Weathering_and_Erosion

Weathering is when rock breaks down because of exposure to the environment and aspects of the environment like the air, water or moisture, or exposure to plants, animals or other organisms which cause the rocks to be physically broken down or to have their chemical make-up altered. Erosion often occurs at the same time as weathering, carrying away the particles that are broken away by weathering, but it is somewhat different from the process of weathering. Where weathering is breaking down or altering the rock, erosion is carrying the particles away. Erosion is often speeded up by deforestation or the removal of vegetation because although the plants may have been weathering the rock, they were also holding much of it together. Severe weather and earthquakes can also speed up the process of erosion due to their violent nature and the amount of earth that the severe wind and rain can move. Erosion is more likely to happen is areas with steep terrain because gravity works to pull the loose parts of the rock downward and carry it away (Mackenzie, Murck, & Skinner, 2009). This paper will discuss types of weathering including mechanical weathering and chemical weathering as well as a few of the types of erosion including erosion from sources such as wind, water, and ice. In mechanical weathering the rocks are physically broken down. There are several different manners in which this happens. One manner in which this happens is called frost wedging. Frost wedging happens first of all because there are joints in the rock. Joints happen because of tectonic activity and they can extend quite far into the rocks. Water enters into these gaps in the rocks and when it freezes it expands, forcing the rocks to move and the cracks in the rocks to expand. After it melts more water gathers into the space and when it freezes again it expands and makes the rocks break apart even further. This happens over and over until the rocks eventually fall apart. The formation of salt crystals works in a similar way, the crystals keep forming and growing and force the rocks apart. Plant roots also wedge themselves into cracks in the rock and grow, forcing the rocks apart. Abrasion is a bit different. Abrasion occurs when particles in the air or water abrade the earth and knock loose other particles. Abrasion could be, for example, the result of sand storms hitting a rock formation over and over (Mackenzie, Murck, & Skinner, 2009). Chemical weathering is basically when minerals in the rocks are dissolved or when the original minerals in the rock are changed or replaced with something different. This can happen due to several different causes. The most well known cause of chemical weathering for most people is acidic water. There are certain minerals which are dissolved by acidic water so when the water comes into contact with these types of rocks, they begin to weather very quickly. Water can become more acidic because of the pollution cause by humans, particularly sulfur and nitrogen compounds. It can also become more acidic after it goes into the ground because it mixes with decaying organic matter and ends up absorbing more carbon dioxide. Oxidation is a type of chemical weathering which seems to get less attention. The process of oxidation where minerals and oxygen get dissolved into water, changes the appearance of minerals like iron. Ion exchange is another form of chemical weathering which also involves water. Basically in ion exchange the ions in acidic water change place with ions in the minerals of the rocks and sometimes the mineral ions they change place with are larger. This causes the rocks to weather and the ions that remain in the water either give it a mineral taste or they are carried off elsewhere (Mackenzie, Murck, & Skinner, 2009). Among the types of erosion, one of those that first comes to mind is probably Water Erosion. Water erosion can occur in streams or rivers as the water carries debris and particles from its original location to a location further downstream. The sediment carried in this way will usually be released when the water moves more slowly and no longer has the power to carry it. The faster the body of water moves, the heavier the sediment it will be able to carry. Water erosion also occurs due to rain splash, basically the rain splashes into the earth and the impact causes particles to be dislodged from the earth. Overland flow is also caused by rainy weather, usually very heavy rain. As the water moves overland it picks up loose soil or sediment and carries it from one location to another (Mackenzie, Murck, & Skinner, 2009). It is easy to picture this type of erosion if only by imagining the rapid and inevitable fall of sand castles created along the shore of the sea. The force and impact of the waves erodes what may have taken hours to build in just moments. Although most wouldn’t usually think of it, the wind is a large source of erosion. Of course, while it’s obvious that hurricanes with high wind speeds or tornados which can rip up vegetation and homes would have great effects on the areas they specifically impact, the wind in general also has a steady affect on the land, especially in areas of sparse vegetation. Particularly in the desert the effects of the wind can be seen as it pushes along the sand and causes it to resemble the waves that ripple on the top of the seas. When the wind erodes the desert the smallest particles are carried on the wind while the slightly larger ones move either in short bursts or simply creep along. While most of the time the wind moves only a little sediment at a time, it can sometimes be extremely powerful. Some satellite photos have shown the wind blowing dust off the Sahara to as far as the Florida coast (Mackenzie, Murck, & Skinner, 2009). Believe it or not, ice is also a source of erosion which can have a heavy impact on large areas. Ice erosion usually involves the movement of glaciers. Glaciers are large bodies of ice that form at the top of mountains. Because they are so large and heavy, gravity begins to pull them down. Glaciers tend to take the path of least resistance, which creates a situation where smaller glaciers often make their way down to the same path which other glaciers are already following, making an even larger glacier as they combine and continue down. Glaciers cause erosion in several ways. First of all when glaciers melt and refreeze they pick up dirt and sediment near their base and drag it along with them. Glaciers also move dirt in a process called scouring. Because the bottom of the glacier has so much rock and sediment mixed it, it abrades the rocks under it, scraping up the surface of the rocks and sometimes even polishing them smooth. Another way that glaciers move rock is called plucking. As the glaciers melt and refreeze they may freeze onto outcroppings or pieces of rock. When the glacier begins to move again these pieces of rock will be ripped up from the ground and carried along with the glacier (Pidwirny, 2006) Another way which ice causes erosion is one which, if you think about it, makes great sense. When it rains in rocky areas or outcroppings the water enters into cracks in the rock. This itself does very little, however, when water freezes it expands. Due to the expansion of the water into ice, small cracks in rock can gradually expand over the years as water freezes, melts, and refreezes. In recent times there are many who work hard to bring attention to environmental concerns and erosion is certainly one of those concerns. While humans can do little to stand in the way of the weathering and erosion that would naturally take place, it would be best if it was understood by as many people as possible the ways in which erosion occurs and how people often contribute to the rapid erosion of areas by stripping the land of vegetation and making it more vulnerable to the environment. Many do, in fact, seem to understand the effects of erosion and many countries have banned the use of agricultural or mining techniques that destroy the land. However, there are still plenty of people out there in the world who don’t understand. Just as the sands of the Sahara can find their way to Florida, the actions of people who destroy the environment thousands of miles away can affect the lives of everyone on the planet. References College of Geosciences. (2008). Aolian Transport of Sand and Dust. Retrieved from http://oceanworld.tamu.edu/resources/environment-book/aeoliantransport.html Earlham College. (n.d.). Frost Wedging. Retrieved from http://www.earlham.edu/~debowke/frost%20wedging.htm Earlham College. (n.d.). Unique Cave Formations. Retrieved from http://www.earlham.edu/~brizeja/caveformations.htm Mackenzie, D., Murck, B.W., & Skinner, B.J. (2009). Visualizing Geology. Hoboken, NJ: John Wiley & Sons. Pidwirny, M. (2006). "Landforms of Glaciation". Fundamentals of Physical Geography, 2nd Edition. July 16, 2010. http://www.physicalgeography.net/fundamentals/10af.html Ritter, Michael E. (2006) The Physical Environment: an Introduction to Physical Geography. July 16, 2010.  http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/title_page.html