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Young volcanic rocks and ash

Young Volcanics Map

The volcanoes of Auckland city, central North Island and Taranaki are well known and they have erupted huge amounts of lava, ash and other products in the last two million years. These volcanoes typically stand proud of the landscape and have largely retained their original form. Other more subtle volcanic centres form harbours (e.g. Orakei Basin ) and lakes (e.g. Pupuke, Rotorua, Taupo).

There are many other volcanic centres less than 23 million years in age including those of Northland, Whangarei, Waitakere Ranges, Coromandel Peninsula, western Waikato, Banks Peninsula, Timaru and Dunedin/Otago Peninsula and some of these still have recognisable cone and crater forms.

Geologists subdivide volcanic rocks in terms of their silica composition. Basalt is a low silica volcanic rock that has been the dominant product of the Northland, Auckland and South Island volcanoes. Taranaki, Waitakere Ranges, Tongariro National Park and much of Coromandel are formed largely of andesite, an eruptive rock with intermediate silica content.

The high silica volcanic rocks are rhyolite and ignimbrite and these are widespread in the Taupo and Rotorua area as well as parts of Coromandel Peninsula. The ignimbrite has resulted from highly explosive eruptions from at least seven huge supervolcanoes that have been active in the last two million years. These ignimbrite and associated ash deposits covered large parts of the North Island with their fall-out although subsequent rain and erosion would have quickly washed the thinner layers away in most places.

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