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Weathering and Erosion Is Often Referred to Sulfuric Acid, Two Liquids Capable of As Erosion, but They Are, in Fact, Two Dissolving Other Materials

Weathering and Erosion Is Often Referred to Sulfuric Acid, Two Liquids Capable of As Erosion, but They Are, in Fact, Two Dissolving Other Materials

UE PG 211-251 2019_UE PG 218-251 2019 2019-07-25 1:18 PM Page 211

Mechanical occurs in a variety WEATHERING of ways. Heat and cold may cause within a rock to expand and shrink at AND different rates, creating cracks. may seep into those cracks and freeze, Background Information expanding and splitting the rock. A raging river or ocean waves can smash rocks The earth’s is constantly changing, against each other, wearing the outsides and, with the exception of new volcanoes smooth and turning rocks into . Or and the mid-oceanic ridges such as the sand carried by the can act like Mid-Atlantic Ridge, the crust is wearing sandpaper, slowly wearing rock away. A down. These changes are the result of two can rub against the rock continuing processes: beneath it, also acting like sandpaper. Even plants can force rocks to split as roots • weathering, the breakdown of rock into creep into cracks and grow. smaller pieces through exposure to wind, water, heat, and cold The second type of weathering is chemical weathering, the breakup of rock caused by • erosion, the movement of that weathered a change in its chemical makeup. Rain is material by gravity, wind, and water the most common producer of chemicals These two processes affect so much of that can weather rock. Rain absorbs carbon physical geography that they merit a dioxide and sulfur dioxide from the separate section. The combination of atmosphere, forming carbonic acid and weathering and erosion is often referred to sulfuric acid, two liquids capable of as erosion, but they are, in fact, two dissolving other materials. The levels of separate processes and are treated as such carbonic and sulfuric acids in rain, while in this section, which expands on the basic generally weak, can over time dissolve rock information about weathering and erosion such as , freeing other types of presented in other sections of this manual. rock. Over very long periods, rain can even The information and activities in this section dissolve enough limestone to create caves are designed for Year 5 and 6 students who and unusual rock formations. have the vocabulary and basic knowledge Many scientists today believe that rain is of physical geography concepts to explore becoming more acidic as a result of the the fascinating topics of weathering and pollution caused by increasing burning of oil erosion in more detail. and gas in the world, for such purposes as Weathering heating buildings, cooking food, and operating vehicles. Acid rain, as it is called, There are two types of weathering. The first has the potential to change the acidity of is mechanical weathering, the gradual lakes and rivers and make it impossible for breakdown of rock to sand, and then to silt, some types of animals and plants to or powdered rock, and finally to clay flourish. Acid rain has also been named as through physical means.

9–12 Physical Geography 211 © NAMC - North American Montessori Center UE PG 211-251 2019_UE PG 218-251 2019 2019-07-25 1:18 PM Page 212

the cause of increased rates of wear on buildings and statues.

Plants and plant-like organisms also play a role in chemical weathering. For example, lichens, which are plant-like organisms, often appear on rock as green, gray, or yellow patches. Lichens secrete a weak acid that helps roughen the surface of the rock, allowing moss and other plants to Mechanical weathering take root there.

Note to the teacher

Formerly, lichens were classified by botanists as plants, but are now classified as plant-like organisms. For more information, please refer to the NAMC upper elementary manual on water botany.

Note to the teacher

Thinking about weathering will inspire some students to explore science, especially concepts that illustrate the forces exerted by heat and cold. For ideas to suggest to students, teachers River weathering can refer to several NAMC upper elementary science manuals, such as Matter and Energy, Scientific Method and Technology, and Astronomy and Ecology. Teachers may also wish to refer to the NAMC lower elementary manual of science experiments.

Plant weathering

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Erosion

The term “erosion” comes from “erodere,” a Latin verb meaning “to gnaw.” Erosion is what usually happens to the material loosened by weathering. Six main processes have an eroding effect, each in its own way (these processes are also listed on a summary sheet shown elsewhere in Surface Chemical weathering this section):

• gravity

• wind

• rain

• rivers

• oceans

Underground Chemical weathering •

The first main eroding process, gravity, is a passive force that moves what has already been loosened by weathering. Though not an active eroding force like wind or rain, the constant pull of gravity toward the center of the earth is what makes rocks fall from and sand settle to the bottom of oceans. Gravity is a factor in all patterns of of weathered material. For example, mountains are often surrounded Acid rain by , loose rock debris fallen from exposed rock.

The second eroding process is the wind. When carrying dust and sand, the wind is a tremendous sculptor of the earth. Not only does wind erode rock, wind also carries away the sand and dust it creates in the process. Anything in the way of sand- and dust-carrying wind will be slowly weathered and eroded away. The sand breaks up Lichen

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whatever surface it encounters, just like At the end of its course, a river deposits sandpaper, and then the wind blows the much of the remaining at its freed material to another location. Examples mouth. If the sediment is not carried away are found wherever persistent occur. into the ocean by the river current or by Such winds not only shape rock, but also ocean tides, it remains and builds up, can scour paint off barns and houses and eventually expanding the mouth of the river lift valuable topsoil, the upper layer of soil by creating islands and sandbars, large that nourishes plant roots, from one place underwater deposits of sand, to make a and deposit it in another. river delta. The river is then forced to branch out into smaller streams to flow Rain is the third erosion process. across the delta and into the ocean. Precipitation works to erode the land on which it falls through rainsplash erosion, Even after water enters the ocean, its ability rain splashing down on the land and to erode does not disappear — oceans dislodging weathered material such as erode in several powerful ways. When it or soil. Heavy rainfall, or large blows across the ocean, the wind creates amounts of melting snow or , can also waves that erode the loose sand on carry away the sediment into streams and . The repeated motion, often many rivers. The rivers continue the process, times a minute, washes the sand carving watersheds where the land is steep back into the ocean. The rising and falling and enriching floodplains where the land tides allow the waves to work on higher and is flat. lower elevations of the , removing material from different levels. Rivers make up the fourth erosion process. Though rivers and streams weather and Efforts by humans to protect shorelines erode the earth, they also build it up by from erosion by building rock walls often depositing the material they erode fail, as the energy of the ocean is downstream. The way in which it is transferred to more vulnerable areas, deposited creates the typical shape of a increasing erosion there. The actions of meandering river. A river slowly winding its waves are heightened during a storm way through flat land flows a little bit faster surge, a dome of water that accumulates on the outside riverbank than on the inside under a major storm and is then driven onto riverbank. This gives the water on the the land by high winds. The high water level outside curve more power to weather the created allows the waves to reach further ground on that riverbank, extending and inland than usual, and the wind causes deepening the river in that direction. The bigger than normal waves. The combination slower water on the inside curve tends to can be devastating to the shoreline, deposit material carried by the river from especially at high tide when the waves can the previous curves, adding material to the be pushed even further inland. inside riverbank. In this way, a meander is expanded sideways, producing a deeper Oceans also erode the land with currents. curve in the river. As an ocean current moves past the shore, it picks up sand washed off the beach by

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A C T I V I T Y 1 Exploring Types of Weathering

Purpose

To learn more about the types of weathering and how they break down the earth’s crust. Material

Illustrations of various types of mechanical and chemical weathering.

Sample of mechanically weathered object (e.g., piece of glass worn smooth by sand).

Physical Geography journals and pencils. Presentation

• Most Montessori teachers present these concepts in Years 5 and 6. This activity can be done in two parts, the first focusing on mechanical weathering and the second on chemical.

• Announce that the students will have an • Explain that mechanical weathering opportunity to explore types of occurs because rocks get broken into weathering. smaller pieces by something exerting force. Add that this force can break a rock in half or just wear it away slowly so MECHANICAL WEATHERING that it gets smaller. • Review what weathering is. Emphasize that the earth’s crust is constantly • With the students, name what kinds of breaking down into smaller bits, with rock forces might cause a rock to split (heat, turning into sand, sand into silt, and silt cold, water, wind, sand, ice, plant roots), into clay. and then discuss and clarify each.

• Explain that there are two types of • Demonstrate the illustrations on weathering: mechanical and chemical. mechanical weathering, and use them to describe each type. As each type of mechanical weathering is discussed,

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invite the students to describe examples • Ask the students to use their journals to of mechanical weathering they have seen define mechanical and chemical or heard about. For example, students weathering and give two examples of may have seen rocks around a campfire each, with illustrations. split from exposure to repeated heat, or picked up a smooth stone on a beach, or Extensions noticed a blade of grass pushing its way • To observe a process similar to how sand up through . smoothes rock and other hard items, invite a local jeweler to come to the • Demonstrate the sample and invite the classroom and demonstrate how to use a students to examine it closely and stone polisher. consider questions like these: What might this sample have looked like when • Conduct a short study of the weathering it fell into the ocean? How long might it force of repetitive cooling and warming have taken for the sand to smooth any on rock. Find several small rocks that rough edges on the sample? have cracks, but have not yet split into pieces. Soak the rocks in water for an CHEMICAL WEATHERING hour, and then put them in a freezer • Explain that chemical weathering occurs overnight. Take them out the next day when a liquid melts or dissolves rock. and let them warm to room . Point out that the acids in rain are the Even better, put them in the sun to get most common cause of chemical hot or place them on a source of heat, weathering, but that some plants and such as a radiator. Repeat this process plant-like organisms, such as lichens, for five days. Write a report about what also have an acidic effect on rock. Add happens and why. that as a result of pollution, rain is • Research and write an illustrated report becoming more acidic. With the students, about an example of weathering that has discuss some of the possible been written about in newspapers in the consequences of this change. past 5 years. Identify the types of • Demonstrate the illustrations on weathering involved, describe their effect, chemical weathering and Lichen. and explain how people dealt with the Discuss with the students. weathering.

• Invite the students to describe any • Research and write an illustrated report examples of chemical weathering they about the effect of acid rain on a famous have seen or heard about. For example, building or statue. Describe the effect, students may have read about a famous and explain how people dealt with it. statue being placed indoors to protect it from acid rain.

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• Sandblasting is an industrial technique • Take a walk through the neighborhood for cleaning buildings. Find out how around the school and record examples sandblasting works and write a report of mechanical and chemical weathering. about it, including what kind of Include as wide a range of examples as weathering sandblasting resembles. possible, from heat and cold to ice and plant roots, and identify which type of weathering each example represents.

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