Evaluation of volcano flank instability triggered by dyke intrusion

Instability of volcano flanks may result from the mechanically and thermally generated pore fluid pressures that accompany dyke intrusion. These complementary methods of pore pressure generation act on potential basal failure planes, decreasing effective stresses and consequently decreasing frictional resistance to failure. The twin agents of pore pressure generation provide a rational and quantifiable means of initiating and sustaining flank instability, even as the driving forces provided by magma pressurization ultimately drop as flank displacement is initiated, Pore pressures developed by mechanical and thermal effects are readily evaluated using simple, but mechanistically rigorous, models. Mechanically induced pore fluid pressures are evaluated through an analogy with a moving line dislocation within a saturated porous-elastic medium. Thermally induced pore fluid pressures are evaluated from a one-dimensional advective-diffusive solution for low Peclet transport, representing behaviour around a plane feeder dyke of infinite extent. Induced pore pressure magnitudes condition stability through the parameters representing the geometry and dimensions of the flank and failing flank block, together with the parameters modulating volumetric magma intrusion rate and heat supply. Where appropriate parameter magnitudes are selected, the resulting mechanical and thermal pore fluid pressures are sufficient to initiate failure. Where the pervasive influence of thermally induced pore pressures is included, or where shear collapse of the saturated pore structure occurs, the disturbance is sufficient to sustain failure. This presents the possibility for long runout instabilities of extremely large volume.