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GOPH 375 > Week 6, Earthquakes and Volcanoes > Flashcards

Week 6, Earthquakes and Volcanoes Flashcards

1
Q

What is the weakest point of many houses?

A

The chimney

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2
Q

What shape is the best for buildings?

A

Box shape

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3
Q

Earthquake Preparedness

A
  • Know safe spots: tables, desks, archways.
  • Practice earthquake drills
  • Learn first aid and CPR
  • Prepare emergency kit with supplies to survive 72 hour unassisted
  • Keep list of emergency phone numbers
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4
Q

Magma

A

Melted rock within the Earth

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5
Q

Lava

A

Melted rock at Earth’s surface

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6
Q

Plutonic rock

A

Magma solidified below Earth’s surface

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7
Q

Volcanic rock

A

Lava solidified above Earth’s surface

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8
Q

Volatiles

A

Dissolved gasses in the magma, what causes a lot of the driving energy behind eruptions.

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9
Q

Magma’s ability to contain gas changes with

A

pressure.

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10
Q

Gas solubility _____ with pressure and _____ with temperature

A

Gas solubility increases with pressure and decreases with temperature.

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11
Q

Viscosity

A

Measure of internal resistance to flow.

Depends on temperature, mineral crystal content, silica content.

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12
Q

More silica gives magma a higher

A

viscosity.

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13
Q

Why are eruptions on oceanic crust more peaceful?

A

Because they have less silica, so the magma is not as viscous, so the eruptions are not as explosive.

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14
Q

What does explosiveness depend on?

A

Amount of dissolved gas in the magma and the ease at which the gas can be released.

Low viscosity, gas can be released, we get a peaceful eruption.

High viscosity, gas is difficult to escape, we get an explosive eruption.

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15
Q

3 magma types from highest melting point to lowest melting point.

A

Basalt
Andesite
Rhyolite

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16
Q

3 magma types from most peaceful to most explosive and how it works

A
  1. Basalt: oceanic crust, low silica
  2. Andesite: intermediate
  3. Rhyolite: more silica, difficult gas escape, explosive eruption.
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17
Q

Process of Eruption

A
  • Begins with heat at depth
  • Heated rock rises, decompression melting
  • Reduced pressure allows dissolved gas to form bubbles, propelling magma upward bubbles act as buoyancy
  • Bubble volume may overwhelm magma, fragmenting it into pieces, which explode as a gas jet.
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18
Q

Decompression causes melting and bubbles to form that

A

reduce the density of the magma and allow it to rise, if the gases can’t escape it’s explosive.

19
Q

Magma type is dependant on

A

tectonic setting.

20
Q

Subduction zone volcanism is

A

explosive.

21
Q

Spreading centre volcanism is

A

not as explosive.

22
Q

90 percent of volcanism is at

A

plate boundaries

23
Q

10 percent of volcanism is at

A

hot spots.

24
Q

Where can we observe low viscosity, peaceful volcanism?

A

Iceland

25
Q

Where can we observe high viscosity, explosive volcanism?

A

Mt. St. Helens

26
Q

80 percent of all magma is produced at

A

mid ocean ridges.

27
Q

How so pillow basalts and sheet flows occur?

A

On the seafloor, as plates diverge hot plastic asthenosphere rises to fill gap, pressure is reduced and it becomes easy to lose gas.

Melt increases and hot basaltic magma creates pillow basalts and sheets flows when it comes into contact with the cool water.

These eruptions are peaceful and occur often.

28
Q

How does subduction zone volcanism occur? And why is it so explosive?

A

When the subducting plate is oceanic, the sediment sitting on top is soaked with water, this water is dragged down into the mantle, gets into the hot interior, water turns into steam and causes asthenosphere rocks to melt.

High buoyancy from gas causes rock to rise. It hits the crust and melts silica material into itself as it rises. The rock collecting and gaining silica content as it rises is what gives these volcanos the potential to be so explosive.

29
Q

Magma types from least amount of silica to mot amount of silica

A
  1. Basalt
  2. Andesite
  3. Rhyolite
30
Q

Explosive eruptions can result in high silica ____ and change climate for decades after an explosion/

A

Explosive eruptions can result in high silica ash and change climate for decades after an explosion.

31
Q

Why are oceanic subductive volcanoes somewhat less explosive?

A

Because magma is flowing through oceanic crust which is thinner and lower in silica.

32
Q

Can we observe volcanism at collision zones?

A

No.

33
Q

Volcanism can be observed at transform faults true or false

A

False

34
Q

Hot spots account for ___ percent of magma

A

Hot spots account for 10 percent of magma

35
Q

How much magma do subduction zones account for?

A

10 percent

36
Q

How are hot spot island formed?

A

Basaltic magma upwells through oceanic crust which is thin and low in silica content, erupts, and creates an island.

37
Q

Why are continental hot spot volcanos more explosive?

A

Because the magma upwells through the crust which is thicker and higher in silica.

38
Q

5 different eruption types from most peaceful to most explosive

A 
Icelandic
Hawaiian
Strombolian
Vulcanian
Plinian
39
Q

Icelandic type eruption

A 
Low viscosity
Basaltic 
Easy gas release
Can result in curtain of fire
Low volcanic plateaus
40
Q

Hawaiian type eruption

A

Peaceful lava outpouring
Easy gas release
Lava fountains
Doesn’t flow as far so you get shield volcanos

41
Q

Strombolian type eruption

A

Light house of the Mediterranean
Explosive eruptions
But not enough to break volcanic cone

42
Q

Vulcanian type eruption

A

Alternates between viscous magma flow and explosive
Characterized by strato or composite volcanos
First phase for most violent eruptions
A layering of strong and weak layer, ash alternating with magma flows

43
Q

Plinian type eruption

A

Massive
Mt. St. Helens
Powerful vertical eruption, gas, ashes and rocks to great heights
Most violent, common final phase
Can explode the whole mountain and cause large earthquakes and tsunamis

44
Q

Eruption intensity is based on

A

Volume of material erupted
Height of eruption column
Duration of eruption

GOPH 375 (13 decks)

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