HR: 12:00h
AN: V11G-07    [PDF]
TI: Megatsunami Generation From Giant Submarine Landslides on Oceanic Islands: New Insights Gained From the Hawaii Evidence and Modeling
AU: * McMurtry, G M
EM: garym@soest.hawaii.edu
AF: School of Ocean and Earth Science and Technology, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822 United States
AU: Tappin, D R
EM: drta@bgs.ac.uk
AF: British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Fryer, G J
EM: gerard@hawaii.edu
AF: School of Ocean and Earth Science and Technology, University of Hawaii, 1000 Pope Road, Honolulu, HI 96822 United States
AU: Watts, P
EM: phil.watts@appliedfluids.com
AF: Applied Fluids Engineering, Inc., Private Mail Box #237, 5710 E. 7th Street, Long Beach, CA 90803 United States
AB: High-elevation marine gravels on the Hawaiian islands of Lanai and Molokai either mark uplifted shorelines or are deposits from massive tsunamis. The subsidence history of those islands has been too ambiguous to differentiate these causes, leading to controversy over the deposit's origins and to confusion over the impacts, or even the existence of megatsunamis generated from giant submarine landslides (GSL) mapped offshore. U-series ages of these deposits that correlate with sealevel high stands have added to the confusion. Landslide tsunami simulations have now advanced to the point where the tsunamigenic potential of GSLs can be affirmed. We show that megatsunamis are a sufficient explanation for the observed pattern of debris height of calcareous marine deposits on the southeast Hawaiian islands. Further, our tsunami simulations, using the Alika GSL as example, can be used to reduce the considerable uncertainty in subsidence history of the different Hawaiian islands. Modeled runups of 800 m occurred directly landward of the Alika 2 slide on west Hawaii and were up to 300 m on west Lanai, in agreement with previous deposit estimates there (Moore \& Moore, 1984, 1988). Recently, we rediscovered calcareous marine deposits on Kohala volcano on Hawaii island, where continuous subsidence is well established from its stairway of submerged reefs. On Kohala, we found a marine fossiliferous basalt boulder conglomerate from 1.5 to 61 m above present sea level exposed at the coast and up to 1 km inland. U-series dates of corals from the deposit are approximately the same age, 100 to 120 ka, as the giant Alika 2 landslide from nearby Mauna Loa volcano, directly dated using sediment stratigraphy (McMurtry et al., 1999). The present depth of the 120-ka shoreline implies that the deposit was left by a tsunami whose runup at 6 km inland exceeded 490 m. For the late Pleistocene, large volcanic failures and exposed marine deposits both correlate foremost with sea level high stands, and in particular with the onset of interglacial conditions that are reflected in Hawaii by the apex ages of the low-stand fringing reefs. We show that such large volcanic failures inevitably generate megatsunamis, and we conclude that persistent climate effects during sea level high stands eventually unleash large volcanic failures and megatsunamis amongst the Hawaiian islands and perhaps all volcanically active oceanic islands, with invariable propagation toward the continental coasts.
DE: 1527 Paleomagnetism applied to geologic processes
DE: 3022 Marine sediments--processes and transport
DE: 4546 Nearshore processes
DE: 4564 Tsunamis and storm surges
DE: 4860 Radioactivity and radioisotopes
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting