Glaciers

Glaciers

Slow moving, thick ice mass formed by accumulation, compaction and recrystallization of snow on mountains and near Earth’s poles

Glaciers are important to

Hydrologic cycle

Rock cycle

Ice sheets

Immense, continental scale, and flow radially from areas of greatest accumulation

Alpine

Relatively small, occupy mountain valleys with downslope flow

Rates of flow

Influenced by friction between ice and bed, greatest in ice most distant from areas of glacier-ground contact, close to surface, brittle deformation

Formation of glacial ice

Snow → granular snow (recrystallizes)→ firn (gets thicker, smaller and spherical) → glacial ice (where thickness of snow and ice is greater than 50m and interlocks to form ice crystals)

Internal deformation

Ice collapses, flows away from the thickest area under gravity influence

Basal slip

Melting point is lower at the base, and liquid water lubricates ice to slip over the bed

Subglacial sediment

Materials underlying the glacier deform because of friction, with the moving ice above

Erosion by glaciers

Plucking: removing particles from bedrock surfaces

Abrasion: scratching bedrock surfaces w flowing ice, aided by rock fragments

Bulldozing: mass movement of dislodged particles by moving ice

Zone of accumulation

Where snow and ice are added

Zone of abalation

Ice is lost at the edge of a glacier

Equilibrium line

Separates zones

Terminus advance

If accumulation greater than abalation

Terminus retreats

IF accumulation less than ablation

Ice flow directiojn

Always toward terminus, there is a constant flow to the zone of ablation

Cirques

Scoop-like feature (a v or u shaped valley) `

Arete

Separates cirques, are teh heads of glacial valleys

After ice melts

Small glaciers feed into large ones that carve deep glacial troughs “hanging valleys” are created

Fjord

Inlets produced when deep glacial troughs are flooded by the sea

Glacial sediment

Rock fragments of bedrock can be carried by glacial ice, the abrasive action produces a large amount of
“rock flour”

Drift

Types of sediment deposits, till: deposited directly by glaciers and usually poorly sorted, Outwash: waterlain deposits in lake, or stream from glacial meltwater are better sorted

Moraine

Accumulation of unconsolidated glacial debris

Lateral moraine

Next to valley walls, mostly debris from valley wall mass wasting

Medial moraines

From merging alpine glaciers, from joining of lateral moraines

Ground moraines

IS: sheet like and beneath a glacier

End morraine

IS: terminal, marks position of max advance, recessional, ridge of till that marks a former terminus

Drumlins

Glacial till assumed to form when glacier overrides a recessional moraine, tear-shaped hills in clusters or SWARMS

Kames and kettles

Pockets of sediment, kames are mounds, and kettle lakes are stranded blocks of ice that produced depressions

Glacial erratics

Large boulders left stranded after the ice sheet melts

Eskers

Stream sediment in tunnels under a glacier, accumulation of well sorted sediment

Outwash plain

Flat area by sediment from meltwater outwash at terminus, usually some degree of sorting by braided streams

Ice age

Long term reduction in Earth’s surface temperature that results in presence or expasion of polar ice sheets and alpine glaciers

Milankovitch cycles

greatest potential for glacial advance when: low eccentricity (more circular orbit and low obliquity: less tilt

Eccentricity of Earth’s orbit

Shape of orbit cycles, more circular when low

Precession

Earth’s axis wobbles

Obliquirt

Tilting of Earth’s axis

Causes for Ice Ages

• Continental configuration, glaciation promoted when theres large landmass near poles

• Oceanic circulation

• CO2 content of atmosphere