Circular calderas in the Mount Edziza volcanic complex were formed as a result of emptying the magma chamber beneath a volcano. If enough magma is erupted, the emptied chamber will not be able to support the weight of the volcanic edifice above it. A roughly circular fracture— a ring fault— develops around the edge of the chamber. These ring fractures serve as feeders for fault intrusions that are also known as ring dikes. Secondary volcanic vents form above the ring fracture. As the magma chamber empties, the centre of the volcano within the ring fracture begins to collapse. The collapse may occur as the result of a single cataclysmic eruption, or it may occur in stages as the result of a series of eruptions. These caldera collapses are relatively small compared to most other caldera collapses. The largest caldera at the Mount Edziza volcanic complex is about in diameter while most calderas are at least in diameter. Volcanic eruptions accompanying these collapses produced trachyte and a white, sodic rhyolite called comendite.