Study Guide Module 3 Volcanoes

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Oct 30, 2023

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Study Guide Module 3 Volcanoes Volcanoes 1. Define active, dormant, and extinct volcanoes. a. Active volcanoes: Volcanoes that have shown activity in recorded history. b. Dormant volcanoes: Volcanoes that have not shown activity in recorded history but exhibit geological evidence of past activity. c. Extinct volcanoes: Volcanoes that are deeply eroded and have not erupted for thousands to millions of years. 2. What factors causes rocks to melt forming magma? The factors that cause rocks to melt and form magma are: a. Increase in temperature. b. Decrease in pressure. c. Addition of water as it shifts the melting curve to lower temperatures. 3. What is the difference between magma and lava? a. Magma is molten rock before eruption. b. Lava is magma after it reaches Earth’s surface. 4. What factors control viscosity of a magma? Two factors that control the viscosity of magma are: a. Chemical composition , specifically the silica content. Viscosity is directly proportional to the silica content; higher silica content leads to more viscosity. b. Temperature is inversely proportional to viscosity. Higher temperature leads to lower viscosity and as magma cools, more bonds form between atoms and molecules and magma becomes more viscous. 5. What are the three basic magma types and what are their characteristics? Three basic types of Magma: a. Basalt Magma (Mafic): composed of 50% silica, low in viscosity and temperature range is 1000- 1300 °C. b. Andesite Magma: composed of 60% silica, intermediate viscosity and temperature range is 800- 1000 °C. c. Rhyolite Magma (Felsic): composed of 70% silica, high in viscosity and temperature range is lowest at 600-800 °C. 6. Where are 2/3rds of the active volcanoes in the world? 2/3 rds of the active volcanoes in the world exist around the expanse of the Pacific Ocean, this area is also called the Ring of Fire. This area displays explosive volcanic activity which is most common along convergent plate boundaries. This leads to extensive amount of tectonic movement, is notable for its many subduction zones where Earth's tectonic plates come together, frequently resulting in volcanic eruptions. As a result, the Pacific Ocean basin, and surrounding plates, ranks among the world's most active regions in terms of both earthquakes and volcanic activity. Locations situated along the Pacific

Ocean's edge, including but not limited to Japan, Indonesia, the Philippines, New Zealand, and the western coasts of North and South America, belong to this volcanic zone. 7. Which three types of volcanoes erupt peacefully? Which three types of volcanoes erupt violently? Three types of volcanoes that erupt peacefully: a. Shield Volcanoes (basalt): These form by basalt eruptions from a hotspot, and eventually build gently sloping pile of thin flows and are far broader than high. Tectonic environment is oceanic hotspots, some volcanic chains. Viscosity is low, slope of flank is gentle, volatility is low, size is relatively large to giant, and eruptions style is quiet lava. Source of magma is deep within the mantle. b. Fissure Volcanoes: Form super mantle plumes originating at core-mantle boundary. There are two types, first is when mid-oceanic ridges erupt basaltic flows onto adjacent ocean floor, second is continental flood basalts, where mid Atlantic ridge extends above sea level e.g., Iceland. These are characterized by thick, flat immense lava flows. c. Cinder Cone Volcanoes (basalt): Usually erupt only over a short period, few months to few years. These build piles of cinders 100-200 meters high, followed by basalt flow, create a steep slope, viscosity is low, have moderate volatiles and relative volume is small. Eruption style is explosive but less dangerous. Three types of volcanoes that erupt violently: a. Stratovolcano (basalt): These have violent pyroclastic flows, and air-fall ash. These appear above active subduction zones, viscosity and slope is moderate, volatiles are moderate to high, and volume size is moderate. Stratified layers built from combination of effusive and explosive activity. Eruption behavior varies dramatically. b. Lava Dome (rhyolite): Rhyolite magmas emerge slowly to solidify in large dome. Extremely viscous magma can create explosive eruptions from trapped gases. Magma within may continue to rise, forcing pieces of dome to break off, broken pieces may tumble downhill. Over time, these form loose, rubbly, steep slopes. c. Giant Continental Calderas: These are mostly explosive, occur at hotspots under continental lithosphere. Basalt magma mixes with partial melt of continental crust to from rhyolitic or andesitic magma. Dissolved water in magma drives explosive eruptions. These erupt rhyolite in enormous volume, until magma chamber has emptied enough for ground surface to collapse in. Then it creates a depression in landscape. Eruptions are infrequent, at intervals of hundreds of thousands of years. 8. Which type of volcano is commonly found at subduction zones? Stratovolcanoes. 9. Which type of volcano is found over a hotspot? Shield Volcanoes 10. Which type of volcano is found in Iceland? Fissure Volcano – Continental Flood Basalt type. 11. What are the various types of hazards associated with volcanic eruptions? a. Lava Flows: Basalt flows many tens of miles, lava my cool, blacken on the outside but still be hot enough to ignite wood structures. Objects that aren’t burnt maybe buried by flow. b. Pyroclastic Fall: Risk of being hit by falling rock fragments. Most death caused by heavy loading of ash on roofs. When mixed with water, this ash becomes extremely heavy and causes the roof to collapse, crushing everyone below.

This ash also causes serious health problems from inhaling it for those with existing respiratory illness. Ash fall destroys crops and animals, including humans who feed on them. Ash also poses serious problem for aircraft, causes loss of jet engine power, damages the engines, and can bring down the aircrafts. c. Weather/Climate: Large eruptions also lead to regional and global cooling, smallest ash particles remain suspended in the upper atmosphere for years, blocking radiation from the Sun. In 1815, eruption from Mount Tambora in Indonesia caused global cooling and a year without summer, which caused a famine. d. Volcanic Lightning: Generated by ash thrown out by the volcano, causes friction that generates and electrical charge. Some fatalities associated to volcanic lightning. e. Volcanic mudflows/Lahars: Ash combines with water, pours down sides of volcanoes, and has the consistency of wet concrete. Can be triggered by eruption of volcano covered in ice or snow, or by heavy rain. Icy to boiling temperatures. Lahars are hot mudflows. Even a small eruption can trigger a major mud flow. f. Pyroclastic flows: When the eruption column collapses, it develops pyroclastic flows. A mix of hot gases and ash rushes down the flanks of volcanoes and moves very rapidly across the surface. g. Poisonous gases: At depth of more than few kilometers, pressure keeps gas dissolved in magma. As magma rises, gases get released and create Vog – volcanic smog. This gas in atmosphere forms aerosols. CO2 in high concentrations is also released from this magma and it is colorless, denser, and heavier than air, hugs the ground and is deadly if concentration goes above 10%. Other volcanic gases include sulfur dioxide, hydrogen sulfide, chlorine compounds, fluorine. SO2 combines with water to form sulfuric acid which is hazardous to health and corrosive. h. Tsunamis: Volcanoes can trigger tsunamis also, such as the 35 meter high tsunami caused by the Krakatoa eruption in 1883, which killed 36,000 people. 12. Which type of pyroclastic fall is the deadliest? Why? When ash loads up on roofs and gets very heavy on mixing with water, causing the roofs to collapse, crushing everyone below. 13. What is the term used for when volcanic gases come out of solution and form aerosols (ex. Term used in Iceland)? Vog – volcanic smog is created when large amounts of gas released from magma. 14. What is the lethal concentration for carbon dioxide gas and what effect does it have on trees? Lethal concentration of CO2 gas is 10%, it kills all the trees – such as in the Long Valley caldera. 15. What is long-term forecasting used for? Ancient studies help scientist create long term forecasting – which helps assess hazards and risk posed by future volcanoes. This information can be used to warn or relocate human populations when a volcanic eruption is expected. 16. What are the indicators for short-term forecasting of an eruption? a. Seismic waves - Increase activity, increasing eruption risk. b. Ground Deformation - swelling of volcano = magma accumulation. c. Changes in groundwater – Increase in gas pressure = rise in ground water level. d. Drop right before eruption. e. Heat flow - Thermal changes at volcano’s surface.

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f. Gas emissions - Increase due to decrease in pressure as magma nears surface or decrease due to sealing of gas passages by hardened magma. 17. What is the best and most effective method for slowing or diverting lava flows? Attempts to slow or divert lava flows have had only partial success. Most effective approach is to cool and solidify front of flow with water.