Corals as proxy recorders of volcanic activity: Evidence from Banda Api, Indonesia

Corals growing on the flanks of Banda Api, Indonesia, contain records of volcanic activity which occurred in May, 1988. Ashfall killed portions of some massive coral colonies (Porites lobata), resulting in the formation of death surfaces. These surfaces were preferential sites for extensive bioerosion and incorporation of volcanic ash into underlying skeletal pores. Subsequent coral regeneration resulted in the preservation of death/regrowth surfaces overlying trapped volcanic ash. An orange-colored iron-rich chemical precipitate is preserved in the skeletons of corals which survived the volcanic event. These distinct orange bands are contemporaneous with the death/regrowth surfaces. The iron banding is interpreted as being a product of hydrothermal activity which accompanied volcanism. X-radiographs of coral skeletons confirm that the timing of formation of both the death surfaces and the orange banding is coincident with the 1988 eruption. The features preserved in these corals may be valuable proxy indicators of volcanic events in analogous recent and ancient environments.