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Chapter 12 - Glaciers and Glaciation
Midterm Number III
45
Geology
11/08/2009

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Term
Glacier
Definition

large, long-lasting mass of ice, formed on land, that moves under its own weight.

develops as snow and is compacted and recrystallized.

Term
alpine glaciation
Definition
found in mountainous regions and high elevations
Term
continental glaciation
Definition

exists where a large part of a continent is covered by glacial ice.

high latitudes (polar regions)

Term
valley glacier
Definition
a glacier that is confined to a valley and flows from a higher to a lower elevation.
Term
pleistocene glacial maximum
Definition

glaciers at their max 18000 years ago.

entered interglacial 10000 years ago.

Term
global distribution
Definition

85% of glacial ice in antarctica

10% in greenland

5% in alpine glaciers

 

Term
volume of water in glaciers
Definition
75% of world's freshwater is in glaciers
Term
ice sheet
Definition
a mass of ice that is not restricted to a valley but covers a large area of land
Term
ice cap
Definition

found in a few mountain highlands in Iceland and on islands.

flows downward and outward from a central high point.

similar to ice sheet but smaller

Term
____ becomes compacted into ____ which eventually recrystallizes into ____ ___
Definition

snow

firn

glacial ice

Term
iceburgs
Definition
blocks of ice break off and float free when a moving glacier reaches a body of water
Term
advancing glaciers
Definition

glaciers with positive budgets (amount of snow it gains i greater than amount of ice it loses) push outward and downward at their edges

 

Term
receding glaciers
Definition
those with negative budgets grow smaller and their edges melt back
Term
zone of accumulation
Definition

upper part of a glacier, part with a perennial snow cover.

snow accumulates and then melts, adding ice to the glacier.

Term
zone of ablation
Definition
the lower part, for there is ice lost or ablated by melting, evaporation, and calving
Term
equilibrium line
Definition
boundary between those two altitudinal zones of a glacier is an irregular line. marks the highest point at which the glacier's winter snow cover is lost during a melt season.
Term
terminus
Definition

lower edge of a glacier. 

its position reflects the glacier's budget

Term
basal sliding
Definition

the sliding of the glacier as a single body over the underlying rock.

meltwater acts as a lubricant

Term
plastic flow
Definition
movement that occurs within the glacier due to the plastic nature of the ice itself
Term
rigid zone
Definition
upper part of the glacier
Term
crevasses
Definition

open fissures

ice is broekn by tensional forces

Term
rock flour
Definition
grinding of rock across rock produces a powder
Term
U-shaped valley
Definition
characteristic of glacial erosion
Term
hanging valleys
Definition
after glaciers disappear, these tributaries carved by them remain high above the valley
Term
truncated spurs
Definition
ridges that have triangular facets produced by glacial erosion at their lower ends.
Term
rock-basic lakes
Definition
may occupy the depressions carved out of the weaker rock.
Term
cirque
Definition
a steep sided, half bowl shaped recess carved into a mountain at the head of a valley carbved by a glacier.
Term
horn
Definition
the sharp peak that remains after cirques have cut back into a mountain on several sides
Term
aretes
Definition
sharp ridges that separate adjacent glacially carved valleys
Term
till
Definition
unsorted and unlayered rock debris carried or deposited by a glacier
Term
erratic
Definition
an ice-transported boulder that has not been derived from underlying bedrock
Term
moraines
Definition
body of unsorted and unlayered till/debris either on a glacier or left behind by a glacier
Term
lateral moraines
Definition
elongate, low mounds of till that form along the sides of a valley glacier
Term
medial moraine
Definition
where tributary glaciers come together, the adjacent lateral morains join and are carried downglacier as a single long ridge of till
Term
end moraine
Definition
a ridge of till piles up along the front edge of the ice if the terminus remains stationary for a few years or advances
Term
ground moraine
Definition
a fairly thin, extensive layer or blanket of till that forms as ice melts and rock debris that has been carried by a glacier that is deposited.
Term
drumlins
Definition
bodes of till shaped into streamlined hills in areas of past continental glaciation
Term
outwash
Definition
material deposited by the debris-laden meltwater
Term
esker
Definition

an outwash feature of unusual shape associated with former ice sheets and some very large calley glaciers.

long, sinuous ridge of water deposited sediment.

Term
kettle
Definition
when the ice block finally melts, this depression forms
Term
varve
Definition

two layers of sediement representing one year's deposition in a lake are called this.

light coloered layer has slightly coarser sediement from warmer part of the year. dark layer is fine sediment that sinks down more slowly during winter.

Term
theory of glacial ages
Definition
states that at times in the past, colder climates prevailed during which much more of the land surface of earth was glaciated than at present
Term
pluvial lakes
Definition
formed in a period of abundant rainfall 
Term
fiord
Definition
a coastal inlet that is a drowned glacially carved valley
Term
velocity profile with depth
Definition
edges and base of glacier move more slowly due to frictional drag on bedrock.