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Earth And Space Science NCEA Scholarship > Y12 Geology > Flashcards

Y12 Geology Flashcards

(53 cards)

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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

Study These Flashcards
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

Study These Flashcards
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

Study These Flashcards
A

Mafic = MAgnesium and FErriC
Darker in colour
Basalt

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

25
Hot spot volcanos definition and process
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
Factors that magma type depends on
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
Reasons why volcanos are formed near subduction zones
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
Shield volcanos
Relatively thin lava flows built up over central vent Mostly balsatic magma Hence relatively non-explosive eruptions Roughly circular / oval
29
Composite volcanos / stratovolcanoes
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
Scoria cones
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
Caldera volcano
Formed after a massive explosive eruption that empties the magma chamber Rhyolitic magma (high in gas) Remaining volcano walls collapse, forming huge crater
32
Dome volcano
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
Lava plateau
When lava erupts from long cracks or fissures, spreads out evenly
34
What is the Taupo volcanic zone and how was it formed?
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
Back arc system
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
TVZ volcanoes
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
How are geothermal areas created
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
Define and explain geyser
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
Fumerole
Jets of steam
40
Three ways earthquakes are created
Volcanic activity - pressure of rising magma Tectonic plate movement - Plates stick together, stress builds, released as earthquakes Landslide
41
Define: Focus Epicentre Seismic waves After shocks
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
How does earthquake depth depend on location?
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
Describe and explain the Benioff Zone
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
Types of seismic waves
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
What are faults and why do they occur
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
Syncline and Anticline
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
Lateral fault
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
Normal fault
Crust material pulled apart Land slumps down and away Exposes a scarp face Eg. TVZ
49
Reverse fault
Crust material pushes together Land climbs up and over Exposed surface = scarp Eg. Marlborough fault, NI fault
50
Major fault zones in nz
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
Events causing a tsunami
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
Continental shelf avalanche
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
What factors determine the speed and wavelength of a tsunami
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

Earth And Space Science NCEA Scholarship (10 decks)

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