Shallow Plumbing Geometry and Eruptive Processes of a Monogenetic Volcano, Lunar Crater Volcanic Field, Nevada.

摘要

Numerical eruption models and hazard assessments assume simple geometries such as straight-sided or flaring cylinders to represent the shape of the near-surface conduit; however, little field data exist to support these assumptions. Also lacking is a coupling of the volcano's eruption styles with its shallow plumbing geometries due to the destruction of the scoria cone typically necessary for exposure of the feeder system. A study of the Pliocene-aged Dark Peak, located in the southern Lunar Crater Volcanic Field, Nevada, focuses on measuring the shallow feeder system's geometry, mapping lithologic units, and performing detailed descriptions of ten features of interest, all intended to fill data gaps related to scoria cone eruptions. The conduit, one of the ten features, is located near the edifice's current summit and characterized by a flaring of the feeder dike 15 meters below the paleosurface. The conduit is funnel-shaped and in cross-section up to 30 meters wide, consistent with published geometries at other monogenetic volcanoes. Along with the conduit, nine other named intrusive (feeder dike, south dike, and boca) and depositional features (east and west features, north and west beds, lava field, and vent area) reveal the pre-eruptive topography and eruptive history of Dark Peak. The paleotopography was dominated by small ridges and drainages that comprised the western slope of a north-south trending ridge of rhyolitic tuff. The Dark Peak scoria cone was composed of clastogenic lava flows, welded and non-welded agglomerate and a summit likely ~125 m above the paleosurface. In situ agglomerate beds indicate the base of the cone was roughly 1000 m in diameter and that it was buttressed against paleo-ridges on its north, east, and south flanks.