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How does magma form volcanic mountains?

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A car drives along the Trans-Canada Highway with Mount Sir Donald's sharp, snow-capped peak rising above forested slopes in the Selkirk Mountains, British Columbia. — mountain Mount Sir Donald in the Selkirk Mountains, British Columbia, looms above a segment of the Trans-Canada Highway.

Volcanic mountains are formed through the process of volcanism, where magma—molten or partially molten rock—rises from the mantle and crust to the Earth's surface.12

Magma typically forms through the partial melting of the mantle or crust, often triggered by plate tectonic activity. At subduction zones, for instance, water trapped in a sinking plate is released, lowering the melting point of the overlying mantle and generating magma. Because this magma is more buoyant than the surrounding solid rock, it rises toward the surface, where it may collect in chambers.23

When internal pressure exceeds the weight of the overlying rock, the magma erupts through vents. The accumulation of this erupted material—such as lava and volcanic debris—builds the mountain landform over time. The specific shape and height of these mountains are determined by factors such as the volume of material, the frequency of eruptions, and the viscosity of the magma, which is influenced by its chemical composition.241