Capstone Project for Applied Earth Science Concepts for Educators in the Context of Polar Regions II By Tammy Orilio

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

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

Examples of Erosion Features on Bedrock…

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

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

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

 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

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

Examples of Erosion Features Associated with Mountains…

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

 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 V-shaped river valley

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

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!

Hanging Valley, Yosemite Nat’l Park

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)

 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 Iceberg Lake, Glacier Nat’l Park

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 Striding Edge Arête, England Matterhorn, Swiss Alps

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