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Lesson 5 of 12

Volcanic hazards

I can explain what pyroclastic flows, ash and lahars are and relate this to real life examples.

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Lesson 5 of 12
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Volcanic hazards

I can explain what pyroclastic flows, ash and lahars are and relate this to real life examples.

Lesson details

Key learning points

  1. Volcanic eruptions can lead to a range of hazards, such as pyroclastic flows, ash and lahars.
  2. Pyroclastic flows are flows of hot volcanic gases, ash and rock.
  3. Ash is made up of tiny pieces of volcanic rock and glass, this can damage lungs, machines, crops and buildings.
  4. Lahars are mudflows caused by volcanic material mixed with water.
  5. Mount Semeru (Java, Indonesia) erupted in 2021, triggering damaging pyroclastic flows, ashfall and lahars.

Keywords

  • Pyroclastic flow - a very hot mix of lava, ash, gases and rock that flows rapidly down the side of the volcano

  • Ash - tiny pieces of volcanic rock and glass

  • Lahar - a mudflow formed when volcanic ash mixes with water

  • Infrastructure - all the basic systems in a country, such as transport and power supply

Common misconception

Lava is the only dangerous aspect to a volcanic eruption and you can just run out of the way.

Ash, lahars and pyroclastic flows are all extremely dangerous volcanic hazards. Pyroclastic flows can reach speeds of 435 mph, which is faster than a car.

Students enjoy imagining themselves experiencing a volcanic eruption. Try to set them up for the misconception above during discussion, this will make the learning more meaningful for them.
Teacher tip

Equipment

Content guidance

  • Depiction or discussion of sensitive content
  • Depiction or discussion of violence or suffering

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Lesson video

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Prior knowledge starter quiz

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6 Questions

Q1.
What is a volcano?

A mountain that erupts
A large crater formed by a meteor
A hole in the ocean floor
Correct answer: A crack in Earth’s crust where magma escapes

Q2.
What is molten rock called before it reaches Earth’s surface?

Lava
Correct answer: Magma
Ash
Water

Q3.
What is the name for molten rock once it has reached Earth’s surface?

Ash
Correct answer: Lava
Pyroclastic flow
Magma

Q4.
What is the name of the hole at the top of a volcano where the lava comes out?

Correct answer: Crater
River
Ocean
Mountain

Q5.
Where are most of the world's volcanoes located?

In the middle of oceans
Correct answer: Around the Pacific Ocean (Ring of Fire)
In deserts
In the Arctic

Q6.
What is the name of the volcano that erupted and destroyed the Roman city of Pompeii?

Mount Etna
Correct answer: Mount Vesuvius
Mount St. Helens
Mount Fuji

Assessment exit quiz

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4 Questions

Q1.
What is a pyroclastic flow?

A type of lava that flows slowly down the volcano
Correct answer: A very hot mix of lava, ash, gases, and rock that flows rapidly down the volcano
A mudflow formed when volcanic ash mixes with water
The smoke emitted from a volcano

Q2.
What is ash in a volcanic eruption?

Liquid rock from the volcano
A gas released by the volcano
Correct answer: Tiny pieces of volcanic rock and glass
A type of lava flow

Q3.
What is a lahar?

A fast-moving lava flow
A type of earthquake caused by a volcano
Correct answer: A mudflow formed when volcanic ash mixes with water
A type of gas released by a volcano

Q4.
Is lava the only dangerous aspect of a volcanic eruption, and can you just run away from it?

Yes, lava is the only dangerous thing, and you can run out of the way
Correct answer: No, pyroclastic flows are faster than cars, ash, and lahars are also dangerous
Yes, lava is the only danger, but you can safely outrun it
No, but only lava is dangerous

Lesson appears in

UnitGeography / Tectonic hazards: Why is Earth restless?

Geography

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