How is weathering important to the rock cycle

Intrusive igneous rock typically crystallizes at depths of hundreds of metres to tens of kilometres below the surface. To change its position in the rock cycle, intrusive igneous rock has to be uplifted and exposed by the erosion of the overlying rocks. Through the various plate-tectonics-related processes of mountain building, all types of rocks are uplifted and exposed at the surface.

Once exposed, they are weathered, both physically by mechanical breaking of the rock and chemically by weathering of the minerals , and the weathering products — mostly small rock and mineral fragments — are eroded, transported, and then deposited as sediments. Transportation and deposition occur through the action of glaciers, streams, waves, wind, and other agents, and sediments are deposited in rivers, lakes, deserts, and the ocean.

Referring to the rock cycle Figure 3. 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. Amphiboles, pyroxene, olivine and Ca-feldspars are almost never found in sedimentary rocks. Rocks sometime expand when exhumed. Repeated expansion and contraction of the rock during heating and cooling.

Sometimes these curved layers fall away like skin on an onion. Soils may also form from transported material derived from elsewhere and deposited in a lowland or basin.

Residual soils develop on plains and lowlands with moderate to gentle slopes and consist of loose, heterogeneous material left behind from weathering. This material may include particles of parent rock, clay minerals, metal oxides and organic matter. This loose material is collectively called regolith , whereas the term soil is reserved for the topmost layer which contains organic matter.

The A-horizon is the topmost layer and is usually a meter or two thick. The upper portion of the A-horizon is often rich in organic matter, called humus , and may also contain inorganic material like insoluble clays and quartz. The A-horizon may take thousands of years to develop depending on the climate and acitivity of plants and animals.

This is the layer that supports crops and other types of vegetation. These precipitated minerals often accumulate in small pods, lenses and coatings. Organic matter is sparse in the B-horizon.

The lowest layer constitutes the C-horizon and is comprised of cracked and variably weathered bedrock mixed with clays. Soils can vary significantly in color and composition. An animated version of the rock cycle can be found at the British Geological Society website. The University of Kentucky website has some amazing animations of physical and chemical weathering surfaces common in the different regions, from warm and wet to dry.

Physical weathering is the breaking of rocks into smaller pieces. This can happen through exfoliation, freeze-thaw cycles, abrasion, root expansion, and wet-dry cycles. Exfoliation: When temperature of rocks rapidly changes that can expand or crack rocks.

This especially happens with granitic rocks as they were cooling, like at Yosemite National Park. Freeze-thaw: When water freezes, it expands. If moisture seeps into cracks before winter, it can then freeze, driving the rocks apart.

Abrasion: When the wind blows, it can pick up sand and silt, and literally sandblast rocks into pieces. Root Expansion: Like freeze thaw, roots grow bigger every year. These roots can drive the roots apart. Chemicals react in the environment all the time, and these cause chemical weathering. Major chemical reactions include carbonation, dissolution, hydration, hydrolysis, and oxidation-reduction reaction. All of these reactions have water involved with them.