Pyroclastic Fall Deposits

433/533 Class Exercise

 For this exercise you are given a set of pyroclastic fall deposit samples which you should examine carefully and describe the following features:

1. Tephra size
1. Maximum size clasts for both pumice and lithics
2. Percent of fine ash
2. Components (weight % of juvenile, crystal, and lithic clasts)
3. Type (composition and phenocrysts of the juvenile rock)
4. Vesiculation of juvenile particles (% of vesicles)
5. Crystallization (percent, size and type of crystals)

 From the data set that you have assembled state your conclusions as to:

1.  Name the explosive eruption type responsible the clasts

2.  Comments on the eruption characteristics and differences between samples, especially compare COT-0301 A, B, & C.

The sample set consists of these samples:

1.     COT-0301A

2.     COT-0301B

3.     COT-0301C

4.     COT-0304

5.     STU-9328

All samples labeled COT came from Cotopaxi Volcano, Ecuador.  Samples COT-0301 were collected at the same outcrop about 10 km from the summit.  The letters A-C refer to collection levels from the base to the top of the exposure.  Samples A & B are the lower and upper parts of the same depositional bed.  A soil separates sample b from sample C.  Sample COT-0304 was from the summit of the volcano.  Sample STU-9304 comes from the 1907 eruption products of Stubel Volcano, Kamchatka.