when volcano erupt it get bigger and bigger. Volcano erupt because of the dentsity and pressure.But there is a good thing about volcano if the ash is fine it break down quickly and get mixed with the soil. It will helped plant grow but it will take a wile to break down.
It is also dangerous for the plant near the volcano it can make bush fire. After the eruption is finish it can break down into soil. the lava is very hot it can burn metal,wood,brick and more it is so hot it can burn gold that's why is so dangerous.