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.
