Weathering, or erosion, refers to the gradual breaking down and dissolving of rocks and minerals on Earth’s surface due to contact with elements like water, oxygen, acids, salts plants and animals.
Rabbit burrowing could create a larger crack in a rock face, weakening and eventually dislodging it altogether. Other physical forms of weathering include abrasion and erosion processes (see image below).
Water
Water is the foundation of all weathering processes, helping wear away at rocks by physically breaking it up or chemically dissolving their minerals, as well as making rocks more weatherproof.
Rainwater is slightly acidic and gradually wears away at rocks such as granite or limestone over time, due to carbon dioxide combining with water as raindrops fall from the atmosphere. Chemical weathering can be enhanced by adding pollutants that produce sulfuric or nitric acids that form acid raindrops faster.
Plants and animals can help break apart and move rocks as well, using their roots to wedge into cracks in rock face or trample it as they search for food and shelter.
Ice
Ice is an integral component of Earth’s system, from glaciers and snowpacks to underground freezing processes and polar ice caps.
Ice can weather rocks by breaking them into smaller pieces through mechanical weathering, an effective technique in areas with temperatures fluctuating above and below freezing.
Mechanical weathering processes such as abrasion and crystallization occur when rocks rub together; thermal fractures occur when hot and cold rocks collide, and hydration shattering removes minerals from rock surfaces by water.
Acids
Acids are substances with a low pH value and can weaken and dissolve rocks and metals through chemical reactions, both naturally and through human activities such as burning fossil fuels.
Chemical weathering processes such as hydrolysis (the dissolving of rock minerals in water), oxidation (the breakdown of rock by oxygen, often giving iron-rich rocks their characteristic red hue), and carbonation (rainwater reacting with limestone) all constitute examples of weathering in action; all three require moisture for maximum speedy effects in hot, humid climates.
Weathering produces the curved layers seen on spheroidal rocks as a result of chemical weathering (Figure 6.6). Chemical weathering also contributes to soil formation – an essential ingredient of life as we know it.
Salts
As temperatures drop, crews work tirelessly to spread salt over roadways to keep them clear of ice, but as temperatures decrease it becomes less effective.
Salts are nonvolatile ionic compounds created through the neutralization reaction between acids and bases, typically without producing volatile by-products such as volatile sulfur compounds. When solid, they often form crystalline structures with relatively high melting and boiling points; when dissolved in water they become highly electrically conducting and are no longer insulating properties when solid.
Acidic salts break blue litmus paper while basic salts make it lighter. The most famous salt is sodium chloride – more commonly known as table salt – which lowers the freezing point of ice and snow by about 15 degrees but beyond this it becomes ineffective.
Plants
Weathering and erosion both transform Earth’s surface over time. They flatten mountains, extend plains and even wash away its highest peaks back into the ocean.
Different minerals weather at various rates; for instance, calcite can weather more rapidly than feldspar. Furthermore, rock’s structure also can influence how it weathers: massive rocks like granite do not contain planes of weakness that allow water to infiltrate them while sedimentary beds contain bedding planes which allow infiltrating through.
Chemical weathering alters rock composition through oxidation, hydrolysis and carbonation processes. Carbonic acid in rainwater reacts with minerals on exposed rock surfaces to form weak acids which slowly dissolve minerals over time.
Animals
Certain animals can sense environmental signals that appear when weather changes occur, like sharks that sense air pressure drop-off prior to storms and act oddly before fleeing from them for safety. This often prompts them to act oddly or flee.
Animals that dig and trample rocks also contribute to physical weathering by widening cracks in rocks, which enables further weathering processes to take place.
Chemical weathering occurs when microbes break down rock minerals. Rain accelerates this process by activating acid raindrops on stones such as limestone. This causes irreparable damage to buildings, statues and gravestones which become unreadable; acid rain also erodes soil exposing rock fragments further weakening them.