So as you are probably all aware, both Mrs M and myself are both geologists and both work as professional geologists (I'm technically a geophysicist but its only really a name).
I thought since we have talked a little about rocks on the blog that I ought to do a special Volcano blog as a lot of New Zealand is made from Volcanoes.
So why does New Zealand have a lot of Volcanoes?
New Zealand sits across an active tectonic plate boundary between the Pacific and Australian plates.
These plates are moving past each other at different rates, with the Pacific plate sliding under the Australian plate in the North Island and vice versa in the South Island.
When one plate is forced under another this is called a subduction zone, and the map earthquake depths highlights the Pacific plate subducting under the Australian plate.
When these rocks are buried they release large amounts of pressured water which begins to melt the mantle of the Australian plate. This molten rock (magma) rises up and pools just below the surface. When this molten rock erupts at the surface (lava) it is called a volcano.
Why are there many volcanoes in one place in NZ?
In areas such as Rotorua or Taupo there are many currently active volcanoes. This is because the subducted Pacific plate melts around the same depth and gives rise to a string of volcanoes called an Island Arc. In New Zealand because the rate of subduction varies across the margin the North Island is getting slightly stretched in places such as the Taupo Volcanic Zone.
This is called a Back-arc Basin and is the locus for volcanoes as the stretching makes it easy for the molten rock to rise.
What kind of volcanoes do you get in New Zealand?
As New Zealand is a subduction zone with an Island Arc it is common to find the magma is made of lots of silica and feldspar (Rhyolite). This means the magma is 'sticky' and contains lots of gasses. Volcanoes from this type of magma tend to be tall, steep sided and produce lots of explosive rock and ash during eruptions (Stratovolcano).
Why is there so much geothermal activity in New Zealand?
in the Back-arc Basin where a lot of magma is pooled in the shallow sub-surface any groundwater is heated by the magma and rises up in the form of geysers, fumaroles and hot springs. These can be used for recreational purposes (spas etc) or for geothermal energy.
So that is a little about volcanoes, there will probably be more to follow as we progress.
Mr M
I thought since we have talked a little about rocks on the blog that I ought to do a special Volcano blog as a lot of New Zealand is made from Volcanoes.
So why does New Zealand have a lot of Volcanoes?
New Zealand sits across an active tectonic plate boundary between the Pacific and Australian plates.
 |
| NZs Geodynamic position |
When one plate is forced under another this is called a subduction zone, and the map earthquake depths highlights the Pacific plate subducting under the Australian plate.
 |
| NZ earthquake hypocenter depths |
Why are there many volcanoes in one place in NZ?
In areas such as Rotorua or Taupo there are many currently active volcanoes. This is because the subducted Pacific plate melts around the same depth and gives rise to a string of volcanoes called an Island Arc. In New Zealand because the rate of subduction varies across the margin the North Island is getting slightly stretched in places such as the Taupo Volcanic Zone.
 |
| Taupo Volcanic Zone |
What kind of volcanoes do you get in New Zealand?
As New Zealand is a subduction zone with an Island Arc it is common to find the magma is made of lots of silica and feldspar (Rhyolite). This means the magma is 'sticky' and contains lots of gasses. Volcanoes from this type of magma tend to be tall, steep sided and produce lots of explosive rock and ash during eruptions (Stratovolcano).
Why is there so much geothermal activity in New Zealand?
in the Back-arc Basin where a lot of magma is pooled in the shallow sub-surface any groundwater is heated by the magma and rises up in the form of geysers, fumaroles and hot springs. These can be used for recreational purposes (spas etc) or for geothermal energy.
So that is a little about volcanoes, there will probably be more to follow as we progress.
Mr M
I see there are no comments on the volcano lesson and I feel it must fall to me to provide a technical response to the dribble above. I think there are lots of volcanos in NZ because it is far to the south, therefore, very hot. Also, there is lots of pressure because the whole world rests on the bottom of the globe which is close to NZ.
ReplyDeleteOnce more your understanding of geology amazes me Prof B...
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