Glacial erosion
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Glacial Erosion. Ch 15: p 277-281. Glaciers:. Enormous masses of moving ice created by the accumulation and compaction of snow. Powerful agents of erosion ~ have carved some of the most spectacular features on Earth’s surface

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Glacial Erosion

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Glacial Erosion

Ch 15: p 277-281


Glaciers:

Enormous masses of moving ice created by the accumulation and compaction of snow.

Powerful agents of erosion ~ have carved some of the most spectacular features on Earth’s surface

The growth of a glacier depends on whether the snowfall from winter is greater than the snow melt in summer!


2 types of Glaciers:

Alpine (aka Valley)

Continental (ice sheets)

  • Mountainous areas

  • long, narrow-wedged mass of ice

  • Best developed valley glaciers found in Alaska, the Himalayas, the Alps…

  • Covers large land areas

  • Found only in Greenland and Antarctica today


Valley Glacier


Continental ice sheet

The Antarctic Ice Sheet is 1.5 times the size of the US and in some places more than 4,000 m thick


How Glaciers form:


Step 1: Snow accumulates.

More snow falls during the winter than melts in the summer.


Trans-Labrador Highway

WOAH!

http://tlhwy.com/south/winter/index.html


Step 2: Snow changes to firn.

As snow accumulates, its weight compresses the individual snowflakes to form firn.


Step 3: Firn is compressed to form solid glacial ice


Step 4: The ice begins to move.

Continental

Valley


Some Facts

  • Glaciers hold 75% of the Earth’s fresh water.

  • 10% of land is covered by them.

  • If they all melted the sea level would go up about 70m

  • Artic ice is over 4,200 m thick in some spots.


2 types glacial movement:

Basal Slip

Internal plastic flow

  • The weight of the ice exerts enough pressure to melt the ice where it contacts the ground

  • This melt water acts as a lubricant and allows the glacier to slip forward, including over small barriers

  • The weight of the ice and gravity causes the ice crystals to slip over each other

  • Speed of this flow is faster nearer the surface and at its center…why?...

    • friction!


How do glaciers erode the surface?

  • Plucking –freeze/thaw process lifts particles into ice

  • Abrasion- like sandpaper-rocks caught up on the bottom scrape the ground under it, making striations


Glaciers pick up lots of sediment as they advance over the land.

http://www.geographyjim.org/Newzealandglacier.jpg


Valley glacier features

http://daac.gsfc.nasa.gov/DAAC_DOCS/geomorphology/GEO_9/geo_images_9/Fig9.20.gif


Cirque

  • A bowl-shaped depression located where a glacier begins to form


http://crevassezone.org/Photos/Graphics/4163L-(Cirque).jpg


Horn

Kinnerly Peak - Glacier National Park

  • A tall, pointed rock peak left at the top of a mountain

http://www2.nature.nps.gov/geology//parks/glac/car0348.jpg


The most famous horn in the Alps… The Matterhorn

  • Located on the boundary between Switzerland and Italy, the Matterhorn’s summit is 4478 m above sea level.


Arete – spines or ridges of rock that separate glacial valleys


U-shaped Valley - Yosemite National Park


V-shaped valleys become U-shaped valleys as glaciers move through them…

Step 2

Step 1

A typical river valley

Over time, running water cuts a deeper V-shape.

Step 3

Glacier fills valley, widening and straightening the channel

Step 4

Glaciers melt leaving a U-shaped valley


U-Shaped Valley Formation


Hanging Valley

  • a small valley that has not eroded as deep as the main valley that it is connected to

  • Waterfalls often form at hanging valleys.


Continental features

Striations- parallel scratches made from rocks in ice scraping against bedrock


Kettle Lakes

A shallow body of water made from ice blocks


Glacial Deposition:

  • Drumlins--hills of sediment deposited by the glacier- till


Drumlin Formation


Glacial DEPOSITION

  • Eskers

    • Winding ridges of stratified drift

    • Deposited by meltwater streams

    • Mined for gravel (aggregate)


Esker Formation


Glacial DEPOSITION

  • Kames

    • Cone shaped stratified deposits

    • Deposited at end of

      meltwater streams


Kames


MORAINES

moraine

  • MADE OF TILL- unsorted sediment

outwash

http://www.helsinki.fi/~jhyvonen/PB/M/Cerro%20Tronador%20moraine-pp.JPG


Moraines

  • Terminal Moraine – Till deposit that marks the furthest advance of the glacier.

  • Recessional Moraine – Till deposit that marks pauses in the ice fronts retreat

Till (moraine)


moraine

outwash


Ground Moraine- flat till deposits between recessional moraines

Recessional moraine

Recessional moraine

Ground moraine

Terminal moraine

outwash


Other Moraines

  • Lateral Moraines- These are on the sides of valley/mountain glaciers

  • Medial Moraines – When two glaciers run along one another/collide these moraines form.

  • Both are composed of till


Glacial DEPOSITION


MORAINES


Types of Glacial sediment:

ERRATICS-

  • Boulders carried great distance by the glacier

  • Don’t match surrounding rock


Types of Glacial Sediments (drift)

  • TILL- unsorted; deposited by ice

  • STRATIFIED DRIFT- layered (sorted into layers by size); deposited by meltwater streams

  • OUTWASH- sorted sand; deposited by meltwater


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