Class 14 - Weathering

Geomorphology

________ is a sub- discipline of geography concerned with the origin of and processes by which landforms change.

Denudation

________ refers to all exogenic processes working to reduce elevations or relief (i.e., flatten the surface)

1. weathering

2. mass movement

3. erosion

4. transportation

5. deposition

Limestone

________ is a sedimentary rock that forms in the ocean from shelled marine organisms (i.e., in the ocean)

Chemical weathering

processes that alter rock chemistry, changing it from one mineral state to another, weakening the overall structure of solid rock.

Physical weathering

processes that modify the physical state of rock only, no chemical change.

Exogenic processes

processes that destroy or modify landscapes.

Landforms

the product of endogenic and exogenic processes

Endogenic processes

build ‘initial landscapes (e.g., rock formation, mountain building)

Weathering

refers to processes that physically or chemically alter rock at or near the surface

Physical weathering

processes that __*modify the physical state of rock only*__, no chemical change

* frost action (freeze thaw)
* root wedging (tree roots)
* salt-crystal wedging
* impact from precipitation, abrasion, and rock falls
* pressure-release jointing/exfoliation

Chemical weathering

processes that __*alters rock chemistry, changing it from one mineral state to another*__, weakening the overall structure of solid rock

* __*Dissolution*__ of carbonate minerals by acidic precipitation (dissolution of limestone or the carbonate cement within sedimentary rock)
* __*Hydration*__ of minerals
* Hydrolysis; deconstructs weak silicate minerals to form clay
* __*Oxidation,*__ rusting of iron-bearing minerals in rock

Karst topography

* associated with limestone dissolution. Limestone is a sedimentary rock that forms in the ocean from shelled marine organisms (i.e., in the ocean).

Erosion

refers to the translocation of weathered materials by wind, water or ice, driven by gravity and solar energy

Erosion Processes (include driving vs resisting forces)

when driving forces exceed the resisting forces

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* **Driving forces -** climate, gravity, momentum, slope, tectonics
* **Resisting forces -** friction, inertia, cohesion of particles, vegetation

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Factors influencing weathering processes

* Rock type
* Rock chemistry
* Rock composition
* Rock structure
* Climate
* Sub-surface water
* Slope orientation
* Vegetation

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\- Parent Material: the consolidated bedrock/ unconsolidated rock from which weathered materials originate

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\- Regolith: the product of weathering. Includes fractured rock, fine sediments, and soil. Susceptible to erosion and transport (because it is not mechanically bound to the parent material)

Dynamic Equilibrium Framework

* Phase 1 - little change in elevation, endogenic and exogenic factors are roughly balanced
* Phase 2 - rapid elevation increase where endogenic > exogenic briefly. roughly equal thereafter.
* Phase 3 - Highly variable but lower elevations, exogenic > endogenic factors
* Phase 4 - Stabilizing mean elevation, overall balance between endogenic and exogenic factors

Mass Movement

* Type of erosion where massive quantities of earth materials flow downslope under the force of gravity, and in some cases aided by other factors that reduce resisting forces such as cohesion and friction.


* Classes of mass movement, sorted by rate of movement and wetness

6 types of mass movements

* Soil Creep: ***Slow, Dry*** Mass movement
* important in cold regions
* Rock Fall: ***Dry, Fast*** Mass movement
* topples are a type of rock fall, fractured rock that is forward leaning
* Rotational slump/slide: ***mostly dry and not too fast/slow***
* Mass has slumped down and sticks out
* Translational slide: ***Slow and middle of slow/fast***
* Mudflow: ***wet and fast***
* higher water content, reduces friction between sediments and regolith (includes boulders and small clay particles)
* Human-induced ***scarification***: ***leads to slides***
* moves more earth today than all natural processes combined