Volcanic Eruptions and Volcano Type

Volcanic Eruptions and Volcano Type

What is a volcano?•A volcano is any place where gas, ash, or melted rock come out of the ground.

Anatomy of a Volcano

• Crater– Lava collects in the

crater, the bowl-shaped area that forms around the volcano’s vent.

Volcano Menu

CraterVent

Lava Flow Pipe

Magma chamber

Side Vent

• Vent– The point on the

surface where magma and gas leave the volcano’s pipe.

Volcano Menu

CraterVent

Lava Flow Pipe

Magma chamber

Side Vent

• Pipe– A narrow, almost

vertical crack in the crust through which magma rises to the surface.

Volcano Menu

CraterVent

Lava Flow Pipe

Magma chamber

Side Vent

• Magma Chamber– A large underground

pocket of magma that forms from magma rising to the surface.

Volcano Menu

CraterVent

Lava Flow Pipe

Magma chamber

Side Vent

• Lava Flow– The river of lava

that pours down a volcano over the land.

Volcano Menu

CraterVent

Lava Flow Pipe

Magma chamber

Side Vent

• Types of Volcanic Eruptions– A volcano’s magma

determines its volcanic cone and influences how the volcano erupts.

– The silica content helps determine whether the volcanic eruption is quiet or explosive.

Shield Cones and Quiet Eruptions (Examples: Grimsvotn of Iceland and Kilauea of Hawaii)

*Form as a result of sea-floor spreading or “hotspots” in the Earth’s mantle.

• Shield Cones and Quiet Eruptions– Magma flows easily.– Dissolved gases in the magma bubble out easily.– Thin runny lava oozes from the vent and flows

• Volcanic Hazards of Quiet Eruptions– Quiet Eruptions:

• Lava flows- set fire and bury everything in their path.

Composite Volcanoes and Explosive Eruptions (Examples: Mount Vesuvius of Italy and Mount Saint Helens Washington State)

*Form as a result of subduction.

• Volcanic Hazards– Time between

eruptions for composite cones can span hundreds of years.

(Dormant Volcano)– Example: Mt. St.

Helens 123 years.– People may be

unaware of the danger.

• Explosive Eruptions• Magma is thick and

sticky.• Thick magma builds up

in the pipe, plugging it like a cork in a bottle.

• Pressure builds up due to the gases in the magma until the volcano explodes.

• Volcanic Hazards of Explosive Eruptions– Lahar:

• A mud flow caused by melted snow.

– Carries ash, trees and rocks.

• Explosive Eruptions• The gases push the

magma out with incredible force.

• The explosion breaks lava into fragments that quickly cool and harden into different sizes.

• Explosive Eruptions• Fragments:

– Volcanic Ash» fine, rocky, grain of

sand sized particles.– Cinders-

» pebble sized particles– Bombs-

» large pieces of rock (baseball to the size of a car)

• Explosive Eruptions• Pyroclastic Flow

– Occurs when an explosive eruption hurls out ash, cinders and bombs as well as gases. (400mph, 1,800˚F)