Morphologic variation of an evolving dome controlled by the extrusion of finite yield strength magma

Degassing-induced crystallization in volatile rich intermediate composition magmas results in material stiffening and strengthening that prior to solidification is reflected in non-Newtonian rheology. We explore the effects of a spectrum of such rheological regimes on eruptive style and morphologic evolution of lava domes, using a two-dimensional (2D) particle-dynamics model for a spreading viscoplastic (Bingham) fluid. We assume that the ductile magma core of a 2D synthetic lava dome develops finite yield strength, and that deformable frictional talus evolves from a carapace that caps the magma core. Our new model is calibrated against an existing analytical model for a spreading viscoplastic lava dome and is further compared against observational data of lava dome growth. Results indicate that a degassing-induced increase in strength of the injected magma causes a transition in the lava dome morphology from a dome with low surface relief evolving endogenously (with apparent bulk yield strength - 10 ⁴ < τ _{0 a} < 10 ⁶ Pa), to a Pelean lava dome with spines (τ _{0 a} > 10 ⁵ – 10 ⁶ Pa) extruded through the dome carapace. The virtual lava dome with τ _{0 a} = 0.6 MPa shows good agreement with the observed dome heights observed at the Soufriere Hills Volcano, Montserrat during a period of endogenous growth. The calculated apparent flow viscosity (1.36 × 10 ¹¹ Pa·s for τ _{0 a} = 0.6 MPa) is in the range of estimated viscosities (10 ⁹ to 10 ¹² Pa·s) for andesitic-dacitic crystal-rich lavas. Our model results indicate a strong correlation between apparent yield strength and dome morphology, with both controlled by degassing-induced crystallization and extrusion rate.