Volcanos Flashcards
How much of the crust is volcanic?
90% of the top 16 km
What makes volcanoes good things to live near?
geothermal energy, form fertile soils
How do volcanos form fertile soils?
they bring nutrients from earth’s interior to the surface; add material to the surface that weathers easily, making fertile soil
When and where was the last major eruption?
1815; Tambora
What is magma?
molten rock
What is lava?
magma on the earth’s surface
What does plutonic mean?
intrusive - from the interior of the crust
What are the 3 components of magma?
solid, liquid, dissolved gases
What does volcanic mean?
extrusive - on the exterior of the crust
What types of material are erupted from a volcano?
lava (liquid), pyroclastics (solid), and volcanic gas
How does lava behave?
as a liquid
In what direction does lava flow?
downhill (usually in stream courses)
How thick are lava flows?
1 to 400 m (average ~ a few metres)
How long can lava flows be?
> 100 km
What can have a volume of 12.5 cubic km?
lava flows
At what velocities can lava flow?
2 to 45+ km/h
What factors control the size and shape of a lava flow?
viscosity, yield stress, topography, source geometry
What controls viscosity of a lava flow?
compositoin
What does viscosity of a lava flow control?
speed
How does yield stress relate to lava flows?
lava flow stops when eruption stops - need to be adding lava for it to keep moving
What are 2 types of lava flow sources?
point sources and line sources (fissure)
What are pyroclastics?
solid debris erupted by a volcano
What happens to pyroclastics upon eruption?
transported and deposited by wind and water
What are the 5 types of pyroclastic particles, from smallest to largest?
dust, ash, lapilli, bomb, block
What sort of size are ash particles?
sand-sized
How big are lapilli?
pebble-sized
How big are bombs?
head-sized
How does the size of pyroclastic particles affect their transportation?
they sort by size, even in stratosphere - currents transport small particles farther than large ones
Why is it dangerous to inhale volcanic ash?
it has sharp edges that can damage lungs
How do volcanoes create their own weather?
water clumps around particles ejected into the atmosphere and the condensed water vapours form rain/clouds
What does the cloud of pyroclastic material from an explosive volcano look like?
tall column above vent; lapilli falling close to the vent; ash falling from higher up; haze of dust spread away by wind; collaspsing column forming a pyroclastic flow down the slopes
What is another term for a nuee ardente?
pyroclastic flow
What is a pyroclastic flow?
density current (gravity flow) of pyroclastic particles and hot gas
What usually causes a pyroclastic flow?
ac olumn collapse
How does a pyroclastic flow move down the slopes of a volcano?
hottest particles at the bottom of the flow gives flow buyancy and heats the soil, giving a cushion of gas for it to flow over
How does a pyroclastic flow behave?
like liquid - flows downhill
What is an ignimbrite?
sheet of tuff (ash/lapilli) left from a pyroclastic flow
What is a lahar?
mudflow of pyroclastic particles and water
How does a lahar travel?
flows in channels down slopes
What gases make up most volcanic gases?
water, CO2, nitrogen, SO2
What gives volcanoes their “rotten egg” smell?
sulfur gases (SO2, SO3, S2)
Why are sulfur gases so dangerous?
they’re toxic and heavy (so they settle near the ground)
What is viscosity?
resistance to stirring/flow
What does viscosity depend on?
composition, temperature, and polymerization of SiO4
How does polymerization of SiO4 relate to temperature?
it increases as temperature drops
What magma is usually at ~1000 deg C?
mafic
What magma is usually at ~700 deg C?
felsic
What is the range of viscosities for natural silicate liquids?
olive oil to cold honey
What makes felsic magma so viscous?
large silicate composition; lower temperature; silicate liquid near freezing point - so starts crystallizing to SiO4 tetrahedra and polymerizing while still a liquid
What is the viscosity of mafic magma and how does it relate to its velocity?
low viscosity, allowing it to flow quickly
What magma forms basalt?
mafic
What are the properties of a basaltic flow?
fluid, hot (1000 deg C), long thin flows
What is the composition of a basaltic flow?
silica poor; Fe and Mg rich
What are the properties of an andesitic flow?
viscous, cool (800 deg C), short thich flows, explosive
Why is an andesitic flow so explosive?
it’s viscous, making it difficult for dissolved gases to get out; gases expand in bubbles and explode out
What is the composition of an andesitic flow?
silica rich; Al, K, Na rich
How much of a mafic magma is silicate?
50%
What makes up mafic magma?
SiO2, Mg, Fe, Ca, Al, calcium feldspar, olivine, pyroxene
What rock is the volcanic rock of the oceans?
basalt
Why is felsic lava rare?
it’s very viscous, so it takes a while to flow up to the crust’s surface
How much silicate makes up felsic magma?
> 65%
What makes up felsic mgma?
SiO2, Na, I, Al, K-feldspar, Na-feldspar, quartz
What type of magma forms basalt?
mafic
What type of magma forms rhyolite?
felsic
How much silicate makes up intermediate magma?
50-65%
What type of rock does intermediate magma form?
andesite
What are two common volcano styles?
shield volcanoes and composite volcanoes
How are shield volcanoes constructed?
non-viscous mafic lava flows spreading out and building up over time (but little ash)
What type of volcano is massive and has gentle slopes?
shield volcanoes
What type of magma forms shield volcanoes?
basalt (mafic magma)
What is another term for composite volcanoes?
stratovolcanoes
What are the 2 main components of composite volcanoes and the ratio between the?
pyroclastic deposites and lava flows; 50:50
What type of magma forms stratovolcanoes?
andesite (intermediate magma)
How does the structure of composite volcanoes differ from that of shield volcanoes?
steeper slopes and smaller cross-sectional areas
Which type of volcanoe is usually more explosive?
composite
What are plateau basalts?
thick accumulations of long fluid flows
What type of source geometry would be needed for a plateau basalt?
fissure eruption?
What type of volcano style has never been experienced in known history?
plateau basalts
What are ignimbrite sheets?
pyroclastic deposits at a similar scale to that of plateau basalts
What is the scale of a plateau basalt?
400 km x 400 km x 4 km
What is caused by the collapse of a composite volcano?
caldera
How does a caldera form?
magma withdrawal from chamber leaves empty space; volcano collapses into chamber after eruption (especially explosive ones)
How large are calderas?
2-30 km in diameter
Where are 3 places volcanoes are often found?
ocean islands, mid-ocean ridges, continental fringe
What is the difference between island chains and island arcs?
island chains only have active volcanoes at one end; arcs have active volcanoes throughout arc
Where are most volcanoes found?
ocean islands
What are mantle xenoliths?
inclusions of material magma brought up from beneath crust
Why are mantle xenoliths important?
gives us knowledge of the mantle
What are some hazards from eruptions?
lava flows, falling ash/lapilli, explosion, landslides, earthquakes, tsunamis, lahars
How are earthquakes caused by volcanic eruptions?
movement of magma breaks rocks underground
