When a hot plume of rock rises through Earth’s mantle to melt through the crust, it can create both a volcanic ocean island and a swell in the ocean floor hundreds to thousands of kilometers long. Eventually the island is carried away by the underlying tectonic plate, and another grows in its place. Over millions of years, this geological hot spot can produce a chain of islands—on which life may flourish before they sink, one by one, back into the sea.
The amount of time an island spends above sea level can determine the course of evolution there, and yet the mechanisms that control this have been unclear. Now, after analyzing 14 volcanic chains, Kimberly Huppert ’11, PhD ’17, and professors Taylor Perron and Leigh Royden of the Department of Earth, Atmospheric, and Planetary Sciences have found that an island’s life span is related to the speed of the underlying plate and the size of the swell generated by the plume. The Hawaiian Islands, for example, persist for millions of years longer than the Galápagos because while the plates beneath the chains travel at similar speeds, it takes longer for the plate to slide over the larger Hawaiian swell.
The Galápagos Islands’ shorter life span may also help explain why they host such unique and rapidly evolving species. “You can imagine all these organisms living on a sort of treadmill made of islands, like stepping stones, and they’re evolving, diverging, migrating to new islands, and the old islands are drowning,” says Perron. “What Kim has shown is there’s a geophysical mechanism that controls how fast this treadmill is moving and how long the island chains go before they drop off the end.”