Igneous Rocks/ Volcanoes

Question 1

Is obsidian extrusive or intrusive rock?

Answer 1

Extrusive

Question 2

Extrusive Rock

Answer 2

igneous rock formed from magma underground that does erupt

Question 3

Intrusive Rock

Answer 3

igneous rock formed from magma underground that did not erupt.

Question 4

Volcanic Rocks

Answer 4

Rocks which erupt and mostly crystallize on the surface of the Earth (Extrusive)
Fast cooling= Small grain size

Question 5

Plutonic Rocks

Answer 5

Crystallize within the crust/upper mantle (intrusive)
Slow Cooling= Coarser grain size
intrusive=magma that didnt erupt

Question 6

Felsic

Answer 6

Lighter color, Higher silica and potassium content, less dense than mafic
-Lower melting temp
-Higher melt viscosity

Question 7

Mafic

Answer 7

Dark color, Higher magnesium, iron, and calcium content, more dense than felsic
-Low SiO2
-Higher melting point
-Lower melt viscosity

Question 8

Magma Differentiation

Answer 8

formation of one or more secondary magmas from parent magma

Question 9

Partial Melting

Answer 9

First to melt, Last to Crystallize: (Highest SiO2 content melts first. As magma cools, lowest SiO2 are the first minerals to crystallize)
Increases silica content of magma by fractionally crystallizing out mafic content

Partial Melt of Mantle: Basalt
Partial Melt of Crust: Felsic Rock

Question 10

Plutons

Answer 10

Magma in magma chamber solidifies
-intrusion crystallizes inside the crust

Question 11

Batholith

Answer 11

large igneous intrusion extending deep within Earth’s crust

Question 12

Dike

Answer 12

Vertical tubular igneous intrusion

Question 13

Sill

Answer 13

Horizontal tubular intrusion

Question 14

Explosive Eruptions

Answer 14

Clouds of hot debris, ash, and gas rapidly shoot out of a volcano
ex: 1980 eruption of Mount St. Helens
-High silica content
-Low temp Magma
-High volatile content
-lava flows short distances, if at all (leads to trapped gas in magma)

Question 15

Effusive Eruptions

Answer 15

Lava pours from vent or fissure
-Low Silica Content
-High Temp Magma
-Lava Flows travel great distances

Question 16

Factors of Eruptive Style?

Answer 16

1.) Volatile Content
-Gases expand as magma rises and pressure decreases. Making the magma more volatile and explosive
2.) Melt Viscosity
-High SiO2 = more viscous melts
-Less viscous lava flows farther (effusive=lava pour from vent/fissure)
-More viscous flows (felsic) may not flow at all; trapping gasses and leading to explosive eruptions

Question 17

High Volatility of magma leads to what type of eruption?

Answer 17

Explosive

Question 18

High melt viscosity leads to what type of eruption?

Answer 18

Explosive

Question 19

Fractional Crystallization:
The first minerals to crystallize are more __a__. This makes the residual melt more __b__. As this process continues and the chem of the melt changes, the melt becomes less and less __c.__. The last minerals to crystallize are highly __d__.

In the context of continuously cooling melt, an example of an early-crystallizing mineral is __e__. An example of a late-crystallizing mineral is __f__.

Answer 19

a.) mafic
b.) silica-rich
c.) dense
d.) felsic
e.) olivine
f.) quartz

Question 20

Extrusive igneous rocks __a__. As such, they have __b__ crystals that cooled __c__.

Intrusive igneous rocks __d__ and in general, have __e__ crystals. Examples of igneous intrusions include __f__, which are vertical intrusions and __g__ are horizontal intrusions.

Answer 20

a.) cool at Earths Surface
b.) small
c.) quickly
d.) cool inside the Earth
e.) larger
f.) dikes
g.) sills

Question 21

Felsic Igneous Rock?
a.) Gneiss
b.) Basalt
c.) Granite
d.) Gravel

Answer 21

c.) Granite

*recall: continental crust mainly made up of Granite. Oceanic made up of basalt (which is more dense) and therefore is subducted at convergent boundaries

Question 22

Shield Volcanoes

Answer 22

Formed by combination of effusive eruptions.
Conduit+ Crater Eruption with lava flowing from fissure/cracks in earths
-Low viscosity
-High magma supply rate
-Common at oceanic hotspots
ex: Kilauea

Question 23

Stratovolcanoes

Answer 23

Formed by a mix of explosive and effusive eruptions of intermediate felsic lavas
Occur @Subduction zones
ex: Mt Fuji (Japan)
Mt St Helens (Washington)

Question 24

Caldera Volcanoes

Answer 24

Strata or Shield Volcano that rapidly loses magma chamber
-central collapse; concaves in on itself
-resurgent dome simetimesforms
*Effusive or Explosive eruptions can lead to caldera formations
->continental hotspots, subduction zones, or rifting
Continental Hotspots: Yellowstone=plume related continental hotspot

Question 25

Flood Basalts

Answer 25

Hot spots can have outpours of lavas
-eruptions of massive volumes of basaltic magma
-attribute to arrival of new magma plume
ex: Colombia River Basalt
-> attributed to the head of Yellowstone’s plume head

Question 26

Volcanic Hazards

Answer 26

1.) Pyroclastic Flows : Big clouds of ash and other volcanic particles
-move very fast
-ash carried by wind; gets into lungs of humans and animals, jet engines
2.) Lava
-covers whole cities
3.) Lahars
-Hot or cold mix of water and volcanic debris
4.) Climate Change
-volcanic material can stay in stratosphere from weeks to years, blocking suns heat-> drastically cools earth