Weathering and soils Flashcards
What is weathering?
physical and chemical breakdown of rocks and minerals at the Earth’s surface.
What is mechanical weathering?
mechanical breakdown into smaller pieces
What is chemical weathering?
decomposition by chemical alteration
What is erosion?
physical removal of the weathered material
What processes can lead to the production of joints via mechanical weathering?
Tectonic, hydraulic, exfoliation, unloading, cooling
What are joints within rock?
weakness that can be exploited by other processes
What is exfoliation of rock?
after a stress release spalling off of sheets of material from the outer surface
What type of rock does exfoliation usually occur in?
granites (can lead to rounded outcrops)
What 2 types of secondary processes can exploit joints?
Ice wedging (freeze thaw)
Salt wedging
How does ice wedging exploit joints on rock?
Water from rain or condensation will flow into cracks in rocks when it freezes it will expand forcing the rock to fracture
How much can water increase in volume upon freezing?
9-10%
Where is salt wedging most likely to occur?
arid settings
What is the process of salt wedging?
gypsum or halite precipitates in pores and joints wedging them apart as salt crystals grow
What are some example of biogenic weathering?
plant roots into joints (slow as plant grows)
Animals can bore into rock
What is scree?
collection of broken up pieces of rock (loose/ unconsolidated)
What is talus?
talus cones – landforms made up of scree
What can chemical weathering be thought of as?
minerals equalising with the environment
What is the main type of chemical weathering?
dissolution
What are the different types of chemical weathering?
Hydration/dehydration
Hydrolysis
OILRIG
How can dehydration/hydration weather a material?
loss or gain of water can affect a minerals mechanical properties (make them weaker)
What is the dehydration example with gypsum?
when hydrated gypsum looses water turns to anhydrite
What is hydrolysis?
substitution of hydrogen ions in solution in acidic waters for cations in solid minerals
What makes rain water slightly acidic?
dissolved CO2 interacts with water to form carbonic acid (part of limestone dissolution)
How do calcium carbonate ad hydrogen cations interact?
hydrogen can replace calcium cation through substitution (limestone dissolution)
What can hydrogen ions do to solids?
can alter into different solids with different mechanical properties
What is oxidation and reduction?
Oxygen is lose of electrons
Reduction is gain of electrons
Where does most oxygen occur?
O2 dissolved in water
What factors can control chemical weathering?
Temperature
Moisture
pH
eH
How can temperature control chemical weathering?
higher temp= more energy for reactions
How can moisture control chemical weathering?
most weathering needs water - more water = stringer weathering
How can pH control chemical weathering?
H+ ions are needed for hydrolysis
Rainwater- 4-6.5 Ocean-8 (weathering more prevalent on land)
What is eH?
the redox potential
What is the redox potential?
likelihood of the gin or loss of electrons
What are the physical parameters of weathering?
Climate
Drainage
Relief
How is climate a parameter of weathering?
changes globally
Past events - snowball
Moving weather belts
Warm temp more weathering
Cold- freeze thaw
How is drainage a parameter of weathering?
well drained environments experience more continuous weathering as weathering reactions require weathering products to be removed
How is relief a parameter of weathering?
higher relief, speed of drainage and mass-wasting increases
What is mass wastage?
with increased altitude mass will become more unstable and prone to collapse
What can trees do to scree slopes?
The roots can bind materials having a stabilising effect
How can grain size affect weathering?
increased surface area of finer grained rocks/minerals means they weather faster than than larger grained rocks/minerals
What will happen to surface area and volume as a material in weathered?
surface area will increase
Volume remains the same
What composition of rock are more resistant to weathering?
Felsic - quartz rich closer to earth surface conditions
What composition of rock is least resistant to weathering?
Mafic- olivine furthest from surface conditions
Is there any isolation of weathering cycles?
No
What is the main weathering cycle?
carbonate-silicate cycles
What can soil be called the bridge between?
life and the inanimate world
What are mineral fragments and weathered rock called?
Regolith
What is soil?
combination of mineral and organic matter, water, and air and the portion of the regolith that plants live from
What controls the formation of soil?
parent material
Time
Climate
Plants/animals
Topography
How do you describe soil profile?
divided into horizontal layers called horizons
What might be the difference in soil profile between a mature and immature soil?
Mature will have well developed horizons
Immature might not have horizons
How many orders of soil are there?
12
What 2 soil horizons are in the top soil?
O
A
What is the O horizon in soil?
loose partly decayed organic matter
What is the A horizon in soil?
mineral matter mixed with some humus
What is the E horizon in soil?
Zone of eluviation and leaching
What soil horizon is classified as the sub-soil?
B
What is soil horizon B?
Accumulation of clay transported from above layers
What is soil horizon C?
partially altered parent material
What do you find below horizon C?
parent material
What is parent material in soil?
weathered rock or deposit soil forms from
