Predicting yield strengths and effusion rates of lava domes from morphology and underlying topography

To investigate the effects of slope on the morphology of lava domes, laboratory experiments were conducted with a PEG–kaolin slurry erupted into cold water on slopes ranging from 0 to 60°. In each experiment the slope, effusion rate, and water temperature were varied, producing four distinct morphologies: spiny, lobate, platy, and no-crust. Each morphology is correlated with ΨB and slope, where ΨB is defined as the ratio of the timescale of solidification to the timescale of advection. As the underlying slope increases from 0 to 40°, each morphology forms at a lower value of ΨB than it would on a horizontal surface. Above 40°, the transitions between morphologies become independent of slope and the platy morphology is no longer observed. Once a range of ΨB values for a dome is determined based on its morphology and slope, its yield strength or effusion rate can be calculated. In the case of active domes, observations of the effusion rate can be used to calculate yield strength, while for prehistoric domes an assumption of yield strength based on composition is used to determine the effusion rate. For active domes we estimate yield strengths of 0.4–7.3×105 Pa, and effusion rate ranges for prehistoric domes of 0.1–330 m3 s−1. These values compare well with yield strengths of 1.0–2.0×105 Pa measured in the laboratory and effusion rates of 0.1–40 m3 s−1 observed during historically active dome eruptions.