Alteration of oceanic volcanoes (e.g., in the Hawaiian Islands) is less well understood than that of continental counterparts. Although growing evidence indicates that active, oceanic volcanoes suffer from large-scale, mass-wasting processes, it is not clear to what extent these processes are controlled, if at all, by alteration of the edifice. Core samples recovered from the Hawaiian Scientific Drilling Project’s 3-km hole within the deep flanks of Mauna Kea are shedding light on these processes. Three zones of progressive alteration have been identified (Walton and Schiffman, 2003) within hyaloclastites, which are the dominant lithology in the submarine portion of the core: incipient (1.1 to 1.3 km), smectitic (1.4 to 1.6 km), and palagonitic (1.6 to 3.0 km). The alteration features observed in this deepest zone (i.e., palagonitic rinds on glassy shards and chabazitic cements) are similar to those that have been described from hyaloclastites collected by submersible from landslide blocks off Oahu and Molokai (e.g., Clague et al., 2002). Hyaloclastites, as initially deposited, generally exhibit minimal consolidation and much higher porosity than those from the palagonitic zone, in which the effects of compaction as well as the extensive precipitation of zeolitic cements have significantly reduced porosity and enhanced consolidation. Locally within hyaloclastites of the HSDP core, early consolidation is found in meter-scale zones of hedenbergite-bearing, contact metamorphic aureoles developed adjacent to basaltic intrusions, apparently emplaced prior to the effects of incipient zone alteration, possibly during auto-intrusion. Our initial studies of the HSDP core suggest that alteration processes appear to have strengthened (as opposed to have weakened) hyaloclastite deposits, and thus may not be a critical factor in contributing significantly to slope failure in Hawaiian volcanoes.

References cited:

Clague, D.A., Moore, J.G., and Davis, A., 2002, Volcanic breccia and hyaloclastite in blocks from the Nuuana and Wailau landslides, Hawaii: A.G.U. Monograph 128, p. 279- 296.

Walton, A.W. and Schiffman, P., 2003, Alteration of hyaloclastites in the HSDP 2 Phase 1 Drill Core: (I) Description and Paragenesis: Geochemisty, Geophysics, and Geosystems v. 4, Paper # 2002GC000368.