Chapter 6 -- Weathering, Erosion and Soil Flashcards
involves removing weathered materials from their place of origin by running water or wind.
Erosion
is the mechanical and chemical alteration of Earth materials at or near the surface.
Weathering
As rocks break down through differential weathering or erosion the resulting material becomes
Sediment
Types of Mechanical Weathering
Water freezes and expands in cracks in rocks, exerting pressure and breaking it. Repeated freezing and thawing disaggregates rocks into angular pieces that may tumble downslope and accumulate as talus.
Occurs in rocks that formed under pressure, like Intrusive igneous rocks (Granite).
Once the rock is exposed, it is no longer under pressure and begins to expand.
Diurnal and seasonal temperature ranges cause rock volumes to change.
Dark and light minerals expand at different rates.
Differential expansion causes rocks to break.
Any organic activity such as tree roots growing in cracks contributes to mechanical weathering.
Organic acids and tendrils of mosses and lichens aid in the chemical alteration of parent material.
Frost Action
Pressure Release
Thermal Expansion and Contraction
Activities of Organisms
The expansion of plutons that are exposed by uplift and erosion to atmospheric pressure.
Exfoliation Dome
Types of Chemical Weathering
Carbonate Rocks rapidly dissolve in acidic solutions.
The atoms making up the minerals in carbonates dissociate, the rock dissolves.
Sandstone may contain iron minerals that will breakdown when exposed to the atmosphere
The atoms making up the minerals dissociate, as the rock rusts away.
Hydrogen ions react with and replace positive ions in potassium feldspar.
Forms clay minerals.
Solution
Oxidation
Hydrolysis
Non lithified material
Soil
Thin upper weathered layers
Consists of four major horizons: O,A,B,C
Horizons differ in texture, structure, composition and color.
Soil Profile
Soil Profile Layers
Thin layer of humus and partially decayed plants
Organically rich, important for plant growth.
Zone of accumulation, especially of clays.
Partially weathered in place bedrock.
O
A
B
C
Types of Soil Profiles
Humid, cool soil
A horizon rich in Al and Fe leached
High clay, iron in B horizon
Dry, hot soil
Low clay
High CaCO3 (caliche) in B horizon.
Humid, hot soil
Extremely deep, leached, low humus
Pedalfer
Pedocals
Laterite
Two types of sediment
Solid particles, products of mechanical weathering
minerals precipitated from solution, products of chemical weathering
Detrital
Chemical
Converts sediments into sedimentary rock
Lithification
Two types of Lification
Reduction in pore space (open space) and volume)
Reduction in pore space and an increase in mechanical strength
Compaction
Cementation
Made of solid particles of pre existing rocks
Classified according to grain (particle) sizes, in decreasing diameter
Detrital Sedimentary Rocks
Made of ions and compounds released by chemical processes such as:
Weathering
Precipitation by chemical reactions
Metabolism of organisms
Chemical and Biochemical Sedimentary Rocks
