Weathering | National Geographic Society (2023)

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 ofbornhardts, 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 Weathering Chemical weathering changes the molecular structure of rocks and soil. For 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 People Weathering 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.

Fast Fact

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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.

Fast Fact

Weathered Mountains
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.

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FAQs

What is weathering in geography? ›

Weathering is the breaking down or dissolving of rocks and minerals on Earths surface. Once a rock has been broken down, a process called erosion transports the bits of rock and minerals away. Water, acids, salt, plants, animals, and changes in temperature are all agents of weathering and erosion.

What are the 4 types of weathering in geography? ›

There are three types of weathering, physical, chemical and biological.

Why is weathering important in geography? ›

Weathering is a very important process because it breaks down rocks and minerals, which helps to create soil. Soil is necessary for the growth of plants, which provide food and oxygen for animals and humans. Weathering also creates landforms such as mountains, valleys, canyons, and plateaus.

How does weathering affect the environment? ›

Over thousands to many millions of years, the weathering and erosion of rocks affects Earth's surface features (that is, its topography), soil, nutrients on the land and in the ocean, and the composition of the atmosphere, which in turn affects global climate and ecosystems.

What are examples of weathering? ›

Weathering is the wearing away of the surface of rock, soil, and minerals into smaller pieces. Example of weathering: Wind and water cause small pieces of rock to break off at the side of a mountain. Weathering can occur due to chemical and mechanical processes.

What is weathering and why does it occur? ›

Physical weathering occurs when physical processes affect the rock, such as changes in temperature or when the rock is exposed to the effects of wind, rain and waves. Water can get into cracks in a rock and, if it freezes, the ice will expand and push the cracks apart.

What are the 5 factors of weathering? ›

Factors affecting weathering
  • Mineral composition.
  • Grain (Particle) size.
  • Presence of lines of weakness.
  • Climate.
Jul 16, 2020

What are the 5 factors that affect weathering? ›

Physical forces like temperature and humidity, chemical forces like oxidation and carbonation, and biological forces like burrowing by animals and human activities are significant factors of weathering.

What is the main type of weathering? ›

The two main types of weathering are physical and chemical weathering.

What are three facts about weathering? ›

The Earth's surface gets broken down through weathering.

Weathering wears away rocks and soil. Water is often the main cause of weathering, either as rain or ice. Rainwater can easily enter cracks in rocks or sidewalks. If this happens during cold months, the water may freeze and expand in the crack.

What is the most important thing about weathering? ›

Perhaps the most important aspect of weathering is its role in the formation of soil. Without soil, life as we know it on earth would not exist. Soil is a much overlooked element of earth's processes and, at current rates of human use and abuse, is becoming a finite resource.

What is the most important effects of weathering? ›

Landslides and soil erosion are two major effects of weathering.

How does weathering cause climate change? ›

The faster weathering reactions would result in enhanced consumption of CO2, eventually reducing the greenhouse effect and causing climate to cool.

How does climate cause weathering? ›

Rainfall and temperature can affect the rate in which rocks weather. High temperatures and greater rainfall increase the rate of chemical weathering. 2. Rocks in tropical regions exposed to abundant rainfall and hot temperatures weather much faster than similar rocks residing in cold, dry regions.

What are the characteristics of weathering? ›

Chief characteristics of weathering

(1) Weathering involves disintegration or decay of solid rocks. (2) It depends on climatic elements and on the characteristics of rocks. (3) Weathering affects the surface of the earth. (4) Weathering causes formation of soil.

What are the 4 main causes of weathering? ›

Lesson Summary

Physical weathering refers to the mechanical breakdown of rocks due to changes in temperature, wind, water, and pressure. One example of physical weathering is when water freezes in the cracks of a rock, causing the stone to break apart as the ice expands within the spaces filled by the water.

What are 3 types of weathering with examples? ›

There are three types of weathering: biological, chemical, and mechanical. Rain is actually mildly acidic, and therefore slowly eats away at rocks - this is an example of chemical weathering. Plants and animals also cause rocks to erode - this is an example of biological weathering.

How do humans affect weathering? ›

When we build cities, we forcibly move countless tons of rocks and dirt, usually dumping it into a river system, affecting both the topography and the river itself. Finally, pollution can impact weathering by weakening the environmental safeguards against erosion, such as tree root systems that hold soil.

Which of the following best describes weathering? ›

The breaking down of rocks, soil and minerals by external agents(wind, rivers etc) is called weathering.

Where does weathering take place? ›

Where does it occur? Physical weathering happens especially in places places where there is little soil and few plants grow, such as in mountain regions and hot deserts.

What are the three main causes of weathering? ›

Plant and animal life, atmosphere and water are the major causes of weathering. Weathering breaks down and loosens the surface minerals of rock so they can be transported away by agents of erosion such as water, wind and ice.

What are the 10 types of weathering? ›

There are four types of weathering: Chemical weathering. Physical weathering. Biological weathering.
...
Types of Mechanical Weathering
  • Freeze-thaw weathering or Frost Wedging.
  • Exfoliation weathering or Unloading.
  • Thermal Expansion.
  • Abrasion and Impact.
  • Salt weathering or Haloclasty.

What are the 7 types of physical weathering? ›

Physical Weathering
  • Abrasion:
  • Frost Wedging:
  • Biological Activity/Root Wedging:
  • Salt Crystal Growth:
  • Sheeting:
  • Thermal Expansion:
  • Works Cited.
Jun 8, 2020

What are the 2 types of weathering? ›

The two main types of weathering are physical and chemical weathering. This page describes mechanical (physical) weathering (and more).

What are the 4 causes of weathering? ›

Weathering breaks down the Earth's surface into smaller pieces. Those pieces are moved in a process called erosion, and deposited somewhere else. Weathering can be caused by wind, water, ice, plants, gravity, and changes in temperature.

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