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Chapter 10 - Glaciers and Glaciation |
| Glaciers occur in regions with average annual temperatures are below freezing—such as in high mountain ranges and in polar regions. In the geologic past, great glaciers covered large portions of North America and Europe where forested landscapes and cities exist today. In contrast, Antarctica and Greenland are still experiencing "ice age" conditions today. However, Around the world glaciers, are melting and retreating, including the great ones in Antarctica and Greenland, and sea level is rising. This chapter reviews landscape features associated with glaciers and past glaciation periods. |
1. Define glacier and glaciation.
2. Explain what an ice age is, and list some of the possible causes of glaciation.
3. Explain how a glacier moves.
4. Describe the landforms created by glacial deposits.
5. Identify some of the indirect efforts of glaciers.
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| Keywords and Essential Concepts |
1. Define glacier and glaciation.
glacier—a slowly moving mass or river of ice formed by the accumulation and compaction of snow over many years, forming on mountains or land masses near the Earth's poles.
glaciation—a period when the ice or glaciers cover or alter the land's surface, resulting in erosion by flowing ice.
ice sheet—an ice sheet is the layer of ice covering extensive regions of the world, notably Antarctica and Greenland. The ice sheets form from the accumulation of thousands or millions of years of snowfall. With compaction, the snow turns to glacial ice.
ice cap—an extensive dome-shaped or plate-like perennial cover of ice and snow that spreads out from a center and covers a large area, especially of land. Examples include upland glacial regions in Iceland and the Canadian and Alaska coastal mountain ice caps.
ice shelf—a thick floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface.
valley glacier—a glacier confined by the walls of a valley in a mountainous region.
piedmont glacier—a thick, continuous ice sheet formed along the base of a mountain range formed by the spreading out and coalescing of valley glaciers supplying ices from higher mountain elevations.
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| Map of Antarctica showing ice sheets, ice caps, and ice shelves |
Greenland with sea ice. |
Ice caps and valley glaciers in British Columbia |
North America at the peak of the last ice age. |
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2. Explain what an ice age is, and list some of the possible causes of glaciation.
ice age—a period in Earth's history when the global temperatures cooled enough for glaciers (both alpine and continental glaciers) to form. Note that parts of the world, e.g. Greenland and Antarctica, are still experiencing ice-age-like conditions.
Pliocene—an epoch of the late Tertiary Period following the Miocene Epoch and proceeding the Quaternary Period (or Pleistocene Epoch) and representing the time span from about 5.3 to 1.8 million years ago. The cycles of ice-age glaciations and intervening warming periods began in Pliocene time.
Pleistocene—the Quaternary Period is subdivided into the Pleistocene Epoch and the Holocene Epoch. The Pleistocene Epoch represents the time span of about 1.8 million to about 11,000 years ago. Many episodes of continental glaciation and intervening ice-free periods occurred within the Pleistocene Epoch. The Holocene Epoch began about 11,000 years ago, about the time that human population growth and distribution expanded worldwide.
Wisconsin Stage—the last, most recent glaciation period within the current ice age occurring in the geologic time interval about 110,000 to 10,000 years ago, at the end of the Pleistocene Epoch. Note that Antarctica and Greenland are still enduring ice-age conditions, whereas continental glaciers on North America and northern Europe vanished at the end of the Wisconsin Stage. |
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| Maximum extent of the Wisconsin Glaciation |
Milankovitch cycles |
Glaciations of the late Pleistocene Epoch |
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3. Explain how a glacier moves.
zone of accumulation—the upper part of a glacier where snow accumulation and ice formation takes place faster that it melts, forming the glacier.
snowline—the location on a mountain glacier where the rate of accumulation is equivalent to the rate of melting.
zone of ablation—the downslope end of a mountain glacier where melting outpaces the accumulation of new ice and snow.
ablation—the removal of snow and ice by melting or evaporation, typically from a glacier or icefield.
surging—the sudden movement of a glacier downslope.
crevasse—a deep open crack, especially one in a glacier.
calving—blocks of ice falling off the face of a parent glacier, ice shelf, or iceberg. |
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| Profile of a glacier |
timberline—the line or altitude above which no trees grow because the annual temperature is too cold. Timberline is about 16,000 at the equator and near sea level north of the Arctic Circle.
tundra—a vast, flat, treeless Arctic region of Europe, Asia, and North America in which the subsoil is permanently frozen. |
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4. Describe the landforms created by glacial deposits.
horn—a pointy mountain peak having concave faces carved by glaciation.
arete—a narrow, jagged mountain ridge that divides two cirques or glaciated valleys.
col—a saddle in a glacially carved mountain ridge (a gap in an arete).
cirque—a bowl-shaped, steep sided hollow at the head of a valley or on a mountainside, formed by glacial erosion.
tarn—a small mountain lake, especially one formed by glaciers; typically found within the basin of a cirque. |
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| Features associated with alpine glaciation |
Features associated with continental glaciation |
An arete with horns and cols
North Cascades National Park, Washington |
Cirque with snow fields
Great Basin National Park, Nevada |
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Moving ice (glaciers) erode bedrock and carry away large quantities of sediment.
Gulkana Glacier, Alaska |
kettle—a shallow, sediment-filled body of water formed by retreating glaciers.
till—unsorted material deposited directly by glacial ice and consisting of rock fragments ranging from large boulders to sand, fine silt, and clay.
moraine—accumulations of rocks and sediment deposited by a glacier, typically as ridges at its edges or its terminal boundary of flow and zone of wastage.
loess—a tan, buff to gray windblown deposit of fine-grained, loamy, calcareous silt or clay; fine-grained deposits typically derived from glacial outwash plains or dust derived from arid regions.
drumlin—a low oval-shaped mound or small hill, typically one of a group, consisting of compacted glacial till shaped by flowing ice in a region that experienced glaciation.
erratic—a rock or boulder that differs from the surrounding bedrock and is believed to have been transported from a distant location by glacial action.
esker—a long, typically winding, ridge composed of gravel and other sediment deposited by meltwater from a retreating glacier or ice sheet.
striations—parallel grooves such as: the scratches left by a glacier on rocks
glacial grooves—trench-like striations carved in bedrock caused by rock-bearing moving ice at the bottom of a glacier.
roche moutonnee—an elongate mound of bedrock worn smooth and rounded by glacial abrasion, typically with a steep slope of cliff on the downhill side formed by the plucking away of blocks of bedrock by the moving glacial ice.
fjord—a long, narrow, deep inlet of the sea between high cliffs typically formed by submergence of a glaciated U-shaped valley.
pater noster lakes—a series of moraine-dammed lakes formed by the intermittent retreat of a valley glacier in a mountainous region. |
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Glacial Striations
New York City, New York |
Glacial moraine
Montauk Point
Long Island, New York |
Glacial till and outwash
Caumsett State Park
Long Island, New York |
Glacial erratic
Jenny Jump State Park, New Jersey |
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Roche moutonnee
Harriman State Park, New York |
Hudson River fjord
Bear Mountain, New York |
Hanging valley in
Yosemite National Park |
Pater noster lakes in
Torrey Canyon, Wind River Mountains, Wyoming |
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5. Identify some of the indirect effects of glaciers.
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| Continental shelves were exposed during the peak of the ice ages. |
The Bering Straight was exposed during the peak of the ice ages. |
Lakes filled the valleys of the Great Basin during the ice ages. |
The Great Lakes were carved by the Laurentide Glaciers. |
Channeled Scablands—a water-scoured network of ancient flood-carved channels that cover large areas in central Washington. The the channels are passages of old flow channels essentially barren of soil and regolith.
Ancient Lake Missoula—an ancient glacier-dammed lake that filled, broke out, and flooded portions of the Columbia Plateau several times between 15,000 and 13,000 years ago (near the end of the Wisconsin Stage). The "Spokane Floods" resulted in the formation of the Channeled Scablands. |
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| Channeled Scablands of central Washington |
Great Falls, central Washington |
Niagara Falls, St. Lawrence River, New York and Canada |
Satellite view of the Finger Lakes, northern New York |
See more about NYC regional geology
glacial rebound—ongoing regional isostatic uplift caused by the melting of continental glaciers (unloading as much as 5 miles of ice from the continental landmass).
Flandrian Transgression—the global rise of sea level of about 400 feet caused by the melting of continental glaciers since the peak of the last Ice Age (Wisconsin Stage) about 20,000 years ago. |
Changing landscapes of the New York City Region
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| Hudson River Fjord and the Flandrian Transgression |
Glaciation and retreat in New York City area |
Pleistocene glacial deposits in New York City region |
Glacial lakes at the end of the last ice age in New York City |
Changes in geography of the New York City Region during the Flandrian Transgression
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| New York City region near the end of the last glaciation |
Early Holocene landscape in New York City region |
Bathymetry and topography of the New York City region |
Elevated marine terraces on the California coastline.
California preserves much evidence of geologic, geographic, and climatic changes caused by ice ages. During the last ice age, alpine glaciers and ice caps covered upland regions in the Sierra Nevada Range and Cascades volcanoes. The formation of continental glaciers in North America and Europe caused sea level to fall almost 400 feet, causing the shoreline to migrate seaward as much as 10 to 70 miles in some locations. With increased regional precipitation and cooler weather conditions, great lakes filled lowland valleys regions in the Mojave region (ancient Lake Manix) and Death Valley (ancient Lake Manly).
Forests and shrublands probably covered many areas that are now deserts and glasslands. The region was also host to many large mammal species, including wooly mammoths, sabertooth cats, and dire wolves, that all were driven to extinction at the close of the last ice age along with the arrival and proliferation of our species in the region—Homo sapiens. |
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| Marine terraces at Davenport, California |
Formation of marine terraces |
Precipitation on shaded relief with streams, California |
California at the peak of the last ice age (Wisconsin) |
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Glossary of Glacier Terminology:
A glossary providing the vocabulary necessary to understand the modern glacier environment.
http://pubs.usgs.gov/of/2004/1216 |
Quiz Questions
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