Transcript plate tectonics

Environmental Science
Unit 1: Geology Basics
Earth’s Layers & Plate
Tectonics
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Lithosphere vs Asthenosphere
• Lithosphere: Crust + upper Mantel
– 80 km deep (50 miles)
– Less dense than Asthenosphere
– Floats on the Asthenosphere
– Plates move slowly! 2”/yr
• Asthenosphere:
– Fluid part of Mantel—ductile, like putty
– Underneath the Lithosphere
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Shape of Earth’s Surface
• Main force: Movement of Earth’s outer
layer by the process of:
– PLATE TECTONICS
• What is a “tectonic plate”?
– Earth’s crust is made up of ~12 “plates” that
fit together like a jigsaw puzzle.
• Plates have continental and ocean crust.
• Plates move around, causing: Earthquakes,
Volcanoes, Mountain Building, and much of the
Rock Cycle.
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Processes that change Earth’s
surface:
• Weathering & Erosion
– Weathering
• Chemical
• Physical
– Wind
– Water
• Volcanism
• Deformation
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Plate Movements
• Converging Plates – plates moving
together, form trenches
• Diverging Plates – Plates moving apart,
form mid-oceanic ridges
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What is “Subduction” ?
• Two sections of crust collide
– One slab is forced down deep into Earth
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Volcanism
• Bring Magma to the surface
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Volcanism
• The most general cause of volcanism on
earth is Subduction of earth’s crust.
– One tectonic plate is forced under another
plate as the plates push together.
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Mid-Ocean Ridges
• Bottom of sea splits apart:
– Magma rises
– New Crust formed
• “Spreading Ridges”
– Lithosphere slides away from elevated region
• 4 cm/yr
– Central portions of oceans
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Rifting
• Continents can also
split apart at “rifts”.
– Continued rifting can
form a new ocean.
Chemical Weathering
• Minerals in rocks are dissolved into rainwater or
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changed from one type of mineral into another.
Occurs most readily in warm, moist areas.
– Warm speeds up chemical reactions.
– Water is required for chemical weathering.
• Minerals differ in their resistance to chemical
weathering.
– Quartz resists chemical weathering.
– Feldspar does not resist well.
• Breaks down into clay minerals.
Chemical Weathering
• Ever been to a cave?
– Caverns develop as water flows underground,
dissolving minerals in rock and transporting
them away.
• Cave features, such as stalactites and stalagmites
form when mineral-carrying water drips and leaves
behind some of its mineral load.
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Cave
• Stalactites “Hang on
tight” to the ceiling.
– Form as minerals
come out of water as
a drip forms.
• “Mighty” Stalagmites
– Form as minerals
come out of water
after it drips to the
floor.
Physical Weathering
• Rocks are broken apart into smaller pieces
by water and other forces.
– Moving liquid water can break rock apart by
knocking rocks together.
• Rivers, Ocean surf, etc.
– Glaciers break, grind, and move rock.
– Water can break rock as it freezes in cracks.
• Water expands as it freezes, and can exert
tremendous forces. Potholes in roads and
exploding soda cans show the power of freezing
water.
Soil
• Bits of broken rocks + remains of plants &
animals
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Soil
• Soil Horizon – Each
layer of soil in a soil
profile
• Soil Profile – The
arrangement of the
layers of soil in an area
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What is a “Fault” ?
• Fracture due to stress on rock
• Cause: pushing & shoving of crust:
– Seafloor spreading
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Making Mountains
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Making Mountains
• Folding
– Colliding plates—neither is subducted
– Plates crash and rise vertically
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