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Earthquakes and Volcanoes

Earthquakes and Volcanoes. Chapter 19 Section 2. Objectives. Identify the causes of earthquakes Distinguish between P waves, S waves, and Surface waves Describe how earthquakes are measured and rated Explain how and where volcanoes occur Describe the different types of common volcanoes.

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Earthquakes and Volcanoes

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  1. Earthquakes and Volcanoes Chapter 19 Section 2

  2. Objectives • Identify the causes of earthquakes • Distinguish between P waves, S waves, and Surface waves • Describe how earthquakes are measured and rated • Explain how and where volcanoes occur • Describe the different types of common volcanoes

  3. Key Terms • Focus • Epicenter • P waves • S waves • Surface waves • Seismology • Richter Scale • vent

  4. What are earthquakes? • Rocks sliding past each other along a fault • There are major and minor faults • Major faults occur at plate boundaries • Minor faults may be found anywhere forces are strong enough to break the rocks

  5. At the plate boundaries Japan California • Has many earthquakes • Have major plate boundaries • Pacific Plate to Asia Plate • Oceanic and continental • Convergent boundary • Has many earthquakes • Have major plate boundaries • Pacific Plate to USA Plate • Oceanic and continental • Transform Fault boundary

  6. Where are the earthquakes generated? • The earthquake begins deep in the earth where stresses fracture the rock • This is the focus of the earthquake • The waves are generated by this breaking • P waves travel the fastest • S waves are next • Surface Waves are slowest • All travel outward from the epicenter at the surface

  7. Seismology • The measurement of earthquakes • Seismographs are machines that measure earthquake movements or waves • Page 620, figure 19-15, shows the arrival time of P, S, and Surface Waves • Three seismograph machines at separate locations may be used to “triangulate” where the quake occured

  8. The Richter Scale • Used to measure the strength of an earthquake • There are many more “small” earthquakes than “large” earthquakes, (see table 19-1, p621)

  9. Volcanoes • A vent is an opening in Earth’s crust through which magma becomes lava • The movement of tectonic plates sometimes triggers eruptions • Subduction zones, or • Hot Spots in the crust • There are three basic types of volcano • Shield • Composite • Cinder Cone

  10. Shield Volcanoes • They are built up on layer after layer of lava • Eruptions are not very explosive, (less gassy) • A wide “footprint” with a gentle slope • The magma is rich in iron and magnesium • Lava flows for great distances, it is very fluid

  11. Cinder Cone Volcanoes • The smallest type of volcano and the most abundant. • The magma is “very gassy” • There are large quantities of ash and cinders that form a tall, steep cone • They may grow thousands of feet in a very short time • Active for a short time, then dormant

  12. Composite Volcanoes • Are made of alternating layers of lava, cinders and ash • Magma is much richer in silica, making it much thicker • Gases can be trapped in the magma causing explosive eruptions • Typically the tallest of all types of volcano • May become active after a long dormancy

  13. Composite Cinder cone

  14. Where to find volcanoes… • Volcanoes occur at: • Convergent plate boundaries • The crust melts at subduction zones causing volcanoes • Silica rich, (sandy), lava is explosive • The Cascade Volcano Range • Divergent plate boundaries • Known as rifts, (Iceland) • Hot Spots • Caused by hotter magma that rises and melts the crust above • Hawaiian Islands

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