Chapter 7: Erosion and Deposition

7.1: Forces wear down and build up Earth’s surface7.2: Moving water shapes land

7.3: Waves and wind shape land7.4: Glaciers carve land and move sediments

7.4 Glaciers carve land and move sediments

Before, you learned:Running water shapes landscapesWind changes landforms

Now, you will learn:How moving ice erodes landHow moving ice deposits sediment and

changes landforms

Glaciers are moving bodies of ice

Glacier: a large mass of ice that moves over landForms in a cold region where more snow falls than

melts per yearThe weight of each following year’s snow compresses the

snow below iceOn a mountains: becomes a heavy mass and can flowOn flatter land: can spread out as ice sheetshttp://academic.brooklyn.cuny.edu/geology/leveson/core

/graphics/nyc_mins2/glac2_rollover.html

Extent of Glaciers

Must be cold enough for water to remain ice year round

Mountains (high elevation/altitude) and land regions near the poles (high latitude)= COLD!

Currently cover ~10% of the Earth’s land surface Ice Ages~30,000 years ago (ya) glaciers covered 30%

“Last Glacial Maximum” ~17,000 yaLasting until ~13 to 10,000 ya

Two Types of Glaciers: (1) Alpine

Aka “valley glaciers”Form in mountains and flow down

through valleysCause erosion (and deposition)Can change a “V-shaped” mountain valley

into a “U-shaped” valley overtimeMelting can occur at the base

Carries sedimentCan break off into the ocean: icebergs

Two Types of Glaciers: (2) Continental Aka “ice sheets” Larger than alpine glaciers Can cover entire continents One covered North America until about

10,000 years ago Still cover most of Greenland and Antarctica

As much as 4500 meters (15,000 ft) thick!

Glacial Movement

Gravity causes glacial ice to move downhill:Flowing: ice near the surface is brittle and cracks

often form in it, but pressure deep inside does notInside ice flows like toothpaste tube being squeezed

Sliding: weight of a glacial and heat from Earth cause melting Layer of water forms under the glaicer - sliding

Interesting During the last glaciation (~26 to 13,000 ya), woolly mammoths and

saber-toothed cats roamed just south of the glaciers At the end of the last ice age ~10,000 ya, these large mammals

became extinctWhy?Hunting?Climate?Diseases from humans?

Glaciers deposit large amounts of sediment

As glaciers melt and treat: shape landscape

As glaciers move and expand: transport sediment (boulders, rocks, sand, clay)Scratches and scrapes

rock: abrasion

Glaciers deposit large amounts of sedimentMoraines

Glaciers push sediment to their sides and frontThese sediment deposits remain after glacial retreatTill: the sediment left directly on the ground surface by a

retreating glacierMoraine: a deposit of till left behind by a retreating

glacierLateral moraine: till at sides of glacierEnd moraine: till at farthest advance of glacierGround moraine: blanket of till along the groundTill is different than the rocks from the area

Glaciers deposit large amounts of sediment

Lakes Melting glaciers leave

behind depressions than can become lakes

Kettle lakes: bowl-shaped depression that was formed by a block of ice from a glacier

Great Lakes Formation

Glaciers in valleys melted and left behind moraines

A million years ago, the Great Lake region had many river valleys Ice sheets gouged out

large depressions and left piles of rock and debris

Prevented water from draining out

Weight of glacier caused the land to sink as much as one kilometer