subaerial processes (weathering) Flashcards
difference between weathering and erosion
-weathering is in situ
-erosion is the movement of broken down sediment
what does sub aerial mean
processes occurring at the land surface
what do weathering processes do
-mechanically disintegrate and/or chemically decompose rocks where they are in (in situ)
-increase vulnerability to mass movement
2 processes of mechanical weathering
-freeze-thaw
-salt crystallisation
whats freeze thaw
-when water expands in volume when freezing
-exerts force within cracks and fissures
-repeated cycles force cracks open
what rocks are vulnerable to freeze thaw
-any rocks w cracks/fissures
which mechanical process is more common on the UK coast
-salt crystallisation
-freeze thaw is uncommon
what is salt crystallisation
-growth of salt crystals in cracks and pore spaces
-exert a breaking force (although less than for freeze thaw)
what rocks are vulnerable to salt crystallisation
-porous and fracture rocks
-effect is greater in hotter, drier climates where evaporation and precipitation is more pronounced
what are the 3 chemical weathering processes
-carbonation
-hydrolysis
-oxidation
what is carbonation
-dissolution of limestone due to rainfall
what rocks are vulnerable to carbonation
-limestone and other carbonate rocks
what is hydrolysis
-breakdown of minerals to form new clay minerals
what rocks are vulnerable to hydrolysis
-igneous and metamorphic rocks
what is oxidation
-addition of oxygen to minerals
-produces iron oxides and increases volume contributing to mechanical breakdown
what rocks are vulnerable to oxidation
-sandstones
-siltstones
-anything that contains iron compounds that can be oxidised
what are the biological processes of weathering
-plant roots
-rock boring
effect of plant roots - weathering
-trees and plant roots growing in cracks and fissures forcing rocks apart
effect of rock boring
-species of clams and molluscs bore into rock and may secrete chemicals that dissolve rocks
what’s the name for when organic acids from plant roots and decaying mater bind to metal ions (resulting in rocks decomposing)
-chelation
where is weathering a dominant process
-low energy
-low tidal range coasts
-such as the Mediterranean
what influences weathering
-meteorological factors such as annual temperature and rainfall
example of the influence of lithology on weathering
-basalt
-weathers at 1-2mm per 1000 years
what type of weathering dominates in cold climates
mechanical
