Erosion and weathering
Make observations and measurements to provide evidence of the effects of weathering or the rate of erosion by water, ice, wind, or vegetation
What a learner can do afterwards
- Define weathering (breaking down of rock in place) and erosion (movement of broken rock/soil)
- Describe the effects of at least three agents of weathering/erosion: water, ice, wind, vegetation
- Provide evidence from observations showing how weathering or erosion has changed a landscape
1 · Read
Weathering breaks rock down where it is. Erosion moves rock pieces or soil away. Water, wind, moving ice and gravity can transport material. Breaking and moving are different actions, though the processes often work together.
Use dated photos or measurements supplied by adults. Outdoor observations must be adult-supervised from a safe place away from water, bank edges and cliffs. Never approach an edge to measure it. A retreating bank shows material was removed. Observed soil transport identifies erosion; widening rock cracks show weathering. Loose rocks alone do not reveal how they broke or moved.
Water can enter a crack and freeze. The ice expands and can widen the crack. Wind-blown sand can wear a rock surface away. Growing roots can push cracks wider. These are weathering examples. Flowing water, wind and moving glaciers can also carry loose material away.
To find the total surface drop at that point, add the separate drops: 1 + 2 + 4 = 7 cm. Do not add readings that already include earlier drops. A lower surface can have other causes, such as soil being pressed down, so also look for evidence of transport. Record the change and time taken. Erosion can be rapid during a storm or gradual over many years.
To check whether a bank has retreated, choose adult-supplied photos of the same bank from the same viewpoint on two dates. Matching the bank and viewpoint helps you compare its position rather than differences between places or camera views. One photo shows only one time.
Weathering breaks rock down; erosion moves material. Use observations and repeatable measurements to explain what changed and how long it took.
The lesson, questions and flashcards were written for this dataset.
The readings were written for this dataset. The linked weathering and erosion video is by Khan Academy.
More to read
What a pebble can tell us
Rubbing against other stones can wear a pebble's sharp edges away. This can happen in rivers and on beaches.
Rounded edges do not reveal an exact travel distance. Rock type and conditions matter too. Record the shape and surface you observe. Keep those observations separate from your explanation of the pebble's history.
Watching a model stream
With adult help, a class can pour water over sand in a tray. A catch tray contains the water and sand.
Watch sand leaving one place and settling elsewhere. Movement is erosion; settling is deposition. Record the change over a set time. A model helps us observe these actions, but its speed is not the exact speed of a real river.
Two effects of roots
A root growing inside a rock crack can push its sides apart. That helps weather the rock.
Roots spreading through soil can also hold soil together, reducing what rain or wind carries away. These effects differ: one breaks rock down; the other helps soil stay in place. Plant roots do not have to transport rock to affect a landscape.
Making measurements comparable
With an adult, mark a measurement point in a model soil tray. Use the same method each time and record units and elapsed time. For real banks or cliffs, use adult-supplied records. Do not approach water or unstable edges to measure.
Label readings as new drops or totals since the start. Adding running totals counts earlier drops twice. Soil being pressed down can also lower a surface, so look for evidence of transport.
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