Why did the volcano erupt?

On the earth where we live, there are often volcanic eruptions. Whenever a volcano erupts, very hot magma from the crater flows everywhere, destroying crops and houses. So why did the volcano erupt?

It turns out that the earth's crust is rock, and magma is deep below the crust. Usually, magma is tightly wrapped by the crust. The temperature inside the earth is particularly high, so the temperature of magma is also very high. Magma flows around inside. I can't stay. I always want to find a place to drill outside. Because some parts of the earth's crust move strongly, cracks appear, and some parts are relatively thin. When these parts are under pressure, magma will erupt from these parts, which is volcanic eruption, or volcanic eruption.

When the volcano is cold, it is a pile of magma. There is a crater on the top of the mountain where the magma is ejected. Some volcanoes erupted only once, called dead volcanoes, while others erupted several times, called active volcanoes.