Transcript Earth`s Crust

Plate Tectonics
Crust
• The crust is formed from continental and
oceanic crust
• The crust covers the whole Earth
Convection currents
• The crust moves on convection currents
formed from heat in the core.
convection currents
Pangea
• pangea into the future
Tectonic plates
• Earth is separated into 12 major tectonic
plates.
You are here
Plate Boundaries
• Where plates come together they form
boundaries.
• There are three types of boundaries.
1) Divergent
2) Convergent
3) Transform
Divergent Plate boundaries
• These boundaries exist where plates are
spreading apart.
• As plates spread magma wells up from the
mantle.
• New crust is formed.
• Lots of volcanic activity and earthquakes.
Divergent plate boundary
Mid Atlantic Ridge
Mid Atlantic Ridge
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 convergent
boundaries plates are
moving together.
• One plate moves under
the other one. This is
called subduction.
• The oceanic plate will
subduct under the
continental plate
because it is less dense.
subduction
Formation of mountains
• Mountains
• Formed at continental-continental plate
boundaries.
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.
CO
Subducting crust melts and rises to the surface
Transform boundaries
• Large jagged edges
are slipping past
each other in a
transform boundary.
• When the edges
stick energy builds
up, when it
suddenly releases
that is an
earthquake.
Three types
• Shield
• Cinder cone
• Composite
Volcanoes
• Formed at divergent or convergent
boundaries.
• Magma rises to the surface.
• Carbon dioxide builds up pressure.
• Pressure releases CO2, ash, lava, pyroclastic
clouds.
Shield Volcanoes
• Largest in the
world
• Formed at
divergent
boundaries
• Slow moving
magma builds
walls gradually
• Hawaii
Mauna Loa, Hawaii largest volcano in the world
Cinder cone
• Smallest volcanoes
• Formed from ash and
not lava
• Usually less than 300400 feet tall
• When they erupt they
force out gases, ash,
and lava in tiny bits.
Composite volcano
Composite Volcanoes
• pyroclastic flow
• “pyro” means fire, “clastic”
means rock, so it is a cloud of
rock, gas and fire.
• These flows can travel
hundreds of miles an hour
• Most volcanoes on the ring of
fire are composite volcanoes, a
mix between cinder cones and
shields.
• Most destructive eruptions
Lahar flow
• Lahars are caused by melting snow, ash, and
mud.
• The mix makes the water have a consistency
of wet concrete.
• Lahars can travel up to 70 mph.
Mt. St. Helen
• eruption of mt st helen
Hot spots
• The Earth’s crust is thin
• In the middle of plates, magma might well up
and melt some of the rock.
• These spots are called hot spots
Hawaii
• Hawaii is in the
middle of the Pacific
plate, not on a
boundary
Yellowstone National Park
yellowstone supervolcano
man falls into volcano
Earthquakes
• When the crust shifts suddenly energy is
released.
• The focus is the place in the Earth where the
energy is first released.
• The epicenter is the point on Earth’s surface
that 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.
• Faults
How energy travels
• When rock breaks within Earth’s lithosphere it
releases energy that is carried by seismic
waves.
• 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 of
refraction
the Earth?
Measuring Earthquakes
• Magnitude: measurement of energy released
at the source.
• Intensity: amount of shaking and damage.
• Richter Scale: Used to compare the sizes of
earthquakes.
• Seismograph: detects earthquakes and
measures their magnitudes.
Richter scale
Earthquake video
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Tsunami
How earthquakes form
What caused Japan's tsunami?
scientist and lava lake