Nisqually glacier data chart answers

Geology Lab Assignment

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

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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.