Lecture - October 29th, Nov. 3rd and 5th
Lecture - October 29th, Nov. 3rd and 5th 11883 - GEO 105 - 01
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This 5 page Class Notes was uploaded by Andrea on Friday November 20, 2015. The Class Notes belongs to 11883 - GEO 105 - 01 at Grand Valley State University taught by Tara Ann Kneeshaw in Fall 2015. Since its upload, it has received 22 views. For similar materials see Living with the Great Lakes in Geology at Grand Valley State University.
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Date Created: 11/20/15
Living with the Great Lakes Notes from class on October 29th, November 3rd and 5th, 2015. Holocene Changes: ● Inbetween glacial advances: Trees and Fossils. LIFE! ○ Quaternary period Pine and Spruce forests covered the Great Lakes region. ■ 15,000 years ago. ● Don’t find it today. Evidence today is shown Ancient forests found. buried under sediments; no oxygen = preserved. ■ Rapid climate fluctuations started occurring 10,000 years ago. ● Conifer and hardwood species. ● Still see today. Fossils: ● Freshwater, clams, snails, fish, amphibians and birds. ○ Today’s beaches freshwater environment today. ● Mammals: ○ Mammoths: teeth in Michigan. Some evidence. ○ Mastodons: LOTS in Michigan. Similar to Mammoths; but different in size and tusks were different. ■ Elephant like. Very hairy. ■ Tusks are not bigger and curved compared to Mammoth. ○ Musks oxen: Still exists today. Cold regions very hairy beasts. ○ Giant Beavers: Following the last ice age. Michigan has the most collection of complete skeletons. ○ Disappeared in North America 10,000 years ago. ■ Population decreased steadily. ■ Thrived in cold climate. ○ Owosso, Michigan. Found most complete skeleton. Lots of bones! ■ Largest footprint trail (mud dried, buried in soil, and turned to shale) ● Longest intact trail (30 feet prints) near Ann Arbor. ○ Official Michigan State Fossil: Mastodon fossil. Deglaciation: Story of the Great Lakes ● Important dates: 14,500 years ago (very young geologically speaking) ○ Coming out of the Pleistocene era. ○ Last time ice covered the Great Lakes region. ○ Significant the shape of the ice sheet before the melt, dicated the main shape of the Great Lakes. ■ Distinct lobes during meltback. ○ 14,000 years ago. ■ Ice is shrinking back. ■ Lobe shape is more obvious. ■ Water/ice filling and persisting at valleys (ancient river valleys) and depressions. ● Middle Lake Maumee (780 ft) ● Early Lake Chicago (640 ft) ■ Lowest elevation was to the South and flowed toward Mississippi River. ● 2 main channels flowing across the state. ● Grand River: At the time deeper and wider, was a main drainage system. ○ Deep channel ○ Lake Border Moraine System was built. ○ 13,000 Slow process. ■ Evidence of Native American living in this region. ● Lake Michigan Lake turned into. ○ Lake Whittlesey (738 ft) ■ Connects and drains to Lake Saginaw (695 ft) and the Mississippi River. ■ Forming: Port Huron Moraine (end moraine). Factors Controlling Lake Levels: 1. Position of ice main position of ice is what helped cause the lake to from. a. As it melts back, it opens up and allows connections to early lakes (as one whole system) which exposes the openings and allows new places for the water to form. 2. Glacial rebound: Massive weight of the Earth. a. Caused massive depression in the mantle. Once the pressure is removed the mantle (because of it’s toothpastelike consistency, bounces back up) i. This is still happening today. Not in MI exactly, except for L. Superior. ii. Mostly in Canada. b. This effects the elevation. Water is sensitive to change, and will start to flow somewhere else as the mantle pushes up. c. Currently, the G.L. region is stable. 3. Erosion of outlets: Rivers and streams carry sediments. Melt water streams/rivers create deep channels. They form on top of loose glacial till blasting soil and sediments away. a. Overtime they carve down into the geology. And will continue to carve down until it reaches something that the water can’t get through = hard bedrock. Or base level. i. This is a stable point and eventually all rivers and channels do this. 1. Ex. Colorado River ii. Creates interesting effects on the Lakes. Effects drainage rates. 1. At one point the drainage rate was too high and all the water nearly escaped out of the Lakes. November 3rd, 2015. Crust Rebounds: ● Elevation changes and stabilizes. ● Isostatic Rebound: Land was relieved of the huge weight of the ice sheets. Earth’s crust from its “depressed” state begins to accelerate. ○ Isostasy: Refers to the state of gravitational equilibrium between the Earth’s lithosphere and asthenosphere. ○ Tectonic plates “float” at an elevation that depends on the thickness and density in the lithosphere. ● Glacial Rebound: Modern rates measured rebound. ○ Different rates in different places. ○ In millimeters per year. (Around Lake Superior it rises 1/10th of an inch per year). ■ Ex. Hudson Bay was the thickest part of the ice sheet. Still rising. ■ Michigan is not really rebounding, only on the edge of L. Superior. ● 6,0004,000 years ago. ○ Highest Lake levels ver. ○ The Great Lakes started to flood. ○ Why did this happen? The North Bay outlet rose enough that it backed up the water and created a natural dam. ● Mississippi Stage: ○ Reverse flow until the North Bay carves deep enough and is able to stabilize. ■ L. Superior was 40ft higher than it is today. ■ High stage carves out present coastal features. ■ Lots of sand was deposited because of high water/waves. ● Wave zones had more energy = sand dunes FOR THE EXAM: BE ABLE TO SAY HOW THE G.L. FORMED Summary: Slowly down rebound, flooded/the outlets hit base level = stable, shifting of outlets, warming of climate. November 5th, 2015. Shoreline: Wave dynamics and Coastal Landforms. ● Created: Most common shoreline in G.L. ○ Sand beaches. ■ Sand deposited with waves from Lake bottoms. ● Sand is the term used to describe particles that range in a diameter from .0625 to 2 mm. ○ Where did sand come from? The Basin. Rock and previous mountain ranges. ■ Weathering and erosion overtime broke down overtime. ○ Sand is made up of: ■ Rocks, crystals, sea shells and minerals. ○ Compositions of sand can change greatly from beach to beach. ■ Hawaii = basalt. Olivine. Dark and red. Volcanic. ■ Caribbean = white. Sea shells from tiny marine organisms. ■ Great Lakes = tan. Grains of quartz. Some iron! ● Ancient Beaches: ○ Had higher lake levels ○ Beach ridges are now buried in vegetation. ■ Harder to see than moraines. ○ Proglacial lakes (present lakes during glacial time) ■ Ancient shoreline ■ Allendale use to be at the beach! Waves: ● Where do they come from? ○ Created by wind as it transfers its energy to the water's surface. ■ Basically a pile of water gets pushed by the wind. ○ The wave gains energy due to the friction between the wind and the water. ■ Example. Waves propagate like ripples on a pond. Wind hits the lakes and sends the energy out in all directions. ● Ripple Pattern: Troughs and Crests ○ Bottom and Top ○ Waves energy can perform work on sediment, rock, and structures. ○ Energy gets released when it hits shore. ■ Collides with bottom of the lake nearer and falls over on itself. ● Topple: The bottom (trough) speeds up and the top (crest) slows down. ■ This energy gets transferred as work and blasts sediment as it hits. ■ Waves deposit more than it removes, depending on how much is in the water. ○ Beneath the wave the water moves in a circular orbits bobbing motion. ○ No water motion beneath the wave base. ○ Size of circular moiton get smaller and smaller. ○ The bottom of the lake floor gets hit by the wave base which creates smaller circles and speeds up the bottom of the wave. ○ Sediments are picked up by the wave base hitting the lake floor and with the energy of the wave crashing are thrown and deposited onto shore. ● Wave Refraction: ○ Wave converge on headlands: ■ Headlands hard rock. Stick out into the water and erosion doesn’t affect those. ■ Irregular coasts become smoother. ■ Softer rocks = bays. ■ Waves refract and converge to headlands. ● Erods eventually to equal the coast line and the bay. ● Coastline becomes straighter. ○ Young = irregular. ○ Older = straight. ■ Caves form when water erodes the base and gradually cuts down the base and above. ● ex. Lake Superior caves ■ Notches form when water cuts only at the base of the rock and erodes it. It cuts out the support for the larger rocks and eventually they collapse. ● Longshore Current: ○ Waves hit at an angle. ○ Net energy is “down” the beach ○ Usually depends on direction the wind is blowing. ■ Moves suspended sand and surf zone ○ Water flows back off the beach more directly ■ Leads to rip currents ○ Not directly parallel to the beach ● Beach Drift: ○ Sediment moves in a zigzag pattern. ○ Generally moves in direction of longshore current, but moving in and out. Not moving in a straight line. ■ Littoral transport: carries sedimentary material both parallel to the shore and perpendicular to the shore. ■ Today: We can predict where sediment is going. ● ex. Miami Beach. In order to maintain it’s most popular beaches and destinations, you need to know where the sand is going to be eroding and dumping.