Chapter 6 Lesson 3

  Earth’s plates bend and break under pressure. Earthquakes p. 246

Vocabulary Fault –a break in the Earth’s crust where rocks can slide past each other. Earthquake-The snap and slide of rocks as energy is released in Earth’s crust. Focus-The point inside Earth where an earthquake begins Epicenter-The point on Earth’s surface directly above the focus of an earthquake

  A fault is the term used when rocks break. A fault is a break in the Earth’s crust where rocks can slide past each other.   Most faults form along plate boundaries but can also form within a plate. Fault

  The point inside the Earth where the earthquake begins.   It can be near the surface or deep within the Earth. Focus

  Plates move; pressure builds up.   Rocks bend and stretch. If they snap, they release energy suddenly in the form of an earthquake. Earthquakes p. 246

  The point on the Earth’s surface directly above the focus of the earthquake Epicenter

  P waves-Primary waves-  Travel through the interior.  Energy travels away from the focus.  P waves are the fastest waves and are the first to be detected.  They compress and expand the ground. (like an accordion) Earthquake Waves

  S waves-Secondary waves-  Travel through the interior  These waves travel across the direction that the P waves are moving.  They move up and down and side to side. Earthquake Waves

  -Surface waves travel along the Earth’s surface.  Some shake the ground from side to side.  Some roll like ocean waves.  Both of these cause most of the damage done to buildings that is done by an earthquake. Earthquake Waves

  Seismographs measure and record motion caused by an earthquake’s energy waves. Measuring Earthquake Strength and Damage p. 250

  Seismographs measure and record motion caused by an earthquake’s energy waves.   The time between the arrival of the P and the S waves is recorded. The more time that elapses, the further away is the epicenter. Measuring Earthquake Strength and Damage p. 250

Richter Scale

  1935, Charles Richter developed a scale to measure earthquake strength.   Uses the size of waves recorded on a seismograph to determine how strong an earthquake is.   Scale estimates the amount of energy released by an earthquake.   2.0 is minor   4.0 can be felt but causes little damage.   6.0 or greater can cause major damage. Richter Scale

  Measures the distance rock along the fault moves. This is used to determine the energy released.   Numbers are similar to the Richter scale but is believed to be more accurate.   Measures earthquake strength. Moment Magnitude Scale

  Measures damage caused.   Uses Roman numerals.   XII means buildings were completely destroyed. Mercalli Intensity Scale

  When an earthquake happens under the ocean the sea floor will rise and fall.   The movement of water can cause a giant wall of water (May be more than 30m.)   May cause massive damage to buildings near shore. Tsunami

Volcanoes

 Some mountains are formed when rocks at convergent boundaries are deformed and lifted.

Volcanoes  Some mountains are volcanoes and are formed when molten rock, or magma is pushed to the surface and builds up.

Volcanoes  Most volcanoes are along the boundaries of plates.

Volcanoes  Some form along divergent boundaries where plates are pulling apart and magma rises to the surface.

Volcanoes  Some form along convergent boundaries where oceanic crust is pushed down.

3 Types of Volcanoes  Shield  Cinder Cone  Composite

Shield Volcano

 Formed by NON-EXPLOSIVE eruptions  Layer after layer builds up slowly.  Broad, slightly dome shaped  May erupt many times

Shield Volcano

Cinder Cone Volcano  Formed by EXPOLSIVE eruptions, composed of ash and rock thrown out of vent  Erode quickly  Steep sides  Erupt for a short period of time.  Few are taller than 300m or 1000 ft.

Cinder Cone Volcano

Composite Volcanoes  Formed by a mixture of explosive and non explosive eruptions  May erupt off and on for many years.

Compostie Volcano

Composite Volcano \

Hawaiian Volcanoes

 These volcanoes are NOT formed at plate boundaries.

Hawaiian Volcanoes  Sometimes magma occurs at another area of a plate, called a hot spot.

Hawaiian Volcanoes The magma pushes up, and if it erupts above the surface, it can form a volcano.

Hawaiian Volcanoes  As the plates move over the hot spot, the volcano that was formed stops erupting and a series of new volcanoes may form.

Hawaiian Volcanoes  If the hot spot lies under the oceanic crust, the series of volcanoes may become a chain of islands.

Hawaiian Volcanoes  The youngest island, Hawai’i, has three active volcanoes.  They have been constantly erupting since 1983.

Hawai’iOahu Kauai