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EAS > Lecture 10 > Flashcards

Lecture 10 Flashcards

1
Q

What is a volcano

A

A vent (fissure) in which a combination of melted rock, solid rock debris and gas is erupted

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2
Q

Volcanic Settings

A
  1. Hot spots under oceans (Hawaii) and continents (Yellowstone)
  2. Divergent boundaries (spreading zones): mid ocean ridges
  3. Young spreading zones: rifts in continents
  4. Subduction and collision zones

OR anywhere where magma is being produced and there is a path for it to reach the surface

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3
Q

Magma

A

Molten rock underground

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4
Q

Lava

A

Molten rock on surface of planet

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5
Q

Igneous rock underground

A

Plutonic (intrusive)

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6
Q

Igneous rock above ground

A

Volcanic (extrusive)

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7
Q

Crystal size in igneous rock depends on

A

How much time they have had to cool (more time=bigger crystals)

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8
Q

Crystal size in plutonic rocks

A

Coarser grained crystals easily visible to the eye (Phaneritic)

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9
Q

Crystal size in volcanic rock

A

Fine grained or no crystals (aphanitic or glass)

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10
Q

How to identify igneous rocks

A
  • silica content (<45% to >70%)
  • mineral assemblages
  • texture (crystal size, shape, etc)
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11
Q

Mafic magma

A
  • 45 to 50% silica
  • typically formed by partial melting of the mantle
  • low viscosity (runny)
  • melt around 1200 degree Celsius
  • forms rock that have abundant ferromagnesian minerals (dark colour as result)
  • mafic lava solidifies to form basalt
  • instructions of mafic lava cause gabbro
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12
Q

Intermediate magma

A
  • 50 to 70% magma
  • typically formed at subduction zones
  • intermediate properties
  • moderate viscosity
  • melt at intermediate temperatures
  • ferromagnesian minerals, Na and Ca feldspar (plagiocase)
  • little or no quartz
  • green/grey/purple colour (depending on crystal size)
  • intermediate lava solidifies to form andesite
  • intrusion of intermediate magma form diorite

Also dacite (extrusive) and granodiorite (intrusive)

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13
Q

Felsic magma

A

> 70% silica

  • formed in association with continental crust
  • high viscosity
  • melt at relatively low temperatures (800 degrees Celsius)
  • abundant K feldspar
  • pale colour
  • felsic lava solidifies to form rhyolite
  • intrusions of felsic magma form granite
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14
Q

Do we use grain size or crystal size or igneous rock

A

Crystal size

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15
Q

Partial melting

A
  • occurs at plate margins, rifts, hot spots etc and is how magma is produced (mafic)
  • because rocks are made up of different minerals, and these minerals melt at different temperatures, the magma is often a different composition than the rock being melted
  • magma type determines by what minerals are undergoing partial melting
  • what melts is dependent based on temperature, composition, pressure, and presence of water
  • on earth’s surface rocks melt between 800-1200 degrees Celsius
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16
Q

Fractional crystallization

A
  • opposite to partial melting

- changes the composition of the magma by the crystallization of minerals (basalt)

17
Q

Differentiation

A

The evolution of magma composition resulting in different igneous rock types

Review charts in lecture notes

18
Q

What and where

A

All starts with partial melting of mantle

End result depends on how much crust the magma needs to travel through

19
Q

Magma types by igneous setting

A

Review lectures slide!!!

20
Q

Composition and eruption style

A

SiO2 content is critical in determining how the molten rock behaves and it’s eruption style

21
Q

Behaviour of mafic magmas

A

Low silica means low viscosity (runny)

Gases in magma can escape easily

Quiet eruptions

Mainly lava flows

Fluid form of basalts tend to form shield volcanoes (e.g. Hawaii)

22
Q

Fissure eruptions

A

Flood basalt e.g. Deccan traps

Can cover huge areas (up to millions of km)

Continuous to semi continuous eruptions that last 10-1000 of years

Can also form in mid ocean ridges

23
Q

Behaviour of felsic and intermediate magmas

A

High silica so higher viscosities

Gases in magma cannot escape easily which causes explosive eruptions

Large amounts of tephra (ash)

Many hazards

24
Q

Stratovolcanoes

A

Also known as composite volcanoes (made of different rock types and different types of deposits)

The classic volcano shape, forms at subduction zones

Felsic and intermediate (mainly intermediates)

25
Q

Rhyolite caldera complexes

A

Big hole in the ground

Hard to see without satellite imagery

26
Q

Volcanic hazards

A 
Lava flows
Temphra (ash) fall
Pyroclastic flows 
Mudflows (Lahars)
Tsunamis 
Gas emissions 
Climate change
27
Q

Lava flows

A
  • large flows limited to fluid magma (I.e., basalt)
  • historical examples relatively small (Hawaii, Iceland)
  • past examples of massive fissure eruptions (Columbia basalts, Deccan traps) May have/ or did affect climate and cover 100s to 1000s of square km
28
Q

Tephra (ash) fall

A

Significant fall limited to explosive eruptions (e.g. dacite, rhyolite can be produced from other compositions in the right conditions)

Major hazard to planes

People with respiratory illness

Mass loading on buildings

Short term climate effects

29
Q

Pyroclastic flow

A

-Fluidized masses of rock fragments and gases that move rapidly in response to gravity
-limited to explosive eruptions (dacite, rhyolite)
-very fast, hot and dense ash flows
Review examples

30
Q

Mudflow

A

Lahar

-a debris flow composed of a slurry of pyroclastic material, rocky debris, and water

31
Q

Lahars

A
  • water source (glacier, snow pack, heavy rainfall)
  • volcano triggered debris flows, far reaching, consistency of concrete
  • review examples
32
Q

Climate effects

A
  1. Large explosive eruptions can cause short term cooling (strato/composite volcanoes)
  2. long term (decades to many thousands of years), effusive eruptions can cause long term climate change (flood basalts)
  3. Over the history of the earth volcanoes help balance co2 levels in the atmosphere
33
Q

Tsunami

A

Krakatau

34
Q

Gas emissions

A

Lake Nyos

35
Q

Short term climate effects

A

Big eruptions inject SO2 into the stratosphere which reacts with water to form sulfuric acid water droplets. These absorb and scatter incoming solar radiation and cause the average global temperature to drop by 0.6 degrees

36
Q

E.g. of short term climate effect

A

Tambora

“The year without summer” which lead to largest famine in Europe

> 100 Tb of SO2 released

Toba (biggest eruption in 2 million years)

-released 1000 Tg of SO2

37
Q

Large igneous provinces (LIPS)

A

Essentially another term for flood basalt, but specifically refer to exceptional events

Erupt for long periods of times (thousands to millions of years)

Continuous injection of aerosols into the atmosphere rather than just one big injection over a short period of time

Extinction events coincide with LIPs

EAS (19 decks)

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