PROJECT EXPLORE INSTRUCTIONAL MODULE #4 FOCUS QUESTION: ANTARCTIC ICE: WHAT'S THERE AND WHERE DID IT COME FROM? ............................................................................ Gerry Hill Rosemount Senior High Rosemount, Minnesota BACKGROUND INFORMATION BACKGROUND INFORMATION 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 time. 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. OBJECTIVES: Process Objectives 1-The students will be able to describe origins, dynamics, extent, and possible future of the Antarctic ice sheet. CONTENT OBJECTIVES 1-The students will learn how glaciers form. 2-The students will learn that 90% of the world's ice is located in Antarctica. 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 cities. EQUIPMENT AND MATERIALS A map with the Trans-Antarctica Expedition route marked on it. EXPLORATION/ PRIOR KNOWLEDGE ASSESSMENT 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? CONCEPT INVENTION ACTIVITY 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 questions: 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 following: 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. APPLICATION ACTIVITIES 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. EVALUATION 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 years. 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? a-50% b-80% c-25% d-90% 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 SHORT ESSAYS: 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.