How dangerous is a volcano?

Volcanoes vary a great deal in their destructive power.

Some volcanoes explode violently, destroying everything in their reach within minutes, while other volcanoes release lava so slowly that you can safely walk all around them.

The severity of the eruption depends mostly on the composition of the magma.

Generally speaking, the more viscous the magma is and the more gas it contains, the more violent the eruptions are.

When is the magma viscous?

If the erupting magma contains a high percentage of silica the lava tends to be very viscous and is pushed up in a blob that will solidify relatively quickly.

This type of volcano has a tendency to explode because the magma often forms a plug.

If, on the other hand, the magma contains relatively small amounts of silica, the lava will be very fluid as it erupts, capable of flowing for long distances.

What happens if there is gas in the magma?

The amount of gas contained in the magma is also crucial: if there are a lot of tiny gas bubbles in the molten rock, the volcano behaves like a soda bottle that has been shaken and is now opened. As the bubbles escape, they push the magma out, causing a spewing eruption. 

Did you know?

The movie you can see in the Volcano Chamber of the blue cube in Danfoss Universe was compiled from material filmed by the French volcanologists Katja and Maurice Krafft.

They were passionate observers of volcanic eruptions and documented about 140 of them.

Tragically, they were killed in an eruption of Mount Unzen (Japan) in 1991.