Glacial erosion landscape features

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 bedrockWhy 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 feedbackThe 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 flowHorn 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 peakStriding Edge Arête,

EnglandMatterhorn, 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