Physical/Mechanical Weathering
- Disintegration of rock by physical processes without changes in chemical or mineral composition
- Regions devoid of vegetation
- Stress applied in and around rocks
Pressure/Release
- Disruptive expansion when the overburden is removed from rocks that have been under high pressure at depth
- Rocks created under high pressure exposed to atmosphere, substantial release in pressure
Freeze-thaw
- Most common form of mechanical weathering
- Water enters cracks in daytime, freezes overnight at -22
- ice occupies 9% more volume than water, causing rocks to shatter off of the main body
Salt Crystalization
- if water entering pore space in rocks is slightly saline, as the water evaporates, salt crystals are likely to form
- growing larger + stresses in rock
- disintegrate and break apart
- often occurs in deserts where capillary action draws moisture to the surface
Thermal Expansion and Contraction
- Rocks expand when heated and contract when cooled
- Most common in deserts
- Situations of extreme temperature
- Changes in temperature can cause different minerals within a rock to expand and contract at different rates
Biological Weathering
- Plant roots grow into and extend along joins and crevices and pry rocks apart over time
- Some plants that grow on the rock surface can release a weak acid and work to further weather the rock
Chemical Weathering
- Break down of rock resulting from surface processes that change the chemical composition of the original material
- Chemical reactions between the elements and the atmosphere and or groundwater, produces a change in substances and solubles
Role of Water
Rate and intensity of chemical weather is greatly influenced by the amount of precipitation in the area
- water removes the weathering products to expose fresh rock for continued weathering
Solution
- Some minerals are soluble and dissolve in water
- Minerals composing the earths crust are soluble to vary degrees in water
- Water also removes the weathering products to expose fresh rock for continued weather
Factors that Increase Rates of Solubility
- pH of water greatly affects the rate of solution - a lower pH = more acidic = faster break down of rocks
- Solubility of materials often increases with rising temperatures
- Circulation also hastens solution by removing dissolves ions from the mineral surface and replace them with fresh water
Oxidation
- Occurs when rocks are exposed to oxygen via the air or water
- Causes rocks to crumble more easily
- Ferric oxides (rust) are insoluble, instead they precipitate as solid compounds on the surface of the rock giving it a yellow/brown/red coating
Hydrolysis
- Most significant chemical process in the decomposition of rocks and the formation of clays
- Hydrogen in water reacts with minerals in the rock
- The formation of the new mineral disrupts the mineral structure and causes the rock to begin breaking down on the mineral level
Carbonation
- Rain water contains carbon dioxide in the solution - Carbonic Acid
- Weak acid reacts with rock with are composed of calcium carbonate
- Limestone dissolves and removed by running water
- Carboniferous limestone which is well-joined and layered in combination with carbonation results in the development of a variety of Karst landforms including cavern system
Types of mass wasting
Rockfall
Rockslide
Slump
Soliflucation
Slump
Most likely in consolidated clays or soils (think slipping back in your seat)
Rockfall
Most likely in fractured rocks at cliffs
Descent of loose rocks
Flow
Most likely in sandy sediments or soils, or unconsolidated claus, especially if wet
Rockslide
Rock failure in which part of the bedding plane of failure passes through intact rock and material collapses en mass and not in individual blocks
Solifluction
The gradual movement of wet soil or other material down a slope, especially where frozen subsoil acts as a barrier to water
Frost shattering
Temperatures are often around freezing point
rocks have exposed cracks
water enters cracks during warmer day and then freezes at night, splitting open rock
Organic weathering
Plants break up rocks with their growing roots or plant acid
Acid Rain
Rainfall made acidic by atmospheric pollution and causes environmental harm
Hydration
Lack of hydration in the rock causes it to become brittle and crack
