Vulcanism

Lesson 1: New Zealand's Geological History

Mount Ruapehu, 1995. Shaky Beginnings (Bryan Bruce Productions, 1999)

Key Content

• Plate tectonics theory.
• Patterns that can be seen in the volcanic environment.
• Subduction, seafloor spreading, collision zones.
• Landscape formation.
• Landscape modification.
• Geological time scale.
• NZ’s geological history.

Learning Outcomes

Students will be able to:

• Briefly outline how New Zealand was formed over time.
• Explain how New Zealand’s landscape has been modified by geological and climatic forces over time.
• Discuss with understanding the theory of plate tectonics.
• Put geological time into perspective.
• Use terminology correctly (eg, subduction, convection currents, andesite volcanoes, etc.).

Relevant Film Archive Footage and Key Questions

1. Land of the Kiwi

Land of the Kiwi (1987)

Emphasise the point that New Zealand is still a very young country in geological terms and that the processes of formation and modification are still taking place.

a. How old is Mount Ngauruhoe?
2500 years – geologically very young.

b. What is the name of the process when the Pacific plate moves under the Indo-Australian plate?
subduction – the video does not mention this.

c. What type of volcano is Mt Ngauruhoe?
Andesitic: Andesite is a volcanic rock intermediate in type between acidic rhyolite and basic basalt. Ngauruhoe has been build up during successive eruptions of ash, scoria and lava and has the layered structure of a composite cone. It is young and has a single vent and is steep sided with a classic cone shape because it has not had time to erode to any great extent.

2. Land of the Kiwi

Land of the Kiwi (1987)

The AD186 Taupo eruption was one of the largest in the world in the last 5000 years. Just think that when you are walking along the shoreline of Lake Taupo you are walking along the rim of a massive volcanic caldera that has filled with water. You can see evidence of successive eruptions in the Tongariro Volcanic Centre in the road cuttings along the Desert Road (Jim Hickey talks more about this in Extract 12).

The Taupo Graben is not mentioned in the footage. The Taupo Graben is a large wedge-shaped chunk of land that has dropped between some of the parallel faults along the Tongariro Volcanic Centre to form a trench about 3.5km deep. Beneath the graben the crust is very thin (approx.15km) and is cracked. It is a very hot place and goes some way in explaining why there is a lot of geothermal activity in the area (eg. geysers and hot springs). So why can we not see this huge depression today? Because the graben has since been filled in with volcanic rock from successive eruptions.

Recently a chain of undersea volcanoes were identified north of White Island near the Kermadac Islands. These volcanoes follow the north-east to south-west line of volcanic activity along the plate boundaries. White Island is an andesitic volcano.

a. What was the popular 19th Century tourist attraction that the 1886 Tarawera eruption destroyed near Rotorua ?
Pink and White Terraces.

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