Science, Maths & Technology

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Volcanic hazards

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# 1.5 Test what you've learned

Now that you've reviewed this course and completed the activities, try answering these questions to test what you've learned.

## Question 1

Give at least three reasons why TYVET Table 5.2 (p. 118) would be an unreliable guide to the relative proportions of fatalities from various volcanic causes during the next 100 years.

1. The data in the table are incomplete or unreliable for many parts of the globe, especially in the first half of the 400-year period considered.
2. Few eruptions of VEI 7 and above occurred in that period. A single such eruption could change the balance completely.
3. Population growth is continuing to put more people at risk.

## Question 2

If you were at the foot of an erupting volcano and wanted to escape with your life, would you rather see a lava flow or a pyroclastic flow heading towards you, and why?

You would prefer to see a lava flow because pyroclastic flows travel much faster than lava flows (about 100 km per hour), whereas most lava flows barely exceed walking pace (although the exceptional Nyiragongo flow in 1977 moved at 30 km per hour). So, provided you are alert and able, you could get out of the way of a lava flow (unless escape routes are blocked), whereas you would be much less likely to evade a pyroclastic flow.

## Question 3

List the different ways in which a pyroclastic flow can be initiated, and for each case cite one example of a specific eruption where this occurred.

A pyroclastic flow can be initiated by:

1. dome collapse, e.g. Mount Pelée in 1902 (also Unzen in 1991, Soufriere Hills, Montserrat in 1997 and many others)
2. directed blast, e.g. Mount St Helens in 1980
3. column collapse, e.g. Mount Pinatubo in 1991 (also El Chichón in 1982, Vesuvius in AD 79, and many others).

## Question 4

Describe the hazards associated with ongoing airfall, and any relevant preventive measures. (One sentence per hazard)