TY - JOUR

T1 - The Hidden Internal Flow Dynamics of Shear‐Thinning Magma in Dikes

AU - Kavanagh, Janine L.

AU - Chalk, Caitlin M.

AU - Jones, Thomas J.

AU - Dennis, David J. C.

PY - 2025/4/30

Y1 - 2025/4/30

N2 - The viscosity of magma has a first‐order control on the explosivity and hazards of a volcanic eruption, and the detection of diking within the subsurface may indicate an eruption is imminent. As magma approaches the surface it is highly likely it will have a non‐Newtonian shear‐thinning rheology (apparent viscosity decreases as shear rate increases), yet most dike models assume magma is a simple Newtonian fluid. Here we use laser light and particle image velocimetry to image flow within a scaled experimental dike hosting a shear‐thinning fluid. The results show that the internal flow dynamics of shear‐thinning magma in dikes are very different to Newtonian dikes. The velocity of shear‐thinning flow radiates out toward the dike margin at similar magnitude across the dike plane; this is very different to the jet flow and recirculation characteristic of the Newtonian dike model at the same conditions. A linear relationship between tip velocity and inlet Reynolds number Re in ${\text{Re}}_{\text{in}}$ in the viscous regime ( Re in ≲ 0.4 ${\text{Re}}_{\text{in}}\mathit{\lesssim }0.4$ ) is confirmed to also apply to shear‐thinning fluids, and transitional flow ( 0.4 ≲ Re in ≲ 100 $0.4\mathit{\lesssim }{\text{Re}}_{\text{in}}\mathit{\lesssim }100$ ) is generated experimentally for the first time. These findings suggest that magma rheology (Newtonian or shear‐thinning) cannot be recognized from external factors, such as the dike tip velocity. These results mark a step‐change in dike modeling, introducing a new physical framework to test the petrological and geochemical evidence of magma ascent dynamics in dikes leading to volcanic eruptions.

AB - The viscosity of magma has a first‐order control on the explosivity and hazards of a volcanic eruption, and the detection of diking within the subsurface may indicate an eruption is imminent. As magma approaches the surface it is highly likely it will have a non‐Newtonian shear‐thinning rheology (apparent viscosity decreases as shear rate increases), yet most dike models assume magma is a simple Newtonian fluid. Here we use laser light and particle image velocimetry to image flow within a scaled experimental dike hosting a shear‐thinning fluid. The results show that the internal flow dynamics of shear‐thinning magma in dikes are very different to Newtonian dikes. The velocity of shear‐thinning flow radiates out toward the dike margin at similar magnitude across the dike plane; this is very different to the jet flow and recirculation characteristic of the Newtonian dike model at the same conditions. A linear relationship between tip velocity and inlet Reynolds number Re in ${\text{Re}}_{\text{in}}$ in the viscous regime ( Re in ≲ 0.4 ${\text{Re}}_{\text{in}}\mathit{\lesssim }0.4$ ) is confirmed to also apply to shear‐thinning fluids, and transitional flow ( 0.4 ≲ Re in ≲ 100 $0.4\mathit{\lesssim }{\text{Re}}_{\text{in}}\mathit{\lesssim }100$ ) is generated experimentally for the first time. These findings suggest that magma rheology (Newtonian or shear‐thinning) cannot be recognized from external factors, such as the dike tip velocity. These results mark a step‐change in dike modeling, introducing a new physical framework to test the petrological and geochemical evidence of magma ascent dynamics in dikes leading to volcanic eruptions.

KW - volcanic plumbing systems

KW - dyke

KW - viscosity

KW - magma ascent

KW - analog experiments

KW - magma rheology

U2 - 10.1029/2024av001495

DO - 10.1029/2024av001495

M3 - Journal article

VL - 6

JO - AGU Advances

JF - AGU Advances

SN - 2576-604X

IS - 2

M1 - e2024AV001495

ER -