Huge erratic boulders in Tonga deposited by a prehistoric tsunami

Along some coastlines there are erratic boulders apparently emplaced by tsunamis or cyclonic storms; evaluating their origin and time of emplacement places constraints on the frequency, severity, and location of coastal hazards. Seven such large coral limestone boulders are present near Fahefa villa...

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Bibliographic Details
Published in:Geology (Boulder) 2009-02, Vol.37 (2), p.131-134
Main Authors: Frohlich, Cliff, Hornbach, Matthew J, Taylor, Frederick W, Shen, Chuan-Chou, Moala, 'Apai, Morton, Allan E, Kruger, Jens
Format: Article
Language:English
Subjects:
absolute age
actinides
Anthozoa
boulders
causes
Cenozoic
clastic sediments
Cnidaria
data processing
dates
digital simulation
erratics
Fahefa Tonga
geologic hazards
Invertebrata
isotopes
Landslides & mudslides
marine environment
mass movements
metals
numerical models
Oceania
Polynesia
Quaternary
Quaternary geology
radioactive isotopes
Rocks
sea-level changes
sediments
shore features
shorelines
Simulation
slumping
Studies
submarine environment
submarine volcanoes
Th-230
thorium
Tidal waves
Tonga
Tongatapu Island
tsunamis
upper Quaternary
Volcanoes
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Summary:Along some coastlines there are erratic boulders apparently emplaced by tsunamis or cyclonic storms; evaluating their origin and time of emplacement places constraints on the frequency, severity, and location of coastal hazards. Seven such large coral limestone boulders are present near Fahefa village on Tongatapu Island, southwest Pacific, apparently emplaced by a prehistoric tsunami. These boulders are 10-20 m above sea level and above any possible source, and all are 100-400 m from the present shoreline. Coral 230Th ages indicate that the limestone formed during the last interglacial sea-level highstand, ca. 120-130 ka. The largest boulder is approximately 20 times more massive than any reported boulders emplaced by historically documented storms and may be the largest known tsunami or storm erratic worldwide situated above its source. We performed computer simulations to assess whether tsunamis produced by earthquakes, undersea landslides, or volcanoes could emplace the boulders. The simulations indicate that either volcanic flank collapse along the Tofua arc approximately 30-40 km to the southwest or undersea landslides on the submarine slopes of Tongatapu could be responsible. Either could explain why these boulders are not widespread on Tongatapu, and instead occur in a localized group along the western coast. This study demonstrates that small (
ISSN:0091-7613
1943-2682
DOI:10.1130/G25277A.1