Earthquakes and Volcanoes
What is a Tsunami? A seismic seawave produced by a volcanic eruption, an underwater landslide, or an earthquake. They sometimes reach heights of over 50 feet. They
are also called tidal waves.
Explain the difference between a focus and an epicenter. The focus is the actual
point of rock breakage or movement. the focus is usually located far below the surface
of the Earth. The epicenter is the point on the surface of the Earth directly above the focus.
Name the three types of earthquake waves. Compression or P waves, Shear or S waves,
and Surface waves.
What is magnitude and how is it related to the Richter Scale?
Magnitude is the measure of the strength of the seismic waves that have been sent
out from the focus. Richter scale is a number used to measure the strength of an
earthquake. A Richter scale measurement of 1-5 is of low intesity and 6-9 is of
What is an fault? A long crack in the Earth's crust. Earthquakes occur along
What are the two definitions for a volcano? 1) An opening in the Earth's crust
in which molten rock and gases can escape. 2) The mountain built by repeated eruptions
of lava, or pyroclasts or, both lava and pyroclasts.
What is the difference between active, dormant, and extinct volcanoes. Active volcanoes are either currently erupting or have erupted in
recorded history. Dormant volcanoes are not currently erupting but are considered
likely to do so. Extinct volcanoes have not erupted in current history and are not
considered likey to do so.
What is the difference between magma and lava? Magma is molten rock under the
Earth's surface. Lava is molten rock on the Earth's surface.
Label the following diagram
A. Magma chamber
C. Side vent
F. Layers of lava and ash
Name and describe the 3 ways that volcanoes form.
What causes earthquakes to occur?
- Volcanoes can form at subduction zones where two plates collide, one being driven
down into the mantle and the other riding over the top. This causes the lithospheric
plate to melt and being less dense than the rock in the mantle it will rise. This
rising magma will produce a volcano.
- Volcanoes can form at a mid-ocean ridge. When the two plates separate magma fills
the void and a volcano is produced. These chains of volcanic mountains are the longest
mountain chain in the world.
- Volcanoes can also form at a hot spot.
Earthquakes occur because the Earth's plate are in motion. The plates do not move
smoothly and evenly. Great stresses build up along the plate boundaries. When a
plate moves suddenly a great amount of energy is released in the form of wave energy.
These waves are what cause the damage from an earthquake.
Where do the majority of earthquakes occur?
Along plate boundaries. The main earthquake zones are the Circum-Pacific belt that
stretches around the rim of the Pacific Ocean and the Alpide Belt in Europe and Asia.
What causes volcanoes to grow larger?
Volcanoes grow larger from their eruptions. When avolcano erupts it ejects lava,
or pyroclasts, or both that builds the cone larger and larger.
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