The domes began forming about 1,100 years ago, beginning with vent-opening eruptions, then vigorous explosive eruptions of pumice and ash followed by effusive activity. This created unstable edifices that partially collapsed and formed pyroclastic flows, similar to the most recent eruptions at the Mono-Inyo Craters. Two of the pyroclastic flows were deposited as one unit, and pumice fell to build a tuff cone at the northern edge of the Crags, while lava dome A formed and magma in the eruptive conduit cooled to plug the eruptive vent. Domes B through F followed in that order, though their exact ages remain unclear. Lasting from 1125 years ago to 1060 years ago, this eruptive phase resembled the Lassen Peak eruptions in May 1915, though the Chaos Crag eruption had a magnitude 100 times greater, with an output volume of . The eruptions also created a cone made of tephra material, along with two pyroclastic flows, which had a volume of about . Six domes were originally formed, though after 70 years of quiescence, one was destroyed by a violent eruption that produced a pyroclastic flow and tephra deposits that can be detected in Manzanita and Lost Creeks. Of the five remaining domes, two have had landslides at their domes. The dome-forming eruptions at Chaos Crags, along with the eruption of Cinder Cone and the 1914-1921 eruptions of Lassen Peak, constitute the only Holocene activity within the Lassen volcanic center. The Chaos Crags event may have been fed by the same reservoir of crystal-containing magma as the 25,000BCE and 1914-1921 eruptions at Lassen Peak, based on shared zircon age spectra, composition, and phenocryst makeup, suggesting that they have all been fed by the same reservoir of crystal-containing magma. This magma chamber has recycled old magma cooling for many thousands of years, eventually heating the mixture so that it can be erupted.