Component 1 - Glaciated Landscapes Flashcards
What is a glacier?
A glacier is a moving body of ice.
Describe glaciers as a system.
Glaciers are open systems with inputs, outputs and interactions with other systems.
What is mass balance?
The difference between inputs (accumulation) and outputs (ablation).
Inputs > Outputs = Positive mass balance. Glacier grows.
Outputs > Inputs = Negative mass balance. Glacier shrinks.
What do you call the colder, higher altitude area with positive mass balance?
Zone of accumulation.
What do you call the warmer, lower altitude area with negative mass balance?
Zone of ablation.
What do you call the area between the zones of accumulation and ablation?
Zone of equilibrium.
Examples of glacier inputs?
Precipitation (snow, sleet, hail), wind-blown snow, de-sublimation (condensation into ice), solar energy.
Examples of glacier outputs?
Meltwater, sublimation (evaporation from ice), calving.
How can ice exist in the zone of ablation in positive mass balance?
Excess mass from the zone of accumulation is transferred to the zone of ablation due to gravity, which causes the glacier to deform and flow.
How does ice form from snow in the zone of accumulation?
When snowflakes fall, they contain air and have a low density. When additional snow falls, the pre-existing snow compacts. Snow that has become compacted and experienced one winter’s freezing and a summer’s melting is referred to as firn snow, which is composed of ice crystals separated by air passages. In summer meltwater percolates into the firn and when it refreezes the snow pack becomes increasingly dense.
After a number of years as successive layers of snow and firn have accumulated to a depth of about 20m, most of the air is squeezed out and glacier ice forms. The rate at which this happens can vary depending on the mass balance equation.
When might a glacier see short-term change in it’s mass balance?
From the transition from winter periods (autumn to winter) to summer periods (spring to autumn), the mass balance may change due to the temperature change.
When might a glacier see long-term change in it’s mass balance?
Change from cold glacial periods to warm interglacial periods.
What was the most recent glacial period called?
The Devensian period.
What are ice sheets?
Dome shape glaciers greater than 50 000km^2
What is the Quaternary period?
The Quaternary is a Geological period representing the last 2.6 million years of Earth’s history. It is characterised by ice-house (permanent ice in Polar regions) conditions and numerous glacial periods interspersed by warmer interglacial periods.
What are the 3 Milankovitch Cycles?
Earth’s tilt (obliquity), Stretch of orbit (eccentricity), and wobble (precession).
Explain obliquity in context of glaciers.
The tilt of the axis changes from 22.1 and 24.5 degrees with respect to Earth’s orbital plane, over a time period of approximately 41 000 years. The greater the tilt the more extreme the seasons become.
Explain eccentricity in context of glaciers.
The elliptical cycle is the change in the shape of the orbit from circular to elliptical, and back again every 100 000 years. The intensity of insolation received at the Earth’s surface through the year varies most during stretch orbits.
Explain precession in context of glaciers.
The axis wobbles with a periodicity of around 26,000 years, changing the position of the seasons on the orbit.
What % variation in insolation do the Milankovitch cycles cause at the mid-latitudes?
The Earth’s orbit around the sun varies due to the Milankovitch Cycles which cause variations of up to 25% in the amount of insolation received at Earth’s mid-latitudes.
When was the Devensian Period?
The glacial period lasted from 80,000 to 11,500 years before present.
When did the Holocene (current interglacial period) start?
11,500 years ago.
How can positive feedback amplify changes in glacial budget? (Think mass balance).
Cooling leads to further cooling and helps the development of glacial periods:
Snow and ice cover – if snow and ice cover increase it can raise the surface albedo (reflectivity of the Earth`s surface) so that more solar energy is reflected back to space. This leads to further cooling and more snow and ice cover across the planet.
Warming leads to further warming and helps the development of interglacial periods:
Increase in temp -> Arctic sea ice melt -> Darker surfaces revealed -> Albedo reduced -> increased absorbtion of solar radiation -> temp increase (cycle)
How can negative feedback reduce changes in glacial budget? (Think mass balance).
Warming can lead to cooling for example the disruption to the thermohaline ocean current circulation:
The thermohaline ocean circulation brings warm salty water to northwest Europe leading to warm winter conditions. For example, the average temperature of England in winter is 5o C, whereas at the same latitude in Russia it is -8oC.
What causes short term climate change and affects the glacial system?
Solar Forcing:
- energy released by sun
- solar output linked to sun spot actibity
- sun spots: high solar output, fluctuate approximately every 11 years
Volcanic Eruptions:
- Explosive eruptions (of VEI >4) propel sulphur dioxide and ash into the stratosphere, where they reflect incoming solar radiation
- Example: Laki in Iceland in 1783. Winter of 1783–1784 in Europe was as cold as 3o C below the average.
Anthropogenic Factors
- burning of fossil fuels increasing concentration of greenhouse gases.
- 1.2*C global avg. temp increase since 1880.
- generally, towards Arctic and Antarctic warming is occurring faster.
What % of the earth is covered by ice?
More than 10%.
What % of the earth’s water is stored in glaciers?
75%.
What is Albedo?
Reflectivity of a surface. In glacier’s, think of ice’s reflectivity.
What is firn?
Snow that has become compacted and experienced one winter’s freezing and a summer’s melting. It is composed of ice crystals separated by air passages.
What is sublimation?
The evaporation of water from ice.
What is the cryosphere?
The crysopshere is the parts of the Earth’s crust and atmosphere that are below 0˚C for at least part of each year. It consists of ice sheets and glaciers, together with sea ice, lake ice, ground ice (permafrost) and snow cover.
What 2 factors impact ice mass morphology (form, shape and structure)?
Climate
Climate controls the annual temperature cycle of a region as well as the amount of precipitation that falls as snow. As we saw in unit 1, climate governs the annual mass balance of glaciers and hence their size (a key part of glacier morphology). Where climatic conditions lead to mass inputs (e.g. snowfall) that are larger than mass outputs (e.g. melting) a glacier will grow. Conversely, where mass outputs exceed mass inputs a glacier will shrink.
Topography
Topography (the natural shape of the land) is also a major control on glacier morphology. Topography not only provides the land surface (e.g. high altitude mountains) on which glacial ice can develop, but it also controls the physical dimensions of glaciers and how they flow.
Difference between constrained and unconstrained ice masses?
Constrained ice masses have a morphology and flow pattern that is strongly dependent on underlying topography.
Unconstrained ice masses have a morphology and flow pattern that is in the most part independent of underlying topography.
What is an ice sheet?
Complete submergence of regional topography, forms a gently sloping dome of ice several kilometres thick in the centre.
Size: 100,000 – 10 million km^2
Example: Greenland and Antarctica
What is an ice cap?
Occupies upland areas, a smaller version of an ice sheet. Outlet glaciers drain both ice sheets and ice caps
Size: 3 – 10,000 km^2
Example: Vatnajokull, 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
Size: 10 – 10,000 km^2
Example: Patagonia, Chilie 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 a tidewater glacier.
Size: 3 – 1,500 km^2
Example: Aletsch Glacier, Switzerland and Athabasca, Canada
What is a piedmont glacier?
Valley glacier that extends beyond the end of a mountain valley into a flatter area and spreads out as a fan
Size: 3 – 1000 km^2
Example: Malaspina, Alaska
What is a cirque glacier?
Smaller glacier occupying a hollow on the mountain side – it carves out a corrie or cirque; a smaller version is known as a niche glacier.
Size: 0.5 – 8 km^2
Example: Hodges Glacier, South Georgia
What is an ice shelf/sea ice?
Large area of floating glacier ice extending from the coast where several glaciers have reached the sea and coalesce
Size: 10 – 100,000 km^2
Example: Ronne and Ross Ice Shelf, Antarctica
What are the characteristics of Cold Based (Polar) Glaciers?
- Found at high latitude locations such as Antarctica and Greenland
- Average ice temperature is well below 0˚C due to temperatures of -20C to -30C at the surface
- May be up to 500m thick
- Glacier is permanently frozen to the bedrock, so there is no debris in the basal layer.
What are the characteristics of Warm Based (Temperate) Glaciers?
- Found outside of the polar region, usually in high altitude areas
- Temperature of the surface fluctuates above and below melting point (depending on time of the year)
- Due to increased pressure of the overlying ice, the temperature at the base of the glacier is close to melting point and water exists as a liquid at temperatures below 0˚C continuously.
- Due to the effects of pressure, geothermal energy, and the percolation of meltwater these glaciers are not frozen to the bedrock.
What is pressure melting in warm based glaciers?
Pressure melting is where ice will melt at temperatures below 0C due to the pressure from the weight of the overlying glacial ice. The Pressure Melting Point is the temperature below 0C at which ice can melt due to pressure (weight) of overlying glacier ice.
- At normal atmospheric pressure, ice melting point is 0*C
- As pressure increases, the temp ice melts at will fall below 0C at a rate of 1C for every 100kg/cm^2 of pressure.
What is regelation?
Regelation is where pressure-melted water below 0*C refreezes in subzero conditions.
What is basal sliding?
When meltwater at the base of a glacier acts as a lubricant, reducing the friction between the base of the glacier and underlying bedrock - enabling movement to occur.
As there is meltwater, this can only occur in warm-based glaciers.
What is enhanced basal creep?
Bedrock is rarely smooth, rocks and boulders often protrude into the overlying ice.
As the ice comes into contact with obstacles on the glacier bed the ice deforms around them but does not reach the pressure melting point, this is sometimes referred to as ‘plastic flow’.
What is regelation slip?
If the temperature of the basal ice is close to the pressure melting point then the increased pressure on the up-glacier side of an obstacle will induce melting.
This will allow the glacier to slip and as the meltwater flows around the obstacle to the down-glacier side the pressure is reduced and the meltwater refreezes.
This continual melting and refreezing is referred to as regelation ice slippage.
What is internal deformation?
Polar (cold-based) glaciers are unable to move by basal sliding as their basal temperature is below the pressure melting point, therefore they move only by internal deformation.
This involves the response of individual grains of ice within the glacier to the overlying pressure. The amount of internal deformation increases with ice thickness and slope angle.
What is intergranular flow?
The displacement of ice grains relative to each other.
What is laminar flow?
Layers of ice within a glacier slipping over each other.
What is ice creep?
The deformation of ice in response to stress. It is a result of the increased ice thickness and/or the surface slope angle.
What happens when a glacier (warm or cold based) cannot deform quick enough?
When ice in either a warm or cold based glacier moves on a steep slope it is often unable to deform quickly enough. This causes it to fracture and ice faulting occurs creating a variety of crevasses at the surface.
What is extensional flow?
When the slope gradient the ice is travelling along is increased, there is an acceleration of ice movement. This produces extensional flow. This often occurs in the zone of accumulation.
What is compressional flow?
When the gradient is reduced compressing flow occurs as the leading ice slows down enabling the ice behind to catch up. This leads to thickening of the ice and often the following ice pushes up and over the slower moving leading ice. Crevasses are usually closed up.
What is subglacial bed deformation?
In warm based glaciers, when a glacier moves over relatively weak or unconsolidated rock the sediment itself can deform under the weight of the glacier, moving the ice on top of it.
In some Icelandic glaciers subglacial bed deformation can account for up to 90% of the glacier’s movement.
What is the range of the velocity of glacial ice movement?
Rates of glacial movement vary enormously from one glacier to another but typically lie in the range of 3 to 300 meters per year.
Warm based glaciers have a greater overall velocity of ice movement than cold based glaciers.
What are glacial surges?
Glacial surges are common Alaska. Surges are periods of rapid movement when a glacier snout advances up to 1000 times faster than normal as a result of a change in the flow pattern of sub-glacial meltwater.
What is the thermal regime of a glacier?
The temperature of the glacial ice.
What is weathering?
The breakdown of rock where it is located (in situ).
Weathering can be physical, e.g. freeze thaw, or chemical, e.g. carbonation.
What is erosion?
The removal of rock by ice, water, wind or gravity.
Explain the process of freeze-thaw weathering.
In glacial environments, temp may fluctuate either side of 0*C.
Water will enter cracks in rock.
When water freezes, it expands by 9% in volume.
When water freezes it exerts pressure on the crack.
Repeated freeze thaw cycle fractures the rock.
What is dilatation?
Rocks can fracture when the overlying pressure is released. This can occur when a glacier is melting, losing weight and hence exerting less downward pressure. Rocks will expand and fracture as this happens with the fractures tending to be parallel to the surface. The removal of bedrock by the glacier has the same effect on the newly exposed bedrock. The process is sometimes called ‘pressure release’ or ‘unloading’.
Name 3 Erosional Processes.
Abrasion, Plucking, Sub-glacial meltwater erosion.
Explain the process of Abrasion.
As a glacier moves, the weather sub-glacial rock debris will scrape against the bedrock and wear it away. This is abrasion
Large pieces of rock debris scratch the bedrock.
Finer sand, silt and clay particles tend to smooth and polish the bedrock.
The sub-glacial debris is also worn down and converted into tiny rock particles called rock flour.
Explain the process of Plucking.
Plucking occurs when melt-water seeps into cracks in the rock of the valley floor and sides. The water then refreezes causing freeze thaw weathering. As the glacier moves it plucks pieces of bedrock.
Plucking also occurs on the down-valley side of rock obstacles that the ice is moving over by the process regelation slip. Plucking is effective at the base of glaciers due to the presence of meltwater due to pressure melting.
Explain the process of Sub-glacial meltwater erosion.
Meltwater may get channelled beneath a glacier before emerging at the snout of the glacier as a pro-glacial stream. The high velocity meltwater can erode material at the glacier`s bed or widen and deepen channels or grooves in the bedrock.
This can result in the formation of relatively large subglacial meltwater channels such as the Gwaun Valley in north Pembrokeshire in S.Wales.
Name 7 Macro-scale erosional landforms.
Corrie/Cirque/Cwm, Arete, Pyramidal Peak, Glacial Trough/U-shaped valley, Hanging valleys, Truncated Spurs, Ribbon lakes.
Name 2 Meso-scale erosional landforms.
Roche Moutonnee, Crag and Tail.
Name a Micro-scale erosional landform.
Striations/Chatter Marks/Polished rock.
