Solidification dynamics in channeled viscoplastic lava flows

Abstract

The influence of a viscoplastic lava rheology on the dynamics of channeled lava flows is analyzed using analogue experiments. The experiments used slurries of polyethylene glycol and kaolin, which flowed with a constant flux down an inclined channel under water. Three sets of complementary experiments are presented: isothermal, cooling, and solidifying flows which quantified the effects of the viscoplastic rheology on shear, internal convection and surface crust formation. The isothermal and cooling experiments showed the formation of unyielded central plug regions which were not broken up by the convective overturning. In the solidifying experiments flows fell into one of three regimes: a tube regime, in which crust covered the entire flow surface; a shear‐controlled regime, with a mobile raft of crust in the channel center and open shear zones near the walls; and a plug‐controlled regime where the width of the central crust was determined by the width of the central plug region. The crust coverage is parameterized in terms of two dimensionless parameters: the ratio wp of central plug region width to channel width and a parameter ϑ which characterizes the relative importance of the strain and solidification rates. Finally the dynamics of typical lava flows on Mt Etna and the 1984 Mauna Loa lava flow are examined. We show that our parameterization agrees with lava flow crust widths observed in the field and find that even small yield strengths have a major effect on crust coverage.