Chapter 11 Notes:

Problem with Strange Boulders

• Early geologists noticed some bizarre findings
• Northern rocks were well-sorted and polished
• Boulders were different from the rocks under them
• Boulders were similar to rocks far north!
• Geologists thought a giant flood could have created this mass of strange rock?
• They called this deposit "drift"
• Current glaciers in the Alps showed that maybe the glaciers moved the materials???

What is a Glacier?

• A large mass of ice found in cold climates
• Valley Glacier: Narrow mass of ice that moves down through mountains and carves away at the mountain sides.
• Continental Glacier: Moving mass of ice 100’s of miles long and covering partial continents and up to three miles thick! Easily destroys everything in its path.
• Glaciers are born in areas of constant snowfall.
• The average temp. of an area must be less than 32 degrees F in order to sustain ice.
• Mountain tops are common places for glaciers
• A snow line forms where the average temp. of an area is less than 32 degrees during the warmest time of the year.
• Snow line is highest near the equator (warmer) and lowest nearer the poles (much colder).

Birth of a Glacier

• Snow often becomes compressed under the weight of the ice on top of it. This is called "Firn".
• Firn forms the start of a glacier.
• The weight of snow and ice on top of the firn is compressed, causing the mass to slide downhill.

Where do Glaciers Occur?

• Valley glaciers are often called "alpine" glaciers
• They have existed in all mountainous areas except Australia
• World’s largest are in Alaska
• Continental glaciers are often called "ice sheets"
• They have existed in all polar regions and have covered millions of square miles!
• Largest today are in Greenland and Antarctica
• Because they cover mountains, great mountain peaks called "nunataks" poke through the ice
• Small ice sheets are named "Ice Caps" and may be only a few thousand miles square

How Glaciers Move

• Glaciers move under their extreme weight
• The weight and pressure actually melts the layers to the point of being flexible
• By "staking" the glacier, scientists can see the movements over a period of time
• Some move only 1cm/day; others 3000cm/day!
• Glaciers move quicker after winters of heavy snow
• Crevasses, or cracks, form when glaciers need to bend downhill or down a steep slope
• Only the top layers crack, bottom is more flexible because of extreme pressure and weight

How Far Glaciers Move

• Glaciers end at the "Ice Front": an area where the ice melts as fast as it freezes.
• Glaciers move forward under expansion and pressure; and recede backward from melting
• As glaciers near the ocean, they begin to melt slightly and weaken, often falling into the ocean water in big chunks – this is called "Calving".
• This calving process creates Icebergs!
• Icebergs have been spotted up to 65 km long!!!

Glaciers Transport Loose Material

• Glaciers pick up loose rock material like lint on a piece of tape
• Large amounts of rock material build up in certain areas of the glacier creating "moraines" when the glacier melts away.
• Material carried in the bottom of the glacier will produce a "ground moraine"
• Material carried on the sides of the glacier will produce "lateral (side) moraines" – usually occur in pairs
• Material built up on the ice front will produce an "end moraine" or multiple end moraines
• Rock flour is the mixture of fine sand and silt formed by the crushing of rock under a glacier
• This rock flour mixes with water runoff to make "glacial milk" because of its whitish color

Glaciers Leave Their Mark

• Glaciers continually rub on the ground and mountains they come in contact with
• Glaciers will produce smooth, polished surfaces on some rocks
• Glaciers can also produce scratched surface on rocks if a trapped rock in the glacier is pressed against the surface creating "striations"
• Glaciers can also move large chunks of rock from a mountain side and drop the chunks in a lower, flat area. The pieces are called "roches moutonnees" which means ‘sleeping sheep’.
• The remaining hole that is formed in the mountain is called a "cirque"
• Mountain peaks that are often carved out and left behind from a glacier are called "Horns" or matterhorns.
• A "glacial trough" forms when one valley glacier carves a trough in the mountain
• Summary: Continental glaciers wear everything down they come in contact with and Valley glaciers simply sharpen mountain peaks.

Deposits by Glaciers

• Most rock material carried by glaciers is deposited by meltwater; this is called "drift"
• "Till" is unsorted, unstratified drift
• "Outwash" is sorted, stratified drift

Glaciers Deposit Many Features

• Moraines

• Ground moraines
• Lateral moraines
• End moraines

1. Recessional moraines
2. Terminal moraines

• Erratics – large glacial boulders
• Drumlins – large upside-down, canoe shaped hills (occur in bunches)
• Eskers – long, winding ridges that form from the glacial meltwater
• Kames – small, cone-shaped hills of stratified sand and gravel (gum drop shaped)
• Kettles – large, circular hollows in the ground that form from blocks of ice that drop from high above the glacier and wedge into the ground and then melt and forms into lakes and ponds, etc.
• Cirque Lakes – lakes that form within the hollows (cirques) created high in the mountains where rocks used to be.
• Kettle Lake – lake created by the meltwater of the chunk of ice that formed the kettle
• Moraine-dammed Lake – lake created by the unique formation of two end moraines combined with a pair of lateral moraines (to form a box).

The Ice Age

• Began 1 million years ago and included 4 advances
• Interglacial periods came after each advance
• Earth may NOW be in an interglacial period!
• Other ice ages may have occurred in the last 600 million years
• Glaciers advanced and receded during the same times in the northern and southern hemispheres
• Did the sun change heat?
• Did earth tilt further on its axis?