Download Earthquakes and Volcanoes

Earthquakes and
Volcanoes
Unit D Chapter 1 Lesson 3
Pgs D22-D29
• 95% of earthquakes occur
near faults, cracks in the
earth’s crust.
• When plates grind past each
other they lock up, bend and
stretch, and eventually snap
releasing the energy.
• This sudden jolt releases
energy as vibrations that are
felt as Earthquakes.
Earthquakes
Overpasses are not the ideal
place to be during an
earthquake.
• The focus is the point inside
earth’s crust where the
movement starts.
• The epicenter is the point on
the surface directly above
the focus.
• A seismograph is an
instrument that detects
earthquake waves.
• A seismogram is the
recording of the earthquake
on paper or in a computer.
Earthquakes
• The energy from an earthquake
travels away from the focus in
waves.
• The P-Wave or “Primary Wave”
is the first wave. It is the fastest
wave and causes push-pull
motion.
• The S-Wave or “Secondary
Wave” is second. It is an up and
down, slower wave in the earth.
• The last wave is the “Surface
Wave.” It travels on the surface
and makes the ground roll and
sway. The most damaging wave.
Earthquakes
• Scientists measure earthquakes
in different ways.
• The Richter Scale measures the
amount of energy released
during an earthquake.
• The largest earthquake
recorded was 9.5 on the
Richter Scale in Chile, 1960.
• An earthquake in Indonesia in
2005 measured 9.1 on the
Richter Scale. The resulting
tsunami killed 230,000 people.
The 2005 Indonesian Tsunami
Measuring Earthquakes
• The Mercalli Intensity
Scale measures the
amount of damage
done.
• The Mercalli scale goes
from I to X11.
• An earthquake with an
intensity of I is hardly
felt. An intensity of XII
means complete
destruction.
There are more than 900,000 earthquakes
with a magnitude less than 2.5 each year.
Measuring Earthquakes
• A volcano is a mountain
that forms around
openings in earth’s crust
where lava builds up.
• Volcanoes are earth’s
chief land builders.
• The Ring of Fire is a
30,000 mile long chain of
volcanoes that surrounds
the Pacific Ocean.
Volcanoes
School bus vs. lava…..lava wins.
House vs. lava…..lava wins
• Shield Volcanoes- have a
broad and slightly domed
shape.
• They are the world’s
largest volcanoes.
• They may erupt for over
1 million years.
• They typically have
“gentle” eruptions of
runny lava.
Mauna Loa in Hawaii is the world’s
largest active volcano.
Types of Volcanoes
• Cinder Cone Volcanoes
are built up of ashes,
cinders and rocks from
violent eruptions.
• Most erupt for a short
period of time and end
up no taller than 1000ft.
• They are typically steep
sided with a flattened
top.
A cinder cone volcano…it’s
made of cinders…..and it’s a
cone shape…..brilliant.
Types of Volcanoes
• Composite or Stratocone
Volcanoes switch between
quiet eruptions of flowing
lava and violent gas
explosions.
• This type of volcano has the
most powerful eruptions of
all.
• Like shield volcanoes,
composite volcanoes may
erupt for up to one million
years.
Mt. St. Helens is a Stratocone Volcano
Types of Volcanoes
• Not all volcanoes form at
the edges of plates.
• Sometimes a single column
of magma called a hot spot
punches through the middle
of a plate.
• If this happens under the
ocean, the build up of lava
can get high enough to form
islands.
• The Hawaiian islands were
formed by a hot spot.
Hot Spot Volcanoes