Weathering and Erosion Flashcards
Define weathering
The destructive process by which rocks are disintegrated into smaller particles and ions by exposure to atmospheric agents.
What is the first stage of the sediment redistribution process
Weathering
Define erosion
A mechanical process that loosens and transports soil and rock fragments downhill. Different rocks have variable resistance.
Define physical weathering
Process of disintegration of a rock without chemical change
Ex. Zones of weakness, frost wedging, mineral crystallization
Define Zone of weakness
Joints or cracks form along pre-existing planes of weakness.
No motion between two surfaces between cracks
Define frost wedging
Process of water expansion as it freezes in joints. This pushes or wedges the rock apart.
Define Mineral crystallization in weathering process
Minerals such as salt grow and usually form from evaporating solutions.
Define sheeting and exfoliation
From igneous rocks, when brought to the surface a pressure release occurs during uplift which causes fracturing parallel to the rock surface
Spheriodal weathering
The peeling of small rock bodies into onion like layers
Define Weathering from biological activity
Process of displacement of minerals from roots, burrowing organisms, and human activity
Surface area changes due to weathering
Physical weathering increases surface area
Chemical weathering rates are directly proportional to surface area
Therefore, physical weathering increases chemical weathering rates.
Why does chemical weathering occur
Water plays a major role
Water is an oxygen atom that is covalently bonded with two hydrogens at an angle of 105 degrees.
This gives the molecular polarity which allows it to be more adhesive to other substances, and be cohesive to other droplets
Because water is a universal solvent, ions can pry ions away from crystals
Define chemical weathering
A series of chemical reactions thereby altering the original composition of the rocks.
Why is the fact that Carbon dioxide when combined with water creates carbonic acid, relevant for chemical weathering
Rainwater is naturally weakly acidic
Chemical weathering in carbonate rocks
Rain can dissolve carbonate rocks completely over time.
This is due to layered properties of carbonate rocks.
Dissolved constituents run off into surface and subsurface over time.
Ex. Travertine
Chemical weathering of silicate rocks
Silicate rocks have less resistant minerals such as feldspar which partially dissolves in water.
What doesn’t dissolve is changed into clay minerals
Minerals with low solubility, such as quartz are not changed.
Chemical weathering in iron Rich rocks
Iron reacts with oxygen in water and atmosphere to form hematite or rust.
Bowen’s reaction series and chemical weathering rate
High temp. + pressure = rapid weathering
Low temp. + pressure + slower weathering, whatever doesn’t dissolve forms clay.
Inmature sandstones, test question on this
Contain a mix of clay Martix’s and sand grains that are angular and poorly sorted.
What is the weathering product of quartz
Quartz
What do most minerals produce
Clay minerals
Factors controlling weathering rates
Parent rock:
Climate: chemical weathering is favoured by humid tropical climates. Physical weathering favours cold climates
Soil: traps water and acidifies it further, which enhances weathering
Time
Define soil
Transition between biosphere and geosphere
Factors of soil formation.
Climate Parent material Topography Organisms Time
How is Nitrogen bacteria relevant to weathering**test question on this
Bacteria converts N2 into compounds such as Ammonia, nitrates which allows plants to make DNA and amino acids.
Human factors that cause erosion
Loss of rainforest exposes soil, which increases topsoil erosion,
Wind erosion and the human element
Unprotected farmland can lead to massive dust storms
What are the special properties of water
Polarity Cohesion Adhesion Hydrogen Bonds Universal solvent
Why are nitrogen fixing bacteria so important in soils.
The bacteria absorb nitrogen from the atmosphere then converted into nitrogen compounds. These compounds are absorbed by plants and used to make DNA amino acids and enzymes. That nitrogen is an essential component of production of proteins and DNA in biological life
What is the relationship between Bowens Reaction Series and Weathering*** test question
Minerals at the top of the Bowen series crystallize under high temperatures and pressures, and chemically weather at a faster rate than minerals ranked at the bottom.
