Large scale topography Flashcards
(172 cards)
1
Q
What does plate et carre mean?
A
Flat and square
2
Q
What does the Mercator projection show?
A
A deformed image of the Earth
3
Q
Why is the Mercator map of the Earth used?
A
Because the spherical (orthographic) representation shows only one side
4
Q
Where is the most deformation on Mercator projection?
A
In the North and South which is why Antarctica looks so big
5
Q
When should the Mercator map not be used?
A
When comparing areas- need to integrate the deformation
6
Q
What is the equal-area Hammer projection aim?
A
To reduce the amount of deformation
7
Q
What is an issue with the equal-area Hammer projection?
A
It distorts other areas
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
9
Q
What is another type of projection?
A
Interrupted Sinusoidal projection
10
Q
What has disappeared the most?
A
The ocean floor
11
Q
Why is a relatively recent time scale needed?
A
Due to erosion
12
Q
What needs to be understood when looking at geomorphology?
A
Need some background on what happened before
13
Q
For which period do we have background information for?
A
Quaternary
14
Q
Define hypsometry
A
Percentage of volume of land below or above a certain altitude
15
Q
How is hypsometry displayed?
A
Through a histogram
16
Q
What do the two peaks in the histogram mean?
A
Deepest point and highest point
17
Q
Where is the deepest point?
A
Mayan trench
18
Q
What is the average elevation of continents?
A
0.8km high
19
Q
What is the average elevation of ocean basins?
A
4 km
20
Q
What is the average depth of ocean trenches?
A
7.5-11km
21
Q
What is the average elevation of mountain islands?
A
6km in relief
22
Q
What are continental shelves part of?
A
Continents
23
Q
What percentage of the Earth is covered in oceans?
A
71%
24
Q
What percentage of the Earth is covered by continents?
A
29%
25
What percentage of the Earth is covered by continental shelves?
5%
26
Why is hypsometry of a catchment useful?
To see if the landscape is active e.g. rivers are affected by uplift, source of deformation
27
What does a hysometry curve show?
The elevation of something e.g. a river
28
What is the x axis on a hypsometry curve?
Relative area
29
What is y a function of in a hypsometry curve?
Y is a function of x
30
What does the y axis show on a hypsometry curve?
Relative height
31
What is the knickpoint?
This is usually where there is an over-steeped section of a river
32
What is hypsometry often used to characterize?
Landscape morphology, fluvial dissection, glacial erosion and tectonic uplift rates
33
What two profiles can hyspometry curves show?
Convex and concave
34
Where is the knickpoint on a hypsometry curve?
In between the convex and concave profiles
35
Where is the convex profile on a hypsometry curve?
It is above the knickpoint
36
Where is the concave profile on a hypsometry curve?
It is below the knickpoint
37
What is hypsometry analysis?
Frequency distribution of elevations
38
What sort of profile does older, more stable landscape have?
Concave
39
What sort of profile does a youthful and tectonically active landscape have?
Convex
40
What does a dip in the knickpoint show?
Retreating base level fall
41
What do rivers do that causes the knickpoint?
Try to smooth out the landscape
42
How thick is the oceanic crust?
7-10km (relatively thin)
43
What is oceanic crust mainly made of?
Basalts
44
What is the density of oceanic crust?
2.9g/cm3
45
What is the thickness of the continental crust?
25-70 km (thick)
46
Why is continental crust so thick?
Because of the mountain ranges, higher the peak the thicker the crust
47
What is the main component of continental crust?
Granite
48
What is the density of continental crust?
2.7 g/cm3
49
Which type of crust is being lost the most quickly?
Oceanic
50
What have seismic waves found?
Discontinuities
51
Where does the oceanic crust material come from?
Material from the mantle
52
What is the Mohorovick discontinuity?
This is at the base of crust
53
Where is the Gutenberg discontinuity?
This separates the upper and lower mantle from the core
54
Where is the Lehmann-Bullen discontinuity
Separates the inner and outer core
55
How thick is the mantle?
2885 km
56
How thick is the outer core?
2270 km
57
How thick is the inner core?
1216 km
58
Where does the information about the Earth's structure come from?
Geochemical
| Geophysical
59
How is geochemical data collected?
Through magma chambers
60
How is geophysical data collected?
Through seismic waves from earthquakes
61
What is the geophysical model split into?
```
Lithosphere
Asthenosphere
Mesospheric mantle
Outer core
Inner core
```
62
When do seismic waves disappear?
When they go through liquid
63
What is the mesospheric mantle?
The lower mantle
64
Where can seismic waves disappear?
Where they try to get across the outer core
65
What state is the outer core?
Liquid
66
What state is the inner core?
Solid
67
What is the lithosphere?
The crust and uppermost mantle
68
What is a lithospheric property?
It is rigid and behaves elastically
69
What does the rigid elasticity in the litmosphere mean in terms of hazards?
Earthquakes can occur
70
What is the asthenosphere?
The region of the upper mantle of the Earth
71
What is the asthenosphere like?
It is highly viscous, mechanically weak and deformed like plastic
72
What is the mesosphere?
The region of the lower mantle
73
What temperature is the material that is dragged down by subduction?
Cold
74
At what temperature does basalt melt?`
1300 degrees
75
What happens to the properties of basalt and quartz upon melting?
They change
| Become more inelastic (plastic ) so will flow rather than break
76
At what temperature does quartz melt?
1100 degrees
77
When did Wegner publish his first paper?
1912
78
What did Wegner propose?
In the past, the continents were not separated but formed one supercontinent
79
What was the supercontinent called?
Pangea 225 Ma
80
Why was Wegner's theory originally dismissed?
He failed to explain continental drift over time
81
Where can fossil evidence be found for plate tectonics?
Gondwana region of central India
| South America and Africa
82
What fossil can be found on all continents?
Glossopteris
83
How do mountains give evidence for continental drift?
Tertiary mountain belts along plate boundaries
84
Why are permo-carboniferous glaciations evidence for continental drift that is hard to spot?
Difficult to find information for past glaciation
85
What did Alexander DuToit show?
Continuity, not only in terms of shape but also in the type and age of the bedrock of Africa and South America
86
What did Wegner think moved the continents?
The tide
87
What is DuToit's evidence?
Lineations on both sides of the two continents (South America and Africa)
88
In which country is there evidence of glaciation?
India
89
Who came up with the convection currents theory?
Arthur Holmes
90
What limited plate tectonic theory in the past?
The thought that the Earth was flat
91
What is island or swell in convection current theory?
Magma rising at the mid-oceanic ridge
92
What is there a variation of?
The rate of extension of plates
93
How long is the lifespan of a mid-ocean ridge?
200-300Ma
94
How often is the ocean floor virtually swept away?
300-400 Ma
95
In what way are continents passed around the mantle?
Passive
96
What is an implication of passive continental crust movement?
The leading edges of the continental crust become very deformed
97
At what rate is the mantle convecting?
1cm a year
98
What does the localisation of earthquakes and volcanoes show?
They are not randomly distributed- mainly linked to plate boundary deformation
99
What is a result of boundary deformation?
Magma rises to form a volcano
| Earthquakes
100
Why is there more evidence for plate tectonics from earthquakes?
The slab can be seen going down because the depth of the earthquake can be found
101
Where are deeper earthquakes?
Away from mid-oceanic ridges
102
Why are deeper earthquakes not found near mid-oceanic ridges?
Because the crust is thinner
103
Briefly explain how plate tectonics work
Magma rises up and the asthenosphere raises at the oceanic ridge, the plates spread apart and one day become subducted at a trench
104
What happens to material over 1100 C?
It is molten
105
What happens if the material is molten?
There is no earthquake
106
What are earthquakes like at ridges?
Shallow
107
What happens at oceanic ridges?
Rising of the asthenosphere and partial melting
108
What happens at the trench?
Magma rises up to form a volcano, pushes the mid-oceanic ridge at the other side.
109
Why are earthquakes found at trenches?
Subduction causes friction and melting
110
Where are sediment accretion wedges found?
At subduction zones
111
What can happen at accretion wedges?
Earthquakes and deformation
112
What is a transform fault?
On the ocean floor
| Two plates slide past each other
113
What is a strike slip fault?
Continental plates
| Two plates slide past each other
114
What are the 3 types of plate boundary?
Divergence
Convergence
Conservative
115
What happens at divergence plate boundaries?
Plates move away from each other
116
At which plate boundary would you find mid-oceanic ridges?
Divergent
117
What are convergence boundaries?
This is where the plates move towards each other
118
What are conservative plate boundaries?
These occur when plates move laterally from each other
119
At which plate boundary would you find transform faults?
Conservative
120
Give an example of a transform fault
San Andreas Fault
121
At which plate boundary would you find oceanic trenches?
Convergence
122
Give an example of an oceanic trench
Peru-Chile trench
123
Give an example of a mid-ocean ridge
Mid-Atlantic ridge
124
Why can South America and Africa still fit together?
Because they have not been deformed
125
In what direction to the mid-oceanic ridges are transform faults?
They are perpendicular to the mid-oceanic ridges
126
Why are transform faults needed at mid-oceanic ridges?
Because of the shape of the Earth
127
What is a translation on a plane on a sphere?
A translation on a plane is a rotation on a sphere
128
What is a spreading ridge?
An extension which is attached by a transform fault because of the shape of the Earth
129
What do all plates have?
A rotation pole
130
Why is more heat coming up at Iceland?
Because of thermal abmormalities as a result of mantle plumes, these are additional to convection currents
131
What does convergence cause?
Compression
132
What do earthquakes do to the accretion of sediment?
They deform it
133
Can mid-oceanic ridges be subducted?
Yes
134
Why do deep earthquakes not cause much damage?
Energy diminshes with distance
135
Why is deformation of subduction complex?
The angle of subduction is complex- dip angle
Slab geometry
Back-arc deformations
Resistance
Trench motions (rollback, advanced or fixed)
136
Why is subduction critical?
Because of the issues associated with the hazards
137
Give an example of a place with back-arc compression
The Andes
138
What is back arc spreading?
As the plate is subducted and melts, some magma rises which leads to an extension of the crust
139
What is slab roll-back?
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
What is a good example of continental collision?
India into Asia
141
What is the Wilson cycle?
A way of organising plate tectonics
142
Talk through the Wilson cycle
Starts with the destruction of crust then developing an ocean floor, initiating subduction which causes two continents to collide together
143
What is the main flaw in plate tectonics?
There is deformation elsewhere
144
Where does the heat come from?
The convection cells
145
How are convection cells structured?
In two layers
146
Which layer of convection cell do subduction slabs reach?
They can reach the top layer or the bottom layer depending on whether they are superficial or not
147
Where do mantle plumes occur?
From the outer core and the mantle
148
What do mantle plumes cause on the crust?
Hot spots
149
What are hot spots important for?
Volcanism
150
What can the trace of volcanism show?
The motion of the plate
151
What is the Siberian Trap?
A large region of volcanic rock, it is over a large hot spot
152
What do we know about the Siberian Trap?
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
What are there traces of in the Siberian Trap?
Material from deeper parts of the Earth's crust
154
What is the largest flood basalt on Earth?
Otong Java
155
Why are igneous provinces useful?
Because of climate impacts, there is a correlation with extension and extinction of species on Earth
156
Explain what happened at the Deccan Traps
65 Ma the volcanism ended and 75% of the species were gone
157
Explain what happened at the Siberian Trap
251 Ma volcanism ended and 90% of the species were gone
158
What is useful about basalt?
Easy to date
159
Which trap was bigger: Siberian or Deccan?
Siberian was 10x bigger
160
What does the age of volcanism from hot spots show?
The direction and rate of motion
161
Are hotspots permanent?
No but they can be active for a very long time
162
What happens to plate motion and direction?
It changes overtime
163
When does the Hawaiian chain change direction from the Emperor Seamount chain?
42.4 Ma
164
What is free air anomaly?
The gravity anomaly of the mass resulting from the volcanism
165
What can happen at the surface of the mantle plume?`
It can spread at the surface
166
What can spreading of the mantle plume explain?
Initiation of crust subduction because it weakens the crust
167
What can the spreading of the mantle plume follow?
Mid-oceanic ridges or faults
168
Where do large plumes come from?
The lowermost mantle layer
169
What is the lower most mantle called?
D2nd
170
Are smaller mantle plumes more long term or short term?
They are more short term
171
What do the plate tectonics help to cool?
They help to cool the mantle
172
What do plumes help to cool?
The Earth's core
