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?