Morphology and dynamics of explosive vents through cohesive rock formations

Shallow explosive volcanic processes, such as kimberlite volcanism and phreatomagmatic and phreatic activity, produce volcanic vents exhibiting a wide variety of morphologies, including vertical pipes and V‐shaped vents. In this study we report on experimental and numerical models designed to capture a range of vent morphologies in an eruptive system. Using dimensional analysis, we identified key governing dimensionless parameters, in particular the gravitational stress‐to‐fluid pressure ratio (Π 2   = P/ρgh ) and the fluid pressure‐to‐host rock strength ratio (Π 3  = P/ C ). We used combined experimental and numerical models to test the effects of these parameters. The experiments were used to test the effect of Π 2 on vent morphology and dynamics. A phase diagram demonstrates a separation between two distinct morphologies, with vertical structures occurring at high values of Π 2 and diagonal ones at low values of Π 2 . The numerical simulations were used to test the effect of Π 3 on vent morphology and dynamics. In the numerical models we see three distinct morphologies: vertical pipes are produced at high values of Π 3 , diagonal pipes at low values of Π 3 , and horizontal sills at intermediate values of Π 3 . Our results show that vertical pipes form by plasticity‐dominated yielding in high‐energy systems (high Π 2 and Π 3 ), whereas diagonal and horizontal vents dominantly form by fracturing in lower energy systems (low Π 2 and Π 3 ). Although our models are two‐dimensional, they suggest that circular pipes result from plastic yielding of the host rock in a high‐energy regime, whereas V‐shaped volcanic vents result from fracturing of the host rock in lower energy systems.