The 'Geology of the Waikato Area' says, The Alexandra Volcanic Group consists of several low-angle composite cones, including Karioi, Pirongia, Kakepuku, Te Kawa and Tokanui volcanoes, aligned southeast from Mount Karioi on the coast to Tokanui. They comprise about 55 km3 of mainly basaltic material erupted from at least 40 volcanic centres. The Alexandra Volcanic Group is the product of Late Pliocene to earliest Pleistocene back-arc volcanism, when both subduction-related basaltic magmas (Karioi, Pirongia, Kakepuku and Te Kawa) and intraplate alkalic basalts (Okete) were erupted. K-Ar ages range from 2.74 to 1.6 Ma, with the ages of the different magma series overlapping. It goes on to say Kakepuku is composed mainly of basalt lava with minor tuff . Kakepuku was formed about 2.5m years ago. See also the geological map http://data.gns.cri.nz/geology/