Chapter 7: Erosion and Deposition
description
Transcript of Chapter 7: Erosion and Deposition
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