1. Auckland Islands Formation Volcanoes and Glaciers
Level 1 Achievement Standard Science 1.13
Demonstrate understanding of the formation of surface features in New Zealand

2. Requirements of the standard
Thoroughly explain the links between external and/or internal processes and the formation of surface features in New Zealand.
Key external and internal processes relevant to the Auckland Islands include:
Hot spot volcanism
Glacial Erosion
Sea level change
Key surface features include:
Shield volcanoes
Glacial Inlets/Fiords

3. Auckland Island - Location
The Auckland Islands lie approximately 450km South of mainland New Zealand.
They sit on the continental shelf of the Pacific Plate.
Auckland Islands

4. New Zealand Volcanism
New Zealand’s volcanoes can be classified into two types: Subduction volcanoes Magma comes from melted crust. Forms tall steep sided volcanoes or large calderas. e.g. volcanoes of the central North Island. Hot Spot volcanoes Magma comes from the mantle. Forms low, wide, shield volcanoes. e.g. volcanoes of Auckland city as well as the Auckland Islands.

5. Subduction
Ocean crust (lithosphere) is more dense than continental (land) crust.
When these two types of crust collide the ocean crust is pushed beneath the continental.
As it moves downwards it heats up and melts forming liquid magma.
The magma expands and rises through the overlying continent and is released during a volcanic eruption.

6. Features of subduction volcanoes
Subduction volcanoes form when melted crust from a subduction zone rises to the surface of the Earth and is released during an eruption.
The magma is viscous (sticky) and explosive.
Because of this the lava does not flow easily and the volcanoes are typically steep and pointed (Mt Taranaki) or large calderas (explosion craters – Lake Taupo).

7. New Zealand’s Subduction Volcanoes
Mt Taranaki

8. Lake Taupo

9. Hot spots
Heat from the Earth’s core causes magma in the mantle to heat up and rise.
The magma can push through the crust and is released during a volcanic eruption.
Magma originating from the mantle is basaltic. Basaltic magma is very hot and has low viscosity (runny).
When released, the lava is able to flow very easily and this results in low, wide, shield volcanoes.

10. Hot Spots
Crust
Mantle
Hot magma rising through mantle

11. New Zealand’s Hot Spot Volcanoes
Rangitoto Island
A typical low, wide, shield volcano

12. Auckland Island
Formed from two ancient basalt volcanoes

13. Types of magma Summary Table Magma Type Solidified Rock
Chemical Composition
Temperature
(oC)
Viscosity
Gas Content
Basaltic
Basalt
45-55 SiO2 %, high in Fe, Mg, Ca, low in K, Na
Low
Andesitic
Andesite
55-65 SiO2 %, intermediate in Fe, Mg, Ca, Na, K
Intermediate
Rhyolitic
Rhyolite
65-75 SiO2 %, low in Fe, Mg, Ca, high in K, Na.
High

14. External Processes – Glaciers and Erosion
A glacier is a slow moving build-up of ice. They are often referred to as frozen rivers.
As a glacier moves it scrapes the rocks on which it sits.
Some of the ice can melt and then refreeze in cracks and around pieces of rock. As the water freezes it expands and this can be strong enough to break rock.
Over time these erosive processes carve out valleys in the rocks.
Glacier valleys are typically steep sided, U-shaped valleys.

15. Franz Joseph Glacier, NZ

16. Earth’s temperature and sea level change
Earth’s temperature has naturally fluctuated over time.
Linked to temperature is the Earth’s sea level.

17. Earth’s temperature and sea level change
70% of the Earth is covered in water – mainly in oceans.
Massive amounts of water are also frozen at each of the Earth’s poles.
During cold periods of Earth’s history more water is frozen at each pole and snow and ice is also found on land closer to the equator.
Because all this water is not in the oceans, it results in a lowering of the Earth’s sea level.
During warm periods, snow and ice on the land close to the equator melts and flows into the ocean causing the sea level to rise.

18. The Auckland Islands
The Auckland Islands at 50o south would have been covered in snow and ice during cold periods (ice ages).
Glaciers have eroded the basalt rocks forming steep, U-shaped valleys.
As the Earth warmed the glaciers melted and sea level rose.
The U-shaped valleys were flooded by the rising ocean and have become the many deep, steep-sided inlets and fiords of the eastern coast of the islands.

19. Mclennan Inlet, Auckland Island
Mclennan Inlet, Auckland Island. A classic deep, steep sided, U-shaped inlet.

20. Aerial view of a U-shaped glacial valley, Auckland Island.