Investigating the causes and consequences of volcanoes and featuring case studies from the Canary Islands, The Democratic Republic of the Congo and Iceland.
Below Earth’s surface, in the upper mantle, the pressure and heat are intense. In some places, the solid rock can melt completely… becoming magma. And when that pressurised magma comes into contact with a weak point in the crust it escapes, as flowing lava.
The weak points in the Earth’s crust are mostly found at the boundaries of tectonic plates…
At constructive boundaries - usually deep under oceans - plates are being pulled away from each other. Gaps form, allowing magma to flow up. As it cools, it adds new, igneous rock to the plate.
At destructive boundaries, plates slowly collide, with one being subducted below the other. The slabs of cooler crust which are pulled down into the mantle slowly melt, forming magma. When it builds up below the crust, it creates great pressure - and can erupt, forming volcanoes.
It’s also possible for volcanoes to occur away from plate boundaries. These are places in which the mantle below the crust is particularly hot - or the crust is unusually thin - and is melted by the hot magma below the surface.
They’re known as ‘hot spots’. As the crust continually moves along, century by century, hot spot sites see repeated eruptions - forming chains of islands, such as Hawaii.
We often think of a volcanic eruption as a catastrophic, explosive event, with rock and lava being blasted up into the air. This kind of eruption does happen - rarely.
When a volcanic eruption occurred on the island of Krakatoa in Indonesia in 1883, the explosion was so powerful that it was heard on the far side of the Indian Ocean.
Most volcanic events have a far more local impact. In 2021 on the Island of La Palma, in the Canary Islands, magma pressure split open the side of the Cumbre Vieja volcano. A river of lava, at a temperature of around 1,000 degrees Celsius, wound its way down the hillside for ten days. All buildings that were in its path were destroyed. Luckily, it wasn’t an area where many people lived.
In the Democratic Republic of the Congo in 2021, when Mount Nyiragongo began erupting, lava began to flow directly towards the nearby city of Goma, home to 2M people.
As the flow advanced at 1kph, the government urged residents to evacuate. It’s estimated that over 400,000 people left their homes, with 8,000 travelling to the neighbouring country of Rwanda for refuge.
In events like this, scientists cannot know much lava will escape - or how long the flow will continue for. In this case, hundreds of homes and buildings were destroyed on the northern edge of the city, but the flow stopped there. Most of Goma stayed safe.
Volcanic activity can also have a wider impact. At Eyjafjallajökull in Iceland, a volcanic fault lies beneath a glacier. In 2010, pressure built up enough to melt the overlying ice and erupt. The melted ice water created local flooding, and a plume of steam and ash rose into the atmosphere, to a height of 11km.
Winds carried the ash cloud all the way across Northern Europe, causing a major hazard to aircraft. Flights all around the world were cancelled for several days, affecting around 10M travellers and losing the global airline industry an estimated £3 billion.
The disruption was hard to predict as wind direction impacted the ash cloud’s spread and severity.
In any volcanically active zone, lives can be severely affected by the tectonic forces below the ground. Their impact depends on the force of an eruption, and how close it is to human settlements - but the danger is always present.
The video
Plate tectonics: Volcanoes
Download/print a transcript of this episode (pdf).
This video explores what a volcano is and what causes volcanic eruptions, focusing on eruptions in the Canary Islands, the Democratic Republic of the Congo and Iceland. Each of the eruptions had very different impacts.
We investigate the different plate boundaries at which volcanic eruptions occur as well as ‘hot spots’, such as the Hawaii.
Through the study of three different case studies, students will see how the impact of volcanic eruptions differs depending on location, lava flow, population density and whether there is a glacier on top of the volcano.
Teacher Notes
Download/print the Teacher Notes for this episode (pdf).
Teacher Notes prepared in partnership with the Geographical Association.
Before watching the video
- Ask students to recap on the causes of earthquakes and tsunamis. This is a good opportunity to revisit the different types of plate boundaries and the hazards that occur at each.
- Task students with creating a spider diagram of what they already know about volcanoes and volcanic eruptions. This might include famous volcanoes, parts of a volcano, hazards associated with volcanic eruptions and impacts.
- Introduce key terms such as:
Magma: molten rock that can be found beneath the Earth’s surface.
Lava: molten rock ejected by volcanoes. This is what erupts from a volcano.
Igneous rock: rock formed when molten rock cools and solidifies.
Hot spots: areas away from plate boundaries where the crust is thinner, which is caused by an unusually hot mantle plume. The plume melts and thins the Earth’s crust.
Ash clouds: dense clouds of volcanic ash, dust and gases which can be hazardous to the aviation industry and people.
While watching
You may wish to stop at relevant points during this short video to pose questions and check understanding, or wait until the end. Useful questions might include:
- Where are weak points on the Earth’s crust found?
- What happens at a constructive plate boundary?
- What happens at a destructive plate boundary?
- What is a hot spot?
- What happened in the Canary Islands in 2021?
- Why were few people impacted by this eruption?
- What happened in the DRC in 2021?
- Why is it difficult to be able to accurately predict lava flows?
- What issues did the Eyjafjallajökull eruption cause widespread issues?
After watching
- To help with their understanding of plate boundaries, students should draw out the different plate boundaries and the processes that occur at each. Students could research where these plate boundaries can be found - for example, there is a constructive plate boundary which divides Iceland and forms the Mid-Atlantic Ridge.
- Look at websites such as the United States Geological Survey and the British Geological Survey volcano maps. Is there a pattern as to where the volcanoes happen? Can students map this to the plate boundary maps? Students could also explore which volcanoes have erupted recently or are currently erupting at the time of study.
- Task students to research the different types of volcanoes: stratovolcanoes and shield volcanoes. Students could look at how different the eruptions are - for example, some eruptions are effusive and some are explosive. They could sketch each volcano type and find examples of each. Students could also look at where these volcanoes occur. Is there a pattern to the types of volcanoes and their global location?
Where next?
- Use the Earth Learning Ideas website to complete investigations into types of lava and why some eruptions are explosive and some are effusive.
- There are lots of great hands-on experiments, such as putting honey into one cup and fizzy drink into another and then blowing into each with a straw.
- Each cup’s contents represent a different viscosity of lava, which in turn would lead to either an explosive or effusive eruption.
Links
Plate tectonics:
https://www.bbc.co.uk/bitesize/topics/zn476sg/articles/zrcgr2p
Volcanoes:
https://www.bbc.co.uk/bitesize/topics/zn476sg/articles/z9k496f
Volcanoes:
https://www.bbc.co.uk/bitesize/guides/z8p9j6f/revision/1
Curriculum notes
This video is suitable for teaching KS3 in England and Northern Ireland, 3rd/4th Level in Scotland and Progression Step 4 in Wales.
In the English National Curriculum this film can be used to help teach the following:
- Physical geography relating to geological timescales and plate tectonics.
Resources
Teacher Notes
Download/print the Teacher Notes for this episode (pdf).
Transcript
Download/print the transcript for this episode (pdf).
