How does composition of rock affect weathering

As the surrounding less resistant rocks were worn away, the resistant center of the volcano remained behind. Different minerals also weather at different rates. Some minerals in a rock might completely dissolve in water, but the more resistant minerals remain.

When a less resistant mineral dissolves, more resistant mineral grains are released from the rock. Climate is determined by the temperature of a region plus the amount of precipitation it receives. Climate is weather averaged over a long period of time. Chemical weathering increases as:. So how do different climates influence weathering? A cold, dry climate will produce the lowest rate of weathering. Erosion relies on transporting agents such as wind, rivers, ice, snow and downward movement of materials to carry weathered products away from the source area.

As weathered products are carried away, fresh rocks are exposed to further weathering. Over time, that mountain or hill is gradually worn down. Oxygen oxidizes minerals to alteration products whereas water can convert minerals to clays or dissolve minerals completely.

Different minerals weather at different rates. Mafic silicates like olivine and pyroxene tend to weather much faster than felsic minerals like quartz and feldspar. Different minerals show different degrees of solubility in water in that some minerals dissolve much more readily than others. Water dissolves calcite more readily than it does feldspar, so calcite is considered to be more soluble than feldspar.

Massive rocks like granite generally to not contain planes of weakness whereas layered sedimentary rocks have bedding planes that can be easily pulled apart and infiltrated by water. Weathering therefore occurs more slowly in granite than in layered sedimentary rocks. Rainfall and temperature can affect the rate in which rocks weather. High temperatures and greater rainfall increase the rate of chemical weathering.

Rocks in tropical regions exposed to abundant rainfall and hot temperatures weather much faster than similar rocks residing in cold, dry regions. Soils affect the rate in which a rock weathers. Soils retain rainwater so that rocks covered by soil are subjected to chemical reactions with water much longer than rocks not covered by soil. Soils are also host to a variety of vegetation, bacteria and organisms that produce an acidic environment which also promotes chemical weathering.

Minerals in a rock buried in soil will therefore break down more rapidly than minerals in a rock that is exposed to air. The longer a rock is exposed to the agents of weathering, the greater the degree of alteration, dissolution and physical breakup. Lava flows that are quickly buried by subsequent lava flows are less likely to be weathered than a flow which remains exposed to the elements for long periods of time.

Chemical weathering is a process where minerals in a rock may be converted into clays, oxidized or simply dissolved.

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. 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 bornhardt s, 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 evaporate s, salt crystals are left behind. As the crystal s 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 dome s 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 root s 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 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.