ETNA shows two types of eruptive activity: persistent activity during which lava issues continuously at a low volumetric rate over a long time, and periodic eruptions during which lava issues at a high rate over a short time. The former is from vents at or near the summit, the latter most commonly from flank vents. In some flank eruptions the lava degasses from the central vent, and in others partly from the flank vents, building scoria cones there.