Chapter 7: Erosion and Deposition

1. 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

2. 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

3. 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

4. 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

5. 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

6. 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!

7. 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

8. 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?

9. 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

10. 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

11. 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

12. 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