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.
All Science Journal Classification (ASJC) codes
- Geochemistry and Petrology