Mafic Plinian volcanism and ignimbrite emplacement at Tofua volcano, Tonga

• Published in: Bulletin of Volcanology
• Main Authors: Caulfield, J. T., Cronin, S. J., Turner, S. P., Cooper, L. B.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2011
• Subjects: Tofua; Mafic; Plinian; Tonga; High-grade; Ignimbrite; Caldera; PYROCLASTIC FLOW DEPOSITS; MOUNT ST-HELENS; CALDERA COLLAPSE; GRAN-CANARIA; CAMPANIAN IGNIMBRITE; ERUPTIVE DYNAMICS; TAMBORA VOLCANO; CHEJU ISLAND; ICE CORE; MODEL; Pacific; ice core
• Online Access: https://pure.qub.ac.uk/en/publications/3175dd17-c23b-4410-89e3-4a1b432dc90e; https://doi.org/10.1007/s00445-011-0477-9

Tofua Island is the largest emergent mafic volcano within the Tofua arc, Tonga, southwest Pacific. The volcano is dominated by a distinctive caldera averaging 4 km in diameter, containing a freshwater lake in the south and east. The latest paroxysmal (VEI 5-6) explosive volcanism includes two phases of activity, each emplacing a high-grade ignimbrite. The products are basaltic andesites with between 52 wt.% and 57 wt.% SiO(2). The first and largest eruption caused the inward collapse of a stratovolcano and produced the 'Tofua' ignimbrite and a sub-circular caldera located slightly northwest of the island's centre. This ignimbrite was deposited in a radial fashion over the entire island, with associated Plinian fall deposits up to 0.5 m thick on islands > 40 km away. Common sub-rounded and frequently cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma-water interaction. The common intense welding of the coarse-grained eruptive products, however, suggests that the majority of the erupted magma was hot, water-undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction with external water. We propose that the development of a water-saturated dacite body at shallow (<6 km) depth resulted in failure of the chamber roof to cause sudden evacuation of material, producing a Plinian eruption column. Following a brief period of quiescence, largescale faulting in the southeast of the island produced a second explosive phase believed to result from recharge of a chemically distinct magma depleted in incompatible elements. This similar, but smaller eruption, emplaced the 'Hokula' Ignimbrite sheet in the northeast of the island. A maximum total volume of 8 km(3) of juvenile material was erupted by these events. The main eruption column is estimated to have reached a height of similar to 12 km, and to have produced a major atmospheric injection of gas, and tephra recorded in the widespread series of fall deposits found on coral ...