Glaciers and Ice Ages By: Liz Alessi Brittany Spalding Megan 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.

Glaciers Where 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 climate Cold polar regions

Glaciers How do glaciers form?  Snowflakes  Granular Snow  Firn  Glacier Ice  Firn: the transition between snow and glacial ice

Glacial Movement Glaciers 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 Movement Glacial 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 Movement Landforms created from glacial erosion  From Alpine Glaciers Forms U-Shaped Valleys, tarns, paternoster lakes, horns, arêtes, hanging valleys, fjords (p. 314)  From Continental Glaciers Forms vast regions- entire mountain ranges Formed the Great Lakes and the Finger Lakes in New York

Glacial Deposits DRIFT: 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 AgeS What 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 Ages When 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 Ages Why do Ice Ages occur?  Because of the change of continental positions.  Because of the uplift of continental blocks.  Because of the reduction of CO 2 in the atmosphere.  Because of changes in the Earth’s orbit.

Ice Ages What 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 Illinois State Museum. 5 November Thompson, Gary and Jon Turk. Earth Science and the Environment. 3rd ed. Canada: Brooks/Cole Thompson Learning, United Streaming Discovery Education. 5 November