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Geology > Igneous Rocks and Processes > Flashcards

Igneous Rocks and Processes Flashcards

1
Q

Define Euhedral

A

Describes a complete crystal, has the perfect crystal shape

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2
Q

Define Subhedral

A

Describes a partially complete crystal

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3
Q

Define Anhedral

A

Describes a crystal with no crystal shape

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4
Q

Define Porphyritic

A

Crystals have different sizes

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5
Q

Define Equicrystalline

A

Crystals are the same size

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6
Q

Define Groundmass

A

Small crystals between phenocrysts in porphyritic rock

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7
Q

Define Phenocryst

A

The big crystal in a porphyritic rock

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8
Q

Define Vesicles

A

Trapped gases in the rock creates hole/cavities

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9
Q

Define Amygdales

A

Vesicles which have been filled in with crystals

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10
Q

Define Crystal Alignment

A

Crystals are aligned

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11
Q

Define Random Orientation

A

Crystals are not aligned

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12
Q

Define Flow Banded

A

Form lines

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13
Q

What is the equation to calculate the degree of magnification?

A

Size of image/Size of real object

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14
Q

What are two trends of oceanic crust?

A

Trend 1 - the crust gets older the further you move from the ridge
Trend 2 - oceanic lithosphere gets thicker the further you move from the ridge

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15
Q

How do pillow lavas form?

A

When lava is erupted into water it causes the lava to cool and crystallise very quickly. This causes it to form a pillow shape and the edges of the pillows will be glassy

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16
Q

What are six features of a pillow lava?

A

Rounded top, Pointed keel, Fine grained basalt, Vesicles, Glassy rind, 1m tall

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17
Q

How can pillow lavas be used as a way up indicator?

A

The pillow has a rounded top and pointed bottom. If the keel can be seen it is the wrong way round

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18
Q

What are the two ways of describing the tops of basalt lava flows (flow tops)?

A

A’a and Pahoehoe

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19
Q

Define A’a

A

Has a rubbly brittle top due to having high viscosity and cooling quickly

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20
Q

Define Pahoehoe

A

Smooth and ropy due to having a lower viscosity and cooling slower

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21
Q

What are three features of an A’a flow top?

A

Thick flow units (2-10m), High flow-front velocity, Forms large channels

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22
Q

What are three features of a Pahoehoe flow top?

A

Thin flow units (0.2-2m), Low flow-front velocity, Forms lava tubes

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23
Q

How do columnar joints form?

A

When an igneous body cools and crystallises the unit contracts inwards, creating cracks arranged in a polygonal shape and columns of rock

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24
Q

What two heat transfer processes are involved in the creation of columnar joints?

A

Conduction and Radiation

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25
Q

Define Intrusive

A

Inside the crust

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26
Q

Define Extrusive

A

Outside the crust

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27
Q

Define Concordant

A

Follows bedding planes

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28
Q

Define Discordant

A

Cuts across bedding planes

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29
Q

Define Chilled Margin

A

Inside the igneous body where the magma has cooled very quickly against the country rock

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30
Q

Define Baked Margin

A

Outside the igneous body where the magma has heated up the country rock, causing it to become harder and more crystalline

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31
Q

What are the four types of igneous body?

A

Lava flow, Sill, Dyke, Pluton

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32
Q

Define Lava Flow

A

An extrusive, concordant body with sheet like morphology, two chilled margins and one baked margin (can have a reddened top due to oxidation)

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33
Q

Define Sill

A

An intrusive, concordant body with sheet like morphology, two chilled margins and two baked margins

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34
Q

Define Transgressive Sill

A

Intruding along bedding planes and then cutting up into higher layers

35
Q

Define Dyke

A

An intrusive, discordant body with sheet like morphology, two chilled margins and two baked margins

36
Q

Define Pluton

A

An intrusive, discordant body with a circular morphology, one baked margin and one chilled margin

37
Q

What is the difference in thickness between a sill and a lava flow?

A

Sills are usually thicker than lava flows

38
Q

What is the difference in baked margins between a sill and a lava flow?

A

Sills have two baked margins whereas lava flows only have one

39
Q

What is the difference in chilled margin between a sill and a lava flow?

A

Sills have two chilled margins whereas lava flows only have one (though the top may be chilled or made of scoria)

40
Q

What is the difference in crystal size between a sill and a lava flow?

A

Sills are medium sized crystals (as they are hypabyssal and cool slowly) whereas lava flows are fine sized crystals (as they are volcanic and cool quickly)

41
Q

What is the difference in arrangement of crystals between a sill and a lava flow?

A

Crystals are not arranged in a sill, whereas the movement of lava does cause them to be aligned

42
Q

What is the difference in weathering of the upper surface between a sill and a lava flow?

A

No weathering of a sill whereas oxydation can chemically weather a lava flow, making it have a reddened top

43
Q

What is the difference in included fragments between a sill and a lava flow?

A

Sills can have xenoliths as it rips up material above and below, whereas no xenoliths are found from above in a lava flow (though could come from below)

44
Q

Define Absolute Dating

A

A method of giving a material/rock a numerical age

45
Q

Define Isotope

A

An element with the same number of electrons and protons, but different number of neutrons

46
Q

Define Half-Life

A

The time taken for the number of unstable parent nuclei to decay to stable daughter elements

47
Q

Define Parent Isotopes

A

The radioactive/unstable isotope

48
Q

Define Daughter Isotopes

A

The product of radioactive decay/stable isotope

49
Q

What can a mass spectrometer measure?

A

The abundance of different isotopes within a whole rock or an individual mineral

50
Q

What will scientist compare to determine the absolute age of a sample?

A

The abundance of parent isotopes compared to daughter isotopes

51
Q

What is the half life for 40K-40Ar (Potassium-Argon)?

A

1,250 million years

52
Q

What is the half life for 87Rb-87Sr (Rubidium-Strontium)?

A

48,800 million years

53
Q

What is the half life for 147Sm-143Nd (Samarium-Neodymium)?

A

106,000 million years

54
Q

What is the half life of 283Ub-206Pb (Uranium-Lead)?

A

4,470 million years

55
Q

What are three problems associated with radiometric dating of igneous rocks?

A

The older the rock the harder it is to detect and count the amount of parent isotope, Small/shallow intrusions cool and crystallise quickly meaning the closure temperature is reached rapidly and the rocks becomes a closed system, Weathering of igneous rocks may cause the soluble element to be removed leading to false ages

56
Q

What volcanic landforms are associated with basaltic lava?

A

Shield shape volcanoes - low angle (5-10 degrees) and up to 9km high

57
Q

What volcanic landforms are associated with andesitic lava?

A

Stratocone shape - steep angle (30 degrees) but up to 3km high

58
Q

What volcanic landforms are associated with rhyolitic lava?

A

Stratocone or caldera shaped - large crater

59
Q

What are three factors controlling the type of volcanic activity?

A

The viscosity in terms of % silica content, The volatile content (carbon dioxide, sulphur dioxide, water), The quantity of mass (amount of rock ejected)

60
Q

What three things is viscosity affected by?

A

Silica content, Temperature of the magma, Volatile content

61
Q

What does the Volcanic Explosivity Index provide?

A

A relative measure of the explosiveness of volcanic eruptions

62
Q

What is VEI based on?

A

Observation e.g. volume of products and eruption cloud height

63
Q

What scale does VEI use?

A

Logarithmic - each point on the scale represents a ten-fold increase in the observed ejecta

64
Q

What are six types of volcanic hazard?

A

Lava flow, Pyroclastic flow, Air-fall tephra, Volcanic gases, Lahars, Blast (lateral blast)

65
Q

Describe Lava Flow

A

Can be any composition or speed, damages property more than life, usually can be outrun

66
Q

Describe Pyroclastic Flow

A

Very dangerous due to unpredictability, usually restricted (but not always) to valleys, high mortality rate and extensive damage

67
Q

Describe Air-Fall Tephra

A

Formed from rock fragments during an explosive eruption, fall from eruption cloud and can settle anywhere, causes buildings to collapse, contaminates water, creates fertile land

68
Q

Describe Volcanic Gases

A

From any volcano, from the crater or fumeroles, can cause climate changes, asphyxiates animals, no damage to property, can contaminate groundwater supply

69
Q

Describe Lahars

A

Mixture of rocks, ash and water, sets like concrete, flows down pre-existing valleys, destroys buildings and farmland, travels further than pyroclastic flow

70
Q

Describe Blast

A

Due to build up and sudden release of pressure, triggers can be landslide or dome collapse, can be very dangerous depending on proximity

71
Q

What are five monitoring techniques?

A

Ground deformation, Gas emissions, Seismic activity, Thermal anomalies, Gravity anomalies

72
Q

How can ground deformation be used to monitor volcanoes?

A

Measure the angle of tilt of the land - increasing tilt could indicate inflation of a magma source

73
Q

How can gas emissions be used to monitor volcanoes?

A

Changes in natural pattern could suggest magma moving to surface - prior to eruption gas levels should erupt unless the vent is blocked

74
Q

How can seismic activity be used to monitor volcanoes?

A

Detects low magnitude earthquakes cause by the movement of magma towards the surface

75
Q

How can thermal anomalies be used to monitor volcanoes?

A

As magma rises to the surface, the ground will get hotter

76
Q

How can gravity anomalies be used to monitor volcanoes?

A

Dense rocks will increase the local gravity field and less dense rocks will reduce it - look for changes in normal value/spring length

77
Q

Define Hazard Maps

A

A map that shows the potential hazards of a volcano, by looking at previous deposits and their extent

78
Q

Who are hazard maps used by?

A

Town planners when considering where to build key buildings e.g. hospitals, schools

79
Q

How do lahar channels manage/control volcanic hazards?

A

Changes and controls the direction of the lahar, and to remove larger debris to lessen the impact

80
Q

How does strengthening rood manage/control volcanic hazards?

A

Stops them collapsing, to protect the building and the people in it

81
Q

What are four ways of controlling lava flows?

A

Spray lava with water, Build a dam/wall, Drop concrete blocks into lava to cool and slow it, Explosives to change the direction of flow

82
Q

What are four benefits of volcanoes?

A

Agriculture (fertile land due to ash), Tourism, Geothermal energy, Building products (e.g. gravel)

83
Q

Define Isopach Maps

A

Maps that show the thickness of deposits

84
Q

What can Isopach maps be used to determine?

A

Where the volcanic vent was and if the deposit was influenced by other external factors

Geology (16 decks)

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