Inside a Volcano
Understand the inside of a volcano: magma is hot melted rock underground, lava is the same material after it reaches the surface, and volcanoes have a magma chamber, vent, and crater
What a learner can do afterwards
- Explain that magma is melted rock underground and lava is the same material above ground
- Name the magma chamber, vent, and crater from descriptions of each part
- Describe the path magma takes from underground to the surface during an eruption
1 · Read
Magma is hot melted rock underground. It can also contain crystals and gas. When melted rock reaches Earth's surface, we call it lava. These names describe where the melted rock is, not two separate rock types. As magma rises, gas can bubble out and escape. Magma becoming lava does not mean that only its name changes.
Magma collects in an underground storage area called a magma chamber. A conduit is a passage through rock that carries magma upward. A vent is the opening where magma reaches the surface. A crater is a bowl-shaped hollow that can surround a vent. This example shows one route. Volcanoes can also have openings on their sides.
Magma can lose gas as it rises. Cooling lava can harden into solid rock.
Chambers store magma. Vents let it out. Craters are hollows. Erupted magma is lava.
More to read
Volcanoes 101
Some mountains are made of solid rock. But some mountains are volcanoes.
A volcano is an opening in Earth's crust. In some places underground, hot rock partly melts. This magma can contain crystals and gas as well as melted rock. It can collect in underground storage areas called magma chambers.
A passage called a conduit can carry magma toward the surface. Magma comes out through an opening called a vent. A bowl-shaped hollow around a vent is a crater. Some vents open on a volcano's sides.
Once magma erupts onto the surface, it is called lava. These names describe location. As magma rises, gas can bubble out and escape, so more than the name can change.
When lava cools down, it turns hard and becomes solid rock again. Layer after layer of cooled lava can build up into the cone-shaped mountain we call a volcano.
Most volcanoes are found around the edges of the giant plates that make up Earth's outer shell, both on land and under the ocean.
Measure a Changing Volcano
The ground around a volcano can rise and sink by small amounts. These movements give scientists clues about what is happening underground.
When magma gathers in an underground storage area, pressure can increase. The ground above may swell upward. Scientists call this inflation.
When magma leaves the storage area, pressure and the amount of magma there can decrease. The ground above may sink. Scientists call this deflation. The magma might move toward an eruption or into another underground passage. It does not have to sink back down.
Scientists use GPS to measure tiny changes in ground position. They compare the movements with other observations to study magma storage and movement. Swelling or sinking is a clue, not a complete picture of the hidden magma.
2 · Watch
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Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.