How does rainwater cause physical weathering

This refers to the repeated freezing and melting of water within small crevices in the rock surface. This expansion and contraction is also a major cause of potholes in streets.

Water seeps into cracks in the rocks, and, as the temperature drops below freezing, the water expands as ice in the cracks. The expansion exerts tremendous pressure on the surrounding rock and acts like a wedge, making cracks wider. After repeated freezing and thawing of water, the rock breaks apart. Plant roots can grow in cracks. Wind can also aid in abrasion. Tiny particles of dust and rock in the wind can collide with exposed rock, smoothing down rock faces over millions of years.

Many rocks form deep underground, under forces of extreme pressure. When erosion or shifting glaciers reveal these rocks, the lack of pressure causes the top of the rocks to split apart into smaller sheets.

To determine if weathering of a rock is which change — physical or chemical weathering — ask yourself whether the chemical composition of the rock has been altered. If not, it is physical weathering. However, oftentimes physical and chemical weathering work together to break rocks down into smaller pieces. Physical weathering can make a rock more susceptible to chemical weathering by exposing more surface area.

Chemical weathering can make a rock more vulnerable to physical weathering forces. Iron in rocks can react with oxygen to form iron oxide, or rust. Image is from Yosemite National Park in California. From here. Biological Weathering Biological weathering is, of course, weathering done by living things. I suppose it could really be called a special case of either physical or chemical weathering, but it is kind of neat that life on the planet can weather rocks. Some examples: Tree roots Tree roots grow into cracks and widen them, which helps physical weathering.

Bacteria Some bacteria and other organisms secrete acidic solutions, which helps chemical weathering. Different Weathering Types Help Each Other Keep in mind that you really can't separate physical from chemical or biological weathering, because all three proceed at the same time though not at the same rates, necessarily. With more surface area exposed, chemical reactions happen faster. Think of dissolving sugar in water. 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 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 cave s. Carlsbad Caverns National Park, in the U.

The largest is called the Big Room. With an area of about 33, square meters , 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, sinkhole s, and caves. 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 bond s 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 slope s, another dramatic example of a landscape formed by weathering and erosion. Living or once-living organisms can also be agents of chemical weathering. The decay ing remains of plants and some fungi form carbonic acid, which can weaken and dissolve rock. Some bacteria can weather rock in order to access nutrient s such as magnesium or potassium. Clay minerals, including quartz , are among the most common byproduct s of chemical weathering.

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 gravestone s, making names and other inscription s impossible to read. Acid rain has also damaged many historic buildings and monument s.

It was carved 1, years ago and sat unharmed for centuries. An innovative drainage system mitigate s the natural process of erosion. Weathering by water's freeze-thaw cycle has split this rock in two. Photograph by George F. Mobley, National Geographic. Spheroidal Weathering.