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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 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
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)
