Name Caleigh Kehoe Learning Unit 3 Volcano Review Ques ons This assignment is designed to assess your understanding of Unit 3 and includes some of the Ques ons for Review at the end of Chapters 6 and 7 from your text plus a few addi onal ques ons Each ques on 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 le and send it back for evalua on and grading through the assignment tab by or before the due date 1 In what tectonic environments to volcanic erup ons typically occur Volcanos typically occur at either seduc on zones at riXing sea oor spreading zones at divergent boundaries or at hot spots 2 What changes in heat and pressure are necessary to melt rock and create magma There will be high temperatures and pressure causing rocks to become liquid form to then create magma as this is deep inside the earth 3 How does felsic rhyolite magma form in the line of arc volcanoes like the Cascades The felsic rhyolite is formed when basalt magma rises from above the subduc on zones slab melts con nental crust 4 What are the two most abundant gases in magmas The two most abundant gases in magmas are water vapor and carbon dioxide 5 What factors in uence the violence or style of an erup on The main factors of violence of erup on are the amount of me since the last erup on the viscosity or thickness of the magma and the gas content within the magma 6 What proper es of ma c magma control its erup ve behavior It is characterized by low silica and low gas content the erup ons have low V E I and the magma comes from divergent boundaries 7 What proper es of felsic intermediate magmas control their erup ve 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 8 What causes di erences in viscosity among the major magma types Three factors that a ect magma viscosity are temperature composi on and presence of dissolved gases 9 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 A pyroclas c ow surge blasted laterally and ahened forests 10 Which of the hazards of volcanoes kill more people than any other Why are they so dangerous Pyroclas c ows are more dangerous due to being fast moving and destruc ve Lava ows are very slow moving and cover a small area posing lihle threat to human life 11 Why do landslides some mes trigger explosive erup ons A landslide may reduce pressure on shallow magma c and hydrothermal systems resul ng in explosions ranging from minor steam explosions to enormous steam and magma driven directed blasts by elimina ng a major por on of the volcano s cone 12 Which gas is heavier than air collects in low areas and can asphyxiate people or animals if it is in high concentra ons Due to the fact that carbon dioxide is heavier than air it may ow into low lying areas and collect in the soil Carbon dioxide gas concentra ons in certain places can be deadly to people and animals 13 An extremely large volcano with very gentle slopes is likely to be what kind of volcano and is likely to have originated from what composi on magma felsic intermediate ma c A shield volcano is most likely to be originated from basalt lava ows Shield volcano gets formed by low viscosity magma 14 A large steep sided volcano is likely to be what kind of volcano and is likely to have originated from what composi on magma felsic intermediate ma c A large steep sided volcano is likely to be a stratovolcano and is likely originated of intermediate to felsic sloping sides 15 Why do stratovolcanoes have steeply sloping sides but shield volcanoes have very gently A shield volcano has gently sloping slides because the lava cone is formed by the basal c volcanism and basalt is more viscous A stratovolcano has a steeply sloping slides layered composite cone it called a composite cone as it formed partly by the explosive erup on and partly by the ow of lava 16 What is the driving force behind the explosive ac vity of a cinder cone When rising basal c magma collides with nearby groundwater escaping steam coughs cinders of bubbling molten lava out of the vent or summit crater 17 Yellowstone Park has two huge calderas each more than 20 km across How do such calderas form Ejec on of a large volume of magma oXen causes collapse into the magma chamber 18 What signs precursors suggest that a volcano may be preparing to erupt No ceable steaming or fumarolic ac vity and new or enlarged areas of hot ground Subtle swelling of the ground surface Small changes in heat ow Changes in the composi on or rela ve abundances of fumarolic gases 19 Harmonic tremors recorded on seismographs near volcanoes are generally interpreted as They form when uid basal c magma rises along a fracture and encounters ground water The steam generated blows fragments of lava violently in the air which solidi es and falls as cinders along the vent forming an oval cone
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