Tectonic processes and submarine flows in the Bismarck Volcanic Arc, Papua New Guinea

Numerous volcanic and sedimentary flows were observed in sidescan and multibeam sonar imagery collected during the Nov.-Dec. 2004 cruise aboard R/V Kilo Moana in the Bismarck Sea, Papua New Guinea. I examined four fields of undulating sediment to assess causal mechanisms. The possible mechanisms include deformation, episodic turbidity currents, and continuous bottom currents. Two of the fields display a similar arcuate and irregular morphology. Each of these fields is associated with evidence of turbidity current activity. These fields are morphologically distinct from a field of turbidity-current sediment waves mapped nearby in Hixon Bay, and thus likely include a deformational component. Also in Hixon Bay, an irregular depression that may be a slide scar appears to have provided the initial topography for a small turbidity current sediment wave field growing within it. Volcanic eruptions on Long Island, Papua New Guinea, occurred 16,000, 4,000, and 300 years ago. The most recent eruption coincides with widespread local legends that referred to "The Time of Darkness", and Long Island was the likely source of the widespread Tibito tephra of that age, with an air-fall volume in excess of 11 km 3. Based on sidescan and multibeam bathymetric imagery, I mapped what appeared to be a large volcanic flow deposit off the coast of Long Island, with dimensions 70 km long and up to 24 km wide. I estimated the volume of the flow to be 14 km3. In March, 2010, samples from the flow were collected to determine the flow's composition. We recovered basaltic andesites. Thus, the flow field is likely a composite of several lava flows. Geochemical analysis shows a strong similarity to material from the Time of Darkness eruption. Several series of drowned reef platforms were mapped in the vicinity of Karkar and Bagabag Islands. Drowned reefs are formed by a combination of rapid sea level rise and rapid subsidence. Flexural modeling indicates that the volcanic construction of Karkar Island, in combination with rapid sedimentation from the nearby, actively uplifting Adelbert Terrane, can account for the amount of subsidence inferred from the mapped depth of the drowned reef platforms.