New Zealand Volcanoes

Extreme Earth Events - 12ESS

Finn LeSueur

2021

Akoranga 11 Mahi Tuatahi

  1. Collect a terms/definitions match-up from the front
  2. Cut up the terms/definitions
  3. Glue them into your book in the correct order
  4. Put all un-crumpled excess paper in the recycling bin

Te Whāinga Ako

  1. Dome, caldera, cone and shield volcanoes - what each looks like, linked to an example and the type of magma it has.

Head up a new page with the date and te whāinga ako.

Volcanoes in New Zealand

Source
  • The type of volcano which forms depends on the magma type
  • The viscosity of the magma largely dictates the shape of the volcano

  • There are four main types of volcanoes in New Zealand:
    • Shield volcanoes
    • Caldera volcanoes
    • Lava dome volcanoes
    • Composite cones (stratovolcanos)
Source

Shield Volcanoes (Basalt)

  • The flattish gently sloping shield volcanoes of Dunedin and Christchurch are built from basalt
  • The Dunedin volcano was active 10-13MYA, and the Lyttelton/Akaroa volcanoes 5.8-13MYA
  • They form because low viscosity lava can flow a great distance before solidifying into solid rock
Source
  • Built of silica-poor basalt magma
  • Magma comes from the mantle, about 100km deep - the hot spot. But they can also be formed by subduction sometimes.
  • The magma has very little water or dissolved gas, so eruptions are very gentle.
  • Eruptions are also gentle because the magma is runny and very hot, therefore it travels a long way before cooling. Therefore the volcanoes build up with very gentle slopes.

Caldera and Dome Volcanoes

  • Formed from viscous rhyolitic magma which is very viscous because it has a high amount of silica.
  • Gas, especially water vapour and carbon dioxide from melted carbonates, gets trapped in the sticky lava which results in very explosive eruptions forming calderas.
  • Sometimes the gas escapes so that the magma is still very sticky without trapped gas. This forms dome volcanoes.

Calera Volcanoes (Rhyolite)

Source
  • Some volcanoes are very wide flat areas which completely collapsed following huge eruptions to form calderas (e.g. Lake Taupō).
  • The eruption would have been extremely large and violent.
  • Taupō last erupted about 186AD.

Dome Volcanoes

  • Mt Tarawera also formed through sticky magma being pushed upwards very slowly.
  • This upward pressure is due to gas.
Source

Cone Volcanoes (Andesite)

  • Steep cone volcanoes like Mt Taranake and Mt Ruapehu are formed when alternating layers of slightly sticky andesite lava and ash build up a cone around the vent.
Source
  • Typically formed at subduction zones
  • Made up of andesitic lava which has an intermediate amount of silica
  • The lava is semi-sticky and cooler. This means that it is not so runny and that it cools more quickly.
  • The combination of these two factors means that it does not travel as far and forms cone shapes.
  • Eruptions can be gentle, erupting lava, or explosive, eruption hot ash.

Rangahau/Research

  1. Cut out each of the images of the NZ volcanoes. Glue into your book and label - 2 per page
  2. Next to/underneath your images, write:
  • A description of the general shape of this volcano
  • How it forms
  • The magma type
  • The typical products of the eruptions this volcano has
  • Any special features this type of volcano has
  • Other examples in NZ

NB: Use your device + textbook pages to help