Horeke basalts

The Horeke basalts is a disused formation that contained Miocene-Pliocene basalt lava flows that covered a large area in central Northland Region of New Zealand, and in places forms a high plateau around Okaihau.

The boulders in the Wairere valley are the erosional remnants of a lava flow out of a volcano near Lake Ōmāpere (near Kaikohe) that has been dated as approximately 2.8 million years old.

There is a slight difference in chemistry in the two rocks that have been dated suggesting that the eruption took the form of several flows that once blanketed the high ground to the east of Horeke.

Erosion of the clay underlay of the basalt plateau (cap) started to create a v-valley.

It is the result of chemical leaching by acidic seepage from the humus on top of the boulders.