Measuring Explosiveness: The Volcano Explosivity Index

Question 1

Because it is difficult to assess the magnitude of an earthquake, the explosiveness of an eruption can be obtained from what?

Answer 1

The airborne volcanic products (tephra) which have been fragmented.
The greater the explosivity the greater the fragmentation of the tephra deposits.

Question 2

What did Chris Newhall and Steve Self develop?

Answer 2

A simple, semi quantitative scheme for estimating the magnitude of historic eruptions.
Volcano Explosivity Index - VEI.

Question 3

Historical eruptions can be assigned a VEI number on what scale? and using what criteria?

Answer 3

Scale of 0 - 8.
Using:
Volume of ejecta
Height of eruption column
Qualitative descriptions - gentle, explosove
Style of past activity
Height of spreading of the eruptive plume head.

Question 4

Which 2 bits of criteria are the most reliable when giving an eruption a VEI number?

Answer 4

The volume of ejecta.

The plume height of eruption column.

Question 5

How is the VEI similar to the richter scale?

Answer 5

Because in each interval on the VEI represents an increase in magnitude of about 10.
Both logarithmic.

Question 6

According to the VEI scale, the higher the magnitude indicates what?

Answer 6

The lower the eruption frequency.

Question 7

What is a negative about the VEI?

Answer 7

It doesn’t measure gas emissions.

Question 8

Give an example of a low magnitude volcano.

Answer 8

Kilauea.

Question 9

Give an example of a high magnitude volcano?

Answer 9

Toba.

Question 10

A volcano with a scale of 0-2 VEI is said to be what?

Answer 10

Frequent.

Low

Question 11

A volcano with a scale of 6-8 VEI is said to be what?

Answer 11

Only several per 100,000 years.

Question 12

Last VEI 8?

Answer 12

73,000 years ago to Toba

Question 13

How to determine frequency ?

Answer 13

Look at previous history of activity

Using deposits of volcano itself