The World's Foundations; or, Geology for Beginners · Ch. XXVIII · Unit 5: Part III: Fire, coral and caves
32. Earthquakes
Goal: Your child can describe what earthquakes do to the land, explain why the book says they make the past hard to read, and knows what to do in an earthquake.
You'll need
- The book, open to this chapter
- Building blocks or dominoes and a baking tray
- Modeling clay (optional)
- A globe, atlas or free online map
- A notebook for a "rock journal" and a pencil
What's in the book
Chapter XXVIII describes earthquakes in New Zealand, Chile, Cutch in India (where a long mound rose, called "The Mound of God"), Caracas, South Carolina and Missouri, Calabria, Lisbon in 1755 and Jamaica. It sums up how earthquakes raise and lower land, open cracks and make faults in moments, and warns that any fold or fault in the rocks might have come about suddenly.
The lesson, step by step
Before you read
Note for you: this chapter has several vivid accounts of people being hurt or swallowed by cracks (Calabria, Lisbon, Jamaica). Preview pages 273 to 277 and skip or soften them for a sensitive child. The key science is on pages 270 to 273 and 277 to 280.
Read together
Read Chapter XXVIII (pages 270 to 280), with any skips. Stop on the summary:
Hills have been formed in a single night. Forests have been levelled at a blow.
Land moved in a moment
List the changes from the book: in Chile in 1822 the whole coast was lifted two to four feet in one night; in New Zealand a cove became dry ground, and a crack eighteen inches wide ran sixty miles; at Cutch a long mound rose and a plain became an arm of the sea. Find Chile, New Zealand and India on a map.
Shake test
Build two towers of blocks on the tray: one tall and thin, one wide at the bottom. Shake the tray gently side to side, then harder. Which stands longer? Talk about why buildings in earthquake lands are built with wide, strong bases.
Count the eruptions
Read:
With regard to volcanic eruptions, it is calculated that, taking large and small together, there may be about twenty in the world every year, on an average, or two thousand every century.
Check the arithmetic together: 20 a year times 100 years is 2,000.
Why it makes geology hard
Giberne says any fold, fault or slip in the rocks might have been made slowly over centuries or suddenly by an earthquake, and afterward the two can look alike. She quotes a saying: "Give me an earthquake, and I will give you any physical condition you please." Ask your child what that means.
Drop, Cover, and Hold On
Practice what to do in an earthquake: drop to your hands and knees, cover your head and neck under a sturdy table, and hold on until the shaking stops. Stay away from windows. Try it once in a room at home.
What we know now
Earthquakes happen when rock suddenly slips along a fault, usually where the earth's plates grind past each other, pull apart or push together. The great sea wave after the Lisbon earthquake is what we now call a tsunami. The book's South Carolina and Missouri shocks are now known as the New Madrid earthquakes of 1811 and 1812. Today's records show more eruptions than the book's estimate: usually around 50 to 70 volcanoes erupt in a year.
Afterwards
Notice it this week: find out with an adult whether earthquakes ever happen where you live, and where your family would take cover.
Answers to the book's problems
Earthquakes can raise or lower land, lift sea-beaches, open cracks, make faults, form hills or lakes, and empty lakes, all within hours. Because a fold or fault made suddenly by an earthquake can look just like one made slowly, the book says we must be careful in drawing conclusions about how fast the rocks were changed. 20 times 100 is 2,000.
Worked out for this site from the scan. If a number in your copy differs, trust the book.