Volcanic flow deposits on the flanks of Long Island, Papua New Guinea: lavas or pyroclastics?

Volcanic eruptions on Long Island, Papua New Guinea, occurred 16,000, 4,000, and 300 years ago (Newhall and Dzurisin, 1988). The most recent eruption coincides with widespread local legends that referred to a "The Time of Darkness" (Blong, 1982), and Long Island was the likely source of the widespread Tibito tephra of that age, with an air-fall volume in excess of 11 km3 (Blong, 1982). Based on sidescan and multibeam bathymetric imagery, we mapped a large volcanic flow deposit with numerous flow fronts off the coast of Long Island, with dimensions 70 km long and up to 24 km wide. We estimate the volume of the flow to be 14 km3. The flow may be composed of pumiceous or pyroclastic material derived from one of these major eruptions, or may be a lava flow. The geometry of the flow indicates that it is not associated with a turbidity- current, unlike the well mapped submarine pyroclastic flow on the flanks of Montserrat in the Lesser Antilles Arc, and therefore may have been a pumiceous or a lava flow. The flow has a relatively high amplitude back scatter in side-scan imagery and appears to cover much of the sedimentary deposits, including an adjacent field of giant sediment waves. Based on estimates of sedimentation rates in this area, we conclude that the flow is not pre-Holocene in age, and may be associated with the last caldera-forming eruption of ~300 year ago, but could be even younger.