While the easternmost on-land occurrence is at Lookout Bluff in north Otago, seismic data provides evidence of offshore underwater centres.

[1] The peak of marine transgression is marked by an Oligocene carbonate platform that means there was at this time near-total submergence under water.

The Crater, a volcano near Middlemarch, is the high-level vent diatreme facies of an approximately 1.5 km (0.93 mi) wide maar and has an age of 24.8 ± 0.6 Ma for its oldest component.

The vent contains volcanic clasts of mainly phonolite, with minor proportions of basanite, basaltic-trachyandesite, trachyandesite, syenite, gabbro, pyroxenite, and hornblendite, as well as fragments of Otago Schist and Cenozoic sedimentary rocks.

Ram Rock, an eroded basanitic pipe to the northeast of this area, is associated with peridotite and pyrometamorphosed Otago Schist xenoliths.

[2] The Swinburn area to the south side of State Highway 85 has coarse doleritic textured basaltic volcanics overlying scoria-fall deposits, which in turn overlie Eocene-Oligocene marine sediments.

[1] In the Pigroot area at the volcano called Trig L, lavas overlie marine sediments and include exotic mantle peridotite and crustal gabbro xenolith-bearing phonolite as the cap.

Mount Dasher, about 1.5 km (0.93 mi) to the northwest of Kattothyrst, has basanite lavas with an intervening phonotephrite flow on the northeast side.

This implies that the mechanism of formation may be connected to the lithosphere, unlike some other intraplate volcanoes such as the Hawaii island chain, which are rooted in the asthenosphere.

If large sections of this already thin lithosphere sank into the asthenosphere, it would be replaced with hotter rock leading to decompression melting.

This theoretically could cause volcanic activity that is locked to the moving lithosphere over many millions of years, as observed in the Dunedin group.