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

Planet EarthSection 2 Key Ideas 〉 Where do most earthquakes occur? 〉 How do scientists learn about earthquakes and the Earth’s interior? 〉 What is a volcano?

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

Planet EarthSection 2 What are Earthquakes? 〉 Where do most earthquakes occur? 〉 By looking at maps showing past seismic activity, one can see that earthquakes occur mostly at the boundaries of tectonic plates, where the plates move with respect to each other.

Planet EarthSection 2 What are Earthquakes? continued Earthquakes occur at plate boundaries. –Earthquakes are vibrations resulting from rocks sliding past each other at a fault. –Seismic waves are waves of energy released during an earthquake. focus: the location within Earth along a fault at which the first motion of an earthquake occurs epicenter: the point on Earth’s surface directly above an earthquake’s starting point, or focus

Planet EarthSection 2 Focus and Epicenter

Planet EarthSection 2 What are Earthquakes? continued Energy from earthquakes is transferred by waves. –The energy released from an earthquake is measured as shock waves. –Earthquakes generate three types of waves: Longitudinal waves, also known as P waves Transverse waves, also known as S waves Surface waves

Planet EarthSection 2 What are Earthquakes? continued –Longitudinal waves travel by compressing and stretching crust. They are also called primary waves (P waves). –Transverse waves travel in an up and downward movement. They are also called secondary waves (S waves).

Planet EarthSection 2 Visual Concept: Longitudinal Waves

Planet EarthSection 2 Visual Concept: Transverse Wave

Planet EarthSection 2 What are Earthquakes? continued Waves move through Earth and along its surface. –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 and has a stronger effect near the surface of the medium than it has in the interior

Planet EarthSection 2 Visual Concept: Seismic Waves: Surface Waves

Planet EarthSection 2 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.

Planet EarthSection 2 Measuring Earthquakes, continued Seismologists detect and measure earthquakes. –Seismologists use sensitive equipment called seismographs to record data about earthquakes. –Records of seismic activity are called seismograms. seismology: the study of earthquakes including their origin, propagation, energy, and prediction

Planet EarthSection 2 Visual Concept: Seismographs and Mapping Earth’s Layers

Planet EarthSection 2 Measuring Earthquakes, continued Three seismograph stations are necessary to locate the epicenter of an earthquake. –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.

Planet EarthSection 2 Measuring Earthquakes, continued Geologists use seismographs to investigate Earth’s interior. –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.

Planet EarthSection 2 Measuring Earthquakes, continued The Richter scale is used to measure earthquakes. –Although the Richter scale was used popularly for much of the 20 th century, scientists today more often use other scales, such as the moment- magnitude scale. Richter scale: a scale that expresses the magnitude of earthquakes

Planet EarthSection 2 Measuring Earthquakes, continued Magnitude scales alone cannot predict how severe an earthquake will be. –Many factors, such as distance from the focus and local construction techniques, affect how much damage an earthquake will cause. Scientists are trying to predict earthquakes. –Scientists are trying to measure changes in Earth’s crust that might signal an earthquake. –The ability to predict an earthquake could save thousands of lives.

Planet EarthSection 2 Volcanoes 〉 What is a volcano? 〉 A volcano is any opening in Earth’s crust through which magma has reached Earth’s surface. crust: an opening in the surface of Earth through which volcanic material passes

Planet EarthSection 2 Visual Concept: Magma and Vents

Planet EarthSection 2 Volcanoes Shield volcanoes have mild eruptions. –Shield volcanoes are some of the largest volcanoes. Composite volcanoes have trapped gas. –Composite volcanoes are made of alternating layers of ash, cinders, and lava. –Composite volcanoes are usually very steep. Cinder cones are the most abundant volcanoes. –Cinder cones are the smallest and most abundant volcanoes.

Planet EarthSection 2 Volcanoes

Planet EarthSection 2 Visual Concept: Types of Volcanoes

Planet EarthSection 2 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.

Planet EarthSection 2 Ring of Fire

Planet EarthSection 2 Volcanoes, continued Underwater volcanoes occur at divergent plate boundaries. –As plates move apart at divergent boundaries, magma rises to fill the gap. –This magma creates the volcanic mountains that form ocean ridges. –Iceland is a volcanic island on the Mid-Atlantic ridge that is growing outward in opposite directions.

Planet EarthSection 2 Volcanoes, continued Volcanoes occur at hotspots. –Some volcanoes occur in the middle of plates. –Mantle plumes are mushroom shaped trails of hot rock that rise from deep inside the mantle, melt as they rise, and erupt from volcanoes at hot spots at the surface. –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.

Planet EarthSection 2 Visual Concept: Hot Spots and Mantle Plumes