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Types of Volcanoes

Key Concept: Tectonic plate

motions can result in volcanic

activity at plate boundaries.

Volcanoes

How do volcanoes work?

How do volcanoes work?

• Magma is forced onto

Earth’s surface.

• It dries and hardens,

this happens many

times over thousands

of years.

• Eventually a mountain

called a volcano is

formed.

Parts of a Volcano • Most volcanoes share a

specific set of features.

• The magma that feeds the eruptions pools deep underground in a structure called a magma chamber.

• At Earth’s surface, lava is released through openings called vents.

• Flowing lava in the interior travels through long, pipelike structures known as lava tubes.

Where do most volcanoes occur?

• Volcanoes occur at

both divergent and

convergent

boundaries and also

at hot spots.

Volcanoes at Divergent

Boundaries • At a divergent boundary, the lithosphere becomes

thinner as two plates pull away from each other.

• A set of deep cracks form in an area called a rift zone.

• Hot mantle rock rises to fill these cracks.

• As the rock rises, a decrease in pressure causes hot mantle rock to melt and form magma.

• The magma that reaches Earth’s surface is called lava.

Basaltic magma rises to Earth’s surface through these fissures and erupts non explosively ( it flows out as runny lava)

Types of volcanoes

Cinder cone volcano

• Smallest type of volcano

• Most common

• Made from pyroclastic material (material

shot out of a volcano)

• Form a large crater

• form from explosive

eruptions, very steep.

• Shield volcano: usually form at hot spots,

• Form from many layers of “runny” lava.

• Very wide, not to steep.

• Biggest type of volcanoes

• Tallest mountain in the world is Mauna Kea (measures from sea floor to top)

• non explosive eruptions kilauea

Mauna Kea, Hawaii

Composite volcano: • Eruptions alternate between explosive and

non-explosive.

• Sometimes they have runny lava layers,

other times the have pyroclastic materials

form layers.

• Have a wide base and steep sides.

• Have a crater

• Mount Fuji

Mount Fuji

• mt fuji

2 Types of eruptions

• Explosive: volcanoes that build enough pressure to blow its top, sending pyroclastic material into the air.

• Non explosive: Build only enough pressure to allow lava to run down its sides.

Non explosive eruption

• Mafic: refers to rocks and magma rich in

iron and magnesium.

• This type of lava that is very runny.

• As magma nears the surface there is little

pressure, causing gasses escape easily.

• Magma low in Silica have quiet eruptions

Explosive eruptions

• Felsic: means magma with high silica and feldspar content.

• Felsic magma traps water and gas bubbles, which leads to lots of pressure.

• Silica acts like a cork

• Explosive eruptions are caused by a build up of high pressure.

• Convergent zones contain lots of water, therefore have explosive eruptions.

Pyroclastic materials

• Material that is thrown into the air during

an explosion.

• Volcanic bombs: large blobs of magma

that harden in the air.

• Lapilli: pebble size rocks

• Volcanic ash: tiny powder like material

Four types of lava

• Aa: lava that is thick and sharp

• Pahoehoe: lava that forms thin crust and

wrinkles

• Pillow lava: lava that erupts under water,

has a round shape

• Blocky lava: cooler, lava that does not

travel far from eruption, jagged when it

dries.

Aa

• lava that is thick and sharp

Pahoehoe:

• lava that forms thin

crust and wrinkles

Pillow lava

• lava that erupts under

water, has a round

shape

Blocky lava

• cooler, lava that does

not travel far from

eruption, jagged when

it dries.