Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering.Once a rock has been broken down, a process called erosion transports the bits of rock and mineral away. No rock on Earth is hard enough to resist the forces of weathering and erosion. Together, these processes carved landmarks such as the Grand Canyon, in the U.S. state of Arizona. This massive canyon is 446 kilometers (277 miles) long, as much as 29 kilometers (18 miles) wide, and 1,600 meters (1 mile) deep.Weathering and erosion constantly change the rocky landscape of Earth. Weathering wears away exposed surfaces over time. The length of exposure often contributes to how vulnerable a rock is to weathering. Rocks, such as lavas, that are quickly buried beneath other rocks are less vulnerable to weathering and erosion than rocks that are exposed to agents such as wind and water.As it smoothes rough, sharp rock surfaces, weathering is often the first step in the production of soils. Tiny bits of weathered minerals mix with plants, animal remains, fungi, bacteria, and other organisms. A single type of weathered rock often produces infertile soil, while weathered materials from a collection of rocks is richer in mineral diversity and contributes to more fertile soil. Soils types associated with a mixture of weathered rock include glacial till, loess, and alluvial sediments.Weathering is often divided into the processes of mechanical weathering and chemical weathering. Biological weathering, in which living or once-living organisms contribute to weathering, can be a part of both processes.Mechanical WeatheringMechanical weathering, also called physical weathering and disaggregation, causes rocks to crumble.Water, in either liquid or solid form, is often a key agent of mechanical weathering. For instance, liquid water can seep into cracks and crevices in rock. If temperatures drop low enough, the water will freeze. When water freezes, it expands. The ice then works as a wedge. It slowly widens the cracks and splits the rock. When ice melts, liquid water performs the act of erosion by carrying away the tiny rock fragments lost in the split. This specific process (the freeze-thaw cycle) is called frost weathering or cryofracturing.Temperature changes can also contribute to mechanical weathering in a process called thermal stress. Changes in temperature cause rock to expand (with heat) and contract (with cold). As this happens over and over again, the structure of the rock weakens. Over time, it crumbles. Rocky desert landscapes are particularly vulnerable to thermal stress. The outer layer of desert rocks undergo repeated stress as the temperature changes from day to night. Eventually, outer layers flake off in thin sheets, a process called exfoliation.Exfoliation contributes to the formation of bornhardts, one of the most dramatic features in landscapes formed by weathering and erosion. Bornhardts are tall, domed, isolated rocks often found in tropical areas. Sugarloaf Mountain, an iconic landmark in Rio de Janeiro, Brazil, is a bornhardt.Changes in pressure can also contribute to exfoliation due to weathering. In a process called unloading, overlying materials are removed. The underlying rocks, released from overlying pressure, can then expand. As the rock surface expands, it becomes vulnerable to fracturing in a process called sheeting.Another type of mechanical weathering occurs when clay or other materials near rock absorb water. Clay, more porous than rock, can swell with water, weathering the surrounding, harder rock.Salt also works to weather rock in a process called haloclasty. Saltwater sometimes gets into the cracks and pores of rock. If the saltwater evaporates, salt crystals are left behind. As the crystals grow, they put pressure on the rock, slowly breaking it apart.Honeycomb weathering is associated with haloclasty. As its name implies, honeycomb weathering describes rock formations with hundreds or even thousands of pits formed by the growth of salt crystals. Honeycomb weathering is common in coastal areas, where sea sprays constantly force rocks to interact with salts.Haloclasty is not limited to coastal landscapes. Salt upwelling, the geologic process in which underground salt domes expand, can contribute to weathering of the overlying rock. Structures in the ancient city of Petra, Jordan, were made unstable and often collapsed due to salt upwelling from the ground below.Plants and animals can be agents of mechanical weathering. The seed of a tree may sprout in soil that has collected in a cracked rock. As the roots grow, they widen the cracks, eventually breaking the rock into pieces. Over time, trees can break apart even large rocks. Even small plants, such as mosses, can enlarge tiny cracks as they grow.Animals that tunnel underground, such as moles and prairie dogs, also work to break apart rock and soil. Other animals dig and trample rock aboveground, causing rock to slowly crumble.Chemical WeatheringFor instance, carbon dioxide from the air or soil sometimes combines with water in a process called carbonation. This produces a weak acid, called carbonic acid, that can dissolve rock. Carbonic acid is especially effective at dissolving limestone. When carbonic acid seeps through limestone underground, it can open up huge cracks or hollow out vast networks of caves.Carlsbad Caverns National Park, in the U.S. state of New Mexico, includes more than 119 limestone caves created by weathering and erosion. The largest is called the Big Room. With an area of about 33,210 square meters (357,469 square feet), the Big Room is the size of six football fields.Sometimes, chemical weathering dissolves large portions of limestone or other rock on the surface of the Earth to form a landscape called karst. In these areas, the surface rock is pockmarked with holes, sinkholes, and caves. One of the world’s most spectacular examples of karst is Shilin, or the Stone Forest, near Kunming, China. Hundreds of slender, sharp towers of weathered limestone rise from the landscape.Another type of chemical weathering works on rocks that contain iron. These rocks turn to rust in a process called oxidation. Rust is a compound created by the interaction of oxygen and iron in the presence of water. As rust expands, it weakens rock and helps break it apart.Hydration is a form of chemical weathering in which the chemical bonds of the mineral are changed as it interacts with water. One instance of hydration occurs as the mineral anhydrite reacts with groundwater. The water transforms anhydrite into gypsum, one of the most common minerals on Earth.Another familiar form of chemical weathering is hydrolysis. In the process of hydrolysis, a new solution (a mixture of two or more substances) is formed as chemicals in rock interact with water. In many rocks, for example, sodium minerals interact with water to form a saltwater solution.Hydration and hydrolysis contribute to flared slopes, another dramatic example of a landscape formed by weathering and erosion. Flared slopes are concave rock formations sometimes nicknamed “wave rocks.” Their c-shape is largely a result of subsurface weathering, in which hydration and hydrolysis wear away rocks beneath the landscape’s surface.Living or once-living organisms can also be agents of chemical weathering. The decaying remains of plants and some fungi form carbonic acid, which can weaken and dissolve rock. Some bacteria can weather rock in order to access nutrients such as magnesium or potassium.Clay minerals, including quartz, are among the most common byproducts of chemical weathering. Clays make up about 40% of the chemicals in all sedimentary rocks on Earth.Weathering and PeopleWeathering is a natural process, but human activities can speed it up.For example, certain kinds of air pollution increase the rate of weathering. Burning coal, natural gas, and petroleum releases chemicals such as nitrogen oxide and sulfur dioxide into the atmosphere. When these chemicals combine with sunlight and moisture, they change into acids. They then fall back to Earth as acid rain.Acid rain rapidly weathers limestone, marble, and other kinds of stone. The effects of acid rain can often be seen on gravestones, making names and other inscriptions impossible to read.Acid rain has also damaged many historic buildings and monuments. For example, at 71 meters (233 feet) tall, the Leshan Giant Buddha at Mount Emei, China is the world’s largest statue of the Buddha. It was carved 1,300 years ago and sat unharmed for centuries. An innovative drainage system mitigates the natural process of erosion. But in recent years, acid rain has turned the statue’s nose black and made some of its hair crumble and fall.Spheroidal WeatheringSpheroidal weathering is a form of chemical weathering that occurs when a rectangular block is weathered from three sides at the corners and from two sides along its edges. It is also called “onion skin” weathering.
The Appalachian Mountains in eastern North America once towered more than 9,000 meters (30,000 feet) high—taller than Mount Everest! Over millions of years, weathering and erosion have worn them down. Today, the highest Appalachian peak reaches just 2,037 meters (6,684 feet) high.
Term Part of Speech Definition Encyclopedic Entry acid Noun
chemical compound that reacts with a base to form a salt. Acids can corrode some natural materials. Acids have pH levels lower than 7.
acid rain Noun
precipitation with high levels of nitric and sulfuric acids. Acid rain can be manmade or occur naturally.
air pollution Noun
harmful chemicals in the atmosphere.
Encyclopedic Entry: air pollution alluvial Adjective
having to do with matter deposited by flowing water (alluvium).
(CaSO4) grey-white mineral found in sedimentary rocks. Also known as anhydrous calcium sulfate.
layers of gases surrounding a planet or other celestial body.
Encyclopedic Entry: atmosphere biological weathering Noun
process in which living or once-living organisms contribute to the disintegration of rocks and minerals (weathering).
isolated rock outcropping shaped as a steep-sided dome at least 30 meters (100 feet) tall.
(c. 563-483 BCE) Indian prince, spiritual leader, and founder of the Buddhist religion. Also called Prince Siddhartha and Gautama Buddha.
substance that is created by the production of another material.
deep, narrow valley with steep sides.
Encyclopedic Entry: canyon carbonation Noun
absorption of, or reaction with, carbon dioxide.
carbonic acid Noun
chemical produced as carbon dioxide dissolves in water.
underground chamber that opens to the surface. Cave entrances can be on land or in water.
chemical bond Noun
attraction between atoms, ions or molecules that enables the formation of chemical compounds.
chemical weathering Noun
process changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions.
type of sedimentary rock that is able to be shaped when wet.
dark, solid fossil fuel mined from the earth.
to shrink or get smaller.
crack in a rock.
chemical weathering process in which the freeze-thaw cycle of ice cracks and disintegrates rock. Also called frost weathering.
type of mineral that is clear and, when viewed under a microscope, has a repeating pattern of atoms and molecules.
to rot or decompose.
area of land that receives no more than 25 centimeters (10 inches) of precipitation a year.
Encyclopedic Entry: desert disaggregation Noun
process of rocks crumbling due to rain, wind, or other atmospheric conditions. Also called mechanical weathering and physical weathering.
to break up or disintegrate.
drainage system Noun
series of pipes, gutters, or other waterways used to carry off excess water.
act in which earth is worn away, often by water, wind, or ice.
Encyclopedic Entry: erosion evaporate Verb
to change from a liquid to a gas or vapor.
process describing the peeling away of outer layers, such as tree bark or rock sheeting.
to grow or get larger.
able to produce crops or sustain agriculture.
flared slope Noun
C-shaped landform consisting of a concave rock wall formed by weathering and erosion of subsurface rocks. Also called a “wave rock.”
weather pattern of temperatures below 0 degrees Celsius (32 degrees Fahrenheit).
frost weathering Noun
chemical weathering process in which the freeze-thaw cycle of ice cracks and disintegrates rock. Also called cryofracturing.
having to do with the physical formations of the Earth.
stone marking a person's burial place, often engraved with the person's name and dates of birth and death.
water found in an aquifer.
Encyclopedic Entry: groundwater gypsum Noun
(hydrated calcium sulfate, CaSO4) soft, colorless or white mineral.
type of physical weathering caused by the growth of salt crystals in and around rocks.
process of a substance or solution chemically combining with water.
process in which a compound is split into other compounds by reacting with water.
event or symbol representing a belief, nation, or community.
new, advanced, or original.
record that has been cut, impressed, painted, or written on a hard surface.
landscape made of limestone.
Encyclopedic Entry: karst landmark Noun
a prominent feature that guides in navigation or marks a site.
the geographic features of a region.
Encyclopedic Entry: landscape lava Noun
molten rock, or magma, that erupts from volcanoes or fissures in the Earth's surface.
type of sedimentary rock mostly made of calcium carbonate from shells and skeletons of marine organisms.
windblown soil or silt.
Encyclopedic Entry: loess marble Noun
type of metamorphic rock.
mechanical weathering Noun
process of rocks crumbling due to rain, wind, or other atmospheric conditions. Also called physical weathering.
nutrient needed to help cells, organs, and tissues to function.
to lower the severity of a natural or human condition.
having to do with the smallest physical unit of a substance.
large structure representing an event, idea, or person.
natural gas Noun
type of fossil fuel made up mostly of the gas methane.
Encyclopedic Entry: natural gas network Noun
series of links along which movement or communication can take place.
substance an organism needs for energy, growth, and life.
Encyclopedic Entry: nutrient oxidation Noun
chemical process of a substance combining with oxygen to change the substance's physical and molecular structure.
fossil fuel formed from the remains of ancient organisms. Also called crude oil.
physical weathering Noun
process of rocks crumbling due to rain, wind, or other atmospheric conditions. Also called mechanical weathering.
scarred with many small indentations.
full of tiny holes, or able to be permeated by water.
force pressed on an object by another object or condition, such as gravity.
common type of mineral.
materials left from a dead or absent organism.
natural substance composed of solid mineral matter.
part of a plant that secures it in the soil, obtains water and nutrients, and often stores food made by leaves.
to dissolve and form a brittle coating, as iron does when exposed to air and moisture.
mineral often used as a seasoning or preservative for food.
salt dome Noun
structure formed as water evaporates from a salty lake or sea. The remaining salt is buried by sediments, but eventually pierces through the rock, forming a hill.
salt upwelling Noun
process in which underground salt domes expand, impacting surrounding rock layers.
solid material transported and deposited by water, ice, and wind.
Encyclopedic Entry: sediment sedimentary rock Noun
rock formed from fragments of other rocks or the remains of plants or animals.
part of a plant from which a new plant grows.
type of physical weathering in which a single layer of rock is broken off. Also called contour weathering.
hole formed in a rock or other solid material by the weight or movement of water.
Encyclopedic Entry: sinkhole soil Noun
top layer of the Earth's surface where plants can grow.
substance in which a gas, liquid, or solid is evenly distributed in another medium.
beneath the surface or upper layer.
degree of hotness or coldness measured by a thermometer with a numerical scale.
Encyclopedic Entry: temperature thermal stress Noun
strain on material usually associated with expansion and contraction due to temperature changes.
rock, earth, and gravel left behind by a retreating or melting glacier.
existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
huge and spread out.
capable of being hurt.
the breaking down or dissolving of the Earth's surface rocks and minerals.
Encyclopedic Entry: weathering wedge Noun