Ash

This is an image of the eruption of Mt. Pinatubo. Click on image for full size version (128K GIF) Image from: U.S. Geological Survey

Ash is formed during an eruption when rock and lava blow apart into millions of tiny pieces.

Falling ash can sometimes cause more damage than flowing lava because ash can be carried great distances through the atmosphere. Volcanoes have a cooling effect on weather because the ash remains in the sky and reduces the amount of sunlight reaching the surface. Ash however, also carries important nutrients to the soil on which it finally lands.