Chapter 3 Review
Cones, Eruptions, and Pyroclasts

Name Answer Key

  1. What is lava?
    Lava is molten rock on the surface of the Earth.

  2. Name the two smallest particles of pyroclastic material.
    Dust is the smallest of the pyroclasts and ash is the second smallest.

  3. Name the two largest particles of pyroclastic material.
    Blocks are large, sharp edged pyroclasts. Bombs are large, smoothly shaped pyroclasts

  4. What is a pyroclastic flow?
    A twirling mixture of very hot ash, gases, and other pyroclastic materials that are heavier than air and flow down a volcano at high rates of speed. (700 degrees and 100 miles per hour)

  5. What is the difference between pahoehoe and aa lava flows?
    Aa lava flows are very rough and fragmented. They are blocky in their appearance. Aa usually flows at a high rate of speed and cools slowly.
    Pahoehoe usually flows at a very slow rate of speed. It is smooth and ropey in appearance.

  6. What is the difference between high and low viscosity magma?
    High viscosity magma is very thick and pasty. It usually has a large amount of dissolved gas . It usually erupts violently.
    Low Viscosity magma is thin and runny with little dissolved gas. It usually erupts with thin flows of lava very quietly.

  7. How does a lava tube form?
    A lava tube forms a tunnel when the surface of the lava flow cools and hardens, while the interior keeps flowing through, draining away , leaving the interior hollow.

  8. Name the two reasons that volcanic eruptions occur?
    Magma will rise to the surface of the Earth when it is less dense than the surrounding rock in the mantle. When the magma reaches the surface of the Earth the pressure difference between the gases in the magma and the surface pressures allows the magma to boil out.

9-14. Draw the three volcanic cone shapes and label each.
Shield Cone-


Cinder Cone-

Stratovolcano or composite cone-

15-16. What are the two most non-explosive eruption types?
Icelandic and Hawaiian eruptions are the least explosive and dangerous of the eruption types.

17-18. What are the two most explosiveeruption types?
Plinian is the most explosive and Pelean is the deadliest.
19. What is a hot spot? Use the term mantle plume in your definition.
A hot spot occurs near the crust where very hot solid rock rises through the mantle (a mantle plume) and forms magma near the surface of the Earth. Hot spots form volcanoes in both oceanic plates and continental plates.

20. What is a caldera?
A caldera is a bowl-shaped depression caused by a volcanic eruption in which the top of the volcano collapses.

21. How does a caldera form?
A caldera will form when a volcanic eruption depletes the magma chamber causing a void under the volcano's summit. The weight of the top of the volcano causes it to collapse. A bowl-like depression or hole forms there.

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