Paper No. 1
Presentation Time: 1:35 PM
MEGA-TSUNAMI MEGA-CONTROVERSY
KEATING, Barbara H., Hawaii Institute of Geophysics & Planetology, Univ of Hawaii, 2525 Correa Rd, Honolulu, HI 96822, keating@soest.hawaii.edu
Moore & Moore (1984; 1988) proposed that coral-bearing units on Lanai, HI, were formed by
"giant waves" that reached 365 m. The "Giant Wave Hypothesis" was based upon several tenets,
e.g. the Hawaiian Isles sink too fast to preserve marine deposits above sea level, but recent
geologic studies do not support these tenets. Coral clasts make up as much as 50% of individual
beds (not 5% as published); a consistent stratigraphy occurs from gully to gully (9 beds in the type
section, not 3 couplets); paleosols occur between beds (indicating significant periods of soil
development, not minutes between waves). Since corals growing on boulders move with waves in
the nearshore environment, they are not preserved in "growth position," making this a non-definitive tenet; no offshore reef exists, instead, giant submarine lava tubes are present
immediately offshore. The deposits do not form a wedge-shaped unit, but instead occur as gully-fillings, and since the run-back of tsunami waves scour existing drainages rather than utilize them
as depositional basins this distribution precludes a tsunami origin.
Fossil bearing deposits above 100 m occur along parallel contours (bathtub ring-like) with the
slopes between them free of coral-bearing deposits. No in-situ fossils are found at either 326 m or
365 m. The biotic assemblages indicate fossils occur in a depth-consistent fashion. The numbers
of extinct species increase up-slope (indicating older deposits are present distal from the beach).
Two coral-bearing units in Kalaukapo Crater include an in-situ boulder/coral platform (ancient
rocky shoreline), and an underlying coral conglomerate. Oxisols occur above 200 m, vertisols
below. Vertisols are highly expansive and work basalt boulders to the surface (in wetting/drying
cycles) producing a surface lag deposit.
Radiometric dating by Rubin et al. (2000) find separate clusters of ages, inconsistent with a single
catastrophic event. Boulder mounds interpreted as giant wave bedforms are instead archaeological
remains. Finally, the assumption of rapid subsidence is incorrect. All islands (except the location
of the current hotspot) preserve reef deposits above sea level. In summary, geological
relationships within the reported tsunami inundation zone do not support the Giant Wave
Hypothesis.