The term “Strombolian” eruption means an activity formed by explosions of low and medium energy, with the launch of bombs and incandescent lapilli around the crater area. Periodically, this activity is also interspersed with the emission of lava flows along the slopes of the volcano. This is the typical activity of Stromboli, and this definition is applied to hundreds of other volcanoes around the world.
Stromboli’s summit craters often change shape and layout. The type of activity is distinguished in different ways, depending on the frequency of the explosive events.
The basic activity is “puffing”, i.e. small puffs of steam from all the craters; each puff occurs every 3-4 seconds. When some gas accumulates under the mouth of the volcano, it can cause a jet of steam up to 30-40 metres tall, which may also be reddish in colour. Usually, but depending on the volcano’s pattern in a certain period, this type of activity takes place every 15-20 minutes, often from one of the outermost craters.
Then there is the real explosion: below the crater several bubbles of gas can accumulate from the depths, coming together to form bubbles that are a little bigger.
At some point the magma is no longer able to contain them and explodes bringing with it scraps of lava in the form of bombs (if larger than 6 cm) and lapilli (1-6 cm).
These types of explosions are the most common and most spectacular and have an interval of 10-20 minutes depending on the volcano’s pattern of activity.
In fact, there are periods in which the volcano is “more active” due to a recent rise of magma from the depths, and periods in which it is more “relaxed”, perhaps after a slightly bigger eruption, such as the escape of lava flows.