1. Earthquakes and Volcanoes! Oh my!

2. Stress Stress: a force that acts on rock to change its shape or volume 3 Types of Stress (happens in the crust): –Tension: pulls on the crust –Compression: squeezes until folded or breaks –Shearing : pushes rocks in opposite directions

4. Faults Faults: the point where rocks break Ex. San Andreas fault 3 Types of faults: –Normal faults: form where rocks are angled with each other; one block or rock lies below the other –Reverse faults: are like normal faults but move in the opposite direction –Strike-slip faults: form when rocks slide past each other

5. Faults

6. Faults: What kind am I?

7. Earthquake Earthquake: shaking & trembling that results from the movement of rock below Earth’s surface Forces of the plates causes earthquakes. Most start in the lithosphere. Focus: area beneath the Earth where the stress occurs & rock breaks Epicenter: point on the surface directly above focus

9. Seismic Waves Seismic waves: vibrations that travel through Earth carrying energy released during an earthquake Seismic waves carry energy from an earthquake away from the focus, through Earth’s interior, and across the surface.

10. Types of Seismic Waves P Waves- compress & expand (back & forth) the ground like an accordion, can damage buildings, travels through solids and liquids S Waves- the crust vibrates from side to side & up and down, shake the ground back and forth, travels through solids Surface Waves- P and S waves that reach the surface. Move very slowly in a wavelike motion

12. Measuring Earthquakes Mercalli Scale-based on level of damage (slight damage, moderate damage, great damage) Richter Scale-based on magnitude based on the size of the earthquake’s seismic waves, good for small, near-by quakes Seismograph- instrument that records the size of the seismic waves Moment Magnitude Scale-estimates total energy released

13. seismograph

17. Volcano Volcano: weak spots in the crust where molten rock (magma) comes to the surface Magma: molten mixture of rock, gases & water from the mantle Volcanoes form when plates converge & diverge (on land & on ocean floor)

18. Island Arcs Island arc: a string of islands formed by the volcanoes along a deep ocean trench (oceanic plates converge) Ex. Japan, New Zealand

19. Hot Spot Volcanoes Hot spot: an area where material from deep inside the mantle rises & then melts A volcano forms above a hot spot when magma erupts through the crust & reaches the surface. Ex. Hawaii

20. Viscosity Viscosity: the resistance of a liquid to flowing (a property of magma) –The greater the viscosity, the slower it flows (ex. honey) –The lower the viscosity, the faster it flows (Ex. water)

21. Viscosity of Magma depends on: silica content & temperature Silica-compound made of silicon & oxygen More silica, higher the viscosity Silica produces light colored magma that is sticky

22. Viscosity increases as temperature decreases Pahoehoe (pah Hoh ee hoh ee):fast moving, hot lava with low viscosity. Produces lava mass with ripples & wrinkles when it hardens Aa (AH ah): slow moving, cooler lava with high viscosity. When it hardens, it forms huge, jagged chunks.

23. Pahoehoe Aa

24. Parts of a Volcano Magma chamber-collection of magma under a volcano Pipe-long tube in the ground that connects the surface to the magma chamber Vent-opening that magma exits through Lava flow-area covered by lava Crater-bowl-shaped area at the top

26. Types of Eruptions Quiet eruptions -magma has low silica content, high viscosity, slow moving Explosive eruptions -magma has high silica content, low viscosity, fast moving –Pyroclastic flow-eruption which hurls hot gases, ash, cinder, and bombs

28. Volcanic Landforms Caldera-huge hole left by the collapse of a volcano (the magma chamber collapses) Volcanic neck-when magma hardens in a volcanic pipe (soft rock wears way exposing the hard rock) Dike-rock layer forming vertically Sill-rock layer forming horizontally Batholith-a large body of cooled, exposed magma

29. Caldera (Crater Lake) in Iceland Devil’s Tower in Wyoming