Study Guide for Volcanology - Exam 2 - Geology 309

One 3x5 index card "cheat sheet" is allowed. Writing only on one side!!!!

Plinian eruptions & airfall deposits

Dynamics - gas thrust region, convective region, umbrella region

How does width of eruption column vary upwards? What does height of eruption column depend on?

Be able to use and interpret the terms tephra, isopleth, isopach, terminal velocity, clast-support envelope, clast size half distance, thickness half distance.

How does size of eruption column control distribution of tephra fallout from a Plinian column?

How does wind control distribution of tephra fallout from a Plinian column? Is tropospheric wind or stratospheric wind more important in deflecting Plinian columns?

Why is the understanding of eruption columns and their fallout so important to aircraft safety? Why is the ash dangerous to aircraft?

If you were a brand new volcanologist sent to map tephra deposits from a Plinian eruption, what would you do? Why? (i.e., what would be your mode of attack for this project? What four features would you look for/measure? Why?)

Be able to calculate from an isopach and isopleth map the clast size half distance and the thickness half distance (see voluntary homework)

Be able to locate where deposits from a particular type of pyroclastic eruption should fall on a Pyle diagram (i.e., understand the diagram)

How do the pyroclastic deposits (not lava flows) from a Hawaiian, Strombolian, Vulcanian, Plinian, Surtseyan, and Phreatoplinian eruption differ? (i.e., characterize each)

Pyroclastic flows – general (see following headings for specifics)

Definition of pyroclastic flow (general)

Types of pyroclastic flows:

• Pumice flows, surges, block and ash flows (nuees ardentes)
• How are they different? How are they the same? (including their clast density and flow density)
• Flow characteristics of each
• Deposits of each (names and characteristics)

Pyroclastic flows - pumice flows

Why does a Plinian column collapse to form pumice flows? How do you lose the density advantage ((describe the major variables - mass eruption rate, eruption velocity, vent radius)?

What type of speeds do these flows travel at?

What are the two main driving forces for their rapid movement?

Characteristics of ignimbrite deposits from pumice flows (standard cross section, particles present, sorting, grading, etc.). Why do ignimbrites often overlie tephra fall deposits?

How might you recognize if an ignimbrite had been highly fluidized while it was being transported?

How can you distinguish between an ignimbrite and a tephra fall deposit?

What does welding do to an ignimbrite? How and why does it happen? In what part of an ignimbrite would you most expect to see welding? What is a fiamme?

Pyroclastic flows - surges

What are they? How do they form?

Know the difference between: Base Surge, Ground Surge, Ash Cloud Surge, Blast Surge. Describe the mechanism for how each of them occur. Describe the characteristics/deposits of each. Which ones are hot/cold?

Pyroclastic flows: nuees ardentes (a.k.a. block and ash flows)

What are they? How do they form?

Are they hot or cold deposits? How do you know?

How are they different than pumice flows? What is the main driving force for their rapid movement (compare to pumice flow)

What are the 3 types of block and ash flows? Describe the origin of each (i.e., how do they differ?). How might their deposits differ?

Debris flows: debris avalanches

Discuss the three types of debris avalanches (Bezymianny, Bandai, cold). How are they different/similar?