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Download 1-10 levels at which an earthquake
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And Earthquakes • Shaking and trembling of the earth’s crust. • The waves travel in all directions • More than 1,000,000 occur a year or one every 30 seconds • Faulting is the most common cause • Earthquakes continue until all the energy is used up • TSUNAMIS- earthquake on the ocean floor: causing waves to become greater than 20 meters high Seismic Waves FOCUS underground point of origin EPICENTER- above ground origin; most violent shaking occurs at the epicenter Types of Waves • Three main types of seismic waves are: P waves, S waves and Surface Waves P Waves • Primary waves • Arrive first at the epicenter • Can travel through solids, liquids, and gases • They are pushpull waves S Waves • Secondary waves • Can travel through solids, but NOT through liquids and gases • Move in up-down motion Surface Waves • Slowest moving seismic waves • Travel on top of Earth’s surface • Cause most of damage to Earth, because they bend and twist the surface Normal Fault • Tension force • Stretching or pulling force • Occurs at divergent boundary • Blocks of crust that are pulled away from each other slide along normal faults Reverse Fault • Compression force • Force pushing something together • Occurs at a convergent boundary • Blocks of crust that are pushed together slide along Reverse Faults • Strike Slip Force • Shear force • Force that operates against a body from different sides • Occurs at a transform boundary • Blocks of crust slide horizontally past each other. John Milne- 1893 Seismograph measures and detects seismic waves Seismogram Paper record of waves Seismologist scientist who study earthquakes Richter Scale a scale that allows scientists to determine earthquake strength based on many readings 1-10 levels at which an earthquake is measured on amount of damage caused; Above a 6 is very destructive VOLCANOES Volcano place on Earth’s surface that allows magma and other material to erupt Magma found beneath the Earth’s surface, it is liquid rock Lava magma that reaches the Earth’s surface Volcanic Fragments Volcanic Dust • less that 0.25 mm in diameter (flour) Volcanic Ash • more than 0.25 less than 5 mm (rice) Volcanic Bombs • few cm to several meters Cinder • volcanic bombs the size of golf balls Types of Volcanoes Cinder Cones made of mostly of cinders; formed from explosive eruptions Shield of quiet lava flows, world’s largest volcanoes Composite made up of alternating layers of rock particles; explosive eruptions, then quiet lava flows Composite Volcano Shield Volcano Cinder Cone Volcano Hot Spot Volcanoes- Hawaiian Islands Types of Lava Viscosity • how lava flows • High viscosity is stiff • Low viscosity is more fluid Aa Lava • Pours out quickly and forms a brittle crust, crust torn into jagged pieces as molten lava continues to flow underneath Pahoehoe • Lava flows slowly, like wax dripping from a candle. Glassy surface with rounded wrinkles Pillow Lava • Forms when lava erupts underwater. Forms round lumps (often shape of pillows) Blocky Lava • Cool, stiff lava that does not travel far from the erupting vent. Oozes and forms piles of sharpedged chunks Volcanic Terminology Crater Caldera • Funnel shaped pit, or depression at the top of a volcano • When a crater becomes too large, it collapses: also can form when the top of a volcano collapses or explodes Dormant Extinct Active • sleeping volcano • not known to have erupted in modern history • Erupts fairly regularly Ring of Fire Water content • Higher water content more likely to have explosive eruption Benefits of volcanoes • Despite the dangers, humans do benefit from volcanoes. • Rock from lava is used in roads • Pumice is used for polishing items • Weathered volcanic ash improves soil • In some areas, volcanic steam is used for heat EXTRA! EXTRA! • Mount St. Helens is a volcano in Washington State • San Andreas Fault in California • New Madrid Fault is where we live