The Interplay Between Submarine Slope Failure and Volcanic Spreading in Hawaii: Evidence from Seismic Reflection and Submersible Studies

Hawaiian volcanoes are subject to massive slope failures, many of which are manifest in large, blocky debris avalanche deposits that surround the submarine flanks of the volcanic edifices. Such past catastrophic flank collapses must have generated enormous tsunami that impacted coastal areas around the Pacific Basin. Recent earthquakes in the islands, and possibly small landslides, have also produced local tsunami and infrastructure damage, and tsunami have been detected as far away as the coast of California. A continuum of event sizes exists between these two end-members, with unknown frequencies, distributions, and regional impacts. Recent submarine investigations of the active volcanoes of Kilauea and Mauna Loa have provided new insights into past and present slope processes, and thus, the prospects and nature of future events. Seismic reflection and submersible surveys, on Kilauea and Mauna Loa, respectively, reveal landslide scars and deposits buried beneath younger, offscraped packages of volcaniclastic strata. This relationship suggests a strong linkage between slope failure and flank motions (i.e., volcanic spreading): the former can reduce resistance to outward flank displacements, favoring increased rates of volcanic spreading; alternatively, seismicity associated with flank movement can trigger slope failure and large-scale landsliding. An active landslide, referred to as the Hilina (or Papa'u) slump, lies along the mobile south flank of Kilauea volcano, and is buttressed by a growing offshore bench. This configuration defines the two critical elements in this unstable system, and may be poised for collapse. Presently, relatively little is known about the rates or modes of offshore deformation that might precipitate catastrophic failure of either feature. Consequently, both structures are prime targets for future submarine observations and monitoring.