Chapter 3


  1. Lava-
    Molten rock on the surface of the Earth.

  2. Pyroclasts (Pyroclastic Rock)-
    Pyro is Greek for fire and clastic means rock. Put them together and it translates into "Rock broken by fire". Pyroclasts are formed from the eruption of a volcano. Pyroclasts range in size from very small pieces of dust to ash to lapilli to bombs and block.

  3. Pahoehoe-
    A Hawaiian term for lava that has a smooth and ropey surface. Pahoehoe forms when the flow is slow and cools slowly.

  4. Aa-
    A Hawaiian term for lava that is rough and fragmented.
    Aa lava forms when the lava flow is faster and the outside cools quickly causing the outside to become rough and fragmented.

  5. Viscosity-
    The resistance of flow in a liquid. Lava/Magma that is thick and pasty is said to have a high viscosity. High viscosity magma can hold a large amount of gas. This lava/magma usually will erupt violently when the gas that is dissolved in the magma escapes rapidly. Lava/magma that is thin and runny is said to have a low viscosity. These lava/magma will usually not erupt very violently. These eruptions will produce large amounts of lava and little pyroclastic material.

  6. Tube-
    A tunnel formed when the surface of a lava flow cools and hardens, while the still molten and flowing interior drains away.
  7. Dust-
    The smallest of the pyroclasts. Dust from volcanic eruptions have been known to stay floating in the atmosphere for years.

  8. Ash-
    Pyroclasts that are larger than dust. Very fine particles of exploded rock that can drift in the atmosphere for days.

  9. Blocks-
    Angular pieces of pyroclastic rock that is exploded from a volcano during an eruption.

  10. Bombs-
    Rounded pieces of pyroclastic material that are exploded during an eruption. These pyroclasts are in semi-plastic state and take their shape as they fly through the air.

  11. Pyroclastic Flows-
    Very hot turbulent gases, ash, and pyroclasts that are heavier than air and will flow down the side of a mountain at high speeds. These flows have killed thousands of people in some famous eruptions such as Vesuvius in 79 A.D., and Pele on the island of Martinique in 1902.

  12. Pumice-
    Pyroclastic rock that is in a semi-plastic state as it is shot through the air. The rock is full of gases that escape as the rock hardens. This rock is so full of holes that it floats on water.

  13. Obsidian-
    Lava rock that hardens very quickly. It can cool when it hits water or flowing down the side of a mountain. This rock is natures glass. It usually is dark green to black in color. Native peoples throughout the world have used it to make arrowheads, spears, and knives. It can be chipped to a very sharp edge.

Lesson #8 Volcanic Cones and Eruptions
  1. Three Volcanic Cone Shapes-
  2. Eruption Types-
Lesson #9 Hot Spots-Hawaii and Yellowstone
  1. Hot Spot-
    A hot spot occurs because of the intense heat of the outer core. This heat radiates through the mantle bringing hot solid rock upward to the hot spot. These areas of rising solid rock are called mantle plumes. Hot spots do not move, but the plates above the hot spot moves producing island chains and the spreading of the oceans at mid-ocean ridges.

  2. Mantle Plume-
    Mantle plumes are areas of hot solid rising rock. This rock moves from the lower reaches of the mantle to the surface of the Earth causing the formation of volcanoes.

  3. Caldera-
    A caldera is a large bowl-shaped crater that is formed by the collapse of a volcanic cone after an eruption.

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