Glaciated Landscapes Flashcards
What is a glaciated landscape?
Glaciated landscapes include any landscapes that are being affected by the action of glaciers. This course also includes ‘post-glacial landscapes’ which do not have glaciers currently acting on them but still have distinctive features from their presence.
What is a glacier?
They are huge flowing bodies of ice that move downhill and carve out landscapes over thousands or millions of years.
What is the importance of glaciers?
- They are a good fresh water source
- They carve out beautiful landscapes
- They create valleys that can be used for dams - hydroelectric power.
- Leusire activities support local economies
- reflect sunlight to keep planet cool
- Melt into the sea causing sea level to rise
- Habitat for many ecosystems
- Create stunning places for towns and people to live.
What properties does a glaciated valley have?
- Flat bottom to the valley’s
- Steep sided mountains
- Jagged rock faces and ridges
- Bare rock faces
- Little vegetation
Where do we find glaciated landscapes?
HIGH ALTITUDE - LOW LATITUDE
LOW ALTITUDE - HIGH LATITUDE
Above the permenant snow line
5 What are the types of glacier?
And description
- Vallery glaciers: tounges of ice confined within valleys in mountainous regions. Constrained glacier - its path and form determined by the landscape.
- Ice sheets: Can be over 2 miles thick and cover whole continents (Antartica, Greenland contain 96% of ice). Unconstrained glacier. Often have valley glaciers coming off side. Greater than 50,000km2
- Ice Caps - cover entire mountainous regions. Up to 50,000km2.
- Piedmonet glaciers - valley glaciers that have spilled out into lowland regions.
- Cirque glaciers - small glaciers that occupy a bowl shaped hollow at the top of the glacial valley.
How much is mountaintop glacier ice disappearing in some parts of the world?
90%
What is the proccess that forms glaciers?
Diagenisis - snow turning into ice.
Explain the process of diagenisis.
- Snowfall remains frozen throughout the year. Every fresh layer of snow falls on top of the previous year. Snow has a density of 0.05g/cm3
- As more and more layers fall, they compress the layers below them. If snow survives one summer without melting it compresses into firn which is more dense at around 0.4g/cm3
- After more years of compaction, the firn becomes glacial ice with a density between 0.83 and 0.91g/cm3. This process takes between 40 - 1000 years. The hardest ice is found around 100m deep into a glacier.
What climatic conditons are required for diagenisis?
Cold enough so that snow doesn’t melt in the summer.
How does pressure impact the temperature that ice melts?
As pressure increases the temperature that ice melts decreases. At high pressures, ice will turn into water at temperatures below 0C. The melting point is lowered by 0.072C per MPa. This increases the production of meltwater which aids glacier flow.
What are typical properties of warm based (temperate) glaciers?
- High altitude locations
- Steep relief
- Basal temperatures above pressure melting point
- Rapid rates of movement, typically 20-200m.
Typically found in locations such as the Alps and Rockies where there are high rates of accumulation and ablation, so very active. Large volumes of ice being transferred across the equilibrium line, and significant seasonal differences. Fast processes.
What are typical properties of cold based (polar) glaciers?
- High latitude locations
- Low relief
- basal temperatures below pressure melting point so frozen to the bedrock
- Very slow rates of movement, often only a few metres a year.
Typically found in Antartica and Greenland, where there is very low accumulation and ablation, so not very active. Small seasonal differences, and very limited processes.
Why does temperature vary with depth in a glacier?
Due to the increasing pressure of the layers of ice as you go deeper.
Where does a glacier move fastest and slowest?
Fastest at the top and in the middle, slowest at the battom and the sides. This is because there is less friction.
What are the three main types of glacier movement?
- Basal sliding
- Internal deformantion
- Bed deformation
What is basal sliding?
The act of a glacier sliding over the bed due to meltwater under the ice acting as a lubricant.
What is internal deformation (creep)?
Gravity and the pressure of the ice causes the ice crystals to slide over each other in a series of parallel planes in a ‘crumpling’ deformation.
What is bed deformation?
The deformation of soft sediment of weak rock beneath the glacier causes it to slip downhill due to gravity.
What are the 3 types of basal sliding
1 - Basal Slip: When a thin layer of water builds up at the ice-rock interface and the reduction in friction enables the ice to slip forwards.
2 - Enhanced basal creep: Ice squeezes up against a larger (>1m wide) obstacle the increase in pressure causes the ice to plastically deform around the feature
3 - Regelation: When ice presses up against a smaller (<1m wide) obstacle and reaches pressure melting point, and rather than deforming, the ice melts on the stoss side, and refreezes on the lee side where pressure is lower.
How do ice sheets move in comparison to valley glaciers?
- Similar processes (basal sliding, internal deformation, bed deformation), except much slower due to far colder temperatures.
- The whole ice sheet doesn’t move, instead there are streams of ice movement in the sheet that often follow topographic features.
- They are thicker in the middle so gravity pulls ice downhill towards the sea.
Why do some glaciers move faster than others?
- Gravity: The fundamental cause of the movement of an ice mass.
- Gradient: The steeper the slope, then the faster the ice will move.
- Thickness of ice: This influences basal temperature and pressure melting point, which in turn influences how the glacier moves. Also influences stress on ice which can impact internal and bed deformation.
- Internal ice temperature: This allows the movement of one area of ice relative to another if they are different temperatures and thus different speeds of movement. Internal deformation happens 100x faster at 0 degrees than -20 degrees.
- Glacial budget (mass balance): A positive mass balance allows glacial advance at the snout.
How does relief impact a glacier?
- As a glacier flows over a steep slope it can’t deform quickly enough so stretches and fractures forming crevasses. This is known as extending flow.
- As the gradient of the slope decreases the ice thickens and compresses closing the crevasses. This is known as compressing flow.
How does climate (seasons) impact a glaciers movement?
- During summer there is a higher level of melting due to higher temperatures, so this causes more basal sliding and thus causes the glacier to have greater velocity. Strong correlation between metling and velocity.
- Internal deformation happens faster in higher temperatures due to greater temperature differences in the ice.