Name Olga Nykilchyk Learning Unit 3 Volcano Review Questions In what tectonic environments to volcanic eruptions typically occur 1 Volcanic eruptions typically occur in tectonic environments such as subduction zones divergent plate boundaries and hotspots 2 What changes in heat and pressure are necessary to melt rock and create magma Changes in heat and pressure are necessary to melt rock and create magma As pressure decreases or temperature increases rocks can undergo partial melting and transform into molten magma 3 How does felsic rhyolite magma form in the line of arc volcanoes like the Cascades Felsic rhyolite magma forms in the line of arc volcanoes like the Cascades through the melting of continental crust as it interacts with subducting oceanic crust This process leads to the generation of silica rich magma 4 How does lava differ from magma Lava is molten rock that has erupted onto the Earth s surface while magma is molten rock beneath the Earth s surface 5 What are the two most abundant gases in magmas The two most abundant gases in magmas are water vapor H2O and carbon dioxide CO2 6 What factors influence the violence or style of an eruption The violence or style of an eruption is influenced by factors such as magma viscosity gas content and the presence of volatile compounds Additionally the interaction between magma and the surrounding rock and the degree of fragmentation can also impact eruption style 7 What properties of mafic magma control its eruptive behavior The properties of mafic magma such as low viscosity and low gas content typically result in effusive eruptions characterized by the flow of lava rather than explosive volcanic activity 8 What properties of felsic intermediate magmas control their eruptive behavior Felsic intermediate magmas tend to have higher viscosities and higher gas contents leading to explosive eruptions with the potential for pyroclastic flows and ash clouds 9 What causes differences in viscosity among the major magma types Differences in viscosity among the major magma types are primarily due to variations in silica content Mafic magmas have low silica content resulting in lower viscosity while felsic magmas have high silica content and higher viscosity 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 The trees lying on the ground parallel to one another at Mount St Helens were knocked down by the lateral blast associated with the 1980 eruption The lateral blast caused by the rapid release of high pressure gas and volcanic material toppled the trees and deposited them in a uniform direction 11 Which of the hazards of volcanoes kill more people than any other Why are they so dangerous Pyroclastic flows which are rapidly moving currents of hot gas ash and rock fragments are among the most deadly volcanic hazards They can travel at high speeds and cover large areas causing severe destruction and posing a significant threat to human life 12 Why do landslides sometimes trigger explosive eruptions Landslides can trigger explosive eruptions when they destabilize the volcanic edifice causing the sudden release of accumulated gas and magma The collapse of material can create a pathway for gas and magma to escape rapidly leading to an 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 The gas that is heavier than air collects in low areas and can asphyxiate people or animals if in high concentrations 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 An extremely large volcano with very gentle slopes is likely to be a shield volcano and is likely to have originated from 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 steep sided volcano is likely to be a stratovolcano composite volcano and is likely to have originated from felsic to intermediate magma 16 Why do stratovolcanoes have steeply sloping sides but shield volcanoes have very gently sloping sides Stratovolcanoes have steeply sloping sides due to the accumulation of alternating layers of solidified lava ash and volcanic debris Shield volcanoes on the other hand have gently sloping sides because of the low viscosity and extensive flow of mafic lava 17 What is the driving force behind the explosive activity of a cinder cone The driving force behind the explosive activity of a cinder cone is the rapid expansion of gas within the magma As gas rich magma reaches the surface the pressure release leads to explosive eruptions that eject fragmented volcanic material including cinders and ash 18 Yellowstone Park has two huge calderas each more than 20 km across How do such calderas form Huge calderas like those in Yellowstone Park form through the collapse of the ground following a massive volcanic eruption or the emptying of a magma chamber The removal of subsurface material causes the surface to sink 19 What signs precursors suggest that a volcano may be preparing to erupt Signs that suggest a volcano may be preparing to erupt include increased seismic activity ground deformation such as swelling or bulging changes in gas emissions such as increased sulfur dioxide or carbon dioxide changes in thermal activity such as increased temperatures and the occurrence of small scale eruptions or volcanic unrest 20 Harmonic tremors recorded on seismographs near volcanoes are generally interpreted as Harmonic tremors recorded on seismographs near volcanoes are generally interpreted as continuous low frequency vibrations caused by the movement of magma or fluid within the volcanic system They are often associated with volcanic activity and can indicate the movement of magma towards the surface
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