Mechanical and Chemical Impacts Of water on Earth’s materials Created by: H. Bradley

How are the hydrologic and rock cycles related? The hydrologic (water) and rock cycles are processes that are constantly occurring on our planet. As water travels over Earth’s lithosphere it causes changes to the rocks on Earth’s surface. Some of these changes are mechanical, meaning the rock undergoes a physical change. For example, a larger rock breaking down into smaller pieces. Some of these changes are chemical, meaning the rock’s underlying elemental structure changes. For example, a rock containing iron oxidizes (rusts), thus changing colors and chemical makeup of the rock.

Mechanical Impacts Rocks are physically broken down into smaller pieces

Erosion The force of moving water can erode rocks over time. The friction of the water against the rocks of the stream or river bed can physically break rock into smaller pieces. The moving water can then carry these small pieces, which will further erode the stream or river bed due to abrasion (rocks breaking down due to friction from other rock particles).

Erosion

Stream Transportation and Deposition The running water of a stream can physically break down rocks into smaller pieces. The faster the stream flows, the faster it will break down the rocks of the stream bed and transport them to a new location. Eventually, the velocity of the stream will slow, and the particles of rock will fall out of solution. The largest rock particles will be deposited first, then the smaller rock particles will fall out of solution.

Stream Transportation and Deposition

Frost-Wedging Water can seep into small cracks in rocks on Earth’s surface. If the temperature drops below freezing, the water trapped within the rock will freeze. As the water freezes, it expands. Over time the repeated freezing and thawing of water within the rock can cause the rock to break apart into smaller pieces.

Frost Wedging

Chemical Impacts Rocks undergo a chemical reaction which changes their underlying elemental structure

Oxidation When rocks containing the mineral iron come into contact with the oxygen atoms in water, they can oxidize. The most commonly recognized oxidation reaction is that of rust. When this reaction occurs, the iron within the rock loses electrons to the oxygen atoms in the water, resulting in a chemical change.

Oxidation

Hydrolysis Rocks that contain silicate minerals, such as feldspar, mica, and quartz, can undergo hydrolysis when they come into contact with water. The water and silicate minerals experience a chemical reaction in which the minerals combine with the water molecules to create a new mineral. For example, when potassium feldspar (a common rock-forming mineral) comes into contact with water, it can form kaolinite, a clay mineral.

Hydrolysis

Carbonation Rocks that contain carbonate minerals, such as magnesium carbonate and calcium carbonate, are easily dissolved in water, especially if the water is slightly acidic. Precipitation can become acidic as it combines with carbon dioxide in Earth’s atmosphere. Water can slowly dissolve the rocks, which over time, can result in karst topography, such as caves, and sinkholes.

Carbonation

Bibliography Chemical Weathering. (2016). Retrieved November 22, 2016, from http://teach.albion.edu/jjn10/chemical- weathering/ Frost Wedging. (n.d.). Retrieved November 22, 2016, from http://legacy.earlham.edu/~debowke/frost wedging.htm Ritter, M. E. (2012, June 5). Geologic Work of Streams. Retrieved November 22, 2016, from http://www.earthonlinemedia.com/ebooks/tpe_3e/fluv ial_systems/geologic_work_of_streams.html