GLACIAL PROCESSES & LANDSCAPES

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Climate Change & Glaciation

** Climate Change:

* climate is dynamic, it doesn’t stay the same

* there are daily, monthly & annual averages, SO

* climate change is a significant change in these averages over

hundreds or thousands of years

* climate system: the interaction of all spheres (atmosphere,

lithosphere, biosphere, hydrosphere)

* when change occurs in one sphere, it usually affects the other spheres

** climates have changed in the past at various times & scales,

so will probably continue to change

* Evidence of climate change:

oxygen isotope analysis of ice cores from Greenland & Antarctica and sea floor

sediments: ratio of 18O to 16O in calcareous marine microfauna and from ice cores indicate glacial vs inter-glcial.

* 18O doesn’t evaporate out of the seawater as easily as 16O under colder water

conditions, thus more 18O will be left in ocean water & thus more will combine

with CaCO3 when it recrystallizes to form shell material

* When ocean water T colder the ratio

in ice cores is 16/O than 18O than under warmer conditions

in seashells is more 18O than 16O than under warmer conditions

tree rings: can indicate dry vs. wet periods; precipitation changes

palynology (study of fossil pollens): indicated wet vs dry & cool vs warm period by type of plant pollen

geologic formations (coal deposits)

human historical records

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* Climate Change Theories:

Non-human Induced Causes:

Plate tectonics: move into or out of a climate zone

Volcanic activity: increased amount of dust & ash in atmosphere

affects T°'s causing them to decrease by blocking incoming sunlight

Astronomical or Milankovitch theory: is comprised of 3 components

which can cause a variation in the amount of solar radiation

received by the Earth

Eccentricity: changing the shape of earths orbit, average cycle 100,000 yrs

Obliquity: change in angle or tilt of Earths axis/ varies 21.8 to 24.4, cycle of about 41,000 yrs

Axial Precession: earths wobble/ every 26,000 yrs

Human Induced Causes of Climate Change:

Changes in atmospheric "Greenhouse Gas" levels:

* “Greenhouse gases” trap outgoing long-wave (LW) radiation & thus help

keep the Earth warm

* if levels increase, can lead to global warming

* since 1800 have seen a 25% increase on CO2 levels from burning of

fossil fuels

* a .5°C T° increase has been detected since 1880, but not sure the only

cause is increased CO2 levels

other “Greenhouse gases”: methane, nitrous oxide, water vapor

* if levels increase, can lead to global warming, thus enhancing an

inter-glacial period & shrinking of glacial ice sheets & increasing

sea levels

* CFC’s also contribute to increased Tºs by altering (lowering) the level

of ozone in the stratosphere, thus allowing potentially more solar

radiation to reach the surface

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** Timing of recent changes

1) Pleistocene Glaciations: before 3 MYBP warmer; then begin a series of

glacial periods or advances & inter- glacial periods or retreats

2) last glacial advance began about 35,000 ybp reaced a peak about 18,000 ybp and ended about 10,000 ybp.

3) 12,000 YBP: still cool with boreal forests in GA

4) 7,000 YBP: warmer & dry; prairies farther east than present

5) up to 2000 YBP: gradual cooling

6) 800-1200 AD: slight warming trend, the Medieval Warm Period

7) 1350-1850: "Little Ice Age", about .5º C colder

8) 1850-1970: slight warming trend, then slight cooling

9) last 20-30 yrs:

* increased CO2, methane & other Greenhouse gases

* 5 of 6 hottest years on record in 1980's & ‘90's

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GLACIAL PROCESSES & LANDSCAPES

GLACIATION

glacier: large body of ice, formed on land from the accumulation and recrystallization of snow that is in motion.

** How is it formed?

* snow accumulates in zone of accumulation or snowfield;

area where snow gain > snow loss

* firn line, above which firn (granular, compacted snow) develops

* through further compaction & recrystallization the firn becomes

glacial ice (denser)

* zone of ablation: a glaciers lower end or area of loss

* have a balance maintained between loss & gain;

gain > loss = glacier enlargement(advance),

gain < loss = shrinkage(recede)

** How does a glacier move?

* respond to weight and pressure (gravity)

* Temp important/ colder ice = slow movement

* internal layers more fluid, so move faster

* create cracks or crevasses in top layers

* speeds vary from 2-3 cm/day to 4-5 m/day; occasionally have a glacier

surge, which means movement > 1 m/hour

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Glacial erosion: 2 main processes

Plucking: blocks or fragments of the bedrock are pulled from the surface by the ice and carried along

* A rock may often freeze in the ice before being plucked.

* rouche mountonee is a mound or hump in surface where plucking occurs primarily on the leeward side of the mound and abrasion on down- glacier side.

Abrasion: scarping of the surface by rock debris in the ice

* varies with the hardness of debris, type of rock surface, & speed

of movement

* may create glacial polish or smoothing of the surface

* may create striations or scratches in the rock parallel to the direction

of movement

* 2 Types of glaciers: Continental ice sheets & Alpine (mountain)

Continental ice sheets: over 3000 m (9800 ft) thick; may cause isostatic

depression of over 2000 m; EX: Greenland & Antarctica ice sheets

* Antarctic Ice Sheet:

* 13 million km2 (5 million mi2)

* more than 4000 m (13,200 ft) thick in spots

* 65 % all fresh water on earth

* if both Greenland & Antarctic ice sheets were to melt,

it would cause a 40-50 ft rise in sea levels by some estimates

* ice cap: smaller and more roundish in shape EX: Iceland

* ice field: smaller and more elongate EX: Patagonian ice field in Andes

Continental Ice Sheet Degradational (erosional) features:

* main feature is the large landscape of polished & striated bedrock,

lack of soil & regolith, scoured-out depressions & valleys

Glacial lakes: formed in depressions scoured by glaciers

* best known are the 5 Great Lakes: Superior, Michigan, Huron, Erie,

& Ontario; also the Finger Lakes of New York

Pluvial Lakes: developed in a presently arid area during times of

heavier precipitation associated with glaciation

EX: Lake Bonneville (Great Salt lake)

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Continental Ice Sheet Aggradational (depositional) features:

Glacial drift: unsorted and sorted solid material carried and deposited by a glacier

* glacial till: unsorted deposits carried at the base of a glacier

* stratified drift: small sized material carried & sorted by meltwater streams

* erratics: large boulders transported far from their source

Moraines: a ridge or mound of glacial debris deposited during the melting phase

of a glacier

* terminal moraine: ridge which marks the farthest advance of the glacier

* recessional moraine: formed when receding glacier stops depositing a second ridge behind the terminal moraine

* ground moraine: glacial till laid down under the glacier

Drumlin: smooth elipital shaped hill of glacial till aligned pararell to the direction of the ice movement

Kame: a small, round, hill or mound of sand & gravel (glacial till)

Kettle or kettle lake: steep-sided, depression formed after an ice block

(a “land iceberg”) that has been buried in the outwash plain, melts

Meltwater deposits: sorted or stratified material moved by running water

underneath &/or away from the glacier terminus

Outwash plain: formed ahead of a receding ice sheet by removal of

material carried in the meltwater; similar to a floodplain or a delta

Esker: ribbon or sinous shaped ridege created by the clogging of a river course withing glacier

Alpine Glaciers

Alpine or mountain: glacier confined within the topography of a mountainous region.

* Valley glacier: ice mass within a stream valley

* Cirque glacier: cirque or bowl shaped recess of a mountain

* Tidal glacier: one that ends in the sea

* may undergo calving, the breaking off of large pieces of ice creating

icebergs in the sea (Calving also occurs with continental ice sheets)

Degradational features of Alpine Glaciers:

Glacial valleys: have a characteristic U-shape; also

called a glacial trough; straighter than stream formed valleys

Hanging valley: a side or tributary valley

Fjord: glacial valley intersects with the ocean and has been flooded by seawater: flooded glacial trough

* Mountain landforms

Cirque: a scooped out basin, or bowl-shaped depression at the head

of an alpine glacier

Arete: sharp ridge that divides 2 cirque basins

Horn: a pyramidal peak caused by several cirque glaciers gouging a mountain on all sides.

Tarn: a small lake which forms/collects in a cirque basin behind

the lip or edge of the cirque

Aggradational features of Alpine Glaciers:

Lateral moraine: moraines on the edges or sides of the ice mass

Medial moraine: a moraine which is located down the middle of a glacier,

often formed when a trunk (main) & tributary glacier join