A conspicuous break in slope at approximately 3,200 metres is a summit plateau representing a caldera less than one hundred millennia old.

It consists of 18 dacitic and trachytic volcanoes including lava domes and possibly an old caldera.

Sulphur Works, an area known for its sharp, putrid scent, is thought to be the center of the old caldera.

Medicine Lake is part of the old caldera, a bowl-shaped depression in the mountain.

Steep sea cliffs on the southwest side of the island cut into the older caldera.

The most prominent area of deformation is the central caldera complex, which consists of an outer, older caldera and an inner, younger one.

Additional lava domes in the northern part of the older caldera are considered to represent flank activity of the younger caldera.

The older caldera (Caldera One) is about 4.8 km in diameter and is centered slightly northeast of the island's midpoint.

It rises above the older caldera of the Volcán Negro del Tromen.

The way this valley's topography is laid out, the whole thing could be what's left of a very large, very old caldera.