الأسبوع 28 · المحور الرابع، الوحدة الرابعة، المفهوم 4.3 «البراكين» (أ): الثورات البركانية والقشرة الأرضية وتدفق الحمم · 3 دروس
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Volcanoes: sudden changes to the land
Discovery Education Science P4: Term 2, Unit 4, pp. 163–178
GoalDescribe what comes out of a volcano, how an eruption changes the land quickly, and why some people live near volcanoes.
New words
volcano · an opening in the Earth’s surface where hot melted rock, ash and gases can come outeruption · the time when a volcano throws out lava, ash and gasesash · tiny bits of rock and glass thrown into the air by a volcano
Explanation
Most changes to the land are slow, but a volcanic eruption can change a place in hours. When a volcano erupts, melted rock called lava can pour out, ash and gases rise into the sky, and heavy rain on loose ash can start a mudslide. Lava flows can bury roads, and thick ash can cover roofs and fields. These are hazards, so scientists watch volcanoes, and people have warning systems and plans. Even so, millions of people live near volcanoes. Volcanic ash is full of minerals that make soil rich for farming. Volcanoes also bring useful minerals, such as sulfur, up from deep underground, and some people collect them. Egypt has no active volcano; we learn about volcanoes from other countries. We can respect the danger and still be curious.
What comes out or follows
How it changes the land
lava
flows over land and cools into new rock
ash
covers fields and roofs; later makes rich soil
gases
can make the air hard to breathe
mudslide
rain on ash runs down as thick mud
Worked examples
Quick or slow? Marwan compares. A mountain wearing down by rain takes a very long time: slow. A volcano dropping ash on a town in one night: quick.
Good things
Hazards
rich soil for farms
ash and lava
minerals such as sulfur
mudslides and gases
Living on the edge. Farida reads about a town near a faraway volcano. The farmers there grow grapes and vegetables in rich soil made from old ash. The town also has an evacuation plan and a siren, so people know what to do.
Thing
Can it come out of a volcano?
lava
yes
ash
yes
gases
yes
seashells
no
Which things can come out of a volcano? Lava, ash and gases can. A seashell cannot, because shells do not come from deep in the Earth.
Class activity
Volcano questions. Write three questions about volcanoes, one beginning with What, one with Why and one with When or How. Then write two safety ideas for people who live near a volcano. Ask a grown-up to help you find answers in a book, and share one question with your class.
Practice
1
Name three things that come out of an erupting volcano.
Lava, ash and gases.
2
Why do some people choose to live near a volcano?
The soil made from ash is rich for farming.
3
Is a mudslide caused by an eruption a quick or a slow change?
