Glacial erosion landscape features

1. Capstone Project for Applied Earth Science Concepts for Educators in the Context of Polar Regions II By Tammy Orilio Glacial erosion landscape features

2. How do glaciers alter the landscape? • Pressure from weight of ice + gradual movement of ice = a changed landscape • Nearly all erosion on a glacier occurs along bed & walls and any channel that contains it

3. 2 Forces of Erosion • ABRASION • Scouring of bedrock by small, jagged particles such as sand grains • PLUCKING • Water from glacier seeps into fractures in bedrock, where it eventually refreezes • Bedrock is now “bonded” to glacier, and is yanked with it as glacier travels

4. Examples of Erosion Features on Bedrock…

5. Striations • Often straight, parallel scratches on bedrock • Result from hard & jagged particles dragged across surface of bedrock

6. Striations are usually found in groups- it’s rare to see just one in the bedrock • Why do you think that is?

7. Glacial Grooves • Grooves in bedrock (like striations), but larger, deeper, and U-shaped • Often found in weaker zones of rock

8. Once formed, glacial grooves often increase in size due to feedback • The trough-like grooves become a channel for water to flow through, resulting in more erosion

9. Friction/Stress Cracks • Crescent-shaped cracks often associated with both striations & glacial grooves • May be used to indicate direction of glacial flow • Horn of crescent points down glacier

10. Examples of Erosion Features Associated with Mountains…

11. U-Shaped Valleys • Mountain glaciers follow the path of least resistance, which is often a streambed, ultimately altering the valley shape

12. V-shaped river valley • Streambeds tend to be V-shaped due to the scouring action of the water along with deposition of sediment on the inside of the bends

13. Glacial U-shaped Valley • HOWEVER, the glacier can’t follow all the twists & turns of a stream, so the bends eventually erode away, forming U-shaped valleys East Fork of the Toklat River, Denali Nat’l Park- U-shaped Valley!

14. Hanging Valleys • Results from differing erosion rates b/t a main glacier and a tributary glacier • Tributary erodes slower, so the distance b/t the two glaciers increases over time • Often results in waterfalls!

15. Hanging Valley, Yosemite Nat’l Park

16. Cirques • Result from a glacier eroding horizontally into the side of a mountain Above the left flank of Midre Lovénbreen is a un-named well-proportioned cirque glacier below the peak of Berteltoppen (Svalbard)

17. Iceberg Lake, Glacier Nat’l Park • Think of an amphitheater- steep sides (seats) form the back wall, rounded bottom (stage) opens downslope • Once ice melts, may leave behind a cirque lake AKA tarn

18. Arêtes: & Horns • Arêtes: • Jagged, narrow ridge formed when back walls of two glaciers meet • Horns: • formed from multiple cirques back into each other • Think of “squishing” the mountain from 3 or 4 sides • Results in a pyramid-shaped peak Matterhorn, Swiss Alps Striding Edge Arête, England

19. In Conclusion • Abrasion creates the smaller erosional features, like striations • Plucking constructs many of the larger, more “scenic” features • By analyzing these features, scientists can learn about glacial extent, movement, and retreat