GEOLOGY 108: Crises of the Earth

Homework #3 - Volcano exercise

The object of this assignment is to review WWW information available for the 1991 eruption of Mt. Pinatubo, in the Philippines. This large eruption had a severe impact both locally and to some extent globally. We would like for you to use as a primary resource the links provided below:

  1. Description of Mt. Pinatubo - from the USGS Cascades Volcano Observatory
  2. Report on 1991 eruption - by E.W. Wolfe (1992)
  3. Effects of large eruptions on climate
  4. The Volcanic Explosivity Index - a measure of eruption size
  5. You may consult any other references you like, although this is not required

We would like for you to address the following questions. The answers may be brief (no more than one page), but they must be informative. This information is due in class on Thursday, 1 March, and will be the basis of some in-class discussion.

Questions:

  1. What was the principal type of volcanic eruption and what kinds of deposits were formed?

  2. What were the main impacts on local communities at the time of the eruption? What is the situation in the vicinity of Pinatubo today - are there continuing effects that persist to the present and what is the outlook for the future?

  3. What was the geographic extent of the impact (e.g., how many square miles or kilometers were blanketed with greater than or equal to 5 cm (~2 inches) of ash or tephra)? What is the radius of a circular area of this extent (remember, A = pi*r2; 1 mile = 1.6 km; pi = 3.14)? How does this compare to the greater Houston area (about a 25 mile radius).

  4. Using the following resources, how does the 1991 Pinatubo eruption compare in size and potential effect with Cascades eruptions (e.g., 1980 Mt. St. Helens, or the 8800 yrs. B.P. Mazama eruptions)? Try to imagine the comparative impact of a another eruption like that at Mazama if it occurred today (we can discuss in class).

  5. How many tephra sets (ash sequences) have originated from Mt. St. Helens in its approximately 50,000 year history? What is the corresponding average recurrence interval (years between events)? Comment on the utility of this number in predicting the next serious eruptive phase?

  6. What would be the likely effect of a similar eruption were it to occur at one of the dormant Cascades volcanoes - say Mount Saint Helens in Washington State?

  7. What was done to lessen the impact of the 1991 Pinatubo eruption? How effective were these measures in terms of saving lives and/or property? What else could be done to minimize effects of the hypothetical MSH eruption

Some helpful resources and overview can be found on Bill's Volcano Hazards web page.

-----LAST MODIFIED: 2/21/01
-----BY: Leeman & Sawyer