Weathering and Erosion
- Introduction
- Concepts
- Motivation activities
- Exploration activities
- Application activities
- Further resources
Introduction
What will our landscape look like in the future?
Students study landforms in the local environment, such as cliffs, river systems, beaches and farmland to investigate and explain how features of the landscape are altered by weathering and erosion. They use appropriate scientific vocabulary to describe and explain their observations and investigations.
They explain how scientific knowledge is used, or could be used, to solve problems relating to erosion caused by human activity.
When planning this unit, it may be useful to incorporate ideas and strategies from The Science Continuum P-10 critical teaching idea ‘Astronomical scale’ which suggests challenges posed by timescales that are difficult to imagine.
Concepts
- Landforms change naturally over time due to processes of weathering and erosion.
- Weathering of exposed surfaces by agents of the weather occurs physically (freeze-thaw and onion-skin flaking) and chemically (chemical solution of minerals).
- Material eroded from land surfaces is transported by wind, water and ice and eventually deposited; heavy particles tend to be deposited first and lighter particles last as energy of movement decreases.
- The effects of erosion can be speeded up by human activity such as clearing land, overgrazing and ploughing; effects can be minimised by contour ploughing, using tree/wind barriers, implementing revegetation programs and controlling run-off.
Motivation
What’s the evidence?
Students walk around the school grounds and look for evidence of change to the surface of buildings, materials and the school grounds. They record their observations in a table and include annotated drawings or photos.
Students design a class table to collate the data collected. They discuss how they could group their findings (possibly by the kind of materials or the location) and then examine their results and discuss how the changes may have occurred. Suggestions might include the effects of wind, water, sun, growth of plants; effect of machines and children's feet. They enter their data and discuss their observations.
Students are introduced to the terms weathering and erosion and classify their observations accordingly.
Exploration activities
How long has it taken?
As a class, students examine photos of a familiar landmark such as the Twelve Apostles showing change over time. They develop a timeline and develop appropriate drawings showing the formation and erosion of the landforms. They predict what will happen in the future and draw pictures to illustrate their predictions, which they place at appropriate places on their timeline.
Students collect illustrations of landforms from magazines or images from the internet (preferably Australian examples). They predict what the landforms might look like in a few thousand years. They search for information about how long it takes for different kinds of rocks to wear down.
What effect could a freeze/thaw cycle have on rocks?
At home, students investigate the expansion of water as it freezes, using a plastic bottle filled with water close to the top and placing it in the freezer. Students are asked to relate this observation to how the expansion of frozen water may cause weathering to occur in rocks. Students demonstrate their understanding with a series of drawings showing how water alternatively freezing and thawing in small cracks in rocks might split rocks.
What is the action of moving water on a landscape?
Working in a sand pit in the school playground or using a stream tray in the classroom, students investigate hill erosion by slowly pouring water on a mound made of a mixture of rock, pebbles, sand, clay and plant matter. Students record observations in a logbook. They discuss formations in the landscape which they may have observed as well as those seen in photographs and illustrations. Formations to explore include: plateau hills; valleys; creek beds; and erosion gullies.
They suggest how the landforms may have formed.
Students brainstorm their understanding of the term erosion. They develop a working definition for the term.
The following Digilearn activity may assist in developing the students understandings of erosion:
How can gully erosion be prevented?
Students investigate the cause of gully erosion through experimentation. They use a tray filled with sand, rocks, dirt and cotton wool that simulates tree roots. Blue food dye can be used to colour the water which is then poured carefully so that it flows from one end to the other. Talcum powder can be sprinkled on top of the water so students get an idea of how fast the water is flowing. Students investigate the effect of varying the water flow (by damming and other methods) on erosion.
Students investigate three factors which could be varied to alter the patterns of erosion. With assistance, they discuss how they can ensure that they carry out fair tests by identifying the variables in their investigations. Students report their observations in a word-processed report which includes hand-drawn diagrams or digital photographs illustrating the erosion-prevention methods used.
Students discuss their understanding of agents causing erosion and distinguish between forms of erosion and forms caused by weathering.
Is soil the same everywhere?
In small groups, students discuss their knowledge of soil and its composition. They collect soils from various locations and record their observations of the types of plants that grow in these locations. They examine the soils collected and identify and describe the various components. Students estimate the proportions of humus (organic material) and other materials present. They use their data to answer questions such as:
- Is soil the same everywhere?
- Does the type of plants depend on the type of soil?
Students should also be encouraged to develop and test their own questions.
For further resources around soil analysis, see ‘soils’ section of the following website:
Which settles first?
Students investigate deposition of sediment and particles by placing a sample of soil containing pebbles, sand, clay and plant matter into a large jar filled two-thirds with water.
Students record how long it takes for the different materials to settle. Students record observations by drawing the different layers and timing how long it took for the various layers to settle. They relate particle size to the time taken to settle.
What effect does wind have on topsoil?
Students predict whether wind has an effect on topsoil. With care, blow air from a hair dryer at varying speeds over trays with different combinations of sand, soil, dampness, and upright twigs that simulate trees.
Students make a visual record and write a description of conditions that affect removal of topsoil. They discuss the effect of removal of soil on growth of crops.
Does planting grass help?
Working in small teams, students design and carry out an investigation comparing the retention of soil on two slopes, one with grass seed planted and the other bare.
Students predict the effect of water and wind action on both slopes. Similar amounts of water are allowed to trickle over the surfaces of both slopes and a hair dryer used to simulate the effect of the wind. Students record their observations including drawings or photos in their report and explain their observations.
Does salinity affect erosion?
Show the students an image of a landscape affected by dryland salinity. Ask them what they notice, what they wonder, what they think (and why they say that).
The following Digilearn resource provides an image of dryland salinity:
As a class, discuss what could have caused the landscape to appear that way and whether they think it could be reversed. Introduce the notion of salinity and suggest that this may have been a contributing factor. Challenge the students to design an experiment to test whether this could have been the case.
Students design and conduct experiments related to the effect of salinity on bean, radish or wheat seedlings. They identify and control the variables associated with the experiment. Four different sets of seedlings are watered with three different concentrations of salt water and with freshwater. Students make predictions, record observations appropriately and graph the growth of the different sets of seedlings over time. Students report on their investigation and relate their findings back to the image/s.
Students suggest what salinity might have to do with erosion and, using additional information, explain how scientific knowledge is used, or could be used, in solving the problem of salinity in a particular Victorian context.
What can be done?
Students plan and act out a role play about possible actions taken by farmers and soil conservationists concerned about erosion of farm land. They suggest possible behaviours and scripts for the different people in their story and act out possible scenarios. They include possible causes of erosion and explain consequences of decisions made such as minimising erosion by not overstocking with sheep or cattle and by planting more trees.
Land Care Project
Using the Internet or local council information, students research any conservation projects in nearby areas. These activities may include the application of students' action plans. This activity may be ongoing throughout the year.
Land care groups, SaltWatch, StreamWatch, Waterwatch and CERES each have excellent resources and information available for student projects.
Students publish their land care achievements on the Internet, and develop email connections with schools that have conducted similar programs.
Applications activities
What can be done? Local Erosion and weathering
Students go on an excursion around their local area to identify areas where erosion and weathering have occurred. Students present a report of their findings identifying the causes as either weathering or erosion. As a class, students are supported to develop an action plan suggesting possible methods of preventing further damage. They illustrate two possible appearances of the landscape in 100 years, depending on community action and climatic events and draw a fishbone diagram to show how these events resulted in the landforms presented. See VCAA graphic organisers
Further resources
The following resources contain sections that may be useful when designing learning experiences:
Digilearn*
- Dryland salanity at Booward, 2001 – Students can view this colour photograph showing a saline seep, an area of land affected by dryland salinity, where the watertable has risen to the surface. It was taken near Boorowa in New South Wales, about 115 km to the north of Canberra. In the foreground is an area of dried-up and cracked earth, with two dead trees in the middle of it. In the background is an expanse of grass, which is short and dry, and one tree, which is barely alive. There is a small green knot of bushes on the horizon.
*Note that Digilearn is a secure site; DEECD login required.
Websites
- Rock Landforms of Australia and New Zealand – through the use of pictures, illustrates key aspects of geomorphology associated with igneous rocks.
- Waterwatch Victoria - includes projects such as catchment surveys by students, examining water samples, bank vegetation, bank erosion and stability.
- Saltwatch – an environmental monitoring program.
- Australian Landforms – explore the formation of the Australian landscape.