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 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 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 Lakes erosion 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