You mentioned a lack of volcanic activity as a stabilizing influence. What about the two fault zones located in or nearby Mira Flores and Pedro Miguel Locks? These faults are classified as "occluded" ??????? being wet, well lubricated and not subject to seismic gaps and pressure buildups. However, please give your ideas on how these two faults could lead to isthmus INSTABILITY over time. Thanks.
I cannot imagine that closing off the isthmus was very peaceful. Wouldn't there be huge overflows across it when it was finally up and preventing the ocean currents their way through as they were used to? What is the difference in the height of both shores? When there's a low tide on the eastern shore, there must be high tide onnthe western shore and when the same forces were at work when the isthmus was closing, there must've been huge bi-directional waterflows. Which part of the isthmus was closed as the last one? Couldn't it be found by tracking such violent waterfalls on the oceanic floor - now elevated high in the mountains? Also, as the ocean was 400 feet lower not so recently, are there clues of such event under the ocean? But I think they will be above water now anyway, in some mountain pass.
Thanks for the talk, most informative. How have varying mean sea levels affected the width of the Isthmus, and thus the ability in different eras for plants and animals to have used it as a land bridge?
cladistic analysis of sister fish species in the eastern pacific/western caribbean have shown that the IoP has opened and closed multiple times due to climatic changes/changes in sea level. I'm sure similar examples exist for terrestrial organisms north and south of the isthmus, but I'm not aware of any at this point.
In the google earth picture, it looks like there is a huge caldera to the west of Panama / Costa Rica on the ocean floor. Is that possibly where the boulders in Panamanian sediments have come from? (they being volcanic in origin)
