Weathering is a natural process that occurs over time. It can often be seen in the peeling paint on an old building or the rugged texture of rocks near the shoreline. Physical weathering involves the breakdown of rock and soil through physical means, such as wind, water, and temperature changes.
But what isn’t an example of physical weathering? That’s what we’re here to discuss today. This topic may seem straightforward, but there are many misconceptions out there about what qualifies as physical weathering and what doesn’t.
If you’ve ever wondered why some materials break down more easily than others, then you won’t want to miss this informative article. We’ll explore some common examples of physical weathering and narrow down what doesn’t count as an example.
“Science is a way of thinking much more than it is a body of knowledge.” -Carl Sagan
Whether you’re a student studying geology or simply someone who enjoys learning new things, this post is for you. So sit back, grab a cup of coffee, and let’s get started.
Dissolution
Dissolution is a process in which a substance dissolves into another substance, typically a solid dissolving in a liquid. This is not an example of physical weathering because it does not involve the breaking down of rock or other materials by physical means such as temperature changes or pressure.
Water as a Solvent
One common type of dissolution occurs when a solid dissolves in water, since water is often referred to as the universal solvent due to its ability to dissolve many different types of substances. When a solute (the substance being dissolved) comes into contact with a solvent (the liquid doing the dissolving), the solute particles will begin to separate and become surrounded by individual molecules of the solvent. Eventually, all of the solute particles will be broken down and dissolved within the liquid.
This process can occur naturally in the environment, as minerals are often slowly dissolved and carried away by groundwater over time. It can also happen as a result of human activities, such as wastewater discharge from industrial facilities that contain high levels of dissolved chemicals and pollutants that can negatively impact aquatic ecosystems.
Chemical Reactions
In addition to simple dissolution, some substances may undergo chemical reactions when they come into contact with water or other liquids. For example, certain metals may corrode and break down when exposed to moisture or acidic solutions, while other substances may react with water to form new compounds.
These chemical reactions can lead to significant changes in the properties of a material, potentially making it more susceptible to physical weathering processes like cracking, chipping, or crumbling.
Influence of Temperature
The rate at which dissolution and other types of chemical reactions occur may be influenced by factors such as temperature, pressure, and the presence of other chemicals. In general, higher temperatures tend to speed up the dissolution process by increasing the energy of the molecules involved.
It is important to note that some substances may be more resistant to dissolution at high temperatures due to their unique chemical properties and molecular structures. Additionally, extreme changes in temperature or pressure can sometimes cause physical weathering processes like expansion and contraction, which can further break down a material over time.
“Dissolution is an important geochemical process that plays a role in many natural phenomena, from the erosion of rocks and minerals to the development of underground aquifers.”
Chemical Weathering
Acid Rain
One type of chemical weathering is acid rain. This occurs when pollutants in the air, such as sulfur dioxide and nitrogen oxide, mix with water droplets to create acidic precipitation. Acid rain has a pH level below 5.6, which means it is more acidic than normal rainwater.
Acid rain can cause significant damage to buildings and structures made of limestone or marble as well as natural environments such as forests and lakes. The acid in the rainfall reacts with the minerals in these materials, resulting in corrosion and erosion.
“The forest floor absorbs about four times as much acid rain each year as it did thirty years ago…” -Robert Krulwich
Oxidation
Oxidation is another form of chemical weathering that occurs when oxygen combines with minerals in rocks, causing them to break down. One common example of oxidation can be seen in the rusting of metal objects. When exposed to moisture and oxygen, iron will react and produce the reddish-brown coating we recognize as rust.
In nature, this process occurs slowly over time and contributes to the breakdown of rocks and minerals. It also plays a role in soil formation by breaking down minerals into smaller particles that plants can use for nutrient uptake.
“The brown stains are caused by oxidized iron. A mild solution of oxalic acid applied to the staining material removes most of the discoloration.” -Ed Seavey
While both acid rain and oxidation contribute to the weathering of rocks and minerals, they are examples of chemical weathering rather than physical weathering processes. Physical weathering typically involves changes due to mechanical or thermal stresses, such as rock fracturing from freezing and thawing.
It’s important to understand the difference between chemical and physical weathering because they can have different impacts on the environment, including changes to soil, water quality, and erosion rates. By studying these processes, scientists can better predict how natural and human-made structures will be affected by weathering over time.
Biological Weathering
Biological weathering is the breakdown of rocks, soils, and minerals due to the activity of living organisms. Unlike physical or chemical weathering that involves natural forces like wind, water, and temperature changes, biological weathering is caused by plants, animals, and other living organisms in the environment.
Root Wedging
One example of biological weathering is root wedging. When plant roots grow into cracks and fissures in rocks, they exert pressure on the surrounding rock material, causing it to break apart gradually. This process can weaken the structure of the rock over time and cause it to disintegrate completely.
“Root wedging can be an important component of the weathering budget in temperate regions where there is a wide range between mean annual temperatures and daytime and night-time temperatures and/or significant freeze-thaw cycles.” -Ezra Lingenfelser
This type of biological weathering occurs more frequently in areas with high plant density and high moisture levels. Certain species of trees like oaks, maples, and elms are especially adept at breaking up rocks with their strong roots.
Animal Activity
Another form of biological weathering is animal activity, which includes burrowing, nesting and scratching by various organisms. Burrowing animals like rabbits, gophers, and moles create holes and tunnels in the soil that can disturb the stability of nearby rocks and boulders. Similarly, nesting birds can loosen smaller stones while larger herbivorous animals scratch rocks to sharpen their teeth or remove parasites.
“From a geological viewpoint, animal disturbance has the capacity to change landscape processes by stimulating regolith production and modifying sediment distribution systems.” -P.W. Huntoon
Animal activity can also contribute to soil erosion, which is another form of weathering that removes rock particles from their original location. This type of biological weathering plays an important role in the ecosystem as it helps create new habitats for other species while also redistributing nutrients in the soil.
Although biological weathering is not as commonly known as physical and chemical weathering, it is still a significant contributor to the breakdown of rocks and minerals in the environment. Root wedging and animal activity are just two examples of how living organisms can impact the geological landscape around us.
Exfoliation
Exfoliation belongs to the category of physical weathering processes that occurs on rocks and minerals. This process describes how layers or sheets split from a rock due to reduction in internal pressure caused by uplifts, which results in exfoliation domes. These smooth dome-shaped surfaces can be observed in various landscapes around the world where granite is present.
The National Park Service explains that Yosemite’s Half Dome is an excellent example of exfoliation geology. As per their report, glacier ice removed the overlying rock, exposing the dome’s underside, contributing to its shape as we now see it.
This method continues until all sheet-like layers come off one after another. Ultimately, the rock transforms into a spheroid surface. To make it clearer, imagine peeling an onion layer-by-layer – exfoliation produces a similar effect.
Sheeting
Sheeting, also known as “pressure flaking,” refers to the gradual removal of thin, seemingly paper-thin slabs from a rock’s surface due to decreased pressure. This loosens sections of the rock, resulting in plate-like structures separating from the primary mass.
National Geographic reports that a type of sheeting with rounded shaping is called torsion exfoliation. As this process takes place, unloading fractures propagate gradually more inward squeezing the nearby solid quantities nearly parallel bedsheets and reduces them according to the depth up to form these spherical patterns.
Dome depletion and tafoni arrangement are two major forms of sheeting evident at granite peaks globally. Working together, both create curved walls while leaving behind huge round blocks that shatter and roll down slopes.
Spheroidal Weathering
Spheroidal weathering happens when edges decompose via exposure to water and air, gradually forming rounded boulders or granules. These materials are produced in a core-and-outer shell pattern, with the external layer usually degraded more than the interior portion.
The Encyclopedia Britannica explains that erosion rates increase on layers which have faced significant weathering, leaving behind stone balls running horizontally along hillsides as well-defined features of this process.
It is worth mentioning that spheroidal weathering sometimes happens because the rock’s material is eroded differently due to uneven mineral strength within it. In some cases, organic acid, created by biological processes like plantroot growth under soil beneath rocks can dissolve or weaken minerals faster creating holes and weakening rocks along these areas
“For instance, Granite Boulder straddles County Creek at 8,040 feet elevation eastward from Mineral King; it’s the name for huge granite orbs in high-altitude places caused by spheroidal weathering,” says John N. Lorenz who conducted research at Los Angeles’ Getty Conservation Institute for over two decades.
Thermal Expansion
Thermal expansion is the tendency of matter to change in shape, area, and volume in response to a change in temperature. Contrary to physical weathering, thermal expansion does not involve any processes that break up or wear away rocks. Instead, it is a form of mechanical weathering that causes stress on rocks by changing their dimensions due to heating or cooling.
Freezing and Thawing
One common example of physical weathering is freezing and thawing. When water gets into cracks or pores in rocks or soil, it can expand when it freezes and creates pressure that breaks the material apart. This process repeats itself as temperatures rise above and drop below freezing point. However, much like thermal expansion, this type of weathering involves changes in the condition of matter and does not directly result in a chemical breakdown of the rock structure.
Forest Fires
Although often associated with destructive wildfires that destroy miles of forest land every year, forest fires are not an example of physical weathering. While they can have an impact on rocks, burn areas typically experience more chemical and biological weathering effects than they do from mere burning alone. Organic materials generated from burned trees decompose and facilitate other types of weathering within the surrounding ecosystem.
Volcanic Activity
Volcanic activity includes explosive events such as eruptions, which can cause significant damage to natural landscapes. Such events can even trigger landslides, flash floods, and debris flows. However, volcanic activity itself is generally considered to be a geological event rather than a physical weathering process caused by climate-related factors such as wind, rain, or temperature fluctuations. Volcanoes typically emit volatile gases and solid fragments during eruption, which can lead to secondary physical weathering processes.
Gravity
Gravity is a fundamental force of nature that plays a crucial role in shaping the Earth’s surface. It refers to the attraction between two objects with mass and determines the direction in which they move towards each other. While gravity is not an example of physical weathering by itself, it can trigger some processes that cause physical weathering.
Landslides
A landslide is a type of mass wasting that occurs when rock, soil, or debris moves down a slope due to the pull of gravity. Landslides often occur after heavy rainfall, earthquakes, or human activities such as construction or deforestation. They can be triggered by factors such as steepness of slope, type of soil or rock, presence of water, or vegetation cover. Once the materials start moving downhill, they can collide with other rocks or structures, causing them to break into smaller pieces through physical weathering.
“Landslides have the potential to cause significant damage and loss of life, especially in urban areas where many people live in areas prone to landslides.” -United States Geological Survey (USGS)
Rockfalls
A rockfall is another form of mass wasting that happens when rocks detach from a cliff or steep slope and fall freely towards the ground. Rockfalls are typically caused by weathering and erosion, which weaken the bonds between the rocks and make them more susceptible to breaking off. Gravity then pulls the rocks downward, and as they hit other rocks or surfaces, they undergo physical weathering and break into smaller fragments. Rockfalls can be dangerous to humans and infrastructures, especially if they happen suddenly and unpredictably.
“Rockfalls remain an ever-present concern for those living beneath rugged terrain, but understanding how these events occur can aid in assessing and mitigating their impacts.” -Science Daily (2016)
While gravity itself is not an example of physical weathering, its pull can initiate and enhance some natural processes that cause physical weathering. Landslides and rockfalls are two examples of such processes, which demonstrate how the interplay between gravity, earth materials, and other environmental factors can shape the Earth’s surface over time.
Frequently Asked Questions
What is chemical weathering?
Chemical weathering is the process of rock breakdown caused by chemical reactions. This can occur through the dissolution of minerals or through chemical reactions with environmental factors like water, air, and acids. These reactions alter the chemical composition of rocks and change their physical properties. Examples of chemical weathering include the rusting of iron, the weathering of limestone by acid rain, and the breakdown of feldspar minerals into clay.
What are some examples of biological weathering?
Biological weathering is the process of rock breakdown caused by living organisms. This can occur through the action of plant roots, burrowing animals, or the acidic secretions of bacteria and fungi. Examples of biological weathering include the growth of tree roots into rock crevices, the erosion of soil by earthworms, and the decay of organic matter into soil. Biological weathering can also occur when animals create holes in rocks by burrowing or scratching.
How does erosion differ from physical weathering?
Erosion is the process of transporting and depositing rock and soil particles by natural agents like wind, water, and ice. Physical weathering, on the other hand, is the process of rock breakdown caused by physical forces like frost action, abrasion, and thermal expansion. While physical weathering breaks down rocks into smaller pieces, erosion transports those pieces away from their original location. Erosion can also cause physical weathering by exposing rocks to new environmental factors like water and wind.
What are some human activities that can cause weathering?
Human activities that can cause weathering include mining, construction, and pollution. Mining can cause physical weathering by removing vegetation and exposing rocks to weathering agents. Construction can cause both physical and chemical weathering by disrupting natural drainage patterns, altering soil composition, and releasing pollutants into the environment. Pollution can cause chemical weathering by releasing acids and other chemicals into the air and water, which can react with rocks and minerals.
How does climate affect physical weathering?
Climate affects physical weathering by influencing the type and intensity of weathering agents. For example, regions with frequent freeze-thaw cycles experience frost action, which causes rocks to crack and break apart. Regions with high temperatures and rainfall experience chemical weathering, as water and acids react with rocks to break them down. Climate can also affect physical weathering by changing the rate of thermal expansion and contraction in rocks, which can cause them to crack and break apart.