Glaciated Landscapes

Define a glaciated landscape system

Parts of the Earth's surface that have been shaped, at least in part, by the processes of glacial erosion, transport, and deposition that occur as a glacier moves through a landscape.

Define a system

A set of interrelated objects comprising stores and processes that are connected together to form a working unit or unified whole.

What type of system is a glaciated landscape system

• Open system

• This means that energy and matter can be transferred from neighbouring systems as an input, and to neighbouring systems as an output

Name the material inputs to a glacier system:

• Precipitation (mainly snow)

• Avalanches from valley sides

• Rock debris from slope erosion (sides or base)

Name the energy inputs to a glaciated landscape system:

• Solar energy powers hydrological cycle

• Potential energy due to gravity

• Geothermal heat energy

• Windblown snow (aeolian)

Name the material stores in a glacier system:

• Water stored as ice

• Meltwater store

• Rock debris store

Name the energy stores in a glacier:

• Gravitational potential energy stored in rock debris

Name the material throughputs/processes in a glacier:

• Ice throughput

• Debris throughput

• Meltwater moves debris

Name the energy throughput/process in a glacier:

• Kinetic energy moves ice downhill

Name the material outputs in a glacier system:

• Sublimation

• Evaporation

• Calving (floating ice) breaks away from glacier

• Rock debris deposited at glacier snout

• Meltwater

Name the energy output from a glacier:

• Heat

What energy is available to a glaciated landscape system?

• Kinetic

• Potential - The higher a glacier, the higher the GPE. it's converted to KE as it moves downslope, powers glacial erosion and transport

• Thermal - increased basal meltwater = better abrasion and plucking. These are also associated with drumlins + eskers

It is this energy that enables work to be carried out by the natural processes that shape the landscape

What type of energy and material are input + output + processes in a glaciated landscape system

• Inputs: KE from wind and moving glaciers, Thermal energy from sun, potential energy from position on slopes. Material from deposition, weathering, and mass movement from slopes and ice from accumulated snowfall

• Processes = Diagenesis, glacial movement

• Outputs = glacial and wind erosion from rock surfaces; evaporation, sublimation and meltwater. meltwater + carving

Define mass movement

The downslope movement of soil and rock under the influence of gravity

What are the potential influences on glaciated landscape systems?

• Climate (including precipitation totals)

• Geology, including lithology and structure

• Latitude and Altitude

• Relief and aspect

Define dynamic equilibrium

When the state of equilibrium (inputs = outputs) is disturbed, the system undergoes self-regulation and changes its form until equilibrium is restored

Define the glacier mass balance / budget

The difference between the accumulation and ablation occuring in a glacier over a one year period. Accumulation MINUS ablation

How does latitude and altitude affect precipitation?

• High latitude = low precipitation (Near the north and south poles). This is also dominated by the location of Earth's Hadley cells - lower precipitation at 90 degrees

• High altitude = high precipitation. As air rises over mountains, it cools and condenses, reducing it's ability to hold water vapour

How does lithology influence glaciated landscape systems?

Lithology describes the physical and chemical composition of rocks.

• Clay is a weak rock, with little resistance to erosion, weathering and mass movements, as the bonds between the particles are quite weak

• Basalt is made of dense interlocking crystals, so highly resistant and more likely to form prominent glacial landforms such as aretes and pyramidal peaks

• Limestone is predominantly composed of calcium carbonate. This is soluble in weak acids, so vulnerable to decay by chemical weathering process of carbonation (especially at low temperatures)

What is the structure of rock and what influence does it have?

Structure concerns the properties of individual rock types such as jointing, bedding, and faulting, and also includes the permeability of rocks.

• Jointed rock = A rock formation that is divided into blocks by fractures or joints

• Bedding = the arrangement of sedimentary rocks in beds or layers of varying thickness and character

• Faulting = the breaking and displacement of rocks along a fracture line

Structure also includes the angle of dip of rocks and can have a strong influence on valley side profiles:

• Horizontal layers = steep cliffs with near vertical profiles

• Inclined layers = profiles tend to follow the angle of dip of the bedding planes

How does latitude and altitude influence glaciated landscapes?

High latitude = cold dry climates with little seasonal variation in precipitation. These tend to develop large, relatively stable ice sheets

High altitude = higher precipitation inputs, but more variable temperatures, especially in summer

How do relief and aspect influence glaciated landscapes?

Relief = the difference between the highest and lowest points in an area.

• The steeper the relief, the greater the resultant force of gravity, the more energy of the glacier

Aspect = the direction a slope faces.

• North-facing in the northern hemisphere = no sun = temperatures stay below zero for longer

These have an impact on microclimate and the movement of glaciers.

Give some facts for diagenesis

• Fresh snow has a density of 0.05g/cm3.

• Diagenisis starts when temps are low enough for snow that falls in one year to remain frozen throughout the year

• Snow that survives one summer is firn and has a density of 0.4g/cm3

• It becomes glacial ice with a density of about 0.9g/cm3

• takes from 40-1000 years

Define a glacier

Glaciers are large, slow-moving masses of ice

Define ice sheets

The largest accumulations of ice, defined as extending for more than 50,000km. There are currently only two - antarctica and greenland

Define valley glaciers

They are confined by valley sides and follow the course of existing river valleys or corridors of lower ground

What do warm-based (temperate) glaciers usually have?

• High altitude locations

• Steep relief

• Basal temperatures at or above pressure melting point

• Rapid rates of movement, typically 20-200m per year

What are cold-based (polar) glaciers characterised by:

• high latitude locations

• low relief

• basal temperatures below pressure melting point and so frozen to the bedrock

• very slow rates of movement, often only a few metres a year

What are the two zones of a glacier where ice moves differently?

• An upper half zone where the ice is brittle and breaks

• A lower half zone where under pressure the ice deforms

What does basal sliding consist of?

• Slippage, where the ice slides over the valley floor as the meltwater has reduced friction between the base of the glacier (and any debris embedded in it) and the valley flow.

  • The friction between the moving ice and valley floor can lead to meltwater

• Creep or regelation, when ice deforms under pressure due to obstructions on the valley floor

• Bed deformation, when the ice is carried by saturated bed sediments moving beneath it on gentle gradients. This is like the ground becomes roller skates for the ice

• Basal sliding accounts for 45% of the movement of the Salmon glacier in Canada, but can account for as much as 90% in extreme cases

What are the two elements of internal deformation?

• Intergranular flow, when individual ice crystals re-orientate and move in relation to each other

• Laminar flow, when there is movement of individual layers within the glacier - often layers of annual accumulation

When does extending flow occur?

• When ice moves over a steep slope, it is unable to deform quickly enough

• It fractures, forming crevasses

• The leading ice pulls away from the ice behind it, which has yet to reach the steeper slope

When does compressing flow occur?

• The planes of movement (slip planes) are at different angles

• Ice thickens, and the following ice pushes over the slower-moving leading ice

• When compressing flow occurs, the valley is over-deepened to form rock basins and rock steps

Define weathering

Weathering is the breaking down or dissolving of rocks and minerals on Earth's surface without displacing them

Define freeze-thaw

• Water enters cracks/joints and expands by nearly 10% when it freezes

• In confined spaces, this exerts pressure on the rock, causing it to split or pieces to break off

• The more frequent and regular the fluctuations of temperature around zero, the more effective the process

Define dilitation

When the weight of overlying ice in a glacier is lost due to melting, or overlying rock lost to plucking, the underlying rock expands and fractures parallel to the surface

Define physical weathering

The breakdown of rocks and minerals through physical forces without altering their chemical composition

Define chemical weathering

The breakdown of rocks and minerals due to chemical reactions, primarily involving water and other substances like oxygen and carbon dioxid

What is carbonation?

Rainwater combines with dissolved carbon dioxide from the atmosphere to produce a weak carbonic acid. This reacts with calcium carbonate in rocks such as limestone to produce calcium bicarbonate.

What is solution?

Any process by which a mineral dissolves in water is known as solution.

Some salts are soluble in water. Other minerals, such as iron, are only soluble in very acidic water, with a pH of ~3.

What is the process of plucking/quarrying?

• Meltwater seeps into joints in the rocks of the valley floor/sides

• It freezes and becomes attached to the glacier, so as it advances it pulls pieces of rock away

• This is particularly effective at the base of the glacier when ice refreezes on the down-valley side of rock obstructions,

What factors affect the rate of glacial abrasion?

• Presence of basal debris

• Debris size and shape (larger = more downward force proportional to weight. angular = more pressure concentrated on smaller area of debris-bedrock touch)

• Relative hardness of particles and bedrock

• Ice thickness

• Basal water pressure

• Sliding of basal ice

• Movement of debris to the base (debris needs to be replenished after worn away by the bedrock)

• Removal of fine debris (so larger particles can abrade the bedrock. this is mainly done by meltwater)

Define nivation

• A complex glacial process thought to include a combination of:

• freeze-thaw

• solifluction (the gradual movement of wet soil or other material down a slope, especially where frozen subsoil acts as a barrier to the percolation of water.)

• transport by running water

• chemical weathering.

What are the names for material deposited during glaciation?

• All material deposited during glaciation is known as drift

• This can be subdvided into:

• till - material which has been deposited directly by the ice

• outwash/glacio-fluvial material - material deposited by meltwater

What are the two types of glacial till?

• Lodgement till - material deposited by advancing ice.

  • Due to the downward pressure exerted by thick ice, subglacial debris may be pressed and pushed into existing valley floor material and left behind as the ice moves forward. Drumlins are the main example of these landforms

• Ablation till - material deposited by melting ice from glaciers that are stagnant or in retreat. Most glacial depositional landforms are this type.

What are the three distinctive characteristics of till?

• Angular/sub-angular in shape - has been embedded into the ice and not subjected to further erosion processes

• Unsorted - when glaciers deposit material, all sizes are deposited en masse

• Unstratified - glacial till dropped in mounds and ridges rather than in layers

How does a corrie form?

• Development starts with nivation of a small hollow on a hillside in which snow accumulates year on year, and diagenisis occurs

• At a critical depth, the ice acquires a rotational movement under its own weight, which enlarges the hollow further

• The rotational movement causes plucking of the backwall, steepening it

• The debris derived from plucking and weathering above the hollow falls into the Bergschund crevasse which abrades the backwall

Define striations

Scratches or grooves made by debris embedded in the base of the glacier

How is a till sheet formed?

Formed when a large mass of unstratified drift is deposited at the end of a period of ice sheet advance, which smooths the underlying surface.

What are the distinctive characteristics of outwash?

• Smaller than till as meltwater streams have less energy than a glacier so carry finer material

• Smooth and rounded by contact with water and attrition

• Sorted horizontally, with the largest material found furthest up the valley

• Stratified vertically, with distinctive seasonal and annual layers of sediment accumulation

Define a kame

A hill or hummock composed of stratified sand and gravel laid down by glacial meltwater

How do delta kames form?

• En-glacial streams emerge at the snout of the glacier and lose energy as they aren't constricted by tight walls, so deposit their load

• Supraglacial streams enter lakes near the ice, and lose energy entering the static body of water, so deposit their load

Define kame terraces and how are they formed

Kame terraces are ridges of material running along the edge of the valley floor.

• Supraglacial streams on the edge of the glacier pick up and carry lateral moraine which is later deposited on the valley floor as the glacier retreats

• Although they may look similar to lateral moraines, they are composed of fluvioglacial deposits that are more rounded and sorted

Define an esker and how is it formed

A long, sinuous ridge composed of stratified sand and gravel laid down by glacial meltwater.

• Material is deposited in sub-glacial tunnels as the supply of meltwater decreases at the end of the glacial period

Define an outwash plain

A flat expanse of sediment in the pro-glacial area

What are the effects of climate change on geomorphic processes?

• Freeze-thaw weathering is dominant in periglacial environments

• Frost heave is a sub-surface process that leads to a vertical sorting of material in the active layer