One of these funnel-shaped vents is a trough that cuts into the amphitheatre, which appears to be a remnant of a fissure vent. A second vent appears to have been about wide before the development of a third vent, which has mostly obscured the first two. The third vent is steep-walled, with a depth of ; it contains a pit that is wide, set within a small mound that is in part nested within the second vent. This third vent is surrounded by concentric faults. At least one of the vents has been described as an ash cone. A fourth vent lies on the southern slope of the composite volcano outside of the amphitheatre and has been described as a maar. It is about wide and deep and appears to have formed during a phreatomagmatic eruption. These vents lie at an elevation of about , making them among the highest vents of a Plinian eruption in the world.