1
Q
what are the igneous environments based ob?
A
There are two categories, they are based on cooling locale
2
Q
what are the two major categories of igneous environments
A
extrusive settings - cool at or near the surface (cool rapidly, chill too fast to grow big crystals)
- intrusive settings: cool at depth (lose heat slowly, crystals grow slowly and large)
3
Q
how does extrusive lava flow cools
A
as blanckets that often stack vertically
3
Q
which type of lava can flow long distances
A
low-viscosity lava (basalt) extrusive
4
Q
how does the lava flow exit the volcano (extrusive settings)
A
exit volcanic vents and spread outward
5
Q
T or F lava cools as it flows
A
T it cools as it flows, eventually solidifying
6
Q
example of an explosive ash eruption
A
Mt. St-Helens
7
Q
caracteristics of an explosive ash eruption (extrusive)
A
- high- viscosity felsic magma erupts explosively
- yield huge volumes of ash that can cover large regions
- pyroclastic flow: volcanic ash and debris avalanche (races down the colcanic slope as a density current, often deadly)
8
Q
Euuroptions of Mt. Ranier
A
pyroclastic flows are often augmented by glacial melt water debirs flows that can travel many km from volcano
9
Q
whats special about Mt. Ranier
A
in the holocene (geological time) (the last 12 000 yrs) have produced ‘Lahars” that have flowed through the valleys all the way to seattle
10
Q
what are lahars
A
mud and water flow that happens from major explosif volcanos
11
Q
Eruption of Mt. Mazama
A
7800 yrs ago, erupted explosively releasing 46-58 km^3 of rock/dust materials that spread continent wide
12
Q
Eruption Mt. Mazama vs St helens
A
mazama was 40 X greater than st helens
13
Q
what did the mazama eruption leave behind
A
left a collpase “caldera” that is about 9 km in diameter called now “ crater lake”
14
Q
what formed lake toba in indonesia
A
75 000 yrs ago, larger super-volcanic eruption (Mt. Toba caldera) almost caused extinction of humans
15
Q
how does magma invades preexisting wall rock (intrusive settings)
A
- magma invades preexisting wall rock by percolating upward between grains and forcing open cracks
16
Q
what does the wall rock reveal when in contact with magma- intrusive
A
high heat
17
Q
what does the wall rock reveal when in contact with metamorphism
A
changes mineral forms
18
Q
what is the baked zone
A
rim of heat-altered wall rock
19
Q
what is the chill margin
A
rim of quenched magma at contact
20
Q
what does the magma initiate when it invades colder wall rock
A
- thermal contact metamorphism and melting
- inflation of fractures, wedging wall rock apart
- detachment of large wall rock blocks (stoping)
- incorporation of wall rock fragments (xenoliths)
21
Q
what happens when the magma that doesn’t reach the surface (intrusive settings)
A
the magma freezes slowly
22
Q
what are tabular intrusions
A
- tend to have uniform thicknesses
- often can be traced laterally
-have to major subdivisions
23
Q
what are the two major subdivisions of tabular intrusions
A
- sill: injected parallels to rock layering
- dike: cuts across rock layering
24
what to dikes and sills modify
modify invaded country rock
25
how do dikes and sills modify invaded country rock
- they cause the rock to expand and inflate
- they thermally alter the counrty rock
26
dikes caracteristics
- cut across preexisting layering (bedding or foliation)
- spread rocks sideways
- dominate in extensional settings
27
sill caracterisitcs
- are injected parallel to preexisting layering
-are usually intruded close to the surface
28
both dikes and sills exhibit wide variability in
- size
- thickness (or width)
- lateral continuity
29
where do dikes somtimes occur
in swarms
ex: three dikes radiate away from shiprock, new mexico volcano has been eroded away into volcanic neck
30
ex of sill
antarctica, intrusion lifted the entire landscape above
basalt bc it is dark
31
what are plutons
subsurface cooled magma chambers
32
what do plutons amass into
a batholith
33
what are batholiths
- immense volumes of intrusives
- from above subduction zones
- may add magma for tens of Ma
- batholiths mark former subduction
34
ex of batholiths
north shore mountains of vancouver are the result of eriosion of an immense granitic plutons, magmatic intrusions, not volcanoes
35
T or F intrusive and extrusive rocks commonly co-occur
T
36
how do intrusive and extrusive rocks co-occur
- magma chambers feed overlying volcanoes
- magma chambers may cool to become plutons
- many igneous geometries are possible
37
how did Mt. Royal form
the gabbroic core of mt royal formed as an intusion at depth (1.3km around 125 Ma). Magma (came from the mantle bc mafic) (and its gabbro) rose into sedimentary section which has since been unroofed.
38
with erosion what progressively deeper features are exposed
- vertical dikes
- horizontal sills
- mushroom-shaped laccoliths
39
what is the influence on the landscape of intrusive and extrusive co-occur
- continued upllift and erosion exposes a plution: (intrusive rocks are more resistant to erosion, so they stand high on the landscape)
- unroofing (erosion of covering geological units) takes long periods of geologic time
40
what is exhumation
erosion of covering geological units over long periods of geologic time
41
ex of ingeous rock used as a building stone extensively
office buildings, kitchens
42
why are igneous rocks used as building stones
- durable (resist erosion)
- beautiful
43
what are igneous rocks often called
granite but not always granite
44
what are the useful descriptions of igneous rock
color and texture
45
size, shape and arragnment of the minerals of igneous rock
- crystalline: interlocking crystals fit like jigsaw puzzle
- fragmental: pieces of [reexisting rocks, often shattered
- glassy: made of solid glass or glass shards
46
what gives an igneous rock its texture
the magma's history
47
fine- grained texture
- rapid cooling
- crystals do not have time to grow
- extrusive
48
coarse- grained textrue
- slow cooling
-crystals have a long time to grow
- intrusive
49
porphyritic texture
(mixture of coarse and fine cystals)
- indicates a two- stage cooling history:
- initial slow cooling create large phenocrysts
- subsequent eruption cools remaining magma more rapidly
50
fragmental textures what are they made from
preexisting rocks that were shattered by eruption
after fragmentation the pieces fall and are cemented
51
glassy textures caracteristics
- solid mass of glass or crystals surrounded by glass
- fracture conchoidally
- result from extremely rapid cooling of lava
52
what is the classigication based on
composition and texture
53
felsic examples of texture
fine: rhyolite
coarse: granite
54
intermediate examples of texture
fine: andesit
coarsed: diorite
55
mafic examples rock of textrue
fine: basalt
coarsed: gabbro
56
ultramafic example rock and textrues
fine: Komatite
coarsed: peridotite
57
pyroclastic are fragments of what
violent eruptions
58
what is tuff
volcanic ash that has fallen on land
59
what is volcanic breccia
made of larger volcanic fragments cemented together
60
where does igneous activity occur
in four plate textonic settings
- in established or newly fromed tectonic plate boundaries
except: hot spots which are independent of plates
61
what are the four plate-tectonic settings
- isolated hot spots
- volcanic arcs bordering deep ocean trenches
- mmid-ocean ridges
- continental rifts
62
most subaerial volcanoes on earth reside where
in arcs
63
what type of tectonic plate boundaries do volcanic arcs have
convergent :
- depp oceanic trenches and accretionary prisms
- subducting oceanic lithosphere adds valatiles (water)
- rocks of the asthenosphere partially melt
- magma rises and creates volcanoes on overriding plate
- magma may differentiate
64
how do volcanic arcs converging tectonic plates form?
- depp oceanic trenches and accretionary prisms
- subducting oceanic lithosphere adds valatiles (water)
- rocks of the asthenosphere partially melt
- magma rises and creates volcanoes on overriding plate
- magma may differentiate
65
what are some examples of volcanic arcs
- aleutian islands
-japan
-java and sumatra
66
how many mantle plume hot spot volcanoes exist
about 50-100
67
what do the plate boundaries of hot pot volcanoes look like
independant
68
hot spot volcanoes may erupt through what kind of crust
oceanic or continetal
- oceanic molsty mafic magma
- continental : mafic and felsic
69
what type of magma do you get from eru[tong from coeanic/continental crust
- oceanic molsty mafic magma
- continental : mafic and felsic
70
examples of hot spots volcanoes
- hawaii, new england and mt royal
71
how are hot pot track created
burn a volcano chian through overiding tectonic plates
72
what is the large igneous provinces (LIP)
unsually large outpourings of magma
73
what time of magma is the LIP
mostly mafic, include som felsic examples
74
how is LIP formed
mantle plume first reaches the base of the lithosphere
- erupts huge volumes of magic magma as glood basalts
75
caracteristics of magma (LIP)
- magic
- low viscosity
- can flow tens to hundreds of kms
- accumulate in thick piles
76
what are continental rifts
places where continental lithosphere is being stretched
77
what does rifting do to the lithosphere and how `
thins it
- causes decompressional melting of mafic rock
- heat transfer melts crust, creating felsic magmas
78
example of continental rift
east african rift valley
79
most igneous activity takes place at what type of ridge
mid-ocean ridges
80
mid ocean ridges have what type of tectonic boundaries
divergent
81
how are mid-ocean rifts from
-fidting spreads plates leading to decompression melting
- basaltic magma wells up and fills magma chamber
- solidifies as grabbro at depth
- moves upward to form dikes or extrude as pillow basalt
82
what is a volcano?
- an erupting vent through which molten rock surfaces
- a mountain built from magmatic eruptions
83
the first rock masses on earth resulted from what
volcanoes
84
volcanoes are a clear result of what
tectonic activity
85
name some vulnerable cities volcanoes pose a threat to
- mexico city
- seattle
- naples, italy
86
mount vesuvius
- 79 C.E
- erupted violently
- pyroclastic debris destroyed pompeii
-killed 20 000
- record of roman life was preserved under ash
87
eruptions are often unpredicle, they can do what to a mountain
- build large mountains
- blow mountains to bits
88
what can a volcanic eruption do to a civilization (good and bad)
- provide highly productive soils to feed a civilization
- extinguish a civilization in a matter of minutes
89
can volnic eruptions affect climate and civilizations
yes
90
name the three forms products of colcanic eurption come in
- lava flows : molten rock that moves over the ground
- pyroclastic debris: fragments blown out of a volcano
- volcanic gases: expelled vapor and aerosols
91
lava flows how can lava be
thin and runny or thick and sticky
92
flow style of lava deponds on what
viscocity
93
what does lava viscosity depend on
- composition: high silica, high viscosity
- temperature
- gas content
-crystal content
94
caracteristics of basaltic lava flow
- very hot
- low silica
- low viscosity
- thin and fluid
95
what type of lava flow can flow rapidly (up to 30 km/h) and for long distances (hundreds of km )
basaltic lava flow `
96
long-distances lava flow is facilitated by what
lava tubes
97
what is the hawaiian word describing basalt with a glassy and ropy texture
pahoehoe (pa-hoy-hoy)when
98
when does pahoehoe form
when extremely hot basalt forms a skin
- with flow, the skin is rolled into ropy ridges and furrows
99
what is the hawaiian word describing basalt that solidifies with a jagges, sharp, angular texture
a'a' (ah-ah)
100
what does a'a' form
when hot flowing basalt cools and thickens
- with flow, lava crumbles unto shards and fragments
101
solidified flows may contract with vertical fractures creating what
polygonal columns (ex: giant's Causway)
102
what is pillow basalt
round blobs of basalt cooled in water
103
what are pillow basalt formed
- the pillow surface is cracked, quenched glass
- lava pressure ruptures a pillow to form the next blob
- the process repeats to form a mound of pillow basalts
104
when are pillow basalt common?
on the mid-ocean ridge
105
what is andesitic lava flow
higher SiO2 content in lava
106
caracteristics of andesitic lava flow
- they do not flow rapidly
- they mound around the vent and flow slowly
107
what happens to the crust in andesitic lava
it fractures into rubble, called blocky lava
108
T or F andesitic lava flows remain close to the vent
T
109
rhyolitic lava flow is common or rare
rarely flows
110
what is special about rhyolite lava flows
has the highest SiO2 and the most viscous lava
111
what does the lava do with rhyolitic lava
lava plugs the vent as a lava dome, sometimes the lava domes are blown to pieces
112
volcanoes often erupt in what type of quantities of fragments
large
113
volcaniclastic deposits include
- pyroclastic debris: lava fragments that freeze in air
- preexisting rock: blasted apart by eruption
- landslide debris: blocks that have rolled downslpe
- lahars: transported as water-rich slurries
114
what do the released gases eject (pyroclastic debris, baslatic eurption)
clots and dropts of molten magma
115
what forms dramatic fountains of lava
basaltic eruptions
116
types a fragments (basaltic eurption)
lapilli- pea-sized fragments
- pele's tears - frozen droplets
- pele's hair - thin glass strands
- blocks: large fragments
117
T or F andesitic or rhyolictic eruptions have more volcanic gases? what does that due
T: make these volcanoes more prone to explode and generate huge volumes of debris
118
what are the different forms of debris made by andesitic or rhyolitic eurptions
- pumice: frothy volcanic glass
- ash: fragments less than 2 mm in diameter
- pumice lapilli: angular pumice gragments
- accretion lapilli: clumps formed by falling through moist air
119
what is campi flegrei
the phlegraen fields: the site of the city of naples, italy siths within a caldera of a super volcano
major euprtions:
- 39000 yrs ago
- 15000 years ago
-(vesuvius/pompeii) CE79`
120
what is pyroclastic flow
- avalanches of hot ash that race downslope (200 to 450 degrees)
- incinerate all in their path (can go 300km/h)
- deadly
-examples: mount vesuvius, mount pelée, mount augustine
121
what are tephra
deposits of pyroclastic debris of any size from andesitic or rhyolitic eruptions
122
what is tuff
lithified ash, may or may not contain lapilli fromed by andesitic or rhyolitic eruptions
- air-fall tuff: accumulations of ash that fall like snow
- ignimbrite: tuff deposited while hot that welds together
123
when do wetted debris that move downhill occur (volcanic debirs flow)
occur where volcanoes are covered with ice and snow or drenched in abundant rain
124
what is lahar
water-rich debris flow of ash and blocks (cam move very fast)
125
how much of magma can be gas and what is its composition
up to 9 %
- water (h2O) - the most abundant gas
- carbon dioxide (CO2) - second in abundance
- sulfur dioxide (o2) and hydrogen sulfide (H2S) - rotten egg smell
126
when are gases expelled during volcanic gas
gases aer expelled as magma rises (when the Pressure drops)
127
how is aerosol sulfuric acid
SO2 reacts with water
128
the violence of the volcanic eruption is controled by the style of gas that escapes (what are these styles)
low viscosity (basalt): easy escape so mellow eruption
- high viscosity (rhyolite): difficult escape so violent release
129
what are gas bubbles in rocks called
vesicles
130
name the characteristic features of a volcano
- magma chamber
- fissures and vents
- craters
- calderas
- distinctive profiles
131
what are the distinctive profiles
- shield volcanoes
- scoria cones (cinder cones)
- stratovolcanoes (composite volcanoes)
132
where are magma chambers located in the volcano
in the the upper crust:
- usually an open cavity or area of highly fractured rock
- may contain a large quantity of magma
133
the magma that cools in the magma chambers from what type of rock
intrusive igneous rock
134
the magma that rises from the magma chamber froms what
a volcano
135
how does the magma rise from the magma chamber
via a conduit to the surface
136
magma may erupt along a fissure. what is a fissure
a linear tear
137
fissure eruptions display what
a curtain of fire
138
what do fissure evolve into
discrete vents and craters
139
what is a crater
a bowl-shaped depression atop a volcano
140
what is the size of a cvrater
up to 500m across and 200m deep
141
how are craters fromed
form as erupted lava piles up around the vent
142
where is a summit eruption located
within the summit crater
143
where is the flank eruption located
along the side of the volcano
144
what is a caldera
is a gigantic volcanic depression
- much larger than a crater (km)
- usually exhibit steep sidewalls and flat floors
145
how are caldera's formed
a magma chamber empties and the volcano collapses in
146
what are shield volcanoes
broad, slighty dome-shaped (like an inverted shield)
- have a low slope and cover large geopgraphic areas
147
how are shield volcanoes constructed
by lateral flow of low-viscosity basaltic lava
148
ex of shield volcanoes
mauna loa on hawaii
149
what are scoria cones (also called cinder cones)
conical piles of tephra; the smallest type of volcano
- often symmetrical, with deep summit crater
- typically from a single eruption event
150
what are scoria cones built off
built of ejected lapilli and blocks piled at a vent
151
what human practice can scoria cones be used for
the cinders are often used in garden decoration
152
what are stratovolcanoes (also called composite volcanoes)
- large, coned-shaped volcanoes with steeper slopes
153
what are stratovolcanoes made of
made of alternating layers of lava, tephra, and debris
154
example of stratovolcanoes
mount fuji, mount rainier, mount vesuvius
155
what are the two dominant styles of eruption
effusive eruptions: produce lava flows
explosive eruptions: blow up
156
effusive eruptions caracteristics
- lava flows stream away from vents
- lava lakes can form near, or inside, the vent
- can produce huge lava fountains
157
what type of magma are effusive eruptions common with
mafic magma (basalt) bc very hot and low viscosity
158
explosive eruptions release pressure catastrophically... characteriristics
- high gas pressure is from more viscous SiO2 rich magma
- create pyroclastic flows and cover the land with tephra
- can eject many cubic km of debris skyward
159
what type of magma are explosive eruptions common with
mostly andesitic and rhyolitic compositions
160
the eruptive style is related to volcano type example
- effusive eruptions form shield volcanoes (hawaii)
- small pyroclastic eruptions form scoria cones
- alternating effusive and pyroclastic eruptions result in stratovolcanoes (mount Etna, Silicy)
- large explosive eruptions create caldera (yellowstone)
161
eruptions to remener example
- phlegraean fields (naples)
- taupo volcano (new Zealand)
- Yellowstone National Park is par of a caldera 72 km across
- Mt. Toba (almost extincted humans)
162
recent eruptions to remember example
mount st helens
- earthquake-triggered landslide released pressure
- an initial vertical blast led to a much stronger lateral blast
163
19th century eruptions to remember example
krakatau
- continued erupting through june and july
- august 27th 1883, island was obliterated: magma chmaber was breached by the ocean, island was blown to pieces, tsunami wave killed people)
164
convergent boundaries give what type of volcanism
most subaerial volcanoes:
- arc volcanoes develop on overriding plates
- continental arcs and oceanic island arcs are common
165
what is the ring of fire
ring of volcanoes convergent boundaries
166
continental rifts give what type of volcanoes
gives volcano types reflecting:
- parial melting of the mantle
- partial melting of the crust
- effusive and explosive eruptions
ex: mount kilimanjaro (stratovolcano)
167
oceanic hot spot what type of boundary
a plume under an oceanic plate that penetrates the plate and successively froms hawaiian islands:
- thousands of thin basalt flows build up trhouhg time
- building above sea level, basalt can flow long distances
- lava builds upward and outward and the island grows
- submarine slumps remove large masses of the volcano
168
what are flood basalts
voluminous alva eruption above a plume :
- when a mantle plum intersects base of rifting lithosphere
- lava spreads over large areas; great thicknesses stack up
- creates a large ingeous province (LIP) ex: columbia river plateau
169
iceland
is a hot spot that straddles the mid-atlantic ridge
- lava has built the hot spot/ridge above sea level
- the island is being torn apart by a divergent boundary
- volcanoes trace the mid-ocean ridge rift valley
170
what are the volcanic hazard
- cause great harm to humans
- many populated areas have active volcanoes
- understanding volcanic bheavior is best defense
171
what are the eruptive volcanoes hazards
- lava flows can destroy immovable objecets
- threat of falling ash and lapilli (tephra is heavy causes roof collapses and it is gritty it abrades car and airplane engines), floodwaters easily move tephra as deadly lahars
- threat of pyroclastic flows - ash clouds
172
volcanic hazard: blast
rare, it is an explosion sideways, most eruptions are vertical
173
volcanic hazards: landslides
- eruptions trigger landslides:
- large masses of material are deposited rapidly near vent
- earthquakes initiate failure of unstable slopes
174
volcanic hazards: lahars
more dense than water, carries everything away ex: nevado del ruiz colombia burried town of armero in 5 m of ash and mud
175
volcanic hazards: earthquakes
moving magma causes earthquakes
- usually small magniture, they are frequent , can cause slope failures and damage structures
176
volcanic hazards: tsunamis
water explosions create giant waves
177
volcanic hazards : threat of gas and aerosols
- aerosols cause respiratory problems
178
how do protect from volcanoes?
- recurrence interval (average time between eruptions): active (erupting), dormant (hastn erupted in a while), exctinct (not capable of erupting)
- tectonics can shut off magma then erosion takes over
- warning signs (earthquake, heat flow, chagnes in shape, emission of gas increases)
cant predict the exact timing or style
179
what are ways we mitigate volcanic hazards
- evacuation
- diverting flows (with explosives, heavy equipment, seawater)
180
can volcanic eruptions alter climate?
yes if large enough:
- ash and aerosols injected into stratosphere
- particles remain in stratosphere
- reflects solar radiation, causing atmospheric cooling
181
are there volcanoes on other plantets?
volcanic activity is evident on the moon and planets ex: jovian moon lo has active volcanoes
182
when did volcanic magmas formed the first surface rock?
around 4.3 Ga
183
what happened to original rocks?
- mostly lost to our observation
-erosion
-subsequent rocks have been multiply cycled trhough tectonic processes
- what is left? a series of layered sediments has overlain the original record.
Mcgill Geology
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