Tafu is a Submarine Tongan Volcano that Erupts More Frequently than Axial Volcano

Abstract:

Let us introduce you to Tafu, an elongated submarine volcanic seamount on the Northeast Lau Spreading Center (NELSC) that has experienced at least three volcanic eruptions in the 11 years between 2006 and 2017. We document those eruptions here using data from repeat bathymetric survey data, dredging, ROV dives, and camera sled runs on expeditions funded by Kordi, NOAA Ocean Exploration, NSF, and Schmidt Ocean Institute (executed in that order). Our last visit to Tafu was on SOI expedition FK171110. The eruptions occurred on the volcano's rifts, at depths between 2000 and 1600m below sea level. There has been no recent volcanic activity at the summit, which rises to 1375m below sea level. Compositional analysis of Tafu lava and tephra indicates each eruption deposit is compositionally distinct and compositionally variable. A closely associated, immediately adjacent ridge 500m to the east of Tafu also erupted once during this time span, in late 2008. We call that eruption "Puipui"; it shares geographic and magma composition attributes with Tafu, effectively adding a fourth Tafu eruption in roughly a decade. For comparison, Axial volcano on the Juan de Fuca Ridge, which is often considered among the most active known submarine volcanoes and the focus of a regional scale observatory, has erupted three times in the 17 years between 1998 and 2015.

The dynamics of Tafu volcano and proximity to ports in Samoa and Fiji make it an ideal location to study submarine eruption conditions. Tafu’s historical volcanic eruptions produced lavas spanning a range of effusion conditions and tephra at a production rate that would be considered high for Axial, but substantially less than observed at nearby West Mata volcano. Tafu sits in an area of en echelon positive relief ridges that make up this magmatically robust part of the NELSC; the NELSC transitions to an axial valley morphology north of Tafu, indicating a reduced magma budget. The NELSC is the easternmost of three sub-parallel spreading centers and accommodates roughly half of the opening of the Northern Lau Basin.

One important question is why is this volcano so frequently active, given its back arc tectonic setting? Compositionally speaking Tafu lavas are not appreciably influenced by the Tofua volcanic arc. Enhanced magma supply to the southern NELSC may be related to a mantle melting anomaly.