Rocks and Weathering — Plate Tectonics + Patterns Flashcards
1
Q
What is the Plate Tectonic Theory?
A
Earth is made up of number of layers
2
Q
What is on the outside of Earth?
A
Thin crust
3
Q
What is underneath the crust?
A
Mantle which makes up 82% of Earth’s volume
4
Q
What is deep in earth?
A
Dense and hot core
5
Q
What happens to the concentric layers?
A
They become increasingly more dense towards centre due to temp and pressure which melts rock
6
Q
How are the rocks close to the surface?
A
Mainly solid and brittle
7
Q
What does the lithosphere (aka upper mantle) have?
A
Crust and upper mantle (70km deep)
8
Q
What is the Earth’s crust divided up into
A
Continental crust and Oceanic crust
9
Q
Thickness comparison: continental and oceanic
A
Continental: 30km to 70km (average)
Oceanic: 6km to 10 km (average)
10
Q
Rock age comparison: continental and oceanic
A
Continental: very old, 1500 million years
Oceanic: very young, 200 million years
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
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
13
Q
How many theories of moving platea are there?
A
Three (3)
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
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
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
17
Q
CCT: what is the asthenosphere?
A
asthenosphere is underlying semi-molten mantle
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
19
Q
What are plate boundaries?
A
Are where major landforms are formed
20
Q
What happens to continental crust?
A
It has a low density and does not sink (permanently settled)
21
Q
What happens to oceanic crust?
A
It is denser thus sinks which means it can form and be destroyed continuously
22
Q
CCT: what is the Eurasian plate?
A
Continental and oceanic plate
23
Q
CCT: what happens to continental crust?
A
It can extend beyond margins of landmass
24
Q
CCT: what does it mean when plate can’t overlap?
A
Means plates must be pushed up on instant
25
CCT: what does it mean by there are no ‘gaps’ on the Earth’s surface?
Means if plates move apart, new oceanic crust (from the mantle) is formed
26
What happens when new oceanic crust is formed?
The older crust is destroyed
27
What is plate movement like?
It is slow and continuous
28
What are sudden movements?
Earthquakes
29
What are the 3 types of plate boundaries?
1) Divergent (constructive)
2) Convergent (destructive & collision)
3) Conservative
30
Divergent: what are the facts?
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
31
Convergent-destructive: what are the facts?
1) 2 plates converge
2) deep-sea trench can form when one plate sub-ducts into mantle
3) deep earthquakes found (700km below surface)
32
Convergent-collision: what are the facts?
1) plates collide with each other
2) no subduction, there s crushing & folding
3) fold mountains form
4) examples: 1) Himalayas, 2)
33
Conservative: what are the facts?
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
34
Construc B: what is sea floor spreading (SFS)?
When plates move away from each other and new crust forms
35
Construc B (SFS): what happens when the plates diverge (move away)?
Molte rock or magma rises from mantle to fill gaps thus creating new oceanic crust
36
Construc B (SFS): what does the magma form?
Key word: row
Submarine volcanoes that, in time, row above sea-level
37
Construc B (SFS): what happens during the mid-ocean ridge system?
The spreading rates are not the same
38
Construc B (SFS): what are slow-spreading ridges in the Mid-Atlantic Ridge?
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
39
Construc B (SFS): what are fast-spreading ridges in the East Pacific Rise? (3)
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
40
Construc B (SFS): how much is the Atlantic Ocean widening annually?
2–5 cm
41
Construc B (SFS): how is the Atlantic Ocean widening?
There is lateral movement along the mid-ocean ridge creating transform faults at right angles to the plate boundary
42
Construc B (SFS): what is another detail about mid-ocean ridges?
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
43
Construc B: what is the Africa’s Rift Valley (ARV)?
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
44
Construc B (ARV): what formed the African Rift Valley?
Key word: brittle crust
On the African continent, the brittle crust as fractured and as sections move apart, central portion dropped forming the valley
45
Destruc B: what are subduction zones (SZ)?
Key word: lithospheric
Form when an oceanic lithospheric plate collides with another plate, whether continental or oceanic
46
Destruc B (SZ): why is the density of the oceanic plate similar to the density of asthenosphere?
Key word: pushed
So, the oceanic plate can be easily pushed down into the upper mantle
47
Destruc B (SZ): what happens to the sub-ducted oceanic crust?
Key words: weight, denser, cooler
It remains cooler and denser than the surrounding mantle where subduction continues once initiated driven by the weight of the plate.
48
Destruc B (SZ): why has the Earth not grown in size?
The amount of subduction balances the amount of production at constructive plate margins
49
Destruc B (SZ): at what angles do subduction zones dip?
30 and 70 degrees where the older crust dips more steeply
50
Destruc B (SZ): why does the older crust dip more steeply at SZ?
Dip of the slap is oppositely related to the velocity of merging at the trench
51
Destruc B (SZ): what are the 3 evidences for subduction?
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
52
Destruc B: what is the Beinoff Zone (BZ)?
A narrow zone of earthquakes dipping away from deep-sea trenches
53
Destruc B (BZ): how far doe the BZ extend?
680km deep
54
Destruc B (BZ): what happens in this zone?
Deep focus earthquakes occur further from subduction
55
Destruc B: what is fold-mountain building in the Himalayas?
When the Indo-Australian plate subducts under the Eurasian plate
56
Destruc B: what are the features of fold-mountain building in the Himalayas?
1) the same as collision plate description
2) no magma escapes, little volcanic activity
57
Destruc B: what is fold-mountain building in the Andes?
When the Nazca oceanic plate sun ducts under the continental South American crust
58
Destruc B: what are the features of fold-mountain building in the Andes?
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
59
Destruc B: what are ocean trenches?
Long, narrow, asymmetric depressions with a steep side towards land mass in the ocean floor
60
Destruc B: how deep are the ocean trenches on the ocean floor?
6000 - 11 000m deep
61
Destruc B: where are the ocean trenches found?
Next to land and stand arcs (most likely in the Pacific Ocean)
62
Destruc B: what are volcanic island arcs?
Chains of volcanic islands on the continental side of an ocean trench
63
Destruc B: how are volcanic island arcs formed? (4 steps)
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
64
Destruc B: what are the features of volcanic island arcs? (3)
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
65
What is weathering?
The breakdown of rocks in situ
66
What is erosion?
The breakdown of material by movement processes
67
Which rocks are least resistant to erosion?
Limestones and sandstones
68
How many physical processes are there in weathering and what do they produce?
There are 5 and they produce small, angular fragments of the same rocks
69
What is the freeze-thaw process?
It occurs in cold areas where ice forms as water freezes in cracks in rocks
70
What are the steps to the freeze-thaw process? (5)
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
What is exfoliation?
Occurs in hot denser with large diurnal energy range (40 degrees to below freezing)
72
What is the process of exfoliation? (4)
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
What is salt crystal growth?
The physical disintegration due to retting (saltwater penetrating) rock surfaces
74
What is the process of salt crystal growth? (2)
1) saline solution evaporates, leaving alt crystals
2) temperature rises, salt expands which exert pressure in the rock causing disintegration
75
Where is the salt crystal growth process more effective in?
Areas with temperatures around 27 degrees here expansion is 300%
76
What materials are used in the salt crystal growth process?
Sodium sulphate, magnesium sulphate and calcium chloride
77
What are the rates of salt crystal growth effected by?
Porosity and permeability
78
What is dilation?
This is the pressure release process
79
What is the process of dilation? (5)
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
During the dilation process, what happens if horizontal pressure is released?
Vertical faults develop and is common on cliff faces
81
What is vegetation root action?
When roots can penetrate rocks or prevent rocks from forming in a specific place
82
What are the physical processes? (5)
1) freeze-thaw
2) exfoliation
3) salt crystal growth
4) dilation
5) vegetation root action
83
What are the different types of chemical processes? (3)
1) hydrolysis
2) hydration
3) carbonation
84
What the chemical processes entail?
Creates altered rock substances and requires water
85
What is hydrolysis?
When acid water breaks down rocks with feldspar mineral (like granite)
86
What is the process of hydrolysis? (4)
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
What is the hydrolysis equation?
Feldspar + water kaolin + silicic acid + potassium hydroxyl
88
What is hydration?
When certain minerals absorb water allowing them to expand and change , producing mechanical and chemical stress
89
What does hydration affect?
Shale/mudstones
90
What happens to clay minerals when they absorb water?
Clay minerals like anhydrite expand to form water bonds than produce hydrates like Gypsum causing 0.5% expansion
91
What are the extreme cases of the hydration process?
There is 1600% expansion which causes cracking and fractures in the rock
92
What is carbonation?
When acid rain breaks down limestone/chalk
93
What is the process of carbonation? (6)
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
What is the equation for the formation of carbonic acid?
CO2 + H2O (equilibrium symbol) H2CO3
95
What is the equation for the formation of calcium bicarbonate?
CaCO3 + H2CO3Ca(HCO3)2
96
What are the factors affecting weathering? (6)
1) climate
2) rock type
3) rock structure
4) vegetation
5) relief
6) human activity
97
What is a periglacial zone?
A landscape than undergoes seasonal freezing and thawing, typically on the fringes of past and present glaciated regions
98
How does rock type affects weathering?
Some minerals, like cements (in sedimentary rocks) re more resistant to weathering than others
99
How does the limestone rock type affect weathering?
It is susceptible to carbonation CaCO3
100
How does the sandstone rock type affect weathering?
Since it contains iron, it is oxidation prone
101
How does the quartz rock type affect weathering?
Since it is chemically resistant, it cannot be chemically weathered
102
How does rock structure affect weathering?
Differential resistance along lines of weakness and grains control water movement
103
How does larger grain rock structure affect weathering?
There is faster weathering since there is a greater void space and high permeability
104
How is weathering increased because of the rock structure?
The natural lines of weakness in rock formations allow water to penetrate
105
What is meant by porous and non-porous?
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
What is meant by permeable and impermeable?
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
What is the rock structure rule?
More permeable the rock = more weathering
108
How does vegetation affect weathering? (3)
1) higher organic acid production and carbon dioxide increases carbonation
2) physical weathering reduces as temperatures are moderate
3) roots increase biological weathering
109
What is the factor relief in affecting weathering?
It is the differences in height from place to place on the land surface and it affects temperatures and exposure
110
How does relief affect weathering? (3)
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
When relief is affecting weathering, what happens in higher altitudes?
There are colder temperatures so the freeze-thaw process is dominant in this region
112
How does human activity affect weathering? (2)
1) increased airborne chemical pollutants and acid ran increase weathering
2) vegetation removal reduces chemical/biological weathering since there are fewer organic acids
113
How is weathering affected by temperature in glacial areas? (4)
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
How is weathering affected by temperature in arid/semi-arid?
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
How is weathering affected by temperature in humid tropical areas? (3)
1) high seasonal rainfall
2) high temperature results in significant chemical rainfall
3) example: florida ppt 0.005mm/yr
116
What is Van’t Hoff’s Law?
The rate of chemical weathering increasing 2-3x for each 10 degrees temperature rise up to 60 degrees
117
What is a slope?
Any inclined surface (hill slope) or slope angle
118
What causes slope failure?
Increased shear stress and decreased shear strength
119
What is increased shear stress in slope failure? (5)
1) The removal of lateral support (undercutting/slope steepening)
2) removal of underlying support
3) slope loading
4) lateral pressure
5) transient stresses
120
What is decreased shear strength in slope failure? (4)
1) weathering effects
2) changes of structure
3) changes in pore-water pressure
4) organic effects
121
What is opposition to movement in slope processes?(4)
1) friction
2) cohesive forces
3) pivoting
4) vegetation
122
What is mass movement?
Processes of erosion, transport and accumulation of material occurring on both gentle and steep slopes mainly owing to gravitational forces
123
What are the different types of mass movement? (6)
1) heaves (soil creep)
2) slumps
3) flows
4) falls
5) slides
6) slip plane
124
What are is soil creep?
Slow movements of material where soil particles are heaved to surface by wetting, heating and freezing of water and occurs manly in winter
125
How do soil creeps form? (4)
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
What evidence shows the formation of soil creep? (4)
1) tension cracks in the road
2) titled poles
3) terracettes
4) soil piled behind field stone walls
127
What is talus creep?
Slow movement of fragments along a scree slope
128
What are slumps?
Weaker rocks like clays slump with a rotational movement along
129
How do slumps form? (3)
1) clay saturates (wet) and flows along slip plane
2) commonly occurs if the base has been undercut
3) produces separate, jerky events
130
What are flows?
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
What more information is there on flows? (4)
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
What are falls?
Bare rock faces and exposed joints falling on steep slopes at greater than 40 degrees
133
How do falls form? (2)
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
What more information is there on falls? (2)
1) they significantly contribute to te retreat of steep rock faces
2) they provide debris for scree slopes
135
What are scree slopes?
Unstable steep mountain slopes composed of rock fragments and other debris
136
What are slides?
When an entire mass of material moves along a slip plane where the material holds shape until hitting the slope bottom
137
What type of slides occur?
Can be rock/land slides or rotational slides
138
What conditions are needed for a slide to occur? (4)
1) weak rocks
2) steep slope
3) active cutting
4) intensely cold conditions
5) sudden changes in water content
139
What are landslides?
When material moves downslope as a result of shear failure
140
What are the facts about landslides? (2)
1) downward force is greater than resistance
2) increase on water content reduces strength (particles are pushed apart) thus more mass is added
141
What are rock slides?
Large rock mass slides down the slip plane
142
What is the slip plane?
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
What is surface wash?
Occurs when the precipitation rate is higher than soil infiltration capacity (aka Hortonian flow conditions)
144
What is sheet wash?
Unchanneled flow of water over soil’s surface
145
What are the facts about sheetwash? (3)
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
What are rills?
Shallow channels that carry water and sediment for a short period of time
147
Where are rills common?
In agricultural lands after harvesting (bare land) and after compaction of soil by heavy machinery
148
How is rain splash relevant on slopes? (2)
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
What happens to rainfall on a 5 degree slope?
60% of movement is downwards
150
What happens to rainfall on a 25 degree slope?
95% of movement is downwards
151
What are the different human activities that have an impact on slope stability? (8)
1) excavations
2) waste heaps
3) loading
4) vegetation removal
5) traffic vibrations
6) footpath trampling
7) construction on slopes
8) erosion processes
152
How do excavations (digs) impact slope stability? (3)
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
How do waste heaps impact slope stability? (2)
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
What is the impact on slope stability due to building loading?
It adds mass to slope and increases slip likelihood
155
How is slope stability impacted by water loading? (3)
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
What is liquefaction in water loading of slope stability?
Pressure between particles making the soil act like a liquid
157
How does vegetation removal impact slope stability? (2)
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
How do traffic vibrations impact slope stability?
Mass movements may be triggered
159
How does footpath trampling impact slope stability?
Causes intensified localised erosion
160
How does construction on slopes impact the slope stability?
Has the same impact like when digs (excavations) impact slope stability with the use of the cut and fill method
161
How can erosional processes can be increased (slope stability)? (3)
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
What are the strategies to modify slopes? (8)
1) pinning
2) netting
3) grading
4) afforestation
5) gabions
6) drainage
7) grouting
8) shotcrete
163
How does pinning modify the slopes? (3)
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
What is netting?
Metal mesh nets attached to slope surface
165
How does netting modify the slopes?
Regents loose rocks from falling onto road/rails below
166
What is grading?
Highly costly process of transporting material away from slope
167
How does grading modify the slope?
It reduces the slope angle by excavation (digging) to decrease the risk of movement
168
How does afforestation modify the slope? (5)
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
What are gabions?
Metal mesh boxes used to stabilise the toe of the landslides
170
How does drainage (water lubricating slope by adding mass) modify the slope?
Trenches dug, filled with permeable aggregate (rock particles and mineral grains), quickly remove water from slope
171
What is grouting in slope modifications?
When permeable rocks are injected with cement to increase strength and reduce pore water capacity
172
What is shotcrete in slope modifications?
When loose surfaces are sprayed with concrete to prevent loose rocks from falling
