Landforms Created by Glaciers

Chapter 15.2

Glacial Erosion1.Glacial Erosion

a. The process that formed the mountains begins with a glacier still high in the valley. i.As a glacier wedges its way through a

narrow valley, it breaks off rock from the valley walls, causing the walls to become steeper.

ii. Blocks of rock are also pulled from the floor of the upper valley.

Glacial Erosioniii.A cirque is a bowled shape

depression created by these glacial actions.1.Cirque means “circus” in French, as it

refers to the circus like round depression of a circus theater.

iv. Arêtes means spine in French, and refers to the sharp and jagged ridges that form between the cirques.

v. A horn is a cluster of several arêtes that form a pyramid like peak.

Cirque & Arêtes

Glacial Erosionb.When a glacier moves down a valley it

picks up many rocks ranging in size from pebbles to boulders.i. These rocks that are now being carried by

the glacier act as another erosion agent.ii. As the glacier and rocks pass over the earth

they polish and round larger rock formations.

Glacial Erosion1. These rounded projections have a

smooth, gently sloping side facing the direction from which the glacier came, with the far side being steep and jagged as rock was pulled away when the ice passed over.

2. These rocks are called roches moutonnees, which means “sheep rock” in French, because they resemble the backs of sheep.

Roches Moutonnees

Glacial Erosionc. The shape of valleys are originally a

“V” shape. However, once a glacier passes through them, it cuts them out to a “U” shape. This is an easy way for scientists to tell if the valley was carved by a glacier.

d. A tributary glacier is a glacier that flows into a larger glacier.

Tributary Glacier

Glacial Erosioni. Tributary glaciers do not cut as deep

“U” shapes since they are much smaller than the main glacier, and when the ice melts they are left high in the valley.

ii. These valleys formed from the melted ice of a tributary glacier are called hanging valleys.

Hanging Valley

Glacial Erosione.The erosion process of

continental ice sheets is very different from valley glaciers. i.Continental ice sheets generally

level landforms and produce smooth, rounded landscapes.

Glacial Erosion1.Existing valleys are gouged

out and deepened, and rock surfaces are scratched and grooved by rocks carried at the base of the ice sheet. These scratches and grooves run parallel to the direction of glacial movement.

Glacial Deposition1.Glacial Deposition

a.Glacial deposition occurs when valley glaciers reach lower elevations or when climate change melts continental ice sheets.

b.Glacial drift is the general term given to all sediments deposited by a glacier or by the meltwaters from a glacier.

Glacial Drift

Glacial Depositioni.When the glacier melts all of the material in the glacier is deposited onto the earth.

ii.Erratics are large boulders that have been carried by the glacier and do not match the composition of the bedrock that they are now on.

Glacial Erratic

Glacial Depositioniii. Till is made of unsorted deposits of

rock material that is deposited from sediments scraped off by the base of the glacier or is left behind when glacial ice melts.

iv. Stratified drift is material that has been sorted and deposited in layers by streams flowing from the meltwater.

Till & Stratified Drift

Glacial Depositionc.Till deposits are landforms

made from glacial till called moraines.i. Moraines are ridges of unsorted

rock material on the ground or on the glacier. We will be discussing five types of till deposits or moraines.

Glacial Deposition2. A lateral moraine is one that is

deposited along the sides of a valley glacier, usually as a long ridge.

3. A medial moraine occurs when two or more valley glaciers join, and their adjacent lateral moraines combine.

Lateral & Medial Moraine

Glacial Deposition4. Ground moraine is the unsorted

material left beneath the glacier when the ice melts. a.Much of the landscape in Ohio

is covered with ground moraine.

Glacial Deposition4.Drumlines are long, low, tear-

shaped mounds of till, often found in clusters

5.A terminal moraine is the till that is deposited at the snout or front of a melting glacier. They are belts of small ridges of till with many depressions that contain lakes or ponds.

Drumline & Terminal Moraine

Glacial Deposition6. In front of a terminal moraine, and

after meltwater has deposited its small rock particles is a large outwash plain. a. An outwash plain is a deposit of

stratified drift, which usually lies in front of a terminal moraine and is crossed by many meltwater streams.

Glacial Deposition7. A kettle forms when a portion of

glacial ice is buried in drift, and when the ice melts it leaves a cavity in the drift, and often forms lakes. a. Kettles are mostly found in

outwash plains.

Kettle

Glacial Deposition8. An esker is formed when

continental ice sheets recede and long, winding ridges of gravel and coarse sand may be left behind. a. Eskers consist of stratified drift

deposited by streams of meltwater flowing in ice tunnels within the glaciers, and may extend for tens of kilometers.

Esker & Ice Tunnel

Glacial Lakes3. Glacial Lakes

a. Glaciers commonly form lake basins by eroding out surface area, leaving depressions in the bedrock, and deepening existing valleys.

b. Glaciers also commonly form lake basins by depositing till. Many lake basins were created by the uneven surfaces of ground moraine deposited by glaciers.

Glacial Lakesc.Another way glaciers form lakes is

when terminal and lateral moraines block existing streams and create a lake basin.

d.The Great Lakes are the result of a combination of erosion and deposition by continental ice sheets.

Glacial Lakesi. Glacial erosion widened and

deepened broad river valleys covered by ice sheet.

ii. Moraines to the south blocked off the ends of these valleys.

iii. As the ice sheets melted, the meltwater flowed into the valleys and was trapped by the moraines to form the Great Lakes.

Glacial Lakes1. During the early stages of the ice retreat the

great lakes were much larger and drained to the south. As the ice sheet retreated, the lakes became smaller and the drainage patter changed. Uplifting of the land, and further ice retreat, reduced the Great Lakes to their present size and established current drainage northeast through the St. Lawrence River.

Glacial Lakese. In areas where evaporation is

high and precipitation is low lakes with high salt content can be formed. i. In the area where the ice age

Lake Bonneville once was is the current, and much smaller Salt Lake in Utah.

Glacial Lakesii. This lake became very salty due

to the fact that it had no drainage, and the only way water could leave was through evaporation. When the water evaporated, the salt was left behind forming the current Salt Lake.

Glacial Lakesi. These high salt content lakes can

also be a location of valuable minerals depending on the dissolved minerals it contains. 1. Minerals can either be brought in

by streams or are the result from the chemical and biologic processes occurring in the lake.

Glacial Lakesi.The salt deposits left in the dry beds of

ancient salt lakes often contain valuable minerals such as borax, which is used as a cleaning material and the manufacturing of glass and steel.

1. Currently the dry lake beds of the Mojave Desert in California contain borax.