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Transcript
Chapter 9 and 10 The interior of the earth and it’s surface The Interior of the Earth We can’t go there Use the shock waves an earthquake makes to investigate it. Called seismic waves Two types – S waves (sheer waves) – P waves (pressure waves) Measured with a seismograph Seismograph Heavy object Drum Seismograph As ground shakes the base moves but the weight stays still Seismic waves Penetrate earth and return to surface. Speed and direction change S waves can’t go through liquids P waves can, but they slow down. As the waves go through the earth at 2900 km down, the S waves stop and the P waves slow down At 5105 Km down the P waves speed up What does this tell us? The Earth’s Core The center of the earth Two layers Inner core – Iron and Nickel – 5000º C – Pressure keeps it solid – Responsible for magnetic field? The Earth’s Core The outer core – Iron and Nickel – 2200º C to 5000º C – Not as much pressure so it is liquid How do they know P waves are pressure waves – Will go through liquid S waves are sheer waves – won’t go through liquids S waves Liquid P waves Shadow No waves Total The Mantle Above the outer core 80% of the earth’s volume 68% of the earth’s volume Studied rocks from volcanoes Have studied rocks from the ocean floor – Silicon, oxygen, iron, magnesium Density increases with depth Because there’s more iron Measured by speed of the seismic waves The Mantle Temperature increases with depth Has plasticity What is plasticity? A solid that can flow like a liquid Silly putty 870º C -2200º C The Moho the thin boundary layer between the mantle and the crust 32-64 km Discovered by Andrija Mohorvičić Found seismic waves changed speed at this level Either different composition or density. The crust Thin outer layer we live on If the earth were the size of an apple, the crust would be thinner than the peel 8-32 km Two kinds – Oceanic – Less than 10 km – all basalt- dense The crust Continental crust – Thicker- averages 32 km, up to 70 km – Top layer granite- less dense, on top of dense basalt Earth’s crust also called lithosphere Lithosphere broken into large plates (called tectonic plates) 0 km Crust 32 km Moho Mantle 2900 km Outer Core 5150 km 6500km Inner Core Continent Ocean Granite Basalt Mantle Chapter 10 How the crust moves Crust Continental – – Thicker – Granite and basalt Oceanic – Thinner – All Basalt Stress- the pushes and pulls on the crust causes changes in the rock – Shape – Volume Compresses or expands Deformation- breaking, tilting, and folding of of Stress Three types Compression- pushed together Stress Three types Compression- pushed together Moves land higher up and deeper Stress Tension Pulled apart Stretches like taffy Thinner in the middle Stress Tension Pulled apart Stretches like taffy Thinner in the middle Stress Shearing- pushes in two opposite horizontal directions Rocks are torn apart or bent Stress Shearing- pushes in two opposite horizontal directions Rocks are torn apart or bent Stress changes Shape Volume Density Can cause cracks - fracture Fracture along smooth surface is called a joint Joints are parallel Faults A break or crack where rocks move Where earthquakes happen Hanging wall- above the fault Foot wall- below the fault Three types of fault tension causes normal fault Compression causes reverse fault and thrust fault Normal fault Tension pulls apart Hanging wall moves down Foot wall Hanging wall Normal fault Tension pulls apart Hanging wall moves down Reverse fault Compression pushes together the hanging wall up Hanging wall Foot wall Reverse fault Compression pushes together the hanging wall up Thrust Fault Compression continues The hanging wall is pushed over the foot wall end up with layers of rock repeated Older rock on top of younger rock Thrust fault Youngest Rock Oldest Rock Lateral Fault Caused by shear stress Blocks move sideways Lateral Fault Caused by shear stress Blocks move sideways Faulted Mountains and Valleys A series of normal faults will cause mountains to be uplifted. Called Fault-block mountains Sierras Valleys will also be formed Called rift valleys Death Valley Fault Block Mountain Fault Block Mountain Rift valleys Rift valleys Folding Some times rock doesn’t break It forms folds- like wrinkles Upward fold- anticline Downward fold- syncline Vary in size, from microscopic to mountain forming Anticline Syncline Why Fold Why don’t they break Temperature- hot rock is easier to bend Pressure- higher pressure more likely to fold Type of rock- some are more brittle, some are more malleable Gradual force bends, sudden force breaks Plateau Flat area made of layers of flat-topped rocks high above sea level Can be formed like fault block mountains Or by lava flows (lava plateau) Colorado plateau- West of the Rocky mountains formed Grand canyon Rivers cut large plateau into several smaller ones Domes Magma forms a bubble underneath the crust, without erupting Half sphere surrounded by flat land If worn into separate peaks they are called dome mountains The Crust Floats On the mantle Because it is less dense The floating crust pushes down The crust pushes up. Balance of forces called isostasy More material floats lower Isostasy Crust Mantle Isostasy Ice Crust Mantle Isostasy Crust Mantle Ice Isostasy Crust Mantle Over time depression will rise back up. Isostasy Sediments wash off continents Continental crust Mantle Isostasy Sediments pile up on ocean floor Continental crust Mantle Isostasy Pushes ocean floor down Continental crust Mantle