 Where do most earthquakes occur?  How do scientists learn about earthquakes?  What is a volcano?

 Most earthquakes occur at boundaries of tectonic plates.

 As plates move, their edges experience stress.  Eventually, the stress becomes so great that it breaks rock along the fault line.  Energy is released as seismic waves.

 The exact point inside Earth where an earthquake originates is the focus.  The point on the surface directly above the focus is the epicenter.

 Energy released by an earthquake is measured as shock waves.

 Earthquakes generate three types of waves: 1.Longitudinal waves ◦ moves fastest, ◦ 1 st wave ◦ Aka – Primary wave or P-wave ◦ Compression wave

 Earthquakes generate three types of waves: 2. Transverse Wave - slower than p-wave - 2 nd wave - Aka – Secondary wave or S-wave - Doesn’t travel thru liquids - Transverse Wave

 Earthquakes generate three types of waves: 3. Surface Waves - slowest wave - 3 rd wave - Aka – seismic wave or l wave - Moves only across Earth’s surface - Most destructive

 Scientists use seismographs to determine the epicenter of an earthquake.

 Geologists use earthquakes to study Earth’s interior.

 Scientists use two scales to measure the effects of earthquakes. ◦ Richter Scale – measures magnitude ◦ Mercalli Scale – measures intensity ◦ us/ us/

 A volcano is any opening in the Earth’s crust through which magma has reached the Earth’s surface.  These openings are called vents.

 There are three main types of volcanoes: 1. Shield Volcanoes 2. Composite Volcanoes 3. Cone Volcanoes

 Volcano formed from a buildup of magma/lava rich in iron and magnesium.  Shield volcanoes are some of the largest volcanoes.

 Example: Mauna Loa in Hawaii 13,000 ft. above sea level – 30,000 ft above sea floor

 Composite volcanoes are made from alternating layers of ash, cinders, and lava.  Eruptions alternate between lava flows and explosive activity.  Typically thousands of meters high and much steeper than shield volcanoes.

 Example: Mt. Fuji, Mt. Hood, Mt. Rainier, Mt. St. Helens

 Cinder cone volcanoes are the smallest and most abundant volcanoes.  Usually active for a short period of time, then dormant.

 Example: Paricutin, Mexico

 Most occur at convergent plate boundaries.  Around the Pacific Plate is known as Ring of Fire.  75% of the active volcanoes in the world are located around Ring of Fire.

 Underwater volcanoes occur at divergent plate boundaries.  Example: Iceland (Mid Atlantic Ridge)

 Volcanoes also occur at hot spots.  Mantle plumes rise from deep within the mantle and erupt at hot spots at the surface.  Example: Hawaii   earth-was-made/videos/the-krakatoa- volcano#the-krakatoa-volcano earth-was-made/videos/the-krakatoa- volcano#the-krakatoa-volcano

1. Where do most earthquakes occur? 2. What is the difference between the epicenter and focus of an earthquake? 3. Identify and describe the three type of volcanoes. 4. Why do surface waves cause the most damage in an earthquake? 5. Why might a sudden increase in the number of earthquakes around a volcano indicate a possible eruption?