Geology

 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)

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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

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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.

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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?

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