Drilling through Kilauea's mobile south flank

T Sisson VHZ, M Coombs AVO, S Hurwitz WRD & VHZ, P Lipman VHZ emeritus

**Statement of problem --** At least 30 enormous young submarine
landslide deposits (0.1-2.0 Ma) blanket the seafloor surrounding the
Hawaiian Islands; they extend as much as 200 km offshore and contain
individual slide blocks to 25 km across. These deposits record repeated
massive failures of the flanks of Hawaiian volcanoes that likely
generated tsunamis destructive across the Pacific Basin. Precursor
conditions conducive to failure were rapid seaward spreading during
shield-stage growth, due to gravitational loading by volcanic edifices
that stand high above the surrounding deep (5000 mbsl) seafloor. Such
edifice spreading is thought to be focused along sub-horizontal faults
(decollements) located at or near the contacts against the underlying
Cretaceous ocean crust, but deformation mechanisms are know only
indirectly through clustering of earthquake hypocenters interpreted as
marking faults, inversion of deformation surveys, and from seismic
imaging. Conditions for initiation of catastrophic landsliding remain
poorly known. A major IODP drilling project through the south flank of
Kilauea would provide unique opportunities to investigate the growth,
deformation, and present-day conditions on the most mobile and actively
erupting oceanic-island volcano on Earth. One or more boreholes would
also be ideal sites for sensitive monitoring instruments.

**Objectives --** To drill through the deforming submarine south flank
of Kilauea, collecting core samples, measuring bore hole conditions (P,
T, permeability, fluids, strain), and siting monitoring instruments to
understand the deformation, seismicity, and catastrophic collapse
potential of large ocean island volcanoes.

**Work strategy --** In recent years, the south flank of Kilauea volcano
has been spreading at \~10 cm/yr at the coastline, where instantaneous
displacements during major earthquakes have been up to 8 m horizontally
and 3.5 m vertical (1975 M=7.2 Kalapana event). Due to its potential
hazards and scientific importance, Kilauea's submarine south flank was
examined and sampled intensively by ROV and manned submersible dives
during four cruises (1998-2002) by the Japan Marine Science and
Technology Center (JAMSTEC). The cruises resulted in numerous
publications by USGS scientists on the morphologic, structural, and
geochemical development of the volcano. Kilauea's basal decollement is
too deep to reach by drilling from onshore locations, but a large
uplifting bench on the offshore south flank is shallow (2500 -- 3000
mbsl) and thin enough (4 km) to reach and penetrate with the new IODP
drill ship *Chikiyu*. Another hole closer to shoreline could penetrate
into the early Kilauea edifice. A project of this scope would take years
to develop and would require broad involvement of the international
academic community. As a start, T. Sisson will be attending the IODP
Hazards workshop in August 2007 to make a case for Kilauea. If response
is positive, the USGS could sponsor one or more international workshops
to build support and lead planning. If a submarine Kilauea drilling
project were approved, the USGS would need to commit at least 5
researchers for multiple years.

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# Relevance and impact -- The two volcano hazards capable of causing substantial multinational loss of life and property are eruption of a large caldera and collapse of the flank of an ocean-island volcano edifice. A drilling project of this type, with monitoring instruments as an integral component, would fundamentally advance knowledge of how large oceanic volcanoes deform and collapse.

## Partnerships -- IODP, JAMSTEC, University of Hawaii, Shimane University, Rice University, and undoubtedly many other institutions.