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Bell Ringer
• What is subduction? At what kind of plate
boundary does subduction take place?
Earthquakes
• When rocks slide past one another (transform
boundary) vibrations occur which are called
earthquakes.
• Earthquakes occur at the boundaries of
tectonic plates.
• If plates cannot move freely past each other
stress builds up until the rocks can break free.
Earthquakes
• Focus- the exact point inside the Earth where
the earthquake started.
• Epicenter- the point on the Earth’s surface
directly above the focus.
Earthquakes
• We already know P waves and S waves carry
energy during earthquakes.
• Surface waves move only across Earth’s
surface. These waves happen as a result of
Earth’s mass shaking like a bell. These are the
most destructive waves.
Earthquakes
• Seismology- the study of earthquakes.
Seismologists use seismographs to measure
earthquakes.
Earthquakes
• Richter scale- how scientists measure
earthquake strength. The scale is from 1 to
10. Each step in the scale is a 30 fold increase.
Volcanoes
• A volcano is an opening in Earth’s crust
through which magma travels to Earth’s
surface.
• Openings in the Earth’s crust are called vents.
• Ash is made of molten rock, small rock, and
mineral particles.
Bell Ringer
• Volcanoes occur when there is an opening in
the Earth’s ____________.
• These openings are called ___________.
Volcanoes
• Shield Volcanoes
– Magma is rich in Fe and Mg so it flows long
distances.
– Eruptions aren’t very explosive and can occur
several times.
– Gently sloping mountains
– Some of the largest volcanoes
Volcanoes
• Composite Volcanoes
– Made of layers of ash, cinders, and lava
– Magma is thick and rich in silica
– Eruptions alternate between lava flows and
explosions.
– Typically tall with steeper slopes.
Volcanoes
• Cinder Cones
– These are the most common and the smallest
volcanoes
– Large amounts of gas become trapped in the
magma and violent eruptions happen.
– Ash and lava are thrown from the vent. It falls
down and forms the cone shape.
Volcanoes
• The Ring of Fire is around the edges of the
Pacific Ocean where there is a convergent
plate boundary. 75% of active volcanoes are
found here.
• Underwater volcanoes happen at divergent
boundaries.
• Iceland is a volcanic island that is expanding
from the center.
Bell Ringer
• What are the three types of volcanoes?
• Sketch an example of each.
Bell Ringer
• Which country is expanding from its center
due to volcanic activity?