Volcano eruptions are a matter of pressure

QUESTION: How do volcanoes explode lava?

ANSWER: A good analogy for a volcano eruption and the spewing of lava is the uncorking of a champagne bottle. You'll often see at a celebratory occasion that when a bottle cork is popped, a large amount of bubbly liquid will gush out of the opening.

Why? This is because in the beverage-making process a lot of carbon dioxide gas is forced into the liquid in a process known as carbonation. The containment of all the gas makes the pressure inside the bottle higher than it is outside. Consequently, when the bottle is opened, the high pressure finds a relief outlet and pushes the liquid and the gas out together. The higher the pressure, the larger the force pushes out the liquid-gas mixture, and thus the farther the champagne sprays.

Getting back to our main question: Volcanoes are like a champagne bottle. Inside of a volcano, you'll find a lot of liquid — magma — and gas. Pressure builds up inside the volcano over time, and when the pressure reaches an extremely high level, it ruptures the ground and out comes the lava.

Obviously, no human beings forced gas into the volcanoes. In some volcanoes, the gas was trapped inside when the earth formed, billions of years ago. In other volcanoes, the gas inside is actually steam. Water above ground or from the ocean finds a passage and flows into a volcano. Once inside, the water touches the super-heated magma, gets evaporated and becomes the steam that is trapped inside. As more water flows in, more steam is generated and builds up the pressure inside until the volcano eventually "pops."

These are only two examples of the possible mechanisms that lead to high pressure inside of volcanoes, as each active volcano has a different composition and a unique underground physical condition.

Fortunately, most volcanoes do not shoot out lava jets like champagne bottles do with its liquid inside. High-flying lava certainly would not bring out any celebratory mood!

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