Volcanic eruptions and feature The magma controls when a volcano erupts and decides how the lava will flow and the volcanic features. Have you ever thought of squeezing a tube of toothpaste and then it comes out slowly ? Imagine instead of toothpaste it has water wouldn't it have an effect on how it flows ? Think of it like a volcano . If the magma controls the way the lava flows then wouldn't it be like the toothpaste and water project? If the lava comes out like toothpaste then it will come out slow and gooey. If it comes out like water then it will come out pretty fast . That is how they will change the eruptions and features.