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What Causes Volcanoes to Grow Bigger?

A volcano is formed when molten rock below Earth's surface, called magma, forces its way above ground. Like other features of Earth's surface, volcanoes comprise materials arranged in layers. The way that these layers form and the materials that contribute to them are the main factors that make volcanoes ̶0;grow.̶1; They build upon the activity that leads to magma erupting and also lend to the distinctions that help us group volcanoes into different types.

Cinder Cone Volcanoes
- While all magma contains gas, the thickness of the magma will determine that gas' explosiveness. Magma that flows at a cooler temperature and contains more of the mineral compound silica is more viscous and traps gas until pressure builds, causing a violent eruption. The molten rock, called lava above ground, flies from Earth's surface in chunks called cinders. Cinders built up around an eruption site to create a cinder-cone volcano that grows as more cinders land.
Shield Volcanoes
- Accumulation of lava blown into the air is one way that a volcano can increase in size. Volcanoes also can grow from slow lava flows that appear simply to spill through cracks in Earth's crust. This less viscous lava eventually cools and hardens. As more lava settles in layers on top of it, it builds up a volcano with gently sloping sides that looks like a warrior's shield, giving it the name ̶0;shield volcano.̶1;
Composite Volcanoes, or Stratovolcanoes
- Molten rock from below the surface is not the only material that may be hurled into the air during a volcanic eruption. An explosion of lava can stir fragments of other rocks from the surrounding landscape and bits of ash into substantial clouds called tephra. When tephra settles in layers, alternating with cooled lava flow, it builds up what is called a composite volcano, or stratovolcano, a steep-sided volcano often reaching high into the sky.
Mantle Flow
- Although material landing on the surface of a volcano plays a major role in growing it, activity below the surface also encourages its growth. At times, the layer of molten rock known as the mantle pushes through the ground at spots far from the boundaries between sections of Earth's crust, where volcanoes usually form. Researchers believe that pressure from this mantle flow may have been enough to grow mountains as well as volcanoes in our planet's past.
Supervolcanoes and Calderas
- Geological studies suggest that Earth's history also has been marked by explosions of supervolcanoes, which eject more than 240 cubic miles' worth of debris when they erupt. While these explosions would have deposited significant amounts of rock and ash, the more likely remnants of their bursts are thought to be calderas, enormous depressions created when magma chambers are completely emptied. The ground sinks, meaning that volcanic activity can reduce the land as well as build it up.

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