Past & Present Ice Cover (Edexcel A Level Geography)
Revision Note
Written by: Jacque Cartwright
Reviewed by: Bridgette Barrett
The Cryosphere
The cryosphere is all the frozen regions on Earth and covers 13% of the planet's surface
The term comes from the Greek word 'kryo', meaning cold
Ice can be found in
High latitudes - Arctic and Antarctic Circles of more than 65° north and south of the equator
High altitudes - found in mountain ranges, which can be at any latitude (Drakensberg Mountains, SA is over 3000m high at a latitude of 29° south of the equator)
Features of the cryosphere include:
Snow
Ice (69% of the world's freshwater is stored as ice)
Permafrost and frozen ground - not all frozen ground is permafrost
Glaciers
Ice caps, sheets and shelves
Icebergs
Sea, river and lake ice
Most of the cryosphere is found in Antarctica (85%) and the Arctic polar region (12%), as ice sheets, shelf ice, and permafrost
The largest, single ice mass on Earth is the Antarctic ice sheet, covering 8.3% of the global land surface
It took millions of years to form; is up to 4.8 km (3 mi) deep in parts; and covers approx. 14 million km² (5.4 million mi²) and contains 30 million km³ of ice
If it melted, it could raise sea levels by 58 meters (190 feet)
Permafrost areas are significant global carbon stores and help regulate levels of carbon in the atmosphere
The cryosphere helps regulate Earth’s climate through its high surface albedo effect
As the climate warms, the cryosphere also changes through feedback mechanisms, which further influences the climate:
Increased snow and ice melt, exposes more dark surfaces to insolation
Which increases surface absorption of solar radiation, causing further melting and release of stored carbon and methane into the atmosphere, which leads to further atmospheric warming
This is a positive feedback loop, which exacerbates the impacts of climate change
Classification of Ice Masses
There are two groups of ice masses:
Constrained - these do not have a dome-like structure, so the flow and shape of the ice is influenced by its surroundings - valley, piedmont and cirque glaciers
Unconstrained - the flow and shape of this ice is not influenced by its surroundings - ice sheets, shelves and caps
These have the basic shape of a broad, slowly moving, central dome, with channels of faster-moving ice that flows to, and at, its margins
Unconstrained
Ice sheets
Continuous masses of ice, that cover areas greater than 50,000 km³
With no surrounding mountains or features to contain them, continental glaciers spread out and cover the surface
They spread out from the centre and can cover whole valleys, plains and mountain ranges with ice
Sometimes only the tips of mountain peaks show above the ice, called nunataks
In 2009, Antarctic scientists found a mountain range, as large as the European Alps, hidden under 2.5 miles (4km) of ice
Ice caps
Cover areas of less than 50,000km³
Usually centred on a mountain's high point (called a massif), the ice flows flow in multiple directions to form a cap
This flow of ice feeds into a series of glaciers at its edges
Polar ice caps are not strictly 'caps' as they are greater than 50,000km³
Ice shelves
These are thick, floating slabs of ice, permanently attached to a landmass
Found where ice flows down to the coast and out onto the ocean's surface
Only found in Greenland, Northern Canada, Antarctica and the Russian Arctic
Constrained
Ice fields
Ice that covers a mountain plateau, but does not extend the high-altitude area
Not thick enough to bury the topography and covers 5 -1500km³
Examples include the Himalayas, Rockies, Andes, and the Southern Alps of New Zealand
Piedmont glaciers
Found at the foot of mountains, where a mass of ice has flowed downslope and fans out, forming lobes of continuous ice
Valley glacier
Ice is surrounded by high mountains and fills the valley
They are usually ribbon-shaped and vary in length from a few kilometres to over 100km
They can be a single feature or made up of multiple glacial tributaries from surrounding valleys
Most begin as mountain glaciers and spread/flow to gorges, basins and across the valley floor
Examples include the Andes, Himalayas and European Alps
Cirque glaciers
Most common type of glacier and found in nearly all areas where snow and ice accumulate - e.g. alpine regions
Confined to either the upper parts of a glacial trough or within the hollowed, cirque basin itself
It is the basin that dictates the size, shape and flow of the glacier
Niche glaciers are smaller versions of cirque glaciers
Thermal regime of ice masses
This refers to an ice mass's basal temperature and indicates whether water or ice will be present
Pressure melting point (pmp)
The temperature at which ice melts at a given pressure is the pressure melting point (pmp)
The melting point of water depends on air pressure above the ice
As air pressure increases, the temperature at which ice melts lowers
At 1 atmosphere pressure, the melting point of ice is 0°C
At 200 atmospheres, the melting point decreases to -1.85°C
Warm-based glaciers
Occur in temperate regions such as southern Iceland and western Norway
They are relatively small and range in width from hundreds of meters to a few kilometres
Melting occurs during the summer months
It is this meltwater that 'lubricates' the base and sides of the glacier, which assists movement (called basal sliding) and increases rates of erosion, transportation and deposition
As such, all ice in these glaciers is at, or close to, the melting point of ice
Temperatures at the base are, therefore, at or just above the pressure melting point
Cold-based glaciers
Occur in polar regions such as central Greenland and Antarctica
They are large, vast sheets and caps of ice covering hundreds of km²
Temperatures remain below melting point, with low rates of precipitation, resulting in low levels of accumulation
Basal temperatures remain below the pmp, therefore, basal sliding does not happen
This results in little erosion, transportation and deposition
Any movement is by internal deformation
The ice stays frozen to the bedrock and moves slowly at 1-2cm a day
Orientation of the ice crystals in the glacier, to the direction of movement, allows the crystals to slide over each other
Polythermal glaciers
These are glaciers with both warm and cold bases but at different altitudes
They usually show a cold base in their upper reaches (high altitudes)
At the lower altitudes, their bases are warm with meltwater
Present Day Distribution of Ice Sheets
Past glaciation
The last glacial maximum was 21,000 years BP, where over 30% of the Earth's surface was glaciated
The polar ice sheets covered much of the UK and major parts of southern Europe were periglacial
Sea levels dropped, and shorelines extended farther out, creating more land (water was trapped in ice sheets)
The climate was drier, because most of the water on Earth's surface was ice, resulting in less precipitation
Earth's average temperature was 6°C (average now is 14-15°C)
The present-day distribution of cold environments can be divided into polar, glacial, alpine and periglacial areas
Polar - considered areas of permanent ice within the northern and southern extremes of the Antarctic and Arctic regions
They are found in areas of high latitude, with long winters and short summers, with high levels of storms and cold winds
The Arctic polar environment can be defined either by the Arctic circle at 66° N or by the July isotherm of 10° C
Isotherms are areas of the same temperature
July is the hottest month and areas north of this line have an average of 10°C or below
Winter sea ice is shrinking
The Antarctic is much colder than the Arctic, with strong westerly winds, cold oceans and a large landmass
Winter sea ice is increasing
Defined by the 10°C January isotherm (January is the hottest month in the southern hemisphere)
Other examples include Greenland and northern Canada
Upland Glaciated Landscapes Today
Glaciated landscapes vary, dependent on location - polar, glacial, periglacial and alpine
Glaciated landscapes can be divided into active (current) or relict (past) landscapes
Geology influences the nature of a glaciated landscape
Igneous rock is harder to erode and often makes up high mountains with steep sides and hollows
Large amounts of poorly sorted sand, gravel, and boulders are plucked and pried from the surface and mountains
As the glacier flows over bedrock, the sediments trapped in the ice, are ground into a fine powder called rock flour
Rock flour acts as sandpaper, that polishes the surface of exposed rock to a smooth finish called glacial polish
Larger rock pieces scrape over the surface creating grooves called glacial striations
The Highlands of Scotland, the Lake District and Snowdonia (Eryri), North Wales show many relict landscapes from the Pleistocene epoch, including arêtes, erratics, cirques/corries, and corrie lakes
Sedimentary and metamorphic rocks are found mainly in low-lying areas (already eroded from the uplands) and are easier to erode
During the last Ice Age, the advancing ice sheet moved chalk, boulder clay etc. into the south and east of England
Examiner Tips and Tricks
If asked to discuss evidence of past glaciated landscapes, remember to include how relict landscapes are a partly preserved snapshot of very different conditions (climate and processes) in the past and that landforms could not have arisen without extensive glaciation in those areas.
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