Download earth`s crust and isostasy

EARTH’S CRUST AND ISOSTASY
Earth’s Lithosphere: Two types of Crust
- Tectonic plates "float” on the ____________________________. Level depends on thickness and
density:
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______________________ Crust – more dense
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_____________________________ Crust – less dense
CONTINENTAL CRUST
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Found under _________________ masses.
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___________________ than oceanic crust.
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Made of ________________________ rocks such as granite, schist and gneiss.
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Thickness varies between 10 and 75 km (6 to 47 miles).
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___________________ rock
• silica
• lighter color
• Density avg. 2.7
OCEANIC CRUST
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Found under the _____________________ floor.
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Made of ____________________________ rocks such as basalt and gabbro.
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About 5-10 km (4 miles) thick.
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___________________ rock
•
•
•
•
less silica
heavier elements – magnesium & iron
darker
Density avg. 3.0
CRUST RESPONDS TO FORCES
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____________________: Force pulling down on crust.
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_______________________: Upward force exerted by fluid asthenosphere.
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To balance:

Less dense plates “float” _____________________.

More dense plates “float” ______________________.
ISOSTASY
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___________________________ forces of gravity and buoyancy.
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Equilibrium between the Earth's lithosphere and asthenosphere.
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Isostatic Equilibrium = forces ________________________.
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Tectonic plates of different densities float at different ________________________ depending on
balance of forces.
CHANGES IN CRUST
- Changes in crust density (mass or volume) affect how tectonic plates “float” on asthenosphere.
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Mountain building ________________________ mass, crust ___________________ into
asthenosphere.
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Weathering and erosion _____________________ mass, crust ___________________ on
asthenosphere.
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__________________________________ can occur when the weight of part of the Earth’s crust
changes.
Effects of Erosion & deposition
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____________________________ decreases mass and tectonic plate rises on asthenosphere.
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____________________________ increases mass and tectonic plate sinks into asthenosphere.
Isostatic Subsidence
- Occurs where sediment is being ________________________:
 Volcanic areas
 Glaciers
 Under water
- ______________________________ in mass on the crust causes it to _________________ until
a new point of equilibrium is reached.
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Often rock layers that sink become ________________________________________ rock.
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Example ____________________________________
o
o
o
o
Constructed in 1935.
Added the weight of 24 billion metric tons of water.
Caused the circular area around the lake to settle.
Area sank approximately 5.5 feet.
Isostatic Rebound
- Occurs in areas of _____________________________ where:
 Mountains and landforms are eroding away.
 Glacial ice is melting.
 Lake or sea water is decreasing.
- ______________________________ in mass on crust causes it to _______________ until a new
point of equilibrium is reached.