changing Earth's magnetic field changes mineral's direction on the ocean floor
plates coming together; 2 types = collision & convergent
center of divergent boundaries; shows the boundary between two plates
where plates meet; a lot of volcanic activity, heat, and earthquakes
Describe what features form when an ocean plate subducts underneath another ocean plate.
volcanic island arc
Describe what features form when an ocean plate subducts underneath a continental plate.
volcanic mountain range
Describe what features form when a continental plate subducts underneath another continental plate.
Rock closest to the mid-ocean ridge are (new, old), while the rocks furthest from the mid-ocean ridge are (new, old).
At a subduction boundary, what causes one plate to sink underneath another?
density; the denser plate sinks
What is the evidence for the theory of plate tectonics?
locations of earthquakes & volcanoes, as well as magnetic reversals
What causes new crust to form at the edge of a tectonic plate?
magma at divergent boundaries
List 3 pieces of evidence that support the Continental Drift Theory.
shape or coastal formations; where rivers empty; plant growth
Why wasn't the Continental Drift Theory widely accepted?
because didn't explain how plates moved
measures amount of ground movement or magnitude
wave created by underwater earthquake
stretches & squeezes rock; travel through any material; primary waves
section of an active fault that has not moved in a long time
after earthquake; 100's can happen after an earthquake; cause damage; lower in magnitude than the original earthquake
S waves; close to the epicenter; faster than P waves
detects earthquake vibrations
What kind of data do scientist use to determine the location of seismic gaps?
location of past foci (foci is plural for focus)
What is the primary cause of most earthquakes?
plates grinding along faults
How many times more energy does a magnitude 8 earthquake give off compared to a magnitude 6?
In California, where is the most likely place for an earthquake to occur?
San Andreas Fault
Where would an earthquake have to occur in order for a tsunami to strike CA?
At which boundary do the deepest earthquakes occur?
What can be determined by one, single seismograph station?
distance to the epicenter
What part of the seismograph does not move?
What type of shaking are buildings more apt to survive in an earthquake?
horizontal, NOT vertical
Describe the movement and size of a tsunami as it approaches the shore.
speed decreases and the height increases
Which 3 types of movements can be recorded on a seismograph?
up/down, east/west, north/south
molten rock under the ground
molten rock on the surface
collapsed volcano; associated with gysers & hot springs
Example of a Shield Volcano
broad base w/gentle sloping sides; quiet eruptions w/little pyroclastic flow
What events would indicate the possibility of a volcanic eruption?
earthquakes, uplifting, calderas, gas emissions
What 3 things must be present/occur in order for magma to form?
temperature, pressure, and water content
List the 3 types of volcanoes from least explosive to most explosive.
least explosive = shield, then cinder cone, then composite = most explosive
Describe how silica changes magma.
more silica = thicker magma = greater viscosity
how slow magma & lava move; greater visosity = moves slower
At what type of plate boundary does the majority of magma come to the surface?
On which plate, the sinking one or the overriding plate, would a volcano form at a subduction boundary?
the overriding plate
What causes magma to rise to the surface?