Dynamic Surface L3 Flashcards
Where are production and transport rates of sediment/particles highest?
Areas of recent tectonic activity
What is weathering?
The process through which clastic sediment particles are formed and which provides dissolved ions for non-clastic sediments
What is the regolith?
The weathered zone of bedrock
What is physical/mechanical weathering?
The process by which rock is broken down mechanically into smaller fragments
What are the 6 types of physical/mechanical weathering?
Exfoliation/exhumation
Insolation weathering
Hydration weathering
Frost shattering
Salt weathering
Wind erosion
What is exfoliation/exhumation?
The sudden reduction of pressure on a rock resulting in the formation of joints parallel to the top of the rock body between the rock body itself and the material below.
What is insolation weathering?
Repeated variation in the temperature of a rock (day-night cycles) causes continuous expansion and contraction
What is hydration weathering?
The reaction of water with a rock, depending on its mineralogy, can cause swelling/expansion
What is frost shattering?
Water enters cracks in a rock, freezes and expands by about 9% and melts.
What is salt weathering?
Salt spray is blown at a rock, the water then evaporates leaving the salt to crystallise between loose grains of the rock surface, forcing them apart.
What is wind erosion?
Wind picks up fine grains and scours away less resistant rocks and leaves behind more resistant rocks.
Where is chemical and biochemical weathering the most rapid?
Tropic and humid temperate lowlands
Which area of the crust does chemical and biochemical weathering affect and why?
The uppermost 100m of the crust as below this, fractures close and cements reduce permeability.
What 2 factors can accelerate chemical weathering?
Dissolved organic acids from plant debris
Ligands
What is congruent dissolution?
The complete disappearance of a material with no minerals left behind to form any kind of residue
What are the chemical reactions involved in the process of congruent dissolution?
H2O + CO2 –> H2CO3 (carbonic acid)
CaCO3 (limestone) + H2CO3 –> Ca2+ + 2HCO3- (bicarbonate ions)
In what conditions do carbonate minerals disappear more rapidly and why?
Cold water as in warm water CO2 is driven off as gas so there is less CO2 to react with water
What is a collapse breccia?
The collapsed roof of a cavity where minerals have been dissolved
What does the rate at which silicate minerals react with water depend on?
The relative strength of cation-oxygen bonds (e.g. Si-O, Al-O, Mg-O)
What does the Goldich series display?
The increasing susceptibility of mineral families to chemical weathering
What is the relationship between the rate of chemical weathering and the complexity of a mineral structure?
The rate of chemical weathering increases as the structural complexity of a mineral decreases (i.e. the simplest minerals will erode the quickest)
What mineral groups produce insoluble Fe3+ oxides and hydroxides via chemical decomposition?
Olivines
Pyroxenes
Amphiboles
Micas
What mineral groups produce insoluble clay minerals via chemical decomposition?
Amphiboles
Micas (biotite and muscovite)
Feldspars
What does quartz produce via chemical decomposition?
Quartz grains
How does bauxite, Al(OH)3, form?
Deep leaching of Al-containing silicates in humid tropical climates
How does laterite, Fe(OH)3, form?
The leaching of ferromagnesium minerals in humid tropical climates
What are 4 types of reactions that chemical weathering can induce?
Redox reactions
Hydration
Acid hydrolysis
Cation exchange
What is an example of a chemical weathering redox reaction?
Pyrite to iron III hydroxide
What is an example of a chemical weathering hydration reaction?
Haematite to limonite
What is an example of a chemical weathering acid hydrolysis reaction?
Dissolution of limestone by carbonic acid
What types of minerals are clays?
Sheet or phyllosilicate minerals
What are the 2 types of sheets in clay minerals?
Tetrahedral
Octahedral
What is the name of the 2-layered clay?
Kandite
What is the name of the 3-layered clay?
Smectite
What is an example of a kandite (2-layered clay)?
Kaolinite
How do 3 layered smectites change as they react with water?
Smectites can shrink and swell as water is absorbed and desorbed
What is the significance of clay minerals?
Can reduce the permeability of sediment and rock
Kaolinite is an indicator of low latitude weathering of more complex silicates
Smectite is an indicator for temperature weathering (they swell). Also used for lining ponds
