A stratocone volcano is a steep pointy volcano. If the magma chamber1 within the volcano grows, it can make the volcano unstable and cause it to collapse. If the volcano is in the sea, this massive disturbance can generate a tsunami2.
Dr Graham Leonard, a natural hazard scientist and geologist3 with GNS Science, works with students from Te Kura4 o Te Pāroa to model the collapse of a magma chamber and the tsunami wave it generates.
Questions for discussion
- In this model, what does the balloon represent?
- What does the water represent?
- What does the sand along the edge of the container represent?
- How does this model represent a collapse at Whakaari/White Island?
- Do you know of other locations where this type of collapse has caused a tsunami?
- What are the strengths of using this activity to model a tsunami caused by a huge disturbance in or under the water? What are the drawbacks?
Transcript
Dr Graham Leonard
Why do you think we’ve got sand and water out for this experiment? What do you reckon we’re gonna …
Student
A volcano.
Dr Graham Leonard
Yeah. So the sand is gonna be the volcano. And why are we using water, what’s the other thing?
Student
A tsunami.
Dr Graham Leonard
Yeah, totally. We’re going to make a volcanic island – this is Whakaari, and we’re gonna finish it in a minute. And this is the coastline nearby. What’s the name of the town near Whakaari?
Students
Whakatāne?
Dr Graham Leonard
Yep. Can you guys help me now? Take two hands, like a double scoop like this, and gently build me a volcano over my magma chamber please.
Student
Oh, so like carry over the sand?
Teacher
Someone else grab the pump. Magic. Yep.
Student
Can I have a go?
Dr Graham Leonard
Yep. Stop.
Student
Sorry. Whoa. Slower?
Dr Graham Leonard
Yep. Just a little bit. You’re going to get to blow it properly in a minute but we’re going to build a volcano first. So take all of the sand in big double scoops – with two hands, yeah, and build me a volcano on top. So don’t be shy – just like this. Cool. Now we’re making a big volcano, keep going.
Student
Oh, I want to see what happens.
Dr Graham Leonard
Keep going. We want to go real high and pointy. Just like in a Disney movie.
Student
So we’re building Whakaari or …
Dr Graham Leonard
We’re building Whakaari, exactly. So Whakaari has in its past often been quite a pointy volcano. OK, add the rest on and don’t pack it down – just put it on gently – on top. Yep, cool. Now, time to come up with an idea, and in science, what’s our word for idea?
Student
Hypothesis5.
Dr Graham Leonard
Yeah, totally. So come up with a hypothesis. So when we inflate the magma chamber – more magma6 inside the volcano – what do you think is going to happen slowly?
Student
Explode.
Dr Graham Leonard
It could explode, yeah. That’s one idea – one hypothesis. What else might happen if we just keep expanding it without it exploding?
Student
Break the volcano.
Dr Graham Leonard
Yeah. And can you describe that a bit? Will it collapse? OK?
Students
It will release the air pressure7. Destroy it.
Dr Graham Leonard
And if it collapses, where’s it gonna go?
Student
Flow out the sides.
Dr Graham Leonard
Yeah, it’s gonna collapse into the …
Student
Ocean.
Dr Graham Leonard
Yeah. And then if it disturbs the ocean, what do we call that?
Student
Tsunami.
Dr Graham Leonard
Yeah! And over here …
Student
Is us.
Dr Graham Leonard
What have we got? This is us, yeah? And these are little …
Student
Houses.
Dr Graham Leonard
These are little whare near the coast and they’re above the waterline, but should we see if our volcano is big enough to cause a collapse and cause a tsunami that will reach the whare? So that’s our hypothesis and now this experiment is going to test it.
So can you slowly pump up the magma for me, please? Yep – yeah, you’re right. Keep going. Bit faster now. Go. Keep going. Keep going. And watch the houses.
Students
Oh!
Dr Graham Leonard
Oh, one or two are OK – they’re a bit higher ground. You’re done, you’re done. All done.
Teacher
So you notice the ones on higher ground?
Student
Yeah.
Teacher
These ones are OK. You see where the water’s come to?
Dr Graham Leonard
Yeah.
Student
Oh, so the balloon expanded, which meant the …
Dr Graham Leonard
Totally.
Teacher
So what kind of volcano is that – do we think, guys?
Students
Ummm … pointy, active.
Teacher
Pointy? Yeah, it is active.
Dr Graham Leonard
What does Whakaari, what does Whakaari look like now?
Students
Oh! Like that!
Dr Graham Leonard
Yeah! And why do you think it looks like that?
Students
Ahhh! Cause it collapsed.
Dr Graham Leonard
Cause it collapsed – just like your experiment.
Acknowledgements
Dr Graham Leonard, GNS Science, Beneath the Waves MBIE Endeavour project
Professor Ben Kennedy, University of Canterbury, Beneath the Waves MBIE Endeavour project
Te Kura o Te Pāroa
Drew Mehrtens, University of Canterbury
