomond Stadial (Younger Dryas)

A period of time (12.9k yrs ago - 11.7k yrs ago) where global average temperatures decreased by 7 degrees, causing glacial advancement which reached as far as the Lake District and North Wales. No known cause of event, however, it is thought that this may have been caused by the draining of a huge proglacial lake (Lake Agassiz) which dramatically effected global ocean circulation

Little Ice Age

A period of time (1550-1750) where global temperatures decreased, this caused glacial re advancement in in Europe, spread of arctic sea ice (reaching Iceland). Bodies of water all over the world froze over including the Thames and the New York harbour, however, it was brought to an end by the industrial revolution

Orbital/Astronomical forcing

A process which can change the amount of energy from the sun reaching the Earth and forces climate to change as a response

Patterned ground

A range of geometric landforms including circles, nets, polygons and steps. Caused by frost-action, this is in the form of frost push and frost heave, causing mass-movement on the surface

Blockfield/Felsenmeer

A surface covered by boulders, rocks and debris; formed by frost weathering below the surface leading to jagged, angular rocks on the surface

Milankovitch cycle

A theory that suggests that changes in the Earth's climate are caused by variations in solar radiation received at the Earth's surface. These variations are due to cyclical changes in the geometric relationship between the Earth and the Sun. It comes in three parts: orbit eccentricity, axial tilt and Earth wobble

Tarn

A type of glacial lake where water fills a corrie

Equilibrium point

Ablation losses and accumulation gains are balanced within a glacier

4.6 billion years

Age of the Earth

Discharge

Amount of water flowing downstream, measured in Cumecs

Resistive Stress

Caused by friction, greatest at bottom and sides of glacier (all points of contact)

Sheer stress

Caused by the mass of glacier, greatest in centre of glacier

Ice sheet

Complete submergence of regional topography; forms a gently sloping dome of ice several kilometres thick in the centre

Transverse Crevasses

Cut across glacier, perpendicular to the direction of flow

Solar spots

Dark spots on the Sun's surface caused by intense magnetic storms

Plucking

Erosive process of particle detachment by moving glacial ice. In this process, basal ice freezes in rock surface cracks. As the main body of the glacial ice moves material around, the ice in the cracks is pulled and plucked out. Also called quarrying

Glacier

Flowing sheet/river of ice

Solifluction

Form of mass movement in environments that experience freeze-thaw action. It is characterised by the slow movement of soil material downslope and the formation of lobe-shaped features

Discontinuous permafrost

Form of permafrost that contains numerous scattered pockets of unfrozen ground

Continuous permafrost

Form of permafrost that exists across a landscape as an unbroken layer

Sporadic permafrost

Form of permafrost that exists as small islands of frozen ground in otherwise unfrozen soil and sediments

Radial Crevasses

Found at the Piedmont where cracks radiate from the centre of the glacial spread

Marginal Crevasses

Found at the sides of a glacier, caused by differences in the rate of flow (as glaciers flow fastest in the middle)

Ice wedge polygons

Frost cracking creates areas of irregular polygons, where the active layer thaws, water flows down into the cracks and subsequently freezes building up a wedge and raising the ground around it

Valley glacier

Glacier confined between valley walls and terminating in a narrow tongue; forms from ice caps/sheets or cirques; may terminate in sea as a tidewater glacier

Glacial distribution

Greater snow cover in high altitudes and greater values of latitude

Corrie

Hollow in mountain-side, arm-chair shaped landform

Pingo

Ice core mounds, very large (30m-70m high), can be conical or elongated. The growth of a core pushes up sediment, forming mounds

Ice field

Ice covering an upland area, but not thick enough to bury topography; many do not extend beyond highland source

Cirque

Landform created by glaciers, grinding an existing valley into a rounded shape with steep sides, often called a corrie or cwm

Ice shelf

Large area of floating glacier ice extending from the coast where several glaciers have reached the sea and coalesce

Ice Field

Large level area of glacial ice found covering a large expanse of land. Similar in size to an ice cap but does not have a dome shape

Névé or firn

Partially melted and compacted snow that survives the year's ablation season (it can become glacier ice)

Glacial Period

Period of time during an ice age when glaciers advance because of colder temperatures

Interglacial Period

Period of time during an ice age when glaciers retreat because of milder temperatures

Pleistocene

Period of time from about 2 million years ago to 11,700 years ago. During this period areas of land at higher and middle latitudes where covered with glacial ice

Abrasion

Physical wearing and grinding of a surface through friction and impact by material carried in water or ice

Nivation

Process where snow patches initiate erosion through physical weathering, melt-water flow and gelifluction

Interstadials

Short-term changes to conditions that lead to ice

Stadials

Short-term changes to conditions that lead to ice re-advances

Cirque glacier

Smaller glacier occupying a hollow on the mountain side- carves out a corrie or cirque; smaller version is known as a niche glacier

Ice cap

Smaller version of ice sheet occupying upland areas; outlet glaciers and ice sheets drain both ice sheets and ice caps

Causes for short term fluctuations of temperature

Solar spots and volcanoes

Arêtes

Steep ridges between corries

Ablation

Surface removal of ice or snow from a glacier or snowfield by melting, sublimation, and/or calving

Albedo

The amount of light or radiation that is reflected by a surface such as ice

Calving

The breaking up of the ice sheet at the glacier snout which then forms icebergs

Eccentricity

The change of the Earth's orbit from circular to elliptical

Anthropocene

The current geological age, the period during which human activity has been the dominant influence on climate and the environment

Cryosphere

The frozen water part of the Earth system

Scree/Talus Slopes

The loose debris on the face of a mountain, a product of rock fall, debris flow and avalanches

Thermohaline circulation

The ocean consists almost entirely of water and salt . The density of water depends on its temperature and salinity. Any changes to this causes the water to flow (currents). Also known as ocean conveyor

Atmosphere

The part of the Earth system consisting of air and anything above the surface

Hydrosphere

The part of the Earth system consisting of water, such as lakes, seas, oceans and clouds

Biosphere

The regions of the surface and atmosphere of the Earth occupied by living organisms

Lithosphere

The rigid outer part of the Earth system, consisting of the crust and upper mantle

Basal Sliding

The sliding of a glacier over the surface it rests on. Caused by the gradient of the slope and the weight of the glacier's mass. Comes in two forms: relegation slip and enhanced basal creep

Permafrost active layer

The top level of soil of permafrost that thaws and freezes during summer and winter

Precession

The wobble of the earth

Obliquity

Tilt of the earth varies between 22.2 and 24.5, the greater the tilt, the more solar energy the Earth receives

Lithology

Type and properties of an area's rock

Talik

Unfrozen ground

Piedmont glacier

Valley glacier which extends beyond the end of a mountain valley into a flatter area and spreads out like a fan

Icehouse conditions

Very cold glacial conditions

Greenhouse conditions

Warmer interglacial conditions

Soft-bed subglacial deformation

When a bed of rock is unconsolidated and the sediment itself deforms and moves along with all ice above it. Can account for 90% of forward motion

Loess

When glaciers grind rocks to a fine powder the wind can transport the fine, mineral-rich material and deposit it creating a new soft rock that is loosely packed and pale in colour. It can range in thickness from a few centimetres to more than 91 metres (300 feet)

Intergranular flow

When individual ice crystals deform and begin to move in relation to each other

Laminar flow

Where individual layers of the glacier move

Truncated Spurs

Where interlocking spurs have been chopped off by the glacier

Tors

where more resistant areas of rock are left; uneroded stacks of smooth rock