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Lecture 7

GLY 1103 Lecture 7: Glaciers and Climate Change notes

8 Pages
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Department
Geology
Course Code
GLY-1103
Professor
Brian Zimmer

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Thursday, November 12, 2015
Glaciers and Climate Change
It’s getting HOT in here
-Seasonal cooling and warming
based on axial tilt (Northern hemisphere toward sun = summer) (N hemisphere
away from sun = winter)
not based on distance from the sun
at poles = permenant ice all over
at Equator = 8 km up - GLACIERS
-Forming a glacier
three conditions are necessary to form a glacier
cold local temp (polar or high elevations)
snow must be abundant (more falls than melts)
snow must not be removed by avalanches or winds
loose on top, packed-thigh ice on bottom (course ice)
-Types of glaciers
glaciers are found @ high latitudes = “continental glaciers”
glaciers @ high elevations = “alpine glaciers”
-Thermal categories
used to classify glaciers determined by climate
temperate - at or above melting temp
polar - well below melting temp
-How do glaciers move?
wet-bottom glacier - water flows along base of glacier
basal sliding - ice/slipping/melt water
dry-bottom glacier - cold base is frozen to substrate
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Thursday, November 12, 2015
movement is by internal plastic deformation of ice
highest velocities on the top and in the middle
lowest velocities on bottom and sides
why? = friction
-Meteorite hunters paradise
all rocks found on surface of Antartica are meteorites
mecca of meteorites
large amount near trans-anartic mountains
great place for meteorite hunting
-Into the ocean
tip of the iceberg
drop stones tell us where glaciers have been
bouancy
-Addition and subtraction
zone of accumulation: year-round snow
zone of ablation: seasonal snow
equilibrium line: boundary between zone of accumulation and zone of ablation
calving is massive falling of glaciers, can cause tsunamis and other dangers
colder - equilibrium line moves down
warmer - equilibrium line moves up
-Advance and retreat
if accumulation = ablation then glacial toe stays in place
if accumulation > ablation then glacial toe advances
if accumulation < ablation then glacial toe retreats
-More subtraction than addition
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Thursday, November 12, 2015
core of Greenland is thickening, however the edges are melting off at an even
greater rate
net loss is ~ 12 mi^3/year
if all Greenland ice sheets melt: 6 meter sea-level rise
-Glaciers as terrain changers
leave tell-tale signs
abraison - leave drag lines on front side
plucking - on back side can lose rock pieces
moraines - pile of sediment/rock that mark the end boundary of glaciers
glaciers will bulldoze existing material, creates huge moraines
are lateral moraines and end moraines
leave indicative features steeper terrains, u-shaped valleys, horns, cirques, arétes,
spurs, etc.
-Glaciers and sea level change
sea-level - ice ages cause seal level to rise and fall
water is stored on land during an ice age - sea level falls
de-glaciation returns water to the oceans - sea level rises
sea-level was ~100m lower during the Wisconsinan
if ice sheets melted, coastal regions would be flooded
-<2 MA glaciations
glacial chronology
there have been several pleistocene glacial advances
in North America, 4 are recognized - youngest to oldest…
wisconsinan
illinoian
kansan
3

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Description
Thursday, November 12, 2015 Glaciers and Climate Change Its getting HOT in here Seasonal cooling and warming based on axial tilt (Northern hemisphere toward sun = summer) (N hemisphere away from sun = winter) not based on distance from the sun at poles = permenant ice all over at Equator = 8 km up GLACIERS Forming a glacier three conditions are necessary to form a glacier cold local temp (polar or high elevations) snow must be abundant (more falls than melts) snow must not be removed by avalanches or winds loose on top, packedthigh ice on bottom (course ice) Types of glaciers glaciers are found @ high latitudes = continental glaciers glaciers @ high elevations = alpine glaciers Thermal categories used to classify glaciers determined by climate temperate at or above melting temp polar well below melting temp How do glaciers move? wetbottom glacier water ows along base of glacier basal sliding iceslippingmelt water drybottom glacier cold base is frozen to substrate 1
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