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Earthquakes and Volcanoes! Oh my! 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 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 Faults Faults: What kind am I? 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 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. 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 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 seismograph 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) Island Arcs • Island arc: a string of islands formed by the volcanoes along a deep ocean trench (oceanic plates converge) Ex. Japan, New Zealand 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 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) • 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 • 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. Pahoehoe Aa 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 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 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 Caldera (Crater Lake) in Iceland Devil’s Tower in Wyoming