• What causes earthquakes?• What causes volcanoes to form?• How do earthquakes and volcanoes

change Earth’s surface?

Earthquakes and Volcanoes

• earthquake• fault• mid-ocean ridge• hot spot

Earthquakes and Volcanoes

• lava flow• volcanic ash• caldera

• Because tectonic plates move very slowly, most changes to Earth’s surface take a long time.

• But some changes occur very quickly and violently.

• An earthquake is the rupture and sudden movement of rocks along a break or a crack in Earth’s crust.

Earthquakes

An earthquake can change Earth’s surface quickly and dramatically.

Dr. Roger Hutchinson/NOAA

• The surface along which the crust moves is called a fault.

• When pieces of crust slide past each other, energy is released, causing the ground to shake.

Earthquakes (cont.)

Photograph by N.J. Silberling, USGS Photo Library, Denver, CO

• Most earthquakes begin in the lithosphere within about 100 km of Earth’s surface.

• The focus is the area beneath Earth’s surface where rock that is under stress breaks, triggering an earthquake.

• The point on the surface directly above the focus is called the epicenter.

Earthquakes

• Earthquakes release energy in the form of vibrations or waves.

• Body waves move through the Earth's interior traveling much more quickly than surface waves.

• Surface waves move over Earth's surface.

Earthquakes

• Primary or P waves are the first energy waves that arrive after an earthquake occurs. They travel through both solids and liquids in a push-pull, linear motion, similar to an earthworm.

• Secondary or S waves are the second energy wave that travels through the interior of Earth. They can only travel through solids in an up and down motion.

Earthquakes-Types of Body Waves

• Love or L waves: originate at the epicenter of an earthquake and arrive after the secondary waves. They are responsible for the most damage

• Rayleigh waves are a second type of surface wave that arrive at a location distant from the epicenter. They travel in a backwards elliptical motion.

Earthquakes-Types of Surface Waves

Most earthquakes occur near plate boundaries, though some occur very far from plate boundaries.

• Earthquakes can create new landforms such as mountains.

• Compression and tension forces produce ridges and mountains as Earth’s crust moves vertically.

Earthquakes (cont.)

• Liquefaction refers to when extreme shaking causes ground that is made up of loose sediment to behave more like a liquid than a solid.

• Earthquakes can trigger landslides, which bring rocks and soil from the tops of mountains into valleys.

Earthquakes (cont.)

Earthquakes that happen underwater can cause tsunamis—huge ocean waves created by movement at a fault.

Earthquakes (cont.)

• Volcanoes are landforms that form when magma erupts onto Earth’s surface as lava.

• Volcanoes can occur at divergent and convergent plate boundaries and at hot spots.

• There are approximately 1,500 active volcanoes on Earth.

Volcanoes

The mountains that form as lava from a volcano at a divergent boundary builds up and cools are called mid-ocean ridges.

At some convergent boundaries, one tectonic plate sinks, melts the mantle, and forms magma that erupts onto the plate that does not sink.

• Hot spots are locations where volcanoes form far from plate boundaries.

• When a hot spot is under oceanic crust, it will form islands such as the Hawaiian Islands.

• When a hotspot is under continental crust, it will form a geyser like Old Faithful at Yellowstone National Park in Wyoming.

Volcanoes (cont.)

• Because magma is hot, it is also less dense than the rock material around it.

• Rising magma and great pressure caused by dissolved gases eventually erupt through cracks in Earth’s surface, creating a volcano.

Volcanoes (cont.)

Most of Earth’s largest volcanoes are located at convergent plate boundaries.

• When melted mantle material erupts, it flows over Earth’s surface, creating long streams of molten rock called lava flows.

• The lava eventually cools and solidifies, forming solid rock.

Volcanoes (cont.)

Royalty-Free/CORBIS

• At convergent plate boundaries, part of the continental crust can become mixed with magma from the mantle.

• When this mixture of molten materials erupts, it does not flow as easily as lava made only of melted mantle.

• Instead of forming lava flows, it often solidifies in the atmosphere, where it breaks into small pieces of lava called volcanic ash.

Volcanoes (cont.)

• Eruptions that eject ash high into the atmosphere are called explosive eruptions.

• Lava also can be produced during these eruptions.

Volcanoes (cont.)

Before a volcano erupts, magma builds up in the crust in a reservoir called a magma chamber.

• Shield volcanoes form after basaltic lava flows have occurred over time.

• Shield volcanoes tend to be large with gentle slopes, such as Mauna Loa in Hawaii.

J.S. Griggs/U.S. Geological Survey

• Composite volcanoes form as lava flows and ash layers deposited by explosive eruptions build up.

• Composite volcanoes often have steep sides and a cone shape.

PhotoLink/Getty Images

Sometimes the surface above the chamber collapses, creating a large depression in the center of the volcano called a caldera.

P.W. Lipman, U.S. Geological Survey

• Volcanic ash and gases from explosive eruptions can blow high into the atmosphere, blocking sunlight.

• This can cause the temperature of the atmosphere near Earth’s surface to decrease.

P.W. Lipman, U.S. Geological Survey

• Earthquakes occur when movement along a fault occurs. Earthquakes occur mostly along plate boundaries. They can cause great damage.

• Volcanoes form at two types of plate boundaries. Lava cools and builds up, forming volcanoes and other landforms.

• Earthquakes and volcanoes change the surface by building mountains, covering land with lava, and shifting the surface along faults.

27. Which happens when extreme shaking causes sediment to behave more like a liquid than a solid?A. compressionB. eruption C. liquefaction D. tsunami

A. mid-ocean ridgeB. lava flowC. faultD. caldera

28. Which is a long stream of molten rock which eventually cools, solidifies, and builds up over time as flat layers?

A. calderaB. compositeC. mid-oceanD. shield

29. Which type of volcano often has steep sides and is cone shaped?

30. Earthquakes occur and volcanoes erupt only near plate boundaries.

31. Volcanoes erupt melted rock.

Do you agree or disagree?