Transcript Glaciers and the Great Ice Ages

Glaciers and the Great Ice Ages
Pleistocene Epoch:
the Great Ice Ages
• 2.0 Ma to 10,000
years ago
• Four (or more) distinct
episodes expansion
and melting of ice
sheets (continental
glaciers)
Why did the climate change so
drastically and repeadedly?
• Climate change and
variations in Earth’s orbit
• Eccentricity: elliptical to
nearly circular cycles
• Obliquity: cyclic changes in
tilt of axis
• Precession: cyclic change
in”wobble” of the axis
• Variations affect amount
and distribution of solar
energy received by Earth
How does a glacier form?
• Cold climate is necessary
• Annual snow accumulation is greater than
annual rate of melting
• Snow builds up over time
• Snow recrystallizes to ice
Glacial Flow
• Ice begins to flow
(plastic deformation)
under the influence of
gravity
• Glacier = mass of
flowing ice
• Glaciers are dynamic
• Flow is constant
• Some parts of glacier
are melting
• Rate of accumulation
vs. rate of melting
determines if glacier
will advance or if end
of glacier will melt
back (glaciers never
flow backwards)
Glaciers and Landscapes
• Flowing ice picks up
sediment, soil, etc.
• Breaks loose pieces
of bedrock
• Modifies landscape
by erosion and
deposition
Erosion by Glaciers
• Striations:
“scratch”marks made
as ice drags rocks
across bedrock
Erosion by Glaciers
• Modifies “V” shaped river valleys to a “U” shape
Deposition by Glaciers
• Erratics – pieces of
“exotic” rock left by
glacier
• Till – unsorted,
unstratified sediments
dumped by ice
• Outwash – sorted and
stratified sand and
gravel deposited by
meltwater
Deposition by glaciers
• Lacustrine sediments
– Lakes form between melting edge of ice and
obstructions (often deposits of till)
– Fine silt and clay settle to the bottom in calm water
– Clay may be used in pottery and brick making
– If lakes drain or fill with sediment:
• bogs and swamps – ecologically important wetlands
– Water-logged lacustrine sediments may cause tilting
and sinking of buildings constructed on them
Glaciers and Landforms
• Characteristic
landforms