Geologically, Strombolicchio is a volcanic plug of extremely hard compacted basalt resistant to erosion, and is the remnant of the original volcano from which the island of Stromboli was built up, whose eruptions ceased approximately 200,000 years ago, since when the volcanic activity has moved about 3 km (1.9 mi) to the southwest. It is the only subaerial part of a submarine platform that extends between it and the main island.