Download Earthquakes

An earthquake is the shaking and
trembling that result from the
sudden movement of part of the
Earth’s surface.
Scientists estimate that more than a
million earthquakes occur each year, but
only about 20 of them cause significant
damage.
What causes earthquakes?
Most earthquakes happen at Faults.
Faults are breaks in the Earth’s crust
where the surrounding rock has moved
or shifted.
Earthquakes usually occur at faults that
are along plate boundaries. The plates
of the Earth push together, pull apart,
or slide past one another.
As these plates move, they put pressure
on themselves and each other. When the
forces get great enough, the crust is forced
to break.
Face partners,
Beginning with A
What causes earthquakes?
The stress is released as energy moves
through the Earth in the form of waves,
called seismic waves.
Where do earthquakes occur? Almost 80%
of the Earth’s earthquakes occur along the
Ring of Fire which circles the Pacific Ocean.
Plate movements usually happen far below
ground. The point beneath the Earth’s
surface where the rocks break is called the
focus – the origin of the earthquake.
Directly above this on the Earth’s
surface is the epicenter. During an
earthquake, the most violent shaking
is found at the epicenter.
Earthquakes also occur on the floor of the
ocean. These earthquakes often produce
giant waves called tsunamis.
A seismograph measures the strength
and duration of an earthquake.
The size of the earthquake is called
its magnitude.
The strength of the earthquake is rated
using a Richter scale.
Round Robin
Beginning
with #2
What did you
learn
about
earthquakes?
A volcano is an opening in the Earth’s
crust through which steam, lava, and
ashes erupt.
When magma (molten rock) gets close
to the surface, it collects in magma
chambers.
Magma and hot gasses continue to
collect in these magma chambers until the
pressure gets too great for the chamber
to hold any more. Then it erupts.
When magma
reaches the
Earth’s surface,
it is called
lava.
Shoulder partner
Beginning with B
What causes volcanoes?
Where do volcanoes occur?
• Divergent plate boundaries: the
plates of the Earth pull apart
Magma seeps up and fills the gap.
Most volcanoes occur at divergent
Plate boundaries. Most of them are
Located under the ocean
• Convergent plate boundaries: the
plates of the Earth come together.
One plate slides under the other
(subduction), leaving a gap for magma
to leak out
• Hot Spots:
localized areas of
hot, rising molten
magma material.
The magma melts
away the oceanic
crust and erupts
to build an active
volcanic island
The Ring of Fire surrounds the Pacific
Ocean, formed at convergent boundaries.
The Ring of Fire has more earthquakes and
volcanoes than any other place on earth.
Face partners
Beginning with A
Where do volcanoes occur?
How are volcanoes classified?
• Active volcanoes: erupt continually
or periodically (every once in a while
• Dormant volcanoes: have not
erupted during modern times, but are
now inactive
• Extinct volcano: have not erupted
within modern history and are not
expected to ever erupt again.
Shoulder partners,
Beginning with B
Explain the 3
Classifications of
volcanoes