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VOLCANOES

VOLCANOES. YEAR 7. 1. VOLCANOES AND PLATE TECTONICS. 1995, Soufriere Volcano in Montserrat (Caribbean). Volcanic pictures A volcano is a weak spot in the crust where molten material, or magma, comes to the surface.

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VOLCANOES

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  1. VOLCANOES YEAR 7

  2. 1. VOLCANOES AND PLATE TECTONICS 1995, Soufriere Volcano in Montserrat (Caribbean). Volcanic pictures A volcano is a weak spot in the crust where molten material, or magma, comes to the surface. Magma is a molten mixture of rock-forming substances, gases and water vapor from the mantle. When magma reaches the surface is called lava.

  3. There are around 600 active volcanoes on land. Many more lie beneath the sea. Volcanoes occur in belts that extend across continents and oceans. One major volcanic belt is the ring of fire. Volcanic belts form along the boundaries of Earth's plates. Most volcanoes occur along diverging plate boundaries, such as the mid-ocean ridge, or in subduction zones around the edges of oceans.

  4. Volcanoes at diverging plate boundaries: • Only in Azores Islands and Iceland, the volcanoes of the mid-ocean ridge rise above the ocean's surface • Volcanoes at converging plate boundaries: • Many volcanoes occur on islands, near boundaries where two oceanic plates collide. The resulting volcanoes create a string of islands called island arc such as Japan, New Zealand, Indonesia.. • Hot spot is an area where magma from deep within the mantle melts through the crust like a blow torch. Far from any plate boundaries. I.e.: Hawaii and Yellowstone (US)

  5. ISLAND ARC

  6. HOT SPOT

  7. 2. PROPERTIES OF MAGMA • Like all substances, magma and lava are made up of elements and compounds • Element is a substance that cannot be broken down into other substances. I.e.: C, H, O. • Compound is a substance made of two or more elements that have been chemically combined. I.e.: water (H2O), Carbon Dioxide (CO2), table salt (NaCl) • Each substance has a particular set of properties (chemical and physical) used to identify or to predict how this substance will behave.

  8. Physical property is any characteristic of a substance that can be observed or measured without changing the composition of the substance (density, hardness, melting/boiling point…) • Chemical property is any property that produces a change in the composition of matter (substance ability to burn, combine or react with other substances)

  9. Viscosity is the resistance of a liquid to flowing (physical property) • Because liquids differ in viscosity, some liquids flow more easily than others. Greater the viscosity, slower it flows. • Liquids have different viscosities due to the movement of the particles that make them up. • The viscosity of magma depends upon its: • Silica content • Temperature.

  10. Silica is made up of Oxygen and Silicon. Silica content of magma ranges from 50-70% • More silica magma contains, higher its viscosity • Viscosity increases as temperature decreases • Different types of lava according to temperatures: • Pahoehoe (fast moving, hot and low viscosity. It forms wrinkles, ropelike coils…) • Aa (higher viscosity. It forms rough surface consisting of jagged lava chunks)

  11. AA LAVA

  12. PAHOEHOE LAVA

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