Construction of an oceanic island : insights from El Hierro 2011–12 submarine volcanic eruption

Abstract

Eight consecutive swath bathymetry data sets were obtained to monitor the submarine eruption that occurred from 10 October 2011 to 5 March 2012 south of El Hierro Island in the Canary Islands. An increase in seismic activity since July 2011 preceded the onset of the eruption, which was marked by seismic tremor and stained waters. The first bathymetry, 15 d after the eruption started, depicts a cone topping at 205 m depth, growing on a preexisting valley. Recurrent mapping shows changes in the morphology and depth of the cone, allowing us to identify collapses and calculate eruptive volumes and rates, which peaked at 12.7 × 106 m3 d-1 of non-dense rock equivalent (NDRE) on 29-30 October. The final cone consists of at least four vents along a north-northwest-south-southeast lineation, with the shallowest summit at 89 m depth. The total accumulated volume was 329 × 106 NDRE m3, of which one-third formed the cone. Similar cones have been identified on the submerged flanks of the island, with volumes ranging from <50 × 106 to >1000 × 106 NDRE m3. As in many other volcanic islands, large-scale landslides play an important role in the evolution of El Hierro. A giant flank landslide (El Golfo, 13-134 ka, 150-180 km3) mobilized, in a single event, a volume equivalent to 450-550 eruptions of the size of the reported one, showing striking differences in the construction and destruction rates of the island. This study is relevant for future monitoring programs and geohazard assessment of new submarine eruptions.