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Magnetic reversals

changing Earth's magnetic field changes mineral's direction on the ocean floor

Convergent boundaries

plates coming together; 2 types = collision & convergent

Rift valleys

center of divergent boundaries; shows the boundary between two plates

Plate boundaries

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.

folded mountains

Rock closest to the mid-ocean ridge are (new, old), while the rocks furthest from the mid-ocean ridge are (new, old).

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

Richter scale

measures amount of ground movement or magnitude


wave created by underwater earthquake

P waves

stretches & squeezes rock; travel through any material; primary waves

Seismic gap

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

Surface Waves

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?

Pacific Rim

At which boundary do the deepest earthquakes occur?

subduction boundary

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

Mauna Loa

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?

less dense

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