EAE 11 - Volcanoes

Question 1

Can you forecast/predict a volcanic eruption ?

3 points.

Answer 1

Yes, some volcanic eruptions can be forecasted.

• However the lead up time is very short, in a matter of hours to minutes before an eminenteruption and in a matter of months before a possible eruption
• Any forecast requires 24/7, sophisticated monitoring of volcanoes (satellite data, chemical analyses of gases, earthquake monitoring).
• This is expensive and work intensive, and often not available in every environment (political, financial or social)

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Question 2

What is volcanic activity?

Answer 2

Volcanic activity occurs when molten rock, or melt, reaches the surfaces.

• This is the point at which magma becomes lava.Volcanic activity constantly occurs on Earth with no exception.
• Most eruptions are submarine.
• Subaerial eruptions occur often through mountains composed of volcanic rock (volcanoes).
• These are channelled flows of subsurface melts towards the surface; sourced from a deep magma reservoir.

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Question 3

Why are undersea volcanoes important?

Answer 3

Undersea volcanoes are extremely important for the interaction of rocks with seawater (element transfer) and deep sea life.

It has been explored for deep sea mining

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Question 4

What are active volcanoes?

Answer 4

Volcanoes that have erupted within historic time

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Question 5

What are dormant volcanoes?

Answer 5

Volcanoes with active plumbing system, Earthquakes, gas release etc.

On human time-scales, dormant volcanoes can appear extinct

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Question 6

What are extinct volcanoes?

Answer 6

No more volcanic activity

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Question 7

Describe historical eruptions

6 points.

Answer 7

Humans often settle close to volcanoes because of the fertile soils

• Plato wrote 360 BC that Atlantis was destroyed by a cataclysm of flood and explosion. Whilst most certainly not true, this event resembles a massive volcanic eruption; i.e., Santorini 3600 years ago.
• The Minoan civilization disappeared around the same time as the volcanic eruption occurred.
• Mount Vesuvius, eruption 79 AD
• Mount Krakatoa, eruption 1883
• Eruptions of volcanoes last back as long as written records exist.
• Descriptions of volcanic eruptions are very accurate but eruptions are not frequent and often do not last in living memory.

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Question 8

What are the key hazard components of eruptions?

5 points.

Answer 8

• Lava
• Ejecta
• Ash
• Gas
• A combination of these

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Question 9

Describe Phreato-magmatic eruptions

3 points.

Answer 9

• Explosive, intense, short & very dangerous eruptions
• (often these are Plinean-typeeruptions)
• Explosive ⇒ involvement of water

e.g., Mt. Pinatubo

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Question 10

Describe Mid-Ocean Ridge eruptions

Answer 10

Any Ridge / most Ocean Islands, e.g., Hawaii

• Slow
• Continuous
• Non explosive
• Effusive

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Question 11

Types of eruptions

What is a plinean type?

4 points.

Answer 11

Vesuvio

• Explosive & dangerous
• Short (one event, day(s))
• Massive!
• Can reach stratosphere

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Question 12

Types of eruptions

What is a volcanian type?

2 points.

Answer 12

Vulcano

• Explosive & dangerous
• Short (multiple events possible)

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Question 13

Types of eruptions

What is a strombolian type?

2 points.

Answer 13

Stromboli

• Moderately explosive
• Short (one event, day(s))

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Question 14

What are Hawaiian-type eruptions?

4 points.

Answer 14

Mauna Loa

• Effusive
• Slow & continous
• Moving (track)
• Non-explosive

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Question 15

What is the Volcanic Explosivity Index (VEI)?

Answer 15

The VEI index is a measure for the explosivityof volcanoes
similar to the Momentum scale in Earthquakes (M).

It is however NOT logarithmic and relies more on observations than measurements

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Question 16

Which are the most dangerous volcanoes?

Answer 16

Volcanoes at convergent tectonic plate margins are more dangerous than those within Earth’s plates.

The main difference is water within the melt.

• Downgoing slab brings oceanic sediments
• Volatiles are liberated by heating wet slab and sediments
• Zone of partial melting under volcanoe
• Magma produced by partial melting

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Question 17

Charactersistics of Phreatomagmatic eruptions

3 points.

Answer 17

• h+ ashfall & small earthquakes prior to extreme violent eruption (of previously hydrous rhyolitic magma)
• Magma ascends with 1 m/sec
• Time interval from magma storage to surface in ca. 4-5 hours

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Question 18

How do phreato-magmatic explosions hit water?

4 points.

Answer 18

• Groundwater - pore water -Hawaii
• Crater lakes (maare)
• Contact with surface waters like rivers
• Snow cover of volcanic peaks -Iceland

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Question 19

Charactersistics of phreatic eruptions?

3 points.

Answer 19

• Phreatic eruptions are short-lived, small in volume, relatively frequent (every few years) and do not include “active” magma.
• A phreatic eruption is “just” water vapour, and dissolved metals and volatiles (Cl-, F-, SO-).
• Gases explode with near supra-sonic speed and have > 300 degrees C.

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Question 20

How does water cause explosive volcanism?

2 points.

Answer 20

• The majority of explosive volcanism is triggered through water that is “dissolved” in the melt.
• Through pressure release, this water converts into gas, which causes melt to burst into ash. The volume increase is 1600x.

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Question 21

What are Volcanic blocks?

2 points.

Answer 21

• Volcanic blocks are solidified rock fragments greater than 64 mm in diameter.
• Blocks commonly are ejected during explosive eruptions and consist of older pieces of the volcano.

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Question 22

What are Volcanic bombs?

2 points.

Answer 22

• Volcanic bombs are large pieces of magma that harden in the air as the erupt out of a volcano.
• They can form in a variety of sizes and shapes. > 64 mm

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Question 23

What is Volcanic Ash?

Answer 23

Formed during defragmentation of rock/melt

< 2 mm

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Question 24

What is Lapilli?

3 points.

Answer 24

• tiny pieces of magma that harden before they hit the ground.
• 2-64 mm in size
• “Little stones” in Italian

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Question 25

What is the impact of volcanic ash?

5 points.

Answer 25

• Volcanic ash is highly disruptive to economic activitybecause it ‘covers’ just about everything, infiltrates most openings, and is highly abrasive.
• Airborne ash can obscure sunlight to cause temporary darkness and reduce visibility to zero during eruptions.
• Ash is slippery, especially when wet; roads, highways, and airport runways may become impassable.
• Automobile and jet engines may stall from ash-clogged air filters and moving parts can be damaged from abrasion, including bearings, brakes, and transmissions.
• So far, volcanic ash is not known to pose any serious health risks

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Question 26

What is the impact of volcanic ash on aircraft?

Answer 26

Rock fragments (ash) melt at ~1100°C; turbines operate at ~1400°C → when ash melts within the engine it may fail

When at lower altitudes, engines may restart as to shatter of frozen melt (glass)

Windscreens can be ‘abraded’ and the view drops to virtually zero (problem during landing)

~90 incidents in the last 30 years with commercial aircraft because of volcanic ash

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Question 27

What is a Pyroclastic flow?

5 points.

Answer 27

• When the steep edge of a gas/ash dome breaks apart and collapses, the falling ash avalanche is called pyroclastic flow
• From Greek: pyro(fire) and klastos(broken)
• High-speed avalanches of hot ash, rock fragments, and gas that moves down the sides of a volcano during explosive eruptions
• Pyroclastic flows can reach >800°C and move at avg. 150-250 km/h (up to 600 km/h)
• pyroclastic flows are capable of knocking down and burning everything in their paths

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Question 28

What is a Pyroclastic Surge?

4 points.

Answer 28

• A more energetic and dilutemixture of searing gas and rock fragments is called a pyroclastic surge
• Surges move easily up and over ridges; flows tend to follow valley
• Pyroclastic Flow and Pyroclastic Surge kill by ‘burning air’, but surges contain more toxic gases such as H₂S
• Surges have a very high kinetic energy → move up to 1000 km/h

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Question 29

What are Lahars?

3 points.

Answer 29

• Mudflow composed of volcanic ash (±lapilli and bombs) and water
• Consistency of concrete (fluid when moving; solid when stopped)
• >100 km/h, up to 300 km long; move downhill

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Question 30

What causes Lahars?

3 points.

Answer 30

• Glacial melt water
• Spring flood (after heavy rain)
• Volcanic eruptions

It often rains during eruptions caused by moisture from the volcano and droplet nucleation around ash.

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Question 31

Toxic gas emissions & acid rain

Answer 31

Acid rain from transport of particles through the Atmosphere

⇒ Global distribution for ash clouds reaching stratosphere

H₂SO₄ and H₂S can form SO₂ ejected from volcanoe

HCl, HF from fluorine and Chlorine

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Question 32

How do volcanoes contribute to global warming?

3 points.

Answer 32

Volcanic CO₂ emission is negligible compared to what humans produce
⇒ No global warming effect

• Anthropogenic emission is > 100 times larger
• Global estimates:
  
  • • Annual present day CO₂ output is 0.13-0.44 billion metric tons from volcanic activity (Avg 0.15-0.26 gigatons/year)
      
      • Anthropogenic CO₂ emission: 35 gigatons/year

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Question 33

What is the impact of Sulphur emission?

4 points.

Answer 33

• SO₂ reacts with sunlight to oxidised sulpheric complexes
• Can cause ‘albedo effect’ (increase reflectivity of the earth → lower temperature.
• Effect depends on the emission and explosivity of volcano
• Particles must reach the stratosphere in order to have an effect

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Question 34

Example of impact of SO₂

6 points.

Answer 34

Mt. Pinatubo

• VEI:6 (e.g., Mt. St. Helens had VEI:5)
• 10 km³ of magma erupted (including ash)
• 10 mill. Tons of SO₂ released
• Global ozone level dropped temporarily
• 3 years of aerosol coverage Contamination of stratosphere (required for global distribution)
• Global temperature dropped by 0.5°C

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