Glaciers

Glaciers

Glaciers January 21, 2011 Glaciers act as agents of erosion and deposition to help to create unique landforms which you will study in this unitGlacier: A large mass of ice resting on land or floating as an ice shelf in the sea adjacent to landGlaciers

GlacierIce: An Agent of Erosionas permanent snow cover increases in thickness, the underlying layers of snow are transformed into ice by tremendous pressure exerted by snow on top

Introductionlarge volumes of ice behave like plastic and under great pressure they begin to flow out in tongues

the weight and abrasive power of these glaciers changes the landscape

Ice: Agent of Erosionduring last 1 000 000 years, scientists estimate that there have been four glacial advances with the last one ending approximately 10 000 years ago

Ice: Agent of ErosionVolcanic eruptions send a layer of ash and dust around the earth in the atmosphere.Solar radiation from the sun is partially blocked resulting in coolingWhy do Ice ages occur?( Theories)A reduction in the amount of carbon dioxide in the atmosphere reduces the earth's ability to absorb long wave radiation being emitted by the surface. Therefore, not as much heat is trapped by the atmosphereWhy do Ice ages occur?( Theories)The amount of energy emitted by the sun has cyclic variations. Glaciation coincideswith periods of reduced solar activity.

Why do Ice ages occur?( Theories)Changes in the tilt of the earth's axis as well as changes in its orbitWhy do ice ages occur? (Theories)Glacial flow is caused by glacial creep and basal sliding.

How do Glaciers Move?Glacial Creep due to the tremendous weight and pressure of the glacier, the ice becomes pliable and flows- it flows fastest in the middle of the glacier where it is thickest (i.e. internal flow)

How do Glaciers move?Basal Sliding - movement along the bottom of the glacier due to the warmth of the earth and internal streamsThis generally only happens in temperate based glaciers, such as in the Alps, where the ground is warmer, allowing the ice to melt

How do Glaciers Move?The rapid, lurching , unexpected forward movement of a glacier.A build up of water pressure under the glacier is a cause

Glacier SurgeAccumulation and ablation

Ablation is the wasting or loss of material from a glacier.

If accumulation > ablation, the tip of the glacier advancesIf accumulation = ablation, the tip of the glacier is stationaryIf accumulation < ablation, the tip of the glacier retreats

The key to whether a glacier advances or retreats depends on the two opposing forces ofAbrasion: is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosionStriations: a scratch or groove cut into the surfaces of bedrock by boulders and pebbles frozen into the bottom of a glacier. How ice Erodes?Glacial Plucking: a process by which sections of the rock, frozen to the bottom of the glacier, are pulled out of place and carried away as ice advances.

How Ice Erodes?Sheer Weight of the IceHow Ice Erodes?Physical Geographers Divide Glaciers into two major groupsA major sheet of ice or an continues mass of ice. Cover the plains and low land areas81% of Greenland90% of Antarctica

Continental GlaciersForm in upland and mountainous regions, within larger valleys and basins.Smaller in SizeValley Glacier is a common subtype

Alpine or Mountain GlaciersA scooped out, amphitheatre-shaped basin at the head of a alpine glacier valley

CirquePage 280: 5A, 6A. B and 7QuestionsCold TemperaturesSummer blanket of snowGlaciers can only form where snowfalls exceed the annual melting over long periods of timeCompacted ice crystals that have not yet been pressed into solid mass form what is called a firn

Snow Becoming Glacial IceFeatures Produced by Alpine GlaciationCirquesCirque Mountain, Labrador

CirquesAfter the ice in a cirque is gone............A lake occupying the bottom of a cirque eroded by a glacier that has since completely melted

TarnA rectangular, sharp-pointed peak formed where several glacial cirques erode back into a single mountain

Horn PeakA knife-edged ridge formed between the steep walls of two or more adjacent glacial cirques

AreteA cirque which breaks the space in a continues ridge forms a col.ColA wide, deep valley with a U-shaped cross-section, formed by glacial erosion in a mountainous region.V shaped river valleys after being occupied by a glacier becomes U-shaped due to erosion

U- Shaped valleyA U-Shaped valley cut by a smaller tributary glacier that lies at a higher elevation then the deeper U-shaped valley eroded by the main glacier.

Hanging ValleyA stream that occupies a hanging valley will enter the main valley as a waterfallWaterfall/Bridal veil fallsTriangular faces on the vertical walls of the u-shaped valley.Ex. Upper Kananaskis River, Alberta

Truncated SpursWherever U-shaped valleys have been cut down below sea level, and are flooded by sea, _____________ are formed The result of the drowning of a u-shaped valley by the seaFiord coasts are found in Norway, BC, Labrador, New Zealand, Southern Chile and Baffin Islands

FiordsDepositional FeaturesTillTalusMoraineDrumlinsKettle holeTillUnsorted glacial sediment deposited from a melting glacier.Vary from clays to mixtures of clay, sand, gravel and boulders.Usually form plains.

TalusShattered bedrock fragments that accumulate at the bottom of rock slopes.Often form a second slope at the bottom of a steep slope.

MoraineAn accumulation of unconsolidated material deposited by glaciers.They tend to have many different sized particles, ranging from fine silt to large boulders.

b) Ground Morainematerial pushed under and compacted under the glacier.

c) Lateral Moraine: material pushed to the side of the glacier

d) Medial Moraine: result of two glaciers moraines coming together with their lateral moraines.

i) Terminal End Moraine: marks glaciers farthest advance.

ii) Recessional End Moraine: smaller end moraines behind the terminal moraine that form as the glacier recedes

DrumlinsElongated, streamlined hill deposits of till.Its long axis is parallel with the movement of the ice, with the blunter end facing into the glacial movement.

Kettle HoleCreated from ice melt from a chunk of glacier that was left behind from a retreating glacier.The sides are built up by glacial drift from the melting ice.

Alps are high altitude pastures ex: Swiss Alps

Alpine Glaciers Cracks that occur as a glacier moves into a wider part of the valley or encounters a change in slope.Eastern Baffin Island, Nunavut

Crevasses

Current Glaciers on Earth

Greenland Ice Sheet

Antarctic Ice SheetPLEASE WATCHVIDEOS