Summarized Background Information

Introduction

Weathering is the breakup of rock due to exposure to processes that occur at or near Earth’s surface (Spaulding, Namowitz, 2003). This is different from erosion because erosion is the removal and transport of materials by natural agents such as wind and running water. (Spaulding, Namowitz, 2003) There are two main types of weathering; chemical and mechanical. The experiment chosen is about the mechanical and chemical weathering process of limestone, granite, sandstone, and shale. The research question asks to test whether limestone weathers faster than the other rocks. The weathering process of limestone is very quick in damp climates. It frequently forms land features like sinkholes and caves. It also forms cliffs in dry areas. Granite mechanically weathers by breaking down to form dome-like hills, similar to those found at Yosemite National Park. When granite chemically weathers it changes to clay, quartz grains. The quartz grains found in sandstone are greatly resistant to weathering and are converted into new sand deposits. Shale, also known of as mudstone, is a fine-grained and soft rock so it weathers very quickly. The clay’s are moved in water by suspension to create muds later making shale. (Bohling, 2009)

Mechanical Weathering

Mechanical weathering is the breakdown of rock that takes place when a rock is broken into smaller pieces of the same material without changing its composition (Spaulding, Namowitz, 2003). The agents of mechanical weathering are ice, water, abrasion, plants, animals, and exfoliation. There are two main types of mechanical weathering; fracturing and abrasion. Fracturing a rock consists of a striking-like motion toward the rock and an angular clast is the outcome. Abrasion is smoothing off the rough edges, functioning like sandpaper. (Nycz, 2010)

Chemical Weathering

Chemical weathering is the breakdown or decomposition of rock that takes place when minerals are changed into different substances (Spaulding, Namowitz, 2003). The agents of chemical weathering are water, carbonic acid, root leaching, and oxidation. The three main types of chemical weathering are dissolution, oxidation, and hydration. Dissolution or leaching is when a rock dissolves in water completely when rain falls upon it. When limestone is dissolved from dissolution karst features such as sinkholes, caves, and underground drainage systems may occur. (Stringfield, Rapp, Anders, 1979) Hydration is when rocks respond with water. They take the water in, making them enlarge and putting pressure onto the rock. Over long periods of time it can lead to weakening of the rock. (Nycz, 2010) The chemical reaction of oxygen with other substances is called oxidation. (Spaulding, Namowitz, 2003) A key indicator is a color change in the rock, one example is rust. (Nycz, 2010)

Weathering Rates

There are various factors that control the type and rate at which rocks weather. Climate controls the type and rate by affecting the possibility of freeze-thaw periods and chemical reactions. In damp tropical climates, chemical weathering is more likely to happen and be more forceful. In very cold climates, decomposition of rock has a higher probability of happening and being more effective. Also, a rock’s mineral composition decides the rate of change or dissolution. The weathering of the rock is affected by its texture. Fine-grained rocks, like shale, are more prone to chemical change, but less susceptible to mechanical change. If the rock has more joints, cracks, or crevices, it could be a channel for water to enter, therefore those rocks are more likely to go through weathering. (britannica encyclopedia)

Karst Topography

In areas with limestone, when acidic rainwater seeps through the soil and into the bedrock, it dissolves the carbonate minerals, forming sinkholes. (Cobb, 2001) Acid rain is rainwater that contains unusually high amount of acids that can be traced back to pollutants, including sulfur dioxide, nitrogen compounds, and carbon dioxide. (Spaulding, Namowitz, 2003) Sinkholes have become a large problem in many areas because they are destroying homes and buildings. Sinkholes are bowl-shaped dips in the ground and they form over voids underground, ranging from just a few feet to a few hundred feet. When this happens over time, this method creates considerable systems of caves and gaps underground. This makes the surface of an area flawed with depressions and it’s called karst topography. Sinkholes can break down slowly or quickly, and they usually cause damage to buildings, bridges, roads, and sewers. Also, these sinkholes produce a passage for surface water to infiltrate groundwater aquifers, so pollution has a much higher percentage due to the small amount of the filtering of the water. (Cobb, 2001)

Conclusion

Weathering is everywhere. It affects even everyday lives and many things around the community in the simplest of ways. It has many forms, such as chemical and mechanical, like acid rain and wind. It alters statues, buildings, gravestones, and creates sinkholes. Weathering is a big part of the progression of the environment and the changing of the earth.