ACHIEVEMENT STANDARD Earth and Space Science 2.3

as 91189

Worth 4 credits

Examplar written by Logan Coleman

Introduction• This assessment activity requires you to study the

Taupo Volcanic Zone in the centre of the North Island and the formation of rocks in this volcanic zone.

• You are to research and produce a report, a pamphlet, poster or a PowerPoint presentation to help visitors to the area understand the formation of two or more rocks found in the Taupo Volcanic Zone.

• You will be assessed on the depth and comprehensiveness of your report, pamphlet, poster or PowerPoint presentation.

Tasks• Using the resources your teacher has provided, begin researching the Taupo Volcanic Zone.

Select two or more rocks found in the Taupo Volcanic Zone and create a report, a pamphlet, poster or a PowerPoint presentation that includes the following aspects for each rock.

• Describe how it is formed. Include the type of rock that it is.• Explain in depth how the rock has been formed. To explain:

– relate the formation of the selected rock to the relevant stage(s) of the rock cycle– relate the selected rock found in the Taupo Volcanic Zone to the geological history of the

Taupo Volcanic Zone– link the type of magma found in the area of the Taupo Volcanic Zone to the formation of

your selected rock.• Explain in depth how the rock has been formed by linking the magma type of the relevant

volcano, to the formation of the selected rock giving reasons for the formation.• Make links between the formation of the selected rock to the relevant stage of the rock cycle

and the geological history of the Taupo Volcanic Zone. • Explain in depth how the features of the Taupo Volcanic Zone are weathered and eroded to

produce the final shapes we see today.

AUCKLAND VOLCANIC FIELD

INFORMATION• The Auckland volcanic field consists of around 50 volcanoes• It occupies an area of 360km2 • The metropolis of Auckland, New Zealand’s largest city is built

upon this volcanic field• There are a variety of different shape volcanoes which have all

been formed from basaltic magma• It is a monogenetic volcanic field (also known as a hotspot) as

the magma does not come from a chamber but instead comes directly from the mantle

YOUNGEST VOLCANO• The youngest volcano is Rangitoto that erupted

from the Waitemata Harbour around 600 years ago• The island has a diameter of 5.5km and is made up

dark basalt rocks that have formed from basaltic magma, it was once quarried for scoria

• Rangitoto is a shield shaped volcano

OLDEST VOLCANO• The oldest volcano is thought to be Lake Pupuke on the North Shore• It is estimated to have been created around 250,000 years ago• Lake Pupuke consists of a scoria tuff ring surrounding 2 craters which

have filled with water known as a maar • Like the rest of the Auckland volcanoes it is formed from basaltic

magma, it reacted violently with the ground water creating a huge pyroclastic explosion

MY TWO ROCK TYPES2 rock types that can be seen in the Auckland Volcanic field are

Basalt Scoria

MAGMA TYPE• All magma is the result of plate tectonic movement and

subduction and melting of convergent plates• Basaltic magma has a high iron (Fe) and magnesium (Mg) content• Basaltic magma has a low viscosity due to the low silica content• As it is a low viscosity this usually means that the eruptions are

not as violent as the stickier magma like andesite and rhyolite.• This means that it flows easily and can basaltic lava flows can

cover large distances before hardening, this is evident in Meola reef and the lava flows along Motions Rd

BASALT

BASALT• Basalt is an igneous rock• Igneous rocks are formed from cooling magma (intrusive)

or cooling lava (extrusive• It is formed from the slow cooling of basaltic lava so it is

an extrusive igneous rock• Basalt is usually black or dark grey in colour due to the

high iron and magnesium content• Basalt may be slightly red/brown in colour as the iron in

the basalt reacts with the air (oxidises)• It may contain a small amount (percentage) of vesicles

which signify that dissolved gases have escaped from the cooling lava

WEATHERING AND EROSION

• Basalt is a hard and dense rock• It is not affected much by normal weathering

such as wind and rain• Weather will tend to smooth the rock down and

wear away rough edges• This is evident in comparing the lava flows from

Rangitoto (600 yrs old) that are sharp and jagged to the lava flows from Lake Pupuke (250,000yrs old) that are smooth and more rounded

WEATHERING AND EROSION

• Basalt can be eroded gradually by wave action• This is evident in tidal zones such as the lava

flows from Lake Pupuke at Takapuna Boat Ramp

SCORIA• Scoria is an igneous rock• Igneous rocks are formed from cooling magma (intrusive) or

cooling lava (extrusive• It is formed from the rapid cooling of basaltic lava so it is an

extrusive igneous rock• Scoria can range from black or dark grey to red due to the high

iron and magnesium content• Red scoria occurs when the iron in the scoria reacts with the air

(oxidises)• Scoria contain a high amount (percentage) of vesicles which signify

that dissolved gases (carbon dioxide and water) have escaped from the cooling lava

• Scoria is formed form the basaltic magma that is erupted and cools quickly in the air

WEATHERING AND EROSION• Scoria is a crumbly and low density rock• It is affected greatly by normal weathering

such as wind and rain• Weather will tend to break scoria down into

very small pieces (to an almost sand-like consistency)

• Examples of finely ground red scoria can be seen around the Auckland volcanoes

BIBLIOGRAPHY

• www.wikipedia.org.nz• http://www.teara.govt.nz/en• Volcanoes of Auckland: The Essential Guide by

Bruce Hayward and Graeme Murdoch and Gordon Maitland