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Volcanic Processes and Igneous Rocks Name: Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY Volcanic Processes and Igneous Rocks Eruption Processes and Types of Volcanoes 1. What is the key ingredient required to make a volcano erupt? large amounts of dissolved gasses in the magma increase the pressure and lower the density 2. Compare a shield volcano (A) to a stratovolcano (B): shield volcano (A) stratovolcano (B) Magma Type Mafic- very low viscosity Felsic- high viscosity, very sticky lava. and Viscosity Shape and slope Very low slope, broad sides and rounded Slope is much steeper; the top of the of the volcano: top. mountain makes a tall peak. Describe what a Often produces violent eruptions that are Typical eruptions are somewhat calm, made typical eruption very explosive and produces pyroclasitic of fire fountains and lava flows. is like. flows and large ash clouds. Name an example of one Kilauea in Hawaii Mt. St. Helens in Washington state. somewhere in the world. Magma Types and Viscosity 3. How is viscosity of a substance different than its density? Viscosity is the thickness or ease of pouring/running of a liquid material. Density is how much room the matter takes up compared to its amount of matter. Thick liquids tend to have low densities and visa versa. 4. How does the viscosity of magma affect the way a volcano will erupt? Thick, felsic lava will build up pressure until the volcano explodes. Thinner mafic lava will produce a calmer eruption. 5. Label and define each of the features shown in the diagram to the right- (A and B are liquid, C and D are solid rock) A. Magma- molten (melted) rock found under the surface B. Lava- molten rock found on the surface C. Intrusive rock- igneous rocks made of slowly cooled magma underground. D. Extrusive rock- igneous rocks made of rapidly cooled magma out on the surface. 1 | P a g e Volcanic Processes Test 2 Study Guide Name: Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY 6. Compare the characteristics of the three magma types based on what you have learned in the lab: Mafic Magma Type: Felsic Intermediate Darker grey color or Color: Lighter colored Darker colored black and white. Name 2 minerals Feldspar and Feldspar and quartz Hornblende and olivine it’s made of: hornblende Viscosity: High- very thick In the middle Low- very thin Where oceanic and Crust type: Continental Oceanic continental mix Density: Lower Middle Higher Name several rocks Granite, rhyolite, pumice, Andesite porphyry and Basalt made of this type: obsidian diorite Igneous Rocks and Their Formation 7. What is a rock made of? A mixture of minerals and organic materials 8. What is an igneous rock? Rock that formed by the cooling, crystallizing, and hardening of molten rock (magma below the surface or lava on the surface depending on the location) 9. What observable characteristics of an igneous rock allow you to infer its cooling rate? The size of the mineral grains – large cooled slowly and small, glass, or vesicular cooled fast 10. Intermediate rocks are formed at subduction zones forming trenches where continental crust compresses and melts on oceanic crust. 2 | P a g e Volcanic Processes Test 2 Study Guide Name: Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY 11. Use this table to explain how the cooling rate of magma impacts its observable characteristics: Location where cooling Type of Texture: Describe its occurred Mineral crystal size Name an example rock: cooling rate. (Intrusive/Extrusive) Intrusive- deep Coarse: slow cooling large crystals Granite or diorite underground Fine: rapid cooling small crystals Rhyolite or basalt Extrusive- at or very close Glassy: very rapid cooling no crystals Obsidian to the surface Vesicular: very rapid cooling no crystals with gas with dissolved gases forming Pumice bubbles bubbles in the rock. Porphyritic: -cooling begins Both- starts deep slowly and then finishes quickly both large and small underground and then gets Andesite porphyry crystals erupted to the surface. 12. While walking around a nearby volcano you notice an igneous rock that is a mixture of light and dark grey colored visible crystals. Based on these characteristics, complete the table below with the correct info: What type of volcano Magma Type: Viscosity: Environment: would this rock form? Stratovolcano – trench Intrusive – cooled slowly Intermediate In between where oceanic and inside continental crust meet 13. Describe the viscosity, magma type, and type of volcano if an observed lava flow was fine-grained, dark-colored basalt that was located several kilometers from the cone of a volcano? What type of volcano Magma Type: Viscosity: Environment: would this rock form? Extrusive – cooled quickly Mafic Thin Shield close to the surface Hazard and Risk Management of Volcanoes – Case Study 14. What does VEI stand for? Volcano Explosivity Index What is the scale used for? Rates the amount of destruction caused by a volcano What range does the scale cover? 0 (no to low impact) to 8 (indescribable and global effects) 3 | P a g e Volcanic Processes Test 2 Study Guide Name: Unit III: The Lithosphere –Volcanic Processes Test 2 - KEY 15. What is the difference between a dormant, active, and extinct volcano? Dormant – not currently erupting, but can in the future Active – currently erupting Extinct – erupted in the past but will not erupt again 16. True or False: Earthquakes are a clue that a volcano is about to erupt 17. Name the volcano that erupted in 1980 and caused damage to Washington and Oregon State Mt. St. Helens 18. Define the following Volcanic Hazards and on the line, state if they are related to Shield or Stratovolcanoes: Stratovolcano Debris – Charred items that are air born and effect a small area Shield Lava Fountain – A spectacular display of molten rock being sprayed in the air Stratovolcano Lahar – Melting snow and rain mixes with mud and ash to create rivers Stratovolcano Landslide – Large amounts of pressure cause serious movement and destruction of the cone. Shield Lava Flow - Liquid molten rock that easily pours down the side of the volcano during an eruption. Shield Lava Tube – Underground pipe-like structures that carry lava far from vent. Stratovolcano Plume – Huge amounts of pressure cause the eruption to throw ash several miles into atmosphere Stratovolcano Pyroclastic Flow – A mass of very hot gas and rock that rush down the sides of a volcano Natural Disasters 19. Describe how an earthquake occurs. Be sure base your thoughts around energy. Plates are in constant motion and driven by convection currents in the mantle – Kinetic Energy. That energy is transferred and stored as potential energy when friction causes the plates to stick. Eventually, an old fault will slip or a new one will form, releasing all of the stored energy at once, as Seismic Waves, in the form of kinetic energy. 20. What is the difference between a focus and an epicenter? The focus is the location in the crust where all of the seismic energy is released from. The epicenter is the location on the Earth’s surface and gives us coordinates and direction of where the center of the earthquake is located. 21. Describe how triangulation is used to locate the epicenter of an earthquake. As a seismic wave radiates from the epicenter, the energy reaches different locations at different times and is recorded on a seismograph. These readings show the arrival of the P and S waves. Knowing the time difference between the arrival of the waves allows us to find the distance the station is from the epicenter, but not the direction. So a circle is draw around three different seismograph cities. Where they intersect is the location of the epicenter – where the fault slipped and the energy radiated from. 22. What is the relationship between the S-P travel time and the distance from the epicenter? The further a city is located from the epicenter, the longer the distance between the P and S Waves. 23. What is the relationship between the S-wave amplitude and the distance from the epicenter? The further a city is located from the epicenter, the lower (less shaking) the amplitude is. 24. What does the Richter scale measure? The amount of energy released from the epicenter. 25. How do you create a tsunami? Displace oceanic crust (underwater) with any type of fault. 4 | P a g e Volcanic Processes Test 2 Study Guide .
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