Antarctic Ice

Instructional Module #4


  Gerry Hill
  Rosemount Senior High
  Rosemount, Minnesota



Antarctica is a desert.  The average yearly total precipitation is about two
inches.  Yet, 98% of the continent is covered with a thick, ancient sheet of
ice.  The average thickness of this ice is 7,000 feet with a maximum depth
of nearly 3 miles (15,000 feet).

To understand where this ice came from, we have to take a look at glaciers
in general.  A glacier is a body of ice formed mainly of snow that has
thawed, refrozen, and become more crystalline and dense.  This
recrystallized snow/ice now flows on a land surface.  Glaciers form when the
yearly snowfall exceeds the yearly melt.  Because Antarctica's temperatures
rarely exceed the freezing point, thick ice sheets can form if given enough

The snow for glaciers starts out as very feathery and porous.  Over time the
snow becomes more dense and more granular in texture as freeze/thaw cycles
and pressure cause it to recrystallize.  We can see this happen (if you live
in the Snowbelt) to old snow in late winter.  As snow piles up, the pressure
of overlying snow and the recrystallization process eventually creates a
substance compact and dense enough to be called ice.

In Antarctica there are both alpine and continental glaciers.  Alpine
glaciers are found in the high basins of mountain ranges and flow down into
valleys.  By contrast, a continental glacier forms on a continental land
mass and flows outward from its source region.

Antarctica is buried under two continental glaciers that are separated by
the Transantarctic Mountains.  Each of these ice sheets has different
characteristics.  The East Antarctic ice sheet is similar to the ice sheet
covering Greenland in that they both cover land masses and are frozen to the
bedrock.  Its ice ranges in thickness from approximately 2,000 to 4,000
meters.  The West Antarctic ice sheet is the world's only remaining marine
ice sheet.  If the ice were removed and the underlying rocks rebounded to
their normal position, its bed would still be below sea level.

Gravity pulls all glaciers and ice sheets downhill and the Antarctica ice
sheets are no exception.  (Glaciers flow because the inner ice is more
flexible due to the pressure from the ice above and is not brittle like the
upper layers.) The ice in Antarctica is flowing to the sea at a rate of
about one to ten meters per year.  This movement has created some hazards
for the Trans-Antarctica Expedition.  When glaciers flow over changing
slopes or uneven land, the brittle top layers crack and form deep fractures
called crevasses.  Blowing snow can cover these crevasses with snow bridges.
Some of these bridges are strong enough to support sleds, dogs, and people
-- others are not.  Thus, careful testing is required before passing over
each crevasse on the snow bridges.  Near the coastal and mountainous areas
of Antarctica, the crevasses are the most dangerous.

The current icy period of Antarctica's history began about 25 million years
ago in the Miocene epoch.  The oldest and deepest parts of the ice are
believed to be 15 million years old.  The total volume of ice is 7.5 million
cubic miles and has pushed the land down about 2,000 feet.  This ice
represents 90% of the world's ice and 70% of the world's fresh water.  If
the ice would totally melt, there would be enough water to raise the level
of all the world's oceans by over 200 feet.


  Process Objectives

1-The students will be able to describe origins, dynamics, extent, and
possible future of the Antarctic ice sheet.


1-The students will learn how glaciers form.

2-The students will learn that 90% of the world's ice is located in

3-The students will learn that there is enough ice on Antarctica to bury the
United States under nearly two miles of ice and that the Trans-Antarctica
Expedition faces dangerous ice crevasses in the mountainous and coastal
parts of their journey.

4-The students will learn that the global climate may be warming,  leading
to large-scale melting and rising ocean level.

5-The students will learn that if all the Antarctic ice melts the oceans
would rise over 200 feet flooding much of the world's coastal areas and


A map with the Trans-Antarctica Expedition route marked on it.


This activity is designed to stimulate student interest in the topic and
provide an indication of the students' prior knowledge of the topic.  This
information is important for determining the starting point and level of
difficulty for instruction.

Begin this part of the module by asking students for oral responses to the
question:  "What is Antarctica like?" Somewhere in the response should be a
reference to the ice sheet that covers the continent.  Follow this up by
having everyone write answers to the following questions:

1-What are glaciers?

2-How do you think glaciers form?

3-Have glaciers ever covered North America?


In order to do these activities, the students need to know how the ice is
really formed, the extent of the glacial mass, and what happens to it as it
moves seaward.  Begin this activity with a short lecture giving the
necessary information about the ice sheet (see the background section, and
be sure to include information about crevasse formation).

Then have the students gather into small groups in order to answer the

1-What dangers do the members of the Trans-Antarctica Expedition face as
they travel across the ice?

2-How would you solve the problems related to the dangers of ice travel?

Be sure the students identify what the ice-related dangers will be and
where the Expedition is likely to encounter them.

Each group should come up with a written statement about the dangers and
ways to solve the travel problems encountered.  When all groups are finished
they can present their ideas in a class discussion.  (Teacher note:
crevasses present the greatest danger, and they are found mostly in the
mountainous areas and along the coasts where the ice is most active.  The
travel is the easiest in the interior.)

The second activity in this section is a short calculation to illustrate the
size of the ice sheet.  Ask the students to calculate how thick the ice
would be if it were placed on the United States.  They will need to know the

1-The average thickness of the ice sheet is about 7,000 feet.

2-Antarctica is 1.4 times the size of the U.S.

The calculation is done by calculating comparative ice volumes.  Antarctica
would be 7,000 feet multiplied by an area of 1.4.  The U.S.  would then be
an unknown (x) multiplied by an area of 1.  Setting the two equal should
give an ice thickness of 9,800 feet over the entire U.S.


The activities in this section all relate to the question:  "What will
happen if the ice melts?" Select one or more of these activities to give
students practice applying their new knowledge.

1-How much deeper will the oceans be if all the ice melts?  The first
activity is to have the students do another short calculation.  "Given that
the ice on Antarctica is 7.5 million cubic miles in volume and that Earth's
oceans cover about 140 million square miles, how much deeper will the oceans
be if all the ice melts?"

If no other factors such as the fact that water and an equal mass occupy
different volumes and that the oceans will expand when they are heated
during global warming are taken into account, the answer should be 280 feet.

2-What will happen to cities around the world if the ice cap melts?  The
second activity is done in small groups and requires a map of the U.S.  The
students are to do the following:

a-Look at a U.S. map and list the major cities that would be flooded if the
oceans rose 200 feet or so.

b-The groups are then to write out a long range disaster plan that assumes
the nearest suitable high ground is 100 miles inland and they have 15 years
to prepare.

c-The plans will be shared in a class discussion and the pros and cons of
each will be debated.  (The answers will probably vary considerably.)

An alternative to this activity is to do a similar problem on a global
scale using a world map and assuming the students are part of a United
Nations commission on global disaster preparation.

3-Library research

A third activity uses whatever resources are available in the school
library.  In this activity the students are to do library research about the
current debate on global warming.  They should look for arguments both pro
and con.  The final result would be a written report that could be shared
orally with the rest of the class and could also be the basis of a class
debate on global warming.

An extra addition to this activity would be to have the students write their
Congressman or Senator to find out what they are doing about global warming
or their position on the issue.


Multiple Choice:

1- Why has a deep ice sheet formed on Antarctica?

  a-Many feet of snow fall each year and change to ice.

  b-Snow melts very slowly and has built up thick ice over millions of

  c-The oceans sometimes flood the continent and freeze as an ice sheet.

  d-The ice has been there since the formation of Earth.

2-How much of the world's ice is in Antarctica?





3-If the Antarctic ice covered the United States, how deep would it be?

  a-Almost 10,000 feet

  b-Under 1,000 feet

  c-10 miles

  d-20,000 feet

4-What is the major ice-related danger that the members of the
Trans-Antarctica Expedition face as they travel across the Continent?

  a-Small pieces of ice blowing into the air.

  b-Losing control of their sleds due to slipping on the ice.

  c-Shifting glaciers.

  d-Falling into crevasses.

5-If all of the Antarctic ice were to melt, about how much deeper would the
world's oceans be?

  a-2 feet

  b-Over 200 feet

  c-20 feet.

  d-Between 50 and 75 feet


6-What would have to happen in North America for us to have large ice
sheets form and cover part of the Continent?

7-If all of Antarctica were mountainous and had much more irregular land
buried under the ice than it does now, how might this change the travel
plans of the Trans-Antarctica Expedition?  Explain your answer.

Patricia A. Weeg
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