Chapter 6 Study Guide
6.1 – Volcano Formation
Know the following terms:
Volcano
Magma
Lava
Ring of Fire
A weak spot in the earth’s crust from which lava comes to the surface
Molten minerals, gases, and water vapor that forms rocks located in the ground
Magma that has reached the earth’s surface
The belt of volcanoes that border the Pacific plate. ¾ of the world’s volcanic activity
occurs here.
A string of islands formed from volcanic activity at convergent boundaries
A thin, weak spot in which the mantle has burned through the middle of a continental or
oceanic plate.
Island Arc
Hot Spot
Two Types of Lava:
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Low silica – runny, thinner lava that flows easily (Hawaii, mid-oceanic ridge)
High silica – thicker, “Stickier” lava – pressure can build up and cause explosive eruptions, lava bombs
Sketch or trace in the ring of fire on a global map:
Know that ¾ of the Earth’s volcanoes are here
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Mostly formed from convergent boundaries
Volcanoes from Divergent Boundaries
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Mid-oceanic ridge
Engine for sea-floor spreading and continental drift
Lava is mostly BASALT from oceanic crust
Found UNDERWATER
Barely ever reaches ocean surface (Iceland is one place they do)
Volcanoes from Convergent Boundaries
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Oceanic crust flows under continental crust
Caused by SUBDUCTION
Salt water trapped in magma weakens the rock above it
o Lower density and higher temperature magma flows up and creates volcanoes
 In ocean = island arcs
 Can occur many miles inland
 Proof of this:
o Aquatic microbes found in magma
o Magma is high in oceanic minerals (hornblende)
6.2 – Volcano Composition and States
Label a volcano with the following terms: Pipe, Vent, Crater, Lava Flow, Magma Chamber
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Pipe – tube in middle of volcano through which magma is forced to the surface
Crater – bowl shaped opening at the top of a volcano
Vent – a smaller opening that branches off the main pipe or throat of the volcano
Lava Flow –lava that runs down the side of the cone
o Pyroclastic Flow
Magma Chamber – the underground “storage” of the magma for the volcano. Can be under pressure
Magma
o High silica – sticky, thick lava
o Low silica – darker, flows easily
Types of Volcanic Eruptions
Quiet Eruption
Explosive Eruption
Lava flows easily (like a liquid)
 Thick and sticky lava
Hawaii and Iceland
 Gas bubbles get trapped – increasing
pressure
Lava leaks out of cracks on the sides
 Explosion can break open the mountain
and launch ash, rock, cinder (pyroclastic
flow)
States of Volcanoes
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Active – at least one eruption in the last 10,000 years
Dormant - has not erupted in the last 10,000 years, but still has a magma chamber and is expected to erupt
again
Extinct – no eruptions in the last 10,000 years and magma chamber has cooled.