Taupo Volcanic Zone:New Zealand
The Taupo Volcanic zone TVZ on New Zealands North Island is responsible for most of New Zealands current volcanic activity.The zone contains the volcanoes of Taupo,Tarawera and Rotorura. The TVZ is an extensional feature called a back arc basin which allows magma from the mantle to well up near the crust causing more activity. The The basin has formed to the east of the subduction zone and is caused by the extension of the crust above the subduction zone.
The TVZ has most of New Zelands active volcanoes. The extension has created two types of volcanism Dacitic/Andesitic/Basaltic traditional cone volcanoes and Rhyolitic Calderas which have produced over 90% of the volcanic material.
Rising magma can come more silica rich as it is contaminated by the overlying continental crust on its ascent and secondly if the magma is collected in an underground reservoir or magma chamber the more silica rich mineras such and quartz and feldspar will crystallise first- fractional crystallisation.
Both of these procesess will result in a more sticky, high silica magma which is more sticky. Andesite magmas such as at White Island have sightly less silica in than Rhyolite magmas as at Tarawera, add gases and steam to either and you have an explosive mix.Where magma comes more directly it tends to be more basaltic,lower in silica and higher in iron ,as at Tarawera and Aukland.
The Calderas hide super volcanoes and have filled with water to form large lakes such as Taupo and Rotorua. Their larger eruptions would have an impact on a global scale and make the the smaller eruptions of White Island and Tarawera seem like an annoying firework!
There have been several phases of volcanic activity on North Island and there are numerous extinct and dormant volcanoes all over.Waitakere ranges (25-15 million)
Northland volcanic field (10 million years-60,000)
Auckland Volcanic Field, 48 small basaltic volcanoes( 140,000 to 600)
Coromandel and Hauraki Volcanic Region(18-4 million)
Waikato basaltic and andesitic strato-volcanoes(2.7-1.6 million)
Egmont volcanoes (1.75 million),including Mt. Egmont and Mt.Taranaki(1755 AD).
www.teara.govt.nz: New Zealands volcanoes
wikipedea: Taupo Volcanic Zone
GNS: Volcanoes of New Zealand
Volcano world:Taupo Volcanic Zone
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