Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
43 Cards in this Set
- Front
- Back
|
glaciers |
- thick masses of recrystallized ice - last all year long - flow via gravity |
|
|
glacial and ice sheet cover |
- presently = ~10% of Earth - ice age = ~ 30% |
|
|
how a glacier forms |
- snowfall accumulates - snow transformed into ice |
|
|
how is snow tranformed into ice |
... |
|
|
may form (2 speeds) |
quickly (tens of years), slowly (thousands of years) |
|
|
conditions necessary to form a glacier |
- Cold local climate (polar latitudes or high elevation) - More snow must fall than melts |
|
|
categories of glaciers |
mountain/alpine and continental |
|
|
continental glaciers |
- vast ice sheets covering large land areas - ice flows outward from thickest part of sheet - makes up largest proportion of ice cover |
|
|
two major ice sheets remain on Earth |
- Greenland - Antartica |
|
|
2 ways glaciers move |
basal sliding, plastic deformation |
|
|
basal sliding |
- significant quantities of meltwater forms at base of glacier - water decreases friction, ice slides along substrate |
|
|
plastic deformation |
- occurs below about 60 km deep - Grains of ice change shape slowly - New grains form while old grains disappear |
|
|
why do glaciers move |
- pull of gravity is strong enough to make ice flow - in continental glacier, ice spreads away from center of accumulation
|
|
|
movement by gravity |
- moves in direction of surface slope - can flow up a local incline |
|
|
movement by spreading |
... |
|
|
variation in rates of flow of glacial ice |
10 - 300 m per year |
|
|
rate of flow controlled by |
slope, basal water, location within glacier |
|
|
slope |
... |
|
|
basal water |
... |
|
|
location within glacier |
.. |
|
|
glacial budget |
zone of accumulation, zone of ablation, equilibrium line |
|
|
zone of accumulation |
- area of net snow addition - colder temp prevent melting - snow remains across the summer months |
|
|
... |
... |
|
|
tow |
leading edge of a glacier |
|
|
ice always |
flows downhill, even during tow retreat |
|
|
tow positon if accumulation = ablation |
glacial tow stays in the same place |
|
|
toe position if accumulation > ablation |
glacial tow advances |
|
|
toe position if accumulation < ablation |
glacial toe will retreat upslope |
|
|
3 ways glaciers are important forces of landscape change |
- erosion - transport - deposition |
|
|
glacial abrasion |
- sandpaper effect on substrate, which pulverizes it to fine rock flour - sand moving in ice polishes bedrock |
|
|
striations |
- gouged by large rocks dragged across bedrock - run parallel to direction of ice movement |
|
|
cirques |
- bowl shaped basins - Form at uppermost portion of glacial valley - After ice melts, cirque often becomes a tarn (lake) |
|
|
u shaped valley |
- carved out by glaciers - distinctive trough shape - broad |
|
|
glacial deposition |
- act like large scale conveyor belts - pick up, transport, and deposit sediment - sediment transport is always in one direction |
|
|
end moraine |
debris at tow of glacier |
|
|
moraines |
unsorted debris deposited by a glacier |
|
|
glacial till |
- sediment dropped by glacial ice - consists of all grain sizes - unmodified by water (unsorted or unstratified) |
|
|
where does glacial till accumulate |
- beneath glacial ice - at the toe of a glacier - along glacial flanks |
|
|
erratics |
- boulders dropped by glacial ice - different from underlying bedrock - often transported long distances |
|
|
consequences of continental glaciation |
- ice loading and glacial rebound - ice sheets depress lithosphere - after ice melts, the depressed lithosphere rebounds - the last ice-age glacial rebound continues slowly today |
|
|
glacial consequences |
- ice ages cause sea level to rise and fall - sea level falls when water is stored on land during ice age - sea level rises after deglaciation which returns water to oceans |
|
|
causes of glaciation |
milankovitch hypothesis - climate variation predicted by cyclic changes in orbital geometry - shape of earth's orbit varies (~100000 year cyclicity) - tilt of earths axis varies from 22.5 to 24.5 degrees (~41,000) - precession |
|
|
precession |
earth's axis wobbles like a top (23, 000 years) |
