Eruption Types & Volcano Shape
Understand that not all volcanic eruptions are the same: some flow gently (effusive) and some explode violently (explosive), depending on the properties of the magma, and that volcano shape is related to eruption type
What a learner can do afterwards
- Contrast effusive eruptions (gentle lava flows) with explosive eruptions (violent blasts of ash and rock)
- Explain that eruption type depends on properties of the magma such as thickness and gas content
- Connect volcano shape to eruption style: shield volcanoes from runny lava, steep cones from thick explosive magma
The lesson
You already know magma sits in a chamber under a volcano. But not every volcano erupts the same way. Some ooze gently. Some blast violently into the sky.
The difference comes down to the magma itself. Thin, runny magma lets gas bubble out easily, so the eruption stays calm. That is called an effusive eruption. Thick, sticky magma traps gas inside it. The trapped gas builds up pressure until it bursts out all at once. That is an explosive eruption.
In Hawaii, thin lava flows slowly down the mountainside like syrup, giving people time to walk away. At Mount St Helens in 1980, thick magma trapped so much gas that a whole side of the mountain blew apart in one violent blast.
You can guess a volcano's history just from its shape. A wide, gently sloped volcano built itself from thin, runny lava. A tall, steep cone built itself from thick, explosive blasts.
Runny magma erupts gently and builds wide, flat volcanoes; thick magma erupts violently and builds tall, steep cones.
Watch it
Where it sits
This opens up
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.