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Volcanoes and Earthquakes For two-column notes, underlined titles are main ideas Volcanoes • Volcanoes – – A mountain that forms in the Earth’s crust when magma (molten material) reaches the surface and cools to form solid rock. When magma reaches the surface, it is called lava Where volcanoes form • At plate boundaries – – At divergent plate boundaries At convergent plate boundaries • where a continental and an oceanic plate meet and the latter is subducted – • Example: Ring of Fire: a belt of volcanoes along the edges of the Pacific plate where two oceanic plate meet – – These often form island arcs, a string of islands Examples: Japan, New Zealand, Caribbean islands Where volcanoes form • Where volcanoes form – At hot spots • • Places where material from the mantle rises through the crust and melts to form magma Hot spots stay in the same place while a plate moves above them – Example: The Hawaiian islands formed from a hot spot under the Pacific plate – Example: Yellowstone National Park is under a hot spot in the state of Wyoming Inside a volcano • Inside a volcano – – – Magma chamber • Pocket where magma collects Pipe • Tube that extends from magma chamber to top of volcano Vent • Opening in volcano (central vent on top; may be several on sides) Inside a volcano • Inside a volcano – Lava flow • Spread of lava as it pours from vent – Crater • Bowl-shaped area that may form around central vent Inside a volcano Draw this and label the diagram Classwork 1 1. 2. 3. 4. 5. 6. At what types of plate boundaries do volcanoes form? What is the difference between magma and lava? What is a hot spot? What is a magma chamber What is a vent? What is a pipe? Volcanic eruptions • • • Dissolved gases in magma expand, forcing magma to flow through pipe and out vent Eruption factors – Silica is a mineral composed of the elements oxygen and silicon and is found in magma – Temperature determines whether lava is thick or thin Types of Eruptions – Quiet Eruptions – Explosive Eruptions Volcanic eruptions • Quiet eruptions - hazards – • Lava sets fire to or buries everything in its path Explosive eruptions - hazards – – – Pyroclastic flow of hot gases, volcanic ash, cinders and bombs can move quickly down the sides of the volcano Landslides of mud, melted snow and rock can occur Volcanic ash can be thrown high into the atmosphere, where it can damage jet plane engines Volcanic activity • Volcanic Activity – Active • – Dormant • – Erupting or shows signs that it may erupt in near future “Sleeping” volcano expect to erupt again one day Extinct • Unlikely to ever erupt again Volcanic landforms • From Ash and Lava – Types of landforms • • • • • Shield volcano – gently sloping lava flows Cinder cone volcano – from explosive eruptions Composite volcano – alternating layers of lava and layers of ash, cinders, bombs Lava plateau – Forms from repeated lava flows along long cracks in an area Caldera – hole left if magma chamber collapses after eruption Volcanic landforms – Ash and lava Lava plateau Volcanic landforms How a caldera forms Volcanic landforms • From Magma – Types of landforms • • • • Volcanic necks – Magma hardened in pipe, softer rock around pipe eroded Dikes and sills – Across rock layers, dike; between rock layers, sill Dome mountains – uplift pushes a hardened mass of magma toward the surface Batholith – Large body of magma forms inside crust Volcanic landforms • From Magma Batholith Classwork 2 1. 2. 3. 4. 5. What are the two types of volcanic eruptions? What are the three types of volcanic activity? Describe the three types of volcano How does a lava plateau form? How does a caldera form? Earthquakes Forces in Earth’s Crust • Stress – Tension • – Compression • – Force that pulls crust and thins rocks in the middle Force that squeezes rocks until they fold or break Shearing • Force that pushes mass of rock in two opposite directions Earthquakes • Stress Draw these three types of stress Earthquakes Forces in Earth’s Crust • Faults A fault occurs when enough stress builds up in rock to break it – Types of faults – • Normal – Fault cuts through rock at an angle – One block of rock sits over fault (hanging wall) – Other block sits under the fault (footwall) – During movement, hanging wall move downward, footwall moves upward Forces in Earth’s Crust • Faults – Types of faults • • Reverse – Same structure as normal fault – During movement, hanging wall moves upward, footwall moves downward Strike-Slip Faults – Rocks on either side of fault slip past each other – Little up or down motion Forces in Earth’s Crust • Faults Draw this normal fault and label the footwall and hanging wall Forces in Earth’s Crust • Faults Draw this reverse fault and label the footwall and hanging wall Earthquakes Forces in Earth’s Crust • Faults Draw this strikeslip fault Forces in Earth’s Crust Creating new landforms • Folding Earth’s crust by compression – – – Anticlines • Fold that bends upward into an arch Synclines • Fold that bends downward like a V Folded mountains • Himalayan mountains in Asia • Alps in Europe • Process requires millions of years Forces in Earth’s Crust Creating new landforms Draw this diagram, label the syncline and anticline and draw in the arrows showing the direction of force Forces in Earth’s Crust Creating new landforms • Stretching Earth’s Crust – Fault block mountains • Two normal faults cause valleys to drop down on either side of a block of rock • As hanging walls of each fault drop down, block in between stands above surrounding valleys Forces in Earth’s Crust Creating new landforms Draw this diagram Forces in Earth’s Crust Creating new landforms • Uplifting Earth’s Crust – Plateaus • Large area of land elevated high above sea level Classwork 3 1. 2. 3. 4. 5. Describe the three types of stress What is a fault? Describe the three types of faults Describe three types of folds in the Earth’s crust How is a plateau formed? Earthquakes Earthquakes and Seismic Waves Seismic Waves • Waves produced by earthquakes that travel through the Earth Earthquakes Types of Seismic Waves – – – P Waves • Seismic waves that compress and expand ground like an accordion (longitudinal) • Fastest waves of the three S Waves • Seismic waves that can vibrate side-to-side or up and down (transverse) • Arrive after P waves Surface Waves • Similar to waves in water; can make ground roll like ocean waves (also transverse) Earthquakes Earthquakes and Seismic Waves Draw and label these P, S and surface wave diagrams Anatomy of an earthquake • • • An earthquake is the shaking and trembling that results from movement of rock beneath the surface The point beneath Earth’s surface where rock breaks under stress and triggers an earthquake is called the focus The point on Earth’s surface directly above the focus is called the epicenter Measuring earthquakes Monitoring Earthquakes How do seismographs work? Measuring earthquakes Monitoring Earthquakes Reading a Seismogram Measuring earthquakes Earthquakes and Seismic Waves How is an epicenter located Measuring earthquakes • Modified Mercalli Scale Rates the amount of shaking from an earthquake – Done by observation (no instruments) – • Richter Scale Measures earthquake magnitude (size) – Measure small earthquakes using seismographs – Take distance into account – • Moment Magnitude Scale – Measure total energy of an earthquake using seismographs Measuring earthquakes Earthquakes and Seismic Waves How are earthquakes measured Moment Magnitude Scale Modified Mercalli Scale Measuring earthquakes Monitoring Earthquakes Earthquake risk in the United States Earthquake Hazards • • • Ground Shaking – Buildings can be damaged by the shaking – Buildings can be damaged by subsidence (the ground beneath them settling to a different level – Soil liquefaction (mixing of sand or soil and groundwater) causes ground becomes very soft and acts similar to quicksand. Ground Displacement – Land on sides of fault moves in different directions Earthquake Hazards • • Flooding – Dams or levees break – Tsunamis (huge wave caused by an earthquake under the ocean) 2004 Indian Ocean tsunami killed over 230000 people – Seiches (occur on lakes shaken by earthquakes) Fires – Broken gas lines and power lines – Tipped over wood or coal stoves. Earthquake risk in the world Pacific Ring of Fire Mid-Ocean Ridge Eurasian-Melanesian Where Earthquakes Occur • Most Earthquakes occur on plate boundaries – • There are three zones: – – – • Some earthquakes can occur on plate boundaries that aren’t active anymore (like in Missouri, US or in central China) Pacific Ring of Fire (mostly subduction but some transform plate boundaries) Mid-Ocean Ridges (diverging ocean plates) Eurasian-Melanesian (continental plates colliding) If there are several faults in an area they can form an interconnected fault zone Classwork 4 1. 2. 3. 4. 5. How does a seismograph work How do you read a seismogram? What is the risk of an earthquake in Florida? What part of the United States has the highest earthquake risk? Where do most earthquakes occur?