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Grade 4 (age 9-10)

grade 4 Volcanoes & Earthquakes

Volcanoes & Earthquakes

A volcano erupts when underground magma is pushed up by pressure and bursts from the crater as lava. How fast that lava cools decides whether the volcanic rock has small or large grains. An earthquake happens when Earth's giant plates push together, build up stress, and release it all at once. Set off an eruption or push the plates and the motion comes into view, along with how to stay safe in a quake.

Why does a volcano erupt?

🌋 How Volcanoes Erupt
①Hot magma lies deep underground
②As magma rises, pressure increases
③When pressure exceeds the limit, it bursts from the crater
④Erupted magma is called lava

Types of Volcanic Rock

Volcanic Rock

Volcanic vs. Plutonic
ItemVolcanicPlutonic
Where it formsNear the surface (cools fast)Deep underground (cools slow)
Grain sizeSmall (hard to see)Large (easy to see)
ExamplesBasalt, rhyoliteGranite, gabbro
FeaturesMay have many holesVisible shiny crystals
💡 Fast cooling vs. slow cooling
①Fast cooling → small grains (no time for crystals to grow)
②Slow cooling → large grains (crystals grow fully)
③Basalt: material of Jeju's Dol Hareubang!
④Granite: paving stones, stone pagodas!

Why does an earthquake happen?

🌍 How Earthquakes Happen
①Earth's surface is split into tectonic plates
②Plates push and pull, stress builds up
③When the stress releases at once → ground shakes = earthquake!
④Earthquakes can shake or crack buildings

Summary

Volcanic Eruption Principle
Magma → pressure rises → erupts at crater → lava
Hot melted rock from underground rises up
Earthquake Principle
Plate motion → stress builds → sudden release → quake
Stored stress from plate pushing releases suddenly
🎯 Key Points
①Volcano: rising magma erupts
②Volcanic rock: fast cool = small grain, slow cool = large grain
③Earthquake: plate motion releases stress
④Quake response: under desks, protect head, evacuate via stairs
⑤Both come from energy inside the Earth

Examples and Unit Test

Example 1
What do we call the material that bursts out of the crater when a volcano erupts?
1
Hot magma deep underground rises, and the pressure builds up.
2
When the pressure becomes too much, magma bursts out of the crater, and this erupted magma is called lava.
▸ Lava
A volcano is when underground magma erupts through the crater due to pressure.
Example 2
Why do earthquakes happen? Explain it in terms of tectonic plates.
1
The surface of the Earth is divided into several plates, and force builds up as they push and pull on each other.
2
When the built-up force is released all at once, the ground shakes; this is an earthquake.
▸ Because the force built up by pushing plates is released all at once
An earthquake happens when force built up by moving plates is released.
Unit-test style
Which statement about volcanoes and earthquakes is correct?
①Magma erupted from a volcano is called an earthquake
②An earthquake happens when force built up by moving plates is released
③A volcano erupts because the underground gets cold
④The more slowly volcanic rock cools, the smaller its grains
⑤During an earthquake you should quickly escape by elevator
▸ ② An earthquake happens when force built up by moving plates is released
1
As plates push on each other, force builds up and is released all at once, shaking the ground in an earthquake.
2
Erupted magma is lava (①), a volcano erupts from the pressure of hot magma (③), slower cooling gives larger grains (④), and during an earthquake you escape by the stairs (⑤).
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