Geography - Tectonics Volcanicity

  1. Why is material in the mantle semi-solid instead of completely fluid?
    Because of the great pressure exerted upon it
  2. What is the difference between extrusive and intrusive volcanic features?
    • Extrusive  - when lava and other materials reach the surface
    • Intrusive - materials injected into the crust, may later be exposed at the surface by erosion of the overlying rock
  3. What is magma?
    Mixture of molten rock and gases, which may be viscous or basaltic
  4. What does viscous (lava) mean?
    Sticky, less runny 

    If something has a low viscosity then it is more runny
  5. What 3 factors affect viscosity?
    • 1. Temperature (the higher the temp, the less viscous it becomes)
    • 2. Dissolved Gasses (more gas = less viscous) 
    • 3. Silica levels (low silica = less viscous)
  6. What is the chemical composition of magma that has a high silica content?
  7. What is the chemical composition of magma that has a low silica content?
  8. Do basaltic/basic lavas produce explosive or nonexplosive eruptions?
  9. Do andesitic or acid lavas produce explosive or nonexplosive eruptions?
    Highly explosive
  10. Where is basaltic lava usually found?
    • Constructive plate boundaries - originates from upward movement of mantle material 
    • Also found in hotspots and more developed rift systems
  11. Where is andesitic lava usually found?
    Destructive plate boundaries where the crust is being destroyed
  12. Where is rhyolitic lava usually found?
    • Collision plate boundary
    • Destructive plate boundary
  13. What are the characteristics of basaltic lava?
    • Low viscosity (flows easily)
    • Gas can easily escape
    • Non-violent eruptions
    • Frequent eruptions
    • Long eruption
    • 1200 degrees celsius
    • Flows long distances
  14. What are the characteristics of andesitic lava?
    • High viscosity 
    • Often form blockages in vents
    • Gas cannot escape as easily and pressure builds in volcano
    • Violent eruptions 
    • Infrequent eruptions 
    • Short eruptions
    • 800 degrees celsius 
    • Flows short distance, solidifies quickly
  15. What are the characteristics of an acid/lava dome volcano?
    • Dome shape 
    • Steep convex sides 
    • Narrow base, high cone
    • May have secondary cone
  16. What are the characteristics of a shield volcano?
    • Gentle sloping cone
    • Wide base, not high
    • Made up of layers of basaltic lava
  17. What are the characteristics of a cinder cone volcano?
    • Slightly concave sides
    • made of successive layers of ash and cinders
  18. What are the characteristics of a composite cone/ stratovolcano?
    • Large 
    • steep and symmetrical sides
    • Made of alternating layers of acidic lava and ash
    • Often has parasitic/secondary cone
  19. What are the characteristics of a caldera?
    • Steep walled
    • Basin shaped depression
    • Lake inside crater
    • may have new volcanic cones growing inside
  20. How are acid/lava dome volcanoes formed?
    • Acidic and andesitic lava cools and solidifies near source which leads to dome appearance. Vent plugging, as lava is very viscous, may lead to formation of secondary vent on side of volcano which is a release of built up gasses that can be explosive.
    • e.g. Puy region in France
  21. How are shield volcanoes formed?
    • Basaltic, low-viscosity lava flows and cools slowly as sheets of volcanic rock which build up the sides of volcano, over successive small and mild eruptions.
    • e.g. Mauna Loa, Hawaii
  22. How are cinder cone volcanoes formed?
    • Steep sides where largest material falls and finer material is carried away to form gently sloping base.
    • e.g. Paricutin, Mexico
  23. How are composite cone/stratovolcanoes formed?
    Alternating layers of asha and andesitic lava build up steep sides when the passage of magma becomes blocked, pressure builds and magma may flow from fissures on the volcanic flank, forming secondary cones. Produces both lahars and a nuée ardente
  24. What is a lahar?
    • Volcanic mudflows carrying material. 
    • Ash and debris mixes with water and moves rapidly over long distances - usually along river valleys

  25. What is a nuée ardente?
    A gas and ash cloud, which can move up to 200km/h
  26. How are calderas formed?
    Due to highly explosive volcanic activity. Magma enters chamber and gradually empties during explosion until there is no magma left to support the roof of the chamber. The mountain collapses and creates a caldera - a bowl shaped depression which fills with water and forms a lake or new magma
  27. How is a lava plateaux formed?
    • Formed during fissure eruptions, where the basaltic lava (known as flood basalts) pour out of cracks in the surface rather than from a central vent. They are layered structures because lava accumulates over older lava flows forming a broad plateaux rather than a mountain.
    • Rivers often cut across the plateaux, forming gorges.
  28. Where are acid/lava dome volcanoes usually found?
    Destructive plate margin
  29. Where are shield volcanoes usually found?
    Constructive margins and hotspots
  30. Where are cinder cone volcanoes usually found?
    Near shield volcanoes on constructive margins or hotspots
  31. Where are composite volcanoes usually found?
    Destructive boundaries
  32. Where are calderas usually found?
    Continental hotspots
  33. Where are lava plateaus usually found?
    Constructive margins
  34. List the seven different volcano types in order from most basaltic lava to most rhyolitic lava
    • Icelandic
    • Hawaiian 
    • Strombolian 
    • Vesuvian 
    • Krakatoan 
    • Pelean 
    • Plinian
  35. What is a fumarole/solfatara?
    • Both steam and gas vents which are common on the flanks of active volcanoes but are also found in geothermal regions, where the temperatures are generally close to the boiling point of water. 
    • In some cases they are hidden in the ground and can be broken into. 
    • The gases are dangerous as they are a sign of active volcanism
  36. How are fumaroles/solfataras formed?
    Gas escaping through tiny cracks or long fissures, usually in clusters and on the surface of lava flows and thick deposits of pyroclastic flows. They may persist for decades and disappear within weeks if they occur atop a fresh volcanic deposit that quickly cools
  37. What are geysers?
    Intermittent turbulent discharge of superheated water ejected and accompanied by a vapour phase. Commonly occur in clusters called geyser fields
  38. How are geysers formed?
    • Porous rock allows for easy access to groundwater.
    • Water is heated by rock that sits above magma.
    • As water is heated by the rock, it rises upwards within fractures in the overlying rock.
    • Water above rises to surface to form a hot spring but is cooler than the water within the chamber.
    • Its weight above the chamber increases the pressure within the chamber,
    • This pressure increases the boiling point and allows intense heat to develop. Eventually the water within the chamber rapidly turns to steam and erupts upwards through the hot spring 
    • on the surface a tall eruption of steam and water is observed
    • A period of recharge is required where water returns back into the pool and also recharges the chamber
  39. What are hot springs/boiling mud?
    • Hot springs are similar to geysers, in that they require a heat source and a supply of groundwater. 
    • Boiling mud spots are iconic in New Zealand. They are large pools of bubbling mixed earth and water.
  40. How are hot springs/boiling mud spots formed?
    • Hot spring: groundwater percolates deep into the crust, making contact with rock. This heats the water, causing it to rise upwards within fractures in the rock until it forms a pool on the surface. 
    • Some hot springs are gaseous and release hydrogen sulphide
    • Boiling mud: Steam and gas tise to the surface under rainwater ponds. Acidic gases attack surface rocks, forming clay. This clay mixes with water to form a muddy, steam heated mud pool. 
    • Rainfall affects the appearance of mud pools. In dry conditions the mud is thick, when it is raining the mud is more fluid
  41. What are the seven features of intrusive volcanic activity?
    • Batholiths 
    • Plutons
    • Lapoliths
    • Sill
    • Dyke
    • Volcanic plug
  42. What is a batholith?
    • Largest type of intrusion, can reach 100s km across
    • Has thick and viscous lava, doesn't flow easily
    • Typical rock type is granite, which contains a high proportion of silica. Granite cools slowly and forms large rock types
    • Image Upload 1
  43. How is a batholith formed?
    • A vast amount of magma cools over time in layers
    • Heat given out by a cooling batholith cooks the country rocks in a band all around the intrusion (metamorphic aureole) which changes their composition and they become metamorphic rock due to the process of contact metamorphism. This can result in the rocks becoming harder and more brittle.
  44. What is a pluton?
    • Igneous body of usually less than 100km²
    • Bigger than a sill or dyke
    • Can be individual or joined together (several plutons form a batholith.
    • Image Upload 2
  45. What is a Lopolith?
    • Saucer shaped intrusions 
    • Usually concordant with the country rock 
    • Lenticular in shape, depressed central region
    • Rare
    • Formed by magma with a low silica content
  46. How is a lopolith formed?
    Magma is forced between laters of sedimentary rock so it is parallel to these layers. Shape is caused by crystal sagging. Made of up several layers, formed by different phases of intrusion. Beneath a lopolith, there will be a vertical 'funnel' along which the magma travels
  47. What is a laccolith?
    • Usually concordant, dome upward intrusion.
    • Land above also domes
    • Formed close to the surface, similar to sills
    • may force a feeder dyke beneath (a funnel for magma to travel through)
    • Formed from high viscosity magma, which causes a buildup of pressure
  48. How are laccoliths formed?
    Magma being intruded is under very high pressure and forces country rock above to dome
  49. What is a dyke?
    A discordant intrusion into sedimentary rock, cutting through layers of sedimentary rock
  50. How are dykes formed?
    Magma is forced along cracks or weaknesses in rock, or when the force of the intruding magma opens up new cracks in the rock
  51. What is a sill?
    • Parallel or concordant to the layers in country rock
    • Vary in thickness from 1cm to hundreds of metres
    • Can cause contact metamorphism 
    • Thinner than batholiths, so less heat & less country rock affected
  52. How is a sill formed?
    Magma forced along between layers of sedimentary rock
  53. Define: country rock
    The original rock of an area, into which magma has intruded
  54. Define: metamorphic rock
    Rock which has had its composition changed
  55. Define: contact metamorphism
    Change which occurs due to contact of material/substances
  56. What is a volcanic plug?
    A closed vent due to magma cooling and solidifying or not flowing easily and so the vent becomes blocked.
  57. What are the primary impacts of a volcanic event?
    • Lava flows
    • pyroclastic flows
    • volcanic gases
    • Tephra
  58. What are the secondary impacts of a volcanic event?
    • Climate change
    • Tsunamis 
    • Flooding 
    • Volcanic landslide
    • Lahars
  59. What is the difference between a volcanic hazard and a volcanic effect?
    Volcanic hazards have an impact upon people/the built environment whereas volcanic effects do not
  60. What are lava flows?
    • Fissure eruptions of basaltic magma
    • Can reach speeds of 50km/h can spread tens of kilometres 
    • Rare events
    • e.g. Kilauea in Hawaii -erupting since 1983
  61. What are pyroclastic flows? (same as neuée ardents)
    • Mixture of hot rock fragments, lava particles and ash buoyed up by hot gases
    • Moves at up to 40km/h
    • Material is denser than surrounding air, so moves close to ground
    • e.g. Mount Pelée, 1902 - killed all but 2 of 29,000 inhabitants
  62. What is ash/tephra fall?
    • Volcanic ash = <2mm diameter 
    • Tephra = >2mm diameter 
    • Form when magma is fragmented or when solid rocks are broken up by water turning into steam 
    • Ash is carried high into the atmosphere and by prevailing winds.
    • e.g. Mt St Helens, Washington state USA
  63. What are the hazards of ash/tephra fall?
    • Breathing difficulties
    • Building collapse
    • Agriculture reduced - animals may eat or die
  64. What are volcanic gases?
    • Active volcanoes produce large amounts of water vapour, carbon dioxide, sulphur dioxide, chlorine, hydrogen sulphide, hydrogen, helium, carbon monoxide and hydrogen chloride
    • but rarely reach toxic levels
  65. Why are volcanic gases dangerous?
    They are heavier than air and collect in depressions where concentrations can become high enough to cause suffocation
  66. What are volcanic landslides?
    • Gravity driven slides of masses of rock and loose volcanic material which occurs as a result of heavy rainfall or earthquakes
    • ground deformations of volcanic slopes by rising magma can also cause landslides
  67. What are tsunamis?
    • Giant waves 
    • secondary effect of volcanic eruption, especially caldera events
  68. What are the four main responses to a volcanic hazard?
    • Do nothing
    • Move to a safer location 
    • Attempt to prevent the hazard
    • Adapt lifestyle to hazard
  69. What is the hazard management cycle?
    Image Upload 3
  70. What is the park model?
    Image Upload 4
  71. What factors does the response to a volcanic hazard depend on?
    • The nature of the hazard
    • The frequency of hazard
    • Magnitude of hazard
    • Population pressure 
    • Level of economic development
  72. What are the benefits of volcanicity? (4)
    • Lava flows can create new land 
    • Hot rocks allow geothermal power (eg in Iceland)
    • Igneous rocks contain valuable mineral deposits 
    • Volcanic sulphur is used in  manufacturing processes including pharmaceutical
    • Igneous rocks (eg granite) make good building materials
    • Forms points of interest - tourism
  73. What are the hazards of volcanicity? (4)
    • Lava flows burn and bury crops
    • Can cause tsunamis 
    • Ash fall may ruin crops or disrupt transport 
    • Violent eruptions lead to pyroclastic flows which destroy life 
    • Lahars 
    • Volcanic dust absorbs solar energy and so lowers atmospheric pressures
  74. What is the Volcanic explosivity index (VEI)?
    An open ended chart used to describe the scale of a volcanic eruption. Each value, from 0 to 8, represents an eruption ten times larger than the previous one (logarithmic)
  75. what is a mantle plume?
    • Long lived areas of high levels of heat flow within the mantle. 
    • Consists of an upwelling long thin conduit and bulbous head and produces huge volumes of magma
  76. What is a conduit?
    A channel for conveying water or other liquid
  77. What does low viscosity mean?
    Not very thick, semi fluid in consistency. Low magnitude of internal friction
  78. What are lava lakes?
    • Rare. Form when lava collects in craters and are a sign that volcanoes are active but not erupting. There is enough magma to create fill a crater floor but not enough to create a flow which extends from the crater.
    • Large gas bubbles form in the lake
  79. What is vog?
    • Gas carried by the wind.
    • Once it reacts with the air, it creates sulphur dioxide.
    • May lead to respiratory problems and may damage crops and contaminate water
  80. What is laze?
    Formed when lava reaches the sea, as often happens in Hawaii, creating steam full of hydrochloric acid
Card Set
Geography - Tectonics Volcanicity
not the case study section