GLACIATION LECTURE NOTES

VOCABULARY: glacier; alpine; cirque; valley; piedmont; continental ice sheet; Pleistocene epoch; Nebraskan; Kansan; Illinoian; Wisconsin; pluvial lake; interglacial period; snowline; zones of a glacier; zone of accumulation; firn; zone of ablation; meltwater; movement of glacier; front; advance; retreat; stationary; stagnant; crevasses; load; frost wedging; glacial plucking; abrasion; cirque; trough; U-shaped valley; tarn; trough lake; finger lakes; paternoster lakes; fiord (fjord); arête; col; horn; hanging valley; hanging trough; till; moraine; drift; ground moraine; terminal moraine; (end moraine); recessional moraine; lateral moraine; medial moraine; drumlin; erratic; stratified; outwash deposits; outwash plains; valley trains; ice contact stratified drift; kame; esker; kettle; loess

In areas of colder climate, ice may accumulate to such a depth that it begins to behave as a plastic and flows--GLACIER

2 types

alpine--occur on mountains; occupy valleys previously made by stream; start as cirque glacier, become valley glacier; may grow to piedmont glacier--on plain at base of mountain range; fed by one or more alpine glaciers

continental ice sheet--broad glacier, irregular shape, blanket terrain

10-11% of earth (6 million sq. miles) covered by glaciers

• 1) low temperature--high latitude or high altitude
• 2) adequate snowfall (more snow falls than melts); usually form above snowline--elevation above which air temperature seldom rises above freezing and snow accumulates

snow accumulation builds the glacier

Pleistocene epoch

pluvial lakes--lakes formed in Pleistocene when area had more rain

• 1) zone of accumulation--snow accumulates; air spaces in crystals allows evaporate to water vapor; so snow becomes granular; compression by weight of overlying snow forms ice--firn, névé SNOW MELTING OCCURS, BUT MORE SNOW IS GAINED THAN IS LOST
  PRESSURE AND GRAVITY PUSH SNOW OUTWARD
  
  
• 2) zone of ablation--net wastage--melting greater than accumulate; replacement is by flow
  

front, terminus, or snout--leading or outer edge of ice

•advance--covering more territory

•retreat--covering less territory

•stationary--not changing the area of coverage

stagnant--dead--no longer a real glacier

position occurs at lowest or farthest extent of the ice

glacial movement--PRESSURE AND GRAVITY

posts in ice

sides and bottom friction slows, center moves fastest

CREVASSES--cracks in brittle upper surface of the glaciers, form as move over irregular surface, drop

LOAD--material is carried on top, sides, and bottom and body

can carry much larger particles than wind, running water

concentrated on base and sides

erodes and deposits

erodes

• frost wedging--breaks off pieces
• glacial plucking--lifts out and removes
• abrasion--scratches, GLACIAL STRIATIONS

direction of movement indicated by upstream side-abraded, striated, gentle slope, downstream side predominantly plucking, steeper slope

alpine--

cirque--head of valley formed by glacier, a steep blunt, bowl shaped valley head in a mountain side at a high elevation

tarn--a lake in a cirque

trough--U-shaped glacial valley--valley cross section from erosion on base and sides of glacier

U-shaped valley--cross section of trough

trough lake--lake formed in a trough (depression in trough)

finger lakes--behind recessional moraines

paternoster lakes--chain of small round lakes

fiord (fjord)--ocean flooded glacial valley

arête--a narrow-jagged knife-edged (saw-toothed) ridge created by two cirques that have eaten into ridge from both sides

col--a saddle on a divide or pass (gap) through an arête

horn--sharp, hornlike or pyramid shaped mountain peak formed by glacial erosion on each side

hanging valley--stream valley where stream drops into trough; floor is notably higher than the floor of the trunk valley into which it leads

hanging trough--smaller tributary glacial valley, higher up, did not have as much erosional power

NOTE: The text improperly defines hanging valley!

continental

scours land out, leaves lots of lakes

depositional--mainly in downstream portions or as retreats

drift--ALL GLACIAL DEPOSITS--water and/or ice deposits

till--non-sorted material (size, weight) where released DIRECTLY FROM ICE

moraines--landforms made of concentrated till

ALL TILL IS DRIFT BUT NOT ALL DRIFT IS TILL

types of moraines

• ground moraine--thin till, generally smooth surface with irregularities, glacier retreats, drops
• terminal moraine--a rugged ridge or belt of till marking outermost margin of a glacier, an end moraine
• recessional moraine--ridge-like accumulation of till deposited by glacier along outer margin back from maximum advance, an end moraine
• lateral moraine--ridge built along edge or sides of glacier
• medial moraine--blending of lateral moraine of two glaciers

other till deposits

drumlins--streamlined hills molded by flowing ice; see text page 499

direction of flow

erratics--pieces of rock different from bedrock beneath brought to an area by a glacier

meltwaters erode, transport, and deposit--sort and stratify

• 1) outwash deposits

  •outwash plain--broad stratified gently sloping deposit formed beyond recessional or terminal moraine by streams from melting glacier

  •valley trains--partially fill valley

• 2) ice-contact stratified drift

  •kame--low conical steep-sided hill, water pours over edge of glacier, stratified and some slumping as ice melts

  •esker--narrow long steep sided snake-like ridge of sand and gravel, stream channels on or in glacier; see

  •kettle--depression in ground moraine, ice chunk buried and melted,

• 3) loess--wind blown deposit