Title : Visualizing the plumbing system of hunga tonga hunga haapai volcano, tonga.
Abstract:
The largest underwater volcano chain in the globe is generated by the Kermadec-Tonga Subduction Zone, with over 2000 km in length; additionally, the Tonga trench is one of the fastest subduction zones, with rates going up to 24 cm/yr. In January 15, 2022 a violent explosion occurred in one the of the members of the volcanic chain: the Hunga Tonga Hunga Ha’apai (HTHH) volcano, it induced worldwide atmospheric perturbations and tsunamis that affected portions of the North, Central and South American littorals. The recent eruption released energy equivalent to an earthquake of M 5.8. HTHH volcano has had repeated eruptions in 1998, 2009, 2015, and 2022; yet its internal structure is poorly known. Local measurements on the volcano are rare given its remote, isolated, and submarine location. Triggering mechanisms postulated for highly explosive mafic eruptions frequently include water–magma interaction or basaltic intrusions into a storage chamber. Ensuing eruption progression and dynamics depend on the mechanism and rate of caldera collapse and resulting modification of the geometry of the plumbing system. Here we use a high-resolution gravity data set, to perform an inversion of the complete Bouguer anomaly of the HTHH volcanic area that yields the density distribution in the volcano’s interior. This distribution unveils the characteristics of the plumbing system. In general, they are the conduits that store and transport magmatic products to the surface. The possibility to map those conduits relies in their low-density characteristics, arising from either gas-filled, semi-hollow paths, or low-density, high-temperature magma chambers. The high-resolution data sets play a definitive roll unveiling the characteristics of volcanic interiors. We perform two 3D inversions using the high-resolution Bouguer Anomaly, obtained for the HTHH area. The models have resolutions of 500 and 250 m, respectively. The former reaches depths of 6 km, whilst the latter reaches 5 km; they complement each other. Major low-density anomalies are unveiled in both models. Strategic slices of the 3D models expose low-density regions that evolve from the bottom of the models to the surface; we associate them with the plumbing system. No low-density distribution within 6 km depth can be identified with a magma chamber, as observed in other surveyed volcanoes. Both models show an important negative anomaly in the NW portion of the inverted area; the system shows at least two feeding conduits at the bottom of the model and in the intermediate to upper levels we identify four trajectories along which the motion of magmatic material could take place to the surface. Groups of horizontal cross-sections show that the near-surface volume concentrates many low-density materials that appear to be associated with circular faulting. These results constitute a baseline to compare with in future explosive modifications of the volcanic structure of HTHH, as well as other members of the volcanic chain.
