How volcanoes erupt

Many of us are interested in how volcanoes erupt.
Many large volcanoes on Earth are capable of explosive eruptions much bigger than any experienced by humanity over historic time.Unlike other mountains, which are pushed up from below, volcanoes are built by surface accumulation of their eruptive products—layers of lava flows, ash flows, and ash. When pressure from gases within the molten rock becomes too great, gases drive the molten rock to the surface and an eruption occurs.This is how volcanoes erupt.
The molten rock that comes out of a volcano has been brought to the surface by a combination of things. The main one is the force of gravity: the molten rock is not as dense as the rocks around it so it tries to go upwards, just as the heated wax in a lava lamp will rise.
The gases dissolved in it are also one thing that helps it erupt (like carbon dioxide and sulphur dioxide), which come out as bubbles as the pressure reduces when it nears the surface and can force it out explosively, a bit like when you shake up a Coke bottle and take the top off: the gas forces out the Coke in a fountain.
Most gases from a volcano quickly blow away. However, heavy gases such as carbon dioxide and hydrogen sulfide can collect in low-lying areas.Although gases usually blow away rapidly, it is possible that people who are close to the volcano or who are in the low-lying areas downwind may be exposed to levels that may affect health.At depth in the Earth nearly all magmas contain gas dissolved in the liquid, but the gas forms a separate vapor phase when pressure is decreased as magma rises toward the surface of the Earth.In 1984, CO2 gas escaping from the bottom of Lake Monoun, a crater lake in the African country of Cameroon, killed 37 people.In 1986 an even larger CO2 gas emission from Lake Nyos in Cameroon killed more than 1700 people and 3000 cattle.Clouds of gas and tephra that rise above a volcano produce an eruption column that can rise up to 45 km into the atmosphere. Eventually the tephra in the eruption column will be picked up by the wind, carried for some distance, and then fall back to the surface as a tephra fall or ash fall.