Dr. Arran Murch

Havre Volcano is a submerged seamount with a post-2012 summit ~700 meter below sea level located along the Kermadec arc between New Zealand and Tonga. Havre is truncated at 900 mbsl by a large oval shaped caldera four by six km in size that is ~600 m deep.

On 18 to 19th July 2012 an eruption ≤21.5 hr long at Havre Volcano from a depth of ~900 mbsl produced a large pumice raft, a sea-surface hot spot, and plume of discolored water, along with an atmospheric vapor plume. Comparison of pre- and post-eruption bathymetry revealed large scale changes to the seafloor. A multinational cruise in 2015 used an ROV and AUV in tandem to conducted detailed bathymetric mapping and sampling of the seafloor deposits from the 2012 Havre eruption. ROV dives showed that seafloor changes resulted from the emplacement of 15 rhyolite domes and lavas. In addition, three distinctive clastic units were deposited across Havre caldera. The lowest of these is called the Giant Pumice unit, composed of pumice blocks >1m in diameter that form a cone with the point around the inferred vent in the SE and extending across the caldera to the NW. Surrounding the inferred vent of the Giant Pumice unit is a second unit termed the Ash, Lapilli, and Block unit, forming several lobes extending away from the vent and burying the Giant Pumice unit. The final unit is called the Ash with Lapilli unit (AL unit) composed of four sublayers and is dominantly made up of fine ash. In terms of volume of magma produced the 2012 Havre eruption is roughly comparable with the 1980 eruption of Mt St Helens. This is the first and only time a deep subaqueous (>500 mbsl) eruption of this size has been ‘observed’ and sampled rapidly following the event, making Havre ideal for the study of large-scale submarine silicic eruptions processes.