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		ICE, SNOW, AND GROUNDWATER
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HOW DEEP IS THE SNOW AND ICE?
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QUESTION: How deep does the snow get in Antarctica?

ANSWER from April Whitt on January 18, 1995
It depends where you are! The dome of the American base at the South 
Pole is drifted in about 40 feet deep (that took almost 25 years to drift, 
though). When I was at McMurdo in 1993, the snow plows were 
removing eight inches of snow that had kept us from landing the day 
before. If you have a chance, look up some of the journals kept by the 
early European explorers describing the howling storms on Antarctica. 
Admiral Byrd's book "Alone" is a good one.

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QUESTION: Does it ever warm up enough to melt the snow, and how 
deep is the snow?

ANSWER from Jack Dibb
This question needs to be a little better defined. Antarctica is a large 
land mass. The coast of Antarctica is about 20 degrees of latitude north 
of the South Pole. For comparison, this is about the same separation 
between San Diego (on US-Mexican border) and Vancouver, BC 
(close to US-Canadian border). If you include the Antarctic Peninsula, 
the latitude range increases by another 5 degrees. So the answer about 
amount of snow and whether it melts depends on where you are 
talking about. The amount of snow fall varies over a wide range, 
depending on distance from the coast and the pattern of winds bringing 
in storms (and blowing snow away in places). 

In general, more snow piles up along the coast and less falls deep in 
the interior. However, it is not always so simple. There are well-known 
"Dry Valleys" right next to the Ross Sea that get their name from the 
fact that there is no snow. (This is largely due to something known as 
katabatic, or drainage, winds. Can you picture how air from the east 
Antarctic Plateau might flow across the Transantarctic Mountains by 
looking at a map?) 

There are other places in the interior that get nearly no snow now, with 
glacial (or blue) ice right at the surface, while other areas get up to or 
over 1 m each year. At the South Pole, the average is about 20-25 cm 
per year; at Vostok it is less than 10 cm; over much of West Antarctica 
0.5-1.0 m is common; and places along the coast can get more. 

Melt is also a function of where you are. On the high plateaus, snow 
rarely, if ever, melts, but some or all of the snow melts along the 
coasts. This does not mean the ground becomes bare everywhere on 
the coast, since the snow is on top of glacial ice nearly everywhere. In 
the interior, snow turns into something called firn (the first step in 
conversion to glacial ice) after it has been buried by more snow. The 
firn can be around 100 m thick, on top of several km of ice (about 2.5 
km at South Pole, more than 3 km at Vostok). 

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QUESTION: How thick is the ice?

ANSWER from Jon Rinkenberger on January 19, 1995
There is a lot of ice here in Antarctica. Ice and snow cover many parts 
of this continent. McMurdo Station, on Ross Island is surrounded by 
ice. On one side is the Ross Ice Shelf. It is estimated to be three 
hundred feet thick at its edge. On the other side is the Ross Sea. Sea 
ice covers the water most of the year. The average thickness of the sea 
ice is between eighty and one hundred inches. At the South Pole 
Station the ice is nine thousand feet thick. This ice is called the Polar 
Plateau. The ice is an important part of maintaining a station here.

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QUESTION: How thick is the polar ice cap, and how do you measure 
it?

ANSWER from Jack Dibb on December 21, 1994
The polar ice cap is very big and its thickness varies in different 
places. Obviously it is quite thin at the edges and gets thicker inland. 
There are also big differences between the West Antarctic ice sheet 
and the East Antarctic ice sheet, both in area and thickness (the eastern 
sheet is much larger).

Thickness is measured by comparing the elevation of the surface of the 
ice and the surface of the underlying rock. One can measure the ice 
surface elevation directly (by several different methods), but until 
many holes are drilled through the ice at different places, the bedrock 
elevation has to be estimated by other means. The most common 
approach is to use radar. (It is also actually easier to get ice surface 
elevations by remote sensing from planes and satellites, since it is very 
difficult to get to enough locations to make a good surface map with 
direct measurements. Radar and laser techniques can be used for this.)

It is not possible to give a single answer to the first part of your 
question, but the thickness of ice at South Pole is about 3 km. Places 
further inland in East Antarctica have even greater thicknesses (near 4 
km at Vostok and a bit more than that at several other sites). There are 
a few sites in West Antarctica felt to be more than 3 km thick, but the 
map of bedrock surface is not as well developed for this region. 
Scientists hope to drill ice cores at several of these sites (both east and 
west) in coming years. These cores will provide much information 
about past climate, but will also give firm values for ice thickness at a 
few more points if they do reach all of the way to the bottom.

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QUESTION: Where is the thickest ice and how deep is it?

ANSWER from Deane Rink on December 23, 1994
The thickest ice is on the polar plateau; it is known as the East 
Antarctic ice sheet and in some places it is two miles thick. Its weight 
is so great that it actually pushes the bedrock of the Antarctic continent 
down to below sea level.

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HOW DOES THE ICE GET THERE?
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QUESTION: How does the water that makes the ice in Antarctica get 
there in the first place, even though Antarctica has such a dry climate?

ANSWER from Katy McNitt on January 12, 1995
The Earth has a series of complicated wind and ocean currents that 
transport air and water all over the planet. When warm, moist air 
approaches Antarctica, it starts to cool, and as it cools, the water vapor 
starts to condense into various forms of precipitation. This is because 
cold air can't hold as much moisture as warm air, though I doubt it's 
quite that simple!

There's a difference, too, between "relative humidity" and the amount 
of water vapor in air. For instance, at the South Pole, the air is 
extremely "dry" because it's too cold to hold much moisture. But the 
relative humidity is often 80 - 90 percent because the air contains 
almost as much moisture as it can!

In fact, we don't even need clouds to get precipitation at the South 
Pole. Almost every day you can see "diamond dust": tiny ice crystals 
that precipitate "out of thin air"! But because of the cold, it's 
impossible to get the big, fluffy snowflakes you might be used to, and 
it certainly never rains. So how do you suppose the South Pole could 
have possibly collected 2,835 meters of snow and ice?

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QUESTION: If the air over Antarctica never gets warm enough to 
evaporate water, where does all the snow come from?
 
ANSWER from Jack Dibb
The air over Antarctica is drier than in many other places, but, as you 
have figured out, it must carry some moisture. Air masses forced up 
and over the continent start over the ocean, so can have quite a bit of 
vapor at the beginning. As they rise and cool, the water condenses and 
can fall out. This results in a pretty marked decrease in snowfall as you 
move away from the coast and onto the high plateau.

There are several other aspects of water vapor exchange between the 
air and snow over Antarctica that can be important. The first is 
sublimation, where water leaves the snow and goes back into the 
atmosphere. This is a kind of reverse snowfall and can greatly reduce 
the accumulation of snow at many places (i.e., more snow falls than 
what piles up). The other unusual phenomena is what is called 
diamond dust, or clear sky precipitation. These are very delicate "snow 
flakes" that form when there are no clouds. The air cools enough to 
condense the small amount of vapor present, but there is so little 
condensable water that clouds cannot form. In large areas on the East 
Antarctic Plateau this kind of precipitation is much more common than 
regular snow.

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ICE SHELF
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QUESTION: What is the largest ice shelf in Antarctica?
 
ANSWER from Craig Mundell
The Ross Ice Shelf is the largest ice shelf in Antarctica. It is roughly 
the size of France.

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PERMAFROST
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QUESTION: Is there permafrost in Antarctica? If so, how much?

ANSWER from Tom Stevens in February, 1995:
Yes, there is permafrost. I guess that's what you would call the polar 
plateau which is covered with ice. It can be up to two miles (over 
10,000 feet) thick, and it covers about 95% of Antarctica. This thick 
layer of ice is why the South Pole is about 10,000 feet in elevation.

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CREVASSES & FALLING THROUGH THE ICE
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QUESTION: Have any of you ever fallen in a crevasse? Will you slip 
if you do not wear spiked boots?

ANSWER from Jon Rinkerberger on January 30, 1995
Crevasses are very dangerous. A few year ago two men from 
McMurdo fell into a crevasse and died. They walked through the 
crevasse field with no idea that they were in danger. The crevasses 
were bridged over from blowing snow making them look like small 
depressions. With the proper training, crevasses can be crossed safely. 
In case of a crevasse accident, we have a SAR team (Search And 
Rescue) that is highly trained in recovery of people who have fallen 
into crevasses.

Proper equipment is always important in whatever we do here. When 
walking over ice or very hard-packed snow, crampons are used. 
Crampons are the spikes that attach to the bottom of the boots.

ANSWER from Eugene Miya on June 8, 1995:
My basic answer is yes, both in the Antarctic and even in the USA.
Smaller crevasses are used by field people to practice holding falls.
You can slip, but most Americans choose not to practice using the spikes
(called crampons [cramp-ons]).  Our particular project involved
travelling through highly crevassed areas on skis, and it is harder to stop
a falling person when you wear skis.  We used skis to distribute our
body weight across snow bridges.  It was still possible to fall in, only
it was less likely.  But we proved to the NSF that it was possible to safely
work (i.e., do science) in these crevassed areas.  We had people occasionally
fall into crevasses, but typically without any injury (they were roped
and belayed).  Falling into a crevasse is not something that I can recommend,
but it was an event for which we practiced our response.

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QUESTION: Do the scientists have to worry about falling through the 
ice? Where would a person go if they did fall through the ice?

ANSWER from Jon Rinkenberger on December 27, 1994
Safety is a big concern for us down here, especially when on the ice. 
There are many dangers that are present when on the ice. The most 
dangerous are cracks, which makes the ice unsafe to travel on. Many 
step are taken to ensure that no one can fall through the ice, but 
sometimes accidents happen. In the event that someone does fall 
through the ice, which can life threatening, we have a small hospital 
here to treat them.

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QUESTION: Has anyone fallen through the ice, and if so, what was 
the result?

ANSWER: (unknown source)
Yes, someone has fallen through the sea ice here at McMurdo. In 1956 
a Seabee tractor driver died near McMurdo when the Caterpillar D8 he 
was driving broke through the ice and sank. Even though he had the 
escape hatch above him open, the vehicle weighed so much it sank too 
quickly for him to get out and save himself. His name was Richard T.  
Williams. The snow runway we use here at McMurdo is named after 
him. In more recent years there was another incident of heavy 
equipment breaking through the ice. I am not certain what year it was, 
nor the name of the operator. I do know that it was a woman, and she 
was able to escape out of the hatch. She swam to the surface and thrust 
her mittened-hand through the pieces of broken ice that had closed in 
after the vehicle fell through. Fortunately she was near the edge of the 
hole created and people had seen her go down. They yanked her up 
and out, and she survived fairly unscathed.

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GLACIERS AND ICEBERGS
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QUESTION: Why do icebergs float?

ANSWER: From Guy Guthridge, Program Manager for the National 
Science Foundation Antarctic Program

When water freezes, it becomes less dense. That is, a given volume 
ofice weighs less than the same volume of water.

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QUESTION: Does the glacier ice calve (break up)?

ANSWER from Katy McNitt on January 26, 1995
Yes, glaciers are calving all the time! I have a friend who works at 
Palmer Station on the Palmer Peninsula, and they frequently hear loud 
crashes when glaciers calve and big chunks of ice fall into the water.

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QUESTION: I have read that there are green icebergs. Have you seen 
any? What makes them green? 

ANSWER from Diane Stoecker
I haven't seen any green icebergs in McMurdo Sound but they may 
occur elsewhere. I've seen blue icebergs in a lagoon in Iceland and in 
McMurdo Sound; they were blue because they were icebergs that had 
rolled over. When glacial ice gets saturated with sea-water and then 
freezes, it changes consistency and gets clearer and bluer.

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GROUND WATER
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QUESTION: Is there ground water that is not frozen under 
Antarctica's ice?

ANSWER from Dave Pernic, Technical Services Center for 
Astrophysical Research in Antarctica, C.A.R.A. University of Chicago 
South Pole Station on January 13, 1995:

As far as I can tell here at the South Pole, the actual elevation of the 
ground is very close to sea level. The elevation where I am is close to 
10,000 feet. I can see nothing but a flat desert of snow in all directions.

It is always cold here; the temperature never climbs above -10F. The 
snow and ice here are almost 2 miles thick. Snow is heavy, and if you 
keep piling up snow more and more then it presses the snow below 
into a blue ice. On the surface the temperature ranges from -10F to 
-120F. If you dig into the snow about 30 ft or so then the temperature 
remains constant at the yearly average of around -60F. So do you think 
there could be any liquid water here? Antarctica is a big place, though. 
In some parts there are known to be volcanoes under an ice sheet. This 
would melt water and make some pockets of liquid, maybe.

What makes ground water? Rain soaks into the earth and is stored in 
the gravel and porous deposits under the topsoil. It is trapped from 
soaking further by some nonferrous material, like clay.

Where I am it is known as the driest place on Earth, meaning that there 
is very little precipitation-less than 2 inches per year, and that is in the 
form of a very fine and cold snow.

So, I don't know if it ever rains in Antarctica, and I'm not sure what 
kind of soil might be in a place where it might rain. I don't think that 
the ground would ever thaw out very deep from the surface, as 
summers even on the coast are very short and not really very warm.

I don't think there are any convention ground water reservoirs, but 
maybe you could research the weather patterns for different areas of 
Antarctica, and find out what the ground is like in those areas. 

Sometimes the glaciers push out over the sea ice. This is called a shelf. 
There is thick freshwater ice over the saltwater of the ocean. I don't 
think this counts as ground water, though.