A variety of breccias record the transformation of the rhyodacite Cimini dome complex from an early intrusive phase to later explosive eruptions. The character of the breccias provides insight into the eruptive styles and the surface expression of the dome complex through this transition to explosive eruptions. The 1.330 Ma crystal-rich rhyodacite lava domes were initially emplaced as cryptodomes into unconsolidated sediments, forming a peperitic breccia carapace around concentrically-banded lava domes. Continued intrusion and uplift combined to produce an emergent dome building phase of volcanism. The early-formed peperitic breccias appear to have been remobilised as debris flows from the margins of the rising edifice. These breccias roughly encircle the domes, and represent a low talus apron, which was then covered by sediment-poor rock fall or debris avalanche deposits. This phase of dome growth appears to have been non-explosive, as most of the breccias were driven by gravity. A series of block-and-ash flow deposits on the plains surrounding the domes document a more explosive phase of lava dome activity. The lava comprising the block-and-ash flow deposits has a somewhat different mineral assemblage and matrix character from any of the remaining lava domes, and may represent the destruction of a particular dome. The destruction of this dome may have depressurised the conduit and led to more explosive eruptions that formed the overlying welded ignimbrites at 1.30 Ma. Block-and-ash flow volcanism has not been previously recognized in this district, and provides a temporal and genetic link between the cryptodomes and the welded ignimbrites.
LA BERGE, R.D., Cimarelli, C., Cas, R.A.F., Giordano, G. (2004). The significance of breccias in the Monte Cimino volcanic system, central Italy: the evolution of a silicic lava dome complex from a series of cryptodomes to a pyroclastic flow generating volcano..