GEOSCIENCE 91191 — QUESTIONS

What are the two tectonic plates involved in NZ?

Pacific Plate and Australian Plate.

What is happening at North Island boundary?

Pacific Plate subducted beneath Australian Plate.

South Island boundary?

plates move past each other along oblique transform boundary, with some areas also involving subduction.

Why many earthquakes?

lies on boundary, movement creates stress, eventually released.

Why South Island significant earthquakes?

plates move past each other along major faults; friction locks, stress accumulates, sudden movement releases seismic energy.

Why North Island earthquakes and volcanic activity?

subduction produces magma conditions and boundary movement produces earthquakes.

How earthquake begins?

stress builds around fault; when stress exceeds strength/friction, sudden movement, stored energy released as seismic waves.

Why plates don’t move smoothly?

friction locks faults; stress accumulates until slip.

What happens to earthquake energy?

stored elastic energy released as seismic waves, ground shaking.

What determines earthquake damage?

size, depth, distance, local geology, duration, vulnerability.

Why shallow earthquakes damaging?

energy released near surface.

Why earthquakes cause other events?

shaking can destabilise slopes/landslides and sometimes seabed displacement/tsunami.

Why North Island volcanism?

subduction creates conditions for partial melting in mantle above subducting plate.

How does water helps in the formation of magma?

volatiles released into mantle lower melting temperature, partial melting.

What after magma forms?

rises due to lower density, accumulates, pressure, reaches surface.

Why subducting plate doesn’t simply melt?

mainly partial melting of mantle above due to water/volatiles.

What happens as magma rises?

pressure decreases, gases exsolve/come out, can contribute to pressure/explosive activity.

What influences explosive eruption?

viscosity and dissolved gas, strongly influenced by composition.

Why high viscosity more explosive?

resists flow, traps gas, pressure builds.

Why low viscosity less explosive?

flows easily, gases escape, less pressure.

Silica effect?

higher silica generally higher viscosity; lower silica lower viscosity.

Gas contribution?

dissolved gases expand as pressure decreases; trapped gas builds pressure.

Why different eruption styles?

different composition/silica/viscosity/gas.

Fundamental tsunami cause?

sudden displacement of large amount seawater.

Causes?

underwater earthquakes, submarine landslides, volcanic eruptions/collapses, large landslides entering ocean.

How earthquake generates tsunami?

significant vertical seafloor movement displaces water; gravity spreads it outward.

Why not all underwater earthquakes?

needs sufficient vertical seafloor/water displacement; mainly horizontal movement may not.

Why subduction earthquakes can make large tsunamis?

sudden vertical displacement of large seafloor area moves huge water volume.

Underwater landslide?

sudden rock/sediment movement displaces surrounding water.

Volcanic eruption?

collapse, underwater explosion, landslides can displace water.

Deep ocean tsunami?

fast, long wavelength, small height, hard to notice from boat.

What does shallow water do to a tsunami wave?

slows, wavelength decreases, height increases.

Why wave height increases near coast?

shallowing slows/decreases wavelength, energy concentrated and height increases.

Why coastal flooding?

large volumes of water move inland, strong currents/inundation.

Why not one wave?

series of waves; heights differ; largest not necessarily first.

Why first may not be largest?

interaction with seabed/coast/local geography varies.

Full subduction→eruption chain.

subduction → volatiles → lower melting temperature → partial melting → magma → rise → eruption.

Full tectonic movement→earthquake chain.

plate movement → friction locks fault → stress accumulates → stress exceeds strength/friction → sudden fault movement → elastic energy released as seismic waves → ground shaking.

Full earthquake→tsunami chain.

large underwater earthquake → vertical seafloor displacement → water displacement → outward waves → shoaling → increased height/inundation.

How one event triggers another?

earthquake can destabilise underwater/coastal slopes, landslide displaces seawater → tsunami.

Why entire chain important?

shows causal/process understanding.

Why NZ exposed to earthquakes?

lies across plate boundary with active faults/different movement.

Why North Island volcanic hazards?

subduction setting generates magma.

Why coastal areas vulnerable to tsunamis?

direct exposure, low-lying areas can inundate.

Why distance matters?

closer may experience sooner/greater energy; farther may have more warning time.

Why coastal geography matters?

seabed/coast shape alters wave behaviour, wave heights/inundation.

Why same earthquake impacts differ?

distance, geology, coastal shape, elevation, population, infrastructure.

“explain how” = cause → process → resulting change → consequence.

Explain the causal chain from what causes something, through the physical process, to the resulting change and consequence.

“why” = explain physical process, not just state outcome.

Explain the physical process that causes the outcome rather than only stating what happens.

Stronger than list = connect facts/causal chain.

Connect relevant facts together to show how one process causes the next.

Strengthen “subduction causes volcanoes” = subduction → volatiles → lower melting temperature → partial melting → magma → rise → eruption.

subduction → volatiles → lower melting temperature → partial melting → magma → rise → eruption.

Strengthen “earthquakes cause tsunamis”

large underwater earthquake → vertical seafloor displacement → water displacement → outward waves → shoaling → increased height/inundation.

Explain different impacts of an earthquakes on humans

event characteristics + physical/human location characteristics.