Geology lab assignment

Glacial Processes.docx

Name: _______________________________

G205: Glaciers

A glacier is a body of ice and snow that moves under the influence of gravity and its own weight. Evidence that a glacier is moving includes crevasses, flow features on the surface of the glacier, and a stream emerging from the terminus of the glacier filled with ground rock called glacial flour.

All glaciers consist of two parts. The upper part is perennially covered with snow, and is referred to as the zone of accumulation. The lower part is the zone of ablation, where calving, melting, and evaporation occur. If, over a period of time, the amount of snow a glacier gains is greater than the amount of water and ice it loses, then the glacier will expand or advance. If the amount of water and ice a glacier loses is greater than the amount of snow it gains, then the glacier will shrink or retreat. This is referred to the mass balance of the glacier.

Figures 13.7 and 13.8 (11th)/13.3 and 13.4(10th)/Figures 13.1 and 13.2 (9th) in your lab manual show some of the unique landscape features created by mountain (also called valley) glaciers. Figures 13.15 and 13.16 show common features created by continental glaciers. Glaciers, especially valley glaciers, can be thought of as "rivers" of ice. In many ways, the rules governing stream flow also govern the flow mechanism of glacial ice. Just as flowing water will naturally seek out the lowest elevation, so will glaciers. Once the glacial ice of a valley glacier begins to flow downslope, the glacier occupies a valley that was formerly cut by stream erosion, thus changing its shape form a "V"-shaped stream valley to a "U"-shape profile that is flat at the base but very steep along the valley walls.

This lab examines the landscapes associated with both types of glaciers, and also the response of glaciers to climate change.

Part 1: Glacier Movement – Deformation or Basal Sliding?

Glacier Model

Materials:

10 ml Borax powder

Airtight container or zip-lock bag

325 ml warm water

Chute made from PVC pipe or cookie sheet

250 ml white glue

Tape/Rubber Bands

2 mixing bowls

Ruler

Mixing spoon

Timer

Food coloring (optional)

Plastic drinking straw or spray bottle and water

Process:

1. Make the glacier gak (already made, but you can make it at home, too):

a. In the first mixing bowl, combine 200 ml warm water and 250 ml glue. Stir until well mixed.

b. In the second mixing bowl, combine 125 ml warm water and 10 ml of Borax powder. Stir until the powder is fully dissolved.

c. Combine the contents of the two mixing bowls. Stir until a single glob forms and cleans the sides of the bowl.

d. Optional: use food coloring to create different gak colors. Put half of the glob back into the first mixing bowl and add a few drops of food coloring. Knead the mixture, wearing rubber gloves to prevent staining your hands with the food coloring, until it is well mixed. Use the alternating colors in the experiment or smush the strips together to form a single striped glob of gak.

Experiment #1

1. Prop up one end of the PVC pipe chute (with books, rocks, etc.) so the glacier will be able to flow downhill. Think about the angle of repose from the mass wasting lab when deciding on how steep the chute might need to be.

3. Place the entire “glacier” at the top of the chute. Use the dry erase marker to mark the position of the front end of the glacier (the terminus), and the right and left sides of the glacier.

4. Set your timer for 5 minutes.

5. At the end of 5 minutes, mark the new location of the glacier terminus.

6. Take the chute down and place on a level surface to prevent further forward movement.

7. Measure and record the distance the glacier traveled from start to finish at the center, the left side, and the right side of the glacier. Repeat to obtain an average. Record the results in the table below. Determine the velocity of the three sections using the distance traveled from the table above and the elapsed time of 5 minutes. Don’t forget to convert minutes to seconds. Record the values in the table below.

Distance traveled by the glacial model (cm)

First Trial (cm)

Second Trial (cm)

Average (cm)

Velocity (cm/sec)

Right side

Center

Left Side

8. When the glacier model initially flowed, what shape did the front of the glacier take (sketch it)?

9. What part of the glacier flowed fastest? Why?

10. Does this experiment more closely approximate glacial movement by deformation of the ice or by basal sliding?

11. What are your predictions for how the glacier will flow when a little water is added to the chute added compared to the first time you ran the experiment?

Experiment #2

1. Set up the experiment again, marking the terminus of the glacier.

13. Poke the plastic drinking straw through the glacier, as close to the top of the glacier as possible. Add 5 ml of water through the straw to simulate meltwater seeping down through the glacier. Alternatively, lightly mist the chute with water from the spray bottle.

14. Set your timer for 5 minutes.

At the end of 5 minutes, measure the distance the glacier traveled from start to finish at the center, the left side, and the right side of the glacier. Repeat and record the results in the table below. Determine the velocity of the glacier with basal water. Record the values in the table below.

Distance traveled by the glacial model (cm)

First Trial (cm)

Second Trial (cm)

Average (cm)

Velocity (cm/sec)

Right side

Center

Left Side

15. Describe the difference between the glacial velocities of the two experiments. Why do you think this change occurred?

Part 2: Mountain Glaciers on Topographic Maps

In this part you will examine the features associated with mountain glaciers using Activity 13.2 (10th)/Activity 13.1 (9th) in your lab manual (10th: p. 349-350/9th: 309-310). Read the instructions in your lab manual and address the modified questions in the space below.

PART A

A.1 and A.2: Complete the profiles on the graph to the right.

A.3: Which of the cross-sections you made is V-shaped? (S-T or G-L?)

A.4: Which cross-section is U-shaped? (S-T or G-L?)

Why do you think a valley carved by a glacier has a different shape than that of a river?

A.5: Complete the topographic profile for A-B across the Harvard glacier on the right.

Label the top surface of the glacier on your profile, and put a dashed line where you think the rock bottom of the valley (or bottom of the glacier) is.

Based on the profile you constructed, what is the maximum thickness of Harvard Glacier along line A-B?

PART B. Read the instructions for this part and answer the associated questions on the space below:

B1:

B2:

PART C: Read the instructions for this part and answer the associated question in the space bellow.

Part 3: Glaciation in Glacier National Park, Montana

Use Figure 13.14 (10th p. 343)/Figure 13.12 (9th p. 305) (Glacier National Park, MT) in the lab manual to find a few glacial landforms. More specifically, list an example of a glacial erosional landform, depositional landform and water body present in this region (the features are listed on pages 335-337 of the lab manual) in the following table.

Type of Glacial Landform

Name on map/General location

Erosional Feature

1.

2.

Depositional Feature

1.

2.

Water Body

1.

2.

16. Using the data provided in the lower right corner of the Glacier National Park map, by what percentage did each of the glaciers below decrease in size between 1850 – 1993? [Hint: ((Initial – Final)/Initial) x 100]

a. Agassiz Glacier ____________________________.

b. Vulture Glacier ____________________________.

17. What was the rate (in km2/yr) that each of the glaciers receded between 1850 and 1993? [Hint: (Initial – Final)/# of Years]

a. Agassiz Glacier ____________________________.

b. Vulture Glacier ____________________________.

18. Based on what you calculated in the question above, in what year will each of these glaciers be completely melted? [Hint: Final/Rate + 1993]

a. Agassiz Glacier ____________________________.

b. Vulture Glacier ____________________________.

Part 4: Continental Glaciation and Landforms on Topographic Maps

In this part you will be examining the effects of continental glaciation on a landscape by viewing topographic maps from Ontario, Canada and Wisconsin. You will essentially be completing most of Activity 13.3 (10th p. 351)/13.2 (9th p. 311) in your lab manual and addressing the questions in the space below. Don’t forget to use Figures 13.8 & 13.9 (10th p. 338/9th p. 301) when addressing these questions!

A1.

A2.

A3. Towards what direction did the glacial ice flow here, and how can you tell?

B1.

B2.

B3.

B4.

B5.

Part 5: Nisqually Glacier and Climate Change

In this part you will be examining data from the Nisqually Glacier of Mt. Rainier, Washington. You are asked to complete most of Activity 13.5 (10th)/Activity 13.4 (9th) (10th: p. 353-354/9th: p. 313-314) in your lab manual, and record your answers in the space below.

PARTS A & B: Read the instructions to parts A & B, then complete the data chart and graph as instructed and then answer the questions below.

C1:

D:

E:

BONUS SECTION! Glacial Landforms and Google Earth

Open Google Earth and type in 63.069323°, -151.006058° in the Search window. Be sure that you have Borders and Labels check-marked in the Layers window in the left-hand panel. Google Earth will zoom in very close so you’ll have to zoom out to answer all the questions below. This section is worth an extra 6 points added on to your lab score, if you choose to do this.

1. What peak is at this location? To which mountain range does it belong? In which state is it located?

2. Locate and identify four glacial features in this area and identify their location using latitude and longitude (in decimal degrees, as we have done before, and as shown above), and put your results in the table below. You might use the figures in your lab manual for ideas.

Feature

Latitude and Longitude

1

2

avg. distance

time

velocity

=

Glacier Lab Handout.pdf

Chapter13.pdf

1 13 Glaciers and the Dynamic Cryosphere C O N T R I B U T I N G A U T H O R S

Sharon Laska • Acadia University

Kenton E. Strickland • Wright State University–Lake Campus

Nancy A. Van Wagoner • Acadia University

L A B O R A T O R Y

BIG IDEAS Earth’s crysphere is its snow and ice (frozen water),

including permafrost, sea ice, mountain glaciers,

continental ice sheets, and the polar ice caps. The extent

of snow and ice in any given area depends on how much

snow and ice accumulates during winter months and

how much snow and ice melts during summer months.

Glaciers are one of the best known components of the

cryosphere, because they are present on all continents

except Australia and have created characteristic

landforms and resources utilized by many people.

FOCUS YOUR INQUIRY THINK About It |

What is the cryosphere, and how do changes in the cryosphere affect other parts of the Earth system?

ACTIVITY 13.2 Mountain Glaciers and Glacial Landforms (p. 330 )

ACTIVITY 13.3 Continental Glaciation of North America (p. 330 )

How is the cryosphere affected by climate change?

THINK About It |

ACTIVITY 13.4 Glacier National Park Investigation (p. 334 )

ACTIVITY 13.5 Nisqually Glacier Response to Climate Change (p. 334 )

ACTIVITY 13.6 The Changing Extent of Sea Ice (p. 335 )

ACTIVITY 13.1 Cryosphere Inquiry (p. 330 )

THINK About It | How do glaciers affect landscapes?

Introduction The cryosphere is all of Earth’s snow and ice (frozen water). It all begins with a single snowflake falling from the sky or a single crystal of ice forming in a body of water. Over time, a visible body of snow or ice may form. Most snow and ice melts completely over summer months, providing much-needed water to communities. However, there are areas of Earth’s surface where the annual amount of ice accumulation exceeds the annual amount of ice melting. Permanent masses of ice can exist there. These areas ( FIGURE 13.1 ) range from places with permanently frozen ground (permafrost), to places

329

Kennicott Glacier, a long (43 km, 27 mi) valley glacier in Alaska. Mountains in the distance are where snow and ice accumulate and form the glacier. Down valley, dark medial moraines of rocky drift are deposited from melting ice. (Photo by Michael Collier)

PRE-LAB VIDEO

330 ■ L A B O R AT O R Y 13

where ice permanently covers the ground (glaciers and ice caps, ice sheets), to places where ice covers parts of the ocean (ice shelves, sea ice). The ice in your freezer may last for days or months, but ice in some of Earth’s ice caps is thousands of years old.

OBJECTIVE Analyze features of landscapes aff ected by mountain glaciation and infer how they formed.

PROCEDURES

1. Before you begin , read the Introduction, Glaciers, and Glacial Processes and Landforms. Also, this is what you will need :

____ ruler, calculator ____ Activity 13.2 Worksheets (pp. 349–350 ) and

pencil

2. Then follow your instructor’s directions for completing the worksheets.

ACTIVITY 13.2 Mountain Glaciers and

Glacial Landforms

THINK About It | How do glaciers affect landscapes?

ACTIVITY 13.1 Cryosphere Inquiry

THINK About It |

What is the cryosphere, and how do

changes in the cryosphere affect other

parts of the Earth system?

OBJECTIVE Analyze global and regional components of the cryosphere, and then infer how they may change and ways that such change may aff ect other parts of the Earth system.

PROCEDURES

1. Before you begin , do not look up defi nitions and information. Use your current knowledge, and complete the worksheet with your current level of ability. Also, this is what you will need to do the activity:

____ pen ____ Activity 13.1 Worksheets (pp. 347–348 ) and

pencil

2. Complete the worksheet in a way that makes sense to you.

3. After you complete the worksheet , be prepared to discuss your observations and classifi cation with other geologists.

OBJECTIVE Analyze features of landscapes aff ected by continental glaciation and infer how they formed.

PROCEDURES

1. Before you begin , read the Introduction, Glaciers, and Glacial Processes and Landforms. Also, this is what you will need :

____ Activity 13.3 Worksheet (p. 351 ) and pencil

2. Then follow your instructor’s directions for completing the worksheets.

ACTIVITY 13.3 Continental Glaciation of

North America

THINK About It | How do glaciers affect landscapes?

Dynamic Cryosphere The total amount of ice on Earth’s surface is ever- changing due to annual variations in global patterns of air circulation and regional variations in things like ground temperature, ocean surface temperature, and the weather (daily to seasonal conditions of the atmosphere, such as air temperature and humidity, wind, cloud cover, and precipitation). Global and regional amounts of ice are also affected by climate —the set of atmospheric conditions (like air temperature, humidity, wind, and precipitaion) that prevails in a region over decades. A region’s climate is generally determined by measuring the average conditions that exist there over a period of years or the conditons that normally exist in the region at a particular time of year.

Climate Change A region’s climate is based on factors like latitude, altitude, location relative to oceans (moisture sources), and location relative to patterns of global air and ocean circulation. Climate change refers to a significant change in atmospheric conditions of a region or the planet. This can occur due to natural factors like changing patterns of global air circulation, variations in volcanic activity, and changes in solar activity. It can also occur due to human factors like construction of regional urban centers (adding regional sources of heat energy) and deforestation (removing a transpiration source of atmospheric water vapor; adding soot and gases to the atmosphere as the forest is burned).

Glaciers and the Dynamic Cryosphere ■ 331

Map of Regional Variations in the Cryosphere

ICE SHELF: A sheet of ice attached to the land on one side but afloat on the ocean on the other side.

SEA ICE: A sheet of ice that originates from the freezing of seawater.

SEASONAL SNOW: Snow and ice may accumulate here in winter, but it melts over the following summer.

PERMAFROST CONTINUOUS: The ground is permanently frozen over this entire area.

PERMAFROST DISCONTINUOUS: The ground is permanently frozen in isolated patches within this area.

ICE SHEET: A pancake-like mound of ice covering a large part of a continent (more than 50,000 km2).

MOUNTAIN GLACIERS AND ICE CAPS: This area contains permanent patches of ice on mountain sides (cirques), river-like bodies of ice that flow down and away from mountains (valley and piedmont glaciers), and dome-shaped masses of ice and snow that cover the summits of mountains so that no peaks emerge (ice cap).

• South Pole

• North Pole

FIGURE 13.1 Cryosphere components. You can also download a complete world map of cryosphere components from this UNEP

(United Nations Environment Programme) website: http://www.grida.no/graphicslib/detail/the-cryosphere-world-map_e290

Glaciers Glaciers are large ice masses that form on land areas that are cold enough and have enough snowfall to sus- tain them year after year. They form wherever the win- ter accumulation of snow and ice exceeds the summer ablation (also called wastage ). Ablation (wast- age) is the loss of snow and ice by melting and by sublimation to gas (direct change from ice to water vapor, without melting). Accumulation commonly occurs in snowfields —regions of permanent snow cover ( FIGURE  13.2 ).

Glaciers can be divided into two zones, accumulation and ablation ( FIGURE 13.2 ). As snow and ice accumulate in and beneath snowfields of the zone of accumulation , they become compacted and highly recrystallized under their own weight. The ice mass then begins to slide and flow downslope like a very viscous (thick) fluid. If you slowly squeeze a small piece of ice in the jaws of a vise or pair of pliers, then you can observe how it flows. In nature, glacial ice formed in the zone of accumulation flows and slides downhill into the zone of ablation , where it melts or sublimes (undergoes sublimation) faster than new ice can form. The snowline is the boundary between the zones of accumulation and ablation. The bottom end of the glacier is the terminus .

It helps to understand a glacier by viewing it as a river of ice. The “headwater” is the zone of accumula- tion, and the “river mouth” is the terminus. Like a river, glaciers erode (wear away) rocks, transport their load

(tons of rock debris), and deposit their load “down- stream” (down-glacier).

The downslope movement and extreme weight of glaciers cause them to abrade and erode (wear away) rock materials that they encounter. They also pluck rock material by freezing around it and ripping it from bedrock. The rock debris is then incorporated into the glacial ice and transported many kilometers by the glacier. The debris also gives glacial ice extra abrasive power. As the heavy rock-filled ice moves over the land, it scrapes surfaces like a giant sheet of sandpaper. Rock debris falling from valley walls commonly accumulates on the surface of a moving glacier and is transported downslope. Thus, glaciers transport huge quantities of sediment, not only in, but also  on the ice.

When a glacier melts, it appears to retreat up the valley from which it flowed. This is called glacial retreat , even though the ice is simply melting back (rather than moving back up the hill). As melting occurs ( FIGURE 13.3 ), deposits of rocky gravel, sand, silt, and clay accumulate where there once was ice. These deposits collectively are called drift . Drift that accumulates directly from the melting ice is unstratified (unsorted by size) and is called till . However, drift that is transported by the meltwater becomes more rounded, sorted by size, layered, and is called stratified drift . Wind also can transport the sand, silt, and clay particles from drift. This wind-transported sediment can form dunes or loess deposits (wind-deposited, unstratified accumulations of clayey silt).

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332 ■ L A B O R AT O R Y 13

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FIGURE 13.2 Mountain glaciation. This is an ASTER infrared satellite image of a 20-by-20 km area in Alaska. Vegetation appears red, glacial ice is blue, and snow is white. (Image courtesy of NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team.)

There are five main kinds of glaciers based on their size and form.

■ Cirque glaciers —small, semicircular to triangular glaciers that form on the sides of mountains. If they form at the head (up-hill end) of a valley and grow large enough, then they evolve into valley glaciers.

■ Valley glaciers —long glaciers that originate at cirques and flow down stream valleys in the mountains.

■ Piedmont glaciers —mergers of two or more valley glaciers at the foot (break in slope) of a mountain range.

■ Ice sheet —a vast, pancake-shaped ice mound that covers a large portion of a continent and flows independent of the topographic features beneath it and covers an area greater than 50,000 km 2 . The Antarctic Ice Sheet (covering the entire continent of Antarctica) and the Greenland Ice Sheet (covering Greenland) are modern examples.

■ Ice cap —a dome-shaped mass of ice and snow that covers a flat plateau, island, or peaks at the summit of a mountain range and flows outward in all directions from the thickest part of the cap. It is much smaller than an ice sheet.

Glaciers and the Dynamic Cryosphere ■ 333

Glacial Processes and Landforms Glaciated lands are affected by either local to regional “mountain glaciation” or more continent-wide “ continental glaciation.”

Mountain Glaciation Mountain glaciation is characterized by cirque glaciers, valley glaciers, piedmont glaciers, and ice caps. Poorly developed mountain glaciation involves only cirques, but the best-developed mountain glaciation involves all three types. In some cases, valley and piedmont glaciers are so well developed that only the highest peaks and ridges extend above the ice. Ice caps cover even the peaks and ridges. FIGURE  13.2 shows a region with mountain glaciation. Note the extensive snowfield in the zone of accumulation. Snowline is the elevation above which there is permanent snow cover.

Also note that there are many cracks or fissures in the glacial ice of FIGURE 13.2 . At the upper end of the glacier is the large bergschrund (German, “mountain crack”) that separates the flowing ice from the relatively immobile portion of the snowfield. The other cracks are called crevasses —open fissures that form when the velocity of ice flow is variable (such as at bends in valleys). Transverse crevasses are perpendicular to the flow direction, and longitudinal crevasses are aligned parallel with the direction of flow.

FIGURE 13.3 shows the results of mountain glaciation after the glaciers have completely melted. Notice the characteristic landforms, water bodies, and sedimentary deposits. For your convenience, distinctive features of glacial lands are summarized in three figures: erosional features in FIGURE 13.4 , depositional features in FIGURE 13.5 , and water bodies in FIGURE 13.6 . Note that some features are identical in mountain glaciation and continental glaciation, but others are unique to one or the other. Study the descriptions in these three figures and compare them with the visuals in FIGURES 13.2 and  13.3 .

Continental Glaciation During the Pleistocene Epoch, or “Ice Age,” that ended 11,700 years ago, thick ice sheets covered most of Canada, large parts of Alaska, and the northern contiguous United States. These continental glaciers produced a variety of characteristic landforms ( FIGURE  13.7 , FIGURE 13.8 ).

Recognizing and interpreting these landforms is important in conducting work such as regional soil analyses, studies of surface drainage and water supply, and exploration for sources of sand, gravel, and  minerals. The thousands of lakes in the Precambrian Shield area of Canada also are a legacy of this continental glaciation, as are the fertile soils of the north-central United States and south-central Canada.

Snowfield

Bergschrund Arête

Horn

Snowline

Cirque glacier

Medial moraines

Valley glacier

Longitudinal crevasses

ZONE OF

ACCUM ULATION

Snowline

Ground moraine

Transverse crevasses

Cirque glaciers

Lateral moraine

ZONE OF

ABLATION

FIGURE 13.3 Active mountain glaciation, in a hypothetical region. Note the cutaway view of glacial ice, showing flow lines and direction (blue lines and arrows).

334 ■ L A B O R AT O R Y 13

Glacier National Park, Montana Glacier National Park is located on the northern edge of Montana, across the border from Alberta and British Columbia, Canada. Most of the erosional features formed

by glaciation in the park developed during the Wisconsinan glaciation that ended about 11,700 years ago. Today, only small cirque glaciers exist in the park. Thirty-seven of them are named, and nine of those can be observed on the topographic map of part of the park in FIGURE 13.14 .

Cirque

Tarn

Tarn

ArêteHorn

Hanging valley

Paternoster lakes

Medial moraine

Waterfall

Present-day misfit-stream valley

Lateral moraines

Ground moraine

U-shaped valley carved by

valley glacier

FIGURE 13.4 Erosional and depositional features of mountain glaciation. The same region as FIGURE 13.3 , but showing erosion features remaining after total ablation (melting) of glacial ice.

OBJECTIVE Evaluate the use of Nisqually Glacier as a global thermometer for measuring climate change.

PROCEDURES

1. Before you begin , read Nisqually Glacier—A Global Thermometer? Also, this is what you will need :

____ ruler ____ Activity 13.5 Worksheets (p. 353–354 ) and

pencil

2. Then follow your instructor’s directions for completing the worksheets.

ACTIVITY 13.5 Nisqually Glacier Response

to Climate Change

THINK About It | How is the cryosphere affected by climate change?

OBJECTIVE Analyze glacial features in Glacier National Park and infer how glaciers there may change in the future.

PROCEDURES

1. Before you begin , read about Glacial National Park, Montana below. Also, this is what you will need :

____ calculator ____ Activity 13.4 Worksheet (p. 352 ) and pencil

2. Then follow your instructor’s directions for completing the worksheets.

ACTIVITY 13.4 Glacier National Park

Investigation

THINK About It | How do glaciers affect landscapes? How is the cryosphere affected by

climate change?

Glaciers and the Dynamic Cryosphere ■ 335

Nisqually Glacier—A Global Thermometer? Nisqually Glacier is one of many active valley glaciers that occupy the radial drainage of Mt. Rainier—an active volcano located near Seattle, Washington, in the Cascade Range of the western United States. Nisqually Glacier occurs on the southern side of Mt. Rainier and flows south toward the Nisqually River Bridge in FIGURE  13.15 . The position of the glacier’s terminus (downhill end) was first recorded in 1840, and it has been measured and mapped by numerous geologists since that time. The map in FIGURE 13.15 was prepared by the U.S. Geological Survey in 1976 and shows where the terminus of Nisqually Glacier was located at various times from 1840 to 1997. (The 1994, 1997, and 2010 positions were added for this laboratory, based on NHAP aerial photographs and satellite imagery.) Notice how the glacier has more or less retreated up the valley since 1840.

Sea Ice Sea ice is frozen ocean water. The largest masses of sea ice occur in the Arctic Ocean and around the continent of Antarctica ( FIGURE 13.16 ). In both locations, the sea

MOUNTAIN GLACIATION

CONTINENTAL GLACIATION

X

X

X

X

X

X

X

X

X

X

X

X

EROSIONAL FEATURES OF GLACIATED REGIONS

Cirque

Arête

Col

Horn

Headwall

Glacial trough

Hanging valley

Roche moutonnée

Glacial polish

Glacial striations and grooves

Bowl-shaped depression on a high mountain slope, formed by a cirque glacier

Sharp, jagged, knife-edge ridge between two cirques or glaciated valleys

Mountain pass formed by the headward erosion of cirques

Steep slope or rock cliff at the upslope end of a glaciated valley or cirque

U-shaped, steep-walled, glaciated valley formed by the scouring action of a valley glacier

Glacial trough of a tributary glacier, elevated above the main trough

Asymmetrical knoll or small hill of bedrock, formed by glacial abrasion on the smooth stoss side (side from which the glacier came) and by plucking (prying and pulling by glacial ice) on the less-smooth lee side (down-glacier side)

Parallel linear scratches and grooves in bedrock surfaces, resulting from glacial scouring

Smooth bedrock surfaces caused by glacial abrasion (sanding action of glaciers analogous to sanding of wood with sandpaper)

Steep-sided, pyramid-shaped peak produced by headward erosion of several cirques

FIGURE 13.5 Erosional features of mountain or continental glaciation.

OBJECTIVE Measure how the extent of sea ice has changed annually in the past, predict how it may change in the future, and infer what benefi ts or hazards could result if Arctic sea ice continues to decline.

PROCEDURES

1. Before you begin, read Sea Ice. Also, this is what you will need:

____ 30 cm (12 in.) length of thread or thin string ____ ruler, calculator ____ Activity 13.7 Worksheets (pp. 355–356) and

pencil

2. Then follow your instructor’s directions for completing the worksheets.

ACTIVITY 13.6 The Changing Extent of

Sea Ice

THINK About It | How is the cryosphere affected by climate change?

336 ■ L A B O R AT O R Y 13

Recessional moraine

Ground moraine

Terminal moraine

Lateral moraine

Medial moraine

Drumlin

Erratic

Boulder train

Outwash

Outwash plain

Valley train

Kame

Esker

Beach line

Glacial-lake deposits

Loess

Sheetlike layer (blanket) of till left on the landscape by a receding (wasting) glacier.

Ridge of till that formed along the leading edge of the farthest advance of a glacier.

Ridge of till that forms at terminus of a glacier, behind (up-glacier) and generally parallel to the terminal moraine; formed during a temporary halt (stand) in recession of a wasting glacier.

A body of rock fragments at or within the side of a valley glacier where it touches bedrock and scours the rock fragments from the side of the valley. It is visible along the sides of the glacier and on its surface in its ablation zone. When the glacier melts, the lateral moraine will remain as a narrow ridge of till or boulder train on the side of the valley.

A long narrow body of rock fragments carried in or upon the middle of a valley glacier and parallel to its sides, usually formed by the merging of lateral moraines from two or more merging valley glaciers. It is visible on the surface of the glacier in its ablation zone. When the glaciers melt, the medial moraine will remain as a narrow ridge of till or boulder train in the middle of the valley.

An elongated mound or ridge of glacial till (unstratified drift) that accumulated under a glacier and was elongated and streamlined by movement (flow) of the glacier. Its long axis is parallel to ice flow. It normally has a blunt end in the direction from which the ice came and long narrow tail in the direction that the ice was flowing.

Boulder or smaller fragment of rock resting far from its source on bedrock of a different type.

A line or band of boulders and smaller rock clasts (cobbles, gravel, sand) transported by a glacier (often for many kilometers) and extending from the bedrock source where they originated to the place where the glacier carried them. When deposited on different bedrock, the rocks are called erratics.

Stratified drift (mud, sand and gravel) transported, sorted, and deposited by meltwater streams (usually muddy braided streams) flowing in front of (down-slope from) the terminus of the melting glacier.

Plain formed by blanket-like deposition of outwash; usually an outwash braid plain, formed by the coalescence of many braided streams having their origins along a common glacial terminus.

Long, narrow sheet of outwash (outwash braid plain of one braided stream, or floodplain of a meandering stream) that extends far beyond the terminus of a glacier.

A low mound, knob, or short irregular ridge of stratified drift (sand and gravel) sorted by and deposited from meltwater flowing a short distance beneath, within, or on top of a glacier. When the ice melted, the kame remained.

DEPOSITIONAL FEATURES OF GLACIATED REGIONS

Long, narrow, sinuous ridge of stratified drift deposited by meltwater streams flowing under glacial ice or in tunnels within the glacial ice

Landward edge of a shoreline of a lake formed from damming of glacial meltwater, or temporary ponding of glacial meltwater in a topographic depression.

Layers of sediment in the lake bed, deltas, or beaches of a glacial lake.

Unstratified sheets of clayey silt and silty clay transported beyond the margins of a glacier by wind and/or braided streams; it is compact and able to resist significant erosion when exposed in steep slopes or cliffs.

MOUNTAIN GLACIATION

CONTINENTAL GLACIATION

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

FIGURE 13.6 Depositional features of mountain or continental glaciation.

Glaciers and the Dynamic Cryosphere ■ 337

ice reaches its maximum thickness and extent during the winter months, then it melts back to a minimum extent and thickness during the summer months. In the northern hemisphere, Arctic sea ice reaches its minimum thickness and extent by September. Sea ice helps moderate Earth’s climate, because its bright white

surface reflects sunlight back into space. Without sea ice, the ocean absorbs the sunlight and warms up. Sea ice also provides the ideal environment for animals like polar bears, seals, and walruses to hunt, breed, and migrate as survival dictates. Some Arctic human populations rely on subsistence hunting of such species to survive.

WATER BODIES OF GLACIATED REGIONS

Tarn

Ice-dammed lake

Paternoster lakes

Finger lake

Kettle lake or kettle hole

Swale

Marginal glacial lake

Meltwater stream

Misfit stream

Marsh or swamp

Small lake in a cirque (bowl-shaped depression formed by a cirque glacier). A melting cirque glacier may also fill part of the cirque and may be in direct contact with or slightly up-slope from the tarn.

Lake formed behind a mass of ice sheets and blocks that have wedged together and blocked the flow of water from a melting glacier and or river. Such natural dams may burst and produce a catastropic flood of water, ice blocks, and sediment.

Chain of small lakes in a glacial trough.

Small lake or water-saturated depression (10s to 1000s of meters wide) in glacial drift, formed by melting of an isolated, detached block of ice left behind by a glacier in retreat (melting back) or buried in outwash from a flood caused by the collapse of an ice-dammed lake.

Narrow marsh, swamp, or very shallow lake in a long shallow depression between two moraines.

Lake formed at the margin (edge) of a glacier as a result of accumulating meltwater; the upslope edge of the lake is the melting glacier itself.

Stream of water derived from melting glacial ice, that flows under the ice, on the ice, along the margins of the ice, or beyond the margins of the ice.

Stream that is not large enough and powerful enough to have cut the valley it occupies. The valley must have been cut at a time when the stream was larger and had more cutting power or else it was cut by another process such as scouring by glacial ice.

Saturated, poorly drained areas that are permanently or intermittently covered with water and have grassy vegetation (marsh) or shrubs and trees (swamp).

Long narrow lake in a glacial trough that was cut into bedrock by the scouring action of glacial ice (containing rock particles and acting like sand paper as it flows downhill) and usually dammed by a deposit of glacial gravel (end or recessional moraine).

MOUNTAIN GLACIATION

CONTINENTAL GLACIATION

X

X

X

X

X

X

X X

X

X

X

X

X

X

X

X

X

FIGURE 13.7 Water bodies resulting from mountain or continental glaciation.

338 ■ L A B O R AT O R Y 13

Terminal moraine

Ice blocks

Delta

Outwash plain

Marginal lake

Tunnel

Braided streams forming braid

plains

Roche moutonnée formed by glacial erosion

Outwash

Bedrock

Till

Plucking

Direction of ice flow

Abrasion

Bedrock

FIGURE 13.8 Continental glaciation in a hypothetical region. Continental glaciation produces these characteristic landforms at the beginning of ice wastage (decrease in glacier size due to severe ablation).

Esker

Swale

Drumlin field

Delta

Marshes

Old lake shorelines Lake

deposits

Recessional moraine

Misfit meandering stream

Terminal moraine

Kames

Outwash plain

Sand and gravel

Outwash

Bedrock

Till

Kettle lakes

Kettle lake

FIGURE 13.9 Erosional and depositional features of continental glaciation. Continental glaciation leaves behind these characteristic landforms after complete ice wastage. (Compare to FIGURE 13.8 .)

G lacie

rs an d

th e

D yn

am ic C

ryo sp

h e

re

3 3

9

A

B

C D

C

D

C

D

C

X Y

Z

FIGURE 13.10: Anchorage (B-2), AK (1960)

Contour interval = 100 ft.

0

1 2 3 kilometers

North

0

1 2/ 1 2 miles

1:63,360

Infrared image of Harvard Glacier in 2000. Snow and ice are blue and white, vegetation is red. Image courtesy of NASA/GFSC/METI/Japan Space Systems, and U.S./Japan ASTER Science Team

(Courtesy of U.S. Geological Survey) 

340 ■ L A B O R AT O R Y 13

Calif.

0 1.5 kilometer

0 1 mile1 2/1 4/

FIGURE 13.11: Yosemite Falls, CA (1992)

Contour interval = 40 ft.

North

1:24,000 Quadrangle location

S

T

G

L

(C o

u rt

e sy

o f

U .S

. G e

o lo

g ic

al S

u rv

e y)

G lacie

rs an d

th e

D yn

am ic C

ryo sp

h e

re

3 4

1

FIGURE 13.12: Peterborough, Ontario (Canadian NTS #031D08)

Contour interval = 10 meters © Department of Natural Resources Canada. All rights reserved.

0 21 kilometers North

0 2 miles1 2/ 1

A

A

342 ■ L A B O R AT O R Y 13

FIGURE 13.13: Whitewater, Wisconsin

Contour interval = 20 ft.

0

1 2 3 kilometers

North

0

1 2/ 1 2 miles

1:62,500 Quadrangle location

Wisconsin

(C o

u rt

e sy

o f

U .S

. G e

o lo

g ic

al S

u rv

e y)

Glaciers and the Dynamic Cryosphere ■ 343

FIGURE 13.14: Glacier National Park (1998)

Contour interval = 80 ft.

North American Datum of 1927 (NAD27) grid.

0

1 2 3 kilometers

North

0

1 2/ 1 4 miles

1:100,000

Montana

Quadrangle location

54 20

00 0m

. N .

54 30

00 0m

. N .

54 10

00 0m

. N .

49° 00’

4 5 61 .5

321

Glacier Data

Name

Agassiz

Vulture

1850 Area (km2)

4.06

0.77

1966 Area (km2)

1.59

0.65

1993 Area (km2)

1.02

0.21

2005 Area (km2)

1.04

0.32

(C o

u rt

e sy

o f

U .S

. G e

o lo

g ic

al S

u rv

e y)

344 ■ L A B O R AT O R Y 13

1997

1994

Visito Cente

FIGURE 13.15

Contour interval 10 meters North

USGS 1976 PLAN (1994, 1997 data added here) NISQUALLY GLACIER

1:10,000 SCALE TOPOGRAPHIC MAP 0 1 kilometer

0 500 1000 2000 3000 feet

N I S Q U A L LY

G L A C I E R

Nisqually River

Bridge

(C o

u rt

e sy

o f

U .S

. G e

o lo

g ic

al S

u rv

e y)

Glaciers and the Dynamic Cryosphere ■ 345

September 1979

September 2012

Arctic Sea Ice

0 500 1000 1500

0 500 1000 1500 miles

2000 2500 km

R us

si a

Alaska

Canada Ca

na da

Greenland Ice Sheet

Arctic Sea Ice

R us

si a

Alaska

Canada Ca

na da

Greenland Ice Sheet

FIGURE 13.16 Extent of Arctic Sea Ice: 1979 and 2012. Sea ice covers essentially all of the Arctic Ocean in winter months, but it melts back to a minimum thickness and extent by the end of summer (September). These NASA satellite images reveal the minimum extent of Arctic sea ice at times 33 years apart. Dark blue areas are ocean; gray areas are mountain glaciers and the Greenland Ice Sheet. White and light blue areas are the Arctic sea ice.

346 ■ L A B O R AT O R Y 13

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optional Pearson eText and more.

347

A C T I V I T Y 13.1 Cryosphere Inquiry

Name: ______________________________________ Course/Section: ______________________ Date: ___________

A. The cryosphere is all of Earth’s snow and ice.

1. In FIGURE 13.1 , what is the sequence of cryosphere regions that you would encounter on the ground if you traveled from Mexico (a beige- to yellow-colored region with no snow or ice) to the North Pole?

2. Notice in FIGURE 13.1 that mountain glaciers and ice caps occur in parts of Greenland, Canada, Russia, Alaska, and the western conterminous United States. Some mountain glaciers also exist very close to the equator (not shown in FIGURE  13.1 ). How do you think it is possible for glaciers to exist at the equator?

3. If the temperature of Earth’s atmosphere were to rise, then how do you think it would affect the cryosphere, hydrosphere, and biosphere?

4. If the temperature of Earth’s atmosphere were to cool, then how do you think it would affect the cryosphere, hydrosphere, and biosphere?

B. Snow and glaciers are two of the best known parts of the cryosphere. Notice the snow and glaciers in the satellite image on the next page. It is a perspective view, looking north, of part of the Himalayan Mountains and was made by draping an ASTER natural color satellite image over a digital elevation model (by the NASA/GSFC/METI/ERSDAC/JAROS and U.S./Japan ASTER Science Team). You can view the same region in Google Earth TM by searching for coordinates 28 09 38 N, 90 03 05 E.

The glaciers in the satellite image formed by compaction and recrystallization of snow at higher elevations. Then they flowed downhill, where they eventually melt. A glacier’s mass balance is the difference between the mass of its ice that is accumulating and the mass of ice that is melting. If a glacier has more ice accumulating than melting, then it has a positive mass balance and will advance downhill. If a glacier melts faster than it accumulates ice, then it has a negative mass balance and will retreat (melt back).

1. The satellite image was acquired in summer of 2009, after most of the seasonal snow had melted. Using a pen, draw a line along the snowline —the line between areas with snow (higher elevations) and areas with no snow.

2. Place arrows on the glaciers to show their direction of flow, like a river of ice. 3. Label the “area of snow and ice accumulation” and two “areas of ablation” (glacial melting). 4. Label the area where the glaciers have “positive mass balance” and the areas where the glaciers have a “negative

mass balance.” 5. Is the mass balance of the snowline that you drew in part B1 positive, negative, or neither? Why?

348

C. Refer to FIGURE 13.2 , an ASTER satellite image of a 20-by-20 km area of southern Alaska. It is an infrared image, so vegetation appears red, glacial ice is blue, and snow is white.

1. Where is the zone of ablation in this image, and how can you tell?

2. Name two resources (used by humans) that were created by the glaciers in FIGURE 13.2 ?

3 miles0 1 2

4 km0 1 2 3

D. REFLECT & DISCUSS In what ways have the glaciers affected the landscape in the above image, and what does it suggest about how extensive these glaciers must have been in the past?

349

A C T I V I T Y 13.2 Mountain Glaciers and Glacial Landforms

Name: ______________________________________ Course/Section: ______________________ Date: ___________

A. FIGURE 13.10 is a topographic map of modern mountain glaciation near Anchorage, Alaska. FIGURE 13.11 is a topographic map of the southeast part of the Yosemite Falls, California quadrangle (Yosemite National Park), which was shaped by Pleistocene glaciers (that have since melted away) and modern streams.

1. On the left-hand side of the graph below, construct and label a topographic profile for line S–T across a valley on FIGURE  13.11 that is being cut by a modern river. Refer to FIGURE 9.16 (Topographic Profile Construction), if needed.

2. On the left-hand side of the graph below, also construct and label a topographic profile for line G–L across a valley on FIGURE 13.11 that was scoured and shaped by a Pleistocene valley glacier.

3. Which of the above cross sections (river or glacial) is “V” shaped: ____________________

Describe the erosional process that you think causes this shape.

4. Which of the above cross sections (river or glacial) is “U” shaped: ____________________

Describe the erosional process that you think causes this shape.

S/G T/L A BYosemite Falls Quad. (Figure 13.11)

Harvard Glacier Valley (Figure 13.10)

FEET ABOVE SEA LEVEL

9500

9000

8500

8000

7500

7000

6500

6000

5500

5000

4500

4000

3500

3000

2500

2000

1500

1000

500

0

350

5. On the right-hand side of the graph on page 349, complete the topographic profile for line A–B across the Harvard Glacier ( FIGURE 13.10 ).

a. Label the part of the profile that is the top surface of the glacier.

b. Using a dashed line, draw where you think the rock bottom of the valley is located under the Harvard Glacier. (Your drawing may extend slightly below the figure.)

c. Based on the profile that you just constructed, what is the maximum thickness of Harvard Glacier along line A–B?

B. Refer back to FIGURE 13.10 , a portion of the Anchorage (B-2), Alaska, quadrangle, for the following questions. In the southwestern corner, note the Harvard Arm of Prince William Sound. The famous Exxon Valdez oil spill occurred just south of this area (it did not affect Harvard Arm).

1. Lateral and medial moraines in/on the ablation zone of Harvard Glacier are indicated by the stippled (finely dotted) pattern on parts of the glacier. If a hiker found gold in rock fragments on the glacier at location C, then would you look for gold near location X, Y, or Z? Explain your reasoning.

2. Notice the crevasses (blue line segments) within a mile of Harvard Glacier’s terminus. What specific kind of crevasses are they, and why do you think they formed only on this part of the glacier?

C. Refer back to the Yosemite Falls, California quadrangle ( FIGURE 13.11 ) and locate the small steep-sided valley upstream from Snow Creek Falls (about 1.5 km northeast of line G–L ). Such valleys are common on the sides of valleys carved by valley glaciers. What is the name of this kind of valley ( FIGURE 13.4 ), and how did it form?

D. REFLECT & DISCUSS Compare the topographic map and satellite image of Harvard Glacier. Does Harvard Glacier have a positive mass balance or a negative mass balance? Explain your reasoning.

351

A C T I V I T Y 13.3 Continental Glaciation of North America

Name: ______________________________________ Course/ection: ______________________ Date: ___________

A. Refer to FIGURE 13.12 , part of the Peterborough, Ontario, quadrangle, for the following questions. This area lies north of Lake Ontario.

1. Study the size and shape of the short, oblong rounded hills. Fieldwork has revealed that they are made of till. What type of feature are they and how did they form?

2. Find the long narrow hill labeled A . It is marked by a symbol made of a long line of tiny pairs of brown dots. What would you call this linear feature, and how do you think it formed?

3. Towards what direction did the glacial ice flow here, and how can you tell?

B. The most recent glaciation of Earth is called the Wisconsinan glaciation. It reached its maximum development about 18,000 years ago, when a “ Laurentide Ice Sheet ” covered central and eastern Canada, the Great Lakes Region, and the northeastern United States. It ended by about 11,700 years ago, at the start of the Holocene Epoch. Refer to FIGURE 13.13 , a portion of the Whitewater, Wisconsin, quadrangle.

1. List the features of glaciated regions from FIGURES 13.8 and 13.9 that are present in this region.

2. Describe in what direction the ice flowed over this region. Cite evidence for your inference.

3. What kinds of lakes are present in this region, and how did they form? (Refer to FIGURE 13.7 .)

4. In the southeastern corner of the map, the northwest-trending forested area is probably what kind of feature?

5. Note the swampy and marshy area running from the west-central edge of the map to the northeastern corner. Describe the probable origin of this feature (more than one answer is possible).

C. REFLECT & DISCUSS How are the glaciated areas of FIGURES 13.12 and 13.13 different from areas affected by mountain glaciation and how are they they same?

352

A C T I V I T Y 13.4 Glacier National Park Investigation

Name: ______________________________________ Course/Section: ______________________ Date: ___________

Refer to the map of Glacier National Park in FIGURE 13.14 .

A. List the features of glaciation from FIGURES 13.3 , 13.4 , 13.8 , or 13.9 that are present in FIGURE 13.14 .

B. Locate Quartz Lake and Middle Quartz Lake in the southwest part of the map. Notice the Patrol Cabin located between these lakes. Describe the chain of geologic/glacial events (steps) that led to formation of Quartz Lake, the valley of Quartz Lake, the small piece of land on which the Patrol Cabin is located, and the cirque in which Rainbow Glacier is located today.

C. Based on your answers above, what kind of glaciation (mountain versus continental) has shaped this landscape?

D. Locate the Continental Divide and think of ways that it may be related to weather and climate in the region. Recall that weather systems generally move across the United States from west to east. 1. Describe how modern glaciers of this region are distributed in relation to the Continental Divide.

2. Based on the distribution you observed, describe the weather/climate conditions that may exist on opposite sides of the Continental Divide in this region.

E. Describe how the size (area in km 2 ) of Agassiz Glacier changed from 1850 to 2005.

F. Describe how the size (area in km 2 ) of Vulture Glacier changed from 1850 to 2005.

G. REFLECT &DISCUSS What do you expect the area (km 2 ) of Agassiz and Vulture Glaciers to be in 2020? Explain.

353

A C T I V I T Y 13.5 Nisqually Glacier Response to Climate Change

Name: ______________________________________ Course/Section: ______________________ Date: ___________

A. Refer to FIGURE 13.15 and fill in the Nisqually Glacier Data Chart below. To do this, use a ruler and the map’s bar scale to measure the distance in kilometers from Nisqually River Bridge to the position of the glacier’s terminus (red dot) for each year of the chart. Be sure to record your distance measurements to two decimal points (hundredths of km).

NISQUALLY GLACIER DATA CHART

Year

Distance in kilometers from Nisqually River Bridge to terminus of Nisqually Glacier

•2010

•1997

•1994

•1976

•1974

•1971

•1968

•1966

•1963

•1961

•1956

•1951

•1946

•1941

•1936

•1931

•1926

•1921

•1918

•1910

•1905

•1896

•1892

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

.8

.6

.4

.2

0

1900 1920 1940 1960 1980 2000 Year

D is ta n c e i n K il o m e te rs f ro m N is q u a ll y R iv e r B ri d g e t o T e rm in u s o f N is q u a ll y G la c ie r

9.7 °C

9.1 °C

8.5 °C

7.9 °C

7.3 °C

49.3 °F

48.3 °F

47.3 °F

46.3 °F

45.3 °F

1900 1920 1940 1960 1980 20001880

Global mean Temperature (1901–2001)

Variation in Annually Averaged Global Land Surface Temperature Since 1880

(Courtesy of NOAA National Climatic Data Center)

354

B. Plot your data from part A (Nisqually Glacier Data Chart) in the graph to the right of the data chart. After plotting each point of data, connect the dots with a smooth, light pencil line. Notice that the glacier terminus retreated up the valley at some times, but advanced back down the valley at other times. Summarize these changes in a chart or paragraph, relative to specific years of the data.

C. Notice the blue and red graph of climatic data at the bottom of your graph (part B) provided by the NOAA National Climatic Data Center (NCDC). NCDC’s global mean temperatures are mean temperatures for Earth calculated by processing data from thousands of observation sites throughout the world (from 1880 to 2009). The temperature data were corrected for factors such as increase in temperature around urban centers and decrease in temperature with elevation. Although NCDC collects and processes data on land and sea, this graph only shows the variation in annually averaged global land surface temperature since 1880.

1. Describe the long-term trend in this graph—how averaged global land surface temperature changed from 1880 to 2005.

2. Lightly in pencil, trace any shorter-term pattern of cyclic climate change that you can identify in the graph. Describe this cyclic shorter-term trend.

D. Describe how the changes in position of the terminus of Nisqually Glacier compare to variations in annually averaged global land surface temperature. Be as specific as you can.

E. REFLECT & DISCUSS Based on all of your work above, do you think Nisqually Glacier can be used as a global thermometer for measuring climate change? Explain.

355

A C T I V I T Y 13.6 The Changing Extent of Sea Ice

Name: ______________________________________ Course/Section: ______________________ Date: ___________

A. Refer to the satellite images of Arctic sea ice in FIGURE 13.16 on page 345 . These images were both taken in the month of September, when sea ice is at its minimum thickness and extent. “Extent” refers to how far the ice extends in all directions: its total area without regard for tiny ice free areas within the overall body of sea ice. It is easy to see that there was less sea ice in September of 2012 than in September of 1979, but how much less? To find out, you need to measure the extent of the sea ice in 1979 and 2012 by following these directions.

Step 1. Start by using a piece of thin string or thread about 30 cm (12 in.) long to measure the circumference of the sea ice. Carefully lay the string along the edge of the body of sea ice so that the string totally surrounds it as perfectly as possible. Then lay that length (segment) of string along the bar scale to determine the circumference of the sea ice in kilometers.

Step 2. Assume that the circumference of sea ice that you just measured is like the circumference of a circle. Circumfer- ence of a circle is equal to 2 times ∏ (3.14) times radius, so radius (r) equals circumference divided by 2 times ∏. So, determine the radius of the ice sheet by dividing the circumference (Step 1) by 6.28.

Step 3. Area of a circle is equal to ∏ (3.14) times the square of its radius. So determine the area of the ice sheet by multiplying the radius from step 2 by itself (to get radius squared), and then multiply that number by 3.14. Your answer will be in square kilometers (km 2 ).

1. Using the three steps above, what was the extent of Arctic sea ice in September of 1979, in millions of km 2 ? Show your work below.

2. Using the three steps above, what was the extent of Arctic sea ice in September of 2012, in millions of km 2 ? Show your work below.

3. Based on your limited set consisting of just two years of data, what has been the rate of Arctic sea ice decline from 1979 to 2012 (in km per year)? Show your work.

B. Scientists at the National Snow and Ice Data Center (NSIDC) have measured the annual September extent of Arctic and Antarctic sea ice in more exact ways. Arctic sea ice fills the Arctic Ocean, which is confined by land masses like Asia (Russia), North America, and Greenland ( FIGURE 13.1 ). A table of the NSIDC data is provided on the next page.

1. Graph all of the data for extent of Arctic sea ice from 1979 to 2013, then use a ruler to draw a “best fit” line through the points so that the number of, and distance to, points above and below the line is similar. Label the line as “Arctic.”

2. What was the average annual extent of Arctic sea ice from 2000 to 2007, in millions of km 2 ? Show your work.

3. What was the average annual extent of Arctic sea ice from 2008 to 2013, in millions of km 2 ? Show your work.

4. Based on your graph and calculations above, would you say that the annual amount of Arctic sea ice is decreasing, increasing, or staying about the same? Explain.

356

5. What do you predict the extent of Arctic sea ice will be in 2015?

6. Graph all of the data for extent of Antarctic sea ice from 1979 to 2013, then use a ruler to draw a “best fit” line through the points. Label the line as “Antarctic.”

7. What was the average annual extent of Antarctic sea ice from 2000 to 2007, in millions of km 2 ? Show your work.

8. What was the average annual extent of Antarctic sea ice from 2008 to 2013, in millions of km 2 ? Show your work.

9. Based on your graph and calculations above, would you say that the annual amount of Antarctic sea ice is decreasing, increasing, or staying about the same? Explain.

C. REFLECT & DISCUSS The changes in Arctic sea ice extent over time are not the same as the Antarctic changes. Why do you think the two bodies of sea ice are so different, and what benefits or hazards could result if the Arctic sea ice continues to decline?

20

15

10

5

0

2000 2001

2002 2004 2006 2008 2010 2012 2014 2003 2005 2007 2009 2011 2013

Year

E x te n t o f S e a I c e ( m il li o n s o f s q u a re k il o m e te rs )

Summer Extent of Sea Ice

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

2011

2012

2013

Arctic Extent

in millions of square kilometers

Antarctic Extent

in millions of square kilometers

Year

3.4

3.5

6.0

6.2

6.1

5.6

6.0

4.3

4.7

5.4

4.9

4.6

3.6

5.4

19.1

18.4

18.2

18.6

19.1

19.2

19.3

19.2

18.5

19.1

19.2

18.9

19.4

19.8

(Courtesy of National Snow and Ice

Data Center (NSIDC))

Table of Contents.html

 
G-205-002: GEOLOGY LAB (Fall 2018) - Lab 9:  Glacial Processes

1. Glacial Processes

2. Glacier Lab Handout

3. Chapter13