Puniu River

The Puniu River is a river of the Waikato Region of New Zealand's North Island. As a tributary of the Waipa River (itself a tributary of the Waikato River), and at a length of 57km, it is one of the longest secondary tributaries in New Zealand.The Puniu flows initially north from sources within the Pureora Forest Park, veering northwest to pass south of the towns of Kihikihi and Te Awamutu before meeting the Waipa River 3km south of Pirongia.GeologyAbout half the river's course from its sources on the edge of the Rangitoto Range is through deep valleys and gorges formed of Late Jurassic to Early Cretaceous Manaia Hill Group greywacke (a form of sandstone, with little or no bedding, fine to medium grained, interbedded with siltstone and conglomerate, and with many quartz veins), which is buried in many places by Quaternary ignimbrites. The main ignimbrite is the Ongatiti Formation, up to 150 m thick of compound, weakly to strongly welded, vitrophyric (phenocrysts embedded in a glassy rock), including pumice-, andesite and rhyolite lavas. In several places the river runs past slopes covered in blocks of ignimbrite, where the underlying greywacke has eroded.