After an eruption, the pressure inside of the volcano is decreased, because large volumes of magma and gas have been released. The empty system of conduits and shallow reservoirs cannot support the weight of the mountain above it, so the volcano collapses on itself.

They can be steep-sided and are often circular. Calderas can be more than 25 kilometers in diameter and several kilometers deep. There can be tectonic activity in calderas, such as earthquakes, uplifts, or ground subsidence. Hot springs, geysers, boiling mud pits, and other signs of geothermal activity are also common in calderas. Caldera activity can be monitored and researched to predict future volcanic eruptions.