Chapter 10 - ESC1000 Flashcards
What is a glacier?
A thick mass of ice originating on land from the compaction and recrystallization of snow that shows evidence of past or present flow.
How glaciers act as erosional agents?
They accumulate, transport, and deposit sediment.
What are the 2 cycles glaciers affect?
The hydrological cycle and the rock cycle.
What are alpine glaciers?
A glacier confined to a mountain valley, which in most instances had previously been a stream valley. Also called valley glacier.
What are ice sheets?
A very large, thick mass of glacial ice flowing outward in all directions from one or more accumulation centers.
When was the Last Glacial Maximum?
About 18,000 years ago.
What is sea ice?
Frozen seawater that is associated with polar regions. The area covered by sea ice expands in winter and shrinks in summer.
How big is the Greenland ice sheet?
About 1.7 million square kilometers and averages 1500 meters thick.
How big is the Antarctic ice sheet?
About 13.9 million square kilometers and attains a maximum thickness of 4300 meters.
What are ice shelves?
A large, relatively flat mass of floating ice that forms where glacial ice flows into bays and extends seaward from the coast but remains attached to the land along one or more sides.
What are ice caps?
A mass of glacial ice covering high upland or plateau and spreading out radially.
What are piedmont glaciers?
A glacier that forms when one or more valley glaciers emerge from the confining walls of mountain valleys and spread out to create a broadsheet in the lowlands at the base of the mountains.
What is an outlet glacier?
A tongue of ice that normally flows rapidly outward from an ice cap or ice sheet, usually from mountainous terrain to the sea.
What are the 2 ways glaciers move?
By plastic flow and when the entire mass slides.
What is plastic flow?
It’s a type of movement within the ice that happens due to stress that exceeds the strength of the bonds between the layers of ice that compose the glacier.
What is the zone of fracture?
The upper portion of the glacier, consisting of brittle ice. Uppermost 50 meters (165 ft).
What is a crevasse?
A deep crack in the brittle surface of a glacier.
Why is the flow of ice greatest at the center of the glacier?
Because the drag created by the walls and floor of the valley slow the base and sides of the glacier.
How fast do glaciers move?
Some glaciers can move up to 800 meters per year while others move slowly at 2 meters per year.
What is the zone of accumulation?
The part of the glacier characterized by snow accumulation and ice formation. Its outer limit is the snowline.
What is the snowline?
The lower limit of perennial snow. For glacier, equivalent to the equilibrium line.
What is the equilibrium line?
For a glacier, the elevation at which the accumulation and wasting of glacial ice is equal.
What is the zone of wastage?
The part of the glacier beyond the zone of accumulation where all the snow from previous winter melts, as does some of the glacial ice.
What is calving?
Wastage of a glacier that occurs when large pieces of ice break off into the water.
What are icebergs?
A mass of floating ice produced by a calving glacier. Usually 20 percent or less of the iceberg protrudes above the water line.
What is the glacial budget?
The balance, or lack of balance, between the ice formation at the upper end of a glacier and ice loss in the zone of wastage.
In what 2 ways do glaciers erode?
By plucking and abrasion.
What is plucking?
The process by which pieces of bedrock are lifted out of place by a glacier?
How does plucking works?
Meltwater penetrates the cracks and joints along the rock floor of the glacier and freezes. When water expands as it freezes, it exerts tremendous leverage that loosens the rock.
What is abrasion?
The grinding and scraping of a rock surface by the friction and impact of rock particles carried by water, wind, or ice.
What is rock flour?
Ground-up rock produced by the grinding effect of a glacier.
What are glacial striations?
Scratches and grooves on bedrock caused by glacial abrasion.
How can scientists use glacial striations?
They provide clues to the direction of glacial movement and by mapping the striations over large areas, glacial flow patterns can be reconstructed.
What 4 factors control the rate of glacial erosion?
- Speed of glacier movement.
- Ice thickness.
- Shape, abundance, and hardness of the rock fragments in the ice at the base of the glacier.
- Erodibility of the surface beneath the glacier.
What is a U-shaped glacial trough?
A mountain valley that has been widened, deepened, and straightened by a glacier.
What is a hanging valley?
A tributary valley that enters a glacial trough at a considerable height above its floor.
What is a cirque?
An amphitheater-shaped basin at a head of a glaciated valley produced by frost wedging and plucking.
What is a tarn?
A small lake that occupies the cirque basin after the glacier has melted away.
What is an arete?
A narrow knife-like ridge that separating two adjacent glacial valleys.
What is a horn?
A pyramid-like peak formed by glacial action in three or more cirques surrounding a mountain summit.
What is a fiord?
A steep-sided inlet of the sea formed when a glacial trough was partially submerged.
What is glacier drift?
An all-embracing term for sediments of glacier origin, no matter how, where, or in what shape they were deposited.
What are the two types of glacier drift?
Glacial till and and stratified drift.
What is glacier till?
Unsorted sediment deposited directly by a glacier.
What is a glacial erratic?
An ice transported boulder that was not derived from the bedrock near its present site.
What is stratified drift?
Sediments deposited by glacier meltwater.
What is a moraine?
It is a layer or ridge of till.
What are the 4 types of moraines?
Lateral moraines, medial moraines, end moraines, and ground moraines.
What is a lateral moraine?
A ridge of till along the sides of an alpine glacier composed primarily of debris that fell to the glacier from the valley walls.
What is a medial moraine?
A ridge of till formed when lateral moraines from two coalescing alpine glaciers joint.
What is an end moraine?
A ridge of till marking a former position of the front of a glacier.
What is a ground moraine?
An undulating layer of till deposited as the ice front retreats.
What is the difference between a terminal end moraine and a recessional end moraine?
A terminal end moraine marks the farthest advance of the glacier while a recessional end moraine forms as the ice retreat stabilizes.
What is an outwash plain?
A relatively flat, gently sloping plain consisting of materials deposited by meltwater streams in front of the margin of an ice sheet.
What is a valley train?
A relatively narrow body of stratified drift deposited on the valley floor by meltwater streams that issue from a valley glacier.
What is a kettle?
A depression created when a block of ice that became lodged in glacial deposits subsequently melted.
What is a drumlin?
A streamlined asymmetrical hill composed of glacial till. The steep side of the hill faces the direction from which the ice advanced. Drumlins are not found single but rather in occur un clusters called drumlin fields.
What are eskers?
A sinuous ridge composed largely of sand and gravel deposited by a stream flowing in a tunnel beneath a glacier near its terminus.
What are kames?
A steep-sided hill composed of sand and gravel that originates when sediment is collected in openings in stagnant glacial ice.
What is a proglacial lake?
A lake created when a glacier acts like a dam, blocking the flow of a river or trapping glacial meltwater. The term refers to the position of such lakes just beyond the outer limits of a glacier.
What is a pluvial lake?
A lake formed during a period of increased rainfall. During the Pleistocene epoch, this occurred in some non-glaciated regions during periods of ice advance elsewhere.
List four effects of Ice Age glaciers, aside from the major erosional and depositional features.
Sea level changes, crustal subsidence and rebound, animals and plant extinction or migration, and changing the flow of the rivers.
When did the Ice Age begin?
Between 2 - 3 million years ago during the Quaternary period.
What is the Quaternary period?
The most recent period on the geologic time scale. It began 2.6 million years ago and extends to the present.
What hypotheses explain the possible causes of glacial periods?
Plate tectonics, variations in Earth’s orbit, and other factors such as chemical composition of the atmosphere, reflectivity of Earth’s surface, and ocean circulation.
Describe the plate tectonic theory as a cause for glacial periods.
Glaciers can only form on land, so the landmasses must be somewhere in higher latitudes before an ice age can commence. As well, shifting landmasses cause climatic changes as they affect the oceanic circulation of heat and moisture.
Describe the variations in Earth’s orbit as a cause for glacial periods.
Plate tectonic changes occur very slow, so the climatic implications occur gradually and doesn’t explain the cycles of glaciation in terms of thousands of years. The Earth’s orbit is affected by eccentricity (variations in the shape of the orbit), obliquity (the angle of Earth’s axis), and precession (the wobbling of Earth’s axis). These factors affect the variations of incoming solar radiation.
What is the percentage of dry regions on land surface?
About 30% of the surface which accounts for about 42 million square kilometers.
How do you define dry climate?
A climate in which yearly precipitation is not as great as the potential loss of water by evaporation.
What are the 2 climatic types recognized within the dry regions?
The desert (arid) and the steppe (semiarid).
What is a desert?
The driest of the dry climates, also called arid.
What is a steppe?
A marginal and more humid variant of the desert that separates it from bordering humid climates, also called semiarid.
What are subtropical highs?
They are pressure systems characterized by subsiding air currents. When air sinks, it is compressed and warmed. Such conditions are the opposite needed to produce clouds and precipitation.
What is an ephemeral stream?
A stream that is usually dry because it carries water only in response to specific episodes of rainfall. Most dessert streams are of this type.
Why middle latitude deserts and steppes exist?
They are sheltered deep in the interior of large masses and far removed from the ocean which is the ultimate source of moisture for cloud formation and precipitation. In addition, the presence of high mountains across the path of prevailing winds further separates this areas from water-bearing maritime air masses.
What is the most important erosional agent in the desert?
Running water.
What is an interior drainage basin?
A discontinuous pattern of intermittent streams that do not flow to the ocean.
What is an alluvial fan?
A fan-shaped deposit of sediment formed when a stream’s slope is abruptly reduced.
What is a bajada?
An apron of sediment along a mountain front created by the coalescence of alluvial fans.
What is a playa lake?
A temporary lake in a playa (flat area on the floor of an undrained desert basin).
What are inselbergs?
Mountain areas that are reduced to a few large bedrock knobs.
What is deflation?
The lifting and removal of loose material by wind.
What is a blowout?
A depression excavated by wind in easily eroded deposits.
What is desert pavement?
A layer of coarse pebbles and gravel created when wind removes the finer material.
What are the 2 types of wind deposits?
Loess and sand dunes.
What is a loess?
Deposits of windblown silt, lacking visible layers, generally buff-colored, and capable of maintaining a nearly vertical cliff.
What are sand dunes?
A hill or ridge of wind-deposited sand.
What is a slip face?
The steep, leeward slope of a sand dune; it maintains an angle of about 34 degrees.
What are cross beds?
A structure in which relatively thin layers are inclined at an angle to the main bedding. It is formed by currents of wind or water.
What are the 6 types of sand dunes?
- Barchan
- Transverse
- Barchanoid
- Longitudinal
- Parabolic
- Star
What is a barchan dune?
A solitary sand dune shaped like a crescent with its tips pointing downward.
What is a transverse dune?
A series of long ridges oriented at right angles to the prevailing wind; these dunes form where vegetation is sparse and sand is very plentiful.
What is barchanoid dune?
A type of dune in which the dunes form scalloped rows of sand oriented at right angles to the wind. This form is intermediate between isolated barchans and extensive waves of transverse dunes.
What is a longitudinal dune?
Long ridges of sand oriented parallel to the prevailing wind; these dunes form where sand supplies are limited.
What are parabolic dunes?
Dunes that resemble barchans, except that their tips point into the wind; they often form along coasts that have strong onshore winds, abundant sand, and vegetation that partly covers the sand.
What is a star dune?
An isolated hill of sand that exhibits a complex form and develops where wind directions are variable.
