Volcanoes are often situated atop the borders of tectonic plates on the earth's crust. When a volcano erupts, it releases a tremendous amount of force, with hot lava spilling out over the surface of the earth. This causes death and destruction of property. In addition, ash and smoke from the volcano causes air pollution in a huge area outside of the vicinity of the volcano. Great clouds of ash can be carried by wind to neighboring countries. For example, when there is a volcanic eruption in Sumatra. Indonesia. ash is often blown to Malaysia and even to some of Thailand's southern provinces.