Extra Credit Opportunity
Before we begin this chapter, we will need copper pennies that are from the year 1981 or older. The reason for this is that before 1982 pennies contained a high percent of the mineral copper, but after 1982 pennies began to be copper-plated zinc and contained 97.5% zinc, and only 2.5% copper. Zinc is much cheaper than copper.
You can earn some extra credit for up to 5 pennies that are from the years, 1981 or older. We will be designing a lab around these pennies so we need to make sure we get plenty.
Section 1: Types of Weathering
In this section we will be discussing and learning about weathering processes. Weathering is the process that breaks rocks apart. Weathering is related to erosion as well, but we are going to do a whole section of erosion later on. Erosion is the process of moving and depositing weathered material.
As part of this unit we are going to be doing a daily YouTube video series called The Daily Dose of Destruction which shows weathering and erosion caught on tape.
Daily Dose of Destruction
There are three main categories of mechanisms for weathering.
- Chemical: Rocks being broken down by chemicals changing the composition of rock.
- Physical: Rock being broken down by physically bumping in to each other. Wind, water, ice.
- Biological: Rock being broken down by processes from plants, animals, fungi, bacteria etc...
There are many agents of weathering that fit inside of the mechanisms for weathering.
- Chemical agents: salt, acid, carbon dioxide, water etc...
- Physical agents: abrasion, ice, thermal expansion etc...
- Biological agents: the actual plant or animal
In short the agent of weathering is the thing that is breaking apart the rock. The mechanism of weather is the process by which the rock is being broken apart.
The activity that you are going to do is find some images that demonstrate that weathering has occurred.
- One person create a Google Presentation and then share it out with each person in your group as well as your teacher.
- Make sure that all of your names appear on the title page of your Presentation.
- Using the internet, find 8 images that demonstrate different mechanisms of weathering and the agents involved in that weathering process.
- You need to make sure that chemical, physical, and biological are all represented.
- You may NOT repeat any individual agent.
- Each slide will contain its own image and explanation.
- Also on each slide describe the climate that your weathering example is found in.
- Ex: Wet, Wet and Dry, Mild, Humid, Marine, Arctic, Polar, Dry, Semi Dry, etc...
- Each slide needs a slide transition.
- Make sure your text and background do not clash.
- Be prepared to justify your explanation to the class.
Section 2: Abrasive Weathering
Daily Dose of Destruction
Weathering is the principle action that forms soil. Without weathering we would never get sedimentary rocks either.
Physical weathering is commonly called mechanical weathering. We will use both terms interchangeably. Physical weathering can be caused by ice. As ice melts during the day, the water infiltrates cracks, and these cracks can be very tiny, and then later on, usually at night the ice freezes again. As the ice freezes it expands and causes the rock to crack even wider. The next morning the ice begins to melt, seeps deeper into the crack, freezes at night and then cracks the rock even more. Over time this action known as ice wedging or frost action, can break even the largest of rocks.
Mechanical Weathering is also caused by abrasion. Abrasion is the bumping of rock and sediment into each other causing rock to break apart and even smooth the edges of rock. Glaciers can pluck rock out of the ground and then drag those rocks across other rock creating glacial grooves. Water pushes sediment down stream where it comes in contact with other sediment, breaking off edges of rock causing the rock to become smooth. Wind blows sediment into other rock, breaking off pieces, causing a smoothing of the rock as well. Ice, water and wind are powerful agents of weathering and cause the landforms, landscapes, and rock formations we see today.
Biological weathering is actually another type of physical and chemical weathering. It is considered biological weathering when plants and animals are involved. Roots of plants can find even the smallest space in a rock and then grow. As it grows it expands slowly prying the rock apart. This is called root pry. As animals dig and burrow into the ground they expose material to the surface where it can be weathered even more. Microbes and lichen that live on rock, alter it's chemical composition which weakens the rock making easier for other types of weather to break pieces off or exposing more surface area to the other elements of weathering.
Weathering by Abrasion
You are now going to demonstrate the power that abrasion has on sediment, by completing the rock tumbler lab.
Now you are going to design an experiment to see what the relationship between surface area and weathering rates is.
Section 3: Rates of Weathering
Daily Dose of Destruction
The rate at which weathering occurs is dependent on rock, mineral and climate types. Different rock and mineral types weather at different rates. Igneous rock weathers slowly because it is difficult for water to penetrate the rock due to the tightness of crystal interlocking. Limestone, however, weathers relatively faster and will weather even faster when it comes in contact with water and acids like carbonic acid. You can see from the image of pieces of granite that it has a couple of mineral veins, probably quartz or feldspar. These veins are harder than the surrounding rock, so they become more pronounced as the rest of the rock weathers away quicker.
The image below is from a formation found in Sedona, AZ. Below the blue line is a layer of protruding rock. This layer must be harder than the surrounding rock. It is weathering slower than both the top and bottom parts of the formation.
Climate also has an effect on the rates at which rock weathers. Climate is defined as the pattern of weather that occurs in a particular area over many years. They use the temperature and weather pattern averages over a 10 year period to determine an area's climate. Cold climates are going to have more ice wedging than hot dry climates. Chemical weathering is going to occur frequently in warm tropical climates due to all the precipitation. The more precipitation an area has the quicker the weathering rates. Below is a Koppen climate type map for the USA. You will use this in the next assignment. Click on the map to enlarge the images.
In the following assignment you are going to research some of the national parks, monuments and reserves that the US has to offer.