Rock mass strength and slope stability of the Hilina slump, Kīlauea volcano, Hawai'i

Abstract

Stability of the Hilina slump, on the south flank of Kīlauea volcano, Hawai'i, is investigated using slope stability analyses based on rock mass mechanics. The Hilina slump is an active example of the giant landslides that are observed around submarine flanks of ocean island volcanoes. Based on edifice topology, along with derived rock mass strength and deformability parameters, slope stability analyses predict that the geometries of present-day failure surfaces of the Hilina slump are shallow, located at less than ∼3.5 km depth below the upper surface of the edifice. The failure surfaces at the base of the Hilina slump are predicted to be structurally independent from a previously interpreted subjacent detachment at the contact between the Kīlauea edifice and the oceanic crust. Based on these model results, the Hilina slump is envisioned to ride atop the south flank of Kīlauea as it spreads seaward along this slipping basal detachment. Under present-day slope and sea-level configurations, local horizontal ground accelerations greater than ∼0.4–0.6 g are predicted to cause slip along failure surfaces within Hilina slump. Therefore, dynamic stress changes due to slip along the subjacent detachment may potentially trigger slip along failure surfaces of the Hilina slump. Model-derived stability and failure surface geometries can account for the distinct observed distribution of slip along specific Hilina faults following the M fa 7.9 1868 Ka'u and M s 7.2 1974 Kalapana earthquakes. Further, the spatial distribution of south flank aftershocks > M 1.5 recorded between 1950 and 1976 are consistent with the predicted distribution of potential earthquake-induced slip of the Hilina faults.