Chapter 3 Test Answer Key

Chapter 3 Test
Cones, Eruptions, and Pyroclasts

Name Answer Key  


1.  ___C___Lava  A. Rough and fragmented lava flows 
2.  ___E___Pahoehoe  B. The most explosive eruption type. Ash plumes may reach 50,000 feet.
3.  ___B___Plinian  C. Molten rock on the surface of the Earth
4.  ___G___Hawaiian  D. Large pyroclasts-over 2 inches long with a rounded shape
5.  ___A___Aa  E. Smooth and ropey lava flows
6.  ___F___Low Viscosity  F. Thin and runny magma that usually erupts quietly with large amounts of lava.
7.  ___D___Bombs  G. Eruption type in which thin and runny magma reaches the surface of the Earth through the main vent and fissures.

8-9. Name 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. 
This is like opening a can of pop when it has been shaken. 

10-15. Name and draw the three kinds of volcanic cones.

Shield cone- Low and broad shaped cone formed from many eruptions of thin and runny lava.

Cinder ConeSteep sided cone formed from the ejection of pyroclastic materials. 

Stratovolcano or composite cone- Formed from many alternating eruptions of ash and lava. Beautifully symmetrical cones. 

16. What is a hot spot?
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. 

Fill in the blank with the correct answer. Use the following words to complete the blanks. Dust, Lava Tube, Mantle Plume, Ash, Caldera, Pyroclastic Flow, Blocks.

17. A large rough edged, angular pyroclast that is ejected during a volcanic eruption is called a block  .

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

19. The smallest of the pyroclasts are called dust  . They may stay in the atmosphere for years.

20. A lava tube  forms when the surface of the lava cools and hardens, while the molten interior flows through and drains away.

21.  Ash  is the second smallest pyroclast. This material along with lava builds stratovolcanoes larger with repeated eruptions.

22. A mantle plume  is very hot, solid rock that rises through the mantle and will become magma as it reaches the surface of the Earth. They form hot spots.

23. A pyroclastic flow  is a very hot, twirling mixture of ash, gases, and small pieces of pumice and other pyroclasts that are heavier than air and move down a volcano at high rates of speed.