MEGA-TSUNAMI MEGA-CONTROVERSY

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.