Short crystal residence times and fast magma ascent prior to effusive eruptions at Mount Ruapehu, New Zealand

Abstract Decoding magma evolution and transport mechanisms requires detailed examination of the groundmass glass and associated mineral phases in the eruptive products. These analyses can help determine crystal residence times and magma ascent rates prior to eruption. Magma storage and ascent rates are particularly relevant when assessing the controls on the type and style of eruptions from andesite volcanoes, which are capable of producing varied eruptive phases from highly explosive to dominantly effusive. Here, we focus on Mount Ruapehu, one of New Zealand’s most active volcanoes and a significant portion of the Tongariro Volcanic Centre, which has a rich geological history of eruptions spanning a broad range of eruptive phases from explosive to effusive. Previous analysis of crystal size distributions of microlites from 10 ka tephra showed that magma ascent occurred over a relatively short period (i.e., ~2 days at ≤0.09 m/s) immediately prior to eruption. Here, we expand this approach to include analysis of massive lava flows emplaced from 50 to