Weathering is the process by which rocks are broken down. As rocks break down they can be fragmented into a variety of sizes ranging from a huge boulder to fine clay. River, ice, waves and wind play a role in the processing of the pieces of fragmented rock. Mechanical weathering is the process by which rocks are fragmented and disintegrated into smaller pieces. However, the rock's mineral composition is not changed. Chemical weathering alters the rock to form new minerals.
Mechanical weathering is the result of rock fragments bouncing down a riverbed or being ground up along the bottom of a glacier and carried along by the glacier, which is how Long Island and Long Island Sound were formed. This process will cause sharp edges to become rounded and large boulders to become worn down into grains of sand. The longer the weathering process takes place, the more a rock will be broken down and the smaller it will become.
Chemical weathering occurs in places where water or other fluids and minerals are in constant contact. Agents of weathering are oxygen, air pollution, water, carbonic acid and other strong acids, such as sulfuric acid from sulfur emissions and nitric acid from auto emmissions. These components will combine with the rock and minerals to form clays, iron oxides and salts.
The most important element in chemical weathering is water. Water combines with the carbon dioxide in soil to form carbonic acid. The carbonic acid will slowly dissolve away the minerals within the rock. The carbonic acid will decompose the insoluable rock into a water soluble product that will travel into the groundwater. If there are high concentrations of dissolved minerals in the water, this can cause the water to be hard. The water can also hydrate minerals by absorbing into the mineral lattice, this is especially true for clay minerals. Through hydrolysis, the water can break down the minerals, for expample silicates and granite are decomposed by this process. Chemical weathering can change the color of a rock, break it down or cause it to form different materials, such as rust or clays, which will form new varieties of rocks.
Gases and acids also play a role in chemical weathering. Oxygen will combine with metals such as iron and manganese commonly found in minerals, to form oxides. Other factors that contribute to chemical weathering are air pollution, volcanic steam vents and abandonded mine sites.
Erosion occurs after rocks have been broken down during the process of weathering. Erosion is the movement of rocks, soils and other parts of the earth. Erosion happens very slowly but eventually can make big changes in the landscape. It is mostly caused by water, ice and wind. The broken down rocks are carried along and deposited to other areas by the ocean currents, streams and rivers, the flowing of rain, waves along the shores of lakes and oceans, flowing glaciers and the wind.