Mangakino caldera complex

The Mangakino caldera complex (other names are Mangakino volcanic center, Mangakino Caldera) is the westernmost and one of oldest extinct rhyolitic caldera volcanoes in the Taupō Volcanic Zone of New Zealand's North Island. It produced about a million years ago (1 Ma) in the Kidnappers eruption of 1,200 km³ (287.9 cu mi), the most widespread ignimbrite deposits on Earth being over 45,000 km² (17,000 sq mi) in area. This eruption was closely followed in time by the smaller 200 km³ (48.0 cu mi) Rocky Hill eruption. The Kidnappers eruption had a estimated VEI of 8 and has been assigned a total eruption volume (not just tephra) of 2,760 km³ (662.2 cu mi).

However this was only in its most recent caldera forming phase from 1.21 to 0.91 million years ago as it had its earliest caldera generating phase from 1.62 to 1.51 million years ago. There are at least 11 major historic eruptions assigned to this complex. At least 5 of these contributed significant welded ignimbrite deposits that represent major pyroclastic events in the central North Island. Ongatiti Ignimbrite (Hinuera Stone) from a 7 VEI event, about 1.3 million years ago, has now been found over a wider area and several meter thick tephra deposits from the eruption exist on drill samples from both Auckland and Wellington.

The earliest characterised eruptives from the complex are andesitic and the mechanism of transition from this to the more explosive later rhyolitic eruptions is related to increased heat flow from the magma sources.

Later many of these deposits were covered over by deposits from other eruptive centres such as those of the Oruanui eruption.

The caldera can be defined by gravitational measurements as 30 km (19 mi) by 15 km (9.3 mi) and its "basement" floor is at least 4 km (2.5 mi) below the present ground surface.