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6-Understanding Planet Earth > Chapter 4: Magma and Igneous Rocks > Flashcards

Chapter 4: Magma and Igneous Rocks Flashcards

1
Q

What is a volcano? Give an example

A

a vent where molten rock comes out of Earth

Ex: Kilauea Volcano, Hawaii

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2
Q

How are igneous rocks formed?

A
  • Hot (~1,200oC) lava pools around the volcanic vent.
  • Hot, syrupy lava runs downhill as a lava flow.
  • The lava flow slows, loses heat, and crusts over.
  • Finally, the flow stops and cools, forming an igneous rock.
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3
Q

Igneous rock is formed by ______

A

cooling from a melt

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4
Q

What is magma?

A

melted rock below ground

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5
Q

What is lava?

A

melted rock once it has reached the surface

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6
Q

At what temperatures do igneous rocks freeze?

A
  • Igneous rock freezes at high temperatures (T).

- 1,100 °C–650 °C, depending on composition.

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7
Q

What are the two types of igneous rocks?

A
  • Extrusive igneous rocks

- Intrusive igneous rocks

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8
Q

How are extrusive igneous rocks formed?

A

cool quickly upon exposure of lava (or pyroclastic debris) at the surface

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9
Q

How are intrusive igneous rocks formed?

A

cool out of sight, underground from a magma.

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10
Q

Which type of igneous rock is found more commonly?

A

Intrusive igneous rocks are typically found in much greater volume than extrusive igneous rocks.

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11
Q

Which type of igneous rock cools faster?

A

Intrusive rocks cool at a much slower rate than extrusive rocks

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12
Q

What are lava flows?

A

streams or mounds of cooled melt

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13
Q

What is pyroclastic debris? What is it composed of?

A

They are cooled fragments and composed of:

  • Volcanic ash
  • Volcanic rock (fragmented by eruption)
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14
Q

What is volcanic ash?

A

fine particles of volcanic glass

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15
Q

Why is the cooling rate of intrusive igneous rocks are slower than extrusive igneous rocks?

A
  • Large volume magma chambers

- Smaller volume tabular bodies or columns

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16
Q

Where is magma formed?

A
  • Magma is not everywhere below Earths crust.

- Magma only forms in special tectonic settings.

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17
Q

Which layer of the Earth does melting of the magma occur?

A

melting occurs in the crust and upper mantle.

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18
Q

What causes the melting of the magma?

A

melting is caused by

  • pressure release
  • volatile addition. (flux melting)
  • heat transfer.
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19
Q

How does pressure affect melting? Explain.

A

Decrease in pressure (P)— “decompression”

  • The base of the crust is hot enough to melt mantle rock. - But, due to high P, the rock doesn’t melt.
  • Melting will occur if P is decreased.
  • P drops when hot rock is carried to shallower depths.
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20
Q

True/False

High pressure melts the mantle rock

A

FALSE

Melting occurs is the pressure is decreased.

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21
Q

When does pressure decrease?

A

P drops when hot rock is carried to shallower depths.

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22
Q

How is the hot rock carried to shallower depths?

A
  • Mantle plumes
  • Beneath rifts
  • Under mid-ocean ridges
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23
Q

How do volatiles affect melting? Explain.

A
  • Volatiles lower the melting T of a hot rock.

- Subduction carries water into the mantle, melting rock.

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24
Q

What are some common volatiles?

A

Common volatiles include H2O and CO2

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25
Q

Where does hydration melting occurs?

A

Subduction zones

26
Q

How does heat transfer affect melting? Explain.

A
  • Rising magma carries mantle heat with it.

- This raises the T in nearby crustal rock, which then melts.

27
Q

What is the difference between magma and lava?

A.Composition: the former contains more magnesium and iron than the latter.
B.Location: the former is molten rock underground whereas the latter is molten rock at the Earths surface. C.Temperature: the former is hotter than the latter.
D.Grain size: the former has bigger crystals than the latter.

A

B

28
Q

In the upper crust of a continent, the geothermal gradient is about . . .

A.350° - 400°C per km
B.150° - 200°C per km.
C.10° - 20°C per km.
D.1° - 2°C per km

A

C

29
Q

Which of the following phenomena will cause melting to produce magma?

A.removal of volatiles (H2O and CO2) from the rock B.increasing pressure, while the temperature stays constant
C.Bogus question: the crust floats on a layer of perpetually molten rock, so there is no need to melt rock to “produce” magma
D.transfer of heat from a hot magma into surrounding wall rock

A

D

30
Q

Where does igneous activity occur?

A

Igneous activity occurs in four plate-tectonic settings.

  • Volcanic arcs bordering deep ocean trenches
  • Isolated hot spots
  • Continental rifts
  • Mid-ocean ridges

Established or newly formed tectonic plate boundaries

31
Q

Where does igneous activity NOT occur?

A

hot spots, which are independent of plates

32
Q

Where are subaerial volcanoes located?

A

Most subaerial volcanoes on Earth reside in arcs.

33
Q

Volcanic arcs mark _____

A

convergent tectonic plate boundaries

34
Q

How are volcanoes formed on volcanic arcs?

A
  • Deep oceanic trenches and accretionary prisms
  • Subducting oceanic lithosphere adds volatiles (water).
  • Rocks of the asthenosphere partially melt.
  • Magma rises and creates volcanoes on overriding plate.
  • Magma may differentiate.
35
Q

Give some examples to volcanic arcs

A
  • Aleutian Islands
  • Japan
  • Java and Sumatra
36
Q

How many hot stops are there in the world?

A

50-100

37
Q

Hot spots are independent _____

A

tectonic plate boundaries

38
Q

Hot spots may erupt through _______

A

oceanic or continental crust.

39
Q

What type of magma do hot spot eruption release from oceanic crust?

A

mostly mafic magma (basalt)

40
Q

What type of magma do hot spot eruption release from continental crust?

A

mafic and felsic (basalt and rhyolite)

41
Q

What creates a hot-spot track?

A

burn a volcano chain through overiding tectonic plate

42
Q

What are continental rifts?

A

places where continental lithosphere is being stretched

43
Q

What are the consequences of continental rifts?

A
  • Rifting thins the lithosphere.
  • Causes decompressional melting of mafic rock.
  • Heat transfer melts crust, creating felsic magmas.
44
Q

Give an example to continental rift

A

East African Rift Valley

45
Q

Most igneous activity takes place at _____. Explain how?

A

mid-ocean ridges

  • Rifting spreads plates leading to decompression melting. - Basaltic magma wells up and fills magma chambers.
  • Solidifies as gabbro at depth.
  • Moves upward to form dikes or extrude as pillow basalt.
46
Q

Where does the heat inside (internal heat) the Earth come from?

A
  • Remnant/primordial heat: –> Leftover heat, mainly coming from the core from Earth’s formation
  • Ongoing heat generation: –> Decay of radioactive elements in the crust and mantle

Earth slowly loses heat to space.
Eventually, Earth will solidify.

47
Q

What causes the ongoing heat generation?

A

Ongoing radiogenic heat production through radioactive isotope decay in the crust and mantle.

48
Q

What is magma viscosity and flow behaviour like?

A

Lava flows sometimes race down the side of a volcano, sometimes it builds up into a rubble-covered mound, and sometimes it oozes like toothpaste.

49
Q

The viscosity (resistance to flow) of a lava depends upon:

A
  • Chemical composition
  • Temperature
  • Gas content
  • Crystal content
50
Q

Give 3 examples to different lava types and explain what they form

A
  • Basaltic lava forms thin sheets.
  • Andesitic lava tends to break up as it flows.
  • Ryolitic lava piles up at the vent as a dome.
51
Q

The surface texture of the basaltic flow, when it freezes, reflects _________

A

the timing of freezing relative to how fast it was moving.

52
Q

What are the two types of volcanoes and what are their characteristic features?

A

Shield volcano

  • lava fountain
  • lava flow

Stratovolcano

  • lava dome
  • ash fall
  • ash flow
53
Q

How does shield volcano eruption occur?

A

low-viscosity lava that erupts from a circular vent or along a crack/fissure

54
Q

What is the largest volcano on Earth?

A

Mauna Loa, Hawaii: A Shield Volcano

55
Q

How does fissure shield volcano eruption occur?

A

Lava may erupt along a linear tear, (a fissure). Fissure eruptions may display a “curtain of fire.”

56
Q

What is the shape of Stratovolcano?

A

Stratovolcanoes are large, cone-shaped volcanoes with steep slopes made of alternating layers of felsic lava, tephra, and debris. Often symmetric, they can acquire odd shapes following landslides, etc.

57
Q

How does Stratovolcano eruption occur?

A

Typically form from medium to high viscosity lava (andesitic), often leading to explosive volcanism

58
Q

What are the fragments that are released by a volcanic eruption called? Give examples to these possible fragments

A

Volcanoes erupt large quantities of fragments—volcaniclastic deposits.

This material includes pyroclastic debris, pre-existing rock, landslide debris, and lahars (mudflow with volcanic ash).

59
Q

Give an example to a classic Stratovolcano on Earth

A

Mt Fuji, Japan

60
Q

What are the two types of silicate structures? Give examples to each

A
  • Neosilicates (Sheet silicate)–> Olivine and mica

- Inosilicates (Pyroxine, Framework silicate)–> Amphibole, Quartz, Feldspar

61
Q

How do silicate structures affect the lava viscosity?

A

silica tends to link into long chains and these increase the lava viscosity

6-Understanding Planet Earth (18 decks)

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