******************************************************** ICE, SNOW, AND GROUNDWATER ******************************************************** ********************************* HOW DEEP IS THE SNOW AND ICE? ********************************* __________ 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. __________ 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). __________ 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. __________ 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. __________ 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. ******************************** HOW DOES THE ICE GET THERE? ******************************** __________ 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? __________ 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. ********** ICE SHELF ********** __________ 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. ************** PERMAFROST ************** __________ 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. ***************************************** CREVASSES & FALLING THROUGH THE ICE ***************************************** __________ 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. __________ 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. __________ 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. ************************* GLACIERS AND ICEBERGS ************************* __________ 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 ofÊice weighs less than the same volume of water. __________ 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. __________ 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. ***************** GROUND WATER ***************** __________ 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.