A Level Geography - Glaciers

WB glacier - basal temp

Basal temperatures at or above pressure melting point

CB glacier - basal temp

Basal temperatures below pressure melting point so movement is limited

How does aspect affect a glaciated landscape?

If a slope faces away from the sun, temperatures remain below zero for longer so less solar energy is received and more melting occurs

WB glacier - surface melting

In summer, rises above 0C allowing some surface melting

WB glacier - erosion

Landforms of erosion Greater erosive power

CB glacier - erosion

Less erosive power

CB glacier - surface melting

Limited summer melting

How does latitude affect a glaciated landscape?

Locations at high latitudes tend to have cold, dry climates with little seasonal variation in precipitation At lower latitudes, places with high altitudes are characterised by dynamic valley glaciers

How does altitude affect a glaciated landscape?

Lower latitudes and higher altitudes create dynamic valley glaciers Temperature decreases with altitude at a rate of approximately 0.6C/100m

WB Glacier - meltwater

Meltwater percolates through glacier and acts as a lubricant for movement

CB glacier - movement

Move slower, often only a few m/yr

Corrie/ Cirque/ Cwms Glacier

Named after the bowl-like hollows they occupy Found on high mountain sides and tend to be wide rather than long

CB Glacier - meltwater

Often frozen to bedrock

WB glacier - movement

Rapid rates of movement (20-200m/yr)

How does relief affect a glaciated landscape?

The steeper the landscape, the greater the resultant force of gravity and the more energy a glacier will have to move downslope

Basal Sliding

Warm based glaciers may move by basal sliding Glacier can slip/slide on a layer of meltwater- lubricant Movement causes friction, enhancing melting Most effective on steep slopes

Surging

rapid movement occurs due to large levels of inputs or large amounts of meltwayer a short-lived phase of accelerated flow glacier surface can become broken up into a maze of crevasses

Serac

(from the french) a tower of unstable ice that forms between crevasses, commonly in ice falls or other regions of accelerated glacier flow

process of deposition

- glaciers deposite their load when their capacity is reduced. This usually occurs due to ablation during periods of retreat or de-glaciation - material can also be deposited during avalanche or when the glacier is overloaded with debris

Process of - Freeze-thaw weathering/rock shattering

- ice occupies nearly 10% more space than water -water enters the cracks and freezes over night, expands and causes pressure -crack widen -process repeats -rocks break off

when does Extending and compressing flow occur?

- occurs when there is a change in gradient

Extending flow

- steep- velocity increases- extentional - ice becomes thinner as it is streached

How does climate affect a glaciated landscape?

-Wind - aerolean processes =erosion, transportation and deposition -Precipitation - provides inputs - Temp. - Above 0C, ice starts to melt and adds to outputs.

diagenesis process

1. Fresh snow falls 2. Snow that survives one summer is called firn 3. With further compaction by subsequent years of snow fall, it becomes glacier ice

What percentage of the worlds land areas do glaciers occupy?

10%

Crevasse

A deep crack or fissure in the ice of a glacier.

Firn

A dense, icy pack of old snow

valley glacier

A long, narrow glacier that forms when snow and ice build up in a mountain valley

How does basal sliding effect the rate of erosion?

Abrasion increases with basal sliding

Soft Bed Subglacial Movement

As soft sediment below the glacier deforms, it moves the ice sheet with it

Sub-glacial moraine

At base of glacier

Process of carbonation

CO2 dissolved in water forms a weak carbonic acid Reacts with calcium carbonate (limestone) -> calcium bicarbonate which then dissolves

process of hydrolysis

Chemical reaction between rock minerals and water. Silicates combine with water producing secondary minerals

How does temperature effect the rate of erosion?

Cold based = decreased erosion

Scree

Debris on side on glacier

Drift

Deposits made by glaciers which include both till and outwash

Diagenesis

Each new fall of snow compresses and compacts the layer beneath, causing air to be expelled and converting low density snow into higher density ice

process of oxidation

Eg. Iron becomes soluble in very acidic conditions and the original structure is destroyed. Often attacks iron rich cements binding sand grains in sandstone

How does velocity effect the rate of erosion?

Faster = increased erosion

Glacial surge/advance

Glaciers may take many years to react to changes in accumulation or ablation but where snowfall is exceptionally heavy the glacier may react quickly and surge forward

rock flour

Ground-up rock produced by the grinding effect of a glacier.

Internal Deformation (creep)

Ice becomes plastic. The crystals orientate themselves in the direction of movement.

How does basal water temperature effect the rate of erosion?

If water at the base is under pressure the glacier can be buoyed up meaning less pressure and erosion

Englacial moraine

In glacier

How does supply of rock fragments effect the rate of erosion?

Increased fractured rock = increased erosion

How does ice thickness effect the rate of erosion?

Increased ice thickness= increased nasal contact pressure= increased abrasion

How does resistance o bedrock relative to debris effect the rate of erosion?

Increased rates when debris is harder than bedrock

striations

Long parallel scars in rocks carved by rock fragments being dragged across them by a glacier (erosional)

Why may slides occur?

May occur due to steepening or undercutting of valley sides by erosion at the base of the slope, adding to the downslope forces

Rotational slides

Movement along a curved slip plane common in weather rocks that become heavier when wetlands

Linear slides

Movement along a straight slip plane as a fault of bedding between layers of rocks

Process of rockfall

On slopes of 40*+ especially if the surface is bare, rocks may become detached from the slope by physical weather in processes.

Supra-glacial moraine

On top of glacier

ablation zone

Outputs exceed inputs

process of solution

Some salts are soluble in water, others are only soluble in very acidic water

Glacial Budget/net balance

The NET balance of accumulation and ablation. It compares the the amount of snow accumulation on the ice sheet and the amount of meltwater leaving the ice sheet. it is measured on a monthly basis.

Equilibrium (firn) line

The dividing line between the two zones

Accumulation

The net gain in an ice mass

plucking

The process by which a glacier picks up rocks as it flows over the land

till

The sediments deposited directly by a glacier

How does debris amount, resistance , size and shape effect the rate of erosion?

These are the tools to erode - intermediate amounts = increased erosion

Hydration

Water molecules + rock minerals -> new minerals of a larger volume. Causes surface flaking in many rocks

Dilitation

Weight of overlying ice reduces, underlying rock expands and fractures

Steady State

When amounts of accumulation and ablation are equal over the course of a year As a result, the snout of the glacier will remain stationary, but the mass of ice will still be passing through

Ice Cap

a covering of ice over a large area, especially on the polar region of a planet. under 50000km2

Macro-scale

a kilometre or greater in size e.g. cirque/corrie

Ice Shelf

a massive extension of glacial ice over the sea, often protruding hundreds of miles

Meso-scale

a metre to a kilometre e.g. roche moutonnee

ice sheet

a very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation center(s). over 50000km2

abrasion

angular material carried by the glacer rubs away at valley floor and sides

Enhanced basal creep

basal ice deforms around irregularities onn bedrock

Moraine

debris on/in glacier

medial moraine

deposit of sediment formed when the lateral moraines of two glaciers meet

Nivation

erosion of the ground beneath and at the sides of a snow bank, mainly as a result of alternate freezing and thawing.

Piedmont Glacier

glacier that reaches a valley floor and spreads out in a bowl shape

WB glacier - altitude / latitude

high altitude

CB glacier - altitude / latitude

high latitude

strong lithology means?

highly resistant due to dense interlocking crystals

structure of rocks?

jointing / cracks = increased permeability

How does geology affect a glaciated landscape?

lithology and structure

weak lithology means?

little resistance to erosion as bonds between particles are weak

CB Glacier - relief

low

What are glaciers?

masses of ice (and debris) compressed over many years which are continually changing

Outwash/ glacio-fluvial material

material deposited by meltwater from a glacier

Micro-scale

metres or less e.g. striations

lateral moraine

moraine that forms along the side of a glacier

Glacier Speed

o Extremely variable o Fastest up to 50m and 400m per year o Flow rates of 1000m a year or more in large ice streams in Antarctica and outlet glaciers in Greenland

why is there an ablation zone?

o Less snowfall o Temperatures are higher

Where is the Ablation Zone?

o Lower altitudes o Towards the snout of a glacier

Why is there an accumulation zone

o More precipitation at higher altitudes (the orographic effect), mainly snow o New snow is highly reflective, so it absorbs less heat and melts more slowly o Strong winds at higher altitudes blow snow into hollows and basins where it can accumulate o Temperatures are low, so sublimation (solid to vapour) is low and meltwater is likely to refreeze

Lithology

physical and chemical characteristics of rock

Relegation slip

pressure melting in up-glacier side of obstacle induces melting. Meltwater flows over obstacle and re-freezes on down-glacier side as relegation ice

compressing flow

reduced gradient- velocity falls - ice catches up with ice in front, compression occurs, ice thickens

Sublimation

solid to gas

WB Glacier - relief

steep

Ablation

the process of wastage of snow or ice, especially by melting

Niche Glacier

very small glacier that occupies gullies and hollows on north-facing slopes (northern hemisphere); may develop into cirque glacier if conditions are favorable.

Accumulation zone of a glacier

where inputs exceed outputs

WB Glacier - pressure melting

yes

Corrie / Cirque Characteristics

• Confined to an armchair or bowl shaped depression - steep back wall, overdeepened basin, rock lip • High altitude • Sheltered location, most favourable for snow accumulation • Can become source of glacier ice • Northern hemisphere, NE facing (shaded and sheltered from westerly winds)