Glaciers and Glaciation
• Glacier
mass of
of ice
ice composed
composed of
of recrystallized
recrystallized
>> aa mass
compacted snow
snow that
that flows
flows under
under its
its own
own
compacted
weight on
on land.
land.
weight
• Presently glaciers cover11//10
10 of the
Earth's surface.
• Glaciers occur in Greenland and
Antarctica and in higher mountain
ranges.
GlaciersImportant in understanding global scale climate change
Related to all 5 of the Earth’s systems
Exosphere- changes in the amount of sunlight cause
glaciations
Hydrosphere- glacial ice is frozen water, part of the
hydrosphere
Geosphere- Glacial ice flows over and modifies land
Atmosphere- alteration of global atmospheric patterns
contributes to glacial ice formation
Biosphere- ice displaces animals and plants
Importance
• Glacial times represent significant time
periods in Earth's history
Proterozoic, Pennsylvanian, Pleistocene
• Represent major climatic departures
from the modern on a Global Scale
• Cyclic in Nature
• Man's Influence???
• Glacial Ice contains records of past
atmospheric changes
Origin of ice
• Snowflakes are melted & deformed by the pressure of
overlying snow, becoming granular snow, then firn, and
finally interlocking crystals of glacial ice.
Descriptive classification of Glaciers
• Valley (or Alpine) Glaciers are confined
to mountain valleys.
> may eventually cover the entire mountain range
becoming a mountain ice sheet
> may also spill onto low flatlands becoming
Piedmont glaciers
• Continental (or Ice Sheets)
> cover vast areas of more than 50,000 km22 .
Today, continental glaciers are only found in
Greenland and Antarctica.
> Not so in the geological past
Response of a Glacier to Changes in Glacial Budget
If accumulation = ablation, then no advance or retreat, but continues to flow
If accumulation > ablation, then glacier advances while flowing
If accumulation < ablation, then glacier retreats, but continues to flow
Effects of Glaciers
• Fills in the low spots
valleys and
and basins
basins get
get filled
filled in
in w/
w/ sediment
sediment
>> valleys
• Knocks down the high spots
mountains and
and hills
hills get
get eroded
eroded
>> mountains
• Reroutes the drainages
valley filling
filling may
may block
block streams,
streams, causing
causing
>> valley
new paths
paths to
to be
be taken
taken
new
• Deposits accumulate in specific
places related to flow and meltwater
characteristics
• James Lobe and Glacial Lake Agassiz
Erosional Processes
･ Important erosional
processes associated
with glaciers include
plucking, abrasion, and
bulldozing.
･ Plucking and abrasion
are most common
> can form a landform
called a roche
moutonnee
Erosional features
Roche Moutonnée
Erosional features
•Hanging Valley
•Horn
•Arete
•Cirque
•U-shaped trough
•Col
•Truncated Spurs
Glacial Deposits
• glacial drift-A general term
referringtotosediment
sedimentformed
formedby
byany
refering
Any glacial
action.
glacial
action.
• Till (Diamicton) poorly sorted,
unlayered material directly
deposited
by
a
glacier;
ice
contact
deposited by a glacier;
• Stratified drift (Outwash)sorted,
layered sediment usually
deposited by meltwater streams.
Proglacial or ice contact
Depositional
featuresglacial erratic
A glacial
erratic
Yellowstone Park
6 ft
Sediments-
Glacial Till exposed in Iowa
Depositional features- moraines
Moraine formation- made of Till, deposited by ice
Depositional features- moraines
Moraine formation- made of Till, deposited by ice
Depositional features- moraines
Moraine formation- made of Till, deposited by ice
Lateral
Lateral
moraines
moraines
Medial
Medial
moraines
moraines
･ Lateral and Medial
Moraines are sediment
eroded from the valley
sides and deposited by
a glacier. They often
appear as dark stripes
in a glacier.
Depositional features- distribution of moraines
Depositional features- Kames, eskers, kettle lakes,
drumlins, outwash plain (sandur)
Depositional features- Kames, eskers, kettle lakes,
drumlins, outwash plain (sandur)
Outwash with kettles
moraine
Kame
terrace
Outwash
Kettle
lakes
Outwash Plain
with eskers and a
braided stream
Pleistocene Glaciation
Glaciations
• The Pleistocene "ice age" began
~1.96 million years ago
• Several glacial and interglacial
Episodes have occurred.
episodes.
Glacial -- aa period
period of
of ice
ice advance,
advance, generally
generally
>> Glacial
interpreted as
as aa globally
globally cool
cool period.
period.
interpreted
Interglacial -- aa period
period of ice retreat, generally
>> Interglacial
interpreted as
as aa globally
globally warm
warm period.
period.
interpreted
We are in an interglacial period right now
MilankovitchOrbital
OrbitalTheory
Theory
Milankovich
• Proposed to account for the cyclical
nature of Glaciations.
• Astronomer & Mathematician Milutin
Milankovitchattributed
attributedthe
theglaciation
glaciationto
to
Milankovich
variation in three parameters of the
Earth's orbit.
Obliquity- not shown
eccentricity
precession
warm
warm
cold
cold
1
3
4
5
Erie
Lobe