Supervolcanoes and calderas !

The Volcanic Explosivity Index- how big is a supereruption ?

VEI- 5 Plinian, Mt St Helens

VEI 3VulcanianMontserrat

VEI 1 Hawaiian

VEI 6 Ultra-plinian Mt Pinnatubo

VEI 8 Imagine 100 Pinnatubos erupting at the same time

Supervolcanoes and calderas !

• Caldera - created from large, explosive eruptions of felsic pyroclastic material. The caldera is created when the roof of the magma chamber collapses.

• Can be 10’s km’s across

• Different from a crater

E.g., • Yellowstone, WY, 1 m.y.

Huge caldera, so big it could only be seen from space

http://youtube.com/watch?v=Abg5-gLdEb0

Supervolcano !

Why are supervolcano eruptions so big ?

• A) There is a higher % of gas in the magma• B) The collapsing magma chamber roof helps

the eruption• C) The magma is more viscous• D) A large volume of magma was ready to erupt• E) Eruptions occur simultaneously from a ring of

vents.

http://www.cotf.edu/ete/movies/caldera.mov

Which type of volcano would you rather live beside and why?

Cinder coneStratocolcano(composite)Sheild volcanoSupervolcano with caldera