Weathering and Erosion
Weathering - processes at or near Earth’s surface that cause rocks and minerals to break down
Erosion - process of removing Earth materials from their original sites through weathering and transport
WeatheringMechanical Weathering - processes that break a rock or mineral into smaller pieces without altering its composition
Chemical Weathering - processes that change the chemical composition of rocks and minerals
Agents of Mechanical Weathering
frost wedging thermal expansion and contraction mechanical exfoliation abrasion by wind and water plants and animals
Chemical Weathering
The process that breaks down rock through chemical changes.
The agents of chemical weathering– Water– Oxygen– Carbon dioxide– Living organisms– Acid rain
Oxygen Iron combines
with oxygen in the presence of water in a process called oxidation
The product of oxidation is rust.
Acid Rain Compounds from burning coal, oil
and gas react chemically with water forming acids.
Acid rain causes very rapid chemical weathering.
Karst Topography A type of landscape in rainy regions
where there is limestone near the surface, characterized by caves, sinkholes, and disappearing streams.
Created by chemical weathering of limestone.
Weathering Controls The type, rate and extent of weathering
depends upon several controlling factors: • Climate dictates the type of weathering
processes that operate, largely by determining the amount of water available and the temperature at which the processes occur. Chemical reactions are faster at higher temperatures, while frost wedging occurs in colder climates.
Rock Type determines the resistance of the rock to the weathering processes that operate in that particular environment. Each rock type is composed of a particular set of minerals, which are joined together by crystallization, chemical bonding or cementing. When the forces of plate tectonics move these rocks from the environment in which they formed and expose them to the atmosphere they begin to weather.
Rock Structure: highly jointed or faulted rocks present many planes of weakness along which weathering agents (e.g. water) can penetrate into the rock mass (Figures 1 & 2).
Time: the duration of the period that the same type of weathering has been operating, uninterrupted by climatic change, earth movements, and other factors, determines the degree and depth to which the rocks have been weathered.
Topography: the slope angle determines the energy of the weathering system by controlling the rate at which water passes through the rock mass. Generally, higher, or tectonically active areas with steeper slopes have more dynamic weathering systems, whereas flat plains have slower weathering systems.
Erosion Processes Erosion processes are usually considered
under four distinct categories: • Mass Wasting: the processes that occur on
slopes, under the influence of gravity, in which water may play a part, although water is not the main transporting medium. Mass wasting, or landsliding
Rapid or Slow Changes Glaciers melt and form rivers. Wind weathers rocks into sand. Earthquakes move land and rocks. Rivers carry sediment and build deltas.