Terrifying Explosions Versus Calm Eruptions
What causes some volcanoes to explode in devastating and deadly eruptions, while other volcanoes calmly pour their lava across the landscape with virtually no explosions what-so-ever?
The most important factor that determines what type of eruptions that a volcano will experience is chemistry. In other words, the substances found in the magma determine how it will erupt. A volcano whose molten magma contains large amounts of a substance called silica tend to explode with great energy.
Volcanoes that contain little or no silica usually do not explode, but instead calmly release rivers of lava across the landscape. Volcanoes do not typically change their eruption type. Volcanoes that explode, will always explode, while those that release their lava in calm flows, will always do so.