Mangrove Mystery – Where Did All the Pumice Come From?

Pumice: Just Scratching the Surface

Since 1902, more than 40 centimeters of mangrove peat could have accumulated at the Belize site, enough to entrap and bury small pieces of pumice. But Juan’s vexing questions persisted: Why hadn’t pumice been discovered in any of the numerous mangrove cores that Maggie had sampled? The pumice on the surface was common enough that the coring device she used to sample peat (seen to the left) should have dug up some evidence, even if it was rare. But with no pumice-laden cores in-hand and continual observations of pumice all over the surface of the peat, they accepted an obvious explanation -- because pumice floats, it may move around with the tides or periodic storm surges and therefore is not easily buried.

Buried or floating, they were still faced with all that pumice in the reef, far from its source. This engendered many more questions requiring information from a wide variety of scientific areas. Julie Herrick, a volcanologist at the Global Volcanism Program, joined Maggie to determine how to continue this investigation. Together, they started looking into Central American volcanic eruption histories and tephra marker units, which are deposits of volcanic ash and pumice which can be dated and chemically identified to be matched with specific eruptions. They also researched riverine pathways from potential pumice deposits to the Caribbean, major storms and flooding that could have washed new loads of pumice down these rivers into the sea, and models of ocean currents that could describe its oceanic route and travel time to Belize.