Lithosedimentological and tephrostratigraphical characterisation of small-volume, low-intensity eruptions: The 1800 years Tufa Trig Formation, Mt. Ruapehu (New Zealand)

Low to moderate-intensity eruptions (VEI ≤ 3) constitute the most frequent eruptions on historical time scales and can last from days to years. Direct observations of historical eruptions (e.g. Ruapehu 1995–1996, Nakadake 2003–2005, Etna 2002–2003) have highlighted the complexity of these eruptions, which often involve multiple phases and sudden changes in eruption behaviour. Eruptive products associated with low to moderate-intensity eruptions are typically characterised by small erupted volumes ≪1 km3 and a significant amount of ash-sized material, making their preservation subject to local environmental conditions. Accordingly, long-term (1000s of years) eruptive records tend to be biased towards the usually less frequent but better-preserved, more intense eruptions with VEI > 4 and volumes >1 km3, leading to an underestimation of the complexity and frequency of small-scale eruptions.