Lecture 5 09 10 2014 What is on the ocean floor sand mud skeletons of things that live in the ocean How do we know what s on the bottom of the ocean we go out and make measurements by drilling down through ocean floor or by sending sound waves through ocean floor and record the echoes as they bounce of We also know how thick the sediments are in the worlds oceans How can you have 10km of sediment if the ocean is only 4km deep 10km of sediment weighs a lot And it sways a lot so the earths crust is depressed and pushed down into the asthenosphere Why is there thick sediment on the East Coast and thin on West Coast there is a subduction zone the Nasca and Pacific plates are subducting under South America there is no active plate tectonics on east coast 09 10 2014 Ocean crust Created at spreading centers Destroyed at subduction zones Continental crust Created at subduction zone volcanoes So how do we destroy it How do we destroy continental crust primarily through processes of erosion weathering breaks down rocks on land into collectively sediments these sediments are then transported downhill onto floodplains then shelves then into ocean Sediment Cycle Magma Granite granite proper or andesite Makes new continental crust Make mountains Rocks Sediment With process of weathering Sediment transported Always downhill from mountains to the ocean mechanisms water rivers glaciers land Sediment deposition Deposited onto ocean floor and into ocean 09 10 2014 Sediment Cycle Making Mountains How do we make mountains 1 Pulling continent apart divergent Continental Rifting Ex Africa Western US 2 Chain of sub zone volcanoes Form volcano near subduction zone Ex Andes Cascades 3 Colliding Continents Convergent Ex Himalayas Alps Appalachians 4 Transform faults when they bend folding can lead to formation of mountains Ex San Andreas fault mountains near LA 5 Hot Spots Ex Hawaii Yellowstone should know what the origin of the mountains are when pointed to on map 09 10 2014 Sediment Cycle Weathering Physical weathering Break down of material into smaller and smaller pieces Rock Sediment Ex paint peeling of of house rock breaking into pieces Chemical Weathering Actually change the substance you have Ex Iron car rusting Limestone formations in caves Agents of weathering 1 Water always the main agent 2 Oxygen usually rusts 3 Sunlight radiative efect heating cooling efect 4 Salt addition of salt can cause breakdown 5 Wind blowing stuf into other things Cold freeze thaw Desert Growth of salt crystals High elevations freeze thaw Low elevations salt crystals Breaking rocks apart weathering Freeze thaw o In mountains Wind and water Growth of salt crystals o On desert floor 09 10 2014