Name Learning Unit 3 Volcano Review Questions This assignment is designed to assess your understanding of Unit 3 and includes some of the Questions for Review at the end of Chapters 6 and 7 from your text plus a few additional questions Each question can be answered in one to two sentences Please limit yourself to a maximum of three sentences Access the assignment complete it with ANSWERS IN A DIFFERENT COLOR FONT as a separate file and send it back for evaluation and grading through the assignment tab by or before the due date 1 In what tectonic environments to volcanic eruptions typically occur Volcanoes typically occur at either seduction zones at rifting and sea floor spreading zones at divergent plate boundaries or at hot spots 2 What changes in heat and pressure are necessary to melt rock and create magma The temperature needs to have increased and the pressure needs to be decreased in order to create lava 3 How does felsic rhyolite magma form in the line of arc volcanoes like the Cascades The seduction forms the felsic rhyolite to intermediate magma and is characterized by relatively high silica and high gas content 4 How does lava differ from magma Magma is how the liquid heat is released before the eruption After it is referred to as lava flows which is molten magma that has flown out onto the earth s surface 5 What are the two most abundant gases in magmas The two most abundant gases are water vapor and carbon dioxide 6 What factors influence the violence or style of an eruption The main factors that the violence of eruptions are the amount of time since the last eruption the viscosity or thickness of the magma and the gas content within the magma 7 What properties of mafic magma control its eruptive behavior It is characterized by low silica and low gas content The eruptions have low V E I and it comes from divergent boundaries 8 What properties of felsic intermediate magmas control their eruptive behavior It is characterized by high silica and high gas content The eruptions have high V E I and the magma comes from convergent boundaries 9 What causes differences in viscosity among the major magma types The viscosity is a measure of a fluid s resistance to flow The more silica in the magma the more viscous it is 10 If you visit Mount St Helens Washington you will see thousands of trees lying on the ground all parallel to one another Explain how they got that way In 1980 Mount Saint Helens producing devastating pyroclastic flow It was so violent that the entire top of the mountain was blown off It knocked down the whole forest stripping the bar completely off the trees 11 Which of the hazards of volcanoes kill more people than anything else Why are they so dangerous The most dangerous to people is probably hazardous gas Carbon Dioxide CO2 the It is heavier than oxygen and it can pour downslope and displace oxygen at the surface It is also colorless and odorless so there is no warning before becomes deadly 12 Why do landslides sometimes trigger explosive eruptions Landslides happen when they are triggered by something such as earthquake or an eruption from a volcano The gases then build up causing and explosive eruption 13 Which gas is heavier than air collects in low areas and can asphyxiate people or animals if it is in high concentrations That gas is Carbon Dioxide CO2 14 An extremely large volcano with very gentle slopes is likely to be what kind of volcano and is likely to have originated from what composition magma felsic intermediate mafic A large volcano with gentle slopes would have mafic magma 15 A large steep sided volcano is likely to be what kind of volcano and is likely to have originated from what composition magma felsic intermediate mafic A large volcano with gentle slopes would have felsic and intermediate magma 16 Why do stratovolcanoes have steeply sloping sides but shield volcanoes have very gently sloping sides Stratovolcanoes have steeply sloping because their magma piles up of tephra around the central vent and the high viscosity of the lava that glues it together Shield volcanoes have gently sloping sides because the low viscosity of the magma which allows lava to flow great distances before it cools 17 What is the driving force behind the explosive activity of a cinder cone They form when fluid basaltic magma rises along a fracture and encounters ground water The steam generated blows fragments of lava violently into the air which solidify and fall as cinders around the vent forming an oval cone 18 Yellowstone Park has two huge calderas each more than 20 km across How do such calderas form Some eruptions of stratovolcanoes are so violent that after the eruption ends the volcano collapse into the empty magma chamber bellow 19 What signs precursors suggest that a volcano may be preparing to erupt Before a volcano erupts one might see the tilt and swelling of the volcano s sides there might be an increase in seismic activity and there could be many small earthquakes There may be seismic exploration There could be increased steam and gas emissions coming from the volcano or there could be a change in the ground water system 20 Harmonic tremors recorded on seismographs near volcanoes are generally interpreted as Increased seismic activity which produces many small earthquakes and they are caused by fresh magma rising below the volcano
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