The World's Foundations; or, Geology for Beginners · Ch. XXVII, part 1 · Unit 5: Part III: Fire, coral and caves
30. Volcanoes: cones, craters and great eruptions
Goal: Your child can name the parts of a volcano and the three classes (active, dormant, extinct), and retell one of the book's great eruptions.
You'll need
- The book, open to this chapter
- A small plastic cup or bottle, a baking tray, and sand or modeling clay to build a cone
- Baking soda, vinegar and a drop of dish soap (red food coloring optional)
- A globe, atlas or free online map
- A notebook for a "rock journal" and a pencil
What's in the book
The first part of Chapter XXVII (pages 255 to 264) explains the cone and crater of a volcano and the three classes, then describes great eruptions: Cotopaxi in the Andes, the birth of Jorullo in a Mexican farmland in 1759, the vast lava streams of Skaptar Jokul in Iceland in 1783, Etna's 1669 eruption that flowed over the walls of Catania, and Galongoon in Java in 1822.
The lesson, step by step
A question to start
SayCould a mountain grow out of a flat field in a few days?
The book says yes. Read to find out where.
Read together
Read pages 255 to 264, up to the paragraph that begins "Two good opposite instances". Note for you: the Java account (pages 262 to 264) includes a grim detail about victims; you may skip that sentence.
Key definitions:
A volcano is generally a cone-shaped mountain or hill, with a deep hollow or basin in the summit called a Crater.
Volcanoes are divided into three classes — Active, Dormant, and Extinct.
Build a volcano model
Outdoors or in a tray: stand the cup in the middle and pile damp sand or clay around it into a cone, leaving the cup's mouth open as the crater. Put two spoonfuls of baking soda and a drop of dish soap in the cup. Pour in vinegar and watch the "eruption".
Label the cone and the crater in the rock journal. Safety: keep faces back from the cup and keep vinegar out of eyes.
Jorullo
Retell the story together: farmland with indigo and sugar-cane; rumblings in June 1759; two months of earthquakes; flames and burning rocks; the ground swelling like a bubble; six cones; forty years later still warm. Find Mexico on the map.
Skaptar Jokul
In 1783 lava from this Icelandic volcano filled a river gorge, a lake and a waterfall, then started down a second river. The book says one stream was fifty miles long. Ask: How far is fifty miles from your home? Name a town that far away.
Etna and Catania
Read about the wall sixty feet high that the people of Catania built, and how the lava piled up and flowed over it. Find Sicily on a map. Ask: Why did the lava move more slowly near the end?
Tell it back
Ask your child to retell one eruption from the chapter in order, as a news reporter would. Then: What is the difference between a dormant and an extinct volcano? Why does the book say we can rarely be sure a volcano is extinct?
What we know now
Most volcanoes are found along the edges of the earth's plates, especially in the "Ring of Fire" around the Pacific Ocean, which includes the Andes, Mexico and Java. In 1943 a new volcano, Parícutin, rose out of a Mexican cornfield, much as Jorullo did, and grew over 1,000 feet tall in its first year. The 1783 Icelandic eruption is now called Laki; its poisonous gases and haze ruined crops and caused a famine in Iceland.
Afterwards
Notice it this week: find the Ring of Fire on a map, and mark the volcanoes from this chapter (Cotopaxi, Jorullo, Skaptar Jokul, Etna, Galongoon).
Tip
Watch only, don't try: real lava and volcanic gases are deadly, and volcano visits should only follow the paths and rules of a park. For the real thing, look up a video of an eruption filmed by scientists.
Answers to the book's problems
Parts: the cone (built of cinders, tufa and lava) and the crater (the hollow at the top). A dormant volcano is only sleeping and may erupt again; an extinct one is thought to be dead. We can rarely be sure, because volcanoes thought dead have suddenly erupted. Etna's lava moved more slowly near the end because it was cooling and stiffening as it went.
Worked out for this site from the scan. If a number in your copy differs, trust the book.