The Fairy-Land of Science · Lecture V, part 2 · Part 5: Lecture V: The two great sculptors, water and ice
14. Ravines, waterfalls, canyons and deltas
Goal: Your child can explain how a stream cuts a ravine and a waterfall eats back its cliff, and can show that heavy stones sink first and fine mud last.
You'll need
- A clear jar with a lid
- A handful each of small stones, sand and garden soil
- Water
- A world map or globe (a free online one is fine)
- Science notebook and pencils
What's in the book
Pages 106 to 114. A ravine growing from a furrow; pebbles rounded in a stream; waterfalls and pot-holes; Niagara Falls eating back its cliff; the Great Canon (Grand Canyon) of the Colorado River, with a full-page picture; gravel and sand sinking in water; and the Nile delta made of river mud.
The lesson, step by step
Hook question
Show a smooth, round pebble if you have one.
SayRocks break off cliffs with sharp corners. So how do pebbles get round?
Let your child guess. (Rolling and grinding in a stream.)
Read together
Read page 107 (the ravine) and page 109 (pot-holes).
Water runs down a little groove, frost cracks the sides, and the stream rolls the pieces over and over until they are round pebbles. In a pot-hole, swirling water spins pebbles round and round,
just as you grind round a pestle in a mortar.
Famous carvings
Find Niagara Falls and the Grand Canyon on the map.
These falls are not nearly so high as many people imagine, being only 165 feet
The falls have cut a gorge seven miles long by wearing back their cliff, little by little. Look at the picture of the Great Canon facing page 111.
For more than three hundred miles the River Colorado, coming down from the Rocky Mountains, has eaten its way through a country made of granite and hard beds of limestone and sandstone
Try it: what sinks first
Read page 112.
If you take a handful of gravel and throw it into a glass full of water, you will notice that the stones in it will fall to the bottom at once, the grit and coarse sand will take longer in sinking, and lastly, the fine sand will be an hour or two in settling down, so that the water becomes clear.
Put the stones, sand and soil in the jar, fill it with water, close the lid tightly and shake. Set it down and watch. Check again tomorrow. Draw the layers.
New land from mud
Read or tell pages 113 and 114. When a river slows down at the sea, it drops its mud and makes new land called a delta. Find the Nile and the Mississippi on the map. Whole towns are built on old river mud.
Tell it back and check
Your child tells back how a stream makes a ravine. Then ask:
1. Why are stream pebbles round?
2. In your jar, what reached the bottom first? What took longest?
3. What is a delta made of?
What we know now
Today Niagara Falls wears back more slowly than in Buckley's time, because much of its water is sent through power stations. The Grand Canyon is still one of the best places on Earth to see what a river can carve.
Afterwards
Notice it this week: look at stones in a creek or gravel path: round or sharp? After rain, look where muddy water slows down and leaves its sand.
Tip
Use a jar with a tight lid, and let your child do the shaking. Leave the jar out for a day; the finest mud settles very slowly, just as Buckley says.
Answers to the book's problems
1. The stream rolls them over and over and grinds them against each other until the corners wear off. 2. The stones first, then the sand; the fine mud took longest. 3. Mud and sand that a river drops where it slows down at the sea.
Worked out for this site from the scan. If a number in your copy differs, trust the book.