Transcript Auckland Islands Formation Volcanoes and

Auckland Islands Formation
Volcanoes and Glaciers
Level 1 Achievement Standard 90952 Science 1.13
Demonstrate understanding of the formation of surface features in New Zealand
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
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
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.
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.
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).
New Zealand’s Subduction Volcanoes
Mt Taranaki
Lake Taupo
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.
Hot Spots
Crust
Mantle
Hot magma rising through mantle
New Zealand’s Hot Spot Volcanoes
Rangitoto Island
A typical low, wide, shield volcan
Auckland Island
Formed from two ancient basalt volcanoes
Types of magma
Summary Table
Temperature
(o
C)
Viscosity
Gas Content
45-55 SiO2 %, high in Fe,
Mg, Ca, low in K, Na
1000 - 1200
Low
Low
Andesite
55-65 SiO2 %, intermediate
in Fe, Mg, Ca, Na, K
800 - 1000
Intermediate
Intermediate
Rhyolite
65-75 SiO2 %, low in Fe,
Mg, Ca, high in K, Na.
650 - 800
High
High
Magma
Type
Solidified
Rock
Chemical Composition
Basaltic
Basalt
Andesitic
Rhyolitic
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.
Franz Joseph Glacier, NZ
Earth’s temperature and sea level change
• Earth’s temperature has naturally fluctuated over time.
• Linked to temperature is the Earth’s sea level.
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.
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.
Mclennan Inlet, Auckland Island.
A classic deep, steep sided, U-shaped inlet.
Aerial view of a U-shaped glacial valley, Auckland Island.