NCEA Level 3 Science (90731) 2010 — page 1 of 3
Assessment Schedule – 2010
Science: Describe geological processes affecting New Zealand (90731)
Evidence Statement
Q
Evidence
ONE
The three main types of magma are:
basalt, andesite and rhyolite.
Basaltic magma has a high temp,
low viscosity, low silica content and
low conc. of gas. This all leads to a
magma that flows easily and takes a
long time to cool therefore creating
low sloping shield volcanoes. The
low viscosity means that gas is not
held easily in the magma, hence the
low concentration of gas.
Andesitic magma has a moderate
temp, moderate viscosity, moderate
silica content and moderate amount
of gas. This leads to lava that is
thicker, but can still flow a bit, thus
creating a steeper sided cone
volcano. The cone is built up in
layers.
Rhyolitic magma has a relatively
low temp, high viscosity, high silica
content and high conc. of gas. This
leads to explosive eruptions, where
there is little lava flow. Calderas.
The high viscosity means that gas is
trapped in the magma, hence the
high concentration of gas and the
extreme explosiveness of the
eruption. The large volume of
magma erupted causes instability
including fractures in the
surrounding rocks. This causes the
ground to collapse causing caldera.
Achievement
Describes relationship
between magma type /
properties and volcano
shape.
Two of three types with
correct shape described.
Eg:
Basaltic: low viscosity /
runny, low spreading
volcano, shield shape.
Andesitic: medium
viscosity / sticky, cone
shaped volcano.
Rhyolitic: very high
viscosity / very sticky,
explosive leading to
collapse of surrounding
rocks forming caldera.
Description of shapes
related to magma
properties but no names.
Achievement with
Merit
Achievement with
Excellence
Explains
relationship
between magma
type and volcano
shape.
Two of three types
with correct shape
explained.
Discussion and valid
comparison of the
magma types and
associated volcanoes.
Discussion and
comparison of two of
three types of magma
with correct shape.
Eg:
Basaltic: low
viscosity, hot so
runs a long way
before cools to rock
resulting in low
spreading volcano
(shield shape).
Eg:
Basaltic: magma is hot
(1200°C) but low
viscosity and low in
silica. The low viscosity
means the hot lava runs
further before it cools
leading to low
spreading
(shield shaped )
volcanoes, eg Rangitoto
Island.
Andesitic: medium
viscosity so runs
slower and cools
faster. Repeated
eruptions build up a
cone shape.
Rhyolitic: high
viscosity and traps
gas
(SiO2) so when
erupts does so with
explosive eruptions
leading to collapse
of surrounding
rocks forming
caldera.
However the medium
viscosity andesitic
magma has a higher
silica content and lower
temperature (1000°C)
than basalt and the lava
cools more quickly
before it has travelled
great distances. The
higher silica content
makes andesitic magma
more explosive than
basalt and the ejected
lava and eruption debris
(ash ) falls close by
contributing to the
formation of a cone
shaped volcano, eg Mt
Ruapehu
The rhyolitic magma
has even lower
temperature ( 750°C)
and high silica content
traps the gases and
when the eruptions
occurs it is the most
explosive of the magma
types shattering the
magma and rock into
large volumes of ash
which can travel great
distances in the air.
NCEA Level 3 Science (90731) 2010 — page 2 of 3
Often the whole magma
volume is erupted so
that the rock
surrounding the magma
chamber is weakened
and fractures falling in
on itself forming a
caldera (depression)
which sometimes fills
with water, eg Lake
Taupo.
TWO
In the North Island ,where the dense
oceanic Pacific Plate (basaltic
composition) subducts under the
less dense continental Australian
Plate, the Pacific Plate crust moves
down into the mantle. When deep
enough, the plate begins to melt and
the molten material (magma) rises
to the surface. If the magma finds a
weakness in the Earth’s crust, it can
move through it and erupt at the
surface as volcanoes. Geothermal
activity results from the
underground waterways heating up,
due to the close proximity of hot
magma in the crust. This can result
in geysers, fumaroles and
geothermal hot pools and is
particularly evident in the Taupo
Volcanic Zone.
Mountain building in the South
Island of New Zealand is a result of
the two continental plates moving
towards each other and the
continental crust is forced up
creating mountains. Both the
Pacific and Australian plates are
continental in composition at this
location and they are colliding at a
convergent plate boundary
Description of TWO
geological features
and the processes that
produce them.
 Geothermal
activity caused by
subduction.
 Mountains are
caused by two
plates colliding.
 Subduction causes
volcanoes.
 Subduction
situation in North
Island described.
Explanation of TWO
geological features linked
to the tectonic processes.
 In North Island
Subduction of the
dense oceanic Pacific
Plate causes crust to be
taken down to a depth
where it melts to
magma and can rise to
surface through cracks
forming volcanoes.
Water near / in contact
with hot magma / rocks
in the crust heats up
and leads to the
geothermal features
(hot pools, fumaroles,
geysers).
 For Southern Alps –
the Pacific and
Australian plates are
the same composition,
so no subduction
occurs. They collide at
the convergent plate
boundary and buckle
up and form mountains.
Composition of magma
giving rise to geothermal
activity / volcanoes and
mountain building
explained.
Discussion of the
relative movement of
the two plates, and
comparison of the two
geological features that
result.
NCEA Level 3 Science (90731) 2010 — page 3 of 3
THREE
P and S waves have different
properties:
P waves are longitudinal waves that
can travel through liquids and solids
at approx. 7 km s–1.
S waves are transverse waves that
can only travel through solids. They
travel at approx. 4 km s–1.
To work out the internal structure of
the Earth, scientists have used large
earthquakes that have been
measured around the Earth. They
look at whether the seismometers
pick up both P and S waves. It was
found that at some sites both were
measured and at others only the P
waves were measured. This data
leads scientist to hypothesis that the
internal structure of the Earth must
contain an area of liquid / molten
rock.
Description and P and S
waves properties.
P, primary, fast
longitudinal (description
of) waves, travel (and
refract) through both solids
and liquids .
S, secondary, slower
transverse (description of)
waves, travel only through
solids.
Explanation of
internal structure of
the earth in terms of
wave motion.
Discussion of how the
properties of P and S
waves are used to find
the internal structure of
the earth.
P waves are bent /
refract at boundaries
of the layers within
the Earth.
S waves cannot be
felt at all places on
the earth
(shadows).
http: / / web.ics.purdue.edu / ~braile
/ edumod / journey / journey.htm
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
2A
1M+1A
OR
1E+1A
1E+1M