What lithic clasts and lithic-rich facies can tell us about diatreme processes: An example at Round Butte, Hopi Buttes volcanic field, Navajo Nation, Arizona

Round Butte (Hopi Buttes volcanic field, Arizona) exposes a diatreme 170–190 m across, 190 below the pre-eruptive surface. The central part of massif is 130–150 in diameter, displaying 20–30 m-high subvertical cliffs. well-known layer-cake stratigraphy sedimentary rocks Colorado Plateau permits identification largest lithic fragments preserved diatreme. We define three main groups pyroclastic facies: undisturbed beds, disturbed beds and non-bedded rocks. Two other minor facies were mapped: megablocks (blocks over 2 long axis), small-volume debris avalanche deposits. Pyroclastic are finer grained richer clasts than most surrounding them. These interpreted as subsided portions maar ejecta ring. Sedimentary originate either from above, or same level, relative to their current location, i.e. no megablock has net upward displacement. Small-volume deposits poorly sorted resulting gravitational destabilization country into syn-eruptive crater. avalanches individual collapse ways which crater grew size laterally during eruption. combine componentry bedded facies, with series conceptual models for rock fragmentation. This exercise further allows us estimate wall slopes 70° Bidahochi Formation approximately depth root zone around 440 Lithic at level exposure come elevations up above (i.e., surface) 250 down zone) locations. units richest content deep origin typically have formed jets