Boom time: hot facts about volcanoes

Did you know that there are about 1500 volcanoes on land that have been active in the past 10,000 years?

And there are about 50 to 60 volcanic eruptions every month? Most of these eruptions don’t cause much damage but they do spew ash, gases and hot liquid rock called lava.

So we thought we’d bring together all the facts you should know about these spectacular and potentially devastating natural events.

What makes a volcano erupt?
There are several different causes of volcanic eruptions but they all fundamentally* come down to a pressure change within the volcano, which forces the magma (or melted rock) inside to overflow.

The most common type of eruption is caused by the movement of tectonic plates*.

When one plate pushes underneath another, it forces molten rock*, sediment* and seawater down into the magma chamber. The rock and sediment are melted into fresh magma, and eventually overfill the chamber until it erupts, releasing sticky and thick lava at temperatures of 800C to 1000C.

The second type of eruption caused by tectonic plates is when the plates move away from each other, allowing magma to rise and fill the gap. This can cause a gentle explosion of thin lava of temperatures between 800C to 1200C.

Decreasing temperatures can cause old magma to crystallise* and sink to the bottom of the chamber and this movement can force fresh liquid magma up and out – similar to dropping a brick in a bucket of water.

Finally, a decrease in external pressure can also trigger an eruption. This kind of eruption can be caused by natural events, such as typhoons or melting ice on top of a volcano, which reduce the force being placed on the earth. The reduction in external force reduces the volcano’s ability to hold back increasing pressure on the inside. Therefore, the magma rises until it overflows.

Melting ice is believed to be one cause behind the 2010 Eyjafjallajökull eruption in Iceland.

How are volcanoes formed?
Volcanoes are formed by eruptions of lava and ash when magma rises through cracks or weak-spots in the Earth’s crust.

A build up of pressure in the earth is released by things such as a plate movement which forces molten rock to erupt into the air.

The lava from this eruption then cools to form a new crust.

Over time, generally several eruptions, the rock builds up and forms a volcano.

What are the different types of volcano?
There are three different types of volcano and each produces and releases a different type of lava:

Shield volcano: These volcanoes have a flat domelike appearance and release lava in a gentle manner that is generally slow and easy for humans and animals to out run. They produce basaltic* lava, which is the most common type found on earth. Shield volcanoes tend to erupt frequently but are relatively gentle eruptions. Kilauea volcano in Hawaii is a shield volcano. They tend to erupt more frequently and on a smaller scale than other volcanoes.

Stratovolcano: This type has the classic cone shape most people think of when they hear the word volcano. These volcanoes produce large, violent eruptions which often lead to mudslides and produce fast moving clouds of hot gas and volcanic matter called pyroclastic flow. Stratovolcanoes produce andesitic* magma, which is molten rock formed at plate boundaries which typically cools and hardens before spreading too far, but can reach temperatures of up to 400C. Krakatoa in Indonesia, Vesuvius in Italy and Mount Agung in Bali are examples of this type of volcano.

Caldera volcano: These volcanoes have a circular, basin-shaped appearance and release a thick lava which is between 650C and 800C. After an eruption, which is normally caused by a pressure build up, the crust above the chamber collapses inwards. This creates a depression in the surface and is sometimes referred to as a crater, but it is actually a type of sink hole. Caldera Volcanoes are a common type of “supervolcano”. A supervolcano is the most explosive volcano, with a Volcanic Explosivity Index of 8. This index measures how much material is expelled* during an eruption. A supervolcano produces at least 1000 cubic kilometres of deposits when it erupts.

This story was originally published by The Sun and is reproduced here with permission

GLOSSARY

• fundamentally: in a basic and important way
• tectonic plates: gigantic pieces of the Earth’s crust and uppermost mantle
• molten rock: also called magma, the hot semifluid rock found beneath Earth’s surface
• sediment: the matter that settles to the bottom of a liquid
• crystallise: form into crystals
• basaltic: a type of volcanic rock
• andesitic: another type of volcanic rock
• expelled: forced out

EXTRA READING

Lava flow makes Spanish island bigger

Erupting volcano becomes tourist attraction

Mount Etna’s spectacular volcanic eruption

Volcano on Pacific Ring of Fire erupts

QUICK QUIZ

1. How many volcanoes on land have been active in the past 10,000 years?
2. How many volcanic eruptions happen every month?
3. The most common type of eruptions are caused by the movement of what?
4. What are the three different types of volcanoes?
5. What does a supervolcano rate on the Volcanic Explosive Index?

LISTEN TO THIS STORY

CLASSROOM ACTIVITIES
1. Diagram of a volcano
Draw a diagram of a volcano labelling the parts and what causes them to erupt. Keep your drawing simple, but detailed enough to explain to someone the different types of volcanoes and why they erupt. Use bold headings, key words and a clear diagram to make it easy to read and easy to understand.

Time: allow 30 minutes to complete this activity
Curriculum Links: English, Science

2. Extension
Write an acrostic poem using the word “volcano”. Use key facts and information from the Kids News article to make your poem interesting and informative.

V
O
L
C
A
N
O

Time: allow 20 minutes to complete this activity
Curriculum Links: English, Science, Critical and Creative thinking

VCOP ACTIVITY
Read this!
A headline on an article – or a title on your text – should capture the attention of the audience, telling them to read this now. So choosing the perfect words for a headline or title is very important.

Create three new headlines for the events that took place in this article. Remember, what you write and how you write it will set the pace for the whole text, so make sure it matches.

Read out your headlines to a partner and discuss what the article will be about based on the headline you created. Discuss the tone and mood you set in just your few, short words. Does it do the article justice? Will it capture the audience’s attention the way you hoped? Would you want to read more?

Consider how a headline or title is similar to using short, sharp sentences throughout your text. They can be just as important as complex ones. Go through the last text you wrote and highlight any short, sharp sentences that capture the audience.