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Earthquakes and Volcanoes Unit D Chapter 1 Lesson 3 Pgs D22-D29 • 95% of earthquakes occur near faults, cracks in the earth’s crust. • When plates grind past each other they lock up, bend and stretch, and eventually snap releasing the energy. • This sudden jolt releases energy as vibrations that are felt as Earthquakes. Earthquakes Overpasses are not the ideal place to be during an earthquake. • The focus is the point inside earth’s crust where the movement starts. • The epicenter is the point on the surface directly above the focus. • A seismograph is an instrument that detects earthquake waves. • A seismogram is the recording of the earthquake on paper or in a computer. Earthquakes • The energy from an earthquake travels away from the focus in waves. • The P-Wave or “Primary Wave” is the first wave. It is the fastest wave and causes push-pull motion. • The S-Wave or “Secondary Wave” is second. It is an up and down, slower wave in the earth. • The last wave is the “Surface Wave.” It travels on the surface and makes the ground roll and sway. The most damaging wave. Earthquakes • Scientists measure earthquakes in different ways. • The Richter Scale measures the amount of energy released during an earthquake. • The largest earthquake recorded was 9.5 on the Richter Scale in Chile, 1960. • An earthquake in Indonesia in 2005 measured 9.1 on the Richter Scale. The resulting tsunami killed 230,000 people. The 2005 Indonesian Tsunami Measuring Earthquakes • The Mercalli Intensity Scale measures the amount of damage done. • The Mercalli scale goes from I to X11. • An earthquake with an intensity of I is hardly felt. An intensity of XII means complete destruction. There are more than 900,000 earthquakes with a magnitude less than 2.5 each year. Measuring Earthquakes • A volcano is a mountain that forms around openings in earth’s crust where lava builds up. • Volcanoes are earth’s chief land builders. • The Ring of Fire is a 30,000 mile long chain of volcanoes that surrounds the Pacific Ocean. Volcanoes School bus vs. lava…..lava wins. House vs. lava…..lava wins • Shield Volcanoes- have a broad and slightly domed shape. • They are the world’s largest volcanoes. • They may erupt for over 1 million years. • They typically have “gentle” eruptions of runny lava. Mauna Loa in Hawaii is the world’s largest active volcano. Types of Volcanoes • Cinder Cone Volcanoes are built up of ashes, cinders and rocks from violent eruptions. • Most erupt for a short period of time and end up no taller than 1000ft. • They are typically steep sided with a flattened top. A cinder cone volcano…it’s made of cinders…..and it’s a cone shape…..brilliant. Types of Volcanoes • Composite or Stratocone Volcanoes switch between quiet eruptions of flowing lava and violent gas explosions. • This type of volcano has the most powerful eruptions of all. • Like shield volcanoes, composite volcanoes may erupt for up to one million years. Mt. St. Helens is a Stratocone Volcano Types of Volcanoes • Not all volcanoes form at the edges of plates. • Sometimes a single column of magma called a hot spot punches through the middle of a plate. • If this happens under the ocean, the build up of lava can get high enough to form islands. • The Hawaiian islands were formed by a hot spot. Hot Spot Volcanoes