How are volcanoes formed?

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Volcanoes are geological structures through which magma from the interior of the Earth rises. They originate primarily at the boundaries of tectonic plates as a consequence of their movement, although there are also so-called hotspots, where magma emerges without interaction between plates [1].

Main mechanisms of formation

1. Divergent boundaries (plates moving apart)

At mid-ocean ridges, tectonic plates move away from each other. The crust stretches and thins, creating a weak zone through which magma rises driven by convection currents from the mantle. This magma solidifies and forms new oceanic crust, building volcanoes along the ridge [2].

2. Convergent boundaries (subduction zones)

When an oceanic plate sinks beneath another plate (continental or oceanic), the material from the subducted plate heats up and partially melts as it descends into the mantle. This magma, less dense than the surrounding rock, rises through the crust and generates volcanic chains at the edge of the upper plate, as occurs in the Pacific Ring of Fire [3].

3. Hotspots

These are plumes of hot material that rise from deep within the mantle, piercing the tectonic plate that moves over them. As the plate moves, a chain of volcanoes of progressive ages is formed, such as the Hawaiian archipelago [4].

From magma to volcanic structure

Magma rises through conduits and magma chambers, mobilizing and deforming rock layers. When it reaches the surface through an eruptive vent, it erupts as lava, ash, and gases. The successive accumulation of these materials around the emission zone builds the volcanic edifice, which can take the form of a cone, shield, or other morphologies depending on the type of eruption and the viscosity of the lava [5].

Types of volcanoes according to their formation

• Shield volcanoes: Formed by very fluid (basaltic) lavas that flow long distances, creating gentle slopes. Typical of hotspots and mid-ocean ridges [6].
• Stratovolcanoes (composite volcanoes): The result of alternating explosive and effusive eruptions, with layers of lava, ash, and pyroclastics. They have steep slopes (e.g., Mount Fuji, Cotopaxi) [6].

In summary, volcanic formation is a prolonged geological process where the Earth's internal heat generates magma which, upon rising and erupting, progressively builds the reliefs that we recognize as volcanoes.