Antarctica: Ice Sheet
1. Zoom from Devils Tower (Wyoming) to Antarctica
2. I struggled with this one. It really isn’t in keeping with the rest of this course
to have an entire continent be one of the Geological Wonders.
a. But I couldn’t figure out what particular feature to highlight, at the
expense of so many others.
b. The whole thing really is a wonder; for most of the continent, you see
things that you can’t see anywhere else on this planet. (At least, not at
this time – I will talk about Ice Ages in a bit).
3. The story here is ice. Ice on a very grand scale.
a. Volume of ice in Antarctica is about 25 million km3.m If it were to
melt, the worlds sea level would rise about 63 m (>200 ft). A lot of
continental area would be flooded [but it HAS melted, and continents
HAVE been flooded --- we have already seen all the ocean sedimentary
rocks in places like the Grand Canyon and Bryce Canyon]
b. Average thickness of ice is about 2 km, but is as thick as 4.7 km. And
Antarctica is about the size of Europe.
c. Everywhere the ice is flowing; flowing out to the ocean, where it
breaks off in giant sheets that are sometimes larger than US states.
d. Most of the ice is in East Antarctica, though some of the fastest flow
rates are in West Antarctica
e. [Explain East/West when you are at the pole!]
f. East/West are separated by Transantarctic Mountains
i. Different geological histories – East is very old continent, like
Australia; West is more recent, assembled from several
different pieces
4. Actually, Antarctica has less ice than in otherwise might have.
a. World’s largest desert (defined by rate of precipitation).
i. Refer back to atmospheric circulation.
b. Averages 16 mm rain/yr (6.5 inches). Mostly as snow. But it stays
around a long time because it is so cold!
i. The mean temperature in the interior is -57C (-70F). The
record low is -89.2C (-128.6F) – coldest every measured at
Earth’s surface. (exposed skin will freeze in seconds!)
ii. In the summer time there (winter here), along the coasts and
especially along Antarctic Peninsula the temperatures can
actually rise a little bit above freezing.
5. The ice is so thick that it actually pushes the rock of the continent down.
a. The average elevation of the rock is only 153 m (about the elevation of
St. Louis), but is much as 2.5 km below sea level in places.
b. End up with mountains around the rim; ice has to flow up and over
Mtn passes; sort of like rivers that flow out at a single point.
c. Largest single glacier in the world (by far!!) is Lambert Glacier, which
drains about 8% of Antarctica ice.
i. 100 km wide (60 miles!), 400 km long, and up to 2.5 km thick.
ii. Drains to the large Amery Ice Shelf; flow more than a km/yr in
places (near the mouth).
6. In many places, ice accumulates in large flat ice shelves that extend out over
the ocean. These are continually breaking up to form icebergs that float away.
a. Ross Ice Shelf the largest – the size of France, and up to 750 m thick.
Some pieces are huge – largest was 12,000 mi2 – about the size of
Belgium. Can take decades to melt!
b. Some people have proposed towing giant icebergs offshore of cities in
dry areas as a source of water – Antarctica contains 2/3 of the world’s
fresh water!
c. Major base – McMurdo Base – is adjacent to the Ross Ice shelf. Need
Ice breaker ship to cross McMurdo sound and bring supplies to the
base each year (especially fuel for heating!).
d. Supplies are then transported by tractor or plane to other bases, such
as the South Pole base.
i. Instruments located right at the pole have to be occasionally
relocated because the ice is flowing about 10 m/yr there!
ii. Strange place to be – it is dark half the year. Even during the
summer, the sun never rises very high, but just moves around
the horizon. (World’s longest sunsets)
iii. Long history of trying to reach the South Pole
1. Antarctica first sighted in 1820; mapped by 1840 (US
admiral Charles Wilkes)
2. The first humans to reach the Geographic South Pole
were Norwegian Roald Amundsen and his party on
December 14, 1911.
3. Another group, led by Robert Scott, got there 34 days
later, but they all died of starvation and cold on the way
back.
7. Many countries have laid claim to parts of Antarctica. However, the Antarctic
Treaty was signed in 1959 by 12 countries; (47 so far). The treaty prohibits
military activities and mineral mining, prohibits nuclear blasts and power,
supports scientific research, and protects the continent's ecozone. Ongoing
experiments of many different types are conducted by more than 4,000
scientists of many nationalities and with various research interests.
a. Example: seismology (a great way to understand how the glacier
works; M7 calving events; chirping along the seafloor)
b. Finding meteorites (explain)
c. Examining the ozone hole (explain)
d. Dry valleys (like Mars!)
e. Blood Falls
f. Interaction of volcanoes and ice (Mt. Erebus; show ice towers; ice
caves)
g. Climate change!
i. Obviously very important to the world – as sea levels are rising
ii. Show map of temperature change in Antarctica
iii. Fastest warming is in Antarctica peninsula – more than 8 deg
in 40 years in places
iv. Talk about Larsen B sudden breakup
v. If West Antarctica Ice melted, 3.5-6 m rise (would flood parts
of most major cities).
vi. If all of Antarctica melted (like it was in time of dinosaurs),
most major cities would be entirely flooded, and more than
half the world’s population would need to be moved!
vii. Fortunately, Antarctica has a continuous record of ice that has
locked in the composition of gases and isotopes over the years.
1. EPICA ice core in Dome C – goes back almost a million
years
2. Gives us the record of ice age cycles
8. Top 5:
a. Greenland – would contribute another 7 m to sea level rise if it melted.
It is melting at a rapidly increasing rate.
b. North Pole Ice cap – show how it has been shrinking; finally opened
up the long sought Northwest Passage!
c. North American and Fennoscandian Ice sheets during the last Ice Age.
Antarctic ice sheet can’t get much larger (strong circum-Antractic
currents and storms would break it up), but the top part of NAmer
gets covered with ice. Chicago under 2 km of ice! Came down as far as
Rte 70 (Mason-Dixon line) in previous ice ages. Left a few remnants,
like the Great Lakes!
Questions:
1) If all of the ice were suddenly removed from Antarctica, the sea level would
rise instantaneously, but then would continue to rise slightly for a long time.
Why?
2) Sometimes airplanes will land on the ice plateaus in East Antarctica. It can be
challenging to get them started again – why?