Volcanoes 3

2 types of volcanic eruptions

1) effusive

2) explosive

effusive meaning

• outpouring of molten magma from the vent

• passive eruption of magma

explosive meaning

• gas driven violent eruptions

• pyroclastic deposits

lava flows are (felsic/mafic/ etc)

mafic intermediate

lava domes are (felsic/mafic/ etc)

felsic intermediate

Pyroclastic flows are

gravitational collapse of lava flows/ domes

Magma produces bubbles during __

ascent

bubbles expand as the magma rises and lowers __

psi

Foaming leads to explosivity. explosivity depends on?

• amount of bubbles

• rate of rise

• bubble retention

As magma rises what happens?

• psi decreases

• bubbles form,

• but viscosity fights bubble growth!

• fragmentation occurs

• pyroclastic material produced

How does fragmentation of lava occur

• pressure rises inside the bubbles

• strength of the liquid magma is overcome

• fragmentation occurs

What magma fragments freze they become?

• ash particles

• ash

• pumice

what type of volcano will produce the most explosive eruptions?

stratovolcano

What are the charicteristics of a safe-ish volcano?

• mafic

• low viscosity

• low gas content —effusive

• gas escapes, pressure released

What are the characteristics of a dangerous volcano?

• felsic

• high viscosity

• high gas content —explosive

• gas kept under increasing pressure

Types of explosive eruptions (on land)

• hawaiian <2 km

• Strombolian <10 km

• vulcanian <20 km

• sub-plinian <30 km

• ultraplinian or plinian <55 km

Types of explosive eruptions (in water land)

• surtseyan <20 km

• Phreatoplinian <40 km

Hawaiian info

• <2km

• low viscosity

• basaltic magma

• effusive

Hawaiian activity

• lava fountain

• lava lake

• lava flow

Strombolian info

• <10 km

• basaltic and andesitic magma

• mildly explosive

Strombolian activity

• lava fountain

• volcanic bomb

• lava flow

Vulcanian info

• <20 km

• viscous andesitic and rhyolitic

• very explosive

Vulcanian activity

• sustained explosions of ash

• ash plume

• lapilli

• volcanic ash fallout

• volcanic bomb

Plinian info

• sub-plinian <30 km

• ultraplinian and plinian < 55km

• andesitic and rhyolitic ash

• violently explosive

Plinian activity

• large sustained column of ash

• pyroclastic flows

• ash plume

• volcanic ash fallout

Phreatomagmatic ingo

• contact between water and magma

• water —> steam

• violently explosive

• surtseyan and phreatoplinian

Phreatomagmatic activity

• water vapour clous

• compressed ash

• crater

• water

VEI scale depends on

1) volume of ash produced

2) height of eruption cloud about vent

3) duration of eruption

Examples of VEI

• Shield Volcano VEI 0-1

• Vulcanian VEI 3

• Mt St Helens VEI 4.5

• Yellowstone VEI 8