Impacts of the mid-15th century eruption at Kuwae caldera, Vanuatu

In the AD 1450s, one of the three largest climate-forcing eruptions of the largest 1000 years took place, with similar impacts as the AD 1815 event of Tambora, Indonesia, that caused the ‘year without a summer’ of AD 1816. The submarine caldera of Kuwae, Vanuatu, has long been suggested to be the source of the AD 1450s eruption, but this is still highly debated.

Today, the 12-by-6 km large Kuwae caldera lies between the islands of Epi and Tongoa. Here, an eruption occurred in the 15^th century eruption and locally caused devastation, covering the islands surrounding it with vast amounts of pyroclastic material. We present the first full stratigraphy of the event, enabling us to reconstruct the eruptive sequence. First, a small ash plume produced fine ash deposits overlying faulted soil sequences, indicating a low-energy, precursory phase. Afterwards, the eruption built a Plinian eruption column, causing lapilli fall in excess of 3 m in proximal locations, and sending volcanic particles and gases high up into the atmosphere. This column then collapsed, producing the first pyroclastic flows that devastated the islands surrounding the caldera, incorporating many trees that became charcoalised and are still fully preserved in the deposits. Following further pyroclastic flow activity, a massive lithic lag breccia contains megaclasts (>10 m breccia), recording the collapse of a pre-existent edifice. Later pumice-rich pyroclastic flows occurred bring the total thickness of the sequence to between 30 and >80 m in proximal locations.

These results are combined with initial results from a recent bathymetric study, mapping the submarine caldera floor, addressing the question of whether the entire caldera was generated during the mid-15^th century event, or whether earlier eruptions have played a part in its collapse. This is essential for estimating the total collapse volume of the mid-15^th century event at Kuwae, representative of the total erupted volume.

We will use information on a) the eruptive sequence (based on field observations), b) eruptive volume (based on bathymetry), c) total emitted sulphur (based on eruptive volume and preliminary geochemistry data), and d) the eruptive date (based on radiocarbon analysis of collected charcoal samples) to characterise the mid-15^th century eruption of the Kuwae caldera and test whether it was the source of the AD 1450s volcanic event that had a global climate impact.