Weathering, or natural erosion, refers to the process by which rocks, soils and minerals decompose when exposed to elements like water, air, salts or living organisms – often on-site and with limited movement compared to erosion.
Hydration and chemical weathering erode rock to produce caves, sinkholes, and towers – a feature known as karst. Other forms of weathering include oxidation, the freeze-thaw cycle of ice formation, and formation of gypsum.
When certain rocks come in contact with water, a chemical reaction occurs that results in weaker minerals that dissolve into the liquid and eventually carry away with the flow. This process is known as chemical weathering.
Chemical weathering can transform rocks into soil. For instance, when granite contains feldspar in contact with water it can chemically change into clay – creating a larger volume and permitting mechanical or physical weathering processes to gradually wear away its core material.
Carbon dioxide in the air reacts with rainwater to form carbonic acid, which then works to dissolve rocks and form caves like Carlsbad Caverns in New Mexico.
Water, both liquid and solid forms, is one of the primary agents of physical weathering. When temperatures fall, it seeps into cracks and crevices in rocks and, once frozen, forms wedge-shaped masses called frost wedging that widen cracks while breaking apart rocks.
Weathering plays an essential role in environments with few plants to support life, such as mountains and deserts, where plants would otherwise struggle to flourish. Furthermore, erosion speeds this process along.
Chemical weathering involves the action of substances dissolved in water or by chemical deposits deposited on rocks’ surfaces, including substances that dissolve in rainwater, as well as acid rainwater from carbon dioxide emissions combining with rainwater to form weak acids that attack and dissolve rock surfaces. Examples include abrasion (which smooths sharp or jagged rocks), acid rainwater reactions that accelerate chemical weathering such as carbon dioxide reacting with rainwater to form weak acids that attack and dissolve rock surface layers and acid rain (in which carbon dioxide reacts with rainwater to form weak acids that attack and dissolve rock surfaces). Carbon dioxide emissions from air pollution react with rainwater to form weak acids that attack and dissolving rock surface layers; some examples include abrasion (which smooth sharp or jagged rocks) and acid rain weathering (accelerating chemical weathering process); carbon dioxide in air reacts with rainwater to form weak acids that attack and dissolve rock surfaces as well as acid rain; acid rain reacting, where rainwater reacts with rainwater to form weak acids which attack and dissolving rock).
Wind transports particles of sand, dust or salt which erode away at rock surfaces through mechanical weathering. This is called mechanical weathering.
Water can also contribute to weathering. It seeps into cracks in rocks and freezes, weakening them further before breaking apart more easily. Furthermore, it forms ice wedges which split rocks. This type of weathering is often visible along roads where these wedges have worn away at their sides causing erosion.
Acidic rain is another contributor to weathering. Its sulfuric and nitric acids erode rocks. Plants, animals and microbes may also weaken and wear away rocks; biological weathering alters molecular structures of rocks to make breaking them down easier.
Air pollution arises from burning fossil fuels such as coal and oil in power plants, vehicles, homes and factories. This releases carbon dioxide, nitric oxide and sulfur dioxide into the atmosphere which then combine with water to form acid rain that accelerates chemical weathering of rocks.
Weather damage to plants and animals makes survival harder. Furthermore, it threatens vital sources of water and food needed for growth.
Time of exposure determines a rock’s susceptibility to weathering; quickly-buried lava rocks, for instance, tend to weather more slowly than sedimentary rocks that have been in the ground for millions of years. Weathering often serves as a precursor to creating soil; as sharp corners on rocks become rounded off and reduced in size over time, small bits of weathered minerals combine with plant, animal and fungal remains to form rich humus-rich layers in which organisms live or die and eventually form rich loam layers over time that cover any remaining vegetation or life forms to form rich soils that thrives over time.
Biological weathering (also called organic weathering) refers to the disintegration of rocks by plants and animals, including trees roots that enter cracks in rocks to expand and increase surface area exposed to physical and chemical weathering processes. This form of weathering works in concert with physical and chemical weathering to weaken and breakdown rocks over time. For instance, tree roots entering cracks of rocks create more surface area which increases exposure to other forms of weathering such as physical weathering.
Animals that burrow underground such as shrews, moles, earthworms and prairie dogs can also aid the weathering process by stirring and moving rock fragments to the surface and increasing exposure to physical, chemical and biological weathering processes. Living organisms may contribute to biological weathering by producing acids which corrode and dissolve rock minerals.