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Geomorphology > Volcanoes > Flashcards

Volcanoes Flashcards

1
Q

where to volcanoes stem from

A

release of magma on to earth’s surface

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2
Q

how many active volcanoes are on the planet

A

15 00

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3
Q

what constitutes an active volcano

A

having at least 1 eruption in recorded history

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4
Q

how many volcanic eruptions happen a year

A

50 volcanos

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5
Q

what is a volcano

A

a landform created when molten magma escapes earth’s interior

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6
Q

what is volcanism

A

geological processes that result in volcanic eruptions

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7
Q

what are the three stages of volcanic activity

A
  1. active
  2. dormant
  3. extinct
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8
Q

define active volcano

A

volcano that is currently erupting or has erupted recently

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9
Q

what is a dormant volcano

A

a volcano has not erupted in the last few thousand years

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10
Q

what is an extinct volcano

A

not erupted for tens of thousands of years

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11
Q

what is an example of an extinct volcano

A

Canadian shield

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12
Q

is there molten rock within an extinct volcano

A

NO

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13
Q

crater

A

a circular depression in the ground typically a basin circular form

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14
Q

what causes a crater to form

A

volcanic activity

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15
Q

where is a crater found in a volcano

A

at the top

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16
Q

does lava only flow from the top

A

NO - can come from all sides

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17
Q

what often fills a volcanic crater

A

a lake or glacier

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18
Q

what volcanic feature is this

A

crater

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19
Q

vent

A

actual side of magma eruption

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20
Q

does a volcano only have one vent

A

no - can have multiple

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21
Q

lava vs magma

A

lava
- outside on the surface of earth

magma
- within the earth’s surface

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22
Q

what volcanic feature is this

A

vent

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23
Q

caldera

A

a cauldron like volcanic feature formed by collapse of land following a volcanic eruption

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24
Q

is a caldera larger or smaller than a crater

A

much larger

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25
Q

describe the steps that form a caldera

A

a very large volcano with a huge magma chamber that when the volcano erupts the chamber collapses in on itself and forms a basin

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26
Q

what volcanic feature is this

A

caldera

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27
Q

what is often growing in the center of a caldera

A

a new volcano

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28
Q

flank eruption

A

an eruption from the side of a volcano

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29
Q

what volcanic feature is this

A

flank eruption

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30
Q

dome

A

roughly circular mound shaped protrusion resulting from the slow eruption of felsic lava

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31
Q

what type of lava forms a dome

A

felsic lava

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32
Q

what volcanic feature is this

A

dome

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33
Q

what is felsic lava

A

a type of lava that has a lot of silica which traps heat and gas in

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34
Q

4 types of lava

A
  1. Aa lava
  2. Pahoehoe lava
  3. Pillow lava
  4. Columnar lava
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35
Q

what is Aa lava

A

rough, jagged blocky texture that moves like its being pushed

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36
Q

what is Pahoehoe lava

A

twisted or ropy texture found in Hawaii volcanoes

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37
Q

what is pillow lava

A

forms when lava enters water, often found on ocean floor near spreading axes

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38
Q

what is columnar lava

A

forms when lava hits ice

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39
Q

what type of lava is this

A

Aa lava

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40
Q

what type of lava is this

A

pahoehoe

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41
Q

what type of lava is this

A

Pillow lava

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42
Q

what type of lava is this

A

columnar lava

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43
Q

does pahoehoe have viscosity

A

NO - flows easily

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44
Q

what are known as materials extruded during a volcano

A

pyroclastic materials

nuees ardentes (glowing avalanche)

lahars

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45
Q

types of pyroclastic debris (7)

A

ash and dust
lapilli
blocks and bombs
scoria
pumice

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46
Q

describe ash and dust pyroclastic debris

A

fine glassy fragments

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47
Q

define lapilli pyroclastic debris

A

walnut sized material

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48
Q

what are the pyroclastic debris larger than lapilli

A

blocks and bombs

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49
Q

define blocks and bombs pyroclastic debris

A

blocks
- hardened or cooled lava (comes out of volcano already a solid)

bombs
- ejected as hot lava (cools in the AIR)

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50
Q

describe scoria vs pumice pyroclastic debris

A

scoria
- vesicular ejecta from MAFIC magma

pumice
vesicular ejecta from SILICA-RICJ magma (felsic)

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51
Q

what type of pyroclastic debris can float on lava

A

pumice

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52
Q

describe the form of pumice (pyroclastic debris)

A

solid object with lots of holes formed from lots of gas in magma

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53
Q

what is a nuees ardentes

A

a mixture of gas, lava, blocks, ash and pumice that moves very fast and is very hot

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54
Q

why can a glowing avalanche move so fast

A

its moving on a cushion of hot air

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55
Q

what is a lahar

A

a mudflow composed of pyroclastic material and water that flows down from a volcano

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56
Q

what is the consistency of a lahar

A

like concrete (fluid when moving but solid when stopped)

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57
Q

does a lahar have to have an eruption to form

A

NO - just has to have a mudflow on the side of a volcano

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58
Q

types of volcanoes

A
  1. fissure
  2. shield
  3. dome
  4. ash-cinder
  5. composite
  6. caldera
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59
Q

what is a composite volcano also known as

A

stratovolcanoes

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60
Q

describe shape of composite volcano

A

a tall, conical volcano composed of layers of hardened lava, tephra and volcanic ash

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61
Q

what is one of the tallest types of volcanoes

A

composite volcano

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62
Q

what is the slope angle for composite volcano

A

30 degrees

63
Q

describe the lava that flows from composite volcano

A

viscous, cools and hardens before spreading

64
Q

what is the source of magma for composite volcanoes

A

felsic

65
Q

where are most active composite volcanoes found

A

along pacific mountain belt (ring of fire)

66
Q

what are composite volcanoes associated with

A

subduction zones

67
Q

what type of eruptions do composite volcanoes have and why

A

the felsic lava that is under large amount of gas under pressure causes explosive eruptions

68
Q

what can a composite volcano eruption leave behind

A

a caldera (if large enough eruption)

69
Q

what type of volcano can emit glowing avalanches

A

composite volcano

70
Q

what type of lava are shield volcanoes associated with

A

mafic lava

71
Q

what viscosity does mafic lava have

A

low viscosity

72
Q

describe shape of shield volcanoes

A

rounded domes with gentle slopes (about 2 - 10 degrees)

73
Q

are shield volcanoes large or small

A

very large

74
Q

is the lava in shield volcanoes thin or thick

A

thin

75
Q

does mafic lava hold lost of gases

A

no - its very thin

76
Q

are shield volcanoes eruptions dramatic or quiet

A

quiet

77
Q

does lava travel far in shield volcanoes eruptions

A

yes

78
Q

what is the largest type of volcano

A

shield volcanoes

79
Q

where do shield volcanoes often form

A

over hotspots

80
Q

what are hotspots

A

stationary plumes of basaltic lava welling up from the mantle

81
Q

what do a chain of islands show

A

the motion of the plate

82
Q

how were Hawaii islands formed

A

from movement of Pacific plate over a hotspot

83
Q

what are formed from erosion of shield volcanoes

A

canyons

84
Q

what type of drainage does shield volcanoes form

A

radial drainage

85
Q

does the erosion of shield volcanoes lower the landscape

A

yes

86
Q

what is a very small volcano

A

cinder cone

87
Q

what are cinder cones made from

A

pyroclastic material

88
Q

describe how a cinder cone is formed

A

when lava pieces fall back to the ground, they cool and harden into cinders that pile up around the volcano’s vent

89
Q

where do lava breach from in cinder cones

A

on the side of the crater OR on a flank

90
Q

do cinder cones have a large or small magma chamber

A

small

91
Q

is erosion fast or slow in cinder cone

A

very fast

92
Q

what is the result of the fast erosion of cinder cones

A

all that is left is the magma center

93
Q

what type of lava forms a dome volcanoe

A

by slow moving and high viscous lava

94
Q

how are dome volcanoes created

A

lava piles up around a vent as they are TOO viscous to spread out

95
Q

what type of volcano forms a scab that traps heat and gas inside

A

dome volcano

96
Q

what type of eruption does a dome volcano have and why

A

explosive = the scab that forms keeps the gas and heat trapped (building pressure)

97
Q

how are fissure volcanoes produced

A

eruptions that occur along elongated fissures where magma filled dikes intersect the surface

98
Q

do fissure volcanoes have lava that flows long distances or short distances

A

LONG distances

99
Q

what other type of volcano can form on shield volcanoes

A

fissure volcano

100
Q

what determines size of fissure volcano

A

magma supply and length of fissure

101
Q

what type of structure is left behind after erosion of fissure volcano

A

lava field

102
Q

caldera volcano

A

when a stratovolcano (mostly) erupts and collapses

103
Q

what accelerates the erosion of caldera

A

collapse of volcano

104
Q

type of volcano

A

stratovolcano (composite volcano)

105
Q

type of volcano

A

shield volcano

106
Q

type of volcano

A

cinder cone

107
Q

type of volcano

A

dome volcano

108
Q

type of volcano

A

fissure volcano

109
Q

is global distribution of igneous activity random

A

NO - most volcanoes located within or near ocean basins

110
Q

where can igneous activity occur at

A
  1. convergent plate boundary (subduction)
  2. divergent plate boundary (spreading axis)
  3. intraplate areas (hotspots)
111
Q

what are some dangers to volcanoes

A
  1. lahars
  2. pyroclastic flows
  3. CO2 emissions
112
Q

what is the most dangerous aspect of volcanoes

A

the pyroclastic flow

113
Q

what are positives to volcanoes

A
  1. new fertile soil
  2. enriched soils from mineral rich volcanic ash
  3. new land based on lava flows reaching ocean boundary
  4. geothermal energy source
114
Q

describe the five levels of volcanic alert system

A

level 5
- evacuation of everyone

level 4
- evacuation of elderly/sick/children

level 3
- no entry into areas surrounding volcano

level 2
- no entry into areas around crater

level 1
potential risk for increased activity

115
Q

what are factors that determine whether a volcano extrudes magma violently or gently

A

temperature of magma

composition of magma (amount of silica)

dissolved gases in magma

116
Q

does controlling viscosity of magma control nature of eruption

A

YES

117
Q

does lava with high silica move more or less viscously

A

more viscous (less likely to move far)

118
Q

does more of less gas in lava result in violent eruptions

A

more gases

119
Q

viscosity

A

measure of a material’s resistance to flow

120
Q

does a high or low viscosity mean fluids flow with greater difficulty

A

high viscosity

121
Q

factors that affect viscosity of lava

A
  1. temperature
  2. composition
122
Q

are hotter magmas more or less viscous

A

hotter magma = less viscous

123
Q

does a high silica content mean high or low viscosity

A

high viscosity

124
Q

does a high silica content equate cold or hot lava

A

cold lava

125
Q

what is the violence of eruption related to

A

how easily gases can escape from the magma

126
Q

what happens to gases in magma as it nears surface

A

gases expand due to decrease in pressure

127
Q

Is there more gases in mobile or immobile lava

A

more mobile

128
Q

can viscous or non viscous lava trap gases better

A

viscous lava

129
Q

is thicker or thinner lava more viscous

A

thicker

130
Q

is thick lava cold or hot

A

cold

131
Q

does mafic lava generate quite or violent eruptions

A

quiet

132
Q

does high or low viscous lava produce explosive eruptions

A

high viscous lava

133
Q

what does the volcanic explosivity index tell about volcanoes

A

explosiveness of volcanic eruptions

134
Q

what is the largest VEI? lowest?

A

largest = 8 (mega colossal eruptions)

lowest = 0 (non-explosive volcanoes)

135
Q

what VEI was st Helens

A

4

136
Q

what is an example of VEI 8

A

Yellowstone caldera

137
Q

types of rocks erupted

A
  1. basalt
  2. andesite
  3. dacite
  4. rhyolite
138
Q

describe basalt rocks

A

silica content between 48% and 55%

139
Q

order the rocks erupted from lowest to highest silica content

A
  1. basalt
  2. andesite
  3. dacite
  4. rhyolite
140
Q

silica content of andesite

A

55% to 60%

141
Q

silica content of Dacite

A

60% to 70%

142
Q

silica content of Rhyolite

A

70% to 77%

143
Q

what rock is associated with felsic lava

A

rhyolite

144
Q

what type of rock is associated with mephic magma

A

basalt

145
Q

type of rock in cinder cones

A

basalt (mildly explosive)

146
Q

type of rock in shield volcanoes

A

basalt (mildly explosive)

147
Q

volcanoes that have basalt rocks

A
  1. shield
  2. cinder
148
Q

rock in composite volcanoes

A
  1. andesite to dacite

( mildly to highly explosive)

149
Q

rocks in lava dome volcano

A

dacite to rhyolite (non-explosive)

150
Q

rocks in caldera

A

andesite to rhyolite (extremely violent explosive)

151
Q

Santorini volcanic eruption

A

a VEI 6 eruption (one of the largest volcanic events on earth in recorded history)

devastated the island of Santorini (was caldera volcano)

some think founded myth of Atlantis

152
Q

Vesuvius eruption

A

had two phases
1. Plinian eruption (produced a rain of pumice)

  1. Pelean phase (pyroclastic flow formed)

destroyed Pompeii and Herculaneum
(only survivor was Pliny the Younger)

eruption column more than 32 km high

now dormant

153
Q

Krakatau eruption

A

VEI of 6 (caldera volcano)

equivalent of 200 megatons of TNT

generated loudest sound historically reported (hear as far as Australia)

shockwave travelled around world 7 times

tsunamis followed the eruption

154
Q

Mount St Helens eruption

A

could be heard in lower mainland BC

deadliest and most economically destructive volcano in US history

mass movement on the side was a SLUMP

reduced elevation of mountain summit by over 1000 feet and replaced with 1 km wide crater

Geomorphology (12 decks)

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