Growth of the volcano-flank Koa’e fault system, Hawaii

Structural mapping of the Koa’e fault system, located on the south flank of Kilauea Volcano, Hawaii, has been carried out to study the relationship between fault propagation and re-surfacing by lava flows. The 1.9-km long White Rabbit Fault faces uphill towards the summit of the Kilauea, and has produced c. 8 m vertical offset of a young lava flow (500–750 years). The fault exhibits multiple peaks in its throw-distance profile, suggesting recent linkage between at least 2 separate faults at the surface. However, the width of a monocline associated with the fault shows a single maximum of c. 40 m, located near the centre of the overall fault trace. We suggest monocline width is related to heave across the fault at depth (a minimum of c. 40 m) beneath the most recent lava that re-surfaced the fault. The surface monocline records re-emergence of a fault that had previously propagated to the surface prior to recent lava deposition rather than upward propagation of a new fault. Overall, the fault displays a growth geometry with displacements increasing with depth. The above implies that the Koa’e faults pre-date the lavas exposed at the surface on the volcano flank, and are a long-lived feature of the volcano dynamics, despite the small offsets across the faults at the surface.