A simulation model of island reef morphology: the effects of sea level fluctuations,growth, subsidence and erosion

Glacioeustatic sea level fluctuations continually cover and expose reefs, alternately allowing growth or erosion to operate. In a simulation model we examine the simultaneous effects of sea level change, island subsidence, reef growth, subaerial erosion, marine backwearing, and fluvial erosion (from central highlands) on reef development. Using values obtained from the literature, we vary the rates of these processes and compare the reefs produced. Our results indicate that subaerial erosion, subsidence and growth are of comparable importance in determining reef morphology. Fore reef terraces, as developed by the model, are primarily drowned growth features; marine backwearing is of little importance in their development. Reef terraces form readily at depths that never had a stable sea stand, their depth is influenced by growth, subaerial erosion, and subsidence rates. Thus reef terraces often do not indicate former sea stands. We examine the causes of reef drowning and attribute it primarily to rapid subsidence and subaerial erosion, not to truncation through marine backwearing. We propose that reefs deeply submerged today are not necessarily drowned out, but may be vertically stable through many sea level cycles. Fluvial erosion is likely an important agent of lagoon formation on high islands in areas with high erosion rates.