Abstract:
The 7,000-year-old Tuhua eruption is the largest known eruption from Tuhua (Mayor) Island. Tuhua represents a unique peralkaline volcanic system in New Zealand with lavas that contain high levels of sodium, potassium and trace elements e.g. fluorine - similar to those from Pantelleria and Colli Albani, Italy. The distinctive composition is likely to influence the eruptive behavior as these elements make erupting magma more “fluid” or “runny”. This impacts gas expansion and may allow larger bubble growth before fragmentation occurs. Pumices generated in this system show low density and thin bubble walls when examined in 3D and SEM 2D analysis. The results of this study show several stages of the eruption from a fairly constant plinian column through column collapse phases. Sustained plinian eruptions emplaced thick ash deposits on the mainland. Along with the physical deposits from the eruption the internal structure of the lapilli pumice indicates that they were influenced by degassing as the magma ascended – this provides evidence of the conditions controlling the eruptions dynamics. Understanding the scale and behavior of past eruptions helps prepare us for future hazards we can expect from Tuhua Island.