Roughly 18,000 yrs ago 30% of the earth’s surface was covered by glaciers.Roughly 18,000 yrs ago 30% of the earth’s surface was covered by glaciers.

This period is known as the GREAT ICE AGEThis period is known as the GREAT ICE AGE

Glacier FormationGlacier Formation• A glacier is a mass of snow covered ice that moves due to

the force of gravity• There are 2 types of Glaciers:

– Valley Glacier (Alpine)– Continental Ice Sheet

• Snow does NOT melt in summer• Recrystallization of snow to form LARGE crystals of ice

(rough and granular)– called FIRN: liked packed snowballs

• Lower layers turn to SOLID ICE under the weight of overlying firn and snow.

Snow becomes FIRNSnow becomes FIRN

- - This type of glacier can carve out “U”-This type of glacier can carve out “U”-shaped valleys.shaped valleys. **Remember, streams **Remember, streams and rivers carve “V”-shaped valleys.and rivers carve “V”-shaped valleys.

– Ex. Glaciers of Alaska Ex. Glaciers of Alaska

Valley Glacier or Alpine GlacierValley Glacier or Alpine Glacier

U-Shaped ValleyU-Shaped Valley

Continental Glacier Continental Glacier or Ice Sheetsor Ice Sheets

• The tremendous weight of these glaciers causes it The tremendous weight of these glaciers causes it to to slowly move outward from the centerslowly move outward from the center (some (some only moving centimeters per year)only moving centimeters per year)

• When the glacier reaches the sea, chunks break When the glacier reaches the sea, chunks break off and become off and become icebergsicebergs (this is called (this is called calvingcalving) )

• *Smaller ice sheets are called *Smaller ice sheets are called ice capsice caps GREENLAND: 1.7 Million SQ MI , 3 KM thickGREENLAND: 1.7 Million SQ MI , 3 KM thickANTARCTIC: 12.5 Million SQ MI, 5 KM thickANTARCTIC: 12.5 Million SQ MI, 5 KM thick

Depth of Greenland & Antarctic Ice SheetsDepth of Greenland & Antarctic Ice Sheets

Glacier MovementGlacier Movement

FastestFastest

• As a glacier moves, rocks that are stuck in As a glacier moves, rocks that are stuck in the ice are dragged across the exposed the ice are dragged across the exposed bedrock. This causes deep scratches and bedrock. This causes deep scratches and gouges in the bedrock called gouges in the bedrock called striationsstriations

• The direction of the striations shows the The direction of the striations shows the path of movement of the glacierpath of movement of the glacier

There were 2 periods of glaciations here. Can you tell which was first? Which directions did

the 2 glaciers move?

Deposition by GlaciersDeposition by Glaciers

• glaciers can carry sediment just as streams and glaciers can carry sediment just as streams and rivers can (only glaciers can carry more and rivers can (only glaciers can carry more and much larger sediment)much larger sediment)

• Since a glacier acts like a bulldozer as it moves, Since a glacier acts like a bulldozer as it moves, the sediment becomes mixed together and is the sediment becomes mixed together and is deposited deposited unsortedunsorted– This is called This is called glacial tillglacial till

• If the sediment is deposited by the running melt If the sediment is deposited by the running melt water from the glacier, it will be water from the glacier, it will be sortedsorted (just like (just like from any stream) from any stream) – This is called This is called outwashoutwash

Glacial till - unsortedGlacial till - unsorted

Landforms Caused by Landforms Caused by DepositionDeposition

Moraines- deposits of unsorted sediment along the edges and end of the glacier. - The moraine that forms at the end of the glacier (showing its farthest advance) is called a terminal or end moraine

(Ex: Long Island)

ErraticsErratics- large boulders that have been transported - large boulders that have been transported into the area by the glacierinto the area by the glacier

- often - often different in mineral compositiondifferent in mineral composition than the than the bedrock of the areabedrock of the area

DrumlinsDrumlins- long, smooth hills made of glacial till. - long, smooth hills made of glacial till. - formed when a glacier runs over a moraine - formed when a glacier runs over a moraine made by a previous glacier, “smearing” it out. made by a previous glacier, “smearing” it out. - The - The drumlin points in the direction that the drumlin points in the direction that the glacier is movingglacier is moving

drumlinsdrumlins

Outwash PlainsOutwash Plains- melt water from the - melt water from the bottombottom of the glacier carries of the glacier carries sortedsorted sediment out in sediment out in

front of the glacierfront of the glacier

Outwash PlainOutwash Plain

KamesKames- melt water from the - melt water from the toptop of the glacier deposits of the glacier deposits sediment when it flows down off the glacier and reaches sediment when it flows down off the glacier and reaches the ground. The sediment is deposited as the ground. The sediment is deposited as small hills of small hills of

sorted sediment.sorted sediment.Also called “dead ice” depositsAlso called “dead ice” deposits

KettlesKettles- circular lakes. Chunks of ice often break off - circular lakes. Chunks of ice often break off the glacier and are buried in the ground by sediment. the glacier and are buried in the ground by sediment. As the buried ice melts, the sediment sinks into the As the buried ice melts, the sediment sinks into the

hole and the water fills it uphole and the water fills it up

Another type of lake, found in New York, is called Another type of lake, found in New York, is called a a moraine-dammed lakemoraine-dammed lake. This is formed when a . This is formed when a

glacial moraine blocks a river valley from draining. glacial moraine blocks a river valley from draining. The river floods the valley and forms a long, The river floods the valley and forms a long,

narrow lake. narrow lake. Ex. the Ex. the Finger LakesFinger Lakes in upstate New York. in upstate New York.

Landscape Features- Landscape Features- Valley Glaciers -”the BIG stuff”Valley Glaciers -”the BIG stuff”

CIRQUESCIRQUES: semi-circular shaped bedrock : semi-circular shaped bedrock feature created as a glacier scours back toward feature created as a glacier scours back toward the mountain (1the mountain (1stst place snow and ice place snow and ice accumulate) accumulate) ARÊTESARÊTES: steep-sided, sharp-edged bedrock : steep-sided, sharp-edged bedrock ridge formed by two glaciers eroding away on ridge formed by two glaciers eroding away on opposite sides of a ridgeopposite sides of a ridgeHORNSHORNS: 3 or more cirques adjacent to one : 3 or more cirques adjacent to one anotheranother

ArêteArêteCirque

U-Shaped U-Shaped ValleyValley

ArêteArête

MorainesMoraines

HornHorn

Kettle Lake

Drumlins

Esker

Outwash

plain

Glacial Stream

TillMoraine-dammed lake

Terminal Moraine