EARTH SCIENCE CHAPTER 15 GLACIERS

GLACIERS Chapter 15 GLACIERS I. What is a Glacier? Types of Glaciers 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 Movement Topic 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 2. Icebergs 3. Ice shelves When glaciers hit sea, blocks break off   2.    Icebergs What you get   3.    Ice shelves Occur 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 

MORAINES B. 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 Do A. Polished mountain tops versus sharpened ones

DEPOSITION III. Deposits By Glaciers Topic 13 Deposition Occurs Drift - all deposits of glaciers 1. 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 Moraines A. 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 Drumlins A. 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 Circular hollows on terminal moraines and outwash plains formed from large blocks of ice settling out and melting C. Deltas When glacial streams empty into lakes

KAMES

OUTWASH PLAIN

CIRQUE LAKES Topic 18 Lakes Made by Glaciers A. Cirque lakes 1. Formation When water fills the rock-floored cirque left by a glacier 2. Examples Lake Louise, British Columbia

CIRQUE LAKE

KETTLE LAKES B. Kettle lakes 1. Formation 2. Examples Water from ice melt left behind in kettles 2. Examples Zillions of them in Minnesota and Wisconsin, not to mention the Great Lakes

C. Moraine – dammed lakes 1. Formation River valleys blocked by glacial moraines 2. Example Devil’s Lake, Wisconsin

ICE AGE IV. The Ice Age Topic 19 How It Happened (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 Evidence A. 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.