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Earthquakes and Volcanoes: Shaking Ground and Erupting Mountains

Learn about earthquakes and volcanoes, including their causes, effects, and how they are measured. Discover the different types of volcanic eruptions and the devastating impact they can have. Explore the seismic waves and the tools used to study earthquakes. Understand the importance of predicting and preparing for these natural disasters.

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Earthquakes and Volcanoes: Shaking Ground and Erupting Mountains

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  1. Chapter 11 Earthquakes and Volcanoes

  2. Earthquakes • The shaking caused by the sudden movement of the crust • Scientists estimate that over one million earthquakes happen every year. • Approximately one earthquake every thirty seconds. • Most so small that no one notices them are recorded by seismographs.

  3. Several thousand per year actually move the surface of the Earth. • About 20 per year cause severe changes in the Earth’s surface. • These have the potential to cause serious damage to buildings and dramatic loss of life in populated areas.

  4. Seismic Waves • Waves travel from the break outward. • Main cause is faulting. • If they occur on the ocean floor they can cause giant waves called tsunamis • Travel at 700-800km/hr • 10 to 20 meters high when they hit the coast.

  5. Seismic Waves • Focus- where the rocks break • below ground • Epicenter- the surface directly above the focus. • Where shaking is worst

  6. Seismic waves • Three types • Primary waves- P waves • Fastest • Travel through solid, liquid, and gases • Pressure wave • Secondary waves- S waves • slower • Don’t go through liquids • Shear waves - side to side

  7. Seismic waves • Surface waves- L waves • slowest • Move like ocean waves - rise up and down • cause the most damage

  8. Seismograph • Detects and measures seismic waves • Seismogram is the record made by it • Studied by a seismologist • Flat line - no motion • Bigger waves, stronger quake

  9. Richter scale • How we compare the strength of earthquakes • Not a machine • Number from 1 to 10 • Higher number stronger earthquake. • Every 1 number higher is 10 times stronger • Bigger than 6 very destructive

  10. Predicting Earthquakes • To be useful must predict • where • when • how strong • Not very good • make buildings differently in earthquake areas • Trying by measuring motion of earth, speed of waves, tilt of earth, electricity

  11. Volcanoes • Magma- melted rock below the surface • Lava- when it reaches the surface • Volcano - where lava reaches the surface • Lava lets us see what is below the crust • Different types of lava • Dark colored, runny lava flows quietly • Light colored hardens inside, pressure builds and it explodes. • Gas bubbles can form pumice and scoria

  12. Rock fragments • Thrown out in eruptions • Different sizes • Volcanic dust- like flour • Volcanic Ash- grains of rice • Cinders- about the size of a golf ball • Volcanic bombs- a few centimeters to several meters across

  13. Types of Volcanoes • Three different types • Cinder cone formed by piling up rock fragments from explosive eruptions • Narrow base and steep sides • Shield volcanoes runny lava pouring out covers the ground in layers • large area, gentle slope - Hawaii

  14. Types of Volcanoes • Composite Volcano- Alternating layers of rock caused by alternating types of eruptions • Explosive lays down rocks • then covered by lava, • Another explosion, • More lava • etc. • large cone shaped mountain forms

  15. Volcano Parts • Vent- The pipe that the lava flows through • Crater- funnel shaped pit at the top of a volcano • Caldera- If the walls of the crater collapse and the crater becomes very large.

  16. Volcano Zones • Ring of Fire- all the way around the Pacific Ocean • Through the Mediterranean Sea • Mid-Atlantic Ridge- Underwater Mountain range down the middle of the Atlantic Ocean

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