An introduction to where, how, and why glaciers form Glacier Basics An introduction to where, how, and why glaciers form

What is a glacier? Large mass of moving ice that originated on land from accumulation, compaction, and recrystallization of snow When snow is added to a glacier faster than ice and snow melt, the glacier gets larger Largest fresh-water reservoir on Earth (75% of world’s fresh water) Two main types Continental glaciers /ice sheets Alpine/valley glaciers

Continental Glaciers Massive sheets of ice that may cover millions of square kilometers, that may be thousands of meters thick, and that are not confined by surrounding topography Are also called ice sheets

Alpine Glacier Narrow, wedge-shaped mass of ice that forms in a mountainous region that that is confined to a small area by surrounding topography

Where are glaciers found? Glaciers are found on every continent except Australia Found in polar regions and mountain ranges (and other planets) Usually glaciers start at higher elevations and flow downward and outward Hugo Ahlenius, UNEP/GRID-Arendal, overview of world glaciers and ice caps, UNEP/GRID-Arendal Maps and Graphics Library, (Accessed 22 June 2009)

Glacier formation Glaciers form wherever more snow accumulates in the winter than melts in the summer. Glaciers form above the snowline or lower limit of perennial snow in the zone of accumulation. Glaciers move downhill in response to gravity Glaciers melt or sublimate in the zone of wastage/ablation Crevasses are large cracks which reach the glacier surface and form by a number of ways

Glacial Movement Glaciers move in 2 ways: Basal Slip: simple response due to gravity whereby the ice moves downhill over bedrock and slipping over a thin layer of water. Internal Plastic Flow: If you stack a LOT of ice, the pressure increases and the ice behaves plastically, meaning that the lower layers will start to deform. Flow in a glacier is smooth at depth, but in the top ~50 m ice is brittle and cracks

Glacial erosion Rate of glacial erosion depends on Rate of glacial movement Ice thickness Underlying rock characteristics

Glacial erosion Plucking Abrasion Deep depression in rock when moving glacier loosens and dislodges rock from bedrock at base or side of glacier Sediment carried and deposited by glaciers is called glacial drift Abrasion Caused by glacial flow Striations form

How do glaciers change a landscape? Lateral moraines Horn Arête Cirque Grosser Aletschgletscher (Bernese Alps), Dirk Beyer Main glacier Medial moraines

How do glaciers change a landscape? Erosional Features Horns Arête Cirque Tarn lake Hanging valley How do glaciers change a landscape? Erosional features Truncated spur Paternoster lakes U-shaped valley Erosional features of a glaciated valley, DK www.wiredantarctica.com

Glacier anatomy: Alpine Glaciers Hanging Valley: Form where a higher elevation glacier flows into a larger glacier that has a deeper canyon Hanging valley U-shaped valley Yosemite Valley www.wiredantarctica.com

Crevasses Form by: Two glaciers colliding Accelerations in glacier speed Changes in underlying topography

Glacial Erosion - Landforms Cirque- Moving glacier pulls blocks of rock from the floor of the valley and create a bowl shaped depression

Glacial Erosion - Landforms Arête- Sharp, jagged ridge forms between cirques

Glacial Erosion - Landforms Horn- When several arêtes join, they form a sharp, pyramid-like peak

Glacial Erosion - Landforms Fjord- forms where a glacier has eroded a valley into the sea. When glacier retreats, the sea fills in.

Glacial Deposition - Landforms Erratic- Large boulders carried a long distance from their original location

Glacial Deposition - Landforms Moraines- The debris that glacier grind up, carry, and push out in front of it

Glacial Deposition - Landforms Drumlins- long, tear shaped mound

Glacial Deposition - Landforms Braided Streams- multiple small, shallow channels

Glacial Deposition - Landforms Kettles- occurring as the result of blocks of ice caving in