Mauna Loa's submarine western flank: Evidence for deep volcanic spreading and hydrothermal alteration (Hawaii)

Observations of submersible dives across Mauna Loa's submarine western flank suggest the flank has been influenced by a number of interacting processes, including large-scale sector collapses, deep volcanic spreading, and hydrothermal alteration. Subaerially derived pillow lavas observed draping the upper flank are in strong contrast to the volcaniclastic debris discovered at the toe of the flank. The distribution of rock types, deformation structures, and alteration phases within the volcaniclastic rocks suggest the mid-slope bench is constructed of a series of thrust sheets formed by seaward sliding of the western flank. Volcaniclastic sediments within the bench have been locally altered by circulation of hot hydrothermal fluids along the faults. The remnant landslide scar, from which much of the clastic debris within the bench derived, has largely been concealed by a flood of new lava flows, many of which crossed the shoreline and were deposited on the upper flank as pillow basalts.