Short answers, pulled from the story.
A volcano is a rupture in a planet's crust where material escapes from a magma chamber below the surface. Most volcanoes form where tectonic plates diverge or converge, allowing hot lava, volcanic ash, and gases to escape through vents.
The 1902 eruption of Mount Pelée destroyed the city of Saint-Pierre in Martinique during the year 1902. This Plinian eruption produced sustained huge eruption columns whose collapse created catastrophic pyroclastic flows that killed thousands of people.
Most of Earth's plate boundaries lie underwater, meaning most volcanoes exist beneath the ocean surface as common features of the ocean floor. Black smokers serve as evidence of this submarine volcanic activity while pillow lava forms thick sequences of discontinuous masses on the seafloor.
Volcanoes at subduction zones tend to be extremely viscous due to high silica content in the magma formed by flux melting. In contrast, shield volcanoes form by the eruption of low-viscosity basaltic or andesitic lava that can flow great distances.
The Smithsonian Institution's Global Volcanism Program database lists 9,901 confirmed eruptions from 859 volcanoes during the Holocene Epoch. Decade Volcanoes include 16 specific sites identified for study due to history of large destructive eruptions such as Mount Etna in Sicily.