Glaciers andIce Ages

By: Liz AlessiBrittany SpaldingMegan Timmers

What is a glacier?Glacier: a massive, long-lasting,

moving mass of compacted snow and ice

2 types: Alpine Glacier Continental Glacier

Glaciers covered the land 10,000 to 20,000 years ago.

GlaciersWhere do they form?

On land where the amount of snow that falls in the winter exceeds the amount that melts in summer

They form in 2 types of environments:High, snowy mountains in any climateCold polar regions

GlaciersHow do glaciers form?

Snowflakes Granular Snow Firn Glacier Ice

Firn: the transition between snow and glacial ice

Glacial MovementGlaciers begin to move when there is

an increase in pressure.2 Types:

Basal slip: movement of the entire mass of a glacier along the bedrock

Plastic flow: ice flows as a thick fluid because of an increase in pressure

Glacial MovementGlacial Erosion:

Glacial Striations: parallel grooves and scratches in bedrock that form as rocks are dragged along at the base of a glacier

These markings show the direction of ice movement and are used to map the flow directions of glaciers.

Glacial MovementLandforms created from glacial

erosion From Alpine Glaciers

Forms U-Shaped Valleys, tarns, paternoster lakes, horns, arêtes, hanging valleys, fjords (p. 314)

From Continental GlaciersForms vast regions- entire mountain rangesFormed the Great Lakes and the Finger Lakes in

New York

Glacial DepositsDRIFT: all rock or sediment transported

and deposited by a glacier 2 types of drift:

Till: deposited directly by glacial ice• Landforms composed of till: Moraines and drumlins

Stratified drift: was first carried by a glacier and then transported and deposited by a stream

• Landforms composed of stratified drift: outwashes, valley trains, outwash plains, kames, eskers, kettle lakes

Ice AgeSWhat are ice ages?

Ice Ages: intervals of time when large areas of the surface of the globe are covered with ice sheets

The most recent ice age is the Pleistocene Ice Age This occurred 2 million years ago in the

Northern Hemisphere.

Ice AgesWhen did ice ages occur?

Glaciations are concentrated into 4 time intervals.

Proterozoic Age (between 800 and 600 million years ago)

Pennsylvanian and Permian Age (between 350 and 250 million years ago)

Late Neogene to Quaternary Age (the last 4 million years)

Ordovician and Silurian Age (between 460 and 430 million years ago)

• Less extensive glaciations.

Ice AgesWhy do Ice Ages occur?

Because of the change of continental positions.

Because of the uplift of continental blocks.

Because of the reduction of CO2 in the atmosphere.

Because of changes in the Earth’s orbit.

Ice AgesWhat controls the advance and

retreat of glaciers? Changes in the eccentricity of the Earth’s

orbit Changes in the tilt of the Earth’s axis The precession of the equinoxes

Works’ Cited Ice Ages. 2003. Illinois State Museum. 5

November 2005. <http://www.museum.state.il.us/exhibits/ice_ages/index.html>.

Thompson, Gary and Jon Turk. Earth Science and the Environment. 3rd ed. Canada: Brooks/Cole Thompson Learning, 2005.

United Streaming. 2005. Discovery Education. 5 November 2005. <http://www.unitedstreaming.com/index.com>.