Glaciated Landscapes and Change Flashcards
What is the Pleistocene Period?
A geological period from about 2 million years ago to 11,700 years ago, the early part of the quaternary which included the most recent age.
What are Interglacial Periods?
Warmer periods similar to present i.e. greenhouse periods.
What are Greenhouse Conditions?
Much warmer interglacial conditions.
What are Glacial Periods?
Cold, ice-house periods within the Pleistocene.
What are Ice-house Conditions?
Very cold glacial conditions.
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 an Alpine Environments?
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 Glaciers Environment?
Slow moving bodies of ice in valleys, which shape the landscape in both polar and alpine environments.
What is a Periglacial Environment?
These environments do not feature glaciers, but are usually found next to glacial areas. They are characterised by permafrost and occur in high latitude areas whereas seasonal temperatures vary above and below freezing point with dry conditions e.g. Siberia, Alaska and northern Canada.
They are also referred to as the tundra - a term describing the treeless vegetation of dwarf shrubs, grasses, lichens and mosses.
What is the Timeline of the different Glacial Periods?
-Start of the Pleistocene epoch/Quaternary period (2.6 million years ago)
-Devensian Glacial Ended (last glacial maximum) (18,000 years ago)
-End of the Pleistocene/Start of the Holocene Epoch (11,500 years ago)
-Lock Lomond Stadial (last UK glacial advance) (10,000-12,000 years ago)
What are Stadials and Interstadials?
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.
What are the Short Term Causes of Climate Change?
-Variations in solar output
-Volcanic causes
What are the Long Term Causes of Climate Change?
-Continental Drift
-Eccentricity of the orbit
-Axil Tilt
-Wobble
What are Variations in Solar Outputs (short term)?
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.
What are Volcanic Causes (short term)?
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 gas can remain in the atmosphere for up to three years which reflect the radiation back into space.
What is Continental Drift (long term)?
3 million years ago the North and South American tectonic plates collided. This rerouted ocean currents so that warm Caribbean waters were forced northwest, creating the Gulf Stream.
What is the Eccentricity of the Orbit (long term)?
The shape of the Erath’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.
What is Axil Tilt (long term)?
The title of the Earth’s axis varies between 21.5° and 24.5° over 41,000 year cycles. This changes the severity of the seasons.
What is Wobble (long term)?
The Earth wobbles as it spins on its axis, which means that the season during which the Earth is nearest to the sun varies.
What are the Facts about Loch Lomond Stadial (the Younger Dryas event)?
-Ice sheets began retreating about 18,000 years ago, with rapid deglaciation by 15,000 years ago.
-12,5000 years ago the temperatures plunged downwards and by 11,500 years ago , glacial conditions occurred with temperatures 6-7°C after the event.
-Glaciers readvanced in many parts of the world including the formation of ice caps in the Scottish Highlands.
What are the Facts about The Little Ice Age (the longest glacial oscillation in historical times)?
-Proxy records from historical document and paintings add increased detail to our knowledge of past climate.
-Between 1350 and 1900, conditions were slightly colder between 1°C and 2°C.
-Between 1550 and 1750 there was a low trough of very cold conditions.
-The release of carbon dioxide triggered climate warming, which dramatically halted the cold period.
There were many impacts:
-The widespread abandonment of upland farms in Scandinavia and Iceland.
-Many glaciers in Europe re-advanced down valleys; the Little Ice Age was a period of predominantly positive net mass balance leaving prominent terminal moraines.
-Arctic Sea ice spread further south.
-The release of carbon dioxide triggered climate warmning, which dramatically halted the cold period.
What is the Cryosphere?
Consists of ice sheet and glaciers, together with sea ice, lake ice, permafrost and snow cover.
What are Warm Based Glaciers?
These 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 temperature causing melting -> land based.
What are 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 -> marine glaciers + land based.
What is an Ice Sheet?
Complete submergence of regional topography; forms a gently sloping dome of ice several kilometres thick in the centre.
Average size - 10-100,000 km².
Example - Greenland and Antarctica.
What is an Ice Cap?
Smaller version of ice sheet occuplying upland areas; outlet glacier and ice sheet drain both ice sheets and ice caps.
Average size - 3-10,000 km².
Example - Vatnajökull, Iceland.
What is an Ice Field?
Ice covering an upland area, but not thick enough to bury topography; many do not extend beyond highland source.
Average size - 10-10,000 km²
Example - Patagonia, Chile and Columbia Canada.
What is a 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 tidewater glacier.
Average size - 3-1,500 km².
Example - Aletsch Glacier, Switzerland and Athabasca, Canada.
What is a Piedmont Glacier?
Valley glacier which extends beyond the end of a mountain valley into a flatter area and spreads out like a fan.
Average size - 3-1,000 km².
Example - Malaspina, Alaska.
What is a 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.
Average size - 0.5-8 km².
Example - Hodges Glacier, Grytviken, Sotuh Gerogia.
What is an Ice Shelf?
Large are of floating glacier ice extending from the coast where several glaciers have reached the sea and merge.
Average size - 10-100,000 km².
Example - Ronne and Ross Ice Shelf, Antarctica.
What is Accumulation?
The addition of mass to the glacier (inputs) e.g. avalanches from slopes above, rock debris, wind deposition, meltwater, precipitation (mainly snow).
What is Ablation?
The loss of mass from the glacier (outputs) e.g. evaporation (sublimation), rock debris, breaking away of ice blocks and ice bergs (calving), melting (water).
How is a Glacier Mass Balance/Annual Budget calculated?
Using the total accumulation and ablation within a year.
How does the Glacial System work?
-Glacials gain mass through the transformation of snow into ice and then flow downhill (in response to gravity) and eventually lose mass due to melting.
-Glaciers accumulate mass from snow falling onto its surface, snow avalanching from the valley sides and by accretion of rime ice by direct freezing of atmospheric moisture onto the glacier.
-Glaciers lose or ablate mass by melting as a result of warm air temperature or applied pressure, evaporation, wind erosion or by calving into icebergs along a floating ice front.
-In extremely cold and arid areas, such as the interior of Antarctica ice, mass can also be lost by sublimation (ice changing directly into water vapour).
What is Systems Analysis?
It involves viewing any part of the physical or human as a entity that consists of stores and transfers of energy and matter, and operates because it receives a constant supply of energy and matter, which in turn are lost from the system as outputs. Changes in the level of inputs may cause instability within the system, and in response to the new amounts of energy, the system initiates feeback processes. The snowballing effect may ultimately cause a shift in the system to a new state of equilibirum.
What is the Glacier Mass Balanace?
Glaciers gain mass in the accumulation zone, i.e. the upper part of the glacier where input (winter snowfall etc) exceeds output (summer melting etc). Mass is lost in the lower ablation zone where outputs exceed inputs. At the transition between the two zones accumulation equals ablation. This boundary is called the equilibrium line, which in turn approximately coincides with the position of the snowline. The gains and the loses of ice experienced by a glacier constitute its mass balance or glacial budget.
How is Glacial Ice Distributed?
-In the South Pole there is more present day ice coverage and less late pleistocene ice sheets -> hasn’t reduced as much.
-In the Northern hemisphere there is a lot more of the lat pleistocene ice sheet have melted -> around northern Europe (Russia, the UK and Skandinavida).
-The late Pleistocene ice sheet in South America have all melted.
-The Laurentide and Cordilleran ice sheets covered east and west of North America stertching around 3000 km in width.
-Major ice extentsions were over North America and Europe (this grew to a thickness of around 3000-4000 m).
-At present, 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 Earths).
-Ice covers at the Pleistocene maximum was more than 3x greater than the present day.
-About 85% of all current glacier ice is contained in Antarctica.
What are the Factors affecting Ice Mass Distribution?
-Latitude
-Altitude
-Aspect
How does Latitude Affect Ice Mass Distribution?
Particulary important fro polar ice masses. In high latitude the sun’s rays hits the ground at a lower angle, so the solar energy received must heat a larger area.
How does Altitude Affect Ice Mass Distribution?
Particulary important for alpine glaciers. High altitudes are impacted by the environmental lapse rate (ELR) whereby tempertaure decline by 1°c for every 100m above sea level.
How does Aspect Affect 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.
What is Permafrost?
-Permafrost is permanently frozen ground where subsoil temperatures remain below 0°c fro at least two consecutive years.
-Around 20% of the Earth experiences periglacial conditions - mainly in the northern hemisphere. During the Pleistocene glaical periods, this was higher at 33% and at much lower latitudes than today.
What is 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.
What is Discontinuous Permafrost?
It 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 is Sporadic Permafrost?
It occurs where the mean annual temperature is only just below freezing and permafrost covers amounts of less than 50% of the slandscape.
What is Isolated Permafrost?
It occurs when less than 10% of an area is affected.
How does Snow Change in a Glacier?
-Snow falls on the 1st layer and collects on the glacier. Fresh layers of snow fall each day and build up.
-As snow becomes compacted it starts freezing together on the 2nd layer, becoming quite granular -> this is called granular snow.
-As the granular snow becomes increasingly compressed it forms névé or firm on the 3rd layer.
-As the snow layers increase and the process continues and the layers become deeper. The névé (or firm) transforms into glacier ice on the 4th layer.
What affected rates of Accumulation and Ablation?
-Amount of precipitation
-Average temperatures
-Levels of solar insolation
-Levels of wind speed
-Latitude
-Continentality (distance from the sea as seas/waters are warmer influencing temperature around glaciers/permafrost).
What are the Short Term Affected of variation in Glaciers?
Positive and negative regimes
-A positive regime is when the glacier is increasing in mass i.e. accumulation exceeding ablation during the winter period.
-A negative regime is when the glacier is decreasing in mass i.e. when ablation exceeds accumulation during the summer.
What are the Long Term Affected of variation in Glaciers?
Trends and Glacier Health
-Trends van be summarised over a decade from annual net balance.
-These long term trends determine the ‘health’ of a glacier and whether it will significantly advance or retreat and if thinning/retreating contributes to increased concerns over global sea level rises.
-Currently it’s estimated that nearly 75% of the world’s ice masses are experiencing ‘rising trends’ in their net negative balances.
What is Net Balance?
The difference between the accumulation and ablation.
Cumulative is the difference added overtime.
What are Negative Feedback Cycles?
-A negative feedback cycle acts to minimise the effect of new inputs in order to regain stability and equilibrium.
-E.g. if there is more snowfall, the glacier would advance (grow) meaning more ice would enter the ablation zone so more snowmelt would occur.
-This would mean that a balance would be gained whereby the input of snowfall would equal the output of snowmelt.
-The system remains balanced.
What are Positive Feedback Cycles.
-A positive feedback cycle amplifies the effects of an input which would cause a shift in the system.
-E.g. if a glacier has a positive mass balance and the glacier surface area is increasing, there will be an increase in ice albedo. This will cause a further reduction in air temperature, thus increasing accumulation and initiating a positive feedback cycle in which the glacier will continue to advance (this works the other way round too).
-The system will not be balanced.
What is the Greenland Ice Sheet Casestudy?
-One of the world’s two remaining ice sheets.
-Covers an area of 1.7 million km².
-It conatins more than 2.5 million km³ of stored ice.
-In the centre, ice is 3 km thick which depresses the earth’s crust by 1km in depth.
-A number of changes have occured to the mass balance of the ice sheet recently.
-Accumulation of snowfall in the central area is +520 km
-Ablation of melting and edges is -290
-Ablation by calving icebergs is -200
-Ablation of sublimation is -60
-Total ablation is -550
-Mass balance is -30
What are the two loops of Snow/Ice melting due to the Greenhouse Effect?
-Snow/ice melt due to the greenhouse effect -> melting reveals bare ground -> albedo effect os reduced, accelerating warmong of land -> less reflection of solar radiation -> increase in global warming (and the cycle repeats).
-Snow/ice melt due to the greenhouse effect -> melting reveals bare ground -> methane released in to the atmopshere -> increase in global warming (and the cycle repeats).
What is the Pressure Melting Point (PMP)?
-This is the temperature at which the ice is on the verge of melting.
-On the surface of the glacier the PMP is usually 0°c.
-However, this can be lower with a glacier due to the pressure (weight of the glacier).
-This means that at the base of the glacier, ice can melt at below 0°c, allowing the ice to move with the help of melt water even if the air temperature is below freezing point.
What are the Two ways that Ice Crystals cause Movements in a Polar Glacier?
-Inter-granular movement: individual ice crystals slip and slide over eachother.
-Intra-granular movement: ice crystals deform due to stress within the ice and eventually moves downhill under the influence of gravity.
How do Temperate (warm-based) Glaciers Move?
-Basal slip which is further subdivided into creep and regelation, extending and compressing flow, surges.
-Internal deformation.
What is Basal Slip?
This occurs when the base of the glacier is at the pressure melting point, which means that meltwater is present and acts as a lubricant, enabling the glacier to slide more rapidly over the bedrock. Basal slip can be further subdivided into several processes.
What is Creep and Regelation?
Basal slip is enhanced by obstacles on the valley floor. A large bedrock obstacle (>1m wide) causes an increase in pressure, which makes the ice plastically deform around the feature (creep). Smaller obstacles (<1m wide) will cause pressure-melting, increasing ice movement by basal slip. The ice refreezes on the downglacier (lee) side of the obstacle. The process of melting under pressure and refreezing is known as regelation.
What is Extending and Compressing Flow?
Over steep slopes, the rate of basal slip will increase and the ice will accelerate and thin. This is known as extending flow. Over shallower slopes, basal slip slows and the ice decelerates and thickens. This is known as compressing flow.
What are Surges?
In these short-lived events a glacier can advance substantially, moving up to 100 times faster than normal. Thry has various causes (e.g. earthquakes) but the most common is enhanced basal sliding triggered by the builf-up of meltwater at the ice-rock interface.
What is Internal Deformation?
This occurs when the weight of glacier ice and gravity causes the ice crystals to deform, so that the glacier moves downslope very slowly.
How do Polar (cold-based) Glaciers Move?
Internal deformation.
What are the Factors that Affect Movement?
-Altitude
-Gravity and gradient slope
-Ice mass/thickness
-Rock type
-Ice movement
-Meltwater
How does Altitude Affect Glacial Movement?
It affects precipitation and temperature. Greater precipitation and lower temperatues increase the supply of snow and ice, and so its mass balance.
How does Gravity and Gradient of Slope Affect Glacial Movement?
Gravity causes ice to move; the steeper the gradient, the faster it flows.
How does Ice Mass/Thickness Affect Glacial Movement?
The heavier/greater the mass, the greater the pressure in the ice which causes faster movement.
How does Rock Type Affect Glacial Movement?
If rock is permeable then meltwater may percolate through, slwoing the movement of the glacier. If rocks are impermeable there will be more meltwater, causing the glacier to move quicker.
How does Ice Movement Affect Glacial Movement?
Colder ice moves slowly as it does not deform as easily and it stays stuck to the bedrock.
How does Meltwater Affect Glacial Movement?
The more melwater there is the faster the movement as basal slippage increases.
What is Entrainment?
The process by which surface sediment is incorporated into a fluid flow (e.g. air, ice or water) as part of erosion.
What is Supraglacial Transport?
Mainly weathered material carried on top of the ice. This includes material falling from hillsides being washed or blown down, plus atmospheric fallout such as volcanic ash (a common feature in Icelandic glaciers).
What is Englacial Transportation?
Formally supraglacial material, but now buried by fresh snow and carried within the ice.
What is Subglacial Transportation?
Material carried below the ice. This includes material eroded from the glacier bed and valley walls, material frozen to the base from subglacial streams, as well as englacial material that has worked its way down through the glacier or ice sheet.
What is Deposition?
This occurs when material is released from the ice at the margins or base of the glacier. Deposition may occur directly on the ground (ice contact) or sediments may be released into meltwater, sometimes over distances of many kilometres. Deposition mechanisms include: release of debris by melting or sublimation of the surrounding ice, lodgement o debris by friction against the bed, deposition of material from meltwater, and disturbance and remodelling of previously deposited sediments.
What is Freeze-Thaw?
A crack in a rock can fill with water which then freezes as the temperature drops. As the ice expands, it pushes the crack apart, making it larger, weakening the rocks.
What is Plucking?
Meltwater at the base of the glacier freezes into the rock. As the ice moves downhill, it plucks and removes rock from the bedrock.
What is Abrasion?
Plucked rock fragments scratch and scrape the bedrock.
Where is a Rock Lip fromed?
Where ice thickens and erosion is reduced.
What is the Shrinking Arctic Sea Ice?
-Since satellite measurements started in 1979, about 1/2 of the summer sea ice volume in the Arctic has been lost.
-This has effects on marine ecosystems, ocean circulation and potential weather events further south of the Arctic.
- The quality of the ice is also changing as the old ice is being replaced by new ice which contains more salty water, so it’s more subject to melting whereas the old snow is mostly from snow precipitations and is a source of freshwater.
Why is the Shrinking Arctic Sea Ice a Problem?
-Climate change is more evident in the Arctic with warming at twice the global rate.
-The sea ice edge supports a large and distinct biological community of specified plants and animals that have evolved to adopt to the place. Species that depend on sea ice face extinction if most of the sea ice is lost.
-The main driver for removing ice through melting is the direct- melting from contact with warm ocean currents. A second driver is wind pushing the ice out of the Arctic. Sea ice is also crucial for the energy balance on Earth. Areas that have lost the sea ice cover absorb almost all incoming solar radiation.
-In summer, the sea ice cover helps cooling our planet as it effectively reflects solar radiation. When the ice disappears, more heat is being absorbed by the ocean, amplifying the warming effects in the Arctic. This is called the Albedo effect.
