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 VolcanoMost 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.

Types of volcanoes

Cinder cone volcanoSmallest 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

Wide crater at the top.

Usually only erupt once as the force of

the explosion destroys the cone.

Usually found near shield volcanoes and

Composite cones eg Mauna Loa in

Hawaii has more than 120

Cinder Cones around Mauna Loa

Mauna Loa

• Shield volcano: usually form at hot spots, Form from many layers of “runny” lava. Usually

form from hot spots or sometimes as constructive plate boundaries

Very wide, not to steep – formed from gentle eruptions – not much explosive material in magma – successive eruptions build up to form gently sloping volcanoes

Biggest type of volcanoes

Tallest mountain in the world is Mauna Kea (measures from sea floor to top = 6.3 miles

non explosive eruptions kilauea

Shield Volcanoes

Kilauea

Mauna Kea, Hawaii

Kilauea

Shield Volcano in New Mexico

Composite volcano: StratoVolcano

Eruptions alternate between explosive and non-explosive – formed at both constructive and destructive boundaries.

Sometimes they have runny lava layers, other times they have pyroclastic materials (ash, dust, rocks) that form layers.

Have a wide base and steep sides sides get steeper towards the summit.

Have a crater

Example - 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.

Explosive eruptions

Felsic flow means magma with high feldspar and silica 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.

Lava has a high viscosity – this means it flows slowly

Convergent zones contain lots of water,

therefore have explosive eruptions.

Associated with subduction

Non explosive

eruptions

Non explosive eruption -Build only enough pressure to allow lava to run down its sides.

Mafic flow: refers magma (and rocks) rich in magnesium and iron

This type of lava is very runny.

It has a low viscosity

As magma nears the surface there is little pressure, causing gasses escape easily.

Magma low in Silica have quiet eruptions

Associated with Mid Ocean ridge

eruptions

Pyroclastic Material

Four types of lavaAa: 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.

Aalava that is thick and sharp

Pahoehoe:lava that forms thin crust and wrinkles

Pillow lavalava that erupts under water, has a round shape

Blocky – pasty lava

lava that does not travel far from eruption, jagged when it dries.

Stages in the life cycle of a Volcano

1 – Active – erupts regularly eg Mt. Etna, Sicily, Mt St Helen’s in USA

2 – Dormant – Has not erupted in a long time but may erupt again eg

Cotoaxi in Peru

Extinct – has not erupted in recorded history – roughly

10,000 years since last eruption

Mt. Togiak in Alaska

Volcanoes at Divergent BoundariesAt 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)