EARTH SCIENCE CHAPTER 15

GLACIERS

GLACIERS

 Chapter 15 GLACIERS

I. What is a Glacier? Mass of moving ice responsible for the most powerful

agents of erosion 

Types of Glaciers  Valley (alpine)

Continental (Greenland, Antarctica)

 

TYPES OF GLACIERS

B. Valley glaciers (Alpine glaciers) Long, slow moving stream of ice

originating in the mountains. C.  Ice sheets (Continental Glaciers) Originating at the poles and expanding in all directions Larger than valley or alpine glaciers.

FACT: ANTARCTICA HAS THE LARGEST CONTINENTAL ICE SHEET IN THE WORLD, 1 AND A HALF TIMES THE SIZE OF THE U.S. AND IN SOME PLACES 4,000 METERS DEEP

FACT: IF GREENLAND AND ANTARCTICA ICE SHEETS WHERE TO MELT THE SEA LEVEL WOULD RISE TO 60 METERS!

SNOW LINE

Topic 3 The Snow line  A.   Definition

Where permanent snow occurs. More is produced than melts

B.   Snowline versus latitude Lower at greater latitudes

BIRTH

Topic 4 Birth of a Glacier  A.  Process

1. Firn (see Fig 11-4 on p. 174) Recrystalization of snow into rough grains

2. Snow to Firn to Glacial Ice

ALPINE GLACIERS

 Topic 5 Where Valley Glaciers Occur (Alpine Glaciers)  A.  Locations Where mountains have

elevations above snow line.

CONTINENTAL GLACIERS

Topic 6 Where Ice Sheets (Continental Glaciers) Occur A.  Location

Where snow line is close to sea level B.   Ice caps

Small ones (Iceland and Islands in Arctic Ocean) C.   Continental glaciers

Antarctic glacier (5 km thick and 1.5 m below sea level)

Greenland D.   Nunnataks

Mountain peaks that project through ice

MOVEMENT

II.  Glacier MovementTopic 7 How Glaciers Move  A.   Process of movement 1. Weight pulls ice down 2. Melting aids lubrication B.   Speed  1.  Movement

From a few cm to 3000 cm /day Faster in the middle.

CREVASSES

HOW FAR?

Topic 8 How Far Glaciers Move A.  Ice fronts - Where they end (can be below snow line)  1.  Factors determining

Where ice melts as fast as it moves

CALVING

B.  Calving 1.   Process

When glaciers hit sea, blocks break off

  2.    IcebergsWhat you get

  3.    Ice shelvesOccur over water where ice hasn’t broken

off yet

TRANSPORT

Topic 9 Glaciers Transport Loose Rock  A.   Range of particle size

Fine powder to giant boulders 

MORAINESB.   Moraines - deposited particles once glacier

recedes 1.  Ground moraines - in glacier before

deposited  2.   Lateral moraines - deposited on sides of

glaciers  3.   Medial moraines -deposited on the sides of two converging glaciers, resulting between the two  4.   End moraines - deposited at the ice front

EROSION Topic 10 Glaciers Leave Their Mark  A.   Description and formation  1.   Striations - long parallel

scratches  2.   Roches moutonnees - sheep

rocks  3.   Cirque - semicircular basins at

head of valley  4.   Arête - knife edge ridge between

2 cirques  5.   Horns - result of 3 or more cirque producing a pyramid shaped peak

STRIATIONS

HORN

CIRQUE

ARETE

GLACIAL VALLEY

Topic 11 Recognizing Glacial Valleys A. Glacial troughs versus river valleys

1. U shaped vs. V shaped B. Hanging troughs and hanging trough

waterfalls SMALL ABANDONED GLACIAL VALLEY SUSPENDED

ON A MOUNTAIN ABOVE THE MAIN GLACIAL VALLEY.

WHAT NATURAL FEATURE DO YOU THINK WILL APPEAR WHEN A STREAM FLOWS FROM A HANGING VALLEY TO THE MAIN GLACIAL VALLEY?

Topic 12 What Continental Glaciers DoA. Polished mountain tops versus

sharpened ones

DEPOSITION

III. Deposits By GlaciersTopic 13 Deposition Occurs

Drift - all deposits of glaciers1. Till - unsorted and unstratified (inside

glacier)2. Outwash - sorted and stratified (left in

front of glacier)

TILL

OUTWASH PLAIN

OUTWASH PLAIN

DEPOSITION

Topic 14 Glaciers Leave MorainesA. Recessional and terminal moraines

- what’s left behind by a glacier and the deposit left by farthest advance.

B. Erratics - large transported boulders

MORAINES

MORAINE

ERRATIC

ERRATICS

DRUMLINS

Topic 15 DrumlinsA. Formation and description - long

smooth canoe - shaped hills made of till produced when advancing glaciers have run over earlier glacial moraines

B. Examples - Southeastern Wisconsin, South of Lake Ontario, Boston, Massachusetts

DRUMLINS

DRUMLINS

Topic 16 Outwash Plains and Eskers A. Outwash plains

Formation and description - broad flat areas in front of glaciers (usually prairies or farmland today)

B. Eskers Formation and description - long winding ridges

where material was deposited in tunnels within glacier

Examples - Maine and New York

OUTWASH PLAIN

ESKER

ESKER

Topic 17 Kames, Kettles, and Deltas A. Kames

1. Formation and description Small cone shaped hills of sand and gravel from

streams on top of glaciers B. Kettles

1. Formation and description Circular hollows on terminal moraines and outwash

plains formed from large blocks of ice settling out and melting

C. Deltas 1. Formation and description

When glacial streams empty into lakes

KAMES

OUTWASH PLAIN

CIRQUE LAKES

Topic 18 Lakes Made by GlaciersA. Cirque lakes

1. Formation When water fills the rock-floored cirque left by

a glacier2. Examples

Lake Louise, British Columbia

CIRQUE LAKE

KETTLE LAKES

B. Kettle lakes1. Formation

Water from ice melt left behind in kettles2. Examples

Zillions of them in Minnesota and Wisconsin, not to mention the Great Lakes

C. Moraine – dammed lakes1. Formation

River valleys blocked by glacial moraines2. Example

Devil’s Lake, Wisconsin

ICE AGE

IV. The Ice Age (NOTE OBJECTIVES A – C ON PAGE 183)

Topic 19 How It Happened A. When it occurred - 1,000,000 years ago, we’re

still in it! B. Extent - Intersection of Ohio and Mississippi

rivers and as far east as NY C. North America’s 3 major centers

1. Labrador center - east 2. Keewatin - central 3. Cordilleran - west

D. Cyclical - Advanced and receded 4x’s; 11,000 years ago was last advance

Topic 20 Ice Age EvidenceA. Limits tied to terminal moraines

Terminal moraines found from New Jersey through Pennsylvania, to Indiana and beyond.

Outwash plains are found beyond.

Topic 21 Causes of Glacial Climates A. Four facts to consider

1. I million years ago, Ice Age began, including 4 major advances of the ice sheets.

2. Warm interglacial periods came between. 3. Other ice ages have occurred in the past 600

million years. 4. In last age, glaciers advanced and receded in

North and South hemispheres at the same time.

B. Possible causes 1. Energy from sun changes. 2. Volcanic activity and dust in atmosphere. 3. During mountain building more land was above

snow line. (More land under ice, might change the climate)

4. Continents in older formations may have prevented hot and cold water currents from mixing.

5. Changes in earth’s tilt.