HR: 11:20h
AN: PP42A-04    [Abstracts]
TI: Megatsunami of the World Ocean: Did They Occur in the Recent Past?
AU: Abbott, D
EM: dallas@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 1000 RT 9W, Palisades, NY 10964, United States
AU: Bryant, T
EM: ebryant@uow.edu.au
AF: University of Wollongong, Wollongong, 2522, Australia
AU: * Gusiakov, V
EM: gvk@sscc.ru
AF: Institute of Computational Mathematics, Pr. Lavrentieva 6, Novosibirsk, 630090, Russian Federation
AU: Masse, W
EM: wbmasse@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop J978, Los Alamos, NM 87545, United States
AB: The comprehensive historical tsunami database collected at the Novosibirsk Tsunami Laboratory, contains data on more than 2250 historical tsunamis in the World Ocean from 1628 BC to present. Even if the historical data set is incomplete for many areas, especially for older times, the world catalog contains enough data to estimate average run-up heights for the largest seismically-induced tsunamis that caused wide-spread damage and many fatalities (1755 Lisbon, 1868 and 1877 Chile, 1952 Kamchatka, 1957 Aleutians, 1960 Chile, 1964 Alaska, 2005 Sumatra). This average run-up does not exceed 30-35 meters on the nearest coast with 10-12 meters at the distances of more than 5000 km. Somewhat larger waves (up to 40-45 m) can be generated by volcanic explosions followed by volcanic cone collapse (Santorini 1628 BC, Kuwae 1453, Unzen 1792, Tambora 1815, Krakatau 1883). Landslide-generated tsunamis have the largest recorded heights (up to 525 m) but normally these events are very local with a width of inundated area from hundreds of meters to several kilometers (1958, 1936, 1853 Lituya Bay, 1936 Norway, 2000 Greenland). Meanwhile, many parts of the World Ocean coastline contain prominent features of catastrophic impact of water currents and waves that came from the ocean. They are large boulders, weighing well above one hundred tons, lying on the top of vertical cliffs at the height up to 60 m and large vortexes cut-down in rather resistive coastal rocks. On a smaller scale, these features include sculptured bedrocks, grooves, canyons, cavettos and flutes, found in areas where hurricanes and severe tropical storms are not common. Sedimentary features of water impacts include mega-ripples found in the north-western Australia and so-called chevrons (parabolic and blade- like sand dunes) that are common along many parts of the Indian Ocean coast. In southern Madagascar, chevrons reach an altitude of 205 m with 30-45 km of in-land penetration. A high energy water flux of that scale could be generated by Storegga-class submarine landslides or Santorini-class volcanic explosions, but for this area does not have nearby active volcanoes or large sedimentary basins with the potential for large-volume submarine sliding. Not widely acknowledged presently, but still a real possibility is the creation of these coastal features by catastrophic oceanic waves generated by deep-water impacts of large comets or asteroids. In the Indian Ocean, several crater candidates (Burckle, Mahuika, Kukla, Christie) have been found recently by geomorphological analysis of detailed bathymetric maps. They are geologically young and analysis of nearby deep-sea cores shows the presence of some elements and minerals typical of oceanic impact structures. This paper discusses the consistency of these data with spatial and azimuthal distribution of the large-scale erosional and sedimentary features found at the Australian and Madagascar coast.
DE: 6022 Impact phenomena (5420, 8136)
DE: 6210 Comets (6023)
DE: 8175 Tectonics and landscape evolution
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Joint Assembly