A Rhythmic Volcanic Engine
For at least two millennia, the island of Stromboli has been in a state of near-continuous eruption. This activity defines a specific eruption style, which volcanologists call "Strombolian," characterized by rhythmic, mild explosions. These bursts occur roughly every 10 to 20 minutes, ejecting incandescent fragments of lava—known as scoria and volcanic bombs—up to a few hundred meters into the air. The volcano's summit stands 924 meters above sea level, but the entire structure rises over 2,700 meters from the floor of the Tyrrhenian Sea.
The mechanism driving this persistent activity is a process of magmatic degassing. The magma feeding Stromboli is a potassium-rich basalt. As it rises, the decrease in pressure allows dissolved gases like water vapor and carbon dioxide to come out of solution and form bubbles. These bubbles coalesce into large pockets known as "gas slugs." These slugs ascend through the magma conduit and burst upon reaching the lower pressure at the surface, throwing molten rock into the air. This process can repeat itself indefinitely because the conduit system is not significantly damaged by these mild eruptions. The shallow magma chamber that fuels this activity is located between 2 and 4 kilometers below sea level.