CH 11: GLACIERS
I.
TYPES OF GLACIERS
A.
The Problem of the Strange Boulders Tl
1.
Geologists noted boulder surfaces differed in N.& S.
Europe/giant ones had compositions different from the
bedrock they rested on
2.
Original explanation = great flood ="drift" of
material (theory before late 1800's)
3.
Modern explanation = glaciation
4.
Louis Agassiz showed great ice sheets covered northern
Europe during long ice age
B.
What Is a Glacier? T2
1.
Valley (Alpine) glacier
a.
Steep valley w/ snow covered ice hundreds if meters
thick
b.
Begins in huge snow/ice field below peak
c.
Moves downhill few meters/day
d.
Lower part thins & ends releasing milky water
e.
Forms - high elevations w/ year round snow
2.
Continental glacier (icesheet)
a.
Polar latitudes where extreme cold/snow year
round
b.
Oval or circular shape
c.
Whole landmass covered by ice thousands of meters
thick
d.
If reaches sea chunks break off = iceberg
e.
Larger than valley glacier/moves out from
center
3.
Glaciers = ice in motion
C.
The Snow Line T3
1.
Found in climates w/ year round snow where permanent
snow reaches lowest level in summer
2.
Highest near equator/lowest near poles
3.
Air temp, drops w/ greater height/distance from
equator
D.
Birth of a Glacier T4
1.
Fresh snow becomes compressed & recrystallizes into
rough granular ice (firn)
2.
Firn compressed = solid ice on snowfield bottom
3.
Ice flows down or out from overlying ice weight
E.
Where Valley Glaciers Occur T5
1.
All continents except Australia
2.
Ex: S. Alaska = largest/Himalayas
F.
Where Continental Glaciers Occur T6
1.
Polar areas where snow line close to sea level/wide
areas above snow line
2.
Today = Greenland/Antarctica (large icesheets)
a. Nunataks (huge mt. peaks) project through Antarctic ice
3.
Small icesheets (icecaps) in Iceland & other large
Arctic Ocean islands
II.
GLACIER MOVEMENT
A.
1.
How Glaciers Move T7
Weight of overlying ice pushes down on lower layers
causing melting/refreezing = ice grains slipping
over each other thus downhill movement
2.
Downhill movement = few to 2000 cm daily
3.
Faster at surface than base/center than sides b/c
friction slows flow
4.
Faster after winters w/heavy snow/during summer/on
steep slopes
5.
Crevasses (cracks) up to 40m deep across width of
glacier form when moves over steep slope (ice
brittle to 40m/more flexible below)
B.
How Far Glaciers Move T8
1.
Ice front: where ice melts as fast as moves
2.
Move forward or recede depending on conditions
3.
Can extend into sea/break off (calving)= icebergs
or form ice shelves (largest = Ross Ice Shelf)
C.
Glaciers Transport Loose Rock T9
1.
Moraines: build up of rock deposited by glacier
a.
Ground: carried in bottom before deposit
b.
Lateral: 2 long rock lines along valley sides
c.
Medial: middle
d.
End: pile at end when melts
2.
Glacial milk from rock flour (sand-silt mixture from
crushed rock underneath)/makes H2O white
D.
Glaciers Leave Their Mark T10
1.
Striations : long parallel scratches on bedrock left
by sand/pebbles/boulders showing movement direction
2.
Roches moutonees: outcrops look like resting sheep
3.
Potholes: from meltwater falling into crevasses
4.
Cirque: semi-circular basin at glacial valley head
5.
Arete: Knife edged ridge from 2 adjacent cirques
6.
Horn: peak from 3 or more cirques cutting in
E.
Recognizing Glacial Valleys Til
1.
Glacial trough: U shaped valley of main glacier
2.
Hanging trough: U shaped valley of tributary glacier
a. Waterfalls from rivers since formed over cliff
F.
What Continental Glaciers Do T12
1.
CG covers mt. tops/grinds peaks/polishes & rounds
2.
VG sharpens peaks by grinding away at sides
III. DEPOSITS BY GLACIERS
A.
Deposition Occurs T13
1.
Most deposits by melting
2.
Drift = all deposits of glacial origin
a.
Till: unsorted/unstratified rock dep. by ice
b.
Outwash: dep. by meltwater = sorted/stratified
B.
Glaciers Leave Moraines T14
1.
Moraines described T9 = ground/lateral/medial/end
a.
Recessional moraine: when receding ice front
stops in new place for length of time forming
new end moraine behind main one
b.
Terminal moraine: end moraine marking glaciers
farthest advance (Cape Cod)
2.
Material ranges from boulders to clay
a.
C.
Drumlins T15
1.
Long smooth canoe shaped hills of till (LWH =
400m/100m/25m)
2.
Found in swarms from advancing glacier running over
earlier deposited moraine
3.
Found in Wisconsin, NY, Boston
D.
Outwash Plains and Eskers T16
1.
OP = sloping stratified meltwater stream deposits
beyond terminal moraine/look like alluvial fan
2.
Eskers = long widening ridges of stratified
sand/gravel from subglacial streams
a.
Found in Miss. Valley/N Cen. states/NY/ME
E.
Kames, Kettles, Deltas T17
1.
Kames: small cone shaped stratified sand/gravel
hills formed on ice top
2.
Kettles: circular hollows from buried ice
3.
Deltas: glacial streams empty into lakes
F.
Lakes Made by Glaciers T18
1.
Cirque lakes
a.
b.
2.
3.
4.
IV.
Erratics: large transported glacial boulders
H2O fills valley glaciers cirque basins
Cirque & rock basin lakes = tarns
(1) Ex: Lake Louise, CAN/St. Marys, Montana
Kettle lakes
a.
Lg #'s form in kettle holes of moraines/OP’s
b.
Ex. Minnesota/Wisconsin/NY/New England
Moraine dammed lakes
a.
Formed Iarge US lakes: Lakes George/NY & Long/ME
b.
Where river valleys blocked by glacial moraine
c .
Long & narrow
Lakes from glacial erosion/deposits
a.
Finger Lakes, NY/Great Lakes
THE ICE AGE
A.
How It Happened T19
1.
1 mill. yrs. ago N. America/Europe cold as Greenland
2 . Ice sheets covered both & advanced/retreated 4 major times w/ climate
change
3.
11,000 yrs. ago = last recession
4.
Now warm interglacial period.
5.
Ice sheets will return 20,000 to mill, of years
B.
Ice Age Evidence T20
1.
Southern limits of ice sheet advances marked by
terminal moraines ex. Long Island, NY
2.
Many erosional/deposition features found
3.
Glacial markings high above valley walls = evidence
of larger glaciers during Ice Age
C.
Causes of Glacial Climates T21
1.
Pg 204: 1-4 (why earth cold enough for Ice Age)
2.
Heat energy given off by sun varies
3.
Volcanic dust in atmosphere
4.
During mt. building periods more land above snow line
5.
Continent position preventing mixing of ocean H2O
6.
Motion changes of Earth
a. Axis tilt (22 to 25 degrees)/orbit either more circle/oval
(Colder = min. tilt/circular orbit)