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Earth And Space > Tectonic plates and volcanoes > Flashcards

Tectonic plates and volcanoes Flashcards

0
Q

What are the effects of eruptions?

A 
Lava flows
Volcanic ash
Pyroclastic flows
Volcanic collapse 
Lahars
Floods 
Volcanic gases
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1
Q

What are the four I dependant spheres that the world is divided into?

A

Atmosphere
Geosphere/lithosphere
Hydrosphere
Biosphere

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2
Q

Give a brief description of the atmosphere

A

Air that extends up from the Earths surface for about 100 km

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3
Q

Give a brief description of the hydrosphere

A

Contains all earths solid, liquid and gaseous water eg. As the ocean, rivers and glaciers

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4
Q

Give a brief description of the biosphere

A

All living organisms, wherever they live

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5
Q

What are the two types of crust?

A

Oceanic and continental

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6
Q

Where is oceanic crust found and characteristics

A

Under the ocean

Denser, thinner and younger

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7
Q

Where is continental crust found and characteristics

A

Is the land and includes the extended continental shelf around New Zealand
Buoyant, thicker, older

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8
Q

Oceanic crust characteristics

A

Crust depth: thin-5-12km
Age: young rocks, less than 200 million yrs old
Density: more dense
Rock type: mainly basalt

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9
Q

Continental crust characteristics

A

Crust depth: thick-40km average
Age: older rocks up to 4500 million yrs old
Density: less dense
Rock type: range of granites

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10
Q

Where do volcanic eruptions generally occur in nz?

A

In Auckland, taranaki and the taupo volcanic zone

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11
Q

Explain why gravity is so important on extreme earth events?

A

Gravity pulls everything towards the centre of the earth. Gravity causes material to fall, such as ash from a volcano or land after an earthquake shake. If land starts to slide after an earthquake, gravity makes it move even faster

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12
Q

What is magma?

A

Molten rock that rises from deep beneath the surface of the earth.

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13
Q

What are the types of magma?

A

Basaltic
Andesitic
Rhyolitic

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14
Q

Characteristics of basaltic magma

A 
Amount of silica: 45-55%
Viscosity: runny
Temp: 1000-1200 •C
Amount of gas: smaller 
Eruption style: effusive with runny lace eg. Auckland volcanic field
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15
Q

Characteristics of Andesitic magma

A 
Amount of silica: 55-65%
Viscosity: sticky
Temp: 800-1000 •C
Amount of gas: larger
Eruption style: explosive eg. Cone volcanoes such as ngauruhoe, ruapehu
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16
Q

Characteristics of rhyolitic magma

A

Amount of silica: 65-75%
Viscosity: very sticky
Temp: 650-800 •C
Amount of gas: largest
Eruption style: extremely explosive eg. Taupo caldera
Dome- gentle and slow because gas has been released in previous eruptions leaving very little gas in the magma

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17
Q

What are the two types of explosions

A

Magmatic explosions

Phreatomagmatic eruptions

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18
Q

What are magmatic explosions

A

Occur when gas is dissolved into the magma. As the magma rises, it forms bubbles and when it reaches the surface the gas bubbles burst into the air. The more viscous the magma is the more gas it can trap and the more gas it can trap the more violent the explosion is.

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19
Q

What are phreatomagmatic eruptions

A

Occur when hot magma comes up beneath a water source (lake, sea, ground water). The heat of the magma makes the water flash into vapour which then has a volume 10,000 times that of the original liquid water

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20
Q

What are lava flows

A

Magma without much gas runs slowly covering anything but doesn’t cover large areas

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21
Q

What is volcanic ash

A

Fine particles carried by wind due to hot expanding then cooling and contracting gas. The ash is abrasive and corrosive

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22
Q

What are pyroclastic flows

A

Dense clouds of hot fragments and gas close to the ground, travel fast (50-150kmh-1) and hot (100-700•C)

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23
Q

What are volcanic collapses

A

Happen when rapidly forming volcano suddenly collapses due to instability caused by the pressure of more magma rising, shaking from an earthquake, or heavy rain saturating the volcano

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24
Q

What are lahars

A

Flows of boulders, ice, water and mud that occur during or after an eruption. Short lived but can be devastating

25
Q

What are volcanic gases

A

Consist mainly of CO2, water vapour and sulfur dioxide with traces of other gases. These gases can be toxic or corrosive and dangerous to life

26
Q

What is tephra

A

Fragments of material produced after a violent explosion

27
Q

What are the 3 different classes of size tephra is separated into

A

Ash- particles smaller than 2mm in diameter
Volcanic cinders- between 2 and 64 mm in diameter
Volcanic bombs- larger than 64mm in diameter

28
Q

Why can tephra be used for dating eruptions

A

Each eruption is different which results in the tephra having a unique chemical fingerprint, trace elements and characteristics for a particular eruption. Therefore analysis of the tephra can be used to identify different eruptions

29
Q

How are subduction volcanoes formed?

A

Where the edge of the pacific plate subducts under the edge of the Australian plate assisted by gravity. When the pacific plate has dived deeply enough, rock melts, assisted by superheated water from subducted sediments, forming magma, which forces it’s way up through vents in the crust forming volcanoes

30
Q

Two ways volcanoes are formed in nz?

A

Subduction eg. Volcanoes of taupo volcanic zone, mt taranaki, kermadec volcanoes
Plume of magma from the mantle in a hot spot eg. Volcanoes in auckland volcanic field

31
Q

Name the three main types of volcano found in the taupo volcanic zone

A

Cones or stratovolcanoes eg. White Island, mt ruapehu, mt ngauruhoe
Caldera eg. Taupo, okataina
Domes eg. Parts of mt tarawera, mt maunganui

32
Q

About cone volcanoes

A

Made up of Andesitic magma
Erupted lava is semi sticky and cools relatively quickly
Eruptions gentle just lava or explosive of pyroclastic flow of hot ash
Cone is formed when layers of ash and lava build up over time

33
Q

About caldera volcanoes

A

Generally erupt rhyolite lava
Eruptions that form calderas create craters
Very violent and explosive eruptions because gas bubbles find it hard to escape sticky magma

34
Q

The stage of caldera volcanoes

A
  1. Gases such as CO2 and water vapour from the melting of subducted limestone in the sediment form bubbles.
  2. Gas bubbles expand as they rise, filling the magma chamber with gaseous magma and putting pressure on the ground above forming cracks in the ground
  3. Magma moves up to surface through weakness in the crust and violently explodes due to high amount of gas emptying the chamber
  4. Weakens the ground causing roof of chamber to collapse forming a giant caldera which fills with water over time forming a lake. Pyroclastic flow sets as ignimbrite rock
35
Q

About dome volcanoes

A

Made from rhyolitic magma from which gas has escaped because of previous violent eruption
Gentle eruptions
Forms a steep convex slope from thick, fast cooling lava

36
Q

Mt ruapehu

A

Largest active volcano in NZ
A ring plain surrounds the mountain due to lahars, landslides and ash falls
3 summit craters have erupted in the last 10,000 years
The active vent is beneath crater lake which contains varying amounts of warm, acidic water fed by snow melt
Major eruptions have been 50 years apart: 1895, 1945, 1995
Minor eruptions have occurred 60 times since 1945
On 24 dec 1953 a train fell into a river killing 151 people and a bridge was swept away

37
Q

How do geothermal areas form?

A

When rainwater or groundwater seeps down through cracks in the rock towards a heat source. The hot water rises as steam or both and emerges at the earths surface. Hot water reacts with the rock it’s comes in contact with and becomes enriched with dissolved minerals

38
Q

What are the features of geothermal areas

A 
Geysers
Fumeroles
Mud pools
Boiling springs
Sinter deposits 
Gases
39
Q

What are geysers

A

Hot springs that eject jets of boiling water and steam into the air

40
Q

Fumeroles

A

Steam and gas vents

41
Q

Mud pools

A

Form where steam and gas rise to the surface under rainwater ponds

42
Q

Boiling springs

A

Occur where geothermal fluids rise quickly to the surface

43
Q

Sinter deposits

A

Are features of boiling springs, composed of almost pure silica but often containing traces of impurities or micro organisms which produce beautiful colours

44
Q

Gases

A

Carbon dioxide and hydrogen sulfide are ground hugging gases that are heavier than air, and can accumulate in dangerous concentrations. The most common death traps are excavations in geothermal ground, or poorly ventilated bathing pools

45
Q

Give a brief description of geosphere

A

The land which includes all minerals, rocks, sediments and soils

46
Q

Where is the tectonic plate boundary in nz

A

NI is on the AP. The tectonic plate boundary cuts through SI, starting at kaikoura leaving Milford sound. The west coasts and nelson area on AP the rest of SI on PP. Also includes the kermadec trench to the north and pusegur trench to the south

47
Q

Pacific plate and crust type

A

PP made up of OC to north of nz and east coast of NI. At kaikoura PP enters SI changes to CC

48
Q

Australian plate and crust type

A

AP made up of CC in NIand most of SI. At Milford sound AP leaves SI becomes OC

49
Q

What shape are volcanoes with basalt magma

A

Shield volcanoes, cinder cones, tuff rings

49
Q

What shape are volcanoes with andesite magma

A

Cone volcanoes

49
Q

What shape are volcanoes with rhyolitic magma

A

Caldera and dome volcanoes

50
Q

What magma is erupted from subduction volcanoes

A

Andesitic or rhyolitic

51
Q

What shape are subduction volcanoes

A

Cones, calderas and dome

52
Q

Examples of cone volcanoes

A

Mt ruapehu, White Island, ngauruhoe, tongariro, taranaki

53
Q

Examples of dome volcanoes

A

Mt tawarewa and mt maunganui

54
Q

How are hot spot volcanoes formed

A

From a plume of molten magma that starts 100 km under Auckland. Basalt magma rises up through the crust at about 5km per hour forming a new volcanic in the auckland volcanic field

55
Q

How geosphere causes volcanic eruptions

A

Oceanic crust of pacific plate subducts under the continental crust of the Australian plate

56
Q

How does the hydrosphere cause volcanic eruptions

A

Wet sediments from the bottom of the ocean are subducted and the water from these becomes superheated. This lowers the melting point of the rock around it which forms magma

57
Q

How does the biosphere cause volcanic eruptions

A

Carbonate rock which had been partially made from the compressed remains of plankton is melted underground releasing CO2

58
Q

How does the atmosphere cause volcanic eruptions

A

Gases are released from magma as it rises through the crust. Ash is also erupted and both can rise tens of kms into the air

Earth And Space (4 decks)

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