2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
Paper No. 149-8
Presentation Time: 8:00 AM-4:45 PM

Unraveling the Source of Large Erratic Boulders on Tonga: Implications for Geohazards and Mega-Tsunamis

HORNBACH, Matthew J., Huffington Department of Earth Sciences, Southern Methodist University, PO Box 750395, Dallas, TX 75275-0395, matth@gmail.com, FROHLICH, Cliff, Jackson School of Geoscience, The University of Texas Institute for Geophysics, J.J. Pickle Research Campus Bldg. 196, 10100 Burnet Rd, Austin, TX 78758-4445, and TAYLOR, Frederick W., Univ Texas - Austin, 4412 Spicewood Springs Rd, Austin, TX 78759-8500

Large erratic boulders located near shorelines are sometimes linked with paleo tsunamis and associated geohazards. Perhaps the finest modern examples of tsunami-derived erratic boulders are the coral boulders deposited by the great 1883 Krakatau eruption, which generated a >40 m high near-field tsunami that devastated the Sunda Strait. Geophysical analysis of tsunami-derived erratic boulders offers insight into the size, energy, frequency, and trigger-mechanism of past mega-tsunamis. In the wake of the 2004 Sumatra earthquake and tsunami, there has been a significant effort to find, document, and analyze large erratic boulders that may represent paleo mega-tsunami deposits in order to constrain the size, frequency, and location of these events.

With this goal in mind, a team of geophysicists at the University of Texas traveled to Tonga last November in search of rumored reports of large out-of-place erratic boulders located along the western flank of Tongatapu. During their expedition, the researchers found a 3 km chain of massive coral boulders that had been deposit 100-400 m inland. Our analysis suggests these boulders may represent the largest known tsunami deposits on Earth. Radiometric dating and structural/sedimentary interpretation indicates these boulders may have been emplaced recently (Holocene). Preliminary results from wave modeling also suggest an unconventional wave-triggering mechanism. In particular, our analysis adds credence to the concept that submarine slides and volcanic eruptions may trigger Earth's largest tsunamis.

2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM
General Information for this Meeting
Session No. 149--Booth# 202
Oceanic Geohazards: Distribution, Controls, and Risks (Posters)
George R. Brown Convention Center: Exhibit Hall E
8:00 AM-4:45 PM, Sunday, 5 October 2008

Geological Society of America Abstracts with Programs, Vol. 40, No. 6, p. 161

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