Basaltic near-vent facies of Vulcan Cone, Albuquerque Volcanoes, New Mexico

Vulcan cone is the largest and central-most fissure vent among the -156-ka Albuquerque Volcanoes. The eruptive center consists of a large central cone (-60 m high) with two smaller flanking cones (-10-15-m high) on the south and southwest. Vulcan exhibits complex facies relationships between welded and nonwelded cinder, agglutinated spatter, clastogenic lava flows, pahoehoe flows and a fountain-fed lava pond that are consistent with Hawaiian-style eruptions. The three cones are spatter cones composed mostly of agglutinate and clastogenic lava flows. The central cone is locally armored by thin pahoehoe lava flows that formed from overflow of a late-stage lava pond from its crater. Abundant spatter and cinder were produced by early-stage lava fountaining that was apparently more vigorous at the southwest flank cone. Shortly thereafter, the dominant lava discharge was established at the central cone. A broad platform of shelly pahoehoe flows north of the central cone was likely constructed by discharge from a breach in the north wall of the central cone. This breach was not persistent, however, and permitted formation of a late-stage lava pond that eventually overflowed the west and northwest sides of the cone where the agglutinate rim was lowest because of westerly prevailing wind. Lava flows from all three vents are mostly thin, shelly pahoehoe, which constructed a broad shield adjacent to the north and west sides of the vent complex. Some lava flows that exited the northern breach and spilled over the northwest rim contain small-diameter surface lava tubes. These tubes formed by roofing over of small lava channels or by continual transport of lava through expanding pahoehoe toes of unusual length (roughly 100 m) that initially formed by rapid descent of toes down moderately steep slopes.