Ch 15: p

 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

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

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. Valley Continental

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.

O_9/geo_images_9/Fig9.20.gif

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

Horn A tall, pointed rock peak left at the top of a mountain Kinnerly Peak - Glacier National Park

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… A typical river valley Over time, running water cuts a deeper V-shape. Step 1 Step 2 Step 3Step 4 Glacier fills valley, widening and straightening the channel 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.

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 MADE OF TILL- unsorted sediment moraine outwash

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 outwash Terminal moraine Recessional moraine Ground moraine

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 Both are composed of till

Glacial DEPOSITION

MORAINES

Types of Glacial sediment: Boulders carried great distance by the glacier Don’t match surrounding rock ERRATICS-

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