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

Volcanism and plutonism, Lectures 6,7,8 Flashcards

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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
Pyroclastic density current/pyroclastic flow
gravity flow of hot gases and particles which flow down the flanks of a volcano
26
What produces a pyroclastic density current deposit?
Pyroclastic density current/pyroclastic flow
27
Pyroclastic density current deposit
material deposited by a pyroclastic density current/pyroclastic flow in the valleys
28
What can a pyroclastic density current/pyroclastic flow result from?
the collapse of a lava dome
29
Lahar
flow of mixture of water and volcanic material - a volcanic mudflow
30
Lahar produces
a lahar deposit
31
Debris avalanche
Flow of landslide material down the flanks of a volcano
32
Debris avalanche produces a
Debris avalanche deposit
33
Phreatic eruption
steam eruption
34
Does a phreatic eruption produce a deposit/ its name
no deposit produced!!
35
Lava flow
Flow of hot lava down the flanks of a volcano
36
Lava flow produces a...
lava
37
Three techniques to find information about igneous intrusions
1. fieldwork 2. geophysical surveying 3. underground mapping
38
Pluton | and its spatial scale
connected intrusions | a few to 10s of km
39
Batholith | and its spatial scale
larger connection of intrusions than a pluton | up to 100km long and 100s of km across
40
Dike
when magma pushes up through older rocks and forms a vertical rock column (discordant)
41
Sill
flat intrusion of igneous rock that forms between pre-existing layers of rock (but not through one layer)
42
Example of a batholith
the Cornubian granite, Cornwall, a solidifed magma chamber that crystallised 300Ma ago
43
Example of a pluton
Ross of Mull, Isle of Mull, Scotland, crystallised 418 Ma ago
44
Three ways igneous rocks are classified
1. silica content 2. grain size 3. proportions of minerals
45
Classifying igneous rocks | Silica content
weight % silica
46
Classifying igneous rocks | grain size
fine-grained, volcanic, extrusive | coarse-grained, plutonic, intrusive
47
Plutonic rock
not been above the surface, | allows time for crystals to develop
48
Classifying igneous rocks | proportions of minerals
explanatory
49
Types of magma 4 (table in notes and lab book)
Ultramafic Mafic Intermediate Felsic
50
Is there just one or many types of granite?
many types
51
Two types of lava (surface characteristics)
Aa | Pahoehoe
52
Aa lava
(blocky lava) | Irregular scoriaceous fragments; form during cooling at high flow rates due to internal shearing
53
Pahoehoe lava
(ropy lava) | patterns of ropes and whorls; form when lava cools at low flow rates
54
Felsic | made up of
feldspar | silica
55
Mafic | made up of
Magnesium | ferric (iron)
56
Volcanic geomorphological features | 7
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
Caldera
Topographic depression greater than 1km in diameter
58
Crater
Topographic depression less than 1km in diameter
59
Example of caldera
Sollipulli, Chile , ice-filled caldera, 4km diameter
60
Formation of calderas
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
Another word for composite volcanoes
stratovolcanoes
62
Composite volcanoes
conical, steep profile, many strata, periodic explosive and effusive eruptions, intermediate-felsic composition
63
Example of a composite volcano
Mount Mayon, Philippines
64
Lava domes
- 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
Examples of lava domes | 2
Volcan de Colima, Mexico | Mount St Helens, USA
66
Shield volcanoes
- low, rounded profiles - composed of low viscosity, mafic lava flows: basalt - magma can seep out of the flanks of the volcano
67
Example of shield volcanoes
Mauna Loa, Hawaii, USA
68
Fissures
Mafic lava flows rapidly away from fissures, rather than constructing a volcanic mountain
69
Example of a fissure
Kilauea, Hawaii, USA
70
Cinder cones
- 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
Hot springs
produced by the emergence of geothermally heated groundwater
72
Geyser
a vent that periodically ejects a column of hot water and steam
73
Example of a geyser
Old Faithful, Yellowstone national park, Wyoming, USA
74
Fumaroles
Volcanic vents that emit gases

Geology, LEC 172 (6 decks)

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