Plate Tectonics
Crust
•The crust is formed from continental andoceanic crust
•The crust covers the whole Earth
Convection currents
•The crust moves on convection currentsformed from heat in the core.
Pangea
Tectonic plates
•Earth is separated into 12 major tectonicplates.
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Plate Boundaries
•Where plates come together they formboundaries.
•There are three types of boundaries.
1)Divergent
2)Convergent
3)Transform
Divergent Plate boundaries
•These boundaries exist where plates arespreading apart.
•As plates spread magma wells up from themantle.
•New crust is formed.
•Lots of volcanic activity and earthquakes.
Divergent plate boundary
Iceland
•Iceland sits right on the mid-atlantic ridge.
•They live on a volcanic island.
As the plates continue to spread
what is going to happen?
Convergent Plate boundary
•At convergentboundaries plates aremoving together.
•One plate moves underthe other one. This iscalled subduction.
•The oceanic plate willsubduct under thecontinental platebecause it is less dense.
Formation of mountains
•Formed at continental-continental plateboundaries.
Pacific Northwest
•Along Washington and Oregon
coast.
This is why we have a lot of mountains
volcanoes, and earthquakes
When the plate sticks, pressure builds up until it releases. This is an earthquake.
Subducting crust melts and rises to the surface
CO
Transform boundaries
•Large jagged edgesare slipping pasteach other in atransform boundary.
•When the edgesstick energy buildsup, when itsuddenly releasesthat is anearthquake.
Three types
•Shield
•Cinder cone
•Composite
Volcanoes
•Formed at divergent or convergentboundaries.
•Magma rises to the surface.
•Carbon dioxide builds up pressure.
•Pressure releases CO2, ash, lava, pyroclasticclouds.
Shield Volcanoes
•Largest in theworld
•Formed atdivergentboundaries
•Slow movingmagma buildswalls gradually
•Hawaii
Mauna Loa, Hawaii largest volcano in the world
Cinder cone
•Smallest volcanoes
•Formed from ash andnot lava
•Usually less than 300-400 feet tall
•When they erupt theyforce out gases, ash,and lava in tiny bits.
Composite volcano
Composite Volcanoes
•“pyro” means fire, “clastic”means rock, so it is a cloud ofrock, gas and fire.
•These flows can travelhundreds of miles an hour
•Most volcanoes on the ring offire are composite volcanoes, amix between cinder cones andshields.
•Most destructive eruptions
Lahar flow
•Lahars are caused by melting snow, ash, andmud.
•The mix makes the water have a consistencyof wet concrete.
•Lahars can travel up to 70 mph.
Mt. St. Helen
Hot spots
•The Earth’s crust is thin
•In the middle of plates, magma might well upand melt some of the rock.
•These spots are called hot spots
Hawaii
•Hawaii is in themiddle of the Pacificplate, not on aboundary
Earthquakes
•When the crust shifts suddenly energy isreleased.
•The focus is the place in the Earth where theenergy is first released.
•The epicenter is the point on Earth’s surfacethat is directly above the focus.
Faults
•Breaks in the crust of the Earth.
•Can form where plates meet and away from
the edge of a plate.
How energy travels
•When rock breaks within Earth’s lithosphere itreleases energy that is carried by seismicwaves.
•Primary waves (p-waves)
Underground, travel fast through the Earth,similar to sound waves.
Seismic waves
•Secondary waves
Underground, travel more slowly than p-waves.
Can only travel through solids.
•Surface waves
Travel along the surface in a rolling motion.
How do we know the structure ofthe Earth?
refraction
Measuring Earthquakes
•Magnitude: measurement of energy releasedat the source.
•Intensity: amount of shaking and damage.
•Richter Scale: Used to compare the sizes ofearthquakes.
•Seismograph: detects earthquakes andmeasures their magnitudes.
Richter scale
Earthquake video