HR: 0800h
AN: OS31A-0168 INVITED    [Abstracts]
TI: 2004 South Asia tsunami left little record of its trace near Yala, southeastern Sri Lanka
AU: * Moore, A L
EM: moorean@earlham.edu
AF: Earlham College, Dept. of Geosciences, Richmond, IN 47374, United States
AU: McAdoo, B G
EM: brmcadoo@vassar.edu
AF: Vassar College, Dept. of Earth Sciences & Geography, Poughkeepsie, NY 12604, United States
AU: Ranasinghe, N
EM: pranasin@kent.edu
AF: Kent State University, Dept. of Geology, Kent, OH 44242, United States
AB: The 2004 South Asia tsunami swept 1 km inland near Yala, on southeastern coast of Sri Lanka, yet little trace of its passage remains on land today. In contrast, 2004 deposits are preserved in lagoons near Hambantota and Rekawa, suggesting that the search for precursor events may be best served in shallow offshore settings. The coastline of Yala is fronted by a 10 m high coastal dune—the tsunami reached inland only through river- mouth gaps in the dune. Where the tsunami did exploit these gaps, however, it reached flow depths of more than 2.5 m inland, with velocities sufficient to mound debris (typically tree branches) in front of savanna trees. The savanna sits on a well developed sandy soil, yet no trace of tsunami inundation rests on that soil, even within tens of meters of the shoreline. Associated with rivers, and behind the coastal dune, several lagoons have formed in flooded river valleys. These lagoons are often sandy on the shoreward side, and become muddy on the landward side, a gradation that spans up to 1 km. Within this gradation, several sandy layers extend ~500 m inland and may represent marine inundations. The sandy layers are 5-15 cm thick, display lateral continuity at least on the order of 10s of meters, and appear to fine inland. These environments sit on a coastline that is strongly progradational. Lagoons and harbors known from 15th century accounts of this area are now dry and well inland. Ridge and swale topography dominates one site in northeastern Yala, also suggesting progradation, as does the presence of a 2500 YBP strand line some 500 m inland. Because of this, we suspect that a successful survey for ancient precursors to the 2004 event in this area will rely on identifying ancient lagoons, and thus will rely on a thorough understanding of the paleoenvironment of the area—a study which remains to be done.
DE: 4558 Sediment transport (1862)
DE: 4564 Tsunamis and storm surges
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting