Vocabulary Chapter 2
Earthquakes and Volcanoes
Lesson 4- Earthquakes
A sudden movement of the Earth's plates that can cause destruction.
Earthquakes occur at plate boundaries when built up pressures in rocks suddenly
release causing the plates to move along a fault line.
- Earthquake belts-
A) Circum-Pacific belt-Encircles the outer rim of the Pacific Ocean. This area is
the most active for earthquakes and volcanoes in the world.
B) Alpide belt-
This earthquake belt runs from Western Europe to Central Asia.
A long crack in the Earth's crust.
The place in the Earth's crust where an earthquake occurs. This is usually
found deep under the surface of the Earth.
The place on the Earth's surface directly above the focus.
- Earthquake Waves-
Also called seismic waves. They are caused by the rapid release
of energy caused by movements in the Earth's crust.
A) Compression waves-
First and fastest waves produced in an earthquake. They are
also called P (Primary) waves. They move in a jackhammer motion.
B) Shear waves-
Second waves to strike an area. Also called S (Secondary) waves.
They travel slower than P waves. They move in an up and down roller coaster motion.
Lesson 4 continued
C) Surface waves-
These are the last waves to strike an area. They are the slowest
waves and are confined to the surface of the Earth. They produce the most damage
to man made materials. There are two kinds of surface waves; 1. Love waves and Rayleigh
Measurement of the intensity of an earthquake.
- Richter Scale-
Scale used to identify the strength of an earthquake. Richter scale
runs from 1-9. Earthquakes with a 6 or above rating are considered powerful.
A graph showing the length and severity of an earthquake.
slip Fault/ San Andreas Fault-A strike-slip fault is located at a transverse
plate boundary. The two plates slide by each other moving in opposite directions.
A very large wave produced from earthquakes, volcanic activity, or an
under water landslide. These waves produce 30-100 foot high crests as they break
onto the shoreline. They can produce enormous damage to seaside communities.
- 2 definitions of volcano-
- An opening in the surface of the Earth that allows lava, gas,
and pyroclastic material to reach the surface.
- The mountain built by repeated eruptions of a volcano.
A volcano in Mexico. This volcano was produced in a farmers field
in 1943 and built a 1300 foot cinder cone over 9 years. The volcano was name for
the village that was destroyed by a large lava flow from its namesake.
- Active Volcano-
A volcano that is currently erupting or has erupted in recorded
- Dormant Volcano-
A volcano that is not erupting currently but has erupted in recorded
time and is considered likely to do so again.
- Extinct Volcano-
A volcano that has not erupted in recorded time and is not considered likely to do so.
- Lava Dome-
A lava dome is a steep mass of very thick and pasty lava that is pushed up from the main vent.
The thickness of lava and magma determine how the volcano will erupt,
what type of lava flow will be formed, and what type of volcanic cone will form.
Viscosity is the measure of how thick or thin the lava is. Thick magma or lava
is said to have a high viscosity, while thin lava or magma is said to have low viscosity.
- 3 ways that volcanoes form
- Subduction Zone Volcanoes-Form where two plate meet, one being driven down into the
mantle. These are the most explosive volcanoes because as the plate is driven into
the mantle ocean water is mixed into the magma causing the production of steam which makes the magma more explosive.
- Rift Zone Volcanoes-These are formed where two plates are separating, magma fills
the void left by the divergent plates. These volcanic mountains form a chain that
circles the Earth. It is the longest continuous mountain chain in the world, over
40,000 miles long.
- Hot Spot Volcanoes-They form where there is a upward flow of very hot solid rock
coming from great depths in the mantle. The Hawaiian Islands and Yellowstone Caldera
were formed from a volcanic hot spot as the plates moved over that particular hot
- Tilt Meter-
Tool that measures the amount of change in the slope of a volcano
or a lava dome. It is used to help predict an upcoming eruption. The movement of
magma in a volcano is a sign that an eruption may be near.
Molten rock under the surface of the Earth.
- Magma Chamber-
A large mass of magma usually located far under the surface of the Earth.
A long crack in the surface of the Earth that allows magma and gases to reach the surface.
An intrusion of magma that becomes a passageway for magma. This passageway connects the conduit to the side vent.
A dike runs through already existing layers of rock.
- Side Vent-
A secondary opening in a volcano that allows magma to reach the surface of the Earth. It is usually located on the flanks of a volcanic cone.
Molten rock that has reached the surface of the Earth.
The main passage for magma.
- Main Vent-
The main opening in a volcano. Located at the top of the conduit.
The steep walled bowl shaped opening surrounding the main vent. This
steep walled structure is formed by repeated eruptions of ash and lava.
The rock that is formed by the mixture of lava and ash. This is the rock
that is formed on the sides of stratovolcanoes.
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