Effusive and explosive volcanism on the northern Futuna Ridge, Lau Basin: A combined bathymetric, magnetic and seismic investigation

The Utu Uli Hill, located on the northern Futuna Ridge in the Lau Basin (Southwestern Pacific Ocean), displays recent volcanism in a complex area, possibly the boundary of one of many intermediate platelets between the Pacific and Australian plates or the result of progressive melting and dismantling of the Vitiaz subduction slab. The combination of bathymetric, magnetic and 3D reflection seismic data allows us to recognize and describe several types of submarine volcanoes, namely clustered small volcanoes, flat-topped volcanoes, elongated volcanic ridges, and volcaniclastic domes, and to unravel the geological evolution of the area. Sea-surface magnetic anomalies reveal that the area formed during the last 780 ka, whereas the large variations of amplitude in the near-seafloor, high-resolution magnetic anomalies suggest scattered ages for individual edifices and widespread volcanism within the whole Futuna Ridge. The spectacular volcaniclastic domes initiate only at depth shallower that 1150–1200 m. They show feeder dyke systems and evidence of hydrothermalism at their summit, and are locally affected by collapse structures.