7 volcanoes Flashcards
Craters vs calderas
craters: at top of volcanoes from rock excavated during eruption
calderas: if down low magma chamber has been used up during eruption it no longer holds up the rock and the rock sinks into the empty magma chamber
Which type of magma will have more explosive eruptions?
***Felsic magma
(Thick, trapped gases)
Mafic magma
(Thin, escaping gases)
explosivity of magma
invisible Dissolved gases
As pressure lessens, gases expand
Once a certain point is reached… too much gas pressure not enough material holding it in
EXPLOSION
Viscosity of the Magma
High silica (felsic) = high viscosity (thicker)
Low silica (mafic) = low viscosity (thinner)
The thicker the magma, the more trapped the gases are they start with the same number of gasses or even felsic has less. They accumulate over time however becasue they are trapped in felsic magma
volcanic products: lava flows
felsic lava flows
Thick, s-l-o-w, cooler
Tend to pile near vent
Steep-sided domes
Basaltic lava flows
Thin, faster, hotter
Usually not too fast
pahoehoe, a’a
volcanic products: lava tubes
?
volcanic products: gas
1 – 6 wt % of magma
Mostly H2O and CO2 have the sulfur rotten egg smell
Low-viscosity basalt
Gases escape easily
High-viscosity rhyolite
Gases are trapped, resulting in violent release
volcanic products: pyroclastic material
whole bubble:0 burst buble:()
a lot of potential energy in gas bubbles rising and expanding to top of volcano. Bubbles at the top can be barely jostled and all explode.
when they burst they explode into the air as little tiny pieces of glass
Pyroclastic mat’l = tephra
Ash
-Small glass shards
Dust
-Pulverized rocks
-Small crystals
Pyroclastic material:Tuffs
When ash is cemented together into a rock (lithification), it is called “tuff”
ex: Cottonwood Wash Tuff, Utah-Nevada
you can see skeletal looking pieces that are the broken bubble walls
additional Pyroclastic material: volcanic block
Volcanic block: solid piece of rock blown off mountainside
big sometimes the size of a house or bigger
additional Pyroclastic material: volcanic bomb
Volcanic bomb: Liquid piece of magma blasted into the air
as it twists into the air it become a streamline footballish shape
recurrence
=Average time between eruptions
Active: erupting, recently erupted, or likely to erupt
Dormant: hasn’t erupted in hundreds to thousands of years, but could possibly erupt someday (not very useful classification)
Extinct: no longer capable of erupting
volcanic edifice classification
Stratovolcanoes: low output rate, frequent eruptions
Shield volcanoes: high output rate, frequent eruptions
Cinder cones: low output rate, rare eruptions
Supervolcanoes/Flood basalts: high output rate, rare eruptions
Stato volcanoes, composite cone
Frequent eruptions
Low output rate
Usually felsic
Usually explosive
ex:MSH, Mt fuji
composite layers of lava flows and tephra build it up
cinder cones
Rare eruptions
Low output rate
Usually mafic (basaltic)
Usually gentle
one constant eruption for years and then they die
ex: paricutin named after town it was in in Mexico
layers of cinder, lava flows, cinder lava flows
cinder cones-Utah
Youngest volcanism in Utah:
Ice Springs lava flow
-720 years old
this is very young in volcanism
Cinder cone field
