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Glaciers and Ice Ages
By:
Caitlin McNeal
Pete Buscemi
Pat Carriglio
(Group 10)
Sec. 13.1- Formation of Glaciers
• Definition of Glacier: - massive, long
lasting, moving mass of compacted snow
and ice.
• Glaciers form in two environments. Alpine
glaciers form at all latitudes on high,
snowy mountains. Continental ice sheets
form at all elevations in the cold polar
regions.
Alpine Glaciers
• Alpine glaciers form in
summits were winter
snowfall is deep and
summers are short
and cool.
• The growth of an
alpine glacier
depends on both
temperature and
precipitation.
Continental Glaciers
• Continental Glaciers
• The Antarctic Ice
form in areas that
Sheet covers about
have winters that are
13 million square
so long and cold and
kilometers, an area
summers are short
almost 1.5 times the
and cool in polar
size of the U.S. It
regions that glaciers
blankets entire
cover most of the land
mountain ranges and
regardless of its
the mountains that
elevation.
rise above its surface.
13.2 – Glacial Movement
• Glaciers move by two
mechanisms: 1. Basal
Slip and 2. Plastic
Flow
• BS= glacier sliding
over bedrock.
• PF= ice flows as a
viscous fluid.
The Mass Balance of a Glacier
• The higher level part of the glacier is
called the zone of accumulation.
• The lower level part of a glacier is called
the zone of ablation.
• The snow line is the boundary between
permanent snow and seasonal snow.
• Glaciers tend to grow and shrink based on
location and temperatures.
Icebergs
• Icebergs: giant
chunks of ice that
break off of glaciers.
• The largest icebergs
in the world are those
that break away from
the Antarctic ice shelf.
• The tallest icebergs
break away from
tidewater glaciers in
Greenland.
Glacial Erosion
Glaciers erode and transport
huge quantities of rocks and
sediment.
Glacial StriationsRocks embedded in the ice
scrape across bedrock, cutting deep,
parallel grooves and scratches.
Erosional Landforms created by
Alpine Glaciers
• A glacier is not confined to a narrow stream bed but instead fills its
entire valley.
• As a result, it scours the sides of the valley as well as the bottom,
carving a broad, rounded, U-shaped valley.
Erosional Landforms created by
Alpine Glaciers cont…..
• A Cirque is a steep cliff that drops off into a horse-shoeshape into the mountain side.
•A cirque forms by snow
accumulates and glacier form,
the ice flows down the mountain
side. As time goes on, the
glacier carries rocks to the lower
part of the valleys.
Erosional Landforms created by
Alpine Glaciers cont…..
• Tarn- a small lake formed by a glacier
melting at the base of the cirque.
• Pasternoster Lakes- A series of lakes
which are commonly connected by rapids
and waterfalls.
Glacial Deposits
•
Drift- All rocks or sediment transported
and deposited by a glacier.
– Drift is divided into two categories
1. Till – Deposited directly by glacial ice
2. Stratified drift – first carried by glaciers
and then transported and deposited by a
stream.
Moraines
• Moraine – a mound or ridge of till
• End Moraine – sediment accumulates at
the terminus to form a ridge
•Dirty, old ice forms at the
bottom and clean snow lies
higher up.
Drumlins
• Drumlins- Elongate hills, that cover parts
of the northern United States
• Typically, 1-2 kilometers long and about
15-50 meters high.
“Snowball Earth”
• “At least twice, possibly as many as five
times, between 750 and 580 million years
ago, massive ice sheets completely
covered all continents, even at the
equator, entombing the entire globe in a
one kilometer thick shell of ice.”
Evidence For “Snowball Earth”
– Tillite
• hard, solid rock that is in every other respect
resembles the Pleistocene tills
• deposited so long ago that it has been cemented
into hard rock
• at least two thick layers of tillite between 750 and
580 million years old on almost every continent
– Some continents lay at the equator when tillite
was formed
Evidence Against “Snowball Earth”
– Contrasts with Pleistocene Ice Age completely
frozen polar seas and ice on 1/3 of the
continents
– Carbon dioxide in the atmosphere was too
high to permit radical global cooling, like
Snowball Earth’s theory presents
• Why didn’t the Earth stay frozen forever?
– Carbon dioxide in the atmosphere would have
melted the ice
– Eventual Greenhouse Effect because of
volcanoes on sea floor
• Last thaw occurred about 580 million
years ago, about the same time
multicellular life bloomed
– “ecologic habitats ready to be colonized
– Newly warmed Earth
• Plants and animals multiplied
• Abundant sources of food
Disappearing Glaciers
• Most glacier loss in the 1990’s, the warmest
decade in history
– Due to an increase in atmospheric carbon dioxide
– First sign of human-caused global warming
• Alpine glaciers reflect this in a highly visible way
– Glacier National Park in Montana glaciers have
shrunk by about a third as a group since 1850 (many
glaciers have disappeared completely!)
• In about thirty years, there could be ZERO glaciers in Glacier
National Park, if they continue disappearing at this pace
A bit about global warming…
• Global climate changes do not occur uniformly
around the world
– North Pole regions are warming faster than the
average for the Earth as a whole
• Ice Shelves
– Thick masses of ice that are floating in the ocean, but
are connected to glaciers on land
– Located mostly around Antarctica
– Respond to temperature change (i.e. global warming)
more sensitively than glaciers
• Mt Kenya, Kenya: lost 92% of it’s mass in the last 100
years.
• Caucasus Mountains, Russia: 50% less since the early
1900’s.
• Duosuogang Peak, China: shrunk by some 60% since
1970’s.
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Sources
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