Volcanoes Flashcards
The pacific ______ ___ _____ is a belt of volcanism that surrounds the pacific
ring of fire
Where in north america is popular for its volcanoes
Yellowstone hot spot
Cascade mountains
What is pyroclastic material
solid rock fragments ejected during an eruption
Define a volcano
a vent from which magma, gases and solids are ejected, pyroclastic
materials and lava flows can build up to form a mountain-like shape
Define eruption
the process of magma and pyroclastic materials being ejected
from a volcano
Define Tephra
Air-borne pyroclastic material. Tephra varies in size:
the largest are bombs, lapilli (gravel size), ash (finest size).
_______ composition is an important factor determining the shape of a volcano and its style of eruption
Magma
magma composition determines
mineralogy - and thus melting
temperature
* how well it traps gasses
influences melting
temperature and
explosiveness
______ polymers are c0ntained in magma
silica
how much silica is in mafic rocks and what is the temperature
50%
1200+oC
how much silica is in intermediate rocks and what is the temperature
60%
1000+oC
how much silica is in Felsic rocks and what is the temperature
70%
800+
o
C
Where do we find mafic rocks
hot spots and divergent plate margins
Where do we find intermediate rocks
source ocean-ocean or ocean-continent convergent
plate margins
Where do we find felsic rocks
ocean
continent plate margins
or continental hot spots
List the following from most mafic to most felsic: Pyroxene, amphibole, mice, Olivine, quartz, biotite
Olivine, Pyroxene, amphibole, biotite mice, quartz
Low silica content results in what viscosity
basalt very low viscosity
High silica content results in what viscosity
More felsic mineral, high viscosity
High volatile content results in what viscosity
Decrease viscosity
Higher temperature results in what viscosity
Low viscosity
Lower temperature results in what viscosity
higher viscosity
define Pahoehoe
basaltic flow of lower viscosity (more fluid),
ropy structure
define Aa lava
sharp, spiny, surface, basaltic deposit of higher
viscosity (less fluid)
Basaltic lava has ____ viscosity and can flow _____ distances
low
long
Andesitic lava is too viscous to flow far, and tends to ____ ____ as it flows
break up
Felsic lava is so viscous that is may _____ ____ in a dome-shaped mass
pile up
All magmas contain small amounts of dissolved gas. What is the range
0.2 - 6%
What are the most common dissolved gases in magma
water vapor and CO2
What is an important volatile to remember is not contained in magma
O2
How do volatiles affect magma
- Breaking up silica polymers, makes magma less viscous
- Generating bubbles of gas – makes magma bubbly
- If the magma is high in silica (felsic), the silica polymers
trap the bubbles, and it is more explosive!
Mafic magma tends to have _____ volatile content
low
Felsic magma tends to have ______ volatile content
higher
How do volatiles change the characteristics of felsic magma
decreases melting temperature
decreases viscosity
Does mafic magma or felsic magma have a greater tendency to form pyroclastic
Felsic magma
Types of intrusions in intrusive volcanic landforms
sill, dike, veins
Types of conduits in intrusive volcanic landforms
pipe, vent, neck
Types of magma chambers in intrusive volcanic landforms
Laccolith, stock, batholith/plutons
What are the volcano shapes and types
*Shield volcano
*Cinder cone
*Stratovolcano
*Flood basalts
*Caldera volcano
*Mid ocean ridges
Describe shield volcanoes
The largest conical volcanoes
Formed from basalt
Gentle slopes
Lava flows quickly and over great distances.
Describe cinder cones
Small volcano, only 100m in diameter
slope angle is 24-32o
Often form on the side of shield volcanoes
Built of pyroclastic material
mostly mafic
Describe composite cones(stratovolcanoes)
Intermediate in size and average composition
Variable slope angle but often have a conical shape
Located along subduction zones
Describe stratovolcanoes and eruptive style
dangerous
Generate plinian eruptions, eject huge amounts of ash, column extending to the stratosphere and distributed over large regions
For a stratovolcano the deposits alternate between _________ lava flow and __________ deposits
andesitic
pyroclastic
Describe a flood basalt
- Basaltic lava flow, very fluid, ejected from a
fissure (crack) and flooding a large area - Fed from mantle plumes
*Creates lava plateau
What does the Giants causeway have that makes it so cool. What type of volcano is is
Columnar joints
Flood basalt
Describe a caldera volcano
*A volcanic crater that develops
from the explosion and
collapse of a composite
volcano.
violent and infrequent
What are some examples of caldera volcanoes
Crater lake
Krakatoa, Indonesia (generated a tsunami that made it to Europe)
What is the most explosive type of volcano
Rhyolite caldera complexes
What are some examples of rhyolite caldera volcanoes
Yellowstone
Taupo
Why do the slides say that yellowstone is breathing
cycle of uplift and
subsidence at Yellowstone
* Caused by movement of magma and/or fluids (hot water
and gases) underneath the caldera
there is more earthqaukes and vertical deformation
Do mid ocean ridge eathqaukes effect humans
Not really because they are so remote
Define lava domes
lava too viscous to flow and piles
up at vent. Cools quickly generating glassy
high silica obsidians.
Define spatter cones
very small basaltic cones, build
up around vents where magma is splattered by
bubbles of gasses
Define volcanic plugs or volcanic necks
lava cools and plugs
the vent.
What are volcanic hazards
eruption column, debris avalanche, pyroclastic flow, fumaroles, lava, dome collapse, bombs, acid rain
Where was there an eruptive blast and earthquake from a volcano exploding that caused a bunch of trees to drop down
Mt. St. Helens
What problems can arise due to ash from volcanoes
The ash reflects the suns light and can decrease the global temperature
it is an abrasive - irritant to eyes and lungs
weighs a lot on your roof
hazardous for engines, especially planes
Destruction of vegetation
What is the benefit of ash
Creates fertile soils after
weathering!
Define fumarole
vents that emit hot gases, can be
1000ºC.
Why are Gases problematic in relation to the ones emitted from volcanos
Gases such a CO
2
and H
S are invisible,
but can asphyxiate or poison people.
2
Gasses can also dissolve in water droplets in the
air and lead to acid rain
What does Nuee ardente mean
glowing cloud - gas cloud that is very hot and turbulent
How large are bombs
pyroclasts
that are >32 mm in
size
What does lahar mean
volcanic debris flow (hot
mud flow)
* a particular hazard when
volcanoes are ice/snow
capped
When lava flow occurs, is it more likely that life is lost, or loss of property and vegetation
loss of property and vegetation is more common
What are phreatic explosions
- Occur when magma comes in contact with water or ice
- Occurs in subterranean volcanoes or island arc volcanoes
- involve the contact of magma and water during the eruption
- Explosive!
long term prediction vs short term prediction
Long term predictions
Identify potential areas of volcanic activity
Short term prediction
Can be very useful, especially in evacuating
personnel.
What is the difference between a non-explosive and explosive volcano
non-explosive means that is is not too dangerous, there is low viscosity magma and low amount of dissolved gas
Explosive means the viscosity of the magma is high and the dissolved gas content is high
What does VEI stand for
Volcanic explosion index
What is the VEI good for
VEI ratings are on a 0-8 scale,
and represent the explosive
tendency of an eruption
- It is based on volume of
ejected material, height of
ejected material and duration
of eruption
What type of boundary would we find a stratovolcano?
Convergent, specifically a subduction zone
What type of boundary would we find a shield volcano
Not at a boundary, it is at a hotspot
What type of boundary would we find sea-floor volcanism
divergent
Where would we expect to see a volcanic plumes/ hot spot volcanoes occur
Hawaii
Yellowstone (caldera containing granitic/rhyolitic magma which makes it highly explosive)
