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Magma and lava are __________ material


How to melt rock?

temperature + pressure

If temp increases enough, rocks will melt but....

not a lot of melts, just a percent or two

What does temperature of rock explain? But does it do a poor job of explaining?

formation of plutonic (intrusive) rocks; volcanoes

Increasing the pressure...

increases the melting temperature

If you can lower the pressure + keep temp the same...

you can induce melting

Adding ___________ lowers the melting temperature


What happens to water at a subduction zone?

water is brought down by subducting plate

What does water at subduction zones help create?


As magma rises, pressure is reduced, which causes what?

water to escape from magma

Water escaping will cause...


2 Main Igneous rock textures...

coarse, phaneritic + fine, aphanitic

3 Main Igneous rock compositions...

felsic, intermediate, mafic

Once we determine texture + composition...

we name igneous rocks

rock names imply both...

texture + composition

Temperature of magma is related to the...

elements/minerals present


resistance to flow

High viscosity?

high resistance to flow (hard for it to flow)

Low viscosity?

low resistance to flow (easy for it to flow)

Volatile content in magma?

H20, dissolved gases, other fluids

Mafic/Basaltic magma temp?


Mafic/Basaltic silica content?


M/B volatile content?


M/B viscosity?


Likelihood of M/B reaching the surface?

high: likely to make volcanic rocks

Felsic/Granitic magma temp?


Felsic/Granitic magma silica content?


F/G volatile content?


F/G viscosity?


F/G likelihood of reaching the surface?

low, likely to make plutonic rocks

What is the most common tectonic setting that mafic/basaltic magmas form?

mid-ocean ridges (divergence between 2 oceanic crusts) + hot spots in oceanic crust

Why is magma M/B at mid-ocean ridges?

b/c the source of the magma is the mantle, which is mafic-ultramafic in composition

Are only mafic rocks (basalt, gabbro, diorite) found at these places?

No, but mafic rocks are the majority

3 processes help make magmas more felsic...

fractional crystallization, assimilation, + magma mixing

Volcanoes at subduction zones are mostly...

intermediate rocks

Fractional crystallization...

as mafic magma cools, minerals crystallize at different times

minerals that crystallize first tend to...

settle out of the magma

resulting magma, after fractional crystallization...

is more felsic in composition


as magma rises, it can melt surrounding rock

Adding these melted minerals will result in a a more __________ magma


2 most common types of rock found at subduction zone volcanoes?

andesite + diorite

andesite + diorite are __________ ________/________ types

intermediate magma/rock

2 other minerals found at subduction zone volcanoes?

basalt + rhyolite

Assimilation can occur at/around __________ as magma rises

subduction zone volcanoes

Eruption style of M/B magmas?


Mafic lavas make....

shield volcanoes

Examples of shield volcanoes...

Hawaii + hotspots in oceanic crust

Characteristics of Hawaii - shield volcano

broad, low angle slopes

eruption style is effusive, not explosive

Eruption style of F/G magmas?


Intermediate + Felsic lavas make...

stratovolcanoes or composite cones

3 Properties of stratovolcanoes?

higher angle slopes;
more explosive eruptions;
range of lava compositions

stratovolcano lava?

mostly intermediate, but some mafic + felsic too

Magma mixing?

as plate is subducted, more magma is generated

younger magmas mix w/ older magmas to change composition



the type of magma/lava determines: (4)

what is erupted;
style of eruption;
frequency of eruption;

Volcanic ejecta?

materials that comes out of volcanoes


basaltic, andesitic, rhyolitic

Pyroclastic material, tephra

explosive material defined by size: bombs, cinders, ash

Other volcanic ejecta?

mudflow: lahars

Fire fragments =


4 properties of pyroclastics

blown out;
usually felsic -> intermediate
glass fragments
forms layers

3 Different fire fragments?

ash, cinders, bombs

Pryoclastic flow....example?

flowing cloud of hot ash + cinders;
eventually becomes welded tuff



volcanic mudflow

How do lahars form?

in a variety of ways; need water, dirt + slope

Lahars are not always related to...


Example of lahar?

Mt. St. Helens

What determines the style of eruption a volcano will have?

type of lava is very important

Lava varies in...

temperature, viscosity, volatile content

Effusive eruption:

runny, low viscosity lava

Explosive eruption:

sticky, high viscosity lava

Forming calderas (4 step cycle)

1. Bulge in surface created by magma chamber
2. Crust thinned over magma chamber (ground surface cracks in ringlike fractures)
3. Tephra columns erupt from fractures + collapse into ash and pumice flows
4. surface crust collapses as magma is depleted forming caldera

Calderas, like Yellowstone, experience...

vertical changes in ground level

Flood/Plateau Basalt; example?

...the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava

Columbia River

Intrusive igneous landforms...

volanco, sill, laccolith, batholith, dike, diatreme


large intrusive igneous bodies


really big plutons

Example of plutons/batholiths?

Sierra Nevada Mtns (Giant granitic plutons)

Chill dog you got this...

true that

Economic importance of igneous rocks

metals; igneous activity is a conduit for more dense material to move from the mantle to the crust

Many metals + minerals are associated with...

igneous activity/bodies

Other types of volcanoes?

Calderas, Flood Basalts (Plateau basalts)

What are flood basalts?

massive basalt flows on the continents

What is the cause/tectonic setting of flood basalts?

unknown; none active today, but many ancient ones

Columbia River flood basalts

more than 300 individual lava flows


large bodies of magma that cooled underground (may be related to magma chambers)


large plutons


thin intrusion of igneous rock parallel to rock layers


thin intrusion of igneous rock, cuts across rock layers

Volcanic neck

vertical section of igneous rock w/ sills and/or dikes radiating from it;
thought to be an old magma chamber feeding a volcano

Examples of plutons/batholiths

Mt. Rushmore, Half Dome

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