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What makes some volcanoes more destructive than others?
Answered by Discovery Channel
  • Discovery Channel

    Discovery Channel

  1. Volcanoes vary greatly in their destructive power. Some erupt violently; others release lava so slowly that tourists can walk around them. The destructive power of a volcano depends on the viscosity and gas content of the magma. Under normal circumstances, the vapor pressure of the dissolved gas is weaker than the confining pressure of the rock surrounding it. When this balance shifts, and the vapor pressure becomes stronger than the confining pressure, the gas begins to expand. As the gas expands, tiny gas bubbles called vesicles are created. The vesicles give the magma a lower density than the surrounding magma, so they explode up to escape. Picture a soda bottle: If you shake it and the gas bubbles inside mix with the fluid, once the cap comes off the bubbles explode out, bringing some of the liquid with them. If a volcano's magma has high viscosity, it doesn't flow easily; in such cases, the gas bubbles in the magma have a hard time escaping, which causes stronger eruptions. If the magma is very fluid, the gas bubbles can escape easily, which then results in weaker eruptions.

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