Spotted by a huge pumice raft of 400 km² by satellites, the eruption of the submarine volcano Havre in July 2012, in the volcanic arc of Kermadec northeast of New Zealand, is considered as the largest deep oceanic eruption of history, involving a rhyolitic magma (70 to 72% by weight of SiO2).
Rafts of pumice - Royal NZ Air Force photo 09.08.2012 / Orion patrol plane flying between Samoa and New Zealand - Samples of pumice / Doc NZ Defense Force - one click to enlarge
Fatally poorly documented directly, it was the subject of investigations in 2015 by various robots: multi-beam imaging made by the robot Sentry (an AUV / Autonomous underwater vehicle) of the entire caldera and its edges allowed to establish a map with a resolution of one meter. Guided by this accurate bathymetry, 12 ROVs / remotely operated vehicles took photos, videos and samples for a total of 250 hours.
3D view of the underwater caldera of the seamount Havre and artist's view, with the lava of 2012 in red / doc. in The largest deep-ocean volcanic volcanic eruption of the past century, by Rebecca Carey & al. 2018 and University of Tasmania
Caldera of Havre volcano - Seafloor roughness, derived from the gridded AUV bathymetry by calculating the surface area in 3 × 3 m bins relative to a flat seafloor. As expected, the steep caldera walls show high roughness. The lavas and domes (outlined in red and labeled A to P) are distinguished by high roughness. The sediment at the lava flow front of lava C is wrinkled. A coarse deposit interpreted as the product of syneruptive mass wasting is located within the caldera extends north-northeast from the truncated edges of lavas G to I (MW in red). The widespread GP deposit has moderate roughness on the caldera floor and flanks and is outlined by solid pink lines. Areas within the GP deposit that are less rough are partially or wholly buried by ALB, and later deposits are derived from the collapse of dome O-P (dashed orange lines). Dashed yellow lines enclose parts of the GP deposits covered by syn- and post-eruption mass-wasting deposits inside the caldera. / in The largest deep-ocean silicic volcanic eruption of the past century, by Rebecca Carey & al. 2018
Observation of Havre seamount / doc. University of Tasmania
Seafloor products of the 2012 Havre eruption.Images taken from the forward-looking ROV cameras of lava, domes, and clastic deposits. - one click to enlarge - Line in each image is 1 m in length. (A) GP clasts are predominantly meter-sized; the clast shown here is 6 m in diameter. (B) Meter-sized GP clasts are stacked more than four clasts high within the caldera, suggesting gentle settling to the seafloor from suspension. (C) GP clasts commonly have curviplanar surfaces and quenched margins with normal joints and breadcrusting. (D) Lava spine on dome O-P. (E) ALB deposit at 1.2 km from the inferred source vent (dome O-P). (F) AL deposit on top of a GP clast; inset shows the complex internal stratigraphy of this unit. / in The largest deep-ocean silicic volcanic eruption of the past century, by Rebecca Carey & al. 2018
The first interpretations were disrupted: besides lava from 14 vents at a depth between 900 and 1,220 meters, giant clastic fragments of pumice over 9 meters in diameter were observed.
Various conclusions emerge:
- Bulky deposits dominated by giant pumice appear as unique characteristic of subaqueous eruptions.
- These giant pumice can be produced at high hydrostatic pressures (9 Mpa).
- The footprint of the giant pumice of Le Havre is the product of a process of explosive release, saturation by water and distribution by ocean currents.
- The prismatic shapes and curviplanal surfaces of giant pumice suggest a mechanical detachment of extruded magma in the ocean. The eruption was not explosive, but extrusive.
- More than 75% of the expelled volume has been divided, to form the pumice raft and transported away from the volcano ... the size of the underwater eruptions in the volcanic arcs, and the magmatic production, can not be extrapolated from the deposits on the ocean floor.
- Advances science mag - The largest deep-ocean volcanic volcanic eruption of the past century - by Rebecca Carey & al. 2018 - link - Science Advances 10 Jan 2018: Vol. 4, no. 1, e1701121 DOI: 10.1126 / sciadv.1701121.
- Global Volcanism Program - Havre seamount / Newsletter report september 2012 - link