Pyroclastic Rocks

 

Study Questions for Exam I

Fall 2003

 

  1. How does the role of magmatic water and carbon dioxide differ in their effect on magmas?  How does their role differ in the cause of explosive eruptions?  Give examples of eruptions in which water played the dominant role.  Give an example of an eruption in which carbon dioxide was the predominant volatile?
  2. Explain how the partial evacuation of a zoned magma chamber could lead to a layered Plinian fall deposits.  Give an example of a fall deposit that illustrates these phenomena. Give as many specific details as you can.
  3. How could the concept of neutral buoyancy lead to the development of a large silicic complex that produces Plinian fall deposits and pyroclastic flows of several hundred km3.  Give some supporting evidence.
  4. What is the effect of air entrainment on the rise of a pyroclastic plume?  Cite the physical factors that effect entrainment and buoyant rise.  Give specific examples of plumes that didn't rise much more than a few hundred meters and those that reached the stratosphere.  Explain why there is such a difference.
  5. Explain the general principles of the conservation of mass, momentum, and energy in a rising plume.
  6. Describe the changes in density (relative to the ambient atmosphere) and velocity with height in a volcanic plume.  Why does column collapse sometimes occur?
  7. Give a physical description of the manner in which the sedimentation equation of Hazen (1904) works.
  8. How do the particle sizes and components of a strong volcanic eruptions, like that of Mount St. Helens or Vesuvius in AD 79, change with distance?  Give some supporting evidence.
  9. What are some of the main characteristic of tephra from Plinian fall deposits that can be recognized in the field?  What specifically can some of these features tell you about the nature of the eruption?
  10. Using a histogram of grain size data, interpret the process(es) responsible for the population(s) represented.
  11. Write down the equations of motion for conduit flow.  What are the assumptions used to be able to write the equations in this form?
  12. How can juvenile pyroclasts be distinguished from hydrovolcanic tephra?  What causes these differences?
  13. Explain how a scoria cones grows.  Show McGetchin's 4 stages of growth.  Explain the physics behind the ballistic ejection of bombs during Strombolian eruptions.