Volcanoes Flashcards
Molten rock beneath the Earth’s surface
Magma
Erupted magma
Lava
- igneous rocks contain a high percentage of dark silicate minerals and calcium-rich plagioclase feldspar (but no quartz) and tend to be dark in color
Basaltic
Contains mainly light-colored silicate minerals - quartz and potassium feldspar
Rhyolite
Intrusive equivalent: granite
Have a composition between basaltic and rhyolitic rocks
Andesitic rocks
Basaltic or
Mafic
Rhyolitic or
Felsic
Basaltic * magmas contain … SiO2
- gas content
- eruptive temperature
- viscosity
Least ~ 50% SiO2
Least ~ 0.5-2.0% Gas
Highest Temperature (1000-1250 C)
Least viscous
Rhyolitic * magmas contain … SiO2
- gas content
- eruptive temperature
- viscosity
Most ~ 70% SiO2
Most ~ 5-8%
Lowest Temperature (650-900 C)
Most Viscous
Basaltic (mafic)
High in Mg, Ca, Fe
Low in Na, K
Rhyolitic (felsic)
High in Na, K
Low in Mg, Ca, Fe
The magmas generated by melting mantle rocks tend to have * composition
/partial melting of solid rock/
Basaltic
In continental crust, the rising molten rock ponds at the crust-mantle boundary, melting the overlying crustal rock. This generates * magna of * composition
Less dense, more silica-rich magma
Andesitic or rhyolitic composition
Nonexplosive eruptions that produce outpourings of fluid lava
Quiescent or efusive
Opposite of effusive eruptions
Explosive eruptions
Two primary factors that determine how magma erupts:
Viscosity and gas content
What type of magma tends to generate quiescent (nonexplosive) eruptions?
Basaltic: fluid + low gas content
What type of magma tends to generate explosive eruptions?
Rhyolitic and andesitic
Silica-rich magmas, most viscous, greatest amount of gases
Magma’s viscosity depends on
Temperature and silica content
Viscous
- SiO2
- C
More silica, more viscous
Lower temperature, more viscous
Most abundant gas found in most magma
Water vapor
Vast majority of Earth’s lava is
> 90%
Basaltic
Two types of lava
Aa
Pahoehoe
Have surfaces of rough jagged blocks with dangerously sharp edges
Aa flows
Exhibit smooth surfaces that sometimes resemble twisted braids of ropes
On which one can walk
Pahoehoe
Dissolved gases held in molten rock by confining pressure
Volatiled
Most abundant-least abundant gas released in the atmosphere
Water vapor (H2O), CO2, SO2
H2S, CO, H2
When volcanoes erupt, they eject pulverized rock and fragments of lava and glass called
Pyroclastic materials
Pyroclastic materials
Etymology; also known as
Pyro = fire, clast = fragment
Tephra
Produced when gas-rich viscous magma erupts explosively
Less than 2mm (0.08 in)
Ash and dust particles
“Little stones”
Small beads to walnuts (2-64 mm)
Lapilli or cinders
Larger than 64 mm or 2.5 in
*hardened, incandescent
Blocks - hardened lava
Bombs - incandescent lava
Vesicular ejecta produced most often during eruption of basaltic magmas
Reddish-brown fragments
Scoria
Usually light color and less dense emitted when magmas with an andesitic or rhyolitic compositions erupt explosively
Pumice
Volcanic activity frequently begins when a * develops in Earth’s crust as magma moves forcefully toward the surface
Fissure (crack)
Path of magma localized into somewhat pipe-shaped * that terminates at a surface opening called *
Conduit, vent
Coneshaped structure created by successive eruptions of lava, tephra
Volcanic cone
Located at the summit of most volcanic cones is a funnel-shaped depression
Crater
Very large circular depressions
> 1 km, at most 50 km
|<1 km|•
Calderas
Collapse pits or craters
Vent that emits only gases
Fumaroles (fumus = smoke)
Produced by accumulation of fluid basaltic lavas
Huge, gently sloping volcanoes built of very thin lava spreading out in all directions from a central vent
Broad, slightly dome structure *oceanic
Shield volcanoes
Result from eruptions of moslty small pieces of scoria and pyroclastics *basaltic
Cinder cones/ scoria cones
Cone-shaped volcanoes composed of layers of lava, ash and rock debris
Composite cone volcanoes “stratovolcanoes”
Built by slow eruptions of highly viscous lava. Any steep-sided mound formed when lava reaching The Earth’s surface is so viscous that it cannot flow away readily and accumulated around the vent
Lava domes
A fluidized mixture of hot rock fragments, hot gases infused with incandescent ash and larger lava fragments
Also called
Pyroclastic flows
Nuee ardentes (glowing avalanches)
The greatest volume of volcanic material is extruded from *
These voluminous accumulations are * because they tend to be rather flat and broad
Fissures
Basalt plateaus
Volcanic object created when magma hardens within a vent on an active volcano
Volcanic plug, volcanic neck or lava neck
Body of intrusive igneous rock that is crystallized from magma slowly cooling below the surface of the Earth
Pluton
Intrusive igneous bodies are generally classified according to their shape as either * or * (large and blob shaped)
Tabular (tabula = table), massive
Orientation: * if they cut across existing structures
- if they intrude parallel to features such as sedimentary strata
Discordant, concordant
Discordant bodies that serve as tabular conduits that transport magma toward Earth’s surface
Dikes
Concordant bodies that tend to accumulate magma and gradually increase in thickness
Sills
Large mass of intrusive igneous rock that forms from cooled magma
> 100 km2
Batholith
Smaller plutons
Stocks
Igneous intrusion that has split apart two strata, resulting in a domelike structure
Concordant pluton that has been injected between two layers of sedimentary rock
Laccolith
Plate motions provide the mechanisms by which mantle rocks undergo partial melting to generate magma. As hot rock rises, it experiences a decrease in confining pressure and mag undergo *
Decompression melting
the process which involves movements of the earth’s crust such that a portion id pushed up, push down or forced sideways
DIASTROPHISM
