Volcanoes Flashcards
1
Q
where to volcanoes stem from
A
release of magma on to earth’s surface
2
Q
how many active volcanoes are on the planet
A
15 00
3
Q
what constitutes an active volcano
A
having at least 1 eruption in recorded history
4
Q
how many volcanic eruptions happen a year
A
50 volcanos
5
Q
what is a volcano
A
a landform created when molten magma escapes earth’s interior
6
Q
what is volcanism
A
geological processes that result in volcanic eruptions
7
Q
what are the three stages of volcanic activity
A
- active
- dormant
- extinct
8
Q
define active volcano
A
volcano that is currently erupting or has erupted recently
9
Q
what is a dormant volcano
A
a volcano has not erupted in the last few thousand years
10
Q
what is an extinct volcano
A
not erupted for tens of thousands of years
11
Q
what is an example of an extinct volcano
A
Canadian shield
12
Q
is there molten rock within an extinct volcano
A
NO
13
Q
crater
A
a circular depression in the ground typically a basin circular form
14
Q
what causes a crater to form
A
volcanic activity
15
Q
where is a crater found in a volcano
A
at the top
16
Q
does lava only flow from the top
A
NO - can come from all sides
17
Q
what often fills a volcanic crater
A
a lake or glacier
18
Q
what volcanic feature is this
A
crater
19
Q
vent
A
actual side of magma eruption
20
Q
does a volcano only have one vent
A
no - can have multiple
21
Q
lava vs magma
A
lava
- outside on the surface of earth
magma
- within the earth’s surface
22
Q
what volcanic feature is this
A
vent
23
Q
caldera
A
a cauldron like volcanic feature formed by collapse of land following a volcanic eruption
24
Q
is a caldera larger or smaller than a crater
A
much larger
25
describe the steps that form a caldera
a very large volcano with a huge magma chamber that when the volcano erupts the chamber collapses in on itself and forms a basin
26
what volcanic feature is this
caldera
27
what is often growing in the center of a caldera
a new volcano
28
flank eruption
an eruption from the side of a volcano
29
what volcanic feature is this
flank eruption
30
dome
roughly circular mound shaped protrusion resulting from the slow eruption of felsic lava
31
what type of lava forms a dome
felsic lava
32
what volcanic feature is this
dome
33
what is felsic lava
a type of lava that has a lot of silica which traps heat and gas in
34
4 types of lava
1. Aa lava
2. Pahoehoe lava
3. Pillow lava
4. Columnar lava
35
what is Aa lava
rough, jagged blocky texture that moves like its being pushed
36
what is Pahoehoe lava
twisted or ropy texture found in Hawaii volcanoes
37
what is pillow lava
forms when lava enters water, often found on ocean floor near spreading axes
38
what is columnar lava
forms when lava hits ice
39
what type of lava is this
Aa lava
40
what type of lava is this
pahoehoe
41
what type of lava is this
Pillow lava
42
what type of lava is this
columnar lava
43
does pahoehoe have viscosity
NO - flows easily
44
what are known as materials extruded during a volcano
pyroclastic materials
nuees ardentes (glowing avalanche)
lahars
45
types of pyroclastic debris (7)
ash and dust
lapilli
blocks and bombs
scoria
pumice
46
describe ash and dust pyroclastic debris
fine glassy fragments
47
define lapilli pyroclastic debris
walnut sized material
48
what are the pyroclastic debris larger than lapilli
blocks and bombs
49
define blocks and bombs pyroclastic debris
blocks
- hardened or cooled lava (comes out of volcano already a solid)
bombs
- ejected as hot lava (cools in the AIR)
50
describe scoria vs pumice pyroclastic debris
scoria
- vesicular ejecta from MAFIC magma
pumice
vesicular ejecta from SILICA-RICJ magma (felsic)
51
what type of pyroclastic debris can float on lava
pumice
52
describe the form of pumice (pyroclastic debris)
solid object with lots of holes formed from lots of gas in magma
53
what is a nuees ardentes
a mixture of gas, lava, blocks, ash and pumice that moves very fast and is very hot
54
why can a glowing avalanche move so fast
its moving on a cushion of hot air
55
what is a lahar
a mudflow composed of pyroclastic material and water that flows down from a volcano
56
what is the consistency of a lahar
like concrete (fluid when moving but solid when stopped)
57
does a lahar have to have an eruption to form
NO - just has to have a mudflow on the side of a volcano
58
types of volcanoes
1. fissure
2. shield
3. dome
4. ash-cinder
5. composite
6. caldera
59
what is a composite volcano also known as
stratovolcanoes
60
describe shape of composite volcano
a tall, conical volcano composed of layers of hardened lava, tephra and volcanic ash
61
what is one of the tallest types of volcanoes
composite volcano
62
what is the slope angle for composite volcano
30 degrees
63
describe the lava that flows from composite volcano
viscous, cools and hardens before spreading
64
what is the source of magma for composite volcanoes
felsic
65
where are most active composite volcanoes found
along pacific mountain belt (ring of fire)
66
what are composite volcanoes associated with
subduction zones
67
what type of eruptions do composite volcanoes have and why
the felsic lava that is under large amount of gas under pressure causes explosive eruptions
68
what can a composite volcano eruption leave behind
a caldera (if large enough eruption)
69
what type of volcano can emit glowing avalanches
composite volcano
70
what type of lava are shield volcanoes associated with
mafic lava
71
what viscosity does mafic lava have
low viscosity
72
describe shape of shield volcanoes
rounded domes with gentle slopes (about 2 - 10 degrees)
73
are shield volcanoes large or small
very large
74
is the lava in shield volcanoes thin or thick
thin
75
does mafic lava hold lost of gases
no - its very thin
76
are shield volcanoes eruptions dramatic or quiet
quiet
77
does lava travel far in shield volcanoes eruptions
yes
78
what is the largest type of volcano
shield volcanoes
79
where do shield volcanoes often form
over hotspots
80
what are hotspots
stationary plumes of basaltic lava welling up from the mantle
81
what do a chain of islands show
the motion of the plate
82
how were Hawaii islands formed
from movement of Pacific plate over a hotspot
83
what are formed from erosion of shield volcanoes
canyons
84
what type of drainage does shield volcanoes form
radial drainage
85
does the erosion of shield volcanoes lower the landscape
yes
86
what is a very small volcano
cinder cone
87
what are cinder cones made from
pyroclastic material
88
describe how a cinder cone is formed
when lava pieces fall back to the ground, they cool and harden into cinders that pile up around the volcano's vent
89
where do lava breach from in cinder cones
on the side of the crater OR on a flank
90
do cinder cones have a large or small magma chamber
small
91
is erosion fast or slow in cinder cone
very fast
92
what is the result of the fast erosion of cinder cones
all that is left is the magma center
93
what type of lava forms a dome volcanoe
by slow moving and high viscous lava
94
how are dome volcanoes created
lava piles up around a vent as they are TOO viscous to spread out
95
what type of volcano forms a scab that traps heat and gas inside
dome volcano
96
what type of eruption does a dome volcano have and why
explosive = the scab that forms keeps the gas and heat trapped (building pressure)
97
how are fissure volcanoes produced
eruptions that occur along elongated fissures where magma filled dikes intersect the surface
98
do fissure volcanoes have lava that flows long distances or short distances
LONG distances
99
what other type of volcano can form on shield volcanoes
fissure volcano
100
what determines size of fissure volcano
magma supply and length of fissure
101
what type of structure is left behind after erosion of fissure volcano
lava field
102
caldera volcano
when a stratovolcano (mostly) erupts and collapses
103
what accelerates the erosion of caldera
collapse of volcano
104
type of volcano
stratovolcano (composite volcano)
105
type of volcano
shield volcano
106
type of volcano
cinder cone
107
type of volcano
dome volcano
108
type of volcano
fissure volcano
109
is global distribution of igneous activity random
NO - most volcanoes located within or near ocean basins
110
where can igneous activity occur at
1. convergent plate boundary (subduction)
2. divergent plate boundary (spreading axis)
3. intraplate areas (hotspots)
111
what are some dangers to volcanoes
1. lahars
2. pyroclastic flows
3. CO2 emissions
112
what is the most dangerous aspect of volcanoes
the pyroclastic flow
113
what are positives to volcanoes
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
describe the five levels of volcanic alert system
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
what are factors that determine whether a volcano extrudes magma violently or gently
temperature of magma
composition of magma (amount of silica)
dissolved gases in magma
116
does controlling viscosity of magma control nature of eruption
YES
117
does lava with high silica move more or less viscously
more viscous (less likely to move far)
118
does more of less gas in lava result in violent eruptions
more gases
119
viscosity
measure of a material's resistance to flow
120
does a high or low viscosity mean fluids flow with greater difficulty
high viscosity
121
factors that affect viscosity of lava
1. temperature
2. composition
122
are hotter magmas more or less viscous
hotter magma = less viscous
123
does a high silica content mean high or low viscosity
high viscosity
124
does a high silica content equate cold or hot lava
cold lava
125
what is the violence of eruption related to
how easily gases can escape from the magma
126
what happens to gases in magma as it nears surface
gases expand due to decrease in pressure
127
Is there more gases in mobile or immobile lava
more mobile
128
can viscous or non viscous lava trap gases better
viscous lava
129
is thicker or thinner lava more viscous
thicker
130
is thick lava cold or hot
cold
131
does mafic lava generate quite or violent eruptions
quiet
132
does high or low viscous lava produce explosive eruptions
high viscous lava
133
what does the volcanic explosivity index tell about volcanoes
explosiveness of volcanic eruptions
134
what is the largest VEI? lowest?
largest = 8 (mega colossal eruptions)
lowest = 0 (non-explosive volcanoes)
135
what VEI was st Helens
4
136
what is an example of VEI 8
Yellowstone caldera
137
types of rocks erupted
1. basalt
2. andesite
3. dacite
4. rhyolite
138
describe basalt rocks
silica content between 48% and 55%
139
order the rocks erupted from lowest to highest silica content
1. basalt
2. andesite
3. dacite
4. rhyolite
140
silica content of andesite
55% to 60%
141
silica content of Dacite
60% to 70%
142
silica content of Rhyolite
70% to 77%
143
what rock is associated with felsic lava
rhyolite
144
what type of rock is associated with mephic magma
basalt
145
type of rock in cinder cones
basalt (mildly explosive)
146
type of rock in shield volcanoes
basalt (mildly explosive)
147
volcanoes that have basalt rocks
1. shield
2. cinder
148
rock in composite volcanoes
1. andesite to dacite
( mildly to highly explosive)
149
rocks in lava dome volcano
dacite to rhyolite (non-explosive)
150
rocks in caldera
andesite to rhyolite (extremely violent explosive)
151
Santorini volcanic eruption
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
Vesuvius eruption
had two phases
1. Plinian eruption (produced a rain of pumice)
2. 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
Krakatau eruption
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
Mount St Helens eruption
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
