EXPERIMENTS ON INTERNAL STRAIN IN LAVA DOME CROSS SECTIONS

Abstract

Simple experiments have been conducted to study the strain evolution in lava dome cross sections. A viscous fluid is injected vertically from a reservoir into a feeding conduit. Silicone putty is used as analogue magma. Two-dimensional experiments allow the assessment of the internal strain within the dome. Particle paths are symmetrical on either side of a central line passing through the feeding conduit and display parabolic trajectories. The highest strain zone is located above the extrusion zone. In cross sections, stretch trajectories show a remarkable concentric pattern, wrapping around the extrusion zone of the analogue magma. To the lateral margins, a triple junction of stretch trajectories defines an isotropic point in the strain field. In the main central part of the dome, an intermediate zone of reversed sense of shearing is caused by a change in the sign of the velocity gradient with respect to that in the upper and lower zones. Knowledge of this evolving strain pattern can provide a better understanding of the evolution of natural domes. Also, it can help to unravel the kinematic history of ancient domes partly removed by erosion.