On Mon, 31 May 2010 22:52:17 -0500, you wrote: >I can't think how to explain this. > Maybe something like a cenote? http://en.wikipedia.org/wiki/Cenote http://yucatantoday.com/en/topics/cenotes-underwater-sinkholes Which, maybe, were birthed by Chicxulub, so-- on topic after all!