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ESCI 111 > Volcanoes > Flashcards

Volcanoes Flashcards

1
Q

What are the volcanic hazards?

Hint:

A
  1. Pyroclastic flows
  2. Lava flows
  3. Telphra
  4. Ash clouds
  5. Lahars
  6. Volcanic gases

Can cause damage to tourism and agriculture.

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2
Q

What are three heat transfer mechanisms?

Note: Heat moves by different processes depending on the properties of the medium it is.

A
  1. Conduction = Diffusive transfer of energy from one body to another (solid to solid), (in inner core).
  2. Convection = The Transfer of energy by fluid motion with diffusion. (efficient, in core and mantle)
  3. Advection = The transfer of energy by fluid motion WITHOUT diffusion (in the crust).
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3
Q

What is the heat budget of Earth?

A

Measured the heat flux from Earth’s surface is 97TW which is similar to 1/4 billion of wind turbines. But it is small compared to 173000TW of incoming solar radiation.

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4
Q

Where does slow and fast spreading occur at?

A

Slow Spreading = Mid-Atlantic Ridge (Iceland), 2.5cm/yr.

Fast Spreading = East Pacific Rise, 20cm/yr.

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5
Q

Why are there volcanos on Earth?

A

They are a mechanism for heat and mass transfer from Earth’s interior.

Crust, mantle (solid), outer core (Fe + Ni, liquid), inner core (Fe, solid).

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6
Q

Where does heat on Earth come from?

A

Heat in Earth comes from two main sources:

  1. Primordial (core)
  2. Radiogenic (mantle)
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7
Q

What is Primordial Heat?

A

Heat in the core, leftover from the original accretion of the Earth.

Can estimate its temperature from geophysics and from experiments on the melting properties of Fe at high temperature.

Inner core = 5,200oC
Outer core = 4,500-5,500oC

Primordial heat makes up 46% of Earth’s heat budget.

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8
Q

What is Radiogenic Heat?

A

Primarily coming from the solid (but convecting) mantle.

Continuously produced by decay of radioactive isotopes (238U, 232Th, 40K).

Mantle 4,000oC at core-mantle boundary and 200oC at crust-mantle boundary.

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9
Q

What is the temperature of the mantle?

A

Mantle 4,000oC at core-mantle boundary and 200oC at the crust-mantle boundary.

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10
Q

What is the temperature of the mantle?

A

Mantle 4,000oC at the core-mantle boundary and 200oC at the crust-mantle boundary.

Radiogenic heat makes up 54% of Earth’s heat budget.

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11
Q

Where do volcanoes occur?

A

Volcanoes occur at divergent and convergent margins, and sometimes in between.

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12
Q

What are the three ways volcanoes can occur?

Hint: Pate boundaries

A
  1. Divergent margins = Mid-ocean ridges
  2. Convergent margins = Subduction zones
  3. Intraplate = Hot spots
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13
Q

What happens at volcanoes at divergent margins?

A

Divergent margins or “spreading centres” were plates move apart.

As plates spread apart, primitive basaltic (50% silica) magma rises and erupts to fill the gap.

The ridge axis is offset by many transform faults, and its shape is controlled by the spreading rate.
E.g Mid-Atlantic 2.5cm/yr and East Pacific Rise, 20cm/yr.

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14
Q

What is the main mechanism to produce new crust?

A

Mid-Ocean Ridge volcanism is the main mechanism by which new crust is formed.

E.g oldest continental crust = 4 billion years old
E.g oldest oceanic crust = 200 million years old

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15
Q

How long do Mid-Ocean Ridges extend around the Earth?

A

> 65,000km

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16
Q

What type of volcanism is present at divergent margins (mid-ocean ridges)?

A

Volcanism is generally EFFUSIVE (not explosive), producing voluminous basaltic lava flows and pillow lavas.

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17
Q

Where are the Mid-Ocean Ridge systems located?

A

Most of the MOR system is > 2000m below sea level.

EXCEPT for Iceland, where it goes onshore.

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18
Q

What happens to volcanoes at convergent margins (subduction zones)?

A

When plates collide, the denser of the two may dive below the other creating a TRENCH, ahead of a VOLCANIC ARC, and backarc basin.

The subducting slab is subject to heating and dehydration reactions that cause MELTING.

Melt ascends because of its LOW density, but only a small amount makes it to the surface.

This can create a continental or island ARC.

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19
Q

Where can you find convergent volcanoes and continental arc?

A

A continental arc is found in the Andes of South America.

The chain of stratovolcanoes are all generated by the subduction of the Nazca Plate below the South American Plate.

A volcanic arc is also seen in NZ which includes TVZ and the Kermadec arc.

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20
Q

What type of magma do subduction zones/convergent margins produce?

A

They generate a wide variety of magma, ranging from basalt (50% silica) to rhyolite (75% silica).

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21
Q

What happens to volcanoes at intraplate (hot spots) regions?

A

Away from plate boundaries, there are anomalous mantle plumes.

Magma generated by the mantle plumes rises through the crust to erupt at a “hot spot” on the Earth’s surface.

Tectonic plates continue to move as normal over top of the mantle plume, so the hot spot remains stationary while the plate moves.

Resulting in ISLAND/VOLCANO CHAINS.

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22
Q

What are mantle plumes?

A

Mantle plumes are regions of particularly hot, upwelling mantle/magma.

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23
Q

Where is an example of a hot spot?

A

Hawaii volcanism.

The Hawaiian Islands are a small part of the larger Hawaiian-Emperor Seamount Chain.

The oldest seamounts formed 85million years ago.
There is a “bend” at 50 million years.

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24
Q

What type of magma is present at hot spot (intraplate) volcanoes?

A 
Mostly basaltic (50% silica) effusive eruptions forming lava flows. 
- Some are more explosive (fountaining).
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25
Q

Are hot spots only at sea?

A

No, there are continental hot spots such as Yellowstone (USA).

The magma type is rhyolite (75% silica), consistent with the continental setting.

Yellowstone is a “supervolcano”, capable of producing some of the most powerfully explosive eruptions on Earth.

Iceland also has a mantle plume/hot spot along with its MOR.

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26
Q

Are there volcanoes on other planets and their moons?

A

Yes, all of the rocky planets and many of their satellite moons have or have had some kind of volcanism.

E.g Earth’s Moon
Large “mare” (seas) on the surface of the moon are actually vast plains of basaltic lava. They are associated with large impact craters and mostly on the near side of the moon.
There is NO evidence there is plate tectonics on the moon, Mercury, Venus, Jupiter, or Saturn.

E.g Mercury and Venus (the most) have volcanoes. Note that the Venusian atmosphere is rich in CO2 and SO2, both important volcanic gases on Earth.

E.g Jupiter Io volcano and its eruptions are driven by tidal forces. Europa volcano has an ice crust where water erupts.

27
Q

What planet and what is the largest volcano in the solar system?

A

Olympus Mons found on Mars.

28
Q

What does the type of volcano result in?

A

The different types of volcanoes result in the type of magma and which in turn results in the type of eruption.

29
Q

What magma has the highest silica content?

A

Rhyolite (68-77%)

  • high viscosity (thick)
  • lower temperature
  • high explosivity
  • very volatile

It goes basalt (48-52%), andesite (52-63%, dacite (63-68%), then rhyolite (68-77%).

30
Q

What does volatile content mean?

A

Meas gas (prefers to be in liquids) and is the fuel of eruptions.

Magma resists the flow (really sticky) and has lots of gas which means it will explode, high explosivity.

31
Q

What type of magma is at MOR?

A

Basalt

32
Q

What type of magma is at subduction zones?

A

Andesite and dacite.

33
Q

What type of magma is at hot spots?

A

Basalt

34
Q

What type of magma is at divergent margins?

A

Rhyolite ?

35
Q

What does an effusive eruption mean?

A

This means they are very explosive and forms lava flows or domes.

36
Q

What are some characteristics of a rhyolite volcano?

A
  1. They are the most explosive
  2. They have a high viscosity resulting in steep volcanoes (e.g. Chatten, Chile). The magma is too thick and sticky to flow fast as it is NOT hot enough, therefore there is a build up over the vent.
37
Q

What does explosive means and how does this affect plumes?

A

At the plumes:
The magma is broken into particles by “fragmentation” (fire)
Pyroclast = broken by fire.
The degree of explositivty is controlled by volatile content (gas), magma viscosity etc.

38
Q

What are some examples of explosive volcanoes and their types of magma?

A 
Kilaue = basalt
Stromboli = basalt 
Karymsky = andesite (1km high approx)
Spurr = rhyolite (called plimmey eruptions) (18-20km high)

Note: viscosity and volatile content are increasing down this list.

39
Q

What are mid-explosivity volcanoes?

A

They are basaltic cinder cones.

They have low gas content and low viscosity making them ideal for mild explosivity of fluid material.

They build steep-sided cones of LOOSE pyroclastic fragments.

Can be one single cinder cone or small ‘satellites’ on a larger volcano.

40
Q

What are some examples of mid-explosivity volcanoes?

A

Paricutin, Mexico

Halea Kala

41
Q

What happens during explosive eruptions?

A

Pyroclastic flows are formed.

As explosive plumes sometimes CANNOT ascend into the atmosphere due to the particles being DENSE or not bouyant. Instead, they COLLAPSE to form “pyroclastic flows.”

42
Q

What are pyroclastic flows?

A

They are ground-hugging flows of hot particles and volcanic gas that can travel >500km/hr at 1000oC and even flow over the water. (vaporise the surface of the water which makes them move even faster).

43
Q

What happens if water is added to the flowing lava?

A

Rapid heat transfer from magma to water can chill a lava flow to restrict its movement, however, this also enhances explosivity.

44
Q

So what can the tectonic setting determine?

Hint: A chain

A

Tectonic setting = Types of magma = Eruption style = Types of magma

45
Q

What are the four types of volcanoes?

A
  1. Fissure volcano
    2, Shield volcano
  2. Composite cone volcano
  3. Caldera volcano
46
Q

What is a fissure volcano?

A
  • It is a linear volcanic vent or a series of vents.
  • Most often associated with effusive BASALTIC eruptions, BUT can be explosive as well.

E.g. Tarawera eruption (1886), over 20 vents.
E.g. Mid-Ocean Ridge volcanism (Iceland).

47
Q

What is a shield volcano?

A

It is a broad, low profile volcano built by a succession of BASALTIC lava flows.

E.g. Mauna Loa (Hawaii), the biggest on Earth.
E.g. Rangitoto volcano (Auckland)
E.g. Olympus Mons (Mars)

48
Q

What is a composite cone volcano (stratovolcano)?

A

They are STEEP-SIDED cones, built up in a succession of layers of lava and pyroclastic material.
- Usually andesite or dacite.

E.g. St Helens (NOrthern America/Canada)

  • Lateral blast (a slip, magma took advantage)
  • Pyroclastic flow (big explosive eruption and low buoyancy).
  • Dome growth
49
Q

What can domes do?

A

Domes can collapse and form pyroclastic flows.

50
Q

What are caldera volcanoes?

A

They are subsidence structures-depressions formed after the underlying magma chamber is evacuated.

Typically HIGHTTLY explosive, large volume = super eruptions.

E.g. Taupo eruption

  • 200m thick pyroclastic flow
  • 10cm ash in the Chatham islands.
51
Q

What does high silica mean?

A

High silica = large eruptions (determines the type of the volcano)

52
Q

What are some techniques used to monitor/observe volcanoes?

A
  1. Ground deformation
  2. seismic activity (e.g. increase frequency)
  3. Gas emission

GPS, webcam, seismometer, gas monitoring, tiltmeter, direct observation, geological mapping, remote sensing.

53
Q

What is the best way to monitor volcanoes?

A

Geophysics/seismology

  • Used to detect earthquakes
  • Activity detected by field instruments (very few on all volcanoes).

Volcanic earthquakes show the movement of magma on the surface.
E.g. Pinatuve eruption was predicted to the day by the use of an emergency network of seismometers.
- Told people to evacuate (2 days later a very big eruption occurred).

54
Q

What can GPS (deformation) detect?

A
  • Can monitor movement
  • Tilt meter measures the amount of tilt in micro radiations (lengths get longer when it is about to erupt - magma rising).
  • Satellites
  • Level lines
55
Q

How are volcanic gases used to monitor volcanoes?

A
  • The amount and chemistry of gas discharge from a volcano can tell a lot about magma.
  • Can see SO2 coming out through an ultraviolet camera
  • Multigas instrument

CO2 is released first
- Can see pluses of magma entering the system.

56
Q

How much gas comes from the South Pacific volcanoes?

A

1/3

Near Vanuatu and Solomon Islands.

57
Q

What percentage of volcanoes are estimated to be submarine?

A

90%

58
Q

What are the benefits of geological mapping?

A

When volcanoes are close to people or infrastructure hazards become risks.

Geological mapping allows eruption scenarios to be estimated and planned for.

Needs to be accessible to the public and easy to understand.

59
Q

What can petrology/geochemistry tell us about the volcano?

A

The minerals in the lava and microchemistry of those minerals tells a lot about the magma history.

60
Q

What did volcanoes do in the early life on Earth?

A

In the early Earth life, volcanoes generated the atmosphere (greenhouse effect) provided water, nutrients, and environments n which life could begin.

Heat associated with volcanic areas drives water circulation in the rocks below the Earth’s surface (geothermal energy). This can be harnessed for energy.

61
Q

How do volcanoes affect vegetation and agriculture?

A

Volcanic eruptions can destroy (covered in ash - stops growth) forests in the SHORT-TERM, but provide nutrients for growth in the LONG-TERM.

62
Q

What are the disadvantages of volcanism tourism?

A

E.g. White Island - 47 people on the island and 22 fatalities.

63
Q

What are the characteristics of lava flows?

A
  • can normally out-run them UNLESS they are really big.
  • They easily destroy property/infrastructure.
  • Large igneous province developed can be linked to mass extinctions and transitions in global record.

ESCI 111 (18 decks)

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