When a volcanic eruption occurs, magma and other materials such as gases, ashes and pieces of rocks are released to the planet's surface. Magma is formed by minerals and rocks melted at high temperatures from the interior of the earth. When it is released on the Earth's surface through an eruption, it turns into lava, which once solid turns into magmatic rocks. What will determine the shape of the volcanic relief is the ownership of the lava and the manner in which the volcanic eruption occurred.
Volcanic eruptions cause magma to rise through cracks or weaknesses in the Earth's crust and when the pressure is released magma explodes causing a volcanic explosion. Hope this helps! :)
