Transcript How The Last Ice Age Shaped Canada

How The Last Ice
Age Shaped Canada
What Were The Ice Ages?
• The Ice Ages began 2.4
million years ago and
lasted until 12,500 years
ago.
• Glacials: cold periods
during which glaciers
covered large parts of the
world
• Interglacials: very warm
periods during which
many of the glaciers
melted.
Ice Ages Cycle
Why were there Ice Ages?
• Many causes have been
suggested for the ice
ages including:
– changes in solar flux
– changes in the shape of
Earth’s orbit & the tilt of
its axis
Probably it was a
combination of
several such
influences.
The Pleistocene Epoch
• The Pleistocene Epoch
is the actual name for
the time period
• This period is the first in
which Homo sapiens
evolved, and by the end
of the epoch humans
could be found in nearly
every part of the planet.
The Last Ice Age
• The world's most recent glacial period began about
110,000 years ago and ended around 12,500 years
ago.
Laurentide Ice Sheet
• A massive ice sheet that
covered most of Canada
and a large portion of the
northern US
• It covered most of
northern North America
between 95,000 and
20,000 years ago.
• It created much of the
surface geology of the
area, leaving behind
many glacial landforms
Retreat of the Laurentide Ice Sheet
• As the ice
sheet
retreated,
it left
behind
many
large
glacial
lakes
How Do Glaciers Form Landscapes?
1) At the base of the glacier, large
amounts of loose rock and
sediment are stuck to the moving
ice
• Then the ice sheet acts like
sandpaper and scours the land
underneath
• Scouring can cause scratch marks
on the rock (striations)
• It can polish the rock smooth
(glacial polish)
• It can also wear off a fine sediment
transported away from the glacier
by meltwater
How Do Glaciers Form Landscapes
2) The glacier picks up or
“plucks” rocks and objects
as it moves.
• All glacial deposits are by
and large known as glacial
drift.
Glacial Landforms
Till: the sediments in a glacier,
they can be deposited around
the edge of a glacier
Moraine: the hill created from
the deposit of till from a glacier
(similar to an esker, a drumlin)
Erratic: a boulder transported
a long distance by a glacier
Kettle Hole: the hole or lake
created from a leftover chunk
of glacial ice
Land Formations Caused
by Retreating Glaciers
Toronto’s Ice Age
• When ice sheets are thick they pick up material, but
when they finally melt, they drop a mixture of
sediment that geologists call till.
Great Lakes and Lowlands
• Most of the Great Lakes’ basins were carved
out by the moving ice.
• Soil and rocks were scooped off the Canadian
Shield and deposited over southern parts such
as Toronto.
Formation of the Great Lakes
Toronto Drumlins
• Toronto has several
drumlins, ridges
created by glaciers.
Don Valley
• The deep wide lower Don valley was formed after the
draining of Lake Iroquois (a huge glacial lake)
• Many streams, including The Don, cut deep U-shapes
ravines through the previously V-shaped valley
Toronto’s Lakeshore
• Modern Lake Ontario is
within the bed of ancient
Lake Iroquois, a
meltwater lake that rose
while Ice Age glaciers
blocked the outlet of the
Saint Lawrence River to
the sea.
• Today Lake Ontario's
shoreline landform varies
considerably over the
length of metropolitan
Toronto.
Oak Ridges Moraine
• North of the city, the hills
and valleys of the Oak
Ridges Moraine rise 820
feet above lake level.
• The moraine's spongy
wetlands and soil were
deposited 12,000 years
ago from the retreating
Wisconsin Glacier, and
are now the headlands of
65 streams, of which 35
pass through the Greater
Toronto Area.
The Toronto Islands
• The Scarborough Bluffs,
for instance, are a section
of the Lake Iroquois
shoreline.
• Toronto Islands were
created from sand
deposits near the mouth
of the Don River, forming
a long, sandy spit that
would eventually be the
Toronto Islands.
Ice Age Videos
• http://www.youtube.com/watch?v=dJ5GYQrkvxI
• 2:08 “What is an Ice Age?”
• http://www.youtube.com/watch?v=x12KS936_fM
– 44:04 “North American Ice Age”