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Chapter 11 (exam three)
glacier |
a thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow, capable of flowing under its own weight |
Valley (alpine) glaciers |
Exist in mountainous areas
Very numerous, found all over the world
Snow accumulates at high altitudes
Flows as a stream of ice down the valley
|
Continental Ice sheets |
Exist on a larger scale than valley glaciers
Two major ice sheets on Earth are over Greenland and Antarctica (though more ice sheets have existed in the past)
Ice flows out in all directions from one or more snow accumulation centers
|
ice caps |
glaciers that cover uplands and plateaus |
exit glaciers |
valley glaciers or ice caps that flow into the ocean
|
Piedmont Glaciers |
form as one or more alpine glaciers exit the mountain valleys and widen out into the broad lowlands
|
glacial ice formation |
starts as snow
air infiltrates snow...causes granular snow
more snow, more dense forms firn
thickness exceeds 50 meters becomes glacial ice |
Zone of Accumulation |
the area where snow accumulates and turns to ice |
firnline |
above this line the snow will survive until the next winter
may change from year to year depending on amount of snow |
ablation |
the amount of ice and snow lost from a glacier
can occur by melting or calving |
glacial budget |
The balance between the amount of ice generated in the zone of accumulation, and the amount of ice lost by ablation |
glacial advance |
If more ice accumulates than is lost |
glacial retreat |
If more ice ablates than is accumulated |
plucking |
lifting of rocks off of the valley floor and transporting them along with the ice |
abrasion |
rocks that are within the ice will scrape along the ground, smoothing the surface below
|
loess |
pulverized “glacial flour” that may be picked up and transported by the wind and deposited in massive bluffs
|
striations |
grooves etched into the rocks formed when other rocks scraped past
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cirque |
bowl shaped features in the higher altitudes; this is where snow accumulates
bowl shaped depressions |
crevasses |
fractures in the ice that form as it flows down the valley |
moraine |
accumulation of rocks and sediment (collectively called till) that have been eroded and entrained in the glacier
Lateral moraine – forms along the sides of the glacier
Medial moraine – forms as lateral moraines from two glaciers meet to form one larger glacier
Terminal moraine – forms at the toe of the glacier where it dumps out all the rocks and sediment it was carrying
|
U-shaped valley |
glacially carved valleys
The ice erodes and flattens the bottom of the valley and creates steep, concave walls
|
hanging valleys |
U-shaped glacial valleys that get cut off by a larger valley
oftentimes there will be waterfalls
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tarn |
cirque lake |
paternoster lakes |
series of tarns connected by mountain streams |
horn |
glacially carved mountain peak
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Arête |
glacially carved mountain ridge
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Fjords |
U-shaped valleys that have been filled in with sea water
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braided streams |
multi-channeled outwash of glacial meltwater
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drumlins |
smooth, elongated parallel hills (tell direction of ice flow long slope
|
eskers |
ridges deposited by streams flowing on top of or beneath the glacier |
kettles |
depressions formed when icebergs become partially buried in the glacial sediment
kettles filled with water form kettle lakes (about 30 ft deep) |
snowball earth |
Stuartian-Varangian ice age
earth entirely covered in ice |
Stages of the Pleistocene Ice Age |
Four recognizable stages of ice advance and retreat (pulses)
Nebraskan (1)
Kansan (2)
Illinoian (3)
Wisconsinan (4)
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causes of ice ages |
plate techtonics (oceanic circulation and climate changes)
variation in earths orbit (Eccentricity, Obliquity, Precession)
variation in earths atmosphere
changes in albedo
changes in ocean currents
|
Eccentricity |
variation in the shape of the earth’s orbit around the sun
Changes on the order of 400,000 years
|
Obliquity |
changes in the tilt of the earth’s axis with respect to the orbital plane
Changes on the order of 41,000 years |
Precession |
wobbling of the earth’s axis
Changes on the order of 26,000 years |
volcanic ash |
tells us age of ice and about volcanism
|
organic material |
paleoclimate and paleobiologic information |
dust and pollen |
paleoclimate indicators
|
air bubbles |
paleoatmosphere |