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Volcanoes
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A volcano is an opening (or vent) in the surface of the earth or sea floor where
magma comes out. This volcanic debris piles up or spreads out to produce many
different kinds of volcanic rocks and landforms. Many of New Zealand’s landscape
features have been shaped over several million years by volcanic activity.
A volcano is an opening (or vent) in the surface of the earth or sea floor where
magma comes out. Much of New Zealand’s landscape has been shaped over several
million years by volcanoes.
Plate Tectonics
Most volcanoes are formed by the movement of tectonic plates on the surface of
the earth. These plates are basically huge pieces of rock that ‘float’ on the mantle.
The tectonic plates are in very slow, constant motion. Sometimes they move
towards each other, other times they move apart, and still other times one will sink
while the other rises above it.
Subduction zone
Beneath New Zealand, the Pacific tectonic plate is colliding with the Australian
tectonic plate and is being forced down into the Earth’s mantle. This creates a zone
of stress, called a subduction zone. Most of the North Island’s active volcanoes are
associated with this process.
Magma
As the Pacific plate is forced down into the mantle, the oceanic crust, which caps
the Pacific plate, begins to heat up. Under increasing pressure and temperature, the
former crustal material undergoes chemical reactions and molten magma is formed.
This magma is very hot and contains gases making it lighter than the surrounding
mantle. It rises towards the surface of the Earth at weak points in the Earth’s crust.
Once this magma reaches the surface at the vent it is called lava (if it erupts
passively) or tephra (if it is blasted apart explosively in the vent).
Taupo volcanic zone
The volcanic region of the central North Island is called the Taupo Volcanic Zone. It
is made up of a line of active and potentially active andesite stratovolcanoes
(volcanic cones) stretching from Ruapehu in the south to White Island in the north.
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Volcanoes
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Auckland volcanic field
Unlike the Taupo Volcanic Zone, the volcanoes of Auckland are not related to a
plate boundary. Instead, they have formed in the middle of a plate. This sort of
activity is known as ‘intraplate’ volcanism. Sometimes these areas of intraplate
volcanism are referred to as “hotpots” or “mantle plumes”. The source of magma in
these areas is the mantle. The type of magma produced in these areas is called
basalt.
Monogenetic eruptions
The Auckland volcanic field is made up of monogenetic volcanoes, which means
they use up all of their magma during the eruptive period, and each new magma
batch or 'bubble' produces a new volcano. That is why there are so many individual
volcanoes in the Auckland volcanic field.
Frequently active versus dormant volcanoes
In New Zealand, volcanoes can be divided into two groups:
1. Frequently active volcanoes such as White Island, Tongariro-Ngauruhoe,
Ruapehu and Raoul Island in the Kermadecs.
2. Dormant (sleeping) volcanoes such as the Auckland Volcanic Field, Mayor
Island, Rotorua, Okataina, Taupo, Taranaki and the volcanic fields in
Northland.
The North Island is home to all of New Zealand’s active volcanoes today. The South
Island’s volcanic heritage belongs to a more distant past but is still evident today at
sites such as the Takitimu Mountains, Mount Tapuaenuku, Mount Somers, Oamaru,
Otago Peninsula, Banks Peninsula, Timaru and Solander Island.
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Image from http://whatstheplanstan.govt.nz/volcano [3]
Ready for a quiz? [4]
[4]
Plate Tectonics
The Earth’s crust is made up of large pieces of rock called tectonic plates.
These plates ‘float’ on the mantle.
Tectonic plates are always moving.
Most volcanoes are formed by the movement of tectonic plates.
Subduction zone
A subduction zone is where one tectonic plate is forced towards the centre
of the Earth by another tectonic plate.
North Island volcanoes are formed as the Pacific plate is forced into the
mantle.
Magma
The ocean crust, which covers the Pacific plate, begins to heat up as it is
forced into the mantle.
Magma is formed from high pressure and high heat.
The magma rises towards the surface.
Once this magma reaches the surface at a vent it is called lava.
Taupo volcanic zone
A volcanic region of the central North Island.
The volcanoes are formed where tectonic plates meet.
There are active volcanoes here.
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Auckland volcanic field
The volcanoes of Auckland are not formed where tectonic plates meet.
Instead, they have formed in the middle of a plate.
Sometimes these areas are called “hotspots” or “mantle plumes”.
Monogentic eruptions
The Auckland volcanic field is made up of monogenetic volcanoes. These volcanoes
use up all of their magma during the eruption. Each new magma 'bubble' makes a
new volcano. That is why there are so many volcanoes in the Auckland volcanic
field.
Frequently active versus dormant volcanoes
New Zealand volcanoes can be put into two groups:
1. Frequently active volcanoes; e.g. Tongariro-Ngauruhoe, Ruapehu
2. Dormant (sleeping) volcanoes; e.g. the Auckland Volcanic Field, Mayor
Island.
The North Island has the only active volcanoes. The South Island’s volcanoes were
active a very long time ago, but not any more.
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Image from http://whatstheplanstan.govt.nz/volcano [3]
Ready for a quiz? [4]
[4]
Māori keywords:
Audio Maori keywords:
puia - volcano [5]
Rūaumoko - god of earthquakes and volcanoes [6]
pahūtanga - eruption [7]
tehepuia - lava [8]
pahū - erupt [9]
You could find the name of your nearest active or extinct volcano. How did it form?
You could find the name of your nearest active or extinct volcano. How did it form?
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[10]
New Zealand lies on a collision boundary between two tectonic plates. This
animation shows what can happen to land when plates move (black arrows)
under power from convection currents in the mantle (red arrows). Note: click
Shift-refresh/reload to see the animation again. Image: LEARNZ.
[11]
A subduction zone is where one tectonic plate is forced towards the centre
of the earth by another tectonic plate. Image: LEARNZ.
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Volcanoes
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[12]
Volcanoes erupt when magma reaches the surface of the Earth. Image:
LEARNZ.
[13]
Volcanoes in the Taupo volcanic zone are formed where tectonic plates
meet. Image: LEARNZ.
[14]
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Volcanoes
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The volcanoes of Auckland are not formed where tectonic plates meet.
Instead, they have formed in the middle of a plate. Image: LEARNZ.
[15]
There are 48 volcanoes in the Auckland volcanic field. Image: Dr. Les
Kermode.
Source URL: http://www.learnz.org.nz/whatstheplanstan164/volcanoes
Links
[1] http://www.learnz.org.nz/sites/learnz.org.nz/files/std-volcanoes.mp3?uuid=5905c
857741c3
[2] http://www.learnz.org.nz/sites/learnz.org.nz/files/easy-volcanoes.mp3?uuid=590
5c85773c1c
[3] http://whatstheplanstan.govt.nz/volcano
[4] http://activities.learnz.org.nz/wp164/wp164-a07-volcanoes/quiz.html
[5]
http://www.learnz.org.nz/sites/learnz.org.nz/files/puia_8.mp3?uuid=5905c8577432f
[6] http://www.learnz.org.nz/sites/learnz.org.nz/files/ruaumoko_4.mp3?uuid=5905c8
5774445
[7] http://www.learnz.org.nz/sites/learnz.org.nz/files/pahutanga_3.mp3?uuid=5905c
85774554
[8] http://www.learnz.org.nz/sites/learnz.org.nz/files/tahepuia.mp3?uuid=5905c8577
465f
[9]
http://www.learnz.org.nz/sites/learnz.org.nz/files/pahu.mp3?uuid=5905c85774768
[10] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-volcanoes-01.gif
[11] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-volcanoes-02.jpg
[12] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-volcanoes-03.jpg
[13] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-volcanoes-04.jpg
[14] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-volcanoes-05.jpg
[15] http://www.learnz.org.nz/sites/learnz.org.nz/files/bg-volcanoes-06.jpg
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