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Paper 2: Environmental Processes and Change > A: The Earth > Flashcards

A: The Earth Flashcards

1
Q

Oppenheimer (2011)

How old is Earth

A

4.567bn years

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2
Q

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Older volcanoes erupted with a greater % of what

A

Olivine

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3
Q

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What % of Earth volume does mantle comprise

A

84%

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4
Q

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Where are most volcanoes found

A

On oceanic ridges formed as tectonic plates separate from each other

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5
Q

Oppenheimer (2011)

Why is there less explosive volcanism in oceans

A

Water exerts greater pressure as 2.5km of water = 250x air pressure

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6
Q

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Magma

A

Molten rock below the surface

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7
Q

Oppenheimer (2011)

Where does almost all volcanism begin

A

Mantle

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8
Q

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What is the mantle mainly composed of (a type of rock)

A

Peridotite

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9
Q

Oppenheimer (2011)

What is Peridotite comprised of

A

Crystalline minerals
- Olivine
- Pyrixen
- Garet
- Feldspar
- Metal oxides
- Oxygen, silicon, magnesium, iron, aluminium, coopper - compose 99% of mass

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10
Q

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What is the state of matter of the mantle

A

Solid

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11
Q

Oppenheimer (2011)

What causes the mantle to flow through creep

A

Heat and gravity

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12
Q

Oppenheimer (2011)

What is primordial heat

A

Heat originating from when Earth was first formed

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13
Q

Oppenheimer (2011)

What continues to release heat into Earth’s interior

A

Radioactive decay of isotopes of uranium, potassium and thorium

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14
Q

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How is heat transferred out of Earth to surface

A

Convection

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15
Q

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Why do volcanoes form? (basic)

A

Because the mantle melts

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16
Q

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2 proceses for mantle melting

A
  1. Oceanic ridges and hotspots
  2. Subduction zones

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17
Q

Oppenheimer (2011)

Decomprssion melting (1)

A
  • Occurs at oceanic ridges and hotspots
  • within 300km of surface
  • minerals melt at different temp (e.g., magnesium rich vs iron rich olivines)
  • Melting points are sensitive
  • less pressure = lower melting point as less energy needed to break intermolecular forces
  • as rises to surface, less pressure = mantle melts
  • Partial melting as only minerals with lowest melting points melt -> 1-20% of peridotite melts

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18
Q

Oppenheimer (2011)

Partial melting

A

Where 1-20% of minerals in Peridotite melt via decompression cooling
- Occurs at subduction zones

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19
Q

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What % silica does Basaltic lava have

A

45%

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20
Q

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Silica chemical symbol

A

SiO2

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21
Q

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What type of melting forms oceanic ridges

A

Adiabatic deocompression melting

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22
Q

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What forms hotspots

A

Mantle plumes formed by adiabatic decompression melting

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23
Q

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What % of heat and magma can be attributed to mantle plumes

A

5-10%

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24
Q

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What are great outpourings of lava scientifically referred to as

A

Large Igneous Provinces (LIPs)

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25
Q

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Average rate of spreading at oceanic ridges per year

A

5cm

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26
Q

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What forms is magma found in

A

Solid, liquid and gas

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27
Q

Oppenheimer (2011)

What is solid magma composed of?

A

Minerals - olivine, feldspar, pyroxene and quartz
Silicate melt - loose arrangements of silicon and oxygen atoms mainly
Volatile components - water, CO2, sulphur and halogens

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28
Q

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What strong bonds form between Oxygen and Silicon

A

Covalent

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29
Q

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What is a major factor affecting how magma moves, volcanic hazards and eruptions

A

The polymerisation of silica tetrahedra

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30
Q

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Primary source of greenhouse gases into atmospehre on geological timescales

A

Volcanic outgassing

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31
Q

Oppenheimer (2011)

How can magma accumulation lead to eruptions

A
  • Magma finds level of neutral buoyancy where gravity can no longer propel it upwards
  • Magma ammasses in Magma chambers
  • Often causes fissure eruptions

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32
Q

Oppenheimer (2011)

Fractional distillation

A
  • As magma cools, crystals grow are composed of minerals with the highest melting/freezing point
  • Can increase eruptions as magma enriched by volatiles such as water and CO2
  • Cooling of volatiles creates bubbles
  • Bubble expansion increases pressure of magma chamber

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33
Q

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How many main types of magma are there

A

3

  • Basaltic (45-52% SiO2 by mass(
  • Intermediate (52-63% SiO2 by mass)
  • Silicic (>63% SiO2 by mass)

Oppenheimer (2011)

34
Q

Oppenheimer (2011)

What substance largely determined the effusivity of eruptions

A

Water

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35
Q

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What plate boundaries have the highest concentrtaion of dissolved volatiles such as water

A

Subduction zones
- derive lots of water from water, sulphur and chlorine from subducted oceanic rocks

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36
Q

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Impact of bubble formation

A
  • Lowers density and increases volume
  • Reduces viscocity

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37
Q

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Impact of water on viscosity

A
  • increases it
  • water inhibits covalent bonding between silca tetrahedra which causes it to string together in chains
  • Increases viscosity
  • contributes to more explosive eruptions

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38
Q

Oppenheimer (2011)

Anaolgy for eruptions

A

Uncorking of champagne
- dissolved carbon dioxide is released as chamber walls fail
- reduction of pressure insude bottle reduces the solubility of CO2, which releases CO2 gas
- CO2 gas expands which releases foam out of the bottle

Oppenheimer (2011)

39
Q

Oppenheimer (2011)

What are hydrovolcanic eruptions

A

Where magma meets water causing steam eruptions
- commonly associated with the reawakening of domant volcanoes

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40
Q

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What do explosive eruptions produce

A

Tephra/pyroclasts - fragmented rocks including pumice, ash and bombs

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41
Q

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What do effusive eruptions produce

A

lavas

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42
Q

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Why are eruptions called Plinian

A

Like the 79CE eruption of Vesuvius recorded by Pliny the Younger

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43
Q

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What are two fundemantal eruption parameters

A
  • Magnitude
  • Intensity

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44
Q

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What is Earth’s interior doing

A

Cooling down

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45
Q

Oppenheimer (2011)

What % of Earth’s volume does the mantle comprise

A

84%

Oppenheimer (2011)

46
Q

Oppenheimer (2011)

Where do most volcanoes lie

A

Oceanic ridges at the boundaries of tectonic plates

Oppenheimer (2011)

47
Q

Oppenheimer (2011)

Why is volcanism less violent 2.5km at the depths of the ocean

A

2.5km water column exerts a pressure 250x sea level pressure
This inhibits explosive volcanism

Oppenheimer (2011)

48
Q

Oppenheimer (2011)

Magma

A

Moltenr rock below Earth’s surface

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49
Q

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Lava

A

What comes out of a volcano

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50
Q

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What is Earth’s core rich in

A

Iron

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51
Q

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What is the mantle comprised largely of

A

Rock called peridotite

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52
Q

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How does the mantle ‘flow’?

A

Creep
- Crystals slop past each other and atoms and ions diffuse from one place to another

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53
Q

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Examples of primordial heat

A
  • Kinetic energy of meterorite hails
  • Chemical reactions
  • Decay of radioactive elements (uranium, potassium, thorium)

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54
Q

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What is the background temperature in space

A

-270.43 degrees c

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55
Q

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What is essential to volcanoes

A
  • Convection of magma in the mantle. The hotter the mantle the lower its density, causing rising; colder regions sink.
  • It is a circulation of solid mantle

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56
Q

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When was the last glacial maximum

A

20,000 years ago

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57
Q

Oppenheimer (2011)

What causes hotspot volcanoes

A

Mantle plumes

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58
Q

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What % magma coming from mantle comes from mantle plumes

A

5-10%

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59
Q

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Total length of ridges globally

A

50,000km

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60
Q

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What is the average spreading rate of divergent plates

A

5cm per year
–> 2.5sqkm more ocean crust created each year

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61
Q

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Hydration

A
  • Seawater reacts with hot volcanic rocks extracting sulphur
  • Seawater hydrates minerals such as olivine
  • Basalt transformed into slippery green rock called serpeninite
  • Water perolates into overlying mantle
  • Water in mantle reduces its melting point, causing partial melting

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62
Q

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Why do bubbles in magma form

A

Less pressure towards surface - process called exsolution
- Produce bubbles of CO2 (causing long term atmospheric changes), waer, sulphur dioxide and hydrogen flouride

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63
Q

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Neutral bouyancy

A

Where the density of magma = density of Earth’s crust
- Tend sto be 3-30km below the surface

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64
Q

Oppenheimer (2011)

How does magma cooling in the magma chamber contribute to eruptions

A
  • Fractional crystaliation
  • Crystals with highest meltin points freeze
  • Leaves behind more silica rich minerals
  • More volatiles left behind
  • Cooling and fractional crystalation lead to bubble formation
  • Bubbles expand magma chamber due to increased pressure
  • Increased pressure fractures the rock wall and initiates and eruption

Oppenheimer (2011)

65
Q

Oppenheimer (2011)

What % of volatiles can magmas at high pressures in Earth’s crust contain

A

10%

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66
Q

Oppenheimer (2011)

What plate boundaries have the most dissolved volatiles

A

Subduction zones
- Due to subducted oceanic rock

Oppenheimer (2011)

67
Q

Oppenheimer (2011)

How can magma encountering water cause eruptions

A

Production of steam
- Hydrovolcanic
- Example: Iceland 2010
- Commonly associated with the re-awakening of dormant volcanoes

Oppenheimer (2011)

68
Q

Oppenheimer (2011)

What are less explosive eruprions called

A

Effusive

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69
Q

Oppenheimer (2011)

Two broad categories for products of explosive eruptions

A

Tephra (fragmented rock: pumice, ash or bombs)
Pyroclasts

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70
Q

Oppenheimer (2011)

What does the intensity of an eruptions refer to

A

The rate at which magma is erupted

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71
Q

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How high do most intense ash columns reach

A

20-30km
Intro stratosphere

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72
Q

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Volcanic hazards

A
  • Ash
  • Gas clouds
  • Lava flows
  • Pyroclastic currents

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73
Q

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Why does intensity and magnitude of eruptions only loosely correlate to human impacts

A

Expsosure and vulnerability of societies varies

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74
Q

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Impact of volcanic eruptions in C20th on people

A
  • 500 events had a human impact
  • 6 million homeless or evauated
  • Fatalities in 250 eruptions
  • Death toll of 100,000

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75
Q

Oppenheimer (2011)

How could volcanoes present a greater threat in the future

A

Due to greater urbanisation

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76
Q

Oppenheimer (2011)

How many people were injured in volcanic eruptions in 20th century

A
  • 12,000
  • Low survival rates

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77
Q

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What is a classic manifestation of a volcanic eruption

A

Cloud of ash, rock and gases

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78
Q

Oppenheimer (2011)

What is Strombolian activity

A

In volcanology, a Strombolian eruption is a type of volcanic eruption with relatively mild blasts, typically having a Volcanic Explosivity Index of 1 or 2.

Oppenheimer (2011)

79
Q
A

Paper 2: Environmental Processes and Change (6 decks)

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