Why weathering occurs

The layers of the rock continue to get weaker through this process, and slabs fall off in a process called exfoliation. Wind can also cause rocks to break into smaller pieces by applying force in crevices and scouring out bits of rock. Another common type of mechanical weathering is freeze-thaw weathering, which happens when weather fluctuates above and below 0 degrees Celsius 32 degrees Fahrenheit. Water flows into the cracks in rocks, but when it freezes, the water crystallizes into a hexagonal form, which takes more space than liquid water, according to the HyperPhysics site maintained at Georgia State University.

During the day, the ice will thaw and refreeze again when the temperature drops. This process widens the cracks in rocks and eventually breaks them apart. Chemical weathering refers to the process by which rocks break down through chemical reactions; this weathering happens on a molecular level. This type of weathering causes rocks to decompose and occurs most often in warm and humid climates.

All rainfall contains carbonic acid, which chemically reacts with the calcium carbonate in rocks like chalk and limestone through a process called carbonation. Through hydrolysis, a mineral such as potassium feldspar is leached of potassium and changed into a clay mineral. Carbon dioxide CO 2 combines with water as raindrops fall through the atmosphere. This makes a weak acid, called carbonic acid.

Carbonic acid is a very common in nature where it works to dissolve rock. Pollutants, such as sulfur and nitrogen, from fossil fuel burning, create sulfuric and nitric acid. Sulfuric and nitric acids are the two main components of acid rain, which accelerate chemical weathering. Oxidation is a chemical reaction that takes place when oxygen reacts with another element.

Oxygen is very strongly chemically reactive. The most familiar type of oxidation is when iron reacts with oxygen to create rust. Minerals that are rich in iron break down as the iron oxidizes and forms new compounds. Iron oxide produces the red color in soils.

Now that you know what chemical weathering is, can you think of some other ways chemical weathering might occur? Chemical weathering can also be contributed to by plants and animals. As plant roots take in soluble ions as nutrients, certain elements are exchanged. Plant roots and bacterial decay use carbon dioxide in the process of respiration. Skip to main content. Weathering, Erosion, and Deposition.

Search for:. Weathering Processes Weathering is the process that changes solid rock into sediments. Mechanical Weathering Mechanical weathering , also called physical weathering, breaks rock into smaller pieces. Gravity causes abrasion as a rock tumbles down a mountainside or cliff.

Silicates comprise almost all minerals in igneous rocks and are also important components in metamorphic rocks. Not all silicates, however, survive weathering processes to become incorporated into sedimentary rocks.

Figure 6. For example, interlocking silicate grains in fresh granite gradually decay along crystal boundaries due to conversion to clays. Eventually cracks open around the boundaries, the rock weakens and easily disintegrates.

Water dissolves some of the solid, leaving behind an altered material and producing a solution containing substances drawn from the original solid coffee grounds. The acid rainwater than reacts with minerals on the exposed rock face. Reaction of silicates with carbonic acid and water produces clays and also releases Si and certain cations into water as dissolved constituents:. The dissolved cations are carried away by rain and river waters and ultimately transported to the oceans.

In tropical regions, clays can further react with water to form Bauxite Al-hydroxide , an ore which is a major source of Al. Slightly acidic rainwater can also react with non-silicates in a rock or soil. For instance, carbonic acid can dissolve carbonates such as calcite so that all constinuents go into solution.

Oxidation involves the combining of certain metals Fe in particular with oxygen in the process of stealing electrons. During oxidation, metals like Fe lose one or more electrons to oxygen. Iron can also dissolve in water as cations. Table 6. Silicates fall within the middle range. The most common silicates in clastic sedimentary rocks are quartz, K-, Na-feldspars and micas.

Mechanical Weathering Mechanical weathering is the disintegration of rock into smaller and smaller fragments. Frost action is an effective form of mechanical weathering.

When water trickles down into fractures and pores of rock, then freezes, its volume increases by almost 10 percent. This causes outward pressure of about 30, pounds per square inch at Frost action causes rocks to be broken apart into angular fragments.

Idaho's extreme temperature range in the high country causes frost action to be a very important form of weathering. Exfoliation is a form of mechanical weathering in which curved plates of rock are stripped from rock below.