Download Science Unit - Western Springs College

Year 10 Science Revision
Unit: Papatuanuku
PAPATUANUKU – EARTH SCIENCE
Key words
Continental Drift
Tectonic plates
Subduction
Convection currents
Earthquakes
Focus
Epicentre
Richter scale
Volcanoes
Magma
Lava
Basalt
Crust – oceanic, continental
Seismometer
Viscosity
Core
Seismograph
Andesite
Mantle
Laurasia,
Rhyolite
Convergent Boundary –
subduction zone –
oceanic trench
Divergent – sea floor
spreading
Key definitions to learn:
Magma
Lava
Focus
Epicentre
Viscosity
p-waves
s-waves
Surface waves
subduction
Molten material inside the mantle
Magma which has been ejected from a volcano
The location of the rock movement occurred
The point on the Earth’s surface above the focus
The thickness/resistance to flow of a liquid
Primary waves – compression and rarefaction waves – arrive
first (These waves can travel through both solid and liquid)
Secondary waves – side to side movement waves – arrive
second (These waves cannot travel through liquid)
Rolling movement of crustal rock – slowest wave
the edge of one plate is forced under another
Key Learning Points:
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The Earth is 4.5 billion years old
The earth has defined structure – inner core, outer core,
mantle, crust
Evidence for Wegener’s continental drift theory:
 Shapes of adjacent continents/continental shelves fit like a jig
saw
 Matching rock strata on both continents either side of ocean gap
 Same fossils in same rock layers on adjacent sides of continents
 Mt ranges/remains of glaciers continuous across neighbouring continents
 Study of earthquake waves reveals details of this
structure
 The earth’s crust is divided into plates
 The plates move due to convection currents in the mantle
 The continents on the Earth have moved from their
original positions
 Earthquakes and volcanoes occur at plate boundaries
 New Zealand straddles two plate boundaries
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Year 10 Science Revision
Unit: Papatuanuku
 North Island Volcanic activity caused by plate subduction
 North Island Volcanoes Andesite in composition
 Taupo – Rhyolite composition (very viscous and explosive)
 South Island Alpine fault caused by transform fault
 Auckland volcanoes caused by hotspot
 Auckland volcanoes formed from Basalt (least viscous)
 Youngest Auckland volcano – Rangitoto
 Earthquakes produce 3 types of waves – primary, secondary and surface waves
 Earthquake energy measured on the Richter scale (1-10)
Convection currents
The core is very hot due to heat produced from nuclear reactions. This heat is a source
of energy for moving the tectonic plates. As the mantle closest to the core heats, the
molten rock expands, becomes less dense and rises. When it reaches the cool crust, the
molten rock loses heat energy, contracts, becomes more dense and sinks towards the
core where it is heated again. The cycles of hot rock rising and cooler rock sinking are
called convection currents. Where they move towards each other the plates converge
(destructive plate boundary, where they move away from each other the plates diverge
(spreading zone or constructive boundary).
New Zealand is geologically active
NZ lies on a plate boundary the movements around
which cause earthquakes and volcanoes. To the north
east of the North Island the oceanic crust of the edge of
the Pacific plate is subducting under the continental
crust of the Australian plate. This subduction causes the
formation of the Hikurangi trench and the friction
beneath the North Island melts rock that is forced to the
surface in the Taupo volcanic zone as volcanoes.
Between the North and South Islands the boundary
twists to become a transform fault, the Alpine Fault,
where the Australian plate is moving northwards and
the Pacific plate is sliding southwards. Off the
southwest coast of the South Island, west of Fiordland,
the Australian Plate is subducting under the Pacific
plate.
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Year 10 Science Revision
Unit: Papatuanuku
The Auckland Volcanic Field
The Auckland volcanic field covers around 360km2 under the city. It Includes 54 separate
volcanoes (5 recently discovered), each of which is considered extinct. However, the field
as a whole remains active. The last eruption was Rangitoto, around 600 years ago.
Volcanic feature
Rangitoto
Brown’s Island
Meola reef
Takapuna boat
ramp
Lake Pupuke
Mt Eden
Orakei Basin
Savage memorial
/Bastion point
Domain
Cause of the land form that we currently observe
Basaltic volcano that erupted through sea water. The summit is
a scoria cone flanked by a crater of an earlier eruption.
Least modified of Auckland’s volcanoes. Shows all 3 features of
Ak volcanoes- it has a scoria cone, a tuff ring and a lava flow
Lava, probably from Three Kings, flowed across a large area to
form a thick layer of rock that runs through Western Springs into
the Waitemata Harbour
Large lava flow which breached the Pupuke crater rim and
flowed seaward . Cooled around trees so has circular holes in it.
Formed by magma rising to hit ground water which rapidly
vaporizes causing a large explosion crater filled with water.
Auckland’s highest cone formed by several “fire fountains” of
molten lava, which, when squirted into the air, cools as red
brittle rock. Crater porous and water seeps into ground and
emerges at Western Springs
Typical explosion crater filled with water to become a caldera. It
is surrounded by an asymmetric tuff ring which is unstable
White coloured, layered cliffs formed about 25 million years ago
by settling of sediment under the sea then was later up lifted.
After a large explosive eruption a smaller fire fountain of molten
lava to formed a smaller scoria cone in the middle of the crater.
Auckland volcanoes are due to a hotspot where magma is close to the surface of the
crust which is relatively thin. The magma forces its way to the surface through weaknesses
or fissures in the crust. The magma has a low percentage of silica so it is runny (has low
viscosity). The lava flows relatively well, so low sided, shield-shaped cones are formed.
When the basaltic lava cools on the surface it forms basalt rock that is grey and dense
and is in large hexagonal crystals. Basalt turns into scoria if it is thrown into the air.
When the basaltic lava is thrown onto the air it reacts with oxygen to form reddish iron
oxide compounds. In addition, carbonates decompose to form CO2 gas that makes the
cooled rock holey. This is scoria –a holey reddish/brown brittle rock
Websites URL for revision:
http://www.bbc.co.uk/schools/gcsebitesize/chemistry/changestoearthandatmosphere/
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Year 10 Science Revision
Unit: Papatuanuku
Revision Questions
1. Draw and label a simple diagram of the earth’s structure.
2. Sketch a diagram of a typical andesite volcano eg Taranaki, and label all parts.
3. The Earth is broken up into plates – what are all the types of evidence for this?
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4. Radioactive processes generate heat inside the earth which causes convection
currents in the mantle. These currents cause the plates to move.
There are 3 types of movement of the plates – move apart (divergent) / collide
(convergent) / rub against each other (transform) – explain using diagrams what
happens when the plates move in these ways.
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5. Describe New Zealand’s position in relation to the Indo-Australian and Pacific
plates.
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Year 10 Science Revision
Unit: Papatuanuku
6. Draw a subduction diagram to show how the central North Island volcanoes formed.
7. Explain why NZ has earthquakes and volcanoes but Australia does not.
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8. What cause earthquakes?
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9. Explain the difference between the focus and the epicentre of an earthquake.
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10. Describe the 3 types of energy waves caused by an earthquake and the speed at
which they move.
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11. Describe how to read a seismograph in order to work out how far away a quake
originated and its intensity.
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12. If you were standing at the epicentre of a magnitude 4 and then a magnitude 7
earthquake, describe what difference you would notice.
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Year 10 Science Revision
Unit: Papatuanuku
Draw a mindmap for this unit:
Add to it, as you develop your learning.
Geology
Well done you have completed another revision unit.
Now reflect on how you can improve further:
Which aspects of the unit do I need to revise more carefully?
Which aspects of the unit do I need help with?
How will I seek this help?
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