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Earth And Space Science NCEA Scholarship > Y12 Geology > Flashcards

Y12 Geology Flashcards

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1
Q

Earth structure

A

Inner core - solid (Fe, Ni)
Outer core - liquid molten metal
Mantle - mainly silica and minerals
Crust - solid top layer

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2
Q

Lithosphere

A

Rigid solid surface layer, made up of the crust and the top layer of the mantle.
Broken into tectonic plates with

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3
Q

Asthenosphere

A

Viscous plastic-like layer of semi molten rock
Lithosphere floats on the asthenosphere

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4
Q

Convection current process

A

Outer core heats mantle
Less dense magma rises
Reaches asthenosphere, pushed sideways by more rising magma
Pulls tectonic plates with it
Magma cools, denser, sinks —> convection currents

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5
Q

NZ tectonics

A

NZ sits on the boundaries of the Indo-Australian and the Pacific plates

Indo-Aus pushed NNE
Pacific pushed WNW

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6
Q

Diverging plate process

A

Plates spread apart due to convection currents
Magma reaches surface, cools
New ocean crust formed - basaltic, forms a mid Ocean ridge

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7
Q

NZ plate tectonics

A

Converging by about 4cm per year
Builds up stress within the lithosphere

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8
Q

Describe continental crust

A

Less dense (granite)
Thicker - 40km
Mainly above sea level

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9
Q

Describe oceanic crust

A

Denser - basalt (high in Fe)
Thinner - 5-10km
Mainly below sea level

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10
Q

Detailed tectonics of NZ

A

North of NI: Kermadec trench
Denser oceanic pacific subducts under continental Aus plate
Hikurangi fault to the east of NI, joins Kermadec trench
Converging boundary causes the softer AP to fold, creating mountain ranges in Eastern NI
Alpine fault across SI, transform movement between continental crusts, creates southern Alps
Puyseger trench: south of SI
Oceanic AP subducts continental PP
Softer AP folds, creating underwater mountain range

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11
Q

Volcano structure

A

Includes what is inside the cone and outside

Magma chamber,
Main vent up to a crater,
May be a second vent and secondary cone

Volcanic flow,
Ash cloud,
Volcanic bombs,
Pyroclastic flow

Volcano builds up layers of lava and ash over successive eruptions

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12
Q

Volcanic eruption process

A

Magma is buoyant, rises through the crust to erupt at the surface.

Large amount of gas + high viscosity magma = explosive eruption

Small amounts of gas a/o low viscosity magma = effusive eruption

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13
Q

Eruption column

A

Material being erupted upwards

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14
Q

Tephra and tephra plume

A

Erupted material of different sizes

Tephra plume = billowing clouds

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15
Q

Volcanic bombs

A

Large fragments
6cm +

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16
Q

Lahar

A

Mixture of erupted material, mud and water

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17
Q

Pyroclastic flow

A

columns of tephra that fall and spread at high speeds close to the ground, with devastating destruction

Ignimbrite is a pumice-dominated pyroclastic flow ejected from an explosive eruption
Can weld into rock
Can be found hundreds of kilometres from site of eruption

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18
Q

Where are volcanoes commonly located?

A

95% are found near converging plate boundaries (subduction zones)

5% are hotspots

80% are found along the subduction zone of the Pacific Ring of Fire

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19
Q

Phreatic eruption

A

Rising magma containing gas comes into contact with groundwater
Created superheated compressed steam, erupts explosively

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20
Q

Types of deposits from volcanoes

A

Air fall:
Material blankets the surface like snow

Pyroclastic flows:
Tend to follow low-lying areas of topography, filling valleys rather than a uniform blanket

Surges:
Tend to hug the ground, producing thicker deposits in valleys and thinner deposits over ridges (non uniform)

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21
Q

Types of magma

A

Basaltic:
Mantle magma
Low silica, low viscosity, low gas
Above 1200C to be molten
No crystallisation
Hotter hence runnier
Forms flatter volcanoes

Andesitic:
Mainly mantle magma with some partial melting or mixing
Intermediate silica, viscosity and gas
880-1000 degrees C
Flowing and moderately explosive

Rhyolitic:
Partial melting, more crustal material present, or fractional crystallisation removing Fe
High silica, viscosity and gas
750-850 C
Cooler hence more sticky, traps gas
Very explosive as heated trapped gas expands rapidly when it escapes the pressure of the earth

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22
Q

Eruption products of different types of magma

A

4 main types of rocks formed, classified by silica content

Basalt: thin flows hence forms shields, scoria cones and craters
Heavy, basic, mafic

Andesite: thick, rubbly lava flows.
Scoria/pumice and ash fall

(Dacite and) Rhyolite:
Pumice and ash fall
Ignimbrite (pyroclastic flow)
Light, acidic, Felsic

Basalt iron rich, less silica, hence dark coloured
Gradient to rhyolite, iron poor, more silica, light coloured

23
Q

How is silica related to properties of lava and rocks

A

Higher silica, lower temp, more viscous, decreasing mobility of lava
Traps more gas, hence more explosive

High silica = acidic
Low silica = basic

24
Q

Mafic and Felsic rocks

A

Mafic = MAgnesium and FErriC
Darker in colour
Basalt

Felsic: FELdspar and Silicates
Lighter elements (Al, K)
Lighter in colour
Granite and Rhyolite

25
Q

Hot spot volcanos definition and process

A

An area of the mantle where a continuous plume of hot magma rises from the same spot being heated by the core.
Pressure builds up, crust cracks, magma forced to surface.
Plates move, chain of islands created

Auckland volcanic field is a hotspot

26
Q

Factors that magma type depends on

A

Initial composition
(Mantle magma or subduction plate material)

Partial melting
Melting at lower temperatures due to water released from the subduction plate

Mixing
Magma melts crust, mixes

Fractional crystallisation
Magma pools in a chamber, minerals high in Fe crystallise and fall out

27
Q

Reasons why volcanos are formed near subduction zones

A

Subjecting plate dives, assisted by GRAVITY

Stress on overriding plate - fault lines, areas of weakness

Convection currents cause spreading of the plate at the back arc zone

Melting and mixing of material causing magma to rise and putting pressure of crust

28
Q

Shield volcanos

A

Relatively thin lava flows built up over central vent
Mostly balsatic magma
Hence relatively non-explosive eruptions

Roughly circular / oval

29
Q

Composite volcanos / stratovolcanoes

A

Most common

Mainly andesitic magma, typically felsic hence high viscosity
Inter layering of lava flows and pyroclastic layers

Intermediate steepness (steep near the top and flatter at the base due to erosion)

Intermittent eruptions but more explosive than shield volcanoes

30
Q

Scoria cones

A

Small, steep sided, with deep central craters

Gas-rich lava, ejected in fire fountains
Cools quickly forming brittle rough rock with gas holes

Scoria is high in iron, dark red colour due to oxidation

31
Q

Caldera volcano

A

Formed after a massive explosive eruption that empties the magma chamber

Rhyolitic magma (high in gas)

Remaining volcano walls collapse, forming huge crater

32
Q

Dome volcano

A

Formed from degassed rhyolitic magma

After violent eruptions, remaining chamber has no gas, magma no longer explosive
High silica rhyolite (high viscosity) so it cools very quickly without flowing far

Steep convex slope

33
Q

Lava plateau

A

When lava erupts from long cracks or fissures, spreads out evenly

34
Q

What is the Taupo volcanic zone and how was it formed?

A

TVZ is an extensional feature called a back arc basin, west of the subduction zone

extends from Mt Ruapehu to White Island

Formed due to the subduction of the PP

Has most of NZ’s active volcanoes

35
Q

Back arc system

A

Secondary convection current is set up behind the subduction zone, resulting in a spreading zone

BOP area is pulled apart by the back arc - many areas below sea level

Back arc has created a 50km by 160km pool under the crust, reservoir for future eruptions

36
Q

TVZ volcanoes

A

Stratovolcanoes: ruapehu, White Island and Ngaruhoe

Ruapehu:
Crater lake above main vent
Fills with melted snow
Has ruptured at times to send lahars (Tangiwai)

Caldera: lake Taupo

37
Q

How are geothermal areas created

A
  1. WATER
  2. DEEP HEAT SOURCE (magma)

Water (rain and groundwater) in porous rock come into contact with magma
Hot water less dense
Rises to the surface

Hydrogen sulfide gives rotten egg smell

38
Q

Define and explain geyser

A

Jets of hot water and steam

Magma chamber heat radiates upwards into surrounding rock

Water underground through fractures in rock
Water reaches hot rock, try to rise back to surface

Overlying cold water keeps pressure on
Causes superheating, until pressure pushes overlying water out of the hole and steam expands rapidly

During this process, hot water dissolved silica, carries it upward to line the fractures, creating a sealed system = plumbing system

39
Q

Fumerole

A

Jets of steam

40
Q

Three ways earthquakes are created

A

Volcanic activity - pressure of rising magma

Tectonic plate movement -
Plates stick together, stress builds, released as earthquakes

Landslide

41
Q

Define:
Focus
Epicentre
Seismic waves
After shocks

A

Where the earthquake originated

Epicentre: point directly above focus

Seismic waves: vibration of energy passing through the ground

After shocks: further sudden movements in earth’s crust causing seismic waves

42
Q

How does earthquake depth depend on location?

A

Shallow -
occur where PP is subducting
Middle of NI due to volcanic activity
Along alpine fault due to lateral mvt

Deep -
Further away from subduction zone on the overriding plate (NI)

43
Q

Describe and explain the Benioff Zone

A

The planar zone of earthquakes produced by an interaction between subducting oceanic plate and continental

Upper part (close to subduction zone)
Rocks sliding past each other, shallow earthquakes

Lower part (under the overriding plate)
Oceanic plate semi-solid, blobs fall off, rocks shift - deep earthquakes

44
Q

Types of seismic waves

A

Body waves and surface waves

Body waves: travel through earth
P waves - primary. Arrive first. Compressions (longitudinal waves)
S waves - secondary. Transverse.

Surface: move along surface, cause the most damage
Love wave - side to side
Rayleigh - circular motion

45
Q

What are faults and why do they occur

A

Breaks/fractures in earth’s crust after movement

Occur as a result of the release of stress

Faults occur along fault lines as they are the weakest areas in the crust which stress can be released

46
Q

Syncline and Anticline

A

Describes folds based on relative ages of rock layers.

Syncline: trough of a curve of a fold.
Youngest rock at the centre axis

Anticline: crest of a curve of a fold. Oldest rock at centre axis

47
Q

Lateral fault

A

Also known as a ‘strike-slip fault’

Sideways movement at a plate boundary

AP moves NE relative
PP moves SW

Sinistral - LEFT side moves
Dextral - RIGHT side moves. Most in NZ

48
Q

Normal fault

A

Crust material pulled apart
Land slumps down and away

Exposes a scarp face

Eg. TVZ

49
Q

Reverse fault

A

Crust material pushes together
Land climbs up and over

Exposed surface = scarp

Eg. Marlborough fault, NI fault

50
Q

Major fault zones in nz

A

NI: NI fault system
Runs from Wellington to BOP
Includes Taupo, Tarawera and Rotorua
Responsible for most of NZ’s volcanic activity

SI:
Marlborough fault system
Alpine fault
Macquarie fault - transition from lateral (strike slip) to subduction near the Puysegur Trench

51
Q

Events causing a tsunami

A

Waves generated when a large body of water is displaced

Meteor impact
Landslides (submarine or into water)
Submarine volcano eruption
Underwater earthquake
Continental slope avalanche

52
Q

Continental shelf avalanche

A

At the edge of a continental shelf there is a continental slope to the ocean floor.

Sediment deposited at top of slope, periodically plunges down, causing tsunami

53
Q

What factors determine the speed and wavelength of a tsunami

A

Depth of ocean and size of earthquake

Deeper - when pulse reaches surface, wave front is so wide it is unnoticeable
Shallow - front of wave slows due to friction with ocean floor, shorter wavelength
Amplitude increases as water compressed, but wave slows (KE to GPE)

Greater force of earthquake —> greater amplitude of water displacement, hence faster wave

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