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Physical Geography > Rocks and Weathering — Plate Tectonics + Patterns > Flashcards

Rocks and Weathering — Plate Tectonics + Patterns Flashcards

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1
Q

What is the Plate Tectonic Theory?

A

Earth is made up of number of layers

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2
Q

What is on the outside of Earth?

A

Thin crust

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3
Q

What is underneath the crust?

A

Mantle which makes up 82% of Earth’s volume

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4
Q

What is deep in earth?

A

Dense and hot core

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5
Q

What happens to the concentric layers?

A

They become increasingly more dense towards centre due to temp and pressure which melts rock

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6
Q

How are the rocks close to the surface?

A

Mainly solid and brittle

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7
Q

What does the lithosphere (aka upper mantle) have?

A

Crust and upper mantle (70km deep)

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8
Q

What is the Earth’s crust divided up into

A

Continental crust and Oceanic crust

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9
Q

Thickness comparison: continental and oceanic

A

Continental: 30km to 70km (average)

Oceanic: 6km to 10 km (average)

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10
Q

Rock age comparison: continental and oceanic

A

Continental: very old, 1500 million years

Oceanic: very young, 200 million years

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11
Q

Rock density + colour comparison: continental and oceanic

A

Continental: lighter density (+-2.6), lighter in colour

Oceanic: heavier density (+-3.0), dark in colour

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12
Q

Rock nature comparison: continental and oceanic

A

Continental: 1) silicon & aluminium are common 2) if rock combines with oxygen, granite forms

Oceanic: 1) basaltic rock where silicon, iron and magnesium are present 2) if rock combines with oxygen, granite forms

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13
Q

How many theories of moving platea are there?

A

Three (3)

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14
Q

What is the dragging theory?

A

1) plates sub-ducted by oldest edges are cold and heavy
2) plates are hot at mid-ocean ridge but cool as they move away (cooling takes 1 mil years)
3) cold plate descend at trenches, pressure causes rock to change and become heavier

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15
Q

What is the hotspot theory?

A

1) hotspot is plume of vertically rising lava through mantle
2) most are found near plate margins
3) are responsible for original rifting of crust
4) Hawaiian hotspot (most lava found) is not on plate margin
5) hotspots cause movement from out flow of viscous rock from centre creating drag force on plates making them move

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16
Q

What is the convection current theory (CCT)?

A

1) states huge convection currents occur in Earth’s Interior
2) hot magma rises through core to surface then spreads at mid-ocean ridges
3) cold solidified crust (heavier & denser than surrounding material) sinks back not Earth’s interior which is caused by radioactive decay in core
4) lithosphere (crust & upper mantle) s divided into 7 larger parts and several smaller parts

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17
Q

CCT: what is the asthenosphere?

A

asthenosphere is underlying semi-molten mantle

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18
Q

CCT: what happens to the rigid plates on the asthenosphere?

A

1) they are moved by currents forming convection celts by heat from Earth’s centre
2) plates move towards, away from or sideways from plates next to them

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19
Q

What are plate boundaries?

A

Are where major landforms are formed

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20
Q

What happens to continental crust?

A

It has a low density and does not sink (permanently settled)

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21
Q

What happens to oceanic crust?

A

It is denser thus sinks which means it can form and be destroyed continuously

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22
Q

CCT: what is the Eurasian plate?

A

Continental and oceanic plate

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23
Q

CCT: what happens to continental crust?

A

It can extend beyond margins of landmass

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24
Q

CCT: what does it mean when plate can’t overlap?

A

Means plates must be pushed up on instant

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25
Q

CCT: what does it mean by there are no ‘gaps’ on the Earth’s surface?

A

Means if plates move apart, new oceanic crust (from the mantle) is formed

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26
Q

What happens when new oceanic crust is formed?

A

The older crust is destroyed

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27
Q

What is plate movement like?

A

It is slow and continuous

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28
Q

What are sudden movements?

A

Earthquakes

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29
Q

What are the 3 types of plate boundaries?

A

1) Divergent (constructive)
2) Convergent (destructive & collision)
3) Conservative

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30
Q

Divergent: what are the facts?

A

1) plates move away from each other
2) new crust forms
3) mostly in the middle of oceans
4) ridges zones have shallow earthquakes less than 50km below surface
5) example: 1) Mid-Atlantic Ridge, 2) East Pacific Rise

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31
Q

Convergent-destructive: what are the facts?

A

1) 2 plates converge
2) deep-sea trench can form when one plate sub-ducts into mantle
3) deep earthquakes found (700km below surface)

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32
Q

Convergent-collision: what are the facts?

A

1) plates collide with each other
2) no subduction, there s crushing & folding
3) fold mountains form
4) examples: 1) Himalayas, 2)

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33
Q

Conservative: what are the facts?

A

1) plates slide past each other creating a transform fault
2) no converging & diverging
3) associated with shallow earthquakes
4) examples: 1) San Andreas Fault in California

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34
Q

Construc B: what is sea floor spreading (SFS)?

A

When plates move away from each other and new crust forms

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35
Q

Construc B (SFS): what happens when the plates diverge (move away)?

A

Molte rock or magma rises from mantle to fill gaps thus creating new oceanic crust

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36
Q

Construc B (SFS): what does the magma form?

Key word: row

A

Submarine volcanoes that, in time, row above sea-level

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37
Q

Construc B (SFS): what happens during the mid-ocean ridge system?

A

The spreading rates are not the same

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38
Q

Construc B (SFS): what are slow-spreading ridges in the Mid-Atlantic Ridge?

A

1) have pronounced rift down the centre
2) are fed by small, discontinuous magma chamber allowing the eruption of a wide range of basalt types

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39
Q

Construc B (SFS): what are fast-spreading ridges in the East Pacific Rise? (3)

A

1) lack central rift and has a smooth topography
2) have large, continuous magma chambers generating magma
3) high magma discharge results in sheet lavas

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40
Q

Construc B (SFS): how much is the Atlantic Ocean widening annually?

A

2–5 cm

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41
Q

Construc B (SFS): how is the Atlantic Ocean widening?

A

There is lateral movement along the mid-ocean ridge creating transform faults at right angles to the plate boundary

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42
Q

Construc B (SFS): what is another detail about mid-ocean ridges?

A

They can appear continuous at first sight but they are all broken into segments by transverse fractures (faults) that displace the ridges by 10s or 100s of km

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43
Q

Construc B: what is the Africa’s Rift Valley (ARV)?

A

It extends for 4000km from Mozambique to the Red Sea where its sides are over 600m high and width varies between 10 to 50 km

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44
Q

Construc B (ARV): what formed the African Rift Valley?

Key word: brittle crust

A

On the African continent, the brittle crust as fractured and as sections move apart, central portion dropped forming the valley

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45
Q

Destruc B: what are subduction zones (SZ)?

Key word: lithospheric

A

Form when an oceanic lithospheric plate collides with another plate, whether continental or oceanic

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46
Q

Destruc B (SZ): why is the density of the oceanic plate similar to the density of asthenosphere?

Key word: pushed

A

So, the oceanic plate can be easily pushed down into the upper mantle

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47
Q

Destruc B (SZ): what happens to the sub-ducted oceanic crust?

Key words: weight, denser, cooler

A

It remains cooler and denser than the surrounding mantle where subduction continues once initiated driven by the weight of the plate.

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48
Q

Destruc B (SZ): why has the Earth not grown in size?

A

The amount of subduction balances the amount of production at constructive plate margins

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49
Q

Destruc B (SZ): at what angles do subduction zones dip?

A

30 and 70 degrees where the older crust dips more steeply

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50
Q

Destruc B (SZ): why does the older crust dip more steeply at SZ?

A

Dip of the slap is oppositely related to the velocity of merging at the trench

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51
Q

Destruc B (SZ): what are the 3 evidences for subduction?

A

1) surrounding landforms like deep-sea trenches and folded sediments (arc shaped, sometimes volcanoes)
2) the beinoff zone
3) the distribution of temperature at depth

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52
Q

Destruc B: what is the Beinoff Zone (BZ)?

A

A narrow zone of earthquakes dipping away from deep-sea trenches

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53
Q

Destruc B (BZ): how far doe the BZ extend?

A

680km deep

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54
Q

Destruc B (BZ): what happens in this zone?

A

Deep focus earthquakes occur further from subduction

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55
Q

Destruc B: what is fold-mountain building in the Himalayas?

A

When the Indo-Australian plate subducts under the Eurasian plate

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56
Q

Destruc B: what are the features of fold-mountain building in the Himalayas?

A

1) the same as collision plate description
2) no magma escapes, little volcanic activity

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57
Q

Destruc B: what is fold-mountain building in the Andes?

A

When the Nazca oceanic plate sun ducts under the continental South American crust

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58
Q

Destruc B: what are the features of fold-mountain building in the Andes?

A

1) collision plate description
2) pieces of the Nazca plate scrap off to become part of the accretionary (growth) wedge which adds to the mountain range
3) partial melting of the Nazca plate produces volcanoes

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59
Q

Destruc B: what are ocean trenches?

A

Long, narrow, asymmetric depressions with a steep side towards land mass in the ocean floor

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60
Q

Destruc B: how deep are the ocean trenches on the ocean floor?

A

6000 - 11 000m deep

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61
Q

Destruc B: where are the ocean trenches found?

A

Next to land and stand arcs (most likely in the Pacific Ocean)

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62
Q

Destruc B: what are volcanic island arcs?

A

Chains of volcanic islands on the continental side of an ocean trench

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63
Q

Destruc B: how are volcanic island arcs formed? (4 steps)

A

1) subduction plate heats up and melts 75 miles deep
2) magma formed rises to surface and meets overriding plate
3) material added to crust, building volcanoes
4) if upper plate is oceanic, volcanoes pile up until they poke through the surface

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64
Q

Destruc B: what are the features of volcanic island arcs? (3)

A

1) trench outer rise caused by sub-ducting
2) gentle outer slope trench broken by faults
3) steep inner slope containing fragments of sub-ducting plate

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65
Q

What is weathering?

A

The breakdown of rocks in situ

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66
Q

What is erosion?

A

The breakdown of material by movement processes

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67
Q

Which rocks are least resistant to erosion?

A

Limestones and sandstones

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68
Q

How many physical processes are there in weathering and what do they produce?

A

There are 5 and they produce small, angular fragments of the same rocks

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69
Q

What is the freeze-thaw process?

A

It occurs in cold areas where ice forms as water freezes in cracks in rocks

70
Q

What are the steps to the freeze-thaw process? (5)

A

1) water collected in the crack freezes and expands 10%
2) a pressure of 14kg/cm squared is exerted on crack
3) crack forced open as pressure exceeds rock”s resistance
4) ice thaws, parts of the rock breaks free and water penetrates deeper
5) repeats until rock is cut through

71
Q

What is exfoliation?

A

Occurs in hot denser with large diurnal energy range (40 degrees to below freezing)

72
Q

What is the process of exfoliation? (4)

A

1) rocks heat via conduction
2) only outer layers expand as rock is a poor eat conductor
3) at night, outer layers cools and contract more rapidly than inner layers, creating stress
4) non-uniform contraction stresses results in outer layers flaking off over time

73
Q

What is salt crystal growth?

A

The physical disintegration due to retting (saltwater penetrating) rock surfaces

74
Q

What is the process of salt crystal growth? (2)

A

1) saline solution evaporates, leaving alt crystals
2) temperature rises, salt expands which exert pressure in the rock causing disintegration

75
Q

Where is the salt crystal growth process more effective in?

A

Areas with temperatures around 27 degrees here expansion is 300%

76
Q

What materials are used in the salt crystal growth process?

A

Sodium sulphate, magnesium sulphate and calcium chloride

77
Q

What are the rates of salt crystal growth effected by?

A

Porosity and permeability

78
Q

What is dilation?

A

This is the pressure release process

79
Q

What is the process of dilation? (5)

A

1) overlying rocks are removed by erosion (unloading) or glacier load is removed
2) underlying rocks expand with reduced pressure
3) fractures form parallel to the surface producing pseudo-bedding planes
4) cracks less prominent deeper down
5) most broken closer to surface

80
Q

During the dilation process, what happens if horizontal pressure is released?

A

Vertical faults develop and is common on cliff faces

81
Q

What is vegetation root action?

A

When roots can penetrate rocks or prevent rocks from forming in a specific place

82
Q

What are the physical processes? (5)

A

1) freeze-thaw
2) exfoliation
3) salt crystal growth
4) dilation
5) vegetation root action

83
Q

What are the different types of chemical processes? (3)

A

1) hydrolysis
2) hydration
3) carbonation

84
Q

What the chemical processes entail?

A

Creates altered rock substances and requires water

85
Q

What is hydrolysis?

A

When acid water breaks down rocks with feldspar mineral (like granite)

86
Q

What is the process of hydrolysis? (4)

A

1) acid water reacts with feldspar in granite
2) kaolin, silicic acid and potassium hydroxyl forms
3) acid and hydroxyl is removed, kaolin is left as the product
4) hydroxyl is carbonated and removed in solution

87
Q

What is the hydrolysis equation?

A

Feldspar + water kaolin + silicic acid + potassium hydroxyl

88
Q

What is hydration?

A

When certain minerals absorb water allowing them to expand and change , producing mechanical and chemical stress

89
Q

What does hydration affect?

A

Shale/mudstones

90
Q

What happens to clay minerals when they absorb water?

A

Clay minerals like anhydrite expand to form water bonds than produce hydrates like Gypsum causing 0.5% expansion

91
Q

What are the extreme cases of the hydration process?

A

There is 1600% expansion which causes cracking and fractures in the rock

92
Q

What is carbonation?

A

When acid rain breaks down limestone/chalk

93
Q

What is the process of carbonation? (6)

A

1) carbon dioxide dissolves in rainwater
2) weak carbonic (acid rain) is formed
3) calcium carbonate in limestone reacts with carbonic acid
4) calcium bicarbonate formed
5) calcium bicarbonate is soluble and is washed away by percolating water
6) limestone is removed

94
Q

What is the equation for the formation of carbonic acid?

A

CO2 + H2O (equilibrium symbol) H2CO3

95
Q

What is the equation for the formation of calcium bicarbonate?

A

CaCO3 + H2CO3Ca(HCO3)2

96
Q

What are the factors affecting weathering? (6)

A

1) climate
2) rock type
3) rock structure
4) vegetation
5) relief
6) human activity

97
Q

What is a periglacial zone?

A

A landscape than undergoes seasonal freezing and thawing, typically on the fringes of past and present glaciated regions

98
Q

How does rock type affects weathering?

A

Some minerals, like cements (in sedimentary rocks) re more resistant to weathering than others

99
Q

How does the limestone rock type affect weathering?

A

It is susceptible to carbonation CaCO3

100
Q

How does the sandstone rock type affect weathering?

A

Since it contains iron, it is oxidation prone

101
Q

How does the quartz rock type affect weathering?

A

Since it is chemically resistant, it cannot be chemically weathered

102
Q

How does rock structure affect weathering?

A

Differential resistance along lines of weakness and grains control water movement

103
Q

How does larger grain rock structure affect weathering?

A

There is faster weathering since there is a greater void space and high permeability

104
Q

How is weathering increased because of the rock structure?

A

The natural lines of weakness in rock formations allow water to penetrate

105
Q

What is meant by porous and non-porous?

A

Porous states a rock has little open spaces to allow liquid or air to pass through
Non-porous states a rock has no spaces to allow liquid or air to pass through

106
Q

What is meant by permeable and impermeable?

A

Permeable states a rock can allow liquids or gases to pass through
Impermeable states a rock does not allow any fluids to pass through

107
Q

What is the rock structure rule?

A

More permeable the rock = more weathering

108
Q

How does vegetation affect weathering? (3)

A

1) higher organic acid production and carbon dioxide increases carbonation
2) physical weathering reduces as temperatures are moderate
3) roots increase biological weathering

109
Q

What is the factor relief in affecting weathering?

A

It is the differences in height from place to place on the land surface and it affects temperatures and exposure

110
Q

How does relief affect weathering? (3)

A

1) weathered material is removed to allow weathering to continue
2) if slope to steep, water runs way
3) if too shallow, no material s removed

111
Q

When relief is affecting weathering, what happens in higher altitudes?

A

There are colder temperatures so the freeze-thaw process is dominant in this region

112
Q

How does human activity affect weathering? (2)

A

1) increased airborne chemical pollutants and acid ran increase weathering
2) vegetation removal reduces chemical/biological weathering since there are fewer organic acids

113
Q

How is weathering affected by temperature in glacial areas? (4)

A

1) freeze-thaw is dominant
2) number and duration of cycles is more important than degree of ice
3) likely slow chemical weathering but common hydration
4) example: Alaska ppt 0.4mm/yr

114
Q

How is weathering affected by temperature in arid/semi-arid?

A

1) evaporation exceeds precipitation thus mechanical processes are dominant
2) the thick organic layers in these semi- arid areas lead to leaching and CaCO3 accumulation
3) example: Egypt ppt 0.0001-2.0mm/yr

115
Q

How is weathering affected by temperature in humid tropical areas? (3)

A

1) high seasonal rainfall
2) high temperature results in significant chemical rainfall
3) example: florida ppt 0.005mm/yr

116
Q

What is Van’t Hoff’s Law?

A

The rate of chemical weathering increasing 2-3x for each 10 degrees temperature rise up to 60 degrees

117
Q

What is a slope?

A

Any inclined surface (hill slope) or slope angle

118
Q

What causes slope failure?

A

Increased shear stress and decreased shear strength

119
Q

What is increased shear stress in slope failure? (5)

A

1) The removal of lateral support (undercutting/slope steepening)
2) removal of underlying support
3) slope loading
4) lateral pressure
5) transient stresses

120
Q

What is decreased shear strength in slope failure? (4)

A

1) weathering effects
2) changes of structure
3) changes in pore-water pressure
4) organic effects

121
Q

What is opposition to movement in slope processes?(4)

A

1) friction
2) cohesive forces
3) pivoting
4) vegetation

122
Q

What is mass movement?

A

Processes of erosion, transport and accumulation of material occurring on both gentle and steep slopes mainly owing to gravitational forces

123
Q

What are the different types of mass movement? (6)

A

1) heaves (soil creep)
2) slumps
3) flows
4) falls
5) slides
6) slip plane

124
Q

What are is soil creep?

A

Slow movements of material where soil particles are heaved to surface by wetting, heating and freezing of water and occurs manly in winter

125
Q

How do soil creeps form? (4)

A

1) particles move perpendicular to the surface (path of least resistance)
2) once particle has dried, cooled or water has thawed, it falls under gravity
3) net movement is down the slope
4) example: 1-3mm/yr in UK and 10mm/yr in the rainforest

126
Q

What evidence shows the formation of soil creep? (4)

A

1) tension cracks in the road
2) titled poles
3) terracettes
4) soil piled behind field stone walls

127
Q

What is talus creep?

A

Slow movement of fragments along a scree slope

128
Q

What are slumps?

A

Weaker rocks like clays slump with a rotational movement along

129
Q

How do slumps form? (3)

A

1) clay saturates (wet) and flows along slip plane
2) commonly occurs if the base has been undercut
3) produces separate, jerky events

130
Q

What are flows?

A

More continuous, smoother form of slump occurring in deeply weathered clay where the particle size is the same or smaller than a grain of sand

131
Q

What more information is there on flows? (4)

A

1) mudflows are faster than earth flows
2) earth flows are deeper and thicker
3) higher water content slows flows to occur on shallower slopes
4) flows can occur on saturated toe of a landslide or as a separated event

132
Q

What are falls?

A

Bare rock faces and exposed joints falling on steep slopes at greater than 40 degrees

133
Q

How do falls form? (2)

A

1) rocks detach and fall freely under gravity
2) a short fall results in a straight scree produced
3) longer falls result in concave scree produced

134
Q

What more information is there on falls? (2)

A

1) they significantly contribute to te retreat of steep rock faces
2) they provide debris for scree slopes

135
Q

What are scree slopes?

A

Unstable steep mountain slopes composed of rock fragments and other debris

136
Q

What are slides?

A

When an entire mass of material moves along a slip plane where the material holds shape until hitting the slope bottom

137
Q

What type of slides occur?

A

Can be rock/land slides or rotational slides

138
Q

What conditions are needed for a slide to occur? (4)

A

1) weak rocks
2) steep slope
3) active cutting
4) intensely cold conditions
5) sudden changes in water content

139
Q

What are landslides?

A

When material moves downslope as a result of shear failure

140
Q

What are the facts about landslides? (2)

A

1) downward force is greater than resistance
2) increase on water content reduces strength (particles are pushed apart) thus more mass is added

141
Q

What are rock slides?

A

Large rock mass slides down the slip plane

142
Q

What is the slip plane?

A

Junction between two layer along bedding lane or joint between two rock types. It is the point between the surface where shear stress is greater than shear strength

143
Q

What is surface wash?

A

Occurs when the precipitation rate is higher than soil infiltration capacity (aka Hortonian flow conditions)

144
Q

What is sheet wash?

A

Unchanneled flow of water over soil’s surface

145
Q

What are the facts about sheetwash? (3)

A

1) high/low velocity sections may develop from sheet wash
2) it transports material dislodged by rain splash by eroding a uniform layer of soil
3) produces rills

146
Q

What are rills?

A

Shallow channels that carry water and sediment for a short period of time

147
Q

Where are rills common?

A

In agricultural lands after harvesting (bare land) and after compaction of soil by heavy machinery

148
Q

How is rain splash relevant on slopes? (2)

A

1) raindrops have an erosive effect
2) the effect is most prominent on slopes with inclines between 33-45 degrees at the start of rainfall and when soil is loose

149
Q

What happens to rainfall on a 5 degree slope?

A

60% of movement is downwards

150
Q

What happens to rainfall on a 25 degree slope?

A

95% of movement is downwards

151
Q

What are the different human activities that have an impact on slope stability? (8)

A

1) excavations
2) waste heaps
3) loading
4) vegetation removal
5) traffic vibrations
6) footpath trampling
7) construction on slopes
8) erosion processes

152
Q

How do excavations (digs) impact slope stability? (3)

A

1) cutting into a slop and leaving loose excavated holes creates a slope to steep to have stability
2) slope prone to failure
3) digs at the toe of a slope removes supporting section of slope

153
Q

How do waste heaps impact slope stability? (2)

A

1) highly porous mounds of waste material from quarrying and mining leaves new unstable steep slopes
2) slips occur with soil saturation after rainfall

154
Q

What is the impact on slope stability due to building loading?

A

It adds mass to slope and increases slip likelihood

155
Q

How is slope stability impacted by water loading? (3)

A

1) drainage routes are disturbed by building foundations
2) excess water in soil increases mass leading to slips (slips have lubricating properties)
3) if saturated soils are subjected to an earthquake, liquefaction occurs

156
Q

What is liquefaction in water loading of slope stability?

A

Pressure between particles making the soil act like a liquid

157
Q

How does vegetation removal impact slope stability? (2)

A

1) deforestation leaves bare land increasing surface runoff and more erosion occurring
2) if roots die or are removed, material is no longer bound together thus compromised stability

158
Q

How do traffic vibrations impact slope stability?

A

Mass movements may be triggered

159
Q

How does footpath trampling impact slope stability?

A

Causes intensified localised erosion

160
Q

How does construction on slopes impact the slope stability?

A

Has the same impact like when digs (excavations) impact slope stability with the use of the cut and fill method

161
Q

How can erosional processes can be increased (slope stability)? (3)

A

1) removal of vegetation
2) ploughing up And down slopes (creates water channels and rills)
3) destruction os soil structure (through overgrazing/growing or allowing granicola deterioration)

162
Q

What are the strategies to modify slopes? (8)

A

1) pinning
2) netting
3) grading
4) afforestation
5) gabions
6) drainage
7) grouting
8) shotcrete

163
Q

How does pinning modify the slopes? (3)

A

1) rock bolts, dowel bars and ground anchors installed
2) holds loose rocks into stable rocks below
3) ground anchors penetrate deeper, through different ock strengths

164
Q

What is netting?

A

Metal mesh nets attached to slope surface

165
Q

How does netting modify the slopes?

A

Regents loose rocks from falling onto road/rails below

166
Q

What is grading?

A

Highly costly process of transporting material away from slope

167
Q

How does grading modify the slope?

A

It reduces the slope angle by excavation (digging) to decrease the risk of movement

168
Q

How does afforestation modify the slope? (5)

A

1) adding vegetation increases interception
2) less surface runoff and erosion occurs
3) reduced mudflows
4) more roots hold the soil bound
5) reduced infiltration meaning slope has less mass

169
Q

What are gabions?

A

Metal mesh boxes used to stabilise the toe of the landslides

170
Q

How does drainage (water lubricating slope by adding mass) modify the slope?

A

Trenches dug, filled with permeable aggregate (rock particles and mineral grains), quickly remove water from slope

171
Q

What is grouting in slope modifications?

A

When permeable rocks are injected with cement to increase strength and reduce pore water capacity

172
Q

What is shotcrete in slope modifications?

A

When loose surfaces are sprayed with concrete to prevent loose rocks from falling

Physical Geography (3 decks)

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