Understanding the Stability of Thrust Sheets Supporting Kilauea’s Submarine Flank: Insights from Direct Shear Experiments

The south flank of Kilauea volcano (Hawaii, USA) is actively moving seaward at rates of up to ~10 cm/year along a basal décollement. This movement is accompanied by earthquakes and landslides. The Hilina Slump is located on top of the mobile flank and has not yet failed catastrophically as seen elsewhere on the Hawaiian Islands. It is thought that stacked thrust sheets at the toe of the submarine flank act as a buttress, helping to stabilize the active slump. The mechanical properties of the slump and thrust sheets are poorly understood but may significantly influence their deformation behavior and the overall stability of Kilauea’s flank. To better understand these systems, we conducted direct shear experiments on samples collected from submarine exposures of both the thrust sheets and the Hilina Slump. Our results reveal both velocity-weakening and velocity-strengthening frictional behavior, depending on sliding velocity. Velocity-strengthening occurs predominantly at low velocities. Intact samples are stronger and tend to exhibit more velocity-strengthening behavior, whereas powdered samples, representative of pre-existing fault zones, are weaker and show more velocity-weakening behavior. This suggests that fault zones could experience unstable sliding. Additionally, altered surface sediments from the Hilina Slump show stick-slip behavior. Overall, the variable material behavior across the submarine flank may explain the range of deformation structures and slip styles observed at Kilauea.