Shallow plumbing and eruptive processes of a scoria cone built on steep terrain

Abstract

Dark Peak (Lunar Crater Volcanic Field, central Nevada, USA) is an eroded Pliocene, monogenetic basaltic volcano that exposes intrusions while preserving some pyroclastic deposits and lavas, allowing reconstruction of the shallow magma feeding system and its relation to eruptive processes. Variably welded agglomerates record Strombolian and Hawaiian fountaining. Dikes fed degassed magma to a bocca on the lower cone slopes and fed a small lava field. The cone was built on the side of a steep ridge with small side drainages, had a maximum diameter of about 1km, and was ~125m high above the highest point on the paleotopography. The eruption was fed by an ~1km long, narrow (1–3m) feeder dike that locally flared in the upper tens of meters to form an ~30m wide conduit around which the cone was built. The conduit shape and the transition depth from feeder dike to conduit are consistent with data from other exposed plumbing systems of small volume basaltic volcanoes that were dominated by magmatic volatile-driven eruption styles, supporting inferences that their conduits are relatively shallow features (upper ~150m).