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Geology, LEC 172 > Volcanism and plutonism, Lectures 6,7,8 > Flashcards

Volcanism and plutonism, Lectures 6,7,8 Flashcards

1
Q

Igneous rocks

Material products of eruptions

A

Form when magma cools and solidifies

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2
Q

Magma

Material products of eruptions

A

molten rock below the Earth’s surface

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3
Q

Lava

Material products of eruptions

A

Molten rock at the Earth’s surface. Magma erupts as lava flows and pyroclastic material.

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4
Q

Example of a volcano with lava flows

A 
E15, Iceland
2010 eruption
lava fountaining and lava flows
no flight distruption due to little ash
tourist attraction
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5
Q

Pyroclasts

Material products of eruptions

A

Form when magma is explosively ejected from a volcano as fragments with volcanic gases.

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6
Q

Pyroclastic rocks

Material products of eruptions

A

Form when pyroclastic sediments consolidate

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7
Q

Three classifications of pyroclasts

A

ash
lapilli
volcanic bombs

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8
Q

Ash

A

<2mm diameter

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9
Q

Lapilli

pyroclast classification

A

2-64mm diameter

little stones in Latin

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10
Q 
Volcanic bombs
(pyroclast classification)
A

> 64mm diameter

fragemenrs hurled from the vent which land close (normally within 100s metres) of the vent, can be house sized!

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11
Q

Four components of ash

Material products of eruptions

A

pumice/scoria
lithics
crystals
glass shards

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12
Q

Pumice/scoria

components of ash

A

fragments of vesicular lava

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13
Q

Lithics

components of ash

A

rock fragments

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14
Q

Crystals

components of ash

A

individual and broken

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15
Q

Glass shards

components of ash

A

chilled magma, vesicle walls

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16
Q

Pumice structure

A

spherical vesicles

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17
Q

Tube pumice structure

A

elongate vesicles

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18
Q

Components of lapilli

2

A

Pumice/scoria

lithics

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19
Q

Pumice

A

Light coloured vesicular igneous rock which forms through rapid solification of melt.

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20
Q

What causes the structure of pumice?

A

gas trapped in the melt at the time solidification

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21
Q

Processes and deposits of eruptions

6

A 
pyroclastic fall
pyroclastic fall deposit
pyroclastic density current (aka pyroclastic flow)
lahar
debris avalanche
phreatic eruption
lava flow
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22
Q

Material products of eruptions

A

lava
pyroclasts
pyroclastic rocks

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23
Q

Pyroclastic fall

A

sedimentation of particles from a volcanic plume

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24
Q

What produces a pyroclastic fall deposit

A

pyroclastic fall

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25
Q

Pyroclastic density current/pyroclastic flow

A

gravity flow of hot gases and particles which flow down the flanks of a volcano

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26
Q

What produces a pyroclastic density current deposit?

A

Pyroclastic density current/pyroclastic flow

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27
Q

Pyroclastic density current deposit

A

material deposited by a pyroclastic density current/pyroclastic flow in the valleys

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28
Q

What can a pyroclastic density current/pyroclastic flow result from?

A

the collapse of a lava dome

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29
Q

Lahar

A

flow of mixture of water and volcanic material - a volcanic mudflow

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30
Q

Lahar produces

A

a lahar deposit

31
Q

Debris avalanche

A

Flow of landslide material down the flanks of a volcano

32
Q

Debris avalanche produces a

A

Debris avalanche deposit

33
Q

Phreatic eruption

A

steam eruption

34
Q

Does a phreatic eruption produce a deposit/ its name

A

no deposit produced!!

35
Q

Lava flow

A

Flow of hot lava down the flanks of a volcano

36
Q

Lava flow produces a…

A

lava

37
Q

Three techniques to find information about igneous intrusions

A
  1. fieldwork
  2. geophysical surveying
  3. underground mapping
38
Q

Pluton

and its spatial scale

A

connected intrusions

a few to 10s of km

39
Q

Batholith

and its spatial scale

A

larger connection of intrusions than a pluton

up to 100km long and 100s of km across

40
Q

Dike

A

when magma pushes up through older rocks and forms a vertical rock column
(discordant)

41
Q

Sill

A

flat intrusion of igneous rock that forms between pre-existing layers of rock (but not through one layer)

42
Q

Example of a batholith

A

the Cornubian granite,
Cornwall,
a solidifed magma chamber that crystallised 300Ma ago

43
Q

Example of a pluton

A

Ross of Mull,
Isle of Mull, Scotland,
crystallised 418 Ma ago

44
Q

Three ways igneous rocks are classified

A
  1. silica content
  2. grain size
  3. proportions of minerals
45
Q

Classifying igneous rocks

Silica content

A

weight % silica

46
Q

Classifying igneous rocks

grain size

A

fine-grained, volcanic, extrusive

coarse-grained, plutonic, intrusive

47
Q

Plutonic rock

A

not been above the surface,

allows time for crystals to develop

48
Q

Classifying igneous rocks

proportions of minerals

A

explanatory

49
Q

Types of magma
4
(table in notes and lab book)

A

Ultramafic
Mafic
Intermediate
Felsic

50
Q

Is there just one or many types of granite?

A

many types

51
Q

Two types of lava (surface characteristics)

A

Aa

Pahoehoe

52
Q

Aa lava

A

(blocky lava)

Irregular scoriaceous fragments; form during cooling at high flow rates due to internal shearing

53
Q

Pahoehoe lava

A

(ropy lava)

patterns of ropes and whorls; form when lava cools at low flow rates

54
Q

Felsic

made up of

A

feldspar

silica

55
Q

Mafic

made up of

A

Magnesium

ferric (iron)

56
Q

Volcanic geomorphological features

7

A
  1. calderas and craters
  2. composite volcanoes
  3. lava domes
  4. shield volcanoes
  5. fissures
  6. cinder cones
  7. hot springs, geysers and fumeroles
57
Q

Caldera

A

Topographic depression greater than 1km in diameter

58
Q

Crater

A

Topographic depression less than 1km in diameter

59
Q

Example of caldera

A

Sollipulli, Chile ,
ice-filled caldera,
4km diameter

60
Q

Formation of calderas

A
  1. magma chamber filled with fresh magma triggers an eruption of lava and ash
  2. the magma chamber becomes partially depleted as eruptions of lava and pyroclastic flows continue
  3. the summit collapses into the chamber which is now empty, pyroclastic flows blanket the collapse
  4. a lake forms in the caldera, hot springs and geysers exist as a minor form of volcanic activity
61
Q

Another word for composite volcanoes

A

stratovolcanoes

62
Q

Composite volcanoes

A

conical, steep profile, many strata, periodic explosive and effusive eruptions, intermediate-felsic composition

63
Q

Example of a composite volcano

A

Mount Mayon, Philippines

64
Q

Lava domes

A
  • viscous intermediate- felsic composition
  • common/dangerous feature of composite volcanoes
  • material blocks the column of the volcano, can overspill the crater walls and go down the volcano flanks
  • ^ plugs the central vent, often occurs before major explosive events
65
Q

Examples of lava domes

2

A

Volcan de Colima, Mexico

Mount St Helens, USA

66
Q

Shield volcanoes

A
  • low, rounded profiles
  • composed of low viscosity, mafic lava flows: basalt
  • magma can seep out of the flanks of the volcano
67
Q

Example of shield volcanoes

A

Mauna Loa, Hawaii, USA

68
Q

Fissures

A

Mafic lava flows rapidly away from fissures, rather than constructing a volcanic mountain

69
Q

Example of a fissure

A

Kilauea, Hawaii, USA

70
Q

Cinder cones

A
  • steep, conical, symmetrical peaks <400m high with a summit crater
  • composed mainly of mafic pyroclastic material (scoria)
  • formed by explosive eruptions or lava fountains
  • common at fissures and composite volcanoes
71
Q

Hot springs

A

produced by the emergence of geothermally heated groundwater

72
Q

Geyser

A

a vent that periodically ejects a column of hot water and steam

73
Q

Example of a geyser

A

Old Faithful, Yellowstone national park, Wyoming, USA

74
Q

Fumaroles

A

Volcanic vents that emit gases

Geology, LEC 172 (6 decks)

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