glaciers Flashcards
pleistocene period
A geological period from about 2 million years ago to 11,500 years ago, the early part of the quaternary which included the most recent age
greenhouse conditions
Much warmer interglacial condition
interglacials
Warmer periods similar to present i.e. greenhouse periods
glacials
Cold, ice-house periods within the Pleistocene
ice house conditions
very cold glacial conditions
what are the 4 main types of cold environment
polar
alpine
periglacial
glacial
what is a polar environment
glacial environments are found in the high latitudes of the Antarctic and Arctic. They are characterised by extremely cold temperatures (average annually of -30 to -40°C and low levels of precipitation.
what is a alpine environment
glacial environments are found at high altitudes in mountain ranges in the mid-low latitudes e.g. European Alps, the Himalayas and Andes. They are characterised by high levels of precipitation and a wide temperature range with frequent freeze-thaw cycles
what is a glaciar environment
are slow-moving bodies of ice in valleys, which shape the landscape in both polar and alpine environments
what is a periglacial environment
hese environments do not feature glaciers, but are usually found next to glacial areas. They are characterised by permafrost and occur in high latitude or high-altitude areas where seasonal temperatures vary above and below freezing point. E.g. Siberia, Alaska and northern Canada
what are eons
the longest span of geological time; eras are the second longest
Eon often refers to a span of around one billion years.
the pleistocene epoch
often known as the ice age as it contained 50 glacial-interglacial cycles and glacials reached their furthest extent in this time.
what was the last glacial maximum
known as the Devensian which was 18,000 years ago
what was the last UK glacial advance
the Lock Lomond Stadial which was 12,000 to 10,000 years ago and marked the end of the Pleistocene epoch
what type of environment is the UK now
UK is now called a relict glacial environment (it no longer experiences glacial conditions but it does display evidence of the Pleistocene glaciation period.)
when was the Start of the Pleistocene epoch/Quaternary period
2.6 million years ago
when did the Devensian glacial end (lasr glacial maximum)
180,000 years ago
when was the End of the Pleistocene/start of the Holocene epoch
11,500 years ago
when was the Lock Lomond stadial (last UK glacial advance)
10,000-12,000 years ago
stadial and interstadial
short-term fluctuations within ice-house and greenhouse conditions; stadials are colder periods that lead to ice re-advances, interstadials are shorter periods of warmth.
why are there fluctuations of glacials and interglacials
long and short term causes of climate change
long term causes of climate change (milankovitch cycles)
continental drift
eccentricity of the orbit
axial tilt
wobble
short term causes of climate change
variations in solar output
volcanic causes
continental drift
3 million years ago the North and South American tectonic plates collided. This re-routed ocean currents so that warm Caribbean waters were forced northwest, creating the Gulf Stream.
eccentricity of the orbit
The shape of the Earth’s orbit varies from circular to elliptical over 100,000 year cycles. The Earth receives less solar radiation in the elliptical orbit when the Earth is farthest from the Sun. (A position known as aphelion)
axial tilt
The tilt of the Earth’s axis varies between 21.5° and 24.5° over 41,000 year cycles. This changes the severity of the seasons.
wobble
the Earth wobbles as it spins on its axis, which means that the season during which the Earth is nearest to the Sun (a position known as perihelion) varies. At present, the northern hemisphere winter occurs in perihelion. i.e. milder conditions than previous winters in aphelion. This varies over approximately 21,000 year cycles resulting in changes in the intensity of the seasons.
variations in solar output
The dark areas of the Sun (sunspots) are caused by intense magnetic activity in the Sun’s interior. An increase in the number of sunspots means that the Sun is more active and giving off more energy. They appear to vary over an 11 year cycle.
volcanic causes
Large eruptions can eject huge volumes of ash, sulphur dioxide, water vapour and carbon dioxide into the atmosphere (volcanic aerosols) which are globally distributed by winds. This aerosol blocks the Sun’s radiation, cooling the Earth. The ash tends to settle back on Earth within a few months, however the sulphur dioxide gas can remain in the atmosphere for up to three years, which reflect the radiation back into space.
what is the cryosphere
The cryosphere consists of ice sheets and glaciers, together with sea ice, lake ice, permafrost and snow cover.
what are mass and energy constantly exchanged between
Mass and energy are constantly exchanged between the cryosphere and other major components of Earth systems; the hydrosphere. Lithosphere, atmosphere and biosphere
what are glaciers
large bodies of ice which flow downhill under the influence of gravity.
what are the two bases of glaciers
land based glacier
marine based
land based glaciers
their base is at or above sea level e.g Mer de Glace flows from Mont Blanc in the Alps, or glaciers flowing from the Rocky Mountains.
marine based glacier
where the base is below sea level. E.g. the West Antarctica Ice Sheet – which is 2000m below sea level actually frozen to the sea bed.
what are the two types of glaciers
warm based glaciers
cold based glaciers
warm based gaciers
occur in high altitude areas outside the polar regions e.g. the Alps. The temperature of the ice is often close to zero and mild summer temperatures cause melting.
cold based glaciers
These occur in polar glacial environments such as Greenland and Antarctica. These glaciers are frozen onto the bedrock below and melting only occurs on the surface in the summer months.
types of ice mass
ice sheet
ice cap
ice field
valley glacier
piedmont glacier
cirque glacier
ice shelf
ice sheet
Complete submergence of regional topography; forms a gently sloping dome of ice several kilometres thick in the centre
ice cap
Smaller version of ice sheet occupying upland areas; outlet glaciers and ice sheets drain both ice sheets and ice caps
ice field
ice covering an upland area, but not thick enough to bury topography; many do not extend beyond highland source
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.
piedmont glacier
Valley glacier which extends beyond the end of a mountain valley into a flatter area and spreads out like a fan
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 shelf
Large area of floating glacier ice extending from the coast where several glaciers have reached the sea and merge.
ice sheet size
10-100,000 sq km
ice cap size
3-10,000 sq km
ice field size
10-10,000 sq km
valley glacier size
3-1,500 sq km
piedmont glacier
3-1,000 sq km
cirque glacier
0.5-8 sq km
ice shelf size
10-100,000 sq km
the glacial system
Glaciers gain mass through the transformation of snow into ice and then flow downhill (in response to gravity) and eventually lose mass due to melting. Hence glaciers can be viewed as systems with inputs, stores, transfers and outputs.
accumulation defintion
the input of snow and ice to a glacier
ablation defintion
the output of snow and ice from a glacier
sublimation
the process of a substance turning from a solid directly to a gas without the liquid stage in the middle.
glacier mass balance
is calculated using the total accumulation and ablation within a year.
equilibrium line
when losses from ablation are balanced by gains from the accumulation in a glacier
accumulation (inputs)
avalanches from above slopes
rock debris
wind deposition
precipitation (mainly snow)
ablation (outputs)
evaporation (sublimation)
break away of ice blocks and ice bergs (calving)
meltwater
melting (water)
glacial budget
A glacier mass balance/annual budget is calculated using the total accumulation and ablation within a year.
what does the glacial system involve
inputs, stores, transfers and outputs
Accumulation
Ablation
Sublimation
Equilibrium line
Mass balance
how much greater was ice cover at the Pleistocene maximum than the present day
more than three times greater
general trends in ice cover
Major ice extensions were over North America and Europe.
Ice extensions over West and South of South America.
ice cover of the Antarctica and Greenland ice sheets
The Antarctica and Greenland ice sheets only covered a slightly greater area than they do today. With the West Antarctica ice sheet expanding 10km either side of the peninsula
ice cover of the Laurentide and Cordilleran ice sheets
The Laurentide and Cordilleran ice sheets covered East and West of North America stretching to around 3000km in width
ice cover of the scandinavian ice sheet
The Scandinavian Ice Sheet across Europe, in particular covering the area of UK the UK widening to 500km
at present what % of Earths land area does ice cover
ice covers over 10% of the Earth’s land area which accounts for 75% of the world’s freshwater (about 1.8 % of all water on Earth.
what % of all glacier ice is contained in Antarctica
85%
what factors affect distribution of ice mass distribution
latitude
altitude
aspect
why is latitude a factor in ice mass distribution
particularly important for polar ice masses. In high latitudes the sun’s rays hits the ground at a lower angle, so the solar energy received has to heat a larger area.
why is altitude a factor in ice mass distribution
particularly important for alpine glaciers. High altitudes are impacted by the environmental lapse rate (ELR) whereby temperature declines by 1° for every 100m above sea level
why is aspect an important factor in ice mass distribution
This can determine the amount of snow falling and where it settles. In the northern hemisphere, north and east facing slopes are both more sheltered and shadier
periglacial meaning
The term ‘periglacial’ has previously been used to refer to cold environments on the margins of glaciers, today though the term is widely used to refer to non-glacial cold environments, which are characterised by periods of extreme cold, dry conditions.
what are periglacial environments also referred to as
the tundra – a term describing the treeless vegetation of dwarf shrubs, grasses, lichens and mosses.
what is permafrost
permanently frozen ground where subsoil temperatures remain below 0°C for at least two consecutive years.
what % of the earth experiences periglacial conditions
20%
mainly in the northern hemisphere. During the Pleistocene glacial periods, this was higher at 33% and at much lower latitudes than today
what are the 3 types of permafrost
continuous
sporadic
discontinous
continuous permafrost
forms in the coldest areas of the world where mean annual temperatures are below -6°C. It is found at the highest latitudes. It can extend downwards for hundreds of metres.
sporadic permafrost
occurs where the mean annual temperature is only just below freezing and permafrost cover amounts of less than 50% of the landscape
discontinuous permafrost
is shallower and permanently frozen ground is fragmented by patches of unfrozen ground (talik). The surface layer of the ground melts during the summer months.
what factors affect periglacial distribution
climate
proximity to water bodies
slope angle and aspect
ground surface
vegetation cover
climate
temperature and moisture determine the presence or absence, depth and extent of permafrost
proximity to water bodies
lakes tend to be warmer so remain unfrozen
slope angle and aspect
influencing solar radiation and therefore melting, freeze-thaw and wind
ground surface
rock and soil types can determine degree and depth of permafrost
vegetation cover
can insulate the ground
what processes shape periglacial landscapes and landforms
freeze thaw weathering
soliflvution
nivation
frost heave
groundwater freezing
ground contraction
aeolian action
meltwater erosion
what is freeze thaw weathering
when water freezes in the cracks and joints of rock, it expands by 10%of its volume, weaknening the rock and causing disintergration through repeated freeze thaw cycles
process is also known as frost action or frost shattering
what landform does freeze thaw weathering create
an accumulation of frost shattered rock fragments known as a blockfield when on a flat surface and scree when on a slope
solifluction
the downslope movement of the saturated active layer under the influence of gravity
known as gelifluction when it occurs over impermeable permafrost
what periglacial landform does solifluction create
a tongue shaped feature at the foot of a slope knwon as a solifluction lobe
nivation
a combination of processes weakens and erodes the ground beneath a snow patch
these processes include freeze thaw weathering solifluction and meltwater erosion
what landform does nivation create
rounded nivation hollows formed in upland areas
frost heave
the freezing and expansion of soil water causes the upward dislocation of soil and rocks
as the ground freezes, large stones become chilled more rapidly than the soil
water below such stones freezes and expands, pushing the stones upwards and forming small domes on the ground surface
what landform does frost heave create
on flat ground stone polygons formed as the large stones settle around the edges of the domes
on slopes stone stripes formed as the stones moved downhill
what is groundwater freezing
where water is able to filter down into the upper layers of the ground and then freeze
the expansion of the ice causes overlying sediments to heave upwards into a dome which may rise as high as 50m
what landform is created by groundwater freezing
an ice cored dome called a pingo
ground contraction
when dry areas of the active layer refreeze, the ground cracks and contracts
ice wedges will form when meltwater enters the crack during summer and freezes at the start of winter
repeated thawing and refreezing of the ice widens and deepens the crack, enlarging the ice wedges
landform created by ground contraction
large scale polygonal patterns on the ground surface knwon as ice wedge polygons
aeolian action
due to limited vegetation cover the wind is able to pick up and transport the fine dry sediment from the ground surface
landform created by aeolian action
extensive accumulations of wind-blown deposits known as loess
meltwater erosion
during the short summer, thawing creates meltwater which erodes stream or river channels
refreezing at the onset of winter causes a reduction in discharge and sediment deposition in the channel
landforms created by meltwater erosion
braided streams with multiple channels separated by islands of deposited material
periglacial landforms
blockfield
solifluction lobe
nivation hollows
stone polygons
pingo
ice wedge polygons
loess
braided stream
ice wedges
When permafrost contracts under extremely low temperatures it cracks.
During summer months, meltwater enters cracks in the ground.
During winter this meltwater freezes, forcing the crack to widen.
patterned ground
The landforms are formed by a series of movements resulting from frost action.
Frost can push sediment upwards as well as outwards.
Larger sediments roll out to the outside of the pattern, leaving finer sediments in the middle
Mass movement can also cause stone nets and stripes – beyond a slope of 30°, these ground features no longer occur
pingo
They are ice core mounds between 30-70m in height and 100 – 500m in diameter.
They can either be conical (cone shaped) or elongated
In the summer when the pingo ice core melts, it’s centre collapses to form a central dip or depression – this can sometimes be filled with water.
where are open system pingos found
Found in discontinuous zone of permafrost or valley floors
open system pingos
hydrolic pingos/east greenland type
Freely available groundwater is drawn towards the expanding ice core, so the pingo grows from below the ground.
where are closed system pingos found
Associated with low-lying flat areas and only form in continuous zones of permafrost
closed system pingos
They form from downward growth of permafrost
On the site of small lakes, groundwater can be trapped by freezing from above and by the permafrost below as it moves inwards from lakeside
Subsequent freezing and expansion of the trapped water pushes the overlying sediments upwards into a pingo form
loess
Many periglacial areas are characterized by extreme aridity because most of the water is frozen and not available for plant growth.
The absence of vegetation provides abundant opportunities for wind action
Cold, strong winds pick up large amounts of material and redeposit it far from its source
In north-west China loess cover large areas and in some places are over 300 metres deep
Similar processes occur in the Gobi Desert today, forming loess in northern China – meaning this Aeolian process is not unique to periglacial environments
how is glacier ice formed
Glacier ice is primarily formed from compacted snow, with smaller contributions from other precipitation such as hail and sleet, which freeze directly on top of or inside the glacier.
how is neve or fern formed
Snow falls and collects on the glacier. Fresh layers of snow fall each day and build up.
As snow becomes compacted it starts freezing together becoming quite granular – this is called granular snow
As the granular snow becomes increasingly compressed it forms névé or firn
As the snow layers increase and the process continues and layers become deeper. The névé (or firn) transforms into glacier ice
what affects rate of accumulation and ablation
Amount of precipitation
Average temperatures
Levels of solar insolation
Levels of wind speeds
Latitude
Continentality
what is continentality
distance from the sea (seas/water are warmer influencing temperature around glaciers/permafrost)