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Volcanic hazards
Volcanic hazards

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1.3 Volcanoes and tsunamis

The collapse of a volcano (or, more usually, part of it) links volcanology with tsunami studies. A debris avalanche is a hazard in its own right but, if it enters the sea or a lake, it can cause a tsunami that is capable of taking lives even on a distant shore. So-called 'megatsunamis' caused by the collapse of a large part of a volcanic island (Figure 6) are a matter of controversy. Collapses definitely occur because giant debris avalanche deposits have been mapped on the ocean floor, but scientists don't know whether such events are generally rapid enough to cause a serious tsunami.

Activity 1b

By what methods can volcanic activity cause tsunamis other than a debris avalanche or giant landslide?

Answer

By underwater explosions, by pyroclastic flows entering the water, and by the collapse of a submarine caldera.

Figure 6 Output of a computer model showing the possible effect of a collapse of Cumbre Viejo in La Palma, Canary Islands generating a megatsunami in the Atlantic Ocean. Numbers are height in metres at the point corresponding to the nearest yellow dot; red is above normal (wave crests) and blue is below normal (wave troughs). (TYVET Figure 5.17 is frame H in this sequence.)
Figure 6 Output of a computer model showing the possible effect of a collapse of Cumbre Viejo in La Palma, Canary Islands generating a megatsunami in the Atlantic Ocean. Numbers are height in metres at the point corresponding to the nearest yellow dot; red is above normal (wave crests) and blue is below normal (wave troughs). (TYVET Figure 5.17 is frame H in this sequence.)

Box 2 One tsunami, two tsunamis?

Tsunami is in origin a Japanese word. The Japanese language has no plural form for most nouns, so some English authors use tsunami interchangeably for both singular and plural. That does not look right to me. In this course I treat tsunami as a naturalised English word, and write tsunamis so it is always clear when I am referring to more than one. I think you would be very surprised if instead of lahars I used the Indonesian plural of lahar , which is laharlahar.