Kernar Von Marilaun translated by F. Huxley, A. Manning, M. Mellanby , Watt Committee Report No. Winkler, E. Spock, L. Skoulikidis, T. Ailor , Wiley Interscience, New York, , pp.
Monte, M. Hawkes, J. Heath, M. Jaynes, S. Gauri, K. Sharp, A. Landforms , 7 — Pilling, N. Metals , 29 — Geike, A. Download references. 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. 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. Hydration is the absorption of water into the mineral structure. A good example of hydration is the absorption of water by anhydrite, resulting in the formation of gypsum. Hydration expands volume and also results in rock deformation. Figure 6. Dehydration is the removal of water from rock or mineral structures.
A good example of dehydration is the removal of water from limonite, resulting in the formation of hematite. Figure 7. The images above show the dehydration reaction of limonite Fe 2 O 3. H 2 O on the left to hematite Fe 2 O 3 on the right. The water, which was a structural component of limonite, has been removed in the process of dehydration. Experiential Activity A small amount of ground calcium feldspar is placed in the mortar.
Experiential Activity A small amount of limonite, Fe 2 O 3.
0コメント