Dating young lava flows is essential for understanding volcano’s eruption frequency, yet challenging due to methodological limitations of commonly used dating techniques. Ruapehu (Aotearoa New Zealand) has produced many lava flows during the Holocene, but constraints on the timing of these eruptions are scarce. Here, we combine paleomagnetic dating and relative stratigraphy to deliver new eruption ages of 18 lava flows with low-to-high error window ranges between 500 and 2700 years (at the 95% confidence level). Our data indicate that the large lava flow field located on the Whakapapa area (northwest Ruapehu) was emplaced during at least three distinct eruptive episodes between 10.6 and 7.4 ka. Two of these episodes closely followed a large collapse event that affected Ruapehu’s northern edifice, and generated large volumes of lava between 10.6 and 8.8 ka, with the third episode producing less voluminous lava flows between 8.1 and 7.4 ka. Following a smaller collapse of the southeastern sector of the edifice at ca. 5.3 ka, several low-volume lava flows were emplaced during at least two distinct eruptive episodes prior to ca. 1.0 ka, which supplied the Whangaehu valley (east Ruapehu) with lava. The youngest age inferred from our data represents the youngest eruption age provided for a lava flow outside Ruapehu’s summit region. This research provides greater detail to the Holocene effusive chronology at Ruapehu, shedding light on partial cone reconstructions after edifice collapses during the early and late Holocene, and the time relationships between trends observed in its effusive and explosive activity.

Volcanogenic tsunami and wave hazard remains less understood than that of other tsunami sources. Volcanoes can generate waves in a multitude of ways, including subaqueous explosions. Recent events, including a highly explosive eruption at Hunga Tonga-Hunga Ha’apai and subsequent tsunami in January 2022, have reinforced the necessity to explore and quantify volcanic tsunami sources. We utilise a non-hydrostatic multilayer numerical method to simulate 20 scenarios of sublacustrine explosive eruptions under Lake Taupō, New Zealand, across five locations and four eruption sizes. Waves propagate around the entire lake within 15 minutes, and there is a minimum explosive size required to generate significant waves (positive amplitudes incident on foreshore of >1 m) from the impulsive displacement of water from the eruption itself. This corresponds to a mass eruption rate of 5.8x10^7 kg s^-1, or VEI 5 equivalent. Inundation is mapped across five built areas and becomes significant near shore when considering only the two largest sizes, above VEI 5, which preferentially impact areas of low-gradient run-up. In addition, novel hydrographic output is produced showing the impact of incident waves on the Waikato river inlet draining the lake, and is potentially useful for future structural impact analysis. Waves generated from these explosive source types are highly dispersive, resulting in hazard rapidly diminishing with distance from the source. With improved computational efficiency, a probabilistic study could be formulated and other, potentially more significant, volcanic source mechanisms should be investigated.