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Fire Beneath Our Feet

Deep below the ground you walk on every day, the Earth stores tremendous heat. This heat has been trapped inside the planet ever since it first formed. Some of that warmth also comes from natural elements that release energy as they decay. In certain regions, rock grows so hot that it melts into a thick, glowing liquid. Scientists call this molten rock magma while it still lies hidden underground. Because magma weighs less than the solid rock around it, it slowly rises toward the surface. Over many years, the magma gathers inside enormous chambers beneath the crust. A volcano is simply a place where this trapped heat finally finds an escape. Once the magma bursts free at the top, we call it lava instead.

Why Pressure Builds

Magma does not rise quietly, because it carries many dissolved gases trapped within it. As the magma climbs higher, the weight of rock pressing down on it steadily decreases. The freed gases then expand, much like the bubbles in a soda bottle that has been shaken. When the swelling pressure grows stronger than the rock above, the volcano finally erupts. The type of eruption depends greatly on how runny or sticky the rising magma is. Thin magma pours out in gentle streams that glow bright orange against the night. Thick magma traps its gases inside, so the eruption can explode with sudden, deadly force. By carefully studying these gases, scientists can sometimes warn people before disaster strikes.