Palaeomagnetic refinement of the eruption ages of Holocene lava flows, and implications for the eruptive history of the Tongariro Volcanic Centre, New Zealand

We present a detailed palaeomagnetic study from 35 sites on Holocene lava flows of the Tongariro Volcanic Centre, central North Island, New Zealand. Prior to the study the eruption ages of these flows were constrained to within a few thousand years by recently published high-precision 40Ar/39Ar geochronological data and tephrostratigraphic controls. Correlation of flow mean palaeomagnetic directions with a recently published continuous sediment record from Lake Mavora, Fiordland, allows us to reduce the age uncertainty to 300–500 yr in some cases. Our refined ages significantly improve the chronology of Holocene effusive eruptions of the volcanoes of the Tongariro Volcanic Centre. For instance, differences in the palaeomagnetic directions recorded by lavas from the voluminous Iwikau and Rangataua members suggest that individual effusive periods lasted up to thousands of years and that these bursts have been irregularly spaced over time. While over the last few millennia the effusive eruptive activity from Mt Ruapehu has been relatively quiet, the very young age (200–500 BP) of a Red Crater sourced flow suggests that effusive activity around Mt Tongariro lasted into the past few centuries. This adds an important hazard context to the historical record, which has otherwise comprised frequent relatively small, tephra producing, explosive eruptions without the production of lava flows.