Transcript Geology of Great Lakes

Geology of Great Lakes
How the lakes formed
Ice age
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Shale and sandstone – soft stones
Bedrock – hard stone
Valleys soft
Lake bottoms hard
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Volcanoe – OK and Lake Superior
Mountains from lava
Retreating rerouted Lake chicago to miss
Huron to Geo bay to niagra
Erie to ohio river
Erie to Michigan
Glaciers and Erosion
Chapter 15
• 15.1 Glaciers: Moving Ice
• 15.2 Landforms Created by Glaciers
• 15. 3 Ice Ages
15.1 Glaciers: Moving Ice
• Glacier - Soft snowflakes become
compacted and pressure forms moving
mass of ice
• A. Formation
• B. Types
• C. Movement
Formation
• Moisture usually runs off to rivers
• High elevations make ice and snow
• Snowline – elevation that snow and ice
stay all year (about 1 mile up)
• Snowfield - motionless mass of ice/snow
• Firn – small grains of ice from melting and
refreezing
• Turns steel blue and flattens with pressure
and starts to slowly slide (move) downhill
Types of Glaciers
• Size and where they are formed:
• 1. Valley – mountainous area, narrow
wedge shape
• 2. Continental – large land mass
• Greenland and Anarctica
• If melted, would raise sea level 60 m
Valley
Continental
Movement of Glaciers
• River of ice
• Moves 100 m per year
• 1. Basal slip – base of ice melts because
of the pressure so acts to lubricate
• 2. Internal plastic flow – slow surface
movement, fastest in center, slower on
sides
Features of Glaciers
• Crevasses – large cracks, danger for
climbers
• Icebergs – ¾ under water, danger for
ships
15.2 Landforms Created by
Glaciers
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Glacial erosion
Glacial deposition
Till deposits
Stratified drift deposition
Glacial lakes
History of the Great Lakes
Salt Lakes
Glacial erosion
• Drag a rock behind a tractor?
• Cirque – bowl shaped depression (from where
the block break off) circus tent
• Aretes – sawtooth ridges (spines)
• Horn – pyramid-like peak (several aretes)
• Ice picks up material and scrapes, gouges,
polishes
• Roches moutonnees – round knobs, sheep
rocks
• Hanging valley – melted water forms draining to
the big valley
Glacial deposition
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Drift – material left when melts
Large boulders – erratics
Till – unsorted sediments
Stratified drift – sorted and deposited in
layers
• meltwater- melting glacier moving
sediments
Till deposits
• Moraines – land forms from till
• Lateral moraine – long ridge on the side of
valley
• Medial moraine – where to valley merge,
dark striped usually
• Ground moraine – unsorted material
becoming soil
• Drumlins – tear-shaped mounds of till
• Terminal moraine – till at front of glacier
till
morraine
Stratified drift deposition
• Outwash plain – melt in front of glacier of
drift
• Kettles – depressions from ice buried in till
• Eskers – ridges of long windy deposits
Glacial lakes
• Minn. Land of 10,000 lakes
• Kettle holes
• History of the Great Lakes
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erosion and deposition by continental ice sheets
1st toward the Miss. River
Hudson valley to Atlantic Ocean
• Salt Lakes
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Southwestern U.S.
No stream outlets
Evaporation
Salt Lake
Mojave Desert deposits of borax
15. 3 Ice Ages
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Ice age – long period of climate cooling
Interglacial periods – during warming temp
1st – 600 million years ago
Last – 114,000 years ago started and finished
11,000 years ago
• Climate during ice ages
• Glacial periods
• Causes of ice ages
Climate during ice ages
• Drop in ave. temp of 5’C
• ^ snowfall
• Advance of continental ice sheets
Glacial periods
• 1/3 of land covered with ice
• Most in N. America and Europe
• So much water is locked up in ice, the seal
level is 140 m lower than today
• Continental ice sheet over Hudson Bay
and down to Ohio
• Mile of ice over Muskegon?
Causes of ice ages
• Milankovitch theory – changes in orbit and
tilt of earth
• Orbit became more elongated every
100,000 years
• Over 41,000 yrs tilt goes from 21.5’ to
24.5’
• Change in axis over time
• Evidence in shells of dead marine life
Other theories
• Solar – sunlight
• Plate motion interferred with ocean
currents
• Volcanoe eruptions
• meteorite