E. Earth and Space Systems · Rocks, Minerals, and Geological Processes

How Geological Processes Shape Ontario and Affect Us

E1.1 A1.1 A3.2About 50 minutes

Learning goals

I can describe slow geological processes (weathering, erosion, deposition, glaciers) and fast ones (earthquakes, volcanoes, landslides).
I can explain the three kinds of weathering: physical (like freeze-thaw), chemical and biological.
I can give Ontario examples of how geological processes have shaped the land.
I can analyse how a geological process affects people and the environment, both in helpful and harmful ways.

Words to know

geological process
A natural process that shapes or changes the Earth's rocks and land, like weathering, erosion, earthquakes and volcanoes.

weathering
The breaking down of rock into smaller pieces, by water, ice, wind, chemicals or living things. Weathering breaks.

erosion
The moving of rock pieces and soil from one place to another by water, wind, ice or gravity. Erosion takes.

freeze-thaw
When water seeps into a crack, freezes and expands, then melts, over and over, making the crack bigger.

glacier
A huge, thick sheet of ice that moves very slowly over land, scraping and carrying rock.

earthquake
A sudden shaking of the ground caused by rock moving deep underground.

The land is always changing

The Earth's surface might seem like it never changes. But it is changing all the time. Some changes are slow: a river wears down its banks a little every year. Some are fast: an earthquake can shake the ground in seconds.

These natural changes are called geological processes. Today you'll learn how they shaped Ontario, and how they affect people and the environment.

Remember from Grade 3

Weathering breaks; erosion takes. In Grade 3 you saw how water, wind, ice and gravity erode soil, and how plant roots hold soil in place. In this lesson you'll see that the same processes shape rocks and whole landscapes, and you'll add new processes like earthquakes and volcanoes.

Three kinds of weathering

Physical weathering: Rock is broken into pieces without changing what it is made of. The best Canadian example is freeze-thaw. Water seeps into a crack. When it freezes, it expands (gets bigger) and pushes the crack wider. When it melts, more water flows in. Over many winters, the rock splits apart. Freeze-thaw also helps make potholes in our roads every spring!
Chemical weathering: Water and substances in it slowly change the minerals in rock. Rain is very slightly acidic, and it slowly dissolves limestone and marble. Acid rain (caused by air pollution) does this faster. Rust on iron-rich rocks is chemical weathering too.
Biological weathering: Living things break rock. Tree roots grow into cracks and push them apart. Lichens (crusty growths on rocks) make substances that slowly wear rock away.

Freeze-thaw weathering. 1: Water fills a crack in a rock. 2: The water freezes into ice and expands, pushing the crack wider. Repeated over many winters, this splits the rock.

Erosion and deposition shape the land

Water: Rivers and waves carry sand and pebbles away and drop them somewhere else. Waves on the Great Lakes wear away cliffs such as the Scarborough Bluffs in Toronto, and the sand they carry builds beaches in other places.
Wind: Wind blows sand into dunes, like those at Sandbanks Provincial Park on Lake Ontario.
Gravity: Rocks and soil fall or slide downhill in rockfalls and landslides.
Ice (glaciers): Thousands of years ago, during the last ice age, thick glaciers covered all of Ontario. As they moved, they scraped the land, carved out basins that became lakes, scratched grooves into Canadian Shield rock, and left huge piles of sand, gravel and boulders when they melted. The Oak Ridges Moraine, north of Toronto, is a long ridge of this sand and gravel.

A tall, steep bluff of pale sand and clay rising above a pebbly beach with waves breaking on a lake. — Tall bluffs like the Scarborough Bluffs in Toronto are worn back by waves, rain and freeze-thaw. Look for the grooves and gullies that water has carved into the cliff. AI-generated image

Fast processes

Earthquakes: Rock deep underground suddenly moves, and the ground shakes. Ontario has small earthquakes from time to time, especially in eastern Ontario near Ottawa. Most are too small to feel. Bigger earthquakes happen in other parts of Canada, like the west coast of British Columbia.
Volcanoes: Magma erupts at the surface as lava, ash and gas. Ontario has no active volcanoes, but Canada has volcanoes in British Columbia and Yukon.
Landslides: Large amounts of rock or soil slide downhill suddenly, often after heavy rain or when a river cuts into a slope.

Process	Effects on people	Effects on the environment
erosion of lakeshore bluffs	homes and roads near the edge can be damaged; people may have to move back	sand is carried to build beaches elsewhere; bluffs give nesting places for some birds, like bank swallows
freeze-thaw	potholes damage cars and roads; repairs cost money	breaks rock into smaller pieces, which helps make soil over time
glaciers (long ago)	left sand and gravel used to build roads and buildings; left good farm soil in some places	carved lakes and rivers, which are habitats for many living things
Niagara Falls erosion	the falls attract many visitors; the river's water is used to make electricity	the falls move slowly upstream, changing the gorge
earthquakes	can damage buildings and bridges; people must build stronger structures	can cause landslides and change the land
volcanoes	ash can harm health, close airports and bury homes	ash and lava can destroy habitats, but over time weathered volcanic rock makes rich soil

How some geological processes affect people and the environment. Most have both harmful and helpful effects.

Worked example

Let's analyse an impact: a crumbling cliff

A family's house is 20 m from the top of a lakeshore bluff. Waves are eroding the bottom of the bluff. Analyse the impacts on people and on the environment, and think of what people could do.

What is happening? Waves (water erosion) wear away the bottom of the cliff. Then gravity pulls the upper part down. The edge moves closer to the house.
Impact on people: the house could become unsafe. The family may need to move it, or pay for protection. The city may need to close paths near the edge.
Impact on the environment: the eroded sand is carried along the shore and helps build beaches. The cliff face can be a habitat for nesting birds.
What could people do? Build farther back from the edge; plant deep-rooted plants on the slope; control rainwater so it doesn't run over the edge; put large rocks at the bottom to break the waves (but this can starve beaches farther along of sand).
Math connection (A3.2): Imagine the edge moves back 1 m each year (an imaginary number for practice). The house is 20 m away. 20 ÷ 1 = 20, so in about 20 years the edge could reach the house.

Shoreline erosion is harmful for the family's home but helpful for beaches and some habitats. Good solutions think about both people and the environment.

A crumbling bluff. Water erodes the base, then gravity pulls the top down, so the edge creeps closer to the house. Not to scale.

Safety

Stay well back from the edges and bottoms of cliffs and bluffs. They can collapse without warning.
Use a plastic container in the freeze test, not glass. Glass can crack and shatter when water freezes inside it.
Know what to do in an earthquake: Drop, Cover and Hold On. Drop to your hands and knees, take cover under a sturdy table, and hold on until the shaking stops.

Just for fun

People joke that Ontario has four seasons: winter, still winter, pothole season and construction season. Pothole season is really freeze-thaw weathering at work on our roads!

Hands-on activity

Freeze-thaw and shake tests

Part 1: Freeze-thaw. You need: a small plastic container with a snap-on lid (or a small plastic bottle with a cap), water, the freezer, a marker.

Fill the container right to the top with water and put the lid on. Mark the water level if you can see it.
Put it in the freezer overnight.
In the morning, look. Did the lid pop up or bulge? What does this show about water when it freezes?
Explain how this would break a rock if the water were in a crack. Use the words expand and freeze-thaw.

Part 2: Shake test (physical weathering and erosion). You need: a plastic jar with a lid, 8 sugar cubes, a timer.

Look at the sharp corners of the sugar cubes. Put 4 in the jar. Keep 4 out to compare.
Close the lid and shake hard for 2 minutes. This models rocks tumbling in a fast river.
Compare: What happened to the corners? What is the powder at the bottom?
Shake for 2 more minutes. Did the cubes keep changing?

Part 3: Research. With a grown-up, find out about one geological process near where you live (a river eroding its banks, a bluff, a glacial landform, a past earthquake). Write: What happened? How did it affect people? How did it affect the environment?

Your turn

What is the difference between weathering and erosion?

Explain freeze-thaw weathering.

Give an example of biological weathering.

What shaped many of Ontario's lakes and left piles of sand and gravel?

Name a fast geological process.

Give one harmful and one helpful effect of erosion.

What should you do during an earthquake?

More practice: warm-up

Weathering ____; erosion ____.

What happens to water when it freezes?

Name a Toronto cliff that is being eroded by waves.

Does Ontario have active volcanoes?

What is a glacier?

More practice: on your own

Why do Ontario roads get so many potholes in spring?

In the sugar cube test, what did the shaking stand for? What did the powder stand for?

Is acid rain dissolving a marble statue physical, chemical or biological weathering? Explain.

Name one way glaciers that melted thousands of years ago still help people in Ontario today.

Why might building a wall of big rocks at the bottom of one bluff cause problems somewhere else?

Challenge

Granite in the Canadian Shield often has smooth, scratched surfaces with long grooves all pointing the same way. What process made them? What do the grooves tell us?

Analyse a volcano's effects: give one harmful and one helpful effect on people, and one on the environment.

A city plans a new park path along the top of a river bank that is eroding. Give two pieces of advice, one about people's safety and one about the environment.

Check your understanding

Quiz

Water freezing in a crack and splitting a rock is...

Which is an example of erosion?

Tree roots splitting a rock is...

What carved many lakes and left the Oak Ridges Moraine in Ontario?

Which is a helpful effect of shoreline erosion?

During an earthquake you should...

Why does freeze-thaw happen so much in Ontario?

For parents and teachers

Big idea (E1.1): Geological processes, slow (weathering, erosion, deposition, glaciation) and fast (earthquakes, volcanoes, landslides), shape the land and affect people and the environment in both harmful and beneficial ways. Analysing an impact means looking at people and the environment, and at more than one point of view.

How to help: Point out geology in daily life: potholes and frost-cracked sidewalks (freeze-thaw), lichens on rocks, eroding stream banks, sand and gravel pits, glacial boulders (erratics) in fields. The math connection (A3.2) uses an imaginary erosion rate; real rates vary a lot. The research part supports A1.1.

Common difficulties:

Weathering vs erosion. "Weathering breaks; erosion takes."
Seeing processes as only harmful. Ask, "Who or what benefits?"
Thinking freeze-thaw needs very cold weather. It needs temperatures that go back and forth across 0°C.

Safety: Plastic containers only in the freezer test (glass can shatter). Teach Drop, Cover and Hold On. Stay away from cliff edges and bases.

Accuracy note: Eastern Ontario lies in the Western Quebec Seismic Zone, where small earthquakes are recorded regularly.