Post on 24-Dec-2015
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