Section 2: Earthquakes and Volcanoes Preview  Key Ideas Key Ideas  Bellringer Bellringer  What are Earthquakes? What are Earthquakes?  Measuring Earthquakes Measuring Earthquakes  Volcanoes Volcanoes

Key Ideas Where do most earthquakes occur? What is a volcano? How do scientists learn about earthquakes and the Earth’s interior?

Bellringer Imagine a corked bottle of soda pop that is standing in a pan of hot water. 1. What do you think will happen as the soda pop heats up? 3. Molten rock in Earth’s mantle is like the soda pop. What happens when pressure builds up in Earth’s mantle? 2. What happens when the pressure builds up in the soda pop?

What are Earthquakes? 〉 Where do most earthquakes occur? - mostly at the boundaries of tectonic plates Earthquakes are vibrations resulting from rocks sliding past each other at a fault.

What are Earthquakes? continued  Seismic waves are waves of energy released during an earthquake. Epicenter: the point on Earth’s surface directly above an earthquake’s starting point, or focus Focus: the location within Earth along a fault at which the first motion of an earthquake occurs

Focus and Epicenter

What are Earthquakes? continued  Energy is transferred by waves.  The energy released from an earthquake is measured as shock waves.  3 types of waves:  Longitudinal waves, also known as P waves  Transverse waves, also known as S waves  Surface waves

What are Earthquakes? continued Longitudinal waves - travel by compressing and stretching crust. - (P waves). Transverse waves - travel in an up and downward movement. (S waves).

Visual Concept: Longitudinal Waves

Visual Concept: Transverse Wave

What are Earthquakes? continued  Both P waves and S waves spread out from the focus in all directions through the earth.  Surface waves move only on Earth’s surface.  surface wave: a seismic wave that travels along the surface of a medium  -has a stronger effect near the surface of the medium than it has in the interior

Visual Concept: Seismic Waves: Surface Waves

Measuring Earthquakes 〉 How do scientists learn about earthquakes and the Earth’s interior? 〉 Because energy from earthquakes is transferred by waves, scientists can measure the waves to learn about earthquakes and about the interior of Earth through which the waves travel.

Measuring Earthquakes, continued  Seismologists detect and measure earthquakes.  Three seismograph stations are necessary to locate the epicenter of an earthquake.  Geologists use seismographs to investigate Earth’s interior.  The Richter scale is used to measure earthquakes.

Visual Concept: Seismographs and Mapping Earth’s Layers

Measuring Earthquakes, continued  There are more than 1000 seismograph stations across the world.  Because P waves travel faster, the difference between the arrival of P waves and the arrival of S waves allows scientists to calculate how far away the focus is.  The way P and S waves travel through Earth’s interior helps scientists make a model of Earth with layers of different densities.  Scientists have used this information to develop a model of Earth’s interior structure. Richter scale: a scale that expresses the magnitude of earthquakes

Visual Concept: Magma and Vents Volcanoes 〉 A volcano is any opening in Earth’s crust through which magma has reached Earth’s surface.

Volcanoes  Shield volcanoes have mild eruptions.  are some of the largest volcanoes due to gently sloping sides (not tallest).  Composite volcanoes have trapped gas.  made of alternating layers of ash, cinders, and lava.  usually very steep due to alternating layers  Cinder cones are the most abundant volcanoes.  are the smallest because the steep sides erode quickly.

Volcanoes Visual Concept: Types of Volcanoes

Volcanoes, continued  Most volcanoes occur at convergent plate boundaries.  75% of the active volcanoes on Earth are located in an area known as the Ring of Fire.  The Ring of Fire is located along the edges of the Pacific ocean, where oceanic tectonic plates are colliding with continental plates.

Volcanoes, continued  Underwater volcanoes occur at divergent plate boundaries.  At divergent boundaries, magma rises to fill the gap.  volcanic mountains here will form ocean ridges.  Iceland is a volcanic island on the Mid- Atlantic ridge that is growing outward in opposite directions.

Visual Concept: Hot Spots and Mantle Plumes

 Volcanoes can occur at hotspots.  Some volcanoes occur in the middle of plates.  Mantle plumes -mushroom shaped trails of hot rock from deep inside the mantle. Melt as they rise, and erupt from volcanoes at hot spots.  The plumes remain in the same place as the tectonic plate moves, creating a trail of volcanoes.  The Hawaiian Islands are an example of this type of volcanic activity. Volcanoes, continued