Earthquakes and Volcanoes » Types of Volcano and Their Features
What you'll learn this session
Study time: 30 minutes
Cambridge spec: 4.2.3, 4.2.4, 4.2.5
- The three types of volcano: strato-volcano, shield volcano and cinder cone
- How to tell active, dormant and extinct volcanoes apart, and why the labels can be wrong
- The main features of a volcano: crater, vent, magma chamber and secondary cone
- How to label a volcano sketch in the exam
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Unlock This CourseNot all volcanoes are the same
A volcano is an opening in the crust where magma reaches the surface. If you picture a tall, pointed mountain with smoke coming out of the top, you are only picturing one kind. Volcanoes differ in shape, size and the way they erupt. What decides this is the lava. You already know that plate boundaries and hotspots make magma (see What Happens at Each Plate Boundary). Here we look at what that magma builds.
Key terms:
- Viscous: thick and sticky, so it flows slowly. Runny is the opposite.
- Explosive eruption: a violent eruption that blasts out gas, ash and rock.
- Effusive eruption: a gentle eruption where lava simply pours out and flows away.
- Tephra: loose fragments of rock thrown out in an eruption, such as ash and cinders.
Think of tomato ketchup and water. Water spreads out fast and flat. Ketchup piles up and barely moves. Lava is the same: runny lava spreads far, and viscous lava stays close and piles up.
The three types of volcano
🌋 Strato-volcano
Also called a composite cone. Tall and steep, with a classic cone shape. It is built from alternating layers of ash and lava. The lava is viscous, so eruptions are explosive. Found at destructive (convergent) boundaries.
🔥 Shield volcano
Wide with gentle slopes, like a shield laid on the ground. It is built from runny basaltic lava that flows a long way. Eruptions are effusive. Found at constructive (divergent) boundaries and hotspots.
⛰ Cinder cone
Small and steep. It is built from loose cinders (tephra) that fall around the vent and pile up. Often forms in a short burst of eruption.
Comparing the three types
| Strato-volcano | Shield volcano | Cinder cone | |
|---|---|---|---|
| Shape | Tall, steep, cone-shaped | Wide, low, gentle slopes | Small, steep-sided cone |
| Made of | Layers of ash and lava | Layers of runny lava | Loose cinders and ash (tephra) |
| Lava | Viscous | Runny, basaltic | Mostly cinders, little lava |
| Eruption style | Explosive | Effusive | Short, small explosive bursts |
| Where | Destructive boundaries | Constructive boundaries and hotspots | Can appear suddenly in open ground, such as a field |
| Example | Mount Fuji, Japan | Mauna Loa, Hawaii | Paricutin, Mexico |
Why does the lava decide the shape? Runny lava spreads out before it sets, so the volcano grows wide and low. Viscous lava cannot spread, so it sets near the vent and builds a tall, steep cone. Gas also gets trapped in viscous magma, builds up pressure and escapes with a bang. That is why strato-volcanoes are the dangerous, explosive ones.
- Mount Fuji is a strato-volcano about 3,776 m high. Its last eruption was in 1707.
- Mauna Loa is a huge shield volcano on the Hawaii hotspot. It rises to about 4,200 m above sea level. Iceland, on the Mid-Atlantic Ridge, also has shield volcanoes.
- Paricutin began in a farmer's maize field in Mexico in 1943. It erupted until 1952 and built a cinder cone more than 300 m high.
Active, dormant or extinct?
Volcanoes are also classified by how likely they are to erupt.
🔥 Active
Erupting now, or has erupted recently and is likely to erupt again. Example: Mauna Loa.
😴 Dormant
Not erupted for a long time, but expected to erupt again. It is sleeping, not dead. Example: Kilimanjaro in Tanzania.
❌ Extinct
Not expected to erupt again, because the magma supply has gone. Example: Arthur's Seat in Edinburgh.
The labels are based on past eruptions, and nobody can see exactly what is happening underground. So they can be wrong. A volcano called dormant can wake up. Mount Pinatubo in the Philippines had been quiet for about 500 years when it erupted violently in 1991. Scientists also disagree about where to draw the line between "active" and "dormant". Treat "dormant" as "could erupt without much warning" and "extinct" as "very unlikely to erupt, but not certain".
The main features of a volcano
Key terms:
- Magma chamber: a large underground pocket of molten rock beneath the volcano.
- Vent: the opening or pipe that magma travels up to reach the surface.
- Crater: the bowl-shaped dip at the top of the volcano, around the main vent.
- Secondary cone: a smaller cone on the side of the main volcano, built around a side vent.
Magma collects in the magma chamber. When pressure builds, it rises up the main vent. Some magma may force its way up a branch, a side vent, and build a secondary cone. At the surface magma becomes lava, and gas and ash are thrown into the air.
How to sketch and label a strato-volcano
1. Draw a tall cone with a bowl-shaped dip (the crater) at the top.
2. Draw a pipe from the crater down into the ground. Label it the main vent.
3. Draw a large oval at the bottom of the pipe. Label it the magma chamber and write magma inside it.
4. Draw a branch off the pipe that comes out on the side. Add a small cone on the slope and label it secondary cone (with side vent).
5. Draw layers of ash and lava as bands inside the cone. Label them.
6. Add a lava flow running down one side and an ash cloud above the crater, and label both.
Common mistakes
- Saying a shield volcano is steep. It has the gentlest slopes of the three.
- Writing "explosive" for every volcano. Shield volcanoes are effusive.
- Mixing up the vent and the crater. The vent is the pipe, the crater is the bowl at the top.
- Writing that dormant means dead. A dormant volcano is expected to erupt again.
- Describing a type without saying why. Always link the lava (viscous or runny) to the shape and the eruption.
Exam-style question
Fig. 1.1 describes two volcanoes. Volcano A is about 3,000 m high with steep sides built from layers of ash and lava, at a destructive boundary. Volcano B is about 4,000 m high but very wide with gentle sides, built from runny lava, on a hotspot.
(a) Identify the type of volcano shown by Volcano A. [1 mark]
(b) Describe two differences between Volcano A and Volcano B. [2 marks]
(c) Define the term dormant volcano. [1 mark]
(d) Explain why Volcano B erupts in a different way from Volcano A. [6 marks]
Model answer
(a) A strato-volcano (composite cone). (1)
(b) Volcano A has steep sides but Volcano B has gentle sides. (1) Volcano A is made of ash and lava layers but Volcano B is made of runny lava only. (1)
(c) A volcano that has not erupted for a long time but is expected to erupt again. (1)
(d) Level 3 (5-6 marks): A clear, linked explanation of both volcanoes, for example: Volcano B is a shield volcano on a hotspot, built from runny basaltic lava. Runny lava lets gas escape easily, so pressure does not build up. The lava pours out gently in an effusive eruption and flows a long way, which builds a wide volcano with gentle slopes. Volcano A is a strato-volcano at a destructive boundary. Its lava is viscous and sticky, so it traps gas. Pressure builds up until the volcano erupts explosively, throwing out ash, and the thick lava sets close to the vent, which builds a steep cone. Level 2 (3-4 marks): some correct points about the lava types or eruption styles, but the links are partly missing. Level 1 (1-2 marks): simple statements, such as one is explosive and one is gentle.
Exam tip
In an "explain" question like (d), use linking words such as "so" and "because" to join the lava type to the eruption style.