James White (University of Otago) and Andy Nichols (University of Canterbury)
On 18-19 July 2012, the Havre Volcano in the Kermadec Islands quietly erupted, releasing about 1.5 cubic kilometres of material underwater. The eruption generated a massive pumice raft, with some fragments more than 1 metre in diameter, which eventually covered an area of 400km².
Observing and sampling deep submarine volcanic eruptions is extremely challenging due to the inaccessible environment. Understanding the process of magma fragmentation is complicated by the pressures of the overlying water. These deep-sea eruptions can drive pyroclastic processes through the release of steam and carbon dioxide, which also complicates modelling and interpretation.
In 2015, samples of seafloor deposits from the eruption were collected using a remotely operated vehicle and were analysed using the Fourier Transform Infrared (FTIR) technique on the Infrared Microspectroscopy (IRM) beamline.
The FTIR technique enabled high-resolution imaging of individual volcanic ash grains at extremely fine, 5 μm resolution. The FTIR analysis revealed that fragmentation occurred under vent-depth pressures, followed by a brief decompression event before the ash quenched. The ash particles underwent pressure reductions possibly due to supersonic conditions in the eruption jet, bubble oscillations, or high-velocity flows resulting from vent constrictions.
This study was the first to use the FTIR technique to investigate water speciation in volcanic ash in such detail. It highlighted a previously unknown process of decompression in deep submarine eruptions and showcased the potential of the FTIR technique for detailed studies of submarine volcanic processes to better understand this newly identified phenomenon.
Reference:
Murch AP, White JDL, Dürig T, Nichols ARL, Carey RJ. 2023. Reconstructing the timing and conditions of fragmentation from water speciation in ash during a deep submarine eruption: 2012 eruption of Havre, Kermadec Arc. Lithos 464-465: 107432. https://doi.org/10.1016/j.lithos.2023.107432
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