Extrusive igneous activity


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  • They are part of a volcanic landscape in Cappadocia, Turkey. The landscape was created by volcanic activity. The region is covered with deep layers of tuff (consolidated volcanic ash), basaltic lava flows and lahar deposits. The combined effects of weathering, water and wind erosion, and the variable strength and dip of the rock layers have created highly unusual features. Where bedding is horizontal and the rock layers relatively strong, rivers have carved steep sided valleys as at Ilhara gorge
  • Where bedding is horizontal and the rock layers relatively strong, rivers have carved steep sided valleys as at Ilhara gorge
  • The famous fairy chimneys are created by erosion processes working on layers of soft tuff covered by layers of hard rock, usually lahar deposits. The hard rock forms a protective cap, preventing the tuff layers from being eroded. The result is a mushroom shape, often with the cap layers perched precariously on top. Eventually, when the cap is eroded away or the base of the rock pillar becomes too narrow, the chimney will collapse. *sometimes called earth pillars, or hoodoos in the USA) People were attracted to the area because of its rich volcanic soils. They discovered that the layers of tuff could be easilyu carved into homes, stables and churches. Local people still use rooms carved out of the rock for storage, animal shelters and as part of their homes. There are several underground cities including schools, stables, churches and cooking areas, used by locals has hiding places when enemy invaders came.
  • Hoodoos in new Mexico and Banff, Canada
  • Tectonic processes are responsible for created incredible landscapes, which may be further modified by physical and human processes (weathering, glacial/fluvial erosion, development etc)
  • A lava plateau is usually an extensive area of basaltic laval, often with a layered structure, formed by major eruptions from vents, or more usually, from a fissure. The layered structure is caused by the accumulation of lava from a series of eruptions over a period of time. The plateau itself tends to be flat and featureless, with limited soil and vegetation cover.
  • 700,000km 2 expanse of basaltic lava covering the majority of Southern India. Formed during the later Cretaceous period, between 67-65 million years ago. It may have been the result of a series of major eruptions from a hotspot that is currently under the island of Reunion in the Indian ocean Take google earth tour???
  • It has a number of river valleys cutting down into it e.g. Wardha and Manjira Picture is of Hogenakal falls (wikipedia)
  • Volcanoes are often found in chains, either because they are at plate boundaries, or because a plate is moving over a hotspot. See google earth of Mt St Helens with volcano layer showing 13 volcanoes within the cascades. A typical cross section you may have come across at GCSE or in Science – the reality is, of course, much more complex!
  • The type of volcano produced by eruptions depends on the type of lava erupted and the nature of the eruptions themselves. These in turn are greatly influenced by the type of plate margin on which they are formed
  • 1. Divergent margins 2. Tend to give rise to fissure eruptions and shield volcanoes. Fissure eruptions occur along fractures and fault lines, while shield volcanoes erupt from a vent. 3. Shield volcanoes are typically low in height with long, gently sloping sides and a wide base. 4. The lava that erupts from them is basaltic, which means it has a low viscosity due to its low silica content. Being quite fluid and hot (about 1200 C, the lava flows quickly and covers long distances before it cool and solidifies, which explains the shape of the cone. 5. Eruptions are frequent but low in magnitude – magma is able to reach the surface relatively easily since the plates are diverging and the crust is fracturing. This means that there is seldom a real build – up pf pressure. 6. Such volcanoes also occur at hotspots 7. At convergent margins 8. Eruptions tend to be less frequent and much more explosive. Rising magma often has a much greater thickness of crust through which to pass, and fractures providing easy routeways tend to be less common. 8. The lava has more than 50% silica. This, along with lower temps of about 800 C make it much thinker and vidcous so it flows slowly and cools quickly, giving rise to a cone with a narrow base and a greater height. 9. They are often composite in structure, with alternating layers of ash and lava. The ash is produced by a highly explosive eruption, often after blocking of the vent, fragmenting parts of the cone or the plug of solidified magma.
  • Oceanic hotspot location Gently sloping sides due to “runny” lava comes directly from the asthenosphere (over 1000C) and can travel up to 60 km/hr, sometimes reaching the sea As the plate has moved north west, the volcanoes have been carried away from the hotspot in a northwest direction creating a chain of volcanic islands and extinct submarine volcanoes A new volcano is erupting 35 km south-east fo hawaii. Loihi is only 3,000 m tall and 2000m below sea level but is expected to reach the surface in 10,000 to 100,000 years.
  • Ash eruptions, pyroclastics flows, mudslides and lava flows have built up a composite volcano
  • Laki (iceland) - fissure Kiluaea – Shield volcano Montserrat – composite volcano Yellowstone – caldera In your explanation, try to include information on what type of eruption caused the volcano
  • There are other types, students should research the main types, with reference to their case studies
  • Extrusive igneous activity

    1. 1. Unit 4: Geographical Research Tectonic Activity and Hazards
    2. 2. What are these? Where are they? How did they get there?
    3. 7. Tectonic landscapes
    4. 9. Lesson 7: What are the landscape impact of extrusive igneous activity? <ul><li>Learning objectives </li></ul><ul><li>To outline the formation of extrusive igneous landforms such as lava plateaus and volcanoes </li></ul><ul><li>To investigate the different types of volcanoes and eruptions </li></ul>
    5. 10. Extrusive igneous activity <ul><li>Once extruded onto the surface of the earth, magma is referred to as lava which cools to form igneous rocks </li></ul><ul><li>The most significant landforms are lava plateaus and volcanoes </li></ul><ul><li>Their distribution is determined by the pattern of tectonic plates </li></ul><ul><li>Their impact on the landscape with vary according to the magnitude and scale of the events causing them and the types of material being extruded. </li></ul>
    6. 11. Lava Plateau
    7. 12. The Deccan Plateau
    8. 14. Volcanoes
    9. 15. Types of volcanoes
    10. 16. Types of volcano <ul><li>The type of volcano will be affected by: </li></ul><ul><ul><li>The type of lava erupted </li></ul></ul><ul><ul><li>The nature of the eruption </li></ul></ul><ul><ul><li>The type of plate margin </li></ul></ul>
    11. 17. Magma type & volcano morphology <ul><li>Basaltic – huge, low relief shield volcanoes plus small scoria cones and fissure vents . </li></ul><ul><li>Andesitic – steep sided strato-volcanoes ; layers of lava, ash and tephra. </li></ul><ul><li>Rhyolitic – central craters with lava plugs / domes , due to high viscosity of the lava. </li></ul>
    12. 18. Types of volcano <ul><li>Divergent margins </li></ul><ul><li>Fissure eruptions and shield volcanoes </li></ul><ul><li>Low, gently sloping sides, wide base </li></ul><ul><li>Basaltic lava, low viscosity, high temp so covers long distances before it cools and solidifies </li></ul><ul><li>Frequent, low magnitude eruptions </li></ul><ul><li>Also found at hotspots </li></ul><ul><li>Convergent margins </li></ul><ul><li>Cone shaped </li></ul><ul><li>Less frequent, more explosive eruptions </li></ul><ul><li>More silica and cooler, so more viscous </li></ul><ul><li>Flows slowly, cools quickly creating cone shape with narrow base and greater height </li></ul><ul><li>Often composite with alternating layers of ash and lava </li></ul>Watch video
    13. 19. Hawaii – shield volcanoes Oceanic hotspot location Volcanoes formed by tectonic plate moving north west over hotspot Gently sloping sides New volcano, 3000m tall and 2000m below sea
    14. 20. Soufriere Hills, Montserrat – Composite volcano
    15. 22. Wherever possible, try to use examples we have already used e.g. Kiluaea, Montserrat, Yellowstone Volcano type Diagram Key features Explanation Example Fissure Shield Dome Cinder Composite Caldera
    16. 23. Types of eruption <ul><li>Hawaiin – calm, non explosive </li></ul><ul><li>Vulcanian – explosive, short lived </li></ul><ul><li>What type of eruption is associated with your case studies? Why? What impact has this had? Add this to the explanation column on your table </li></ul>
    17. 24. Suggested resources <ul><li>Read pages 253-255 OUP text book </li></ul><ul><li>Pages 162-165 Byrne et al </li></ul><ul><li>Page 67 Frampton et al </li></ul><ul><li>Page 14-15 Nagle </li></ul><ul><li>Page 22-26 Waugh </li></ul><ul><li>National geographic “Forces of nature” – see types of volcano link on Moodle </li></ul><ul><li>Explore google earth locations </li></ul>
    18. 25. Next lesson …. <ul><li>Intrusive igneous landforms </li></ul>