geology of great lakes how the lakes formed. ice age
TRANSCRIPT
Geology of Great Lakes
How the lakes formed
Ice age
• Shale and sandstone – soft stones• Bedrock – hard stone• Valleys soft• Lake bottoms hard
• 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 ErosionChapter 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
• 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
• 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 Lakeserosion and deposition by continental ice sheets
• 1st toward the Miss. River• Hudson valley to Atlantic Ocean
• Salt Lakes• Southwestern U.S.• No stream outlets• Evaporation• Salt Lake• Mojave Desert deposits of borax
15. 3 Ice Ages
• 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