Question

how volcano erupt. what damage it do to earth

Answer 1

Volcanoes erupt because of density and pressure. The lower density of the magma relative to the surrounding rocks causes it to rise (like air bubbles in syrup). It will rise to the surface or to a depth that is determined by the density of the magma and the weight of the rocks above it.

damages are
The gases and dust particles thrown into the atmosphere during volcanic  eruptions have influences on climate.
Volcanic eruptions can cause earthquakes, fast floods, mud slides, and rock falls. Lava can travel very far and burn, bury, or damage anything in its path, including people, houses, and trees.