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GEO1020 > Large scale topography > Flashcards

Large scale topography Flashcards

1
Q

What does plate et carre mean?

A

Flat and square

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2
Q

What does the Mercator projection show?

A

A deformed image of the Earth

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3
Q

Why is the Mercator map of the Earth used?

A

Because the spherical (orthographic) representation shows only one side

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4
Q

Where is the most deformation on Mercator projection?

A

In the North and South which is why Antarctica looks so big

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5
Q

When should the Mercator map not be used?

A

When comparing areas- need to integrate the deformation

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6
Q

What is the equal-area Hammer projection aim?

A

To reduce the amount of deformation

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7
Q

What is an issue with the equal-area Hammer projection?

A

It distorts other areas

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8
Q

What should be done when using an equal-area Hammer map?

A

It should be centred to the location you are looking at to avoid distortion

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9
Q

What is another type of projection?

A

Interrupted Sinusoidal projection

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10
Q

What has disappeared the most?

A

The ocean floor

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11
Q

Why is a relatively recent time scale needed?

A

Due to erosion

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12
Q

What needs to be understood when looking at geomorphology?

A

Need some background on what happened before

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13
Q

For which period do we have background information for?

A

Quaternary

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14
Q

Define hypsometry

A

Percentage of volume of land below or above a certain altitude

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15
Q

How is hypsometry displayed?

A

Through a histogram

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16
Q

What do the two peaks in the histogram mean?

A

Deepest point and highest point

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17
Q

Where is the deepest point?

A

Mayan trench

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18
Q

What is the average elevation of continents?

A

0.8km high

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19
Q

What is the average elevation of ocean basins?

A

4 km

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20
Q

What is the average depth of ocean trenches?

A

7.5-11km

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21
Q

What is the average elevation of mountain islands?

A

6km in relief

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22
Q

What are continental shelves part of?

A

Continents

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23
Q

What percentage of the Earth is covered in oceans?

A

71%

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24
Q

What percentage of the Earth is covered by continents?

A

29%

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25
Q

What percentage of the Earth is covered by continental shelves?

A

5%

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26
Q

Why is hypsometry of a catchment useful?

A

To see if the landscape is active e.g. rivers are affected by uplift, source of deformation

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27
Q

What does a hysometry curve show?

A

The elevation of something e.g. a river

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28
Q

What is the x axis on a hypsometry curve?

A

Relative area

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29
Q

What is y a function of in a hypsometry curve?

A

Y is a function of x

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30
Q

What does the y axis show on a hypsometry curve?

A

Relative height

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31
Q

What is the knickpoint?

A

This is usually where there is an over-steeped section of a river

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32
Q

What is hypsometry often used to characterize?

A

Landscape morphology, fluvial dissection, glacial erosion and tectonic uplift rates

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33
Q

What two profiles can hyspometry curves show?

A

Convex and concave

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34
Q

Where is the knickpoint on a hypsometry curve?

A

In between the convex and concave profiles

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35
Q

Where is the convex profile on a hypsometry curve?

A

It is above the knickpoint

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36
Q

Where is the concave profile on a hypsometry curve?

A

It is below the knickpoint

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37
Q

What is hypsometry analysis?

A

Frequency distribution of elevations

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38
Q

What sort of profile does older, more stable landscape have?

A

Concave

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39
Q

What sort of profile does a youthful and tectonically active landscape have?

A

Convex

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40
Q

What does a dip in the knickpoint show?

A

Retreating base level fall

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41
Q

What do rivers do that causes the knickpoint?

A

Try to smooth out the landscape

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42
Q

How thick is the oceanic crust?

A

7-10km (relatively thin)

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43
Q

What is oceanic crust mainly made of?

A

Basalts

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44
Q

What is the density of oceanic crust?

A

2.9g/cm3

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45
Q

What is the thickness of the continental crust?

A

25-70 km (thick)

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46
Q

Why is continental crust so thick?

A

Because of the mountain ranges, higher the peak the thicker the crust

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47
Q

What is the main component of continental crust?

A

Granite

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48
Q

What is the density of continental crust?

A

2.7 g/cm3

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49
Q

Which type of crust is being lost the most quickly?

A

Oceanic

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50
Q

What have seismic waves found?

A

Discontinuities

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51
Q

Where does the oceanic crust material come from?

A

Material from the mantle

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52
Q

What is the Mohorovick discontinuity?

A

This is at the base of crust

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53
Q

Where is the Gutenberg discontinuity?

A

This separates the upper and lower mantle from the core

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54
Q

Where is the Lehmann-Bullen discontinuity

A

Separates the inner and outer core

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55
Q

How thick is the mantle?

A

2885 km

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56
Q

How thick is the outer core?

A

2270 km

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57
Q

How thick is the inner core?

A

1216 km

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58
Q

Where does the information about the Earth’s structure come from?

A

Geochemical

Geophysical

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59
Q

How is geochemical data collected?

A

Through magma chambers

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60
Q

How is geophysical data collected?

A

Through seismic waves from earthquakes

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61
Q

What is the geophysical model split into?

A 
Lithosphere
Asthenosphere
Mesospheric mantle
Outer core
Inner core
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62
Q

When do seismic waves disappear?

A

When they go through liquid

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63
Q

What is the mesospheric mantle?

A

The lower mantle

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64
Q

Where can seismic waves disappear?

A

Where they try to get across the outer core

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65
Q

What state is the outer core?

A

Liquid

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66
Q

What state is the inner core?

A

Solid

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67
Q

What is the lithosphere?

A

The crust and uppermost mantle

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68
Q

What is a lithospheric property?

A

It is rigid and behaves elastically

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69
Q

What does the rigid elasticity in the litmosphere mean in terms of hazards?

A

Earthquakes can occur

70
Q

What is the asthenosphere?

A

The region of the upper mantle of the Earth

71
Q

What is the asthenosphere like?

A

It is highly viscous, mechanically weak and deformed like plastic

72
Q

What is the mesosphere?

A

The region of the lower mantle

73
Q

What temperature is the material that is dragged down by subduction?

A

Cold

74
Q

At what temperature does basalt melt?`

A

1300 degrees

75
Q

What happens to the properties of basalt and quartz upon melting?

A

They change

Become more inelastic (plastic ) so will flow rather than break

76
Q

At what temperature does quartz melt?

A

1100 degrees

77
Q

When did Wegner publish his first paper?

A

1912

78
Q

What did Wegner propose?

A

In the past, the continents were not separated but formed one supercontinent

79
Q

What was the supercontinent called?

A

Pangea 225 Ma

80
Q

Why was Wegner’s theory originally dismissed?

A

He failed to explain continental drift over time

81
Q

Where can fossil evidence be found for plate tectonics?

A

Gondwana region of central India

South America and Africa

82
Q

What fossil can be found on all continents?

A

Glossopteris

83
Q

How do mountains give evidence for continental drift?

A

Tertiary mountain belts along plate boundaries

84
Q

Why are permo-carboniferous glaciations evidence for continental drift that is hard to spot?

A

Difficult to find information for past glaciation

85
Q

What did Alexander DuToit show?

A

Continuity, not only in terms of shape but also in the type and age of the bedrock of Africa and South America

86
Q

What did Wegner think moved the continents?

A

The tide

87
Q

What is DuToit’s evidence?

A

Lineations on both sides of the two continents (South America and Africa)

88
Q

In which country is there evidence of glaciation?

A

India

89
Q

Who came up with the convection currents theory?

A

Arthur Holmes

90
Q

What limited plate tectonic theory in the past?

A

The thought that the Earth was flat

91
Q

What is island or swell in convection current theory?

A

Magma rising at the mid-oceanic ridge

92
Q

What is there a variation of?

A

The rate of extension of plates

93
Q

How long is the lifespan of a mid-ocean ridge?

A

200-300Ma

94
Q

How often is the ocean floor virtually swept away?

A

300-400 Ma

95
Q

In what way are continents passed around the mantle?

A

Passive

96
Q

What is an implication of passive continental crust movement?

A

The leading edges of the continental crust become very deformed

97
Q

At what rate is the mantle convecting?

A

1cm a year

98
Q

What does the localisation of earthquakes and volcanoes show?

A

They are not randomly distributed- mainly linked to plate boundary deformation

99
Q

What is a result of boundary deformation?

A

Magma rises to form a volcano

Earthquakes

100
Q

Why is there more evidence for plate tectonics from earthquakes?

A

The slab can be seen going down because the depth of the earthquake can be found

101
Q

Where are deeper earthquakes?

A

Away from mid-oceanic ridges

102
Q

Why are deeper earthquakes not found near mid-oceanic ridges?

A

Because the crust is thinner

103
Q

Briefly explain how plate tectonics work

A

Magma rises up and the asthenosphere raises at the oceanic ridge, the plates spread apart and one day become subducted at a trench

104
Q

What happens to material over 1100 C?

A

It is molten

105
Q

What happens if the material is molten?

A

There is no earthquake

106
Q

What are earthquakes like at ridges?

A

Shallow

107
Q

What happens at oceanic ridges?

A

Rising of the asthenosphere and partial melting

108
Q

What happens at the trench?

A

Magma rises up to form a volcano, pushes the mid-oceanic ridge at the other side.

109
Q

Why are earthquakes found at trenches?

A

Subduction causes friction and melting

110
Q

Where are sediment accretion wedges found?

A

At subduction zones

111
Q

What can happen at accretion wedges?

A

Earthquakes and deformation

112
Q

What is a transform fault?

A

On the ocean floor

Two plates slide past each other

113
Q

What is a strike slip fault?

A

Continental plates

Two plates slide past each other

114
Q

What are the 3 types of plate boundary?

A

Divergence
Convergence
Conservative

115
Q

What happens at divergence plate boundaries?

A

Plates move away from each other

116
Q

At which plate boundary would you find mid-oceanic ridges?

A

Divergent

117
Q

What are convergence boundaries?

A

This is where the plates move towards each other

118
Q

What are conservative plate boundaries?

A

These occur when plates move laterally from each other

119
Q

At which plate boundary would you find transform faults?

A

Conservative

120
Q

Give an example of a transform fault

A

San Andreas Fault

121
Q

At which plate boundary would you find oceanic trenches?

A

Convergence

122
Q

Give an example of an oceanic trench

A

Peru-Chile trench

123
Q

Give an example of a mid-ocean ridge

A

Mid-Atlantic ridge

124
Q

Why can South America and Africa still fit together?

A

Because they have not been deformed

125
Q

In what direction to the mid-oceanic ridges are transform faults?

A

They are perpendicular to the mid-oceanic ridges

126
Q

Why are transform faults needed at mid-oceanic ridges?

A

Because of the shape of the Earth

127
Q

What is a translation on a plane on a sphere?

A

A translation on a plane is a rotation on a sphere

128
Q

What is a spreading ridge?

A

An extension which is attached by a transform fault because of the shape of the Earth

129
Q

What do all plates have?

A

A rotation pole

130
Q

Why is more heat coming up at Iceland?

A

Because of thermal abmormalities as a result of mantle plumes, these are additional to convection currents

131
Q

What does convergence cause?

A

Compression

132
Q

What do earthquakes do to the accretion of sediment?

A

They deform it

133
Q

Can mid-oceanic ridges be subducted?

A

Yes

134
Q

Why do deep earthquakes not cause much damage?

A

Energy diminshes with distance

135
Q

Why is deformation of subduction complex?

A

The angle of subduction is complex- dip angle
Slab geometry
Back-arc deformations
Resistance
Trench motions (rollback, advanced or fixed)

136
Q

Why is subduction critical?

A

Because of the issues associated with the hazards

137
Q

Give an example of a place with back-arc compression

A

The Andes

138
Q

What is back arc spreading?

A

As the plate is subducted and melts, some magma rises which leads to an extension of the crust

139
Q

What is slab roll-back?

A

Older and colder oceanic crust is subducted at a steep angle and can roll back into the mantle, taking some of the overlying plate with it

140
Q

What is a good example of continental collision?

A

India into Asia

141
Q

What is the Wilson cycle?

A

A way of organising plate tectonics

142
Q

Talk through the Wilson cycle

A

Starts with the destruction of crust then developing an ocean floor, initiating subduction which causes two continents to collide together

143
Q

What is the main flaw in plate tectonics?

A

There is deformation elsewhere

144
Q

Where does the heat come from?

A

The convection cells

145
Q

How are convection cells structured?

A

In two layers

146
Q

Which layer of convection cell do subduction slabs reach?

A

They can reach the top layer or the bottom layer depending on whether they are superficial or not

147
Q

Where do mantle plumes occur?

A

From the outer core and the mantle

148
Q

What do mantle plumes cause on the crust?

A

Hot spots

149
Q

What are hot spots important for?

A

Volcanism

150
Q

What can the trace of volcanism show?

A

The motion of the plate

151
Q

What is the Siberian Trap?

A

A large region of volcanic rock, it is over a large hot spot

152
Q

What do we know about the Siberian Trap?

A

There is large thermal anomaly- not just because of asthenosphere melt because the composition of the deposits is not the same as what is found at mid-oceanic ridges.

153
Q

What are there traces of in the Siberian Trap?

A

Material from deeper parts of the Earth’s crust

154
Q

What is the largest flood basalt on Earth?

A

Otong Java

155
Q

Why are igneous provinces useful?

A

Because of climate impacts, there is a correlation with extension and extinction of species on Earth

156
Q

Explain what happened at the Deccan Traps

A

65 Ma the volcanism ended and 75% of the species were gone

157
Q

Explain what happened at the Siberian Trap

A

251 Ma volcanism ended and 90% of the species were gone

158
Q

What is useful about basalt?

A

Easy to date

159
Q

Which trap was bigger: Siberian or Deccan?

A

Siberian was 10x bigger

160
Q

What does the age of volcanism from hot spots show?

A

The direction and rate of motion

161
Q

Are hotspots permanent?

A

No but they can be active for a very long time

162
Q

What happens to plate motion and direction?

A

It changes overtime

163
Q

When does the Hawaiian chain change direction from the Emperor Seamount chain?

A

42.4 Ma

164
Q

What is free air anomaly?

A

The gravity anomaly of the mass resulting from the volcanism

165
Q

What can happen at the surface of the mantle plume?`

A

It can spread at the surface

166
Q

What can spreading of the mantle plume explain?

A

Initiation of crust subduction because it weakens the crust

167
Q

What can the spreading of the mantle plume follow?

A

Mid-oceanic ridges or faults

168
Q

Where do large plumes come from?

A

The lowermost mantle layer

169
Q

What is the lower most mantle called?

A

D2nd

170
Q

Are smaller mantle plumes more long term or short term?

A

They are more short term

171
Q

What do the plate tectonics help to cool?

A

They help to cool the mantle

172
Q

What do plumes help to cool?

A

The Earth’s core

GEO1020 (16 decks)

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