Chapter 7: Erosion and Deposition 7.1: Forces wear down and build up Earth’s surface 7.2: Moving water shapes land 7.3: Waves and wind shape land 7.4: Glaciers carve land and move sediments

7.4 Glaciers carve land and move sediments Before, you learned: Running water shapes landscapes Wind changes landforms Now, you will learn: How moving ice erodes land How moving ice deposits sediment and changes landforms

Glaciers are moving bodies of ice Glacier: a large mass of ice that moves over land Forms in a cold region where more snow falls than melts per year The weight of each following year’s snow compresses the snow below  ice On a mountains: becomes a heavy mass and can flow On flatter land: can spread out as ice sheets http://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 ya Lasting until ~13 to 10,000 ya

Two Types of Glaciers: (1) Alpine Aka “valley glaciers” Form in mountains and flow down through valleys Cause erosion (and deposition) Can change a “V-shaped” mountain valley into a “U-shaped” valley overtime Melting can occur at the base Carries sediment Can 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 not Inside 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 extinct Why? 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 sediment Moraines Glaciers push sediment to their sides and front These sediment deposits remain after glacial retreat Till: the sediment left directly on the ground surface by a retreating glacier Moraine: a deposit of till left behind by a retreating glacier Lateral moraine: till at sides of glacier End moraine: till at farthest advance of glacier Ground moraine: blanket of till along the ground Till 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