The upper part of the magma chamber froths, expands and flows up the vent. The magma chamber is then depleted in gases and minor volcanic activity can persist along the ring fracture for as much as a million years. Large resurgent calderas are among the most destructive natural catastrophes on Earth. Other resurgent caldera examples are Long Valley caldera in California, Yellowstone caldera in Wyoming, and Toba caldera in northern Sumatra. Olympus Mons on Mars is the largest and most spectacular caldera ever discovered.
Gas is also a part of the pyroclastic flow.
After the pyroclasts settle, the deposit areas lithify and become cemented together. The resulting rocks formed by the smaller pyroclasts are called tuffs . The lower Bandelier tuff which can be seen along canyon walls west of the Valles caldera, including San Diego canyon, is related to the eruption and collapse of the Toledo caldera. The upper Bandalier tuff is believed to have been deposited during eruption and collapse of the Valles caldera. The now eroded and exposed orange-tan, light colored Bandelier tuff from these events create the stunning mesas of the Pajarito Plateau.