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

http://www.google.com/imgres?imgurl=http://static.guim.co.uk/sys-images/Guardian/Pix/pictures/2009/4/28/1240928227064/Glaciers-under-treat-Smal-004.jpg&imgrefurl=http://www.guardian.co.uk/environment/gallery/2009/apr/28/glaciers-melting-climate-change%3Fpicture%3D346586096&usg=__zhMNEJeZo04S5SAtNlzhhEboJ0U=&h=390&w=630&sz=90&hl=en&start=63&sig2=PQOwwPWGnqUQ7bvtfNK98g&itbs=1&tbnid=s5o0MFZGG87LIM:&tbnh=85&tbnw=137&prev=/images%3Fq%3Dglaciers%2Bpictures%26start%3D60%26hl%3Den%26sa%3DN%26gbv%3D2%26ndsp%3D20%26tbs%3Disch:1&ei=FhL9S_vZPJWeMsz3oN8H

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