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July 9, 2013

Landform Geography. Earthquakes and Volcanoes. July 9, 2013. Earthquakes. Sudden release of tectonic stress creates movement in Earth’s crust & shockwaves through lithosphere. Earthquake Processes. Earthquake Energy. Waves released by an earthquake:

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July 9, 2013

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  1. Landform Geography Earthquakes and Volcanoes July 9, 2013

  2. Earthquakes • Sudden release of tectonic stress creates movement in Earth’s crust & shockwaves through lithosphere

  3. Earthquake Processes

  4. Earthquake Energy • Waves released by an earthquake: • P-waves – primary, compressional waves that travel 1.5-8 km/sec • S-waves – secondary, vertical waves that travel 60-70% slower than P waves

  5. Triangulation to Locate ‘Quake Known distance to stations A, B and C shows location of epicenter

  6. Measuring Earthquakes • Richter Scale – logarithmic measure where each whole number represents 10X the shaking of the next smaller number

  7. Faulting • Earthquakes occur along faults – cracks in Earth’s crust where rocks or plates are displaced • Fault Types: • Normal – • Reverse – • Strike-Slip – • Overthrust –

  8. Normal Fault

  9. Reverse Fault

  10. Strike-slip Fault

  11. Movement Movement San Andreas Fault (Transform Fault)

  12. Overthrust fault

  13. 1886 Charleston Earthquake

  14. Volcanoes • Mts or hills w/ a conduit down into upper mantle through which magma, ash & gases are ejected • 3 basic types: • Cinder-cone Volcanoes • Composite (strato) Volcanoes • Shield Volcanoes

  15. Where to find volcanoes • Subduction zones, Sea-floor spreading, and Hot spots

  16. Cinder-Cone Volcanoes • Small, steep-sided volcano made of magma fragments & rock debris from central vent

  17. Composite Volcanoes • Large, steep-sided volcano built up by layers of lava & rock debris – over subduction zones – viscous, silicate magma - explosive eruptions Mt. Fuji Cross Section

  18. Pacific “Ring of Fire” • Concentration of composite volcanoes around the Pacific Basin over subduction zones

  19. Shield and Composite Volcanoes Mauna Loa, Hawaii

  20. Shield Volcanoes • Broad, gentle-sided volcanoes formed from low-silica, low-viscosity magma – lava flows cool & harden to become basalt

  21. Volcanic Output • Volcanic ash consists of powder-size to sand-size particles of igneous rock material that have been blown into the air by an erupting volcano. • An ash field is a geographic area where the ground has been blanketed by the fallout of an ash plume. • Silicosis • Dry ash weighs about ten times the density of fresh snow

  22. Volcanic Ash

  23. Volcanic Lightning • Volcanoes produce 2 kinds of lightning: • First occurs in the smoke • The second is produced by the mouth of the volcano • Not all volcanoes produce lightning

  24. Hot Spots • Stationary points in asthenosphere from which a magma plume intermittently pushes through the crust above • Plates move over hot spots, carrying deposits of basalt with them • Hawaii (& the Emperor Seamount Chain) & Yellowstone have been shaped by hotspots

  25. 70 mya Present Formation of Hawaii Hawaii Kauai Oldest – Big Island (Hawaii) still over hot spot Emperor Seamount Chain 70 M yrs old – Pac. Plate 1st moved North, then NW

  26. Hot Spot Tracks

  27. Calderas from eruptions in past 2 M yrs Yellowstone Hot Spot North American Plate has moved west, then northwest over past 16.5 M yrs

  28. Supervolcano • A supervolcano is an eruption that rates a magnitude of 8 on the Volcanic Explosivity Index. • The VEI is a scale that rates eruptions on their ejected volume, plume height and duration. The scale ranges from 0 through 8. • Only a few dozen eruptions in all of Earth's history are known to have a VEI of 8. • Two of those eruptions, the Lava Creek eruption (640,000 years ago) and the Huckleberry Ridge eruption (2.2 million years ago), occurred at Yellowstone. • These eruptions were given the VEI rating because their ejected volume exceeded 1000 cubic kilometers

  29. Geyser Cross Section

  30. Calderas • Large depression formed when a volcanic mountain collapses after erupting Crater Lake, Oregon

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