1. Earthquakes and Volcanoes

2. Earthquakes An earthquake is the shaking and trembling that results from the sudden movement of part of the Earth’s crust. The most common cause of earthquakes is faulting. During faulting, energy is released. Rocks continue to move until the energy is used up.

3. Seismic Risk Map of the U.S.

4. San Andreas Fault The San Andreas fault extends 960 km from Mexico to the north of California. The land to the west is moving north. The land to the east of the fault is moving south. All the rocks do not move at the same time so earthquakes occur in one area and then another.

5. San Francisco Quake In 1906, movement along the San Andreas fault caused an earthquake in San Francisco.

6. The Seismograph Invented in 1893 by John Milne, a seismograph detects and measures seismic waves. A weight attached to a spring remains nearly still even when the Earth moves. A pen attached to the weight records any movement on a roll of paper on a constantly rotating drum. The drum moves with the Earth and affects the line.

7. Seismologists Seismologists study earthquakes. They can determine the strength of an earthquake by the height of the wavy line recorded on the paper. The seismograph record of waves is called a seismogram. The Richter scale is used to calculate the strength of an earthquake.

8. The Richter Scale Richter Earthquake Magnitudes Effects Less than 3.5 Generally not felt, but recorded. 3.5-5.4 Often felt, but rarely causes damage. Under 6.0 At most slight damage to well- designed buildings. Can cause major damage to poorly constructed buildings over small regions. 6.1-6.9 Can be destructive in areas up to about 100 kilometers across where people live. 7.0-7.9 Major earthquake. Can cause serious damage over larger areas. 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

9. Predicting Earthquakes Scientists have identified warning signals the help predict earthquakes with greater accuracy. Sometimes slight changes in the tilt of the Earth’s surface can be detected. Some scientists believe animals behavior is affected.

10. Formation of a Volcano

11. Magma Deep within the Earth, under tremendous pressure and at great temperatures, rock exists as a hot liquid called magma. This molten rock is found in pockets called magma chambers.

12. Lava When the magma reaches the surface, it is called lava. The place in the Earth’s surface through which magma and other materials reach the surface is called a volcano. In some places, lava can build up to forma cone-shaped mountain. The opening from which lava erupts is the vent. Volcanoes often have more than one vent.

13. Volcanic Eruptions During volcanic eruptions, many rock fragments are blown into the air. The smallest particles are called volcanic dust. (less than 0.25 mm) Volcanic Ash ( 0.25 -5mm) falls to the Earth and forms small rocks. Volcanic bombs (a few cm to several meters) are molten and harden as they travel through the air.

14. Cinder Cone Volcano

15. Shield Volcanoes

16. Mount Vesuvius

17. Composite Volcano

18. Volcanic Activity Volcanoes are rather unpredictable. Some erupt regularly, others have not erupted in modern history. Scientists classify them as active, dormant or extinct.

19. Volcano and Earthquake Zones Most major earthquakes and volcanic eruptions occur in three zones of the world. Scientists believe that there is a great deal of movement and activity in the Earth’s crust in these three zones.

20. Ring of Fire One major earthquake and volcano zone extends nearly all the way around the edge of the Pacific Ocean. This zone goes through New Zealand, the Philippines, Japan, Alaska and along the western coasts of North and South America. The San Andreas fault is part of this zone.

21. Earthquake Belts