Download Lesson 4 - Glacier Formation Notes

Grade 9 Academic Geography –Strand D The North
Facts about Glaciers
There have been five major ice ages on Earth
 About 250 million years ago (MYA), South America, India, Africa and Australia were glaciated as
part of the singe Pangaea supercontinent. In this period, North America and Europe were
located near the equator; these areas were not covered in ice.
 The most recent Ice Age occurred between 1 and 2 MYA. Ice sheets covered all of Canada, parts
of USA, Europe and South America.
 During an ice age, unbelievable volumes of water freeze into large ice sheets and ocean levels
drop. The sheets of ice (i.e., glaciers) advance and retreat. During the last Ice Age, glaciers
advanced and retreated four times. Why? A question for you to ponder and solve.
 The last glacial advancement began about 100 000 years ago and ended 6 000 year ago. During
glacial advancement, the Earth’s climate is cooler and snow accumulates. Over the years, the
snow became over 100 000 meters thick.
Now, glaciers exist on all of the world’s continents, but most of the world’s glaciers are found near the
North and South Poles. Presently, 10% of the Earth’s land area is covered with glacial ice, including
glaciers, ice caps, and the ice sheets of Greenland and Antarctica. Glacierized areas cover over 15 Mkm2.
Glaciers store about 75% of the world's freshwater.
Thick, dense glacial ice appears blue. Years of compression forces out the tiny air pockets between the
ice crystals. When glacier ice becomes extremely dense, the ice absorbs a small amount of red light,
leaving a bluish tint in the reflected light (…what we see). When glacier ice is white, that usually means
that there are many tiny air bubbles still in the ice.
The Antarctic ice is up to 4.7 kilometers thick in some areas. It is so heavy, the ice forces the land to
sink. The land underneath parts of the West Antarctic Ice Sheet may be up to 2.5 kilometers below sea
level.
Task

Working in small groups, answer the following questions. You have 15 minutes
 How do glaciers form?
 What climatic conditions are needed for glacial formation?
 How do glaciers move (i.e., advance and retreat)?
 How do large rocks trapped in the glacial ice influence the rate of glacial retreat?
 Why are glaciers so structurally strong?
 How do glaciers create or build various land formations (e.g., drumlins, eskers,
moraines)?
 The last glacial period ended over 6 000 years ago; yet, the formations from glacial
activity are still visible. Why?
 How did the Great Lakes form?
 BONUS. Peru's Quelccaya ice cap is the largest glacier area in the tropics. It is 15 538
meters in length. This glacier is the drinking water supply and electricity generation for
many thousands of Peruvians. It is contracting (…retreating) at a rate of 182.8 meters
per year. At its present melt rate, in which year will the Quelccaya disappear?
Grade 9 Academic Geography – Strand 4 The North
Glaciers
Glacial Formation
To ensure that the snow that accumulates in the winter is not lost during the summer, glaciers require very specific
climatic conditions. Such conditions typically prevail in polar and high alpine regions.
 Regions of high snowfall in winter
 Cool temperatures in summer
 Large accumulations of precipitation (e.g., snowfall, freezing rain, avalanches or wind-drifted snow)
A glacier forms when snow accumulates over time, turns to ice, and begins to flow outwards and downwards
under the pressure of its own weight. In polar and high-altitude alpine regions, glaciers generally accumulate more
snow in the winter than they lose in the summer from melting, evaporation, or calving.
Watch the YouTube presentation about calving at http://www.livescience.com/31989-major-glacier-calvingcaptured-in-time-lapse-video-video.html
If the accumulated snow survives one melt season, it forms a denser, more compressed layer called firn. Snow and
firn are compressed by overlying snowfall, and the buried layers slowly grow together to form a thickened mass of
ice. Each year’s new snowfall continues to compact the underlying layers, and the snow grains become larger ice
crystals randomly oriented in connected air spaces. These ice crystals can eventually grow to become several
centimeters in diameter.
As compression continues and the ice crystals grow, the air spaces in the layers decrease, becoming small and
isolated. This compaction compresses more air spaces out of the snowpack, and compacts the remaining air into
bubbles. At greater depth (hundreds of meters) the air in these bubbles is squeezed into the crystal structure of
the ice. Thus dense glacial ice has no air bubbles but contains trapped air.
Moving
Glaciers move in two different ways
 Force of gravity from high elevations to low elevations. The movement sharpens the points of the upper
portions of mountains. When they move into valleys at lower elevations, the glaciers scrape away the
mountain walls to form U-shaped valleys. This type of glaciers is called an alpine glacier. The Columbia
Icefield in the Banff-Jasper National Parks region of the Western Cordillera landform is the largest area of
ice in southern Canada. It consists of 30 glaciers covering about 300 km2 of land to depths of 365 meters.
 Continental glaciers occupy greater areas of land than alpine glaciers and move by the forces of their own
weight. During the last glacial advance, about 8 Mkm2 of North America was covered by glaciers. In some
spots, the glaciers were 4 km thick. A continental glacier spreads out from its zone of accumulation.
Advancing and retreating creates higher points of land by filling in lower areas with eroded materials.
Antarctica is covered in continental glaciers.
 Advance if Δmelt < Δaccumulation
 Stationary if Δmelt = Δaccumulation
 Retreat is Δmelt > Δaccumulation
Why are glacial features created many years ago still apparent today?
 Glaciation is a very, very powerful force. Thus, the changes made are (i) large and (ii) very visible
 Glaciation happened very recently relative to geological times. As such, there has not been enough time
for the impact of the most recent glaciation to be worn away
Erosional Processes of Glaciation
 Large rocks are carried in the glacial ice. As these rocks move with the ice, they create grooves in the
ground. These are called striations. They run in the direction of the glacial movement

Spillways are formed by huge volumes of meltwater. The water craves out deep gouges in the ground
that become the pathways for rivers
Ice Depositional Processes of Glaciation
 Till (i.e., clay, sand, gravel) is deposited directly by an ice sheet. Ice pushes and erodes the materials.
NOTE: Materials are NOT sorted by size.
 If the till becomes a gently rolling landscape, it is a Till Plain which is rich and thick soil
 If the till material forms a ridge, it is a Moraine which is characterized by thin soil, hills and swamps
 Drumlin is an egg-shaped hill which is steep on one side and gently sloped on the other side
 Erratics are large rocks that have been carried many kilometers from their origin to a new location. They
are easy to identify because the rock type of the erratic does not match the surrounding rock types.
Meltwater Depositional Processes of Glaciation
 Esker forms from gravel and sand carried by meltwater. The eroded materials are laid down on a river
bed. When the river retreats, an esker is established.
 Lake Plains are large lakes that occur after the glacial retreat.