Volcanoes Belch Out Ash, Why?
Volcanic ash is not like traditional ash. Normally, ash is what is left after the burning of organic material — a definition that does not include the stuff that comes out of volcanoes in large clouds. The reason this fine volcanic material is still called ash is that it looks and behaves like real ash. But it is created in a totally different way.
A volcano is formed where magma from the interior of the Earth moves all the way to the surface through the Earth’s crust. It often happens where the crust is thin and there is a magma overpressure at the same time. While the magma moves upward, it is subjected to ever lower pressure from its surroundings.
When it finally breaks through the Earth’s surface, there is one last significant loss of pressure, and the magma cools down very quickly. Thus, a fine, hardened powder called ash is formed.
Some ash remains in the crater, while the rest may travel more than 12 miles high with the hot air above the volcano. Different types of volcanoes generate different amounts of ash. Generally, stratovolcanoes generate more ash than volcanoes with easy-flowing magma.
Liquid magma is converted to ash
When magma moves up through the Earth’s crust, it is subjected to ever lower pressure; gases that have been mixed into the magma under high pressure are released as bubbles, which turn into ash.
1 . At first, only a few small bubbles form, but they grow and increase in number as more and more gas is released due to loss of pressure.
2. At some point, the bubbles make up most of the magma (“magma” refers to both the gaseous and the liquid state).
3. The bubbles collect, and the mixture turns from a liquid with gas bubbles to a gas with liquid drops.
4. When the magma exits the crater, the temperature of the drops falls quickly, and they harden, becoming ash.