GlaciersErosive forces

Glacier• persistent body of dense ice that is constantly

moving under its own weight.

• It forms where the accumulation of snow exceeds its ablation (melting and sublimation) over many years.

Glacier formation Snowfall• Glaciers form where the accumulation of snow and ice

exceeds ablation.o This snow collects and is compacted by the weight of the snow falling above it,

crushing the individual snowflakes and squeezing the air from the snow

Firn• left over from past seasons and has been recrystallized

into a denser substance• snow repeatedly freezes and thaws, changing into

granular iceGlacial Ice• Once all air has been squeezed from it, the snow is

turned into extremely dense glacial ice

• When the mass of snow and ice is sufficiently thick, it begins to move due to a combination of surface slope, gravity and pressure.

Explain what the growth of a glacier

depends on• The balance between snow fall received and the

amount of ice lost be melting and sublimation(evaporation)

Advance v. Retreat • Advance

o Snow accumulation is greater than ablation

• RetreatoAblation is greater than snow

accumulation

Glacier TypesAlpine (Valley) Continental

• Long, narrow wedge shaped

• form on the crests and slopes of mountains.o Ex. Alaska, Himalayas,

Alps, Andes

• Wide, very large millions of km2

• Polar regionso Only found in two places

• Greenland and Antarctica

Glacial MovementBasal Slip Internal Plastic Flow

• glacier slides over the terrain on which it sits, lubricated by the presence of liquid water.o Refreezes as pressure

removed

• Solid ice crystals slip over each other, causing slow forward motion.o Slopeo Thicknesso Temperature (of Ice)

• Surface faster o Friction

Erosion • Plucking/ Ice wedging :

Plucking: “pluck” material from V sides makes a U shaped valley

Ice wedging: water seeps into cracks and expands leaving larger cracks.

Erosion• Abrasion:oMechanical erosion of rocks (think

sand paper) as glacier scrapes over the landscape/ bedrock below

Features caused by Erosion• Cirques:

o start of a classic valley glacier is a bowl-shaped

• Horns:o 3 or more cirques or Arêtes that encircle a single mountain

(looks like a pyramid)

• Arêtes: o Two glacial cirques may form back to back and erode their

back walls until only a narrow ridge or “spine” is formed

• U-shaped valley:o widened, deepened, and smoothed, by a glacier forming a

"U"-shaped glacial valley

Features caused by Erosion

• Hanging valleys:o when glaciers recede, the valleys of the tributary

glaciers remain above the main glacier's depression ( water falls often)

• Striations:o Grooves from plucking/ and abrasion

• Kettle lakeo shallow, sediment-filled body of water formed by

retreating glaciers or draining floodwaters.

Deposition• Drumlins:

o elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated till or ground moraine.

Deposition• Eskers:

o An esker is a long, winding ridge of stratified sand and gravel.

Deposition• Kames:

o an irregularly shaped hill composed of sand, gravel and till that accumulates in a depression on a retreating glacier.

Deposition• Moraines:

o are accumulations of dirt and rocks that have fallen onto the glacier surface or have been pushed along by the glacier as it moves.

o End/recessional: between glacier and last moraine

o Terminal= farthest forward motion

o Lateral: side (parallel)

Glacial sediment• Erratics:

o are stones and rocks that were transported by a glacier, and then left behind after the glacier melted.

Glacial sediment• till:

oGlacial till is unsorted sediment deposited directly by glacial ice.

Glacial sediment• Outwash:

oGlacial outwash is sand and gravel deposited by running water from the melting ice of a glacier.

Michigan’s Glacial History

Big idea Great lakes Each of the Great Lakes began as a

river.

As the climate cooled…

• The rivers froze.

• Glaciers moved through them – widening and deepening them to form today’s “U” shaped lake bottoms.

Why do scientists believe that glaciers once covered Michigan?

• The unsorted moraine deposits follow the outline of Great Lakes.

• Other depositional features such as drumlins and kettle lakes are found throughout Michigan.

• Erosional features like striations are found in Michigan as well.

Explain what happens to Earth’s crust when a glacier is removed.

• Isostatic Rebound– The upward movement of the Earth’s crust