Natural Hazards

, Volume 63, Issue 1, pp 119–131 | Cite as

Inland fields of dispersed cobbles and boulders as evidence for a tsunami on Anegada, British Virgin Islands

Original Paper


Marine overwash from the north a few centuries ago transported hundreds of angular cobbles and boulders tens to hundreds of meters southward from limestone outcrops in the interior of Anegada, 140 km east–northeast of Puerto Rico. We examined two of several cobble and boulder fields as part of an effort to interpret whether the overwash resulted from a tsunami or a storm in a location where both events are known to occur. One of the cobble and boulder field extends 200 m southward from limestone outcrops that are 300 m inland from the island’s north shore. The other field extends 100 m southward from a limestone knoll located 800 m from the nearest shore. In the two fields, we measured the size, orientation, and spatial distribution of a total of 161 clasts and determined their stratigraphic positions with respect to an overwash sand and shell sheet deposit. In both fields, we found the spacing between clasts increased southward and that clast long-axis orientations are consistent with a transport trending north–south. Almost half the clasts are partially buried in a landward thinning and fining overwash sand and none were found embedded in the shelly mud of a pre-overwash marine pond. The two cobble and boulder fields resemble modern tsunami deposits in which dispersed clasts extend inland as a single layer. The fields contrast with coarse clast storm deposits that often form wedge-shaped shore-parallel ridges. These comparisons suggest that the overwash resulted from a tsunami and not from a storm.


Caribbean Tsunami Storm 



We would like to thank Cynthia Rolli (British Virgin Island Disaster Management Agency) for sharing high-resolution aerial photos of Anegada for our field work and in this manuscript. Critical reviews by Uri Ten Brink and Brian Atwater improved the manuscript. Funding was provided by the “Tsunami Hazards Potential in the Caribbean” project of the U.S. Geological Survey and Marine Geology Program.

Supplementary material

11069_2011_9848_MOESM1_ESM.pdf (65 kb)
Supplementary material 1 (PDF 65 kb)


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Copyright information

© Springer Science+Business Media B.V. 2011

Authors and Affiliations

  1. 1.U.S. Geological SurveySanta CruzUSA

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